JP2002331630A - Polyester film for laminating metal sheet, film laminated metal sheet and metal container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film excellent in heat resistance capable of stably coating the surface of a metal sheet even if receiving heat history in a can making process, also excellent in barrier properties or corrosion resistance, and suitably used as a material for forming a metal container for food having film strength reaching a especially good level in film laminate operability or handling properties, and also to provide a film laminated metal sheet and a metal container. SOLUTION: The polyester film has two-layered constitution of A/B constituted of A- and B-layers comprising polyester thermally fixed under a specific temperature condition. The coefficient of dynamic friction at 80 deg.C of the film surface of the A-layer after the B-layer is set to the metal sheet side to be laminated to the metal sheet is not more than 0.45. The film surface resin layer contains 0.70 wt.% or less of an ethylene terephthalate cyclic trimer. The dimensional change ratio of the film surface resin layer heat-treated for 2 min in an atmosphere of 210 deg.C is not more than 2.0%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film used for the purpose of preventing corrosion of metal containers for foodstuffs such as soft drinks, beer and canned foods, and a film-laminated metal obtained by laminating the film on a metal plate. The present invention relates to a plate and a metal container formed by molding the film-laminated metal plate.

[0002]

2. Description of the Related Art Conventionally, paint is generally applied to prevent corrosion of the inner and outer surfaces of a metal can, and a thermosetting resin is used as the paint.

[0003] In the method of applying a thermosetting resin coating material, a solvent type coating material is mostly used. The formation of the coating requires heating at 150 to 250 ° C. for a few minutes at a high temperature and for a long time, and a large amount of organic solvent is scattered during baking. Have been.

[0004] In addition, it is inevitable that a small amount of organic solvent remains in the coating film formed under the above-mentioned conditions. When filled, the organic solvent migrates to foodstuffs and may adversely affect the taste and smell of the foodstuffs. Furthermore, additives contained in the paint and low-molecular-weight substances caused by incomplete crosslinking reaction may migrate to foodstuffs, and may have the same adverse effects as in the case of the residual organic solvent described above.

As another method, there is a method using a thermoplastic resin film. For example, a polyolefin film such as a polypropylene film or a polyester film is laminated on heated tin-free steel, and the film-laminated metal plate is used for a metal can.

The method using a thermoplastic resin film can solve the above problems such as simplification of steps and prevention of pollution.

However, among the thermoplastic resin films, for example, when a polyolefin film such as polyethylene or polypropylene is used, the heat resistance is inferior, so that the heat history in the can-making process, the retort treatment after the can-making, etc. , The film may peel off from the film-laminated metal plate.

On the other hand, a method using a polyester film as the thermoplastic resin film is the most preferable method because the problems of the above-mentioned polyolefin film are improved.

On the inner surface side of the can, since the polyester film has excellent heat resistance and generates less low molecular weight substances, the taste and odor of foodstuffs deteriorate due to the migration of the low molecular weight substances as compared with the polyolefin film. Is unlikely to occur. It is excellent in so-called flavor resistance.

[0010] However, even when a polyester film containing polyethylene terephthalate as a main component is used for the purpose, it is necessary to improve the finish of the can at the time of can making after lamination, or to apply a film to the joint of the can. When performing heat treatment for the purpose of repairing using a belt-shaped film, etc., because there is an uncoated portion, the heat resistance of the polyester film is insufficient, and as a result, only the film portion of the film laminated metal plate Since the dimensional change occurs, there is a problem that the surplus film may be loose or the surface of the metal plate may not be completely covered.

Further, when a polyester film containing polyethylene terephthalate as a main component is used for the purpose, for example, when it is used for an inner surface of a can, a barrier of the film depends on the nature and type of foodstuffs that come into contact with the film. In some cases, the corrosion resistance was poor due to insufficient corrosion resistance. On the other hand, when used for the outer surface of a can, similar adverse effects may occur depending on the surrounding environment where the can is placed.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide a metal sheet having excellent heat resistance, a stable coating on the surface of a metal plate even when subjected to a heat history in a can-making process, and a barrier property and corrosion resistance. Polyester film, which is preferably used as a material for forming a metal container for foodstuffs, a film-laminated metal sheet having excellent can-making processability, and excellent corrosion resistance and excellent protection of foodstuffs as contents. To provide a metal container.

[0013]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, the melting point was 240 to 2
A layer of polyester at 60 ° C. and a melting point of 20
An A / B two-layer structure comprising a polyester B layer having a temperature of 0 to 235 ° C., wherein the temperature is at least 5 ° C. lower than the melting point of the polyester of the B layer and 15 ° C. or lower than the melting point of the polyester of the A layer. A film which is heat-set at a temperature of not more than ℃ lower temperature, and a film laminated metal plate is formed by laminating the layer B with the metal plate side,
The coefficient of kinetic friction at 80 ° C. on the film surface of the layer is 0.
45 or less, the ethylene terephthalate cyclic trimer content of the film surface resin layer is 0.70% by weight or less, and the dimensions when the film-laminated metal plate is heat-treated for 2 minutes in an atmosphere of 210 ° C. The inventors have found that the above object can be achieved by a polyester film having a rate of change of 2.0% or less, and have reached the present invention.

That is, the present invention has a melting point of 240 to 260 ° C.
A layer made of polyester having a melting point of 200 to 2
An A / B two-layer structure comprising a polyester B layer at 35 ° C., wherein the temperature is at least 5 ° C. lower than the melting point of the polyester of the B layer and 15 ° C. lower than the melting point of the polyester of the A layer. A film heat-set at a temperature not higher than the temperature, wherein a film-laminated metal plate is formed by laminating the layer B with the metal plate side, and the dynamic friction coefficient at 80 ° C. on the film surface of the layer A is 0. 45 or less, the ethylene terephthalate cyclic trimer content of the film surface resin layer is 0.70% by weight or less,
Provided is a polyester film, wherein a dimensional change rate of the film-laminated metal plate when subjected to a heat treatment in an atmosphere of 210 ° C. for 2 minutes is 2.0% or less.

In a preferred embodiment, the film contains crosslinked polymer particles and / or inorganic fine particles.

The present invention also provides a film-laminated metal plate obtained by laminating the above-mentioned polyester film on at least one side of a metal plate.

Further, the present invention provides a metal container formed by molding the above-mentioned film-laminated metal plate.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester film of the present invention has an A / A layer composed of a polyester layer A having a melting point of 240 to 260 ° C. and a polyester layer B having a melting point of 200 to 235 ° C. A film heat-set at a temperature not lower than 5 ° C. lower than the melting point of the polyester of the layer B and not higher than 15 ° C. lower than the melting point of the polyester of the layer A, and A laminated metal plate is formed by laminating the layer B with the metal plate side, and the layer A
The coefficient of kinetic friction at 0.45 ° C. is 0.45 or less, the ethylene terephthalate cyclic trimer content of the resin layer on the film surface is 0.70% by weight or less, The dimensional change rate after a heat treatment for 2 minutes is 2.0% or less.

The polyester used for the polyester film in each of the above-mentioned layers is mainly formed by polycondensation of a polycarboxylic acid and a polyhydric alcohol.

Examples of the polycarboxylic acid component include dicarboxylic acids, for example, aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid and biphenyldicarboxylic acid; adipic acid, azelaic acid, sebacic acid; Aliphatic dicarboxylic acids such as decanedicarboxylic acid, dodecanedicarboxylic acid and dimer acid; and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid.

The polyhydric alcohol component includes glycols, for example, aliphatic diols such as ethylene glycol, diethylene glycol, triethylene glycol, propane diol, butane diol, hexane diol, dodecamethylene glycol, and neopentyl glycol; cyclohexane Alicyclic diols such as dimethanol; aromatic diols such as an ethylene oxide adduct of a bisphenol derivative;

The polyester is preferably obtained by polycondensing a dicarboxylic acid selected from terephthalic acid and isophthalic acid with a glycol selected from ethylene glycol, diethylene glycol and butanediol. Further, the melting point of the polyester is preferably 200 to 260 ° C, more preferably 210 to 260 ° C.
° C, particularly preferably 215 to 255 ° C. Melting point 2
If the temperature is lower than 00 ° C., the fluidity increases due to the heat history in the can-making process or the like, and the dimensional change may increase. On the other hand, the temperature exceeding 260 ° C. increases the manufacturing cost and is economical. This is because it is disadvantageous.

The intrinsic viscosity of the polyester is preferably from 0.5 to 1.5, more preferably from 0.55 to 1.2, from the viewpoint of mechanical properties.

The polyester film of the present invention has a thermal shrinkage at 150 ° C. of not more than 5.0%, preferably not more than 4.0%, more preferably not more than 3.0%, as measured by the measuring method described later. is there. By setting the heat shrinkage to 5.0% or less, the polyester film can stably cover the surface of the metal plate even when heat-treated in a laminating step or the like.

The method for reducing the heat shrinkage of the film to 5.0% or less is not particularly limited.
A method of improving the dimensional stability by copolymerizing butanediol as a component of the polyester to increase the crystallization rate to increase the crystallization rate, and when the polyester film is a biaxially stretched film described below. A method of improving the dimensional stability by heat setting under the temperature conditions described below, and a method of improving the dimensional stability by providing a relaxation step after stretching when the polyester film is a stretched film described later. Is mentioned.

The film has a coefficient of kinetic friction at 80 ° C. of a surface at the time of forming a film-laminated metal plate in accordance with the method of measuring a dimensional change rate described below of 0.45 or less, preferably 0.43 or less, more preferably 0.40 or less. When the kinetic friction coefficient is 0.45 or less, it is possible to prevent the film from being scratched in the can-making process and the like, and the contamination of the can-making process due to film scraping and the like.

The coefficient of kinetic friction of the film surface is 0.45
Examples of the method to be described below include a method of including a crosslinked polymer particle and / or an inorganic fine particle in a film, a method of forming fine spherulites of a polyester resin, and the like.

The above-mentioned film has an ethylene terephthalate cyclic trimer content of 0.3 when a film-laminated metal plate is formed in accordance with the method for measuring a dimensional change rate described later.
It is 70% by weight or less, preferably 0.50% by weight or less. When the ethylene terephthalate cyclic trimer content is 0.1.
When the content is 70% by weight or less, a protective effect for food can be obtained, and it is possible to prevent the aesthetic appearance of the can from being impaired.

As a method for reducing the content of the ethylene terephthalate cyclic trimer in the film to 0.70% by weight or less, for example, a low-pressure heat treatment method, a solid-phase polymerization method, etc. Examples of the method include a method for producing polyester, a method for extracting the cyclic trimer with water or an organic solvent after polyester production or film formation, and a method combining these methods.

The above-mentioned film is preferably a biaxially stretched film. By biaxially stretching the polyester-based film, the flavor resistance of the polyester-based film can be further improved. The method for biaxial stretching is not particularly limited, and a known biaxial stretching method (simultaneous or sequential, etc.) can be used. in this case,
The stretching ratio in the machine direction is preferably 2 to 5 times, more preferably 2.5 to 4 times, and the stretching temperature is preferably 80 to 120 ° C, more preferably 90 to 110 °.
° C. The stretching ratio in the transverse direction is preferably 2
The stretching temperature is 5 times, more preferably 2.5 to 4 times, and the stretching temperature is preferably 80 to 120 ° C., more preferably 9 to 120 ° C.
0-110 ° C.

When the polyester film is a biaxially stretched film, the residual shrinkage stress due to the biaxial stretching is preferably reduced or removed by a heat setting method or the like. By doing so, it is possible to reduce the dimensional change due to the heat history in the can making process and the like. The reduction or removal of the residual shrinkage stress by the biaxial stretching is preferably performed by heating the film at a temperature in the range of 40 ° C. to 15 ° C. lower than the melting point of the polyester, more preferably 35 ° C. lower than the melting point of the polyester. To 15 ° C
This can be achieved by heat setting under temperature conditions in a range up to a low temperature.

The thickness of the film is 4 to 65 μm.
m is preferable, and a range of 5 to 30 μm is more preferable. If the thickness is less than 4 μm, the barrier properties are poor and the corrosion resistance is poor, and the low molecular weight substance from the metal container penetrates into foods and beverages, which is not suitable.
On the other hand, if the thickness of the film exceeds 65 μm, it is economically disadvantageous.

The film preferably has a melting point of 240
A / A composed of a polyester layer (referred to as A layer) having a melting point of 200 to 235 ° C., preferably 210 to 235 ° C. (referred to as a B layer).
B is a two-layer configuration. This is because layer A needs to have heat resistance in the can making process, and layer B needs to have laminate adhesion by thermocompression bonding in addition to the same heat resistance as layer A. Further, when a metal container is formed from a film-laminated metal plate obtained by laminating the polyester-based film on a metal plate, the layer A is a layer in contact with foodstuffs as contents or a layer serving as a surface of the container, and the layer B is a metal layer. This is a layer to be laminated on the board side.

The polyester used for the layer A includes:
Although what is obtained from the above-mentioned dicarboxylic acid and glycol is mentioned, a combination system of a terephthalic acid-ethylene glycol component system and a terephthalic acid-butanediol component system is preferable. More preferably, the weight ratio (terephthalic acid-ethylene glycol component system / terephthalic acid-
Butanediol component system) is 98/2 to 50/50, particularly preferably 95/5 to 70/30. By using the above-mentioned components, even when performing a heat treatment for the purpose of repairing using a band-shaped film at the time of can manufacturing, the film does not shrink or the surplus film does not stick, and the metal plate Can be completely covered.

The melting point of the polyester used for the layer A is 240 to 260 ° C., preferably 245 to 25 ° C.
5 ° C. When the melting point is lower than 240 ° C., heat resistance in a can-making repairing step or the like becomes insufficient, which is not preferable. Also,
If the melting point exceeds 260 ° C., the production cost increases, which is economically disadvantageous.

The melting point of the polyester used in the layer B is 200 to 235 ° C., preferably 210 to 235 ° C., and more preferably 215 to 230 ° C. If the melting point is lower than 200 ° C., the fluidity of the layer B increases due to the heat history in the can-making process and the like, and the dimensional change of the layer A is undesirably increased. On the other hand, when the melting point exceeds 235 ° C., the melting point of the layer A approaches the melting point, so that the residual shrinkage stress of the layer A is insufficiently reduced or removed, and the dimensional change of the layer A is also undesirably large. Examples of such a polyester include those obtained from the above-mentioned dicarboxylic acids and glycols as in the case of the layer A. Preferably, the acid component is terephthalic acid and isophthalic acid [preferably in a molar ratio (terephthalic acid / isophthalic acid). 95/5 to 80/20, particularly preferably 95 /
5 to 85/15], and the glycol component is ethylene glycol. More preferably, the acid component is a combination of terephthalic acid and isophthalic acid-ethylene glycol component and the acid component is terephthalic acid and isophthalic acid-butanediol component. Still more preferably, the weight ratio (acid component is terephthalic acid and isophthalic acid-ethylene glycol component system / terephthalic acid-butanediol component system) is 9
8/2 to 50/50, more preferably 95/5 to 7
0/30. More preferably, the intrinsic viscosity of the terephthalic acid-butanediol component is 0.55.
~ 1.00. By using the terephthalic acid-butanediol component of the limiting viscosity grade, when the terephthalic acid-butanediol component having the limiting viscosity of more than 1.00 is used, sufficient lamination adhesion is obtained by laminating a metal plate. And may be peeled off from the metal plate.

The layer A becomes a surface layer when a film-laminated metal plate is formed in accordance with the method for measuring the dimensional change rate described later. Therefore, the film surface of the film surface at the dynamic friction coefficient at 80 ° C. is there. The coefficient of kinetic friction at 80 ° C. of the surface of the layer A is 0.45 or less, preferably 0.43 or less, more preferably 0.40 or less. When the kinetic friction coefficient is 0.45 or less, it is possible to prevent the film from being scratched in the can-making process and the like, and the contamination of the can-making process due to film scraping and the like.

The coefficient of dynamic friction of the film surface is set to 0.45
Examples of the method to be described below include a method of including a crosslinked polymer particle and / or an inorganic fine particle in a film, a method of forming fine spherulites of a polyester resin, and the like.

The layer A has a protective effect on foodstuffs,
Since the content of the ethylene terephthalate cyclic trimer is preferably small so as not to impair the aesthetics of the can, the polyester used in the layer A should be one having a low ethylene terephthalate cyclic trimer content. Is preferred. The content of the ethylene terephthalate cyclic trimer in the polyester is preferably 0.70% by weight.
Or less, more preferably 0.50% by weight or less. The polyester having a low content of the cyclic trimer is, for example, a method of producing a polyester having a low content of the cyclic trimer such as a heat treatment under reduced pressure, a solid-state polymerization method, or the like. It can be produced by a method of extracting a trimer, a method of combining these, or the like.

The thickness of the above-mentioned layer A is 3 from the viewpoints of can processability, dimensional stability due to heat history at the time of can process, film laminating operability and handling, barrier properties, corrosion resistance, economy and the like. ５０50 μm is preferable, and 4-40 μm is preferable.
The range of m is more preferred. On the other hand, the thickness of the layer B is determined from the viewpoints of adhesiveness, heat resistance against heat history during can making, and the like.
The range is preferably from 1 to 15 μm, more preferably from 1 to 10 μm.

The method for producing the polyester film having the two-layer structure of A / B is not particularly limited as long as a film satisfying the above requirements can be produced.
Examples include a multilayer extrusion method and an extrusion lamination method.

When the polyester film having a two-layer structure of A / B is a biaxially stretched film, the residual shrinkage stress due to the biaxial stretching of the A layer is preferably reduced or removed by a heat fixing method or the like. . By doing so, it is possible to reduce the dimensional change due to the heat history in the can making process and the like. In addition, the B layer is formed by heat-fixing the A layer to reduce or remove the residual shrinkage stress.
It is preferable that the material is made amorphous or non-oriented by its heat history or the like. Thereby, when laminating the film on the preheated metal plate, a sufficient lamination adhesion force can be obtained without preheating the metal plate to the melting point of the layer B. This can be realized. In addition, even if the amorphous material is achieved by using an amorphous raw material for the layer B and the laminating process can be performed at a low temperature, the film is exposed to high temperatures in the repair process after the can molding, and the film shrinks, and the value of the product as a product is reduced. It is not preferable because it is not available.
The reduction or removal of the residual shrinkage stress by biaxial stretching of the A layer and the amorphous or non-oriented state of the B layer are preferably performed by forming the film at a temperature 5 ° C. lower than the melting point of the polyester constituting the B layer, A temperature lower than the melting point of the polyester constituting the A layer by 15 ° C. or lower, more preferably the B
Heat fixing at a temperature of at least 2 ° C. lower than the melting point of the polyester forming the layer and at most 20 ° C. lower than the melting point of the polyester forming the A layer. The above impact strength, so-called laminating operability or handling property. It can be achieved including securing. Further, when the heat setting temperature condition is out of the above range, it may cause breakage or poor adhesion to a metal plate. Further, the melting point of the layer A and the melting point of the layer B are determined within a range where the above temperature conditions can be set.

The polyester film of the present invention preferably contains crosslinked polymer particles and / or inorganic fine particles. By containing the crosslinked polymer particles and / or inorganic fine particles, can processability can be improved, and scratch resistance (scratch resistance) can be imparted.
These may be used alone or in combination of two or more.

The crosslinked polymer particles are not particularly limited as long as they have heat resistance enough to withstand the temperature during melt molding of the polyester. Examples of the material forming such crosslinked polymer particles include, for example, acrylic monomers such as acrylic acid, methacrylic acid, acrylates, and methacrylates; and styrenes such as styrene and alkyl-substituted styrene. Monomer and divinylbenzene,
Copolymers with crosslinkable monomers such as divinyl sulfone, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, and pentaerythritol tetramethacrylate; melamine resins; benzoguanamine resins; phenol resins; silicone resins. . The crosslinked polymer particles can be produced from these materials by a conventionally known emulsion polymerization method, suspension polymerization method or the like. Further, in order to adjust the particle size and particle size distribution of the crosslinked polymer particles, pulverization, classification and the like may be performed.

The inorganic fine particles are not particularly limited as long as they are insoluble and inactive in the polyester.
Specific examples include metal oxides such as silica, alumina, zirconia, and titanium oxide; complex oxides such as kaolin, zeolite, sericite, and sepiolite; calcium sulfate;
Sulfates such as barium sulfate; phosphates such as calcium phosphate and zirconium phosphate; carbonates such as calcium carbonate. These inorganic fine particles may be natural products or synthetic products. The shape of the particles is not particularly limited.

The particle size of the crosslinked polymer particles and / or inorganic fine particles is preferably 0.5 to 5.0 μm, more preferably 0.8 to 4.0 μm. Particle size 0.5 μm
If it is less than the above, the effect of improving the slipperiness between the film and the metal at a high temperature is small, and the film is apt to be scratched. This is because there is a tendency that the film easily falls off, the film is easily broken at the time of film formation, and the impact strength is reduced.

The content of the above-mentioned crosslinked polymer particles and / or inorganic fine particles in the polyester film is preferably from 0.3 to 5.0 based on the total amount of the polyester film.
0% by weight, more preferably 0.5 to 3.0% by weight. If the content is less than 0.3% by weight, the effect of improving the sliding property between the film and the metal at a high temperature is small, and the film is easily damaged. If the content exceeds 5.0% by weight, the above effect is saturated. This is because there is a tendency that the film forming property of the film decreases, the impact strength decreases, and the like. In addition, a defect of detecting a processing defect of a metal laminated plate obtained by laminating a film on a metal plate by appropriately adding cross-linked polymer particles and / or inorganic fine particles having an appropriate haze, that is, a haze of 25 to 50%. It is also possible to prevent malfunction of the detector.

The above-mentioned crosslinked polymer particles and / or inorganic fine particles may be incorporated into the polyester film in the step of producing the polyester resin, or the above components may be added to the polyester resin and melt-kneaded. . Alternatively, a polyester resin containing the above components in a high concentration may be produced, and this may be used as a master batch and melt-kneaded together with a polyester resin containing no or a small amount of the above components.

The polyester film of the present invention may contain, if necessary, an antioxidant, a heat stabilizer, an ultraviolet absorber, a plasticizer, a pigment, an antistatic agent, a lubricant, a crystal nucleating agent and the like. Can be.

The film-laminated metal plate of the present invention is obtained by laminating the above-mentioned polyester-based film on at least one side of the metal plate, and has excellent can-making processability.

The metal plate used for the film-laminated metal plate is not particularly limited, and examples thereof include tin, tin-free steel, and aluminum. Further, the thickness is not particularly limited, but is economical represented by the cost of the material and the speed of the can-making process, and, on the other hand, from the viewpoint of securing the material strength, preferably 100 to 500 μm,
More preferably, it is 150 to 400 μm.

As a method of laminating the polyester film on at least one surface of a metal plate, a conventionally known method can be applied and is not particularly limited, but a thermal lamination method is preferred, and a metal plate is particularly preferred. There is a method of performing thermal lamination by heating with electricity. Further, the polyester-based film may be laminated on both sides of the metal plate. When laminating a polyester-based film on both sides of a metal plate, it may be laminated simultaneously or sequentially.

When a polyester film having the two-layer structure of A / B is laminated on at least one surface of a metal plate, the layer B is used as a layer to be laminated on the metal plate side as described above. In order to improve the barrier properties and corrosion resistance of the B layer and further improve the adhesion of the laminate, a conventionally known adhesive mainly composed of a thermosetting resin is applied to the B layer in advance, and the laminate is laminated. May be implemented.

The metal container of the present invention can be obtained by molding using the above-described film-laminated metal plate.
The shape of the metal container is not particularly limited, for example, a can shape,
It can be bottle-shaped, barrel-shaped, or the like. In addition, the method for forming the metal container is not particularly limited, either. For example, a known method such as a draw forming method, an ironing method, or a draw ironing method can be used.

[0055]

EXAMPLES Hereinafter, the contents and effects of the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to the following examples unless departing from the gist thereof.

The methods for measuring the properties of the films in Examples and Comparative Examples are described below.

(1) Method of Measuring Heat Shrinkage The heat shrinkage after 30 minutes at 150 ° C. in all directions in the plane of the film was measured according to JIS C-2318. The measurement direction was a vertical direction and a horizontal direction.

(2) Measurement method of dimensional change rate of polyester film in heat treatment of film-laminated metal plate Degreasing-treated metal plate of 190 μm thickness (tin-free steel, L type bright finish, surface roughness 0.3 to
0.5 μm, manufactured by Nippon Steel Corporation) was preheated to 200 ° C., and the metal plate and one side of a polyester film sample having a thickness of 12 μm were combined, and a rubber roll and a rubber roll having a pressure of 500 N / cm were used. And then rapidly cooled with water to obtain a film-laminated metal plate [202 μm thick (polyester film / metal plate = 12 μm / 190 μm)]. The obtained film-laminated metal plate is placed on a film such that one side is parallel to the film longitudinal stretching direction (biaxially stretched film), the film stretching direction (uniaxially stretched film), or the film forming direction (unstretched film). The sample portion and the metal plate portion were cut into a 60 mm × 60 mm square with the same area. Next, this film-laminated metal plate sample was suspended from the ceiling in a hot-air oven adjusted to a wind speed of 1 to 10 m / sec and a temperature of 210 ° C. so as to be in the middle of the oven, and heat-treated for 2 minutes. The sample was taken out of the oven, immediately immersed in water at 25 ° C. or lower for 1 second or more, and rapidly cooled with water. Next, in the film portion of the sample, the length in the film transverse stretching direction (biaxially stretched film), or in the film stretching direction (uniaxially stretched film) or in the direction perpendicular to the film forming direction (unstretched film) in the film plane is read. , Dimensions after heat treatment (I: unit mm). From the obtained I, the dimensional change rate was calculated by the following equation. Dimensional change rate (%) = (| 60−I | / 60) × 100

(3) Method for quantifying ethylene terephthalate cyclic trimer A sample was immersed in hexafluoroisopropyl alcohol / chloroform = 2/3 (V / V) to dissolve the polyester. Next, the polyester was precipitated with methanol, and the precipitated polyester was separated by filtration and dried, and the amount was measured. The filtrate obtained when the precipitated polyester was separated by filtration was evaporated to dryness, and the evaporated product was dissolved in N, N-dimethylformamide. The solution was developed by liquid chromatography, and the amount of ethylene terephthalate cyclic trimer was determined.

(4) Method for Determining Oligomer Precipitation The film-laminated metal plate obtained as described in (2) above has one side stretched in the film longitudinal direction (biaxially stretched film), the film stretched direction (uniaxially stretched film) or The area of the film sample portion and the area of the metal plate portion are set to 10 so as to be parallel to the film forming direction (unstretched film).
It was cut into a square of 0 mm x 100 mm to obtain a sample. This sample was mixed with 500 cc of distilled water at 120 ° C. for 30 minutes.
It was retorted for a minute. The film-laminated metal plate after the treatment was air-dried, and the state of the film surface was observed with a loupe, and the presence or absence of oligomer precipitation was determined based on the following criteria. Yes: oligomer crystals are observed on the film surface. None: No oligomer crystals are observed on the film surface.

(5) Method of Measuring Dynamic Friction Coefficient The film-laminated metal plate obtained as in the above (2) was prepared by setting the long side to the film longitudinal stretching direction (biaxially stretched film), the film stretching direction (uniaxially stretched film) or The area of the film sample portion and the area of the metal plate portion are set to 15 so as to be parallel to the film forming direction (unstretched film).
It was cut into a rectangle of 0 mm x 100 mm to obtain a sample. Then a weight 1. having a contact area of 50 mm × 70 mm.
A 5 kg slide is set so that the film sample is oriented such that the longitudinal direction of the film (biaxially stretched film) or the direction of stretching the film (uniaxially stretched film) or the direction of film formation (unstretched film) is parallel to the sliding direction. Then 8
The coefficient of kinetic friction when sliding on a tin-free steel plate at 0 ° C. at a speed of 250 mm / min was measured.

(6) Method of Measuring Melting Point A sample was heated and melted at 300 ° C. for 5 minutes, and then rapidly cooled with liquid nitrogen. Using 10 mg of the sample as a sample, an endothermic peak temperature based on crystal melting which appeared when the temperature was raised at a rate of 10 ° C./min was measured with a differential scanning calorimeter.

(7) Measurement method of intrinsic viscosity A sample was dissolved in a mixed solvent of phenol / tetrachloroethane (weight ratio: 6/4) so as to have a concentration of 0.4 g / dl, and the solution was dissolved in an Ubbelohde type viscosity tube. The measurement was performed at a temperature of 30 ° C.

Example (Production of Polyester Film) As polyester for the layer A, 0.3% by weight of aggregated silica having an average particle size of 1.5 μm and trimethylolpropane trimethacrylate having an average particle size of 3.0 μm were used. It contains 1.0% by weight of crosslinked spherical polymethyl methacrylate particles, and has a reduced ethylene terephthalate cyclic trimer content of 0.3% by extraction.
95% by weight of polyethylene terephthalate having an intrinsic viscosity of 3% by weight, an intrinsic viscosity of 0.70 and a melting point of 250 ° C.
10. Polybutylene terephthalate having a melting point of 224 ° C. 5
Mixture with parts by weight (melting point 250 ° C, intrinsic viscosity 0.70)
Was used. On the other hand, as a polyester for the layer B, a copolymerized polyester of terephthalic acid / isophthalic acid (molar ratio: 90/10) containing 0.1% by weight of spherical silica having an average particle diameter of 1 μm and ethylene glycol (melting point: 215 ° C., intrinsic viscosity 0.65) was used. The polyesters for the layer A and the layer B were melted by separate extruders, and the melts were combined in a die and then extruded on a cooling drum to form an amorphous sheet. Thereafter, the amorphous sheet is stretched 3.5 times in the longitudinal direction and 3.5 times in the transverse direction at 90 ° C.
By heat-setting at 220 ° C., a polyester film having a layer A thickness of 9.5 μm and a layer B thickness of 2.5 μm (total thickness 12 μm) was obtained. The heat shrinkage of the film by the method described above was 2.2% in the vertical direction and 0.9% in the horizontal direction.

(Production of Film-Laminated Metal Plate) 190 μm-thick metal plate (tin-free steel, L-type bright finish, surface roughness 0.3 to 0.5)
μm, manufactured by Nippon Steel Corporation) was preheated to 200 ° C., and the metal plate and the surface of the polyester film on the layer B side were joined together. Passed under the condition of a speed of 10 m / min, then quenched with water to obtain a film-laminated metal plate [202 μm thick
(Polyester film (layer A / layer B) / metal plate = 1
2 μm (9 μm / 3 μm) / 190 μm)]. At this time, there was no problem in handling properties such as breakage of the film, and the film was good. The dimensional change of the resulting film-laminated metal plate due to the heat treatment of the polyester film shown above was measured and found to be 0.5%. The coefficient of kinetic friction at 80 ° C. on the film surface and the content of ethylene terephthalate cyclic trimer in the film were measured to be 0.39 and 0.4, respectively.
It was 1% by weight. Further, when the presence or absence of oligomer precipitation was observed, no oligomer was precipitated on the film surface.

(Production of Metal Container) A three-piece can was manufactured using the above-described film-laminated metal plate.
The can was made at a high speed in the can making process, and even after the heat treatment in the process, no problems such as looseness of the film and surface exposure of the metal plate occurred. The can thus obtained was filled with foodstuffs, subjected to a retort treatment at 125 ° C. for 30 minutes, and subjected to a storage test at 40 ° C. for 6 months. It was excellent.

COMPARATIVE EXAMPLE As the polyester for the layer A in the above example, 100 parts by weight of the above-mentioned polyethylene terephthalate having a cyclic trimer content of 0.33% by weight was used without using polybutylene terephthalate, and a film was formed. A polyester film and a film-laminated metal plate were produced in the same manner as in the above example except that the heat setting temperature under the conditions was 160 ° C.

The heat shrinkage (longitudinal and horizontal directions), dimensional change, dynamic friction coefficient and ethylene terephthalate cyclic trimer content of the polyester film in the heat treatment of the film-laminated metal plate were 4.5%, respectively.
7.5%, 3.0%, 0.38 and 0.38% by weight.

When a film-laminated metal plate was produced using the polyester film, the film was easily wrinkled and the yield was low. Furthermore, when a metal container was manufactured using a good portion without wrinkles of the film-laminated metal plate, a defective finish of repairing a joint portion due to shrinkage of the film occurred after heat treatment during a can-making process, resulting in low commercial value. Met.

[0070]

The polyester film of the present invention has excellent heat resistance while showing good handling properties without film breakage at the time of laminating, and can maintain the surface of a metal plate even after heat treatment such as a can making process. In addition to being able to be coated stably, it also has excellent barrier properties, corrosion resistance, flavor resistance, etc., so there is no surface exposure etc. of the metal plate, the finish of the can is good, and the corrosion resistance and contents A metal container excellent in the protection of food products can be provided.

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor: Nagano, 344, Maebata, Kizu, Inuyama-shi, Aichi Prefecture F-term in the Inuyama Plant of Toyobo Co., Ltd. (reference) 4F100 AA20B AA20H AB01C AK25A AK25H AK41A AK41B AK42A AK42B AL01B AL05A BA02 BA03 BA07 BA10A BA10C CA23A CA23B DA01 DE01A DE01B DE01H EJ37 GB16 JA03 JA04A JA04B JA20 JB02 JJ03 JK16 JK16A YY00 YY00A YY00B

Claims (4)

[Claims] 1. An A / B two-layer structure comprising an A layer made of polyester having a melting point of 240 to 260 ° C. and a B layer made of polyester having a melting point of 200 to 235 ° C. A film heat-set at a temperature of 5 ° C. or lower than the melting point of the polyester of the B layer and a temperature of 15 ° C. or lower than the melting point of the polyester of the A layer,
A film-laminated metal plate is formed by laminating the layer B with the metal plate side, the coefficient of kinetic friction at 80 ° C. on the film surface of the layer A is 0.45 or less, and the ethylene terephthalate ring of the resin layer on the film surface is The trimer content is 0.70% by weight or less, and the dimensional change when the film-laminated metal plate is heat-treated in an atmosphere at 210 ° C. for 2 minutes is 2.0% or less. Polyester film. 2. The polyester film according to claim 1, which comprises crosslinked polymer particles and / or inorganic fine particles. 3. A film-laminated metal plate obtained by laminating the polyester film according to claim 1 on at least one surface of the metal plate. 4. A metal container formed by molding the film-laminated metal plate according to claim 3.