JPH11254625A - Polyester film for laminating molding of metal plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film for laminating a metal plate 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 lamination properties, taste properties, bubbling properties, and particularly excellent bond properties after retorting can be provided. SOLUTION: In the biaxially oriented laminated polyester film comprising two or more layers, a polyester of a nonmetallic plate side layer contains particles of 1 wt.% or less each having a shape function (a ratio of a maximum length D to a minimum length d) defined by an equation (D/d) of less than 1.1 in the film. A polyester of a metallic plate side layer contains particles of 0.05-1 wt.% each having a shape function of 1.1 or more and contains particles of 0.1 wt.% or less each having a shape function of less than 1.1.

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 laminated polyester film. More specifically, by adhesiveness, adhesiveness after retorting in a can obtained by squeezing and / or squeezing, in particular by pressing, and foaming when filled with carbonated beverages and molding processing having excellent taste characteristics. The present invention relates to a polyester film for metal plate lamination molding suitable for a container to be produced, particularly a metal can.

[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.

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 subjecting the metal plate to various surface treatments such as plating. When a metal can is manufactured by drawing or ironing a laminated metal plate of a film, the 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 impaired 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, as the speed of can making has been improved, the ratio of forming cans from laminated steel sheets has increased, and further laminating properties, moldability, and adhesion between films and steel sheets have been desired. In particular, when the increase in the forming ratio is achieved by ironing and / or drawing, there is a problem in particular that the adhesion between the film and the steel sheet due to the retort after can forming is reduced. In addition, there is also a demand for an improvement in foaming properties, particularly when a carbonated beverage is filled, and the above proposals are no longer able to satisfy these required properties comprehensively.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to satisfy recent stricter requirements, in addition to excellent laminating properties, taste properties and foaming properties, especially retort. An object of the present invention is to provide a polyester film for metal plate lamination molding suitable for use in a metal can, which can exhibit excellent adhesion even afterwards.

[0006]

In order to solve the above-mentioned problems, a polyester film for laminating and forming a metal plate according to the present invention is a biaxially stretched laminated polyester film having two or more layers, The particles of the layer whose polyester is less than 1.1 in shape (ratio of the maximum length D to the minimum length d of the particles) in the film defined by the following formula (1):
% Or less, and the polyester of the metal plate side layer contains 0.05 to 1% by weight of particles having a shape degree of 1.1 or more and 0.1% by weight or less of particles having a shape degree of less than 1.1. Characterized by the following. Shape degree = D / d (1)

That is, in the polyester film for laminating and forming a metal plate of the present invention, the polyester layer on the non-metal plate side layer contains particles having a relatively small shape, that is, particles having a relatively spherical shape in a specific amount or less. By improving the foaming property, the polyester layer of the metal plate side layer contains a relatively small amount of particles having a relatively large shape and a very small amount of particles having a relatively small shape. The purpose is to ensure excellent adhesiveness. In addition, by using particles having a small shape in combination with particles having a large shape in the metal plate side layer, it is possible to improve the slipping property and further improve the laminating property.

[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.

Further, the polyester of the present invention preferably has at least 80 mol% of ethylene terephthalate and / or ethylene naphthalate units as a main constituent polyester, particularly from the viewpoint of imparting heat resistance. It is at least 85 mol%, more preferably at least 90 mol%. In particular, it is preferable that the polyester constituting the non-metal plate side layer is 2,6-naphthalenedicarboxylic acid copolymerized polyethylene terephthalate.

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.

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.

The film according to the present invention is required to be a biaxially stretched laminated polyester film of two or more layers having a non-metal plate side layer and a metal plate side layer. The present invention is intended to make the non-metal plate side layer and the metal plate side layer have optimum characteristics on the biaxially stretched laminated polyester film having two or more layers.

In the biaxially stretched laminated polyester film according to the present invention, first, the polyester of the non-metal plate side layer has a shape degree (maximum length with respect to the minimum length d of the particles) in the film defined by the following formula (1). Particle ratio less than 1.1)
% By weight or less. Shape degree = D / d (1)

Since the film layer on the non-metallic plate side is in contact with the beverage, its foaming property is required especially when filling a carbonated beverage, but particles having a relatively small shape, that is, particles having a relatively nearly spherical shape are required. In this layer, uniform unevenness can be provided on the surface, the surface roughness can be made uniform, and the foaming property can be improved. In addition, by making the surface roughness uniform, good slip properties can be provided, and the occurrence of troubles during the production process of the film itself can be suppressed, thereby facilitating production.

The content of the particles having a degree of shape of less than 1.1 is as follows:
If the amount is too large, the abrasion resistance is extremely reduced.

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 This is the shortest parallel line interval in contact with the contour.

On the other hand, the film layer on the metal plate side is required to have good laminating properties particularly with the metal plate, and particularly excellent adhesiveness after retorting. Particles of 0.05 to 1% by weight, shape degree 1.1
By containing less than 0.1% by weight of particles,
For example, good adhesiveness at the can body, particularly excellent adhesiveness after long-term storage of the retort can be ensured. More specifically, particles having a shape degree of 1.1 or more have a high holding strength in polyester, and are contained in a small amount (0.05 to 1% by weight) to such an extent that other characteristics are not deteriorated. By achieving excellent adhesiveness after retorting for a long period of time and containing only a small amount (0.1% by weight or less) of particles having a shape degree of less than 1.1, it is possible to ensure good slipperiness during the film production process. In particular, smooth laminating properties can be exhibited without bubbles being trapped during high-speed laminating.

In addition, since both layers contain particles having a shape of less than 1.1 in common, the recovery in the film production process is facilitated, and the production of the film is facilitated.

The thickness of the biaxially stretched laminated film of the present invention is as follows:
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. . It is preferable that the thickness ratio (thickness of the polyester film of the non-metal plate side layer / thickness of the polyester of the metal plate side layer) is less than 3. Can be secured relatively large,
In particular, it is possible to further improve the excellent adhesiveness with the metal plate after long-term storage of the retort.

In the present invention, the polyester constituting the non-metal plate side layer has a carboxyl terminal group content of 3 from the viewpoint of suppressing the amount of eluate from the film and improving the taste characteristics.
It is preferably less than 5 equivalents / ton, particularly preferably less than 30 equivalents / ton.

In the present invention, in order to improve the adhesion between the film and the metal plate, the amount of the carboxyl terminal group of the polyester constituting the metal plate side layer is 35 to 50 equivalents /.
Tons, particularly preferably 37 to 47 tons.
Equivalent / ton.

The melting peak temperature of the polyester in the present invention is preferably in the range of 215 to 265 ° C., more preferably 220 to 26, from the viewpoint of heat resistance and moldability.
0 ° C, more preferably 246 to 260 ° 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. 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, each polyester in the laminated film has more laminating properties,
From the viewpoint of improving the adhesion between the metal sheet and the film after retorting, the melting peak temperature (TmB) of the polyester forming the non-metal plate side layer and the melting peak temperature (TMA) (TmB) of the polyester forming the metal plate side layer −TmA) is 0.5 to 35
° C, more preferably 1-1.
0 ° C, more preferably 1-5 ° C.

Also, regarding each layer of the laminated film, the melting peak temperature of the polyester constituting the layer should be 246 to 260 ° C., especially for the non-metal plate side layer, in order to improve heat resistance and workability. It is preferable that the metal plate side layer has a melting peak temperature of 246 to 260 ° C. of the polyester constituting the layer, particularly from the viewpoint of improving abrasion resistance and adhesion to the metal plate after retorting. .

The biaxially stretched film of the present invention preferably has a plane orientation coefficient of from 0.095 to 0.130, more preferably from 0.100 to 0.10, 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 1.0.
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, but, for example, after drying each polyester as required, it is supplied to each known melt extruder, 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 a mean 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.
The thing less than 1 includes, for example, monodispersed spherical silica, aluminum silicate, spherical organic particles, spherical calcium carbonate, wet-agglomerated silica, etc., and spherical silica is particularly preferred, but is not limited thereto. Further, from the viewpoint of improving the foaming property, the degree of shape is preferably less than 1.1, and more preferably less than 1.05. The average particle size is also preferably 0.1 to 2.0 μm, more preferably 0.1 to 2.0 μm.
5 to 1.5 μm, more preferably 0.3 to 1.0 μm
It is. Examples of the film having a shape degree of 1.1 or more include aggregated inorganic particles, but are not particularly limited as long as the shape degree is 1.1 or more.

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.

It is preferable to improve the adhesiveness by subjecting the film to a surface treatment such as a corona discharge treatment in order to further improve the characteristics. At this time, the E value is 5 to 50, preferably 10 to 45.

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 of polyester (IV) Polyester is dissolved in orthochlorophenol,
Measured in ° C.

(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 This is the shortest parallel line interval in contact with 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) Laminability Heating a tin-free steel metal plate having a thickness of 0.18 mm (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 0.02-0.
03), the film is bonded at 150 m / min, quenched, and the surface orientation coefficient of the film after being laminated on a metal plate is measured. This was performed for ten samples, and the lamination property was evaluated based on 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

(7) Adhesion after long-term storage after retort After laminating the above laminated steel sheet, coil 1 was drawn with a drawing machine.
000 m molding (molding ratio (maximum thickness / minimum thickness) = 1.
6, molded in a moldable temperature range) to obtain a can (diameter 6 cm, height 13 cm). The obtained can was subjected to a pressurized steam treatment at 125 ° C. × 25 minutes, filled with an acidic beverage, allowed to stand at 30 ° C. for 3 months, and then opened to open a can side with a 5 cm circle in the can height direction. Take a 1 cm sample with the width in the circumferential direction, measure 180 ° adhesive strength, find the average of 30 pieces,
Evaluation was made according to the following criteria. Class A: 0.7 kg / cm or more Class A: 0.5 kg / cm or more and less than 0.7 kg / cm Class B: 0.4 kg / cm or more and less than 0.5 kg / cm Class C: 0.2 kg / cm or more 0 Less than 0.4 kg / cm D class: less than 0.2 kg / cm

(8) Foaming property Foaming property when the above-mentioned molded can was filled with a carbonated beverage was evaluated according to the following criteria. Special Class A: Small bubbles bubbling in appropriate amount Class A: Somewhat large bubbles are mixed and foaming Class B: Large bubbles are mixed and foaming Class C: Bad foaming Class D: Very poor foaming

(9) Taste Characteristics After the above can was subjected to a pressurized steam treatment at 125 ° C. × 15 minutes,
After filling with water and sealing at 40 ° C., it was left for 1 week, then opened and evaluated by the following criteria based on the turbidity of the liquid. 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.

(10) Heat Resistance After heat treatment of the above-mentioned can at 200 ° C. for 30 seconds, the impact resistance was measured, and the heat resistance was evaluated based on its superiority. The impact resistance was measured by putting a 1% saline solution into a molding can, leaving it to stand for 1 day, applying a voltage of 6 V to the electrode and the metal can in the saline solution, reading the current value 10 seconds later, and measuring the average value after measuring the 10 cans. The value was determined. Class A: less than 0.1 mA Class B: 0.1 mA or more and less than 0.2 mA Class C: 0.2 mA or more and 0.4 mA or less Class D: 0.4 mA or more

Example 1 Monodispersed spherical silica having an average particle diameter of 1.7 μm was 0.001 as polyester A constituting a side layer of a metal plate (steel plate).
%, Secondary particle diameter 0.45 μm (primary particle diameter 40 n
m, isophthalic acid copolymerized polyethylene terephthalate containing 0.14% by weight of agglomerated dry silica particles having an average particle size of 0.45 μm (intrinsic viscosity 0.69 dl / g, melting point 2)
26.2 ° C., carboxyl terminal amount 32 equivalents / ton)
0.95 monodispersed spherical silica having an average particle diameter of 1.7 μm as polyester B constituting the non-metallic plate (steel plate) side layer
Isophthalic acid copolymerized polyethylene terephthalate (intrinsic viscosity: 0.68 dl / g, melting point: 226 ° C.,
Carboxyl terminal amount 34 equivalents / ton) at 180 ° C
After vacuum drying for a period of time, supply to separate extruders, laminate with A / B = 5: 1 with pinol, discharge from die, cool and solidify with mirror cooling drum while applying static electricity (6.7 kv) Thus, an unstretched film was obtained. The unstretched film is heated at a temperature of 9
In the longitudinal direction at 7 ° C., it is multiplied by 3.06 and the preheating temperature is 96 ° C. (3
Second), stretched 3.02 times in the width direction at a stretching temperature of 108 ° C, relaxed at 180 ° C for 4% for 4 seconds, and heat-treated at a thickness of 20 ° C.
A μm biaxially stretched laminated polyester film was obtained. The shape of the agglomerated dry silica particles in the metal plate side layer in the obtained film is 9, the shape of the monodispersed spherical silica particles is 1.08, and the shape of the monodispersed spherical silica particles in the non-metal plate side layer. Was 1.08. The film properties and can properties were as shown in Table 1, and excellent properties could be obtained.

Examples 2 to 7, Comparative Examples 1 and 2 Biaxially stretched laminated polyester films were obtained in the same manner as in Example 1 except that the conditions were changed as shown in Table 1. Table 1 shows the properties and can properties of the obtained film.

[0054]

[Table 1]

[0055]

According to the present invention, by controlling the lamination structure and the additive particle properties of the polyester film for laminating and processing a metal plate, excellent laminating properties, taste properties, and foaming properties, and particularly excellent even after retorting. In addition, it is possible to obtain high adhesiveness.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 509: 00 B29L 9:00

Claims (8)

[Claims] 1. A biaxially stretched laminated polyester film having two or more layers, wherein the polyester of the nonmetallic side layer has a shape degree (with respect to the minimum length d of particles) in the film defined by the following formula (1). Particles having a ratio of the maximum length D) of less than 1.1
% Or less, and the polyester of the metal plate side layer contains 0.05 to 1% by weight of particles having a shape degree of 1.1 or more and 0.1% by weight or less of particles having a shape degree of less than 1.1. A polyester film for a metal plate laminating process. Shape degree = D / d (1) 2. The thickness ratio (thickness of polyester film in non-metal plate side layer / thickness of polyester in metal plate side layer) is 3
The polyester film for laminating and processing a metal plate according to claim 1, which is less than. 3. The polyester constituting the non-metallic plate side layer has a carboxyl terminal group amount of less than 35 equivalents / ton, and the polyester constituting the metal plate side layer has a carboxyl terminal group amount of 35 to 50 equivalents / ton. The polyester film for laminating and processing a metal plate according to claim 1 or 2. 4. The polyester film for laminating a metal plate according to claim 1, wherein the polyester constituting the non-metal plate side layer is 2,6-naphthalenedicarboxylic acid copolymerized polyethylene terephthalate. 5. The difference between the melting peak temperature of the polyester constituting the non-metallic plate side layer and the melting peak temperature of the polyester constituting the metallic plate side layer is in the range of 0.5 to 35 ° C. The polyester film for bonding and processing a metal plate according to any one of the above. 6. The film has a main melting peak temperature of 24.
The polyester film for metal plate lamination processing according to any one of claims 1 to 5, which is at least 6 ° C. 7. The polyester film according to claim 1, wherein the polyester constituting the non-metallic plate side layer has a melting peak temperature of 246 to 260 ° C. 8. The polyester film according to claim 1, wherein the polyester constituting the metal plate side layer has a melting peak temperature of 246 to 260 ° C.