JPH07314625A - Polyester composite film for metal laminate, laminated metal panel and metal container - Google Patents

Abstract

PURPOSE:To obtain a polyester composite film enhanced in moldability and heat resistance, suppressed in the elution of an oligomer and capable of being thermally bonded to a metal panel by laminating an adhesive layer composed of polyester having a specific m.p. to a base material layer composed of a compsn. containing a specific polyester copolymer. CONSTITUTION:A base material layer composed of a compsn. containing 70-98wt.% of polyethylene terephthalate and 2-30wt.% of a butylene terephthalate copolymer containing 90mol% or more of a butylene terephthalate unit is prepared and an adhesive layer composed of polyester with an m.p. of 180-240 deg.C is laminated to the single surface of the base material layer to obtain a polyester composite film for a metal laminate. Herein, the content of an ethylene terephthalate cyclic trimer in the composite film is pref. 0.7wt.% or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester-based composite film laminated to a metal material mainly used for food containers such as soft drinks, beer and canned foods, a metal plate laminated with the film, and a laminated metal plate. The present invention relates to a metal container formed by, for example, forming a can.
More specifically, it exhibits excellent moldability when performing can-making processing such as drawing, and because it can be heat-bonded without using an adhesive, it can prevent the taste and odor of foodstuffs from residual solvent caused by the adhesive. A polyester-based composite film suitable for laminating with a metal and the film are laminated, which can avoid adverse effects, and further suppress the amount of oligomers eluted from the laminated film due to heat treatment after food filling such as retort treatment. Laminated metal plate,
The present invention also relates to a metal container formed by forming the laminated metal plate into a can shape.

[0002]

2. Description of the Related Art Conventionally, a paint is generally applied to prevent corrosion on the inner and outer surfaces of a metal can, and a thermosetting resin is used as the paint. Another method of preventing corrosion is to use a thermoplastic resin film. For example, it has been attempted to laminate a polyolefin film such as a polypropylene film to heated tin-free steel. Further, it has been studied to laminate a polyester film having good heat resistance on a metal plate and use the laminated metal plate for a metal can.

[0003]

Most of the methods for coating thermosetting resin paints use solvent type paints.
Further, the formation of the coating film requires heating at a high temperature of 150 to 250 ° C. for several minutes for a long time, and since a large amount of the organic solvent is scattered during baking, it is possible to simplify the process and improve pollution prevention. Is requested. Further, in the coating film formed under the conditions as described above, it is inevitable that a small amount of organic solvent remains, for example, when a food product is filled in the metal can on which the coating film is formed, the organic solvent Shifts to groceries, which adversely affects the taste and smell of groceries. Furthermore, additives contained in the paint and low molecular weight substances due to incomplete crosslinking reaction migrate to food products, and have the same adverse effect as the above-mentioned residual organic solvent.

The method using a thermoplastic resin film can solve the above-mentioned problems such as simplification of the process and prevention of pollution. However, of the thermoplastic resin film,
For example, when a polyolefin film such as polyethylene or polypropylene is used, it has low heat resistance and may be whitened by retort treatment (heat treatment), and the film may peel off from the laminated metal plate. Further, since the polyolefin film is soft, there is a problem that scratch resistance is poor. If the scratch resistance of the film is inferior, scratches will occur on the film surface, for example, when the laminated metal sheets are transferred in the can manufacturing process or during processing such as winding and tightening, which reduces the commercial value. There's a problem. In addition, the method using a polyolefin film solves the problems due to the migration of residual solvent, which was observed with the method using a thermosetting resin paint, but the addition of low molecular weight substances and heat stabilizers generated during film formation The transfer of agents to food products adversely affects the taste and smell of food products. In addition, the polyolefin film has a problem that it is inferior in flavor resistance because it absorbs aroma components in foods.

On the other hand, the method of using a polyester film as the thermoplastic resin film is the most preferable method so far because the problems of the above polyolefin film are improved. Polyester films have attracted attention as polyethylene terephthalate films having balanced properties, and some proposals based on these have been made. For example, a method of laminating a biaxially oriented polyethylene terephthalate film on a metal plate via adhesion with a low melting point polyester, and using the laminated metal plate as a can-making material (Japanese Patent Laid-Open No. Sho 5).
6-10451, JP-A-1-192546), a method in which an amorphous or extremely low crystalline aromatic polyester film is laminated on a metal plate and the laminated metal plate is used as a can-making material (JP-A-1). -192
No. 545) has been proposed. However, in these methods, there is a problem of insufficient heat resistance such as peeling of the film due to poor adhesion of the film in the molding processability, the heat treatment in the can making process and the retort treatment process after filling the contents. Further, the polyester film is excellent in heat resistance, does not require additives such as heat stabilizers, and produces less low molecular weight substances, and is a food product due to migration of the low molecular weight substances compared to the above polyolefin type films. The taste and smell problems are greatly improved. However, in the polyester film containing polyethylene terephthalate as a main component, there is a low molecular weight compound produced in a polymerization process or a film forming process, that is, an oligomer mainly containing a so-called ethylene terephthalate cyclic trimer (hereinafter sometimes referred to as an oligomer). It is contained, and there is a problem that the oligomer is eluted from the film and transferred to foods, or is deposited on the surface of the laminated film to impair the appearance, and its solution has been desired.

The object of the present invention is to solve the above-mentioned problems of the prior art, to be excellent in moldability and heat resistance, to suppress the elution of oligomers, and to allow thermal adhesion to a metal plate. To provide. Also,
An object of the present invention is to provide a laminated metal plate which is excellent in moldability and heat resistance and can be easily formed into a can. Further, an object of the present invention is to prevent the peeling of the laminated film from occurring even when subjected to heat treatment, and to prevent the oligomer from migrating to the filled food product or the oligomer being deposited on the surface of the laminated film. To provide a container.

[0007]

The present inventors have arrived at the present invention as a result of extensive studies to achieve the above object. That is, the polyester-based composite film for metal laminate of the present invention comprises polyethylene terephthalate 70-
The melting point is 18 at least on one surface of the base material layer (A layer) composed of a composition containing 98% by weight and 2 to 30% by weight of a butylene terephthalate copolymer having a polybutylene terephthalate or butylene terephthalate unit of 90 mol% or more.
The adhesive layer (B layer) made of polyester at 0 to 240 ° C. is laminated. In the present invention, the content of the ethylene terephthalate cyclic trimer in the composite film is preferably 0.7% by weight or less, more preferably 0.5% by weight or less. The laminated metal plate of the present invention is obtained by laminating the above polyester-based composite film on at least one surface of the metal plate so that the adhesive layer of the film and the metal plate are in contact with each other. The metal container of the present invention is formed by molding the above laminated metal plate.

The present invention will be described in detail below. In the present invention, the base material layer (A layer) is a polyester composition containing 70 to 98% by weight of polyethylene terephthalate and 2 to 30% by weight of polybutylene terephthalate or a butylene terephthalate copolymer having a butylene terephthalate unit of 90 mol% or more. It consists of things. Only in this composition range, excellent impact resistance after lamination can be formed without causing cracks in the film in the can-making process, and the amount of shrinkage of the film due to the thermal covering history after lamination is small, for example, Wrinkles and peeling of the film do not occur during heat treatment such as retort treatment, and the film can be usefully used as a metal laminating film. A preferred composition range is polyethylene terephthalate 75-
95% by weight, 5 to 25% by weight of a butylene terephthalate copolymer having a polybutylene terephthalate or butylene terephthalate unit of 90 mol% or more.

Examples of the polycarboxylic acid component other than terephthalic acid in the above butylene terephthalate copolymer include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, naphthalenedicarboxylic acid and diphenyldicarboxylic acid,
Examples thereof include adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, aliphatic dicarboxylic acids such as dimer acid, and cyclohexanedicarboxylic acid. Among the above, it is preferable to use an aromatic dicarboxylic acid such as isophthalic acid or naphthalenedicarboxylic acid from the viewpoint that the flavor resistance is less deteriorated. Further, as the polyhydric alcohol component of the butylene terephthalate copolymer,
Glycol, for example, ethylene glycol,
Aliphatic diols such as diethylene glycol, triethylene glycol, propanediol, hexanediol, dodecane methylene glycol, neopentyl glycol, alicyclic diols such as cyclohexanedimethanol,
Examples thereof include aromatic diols such as ethylene oxide adducts of bisphenol derivatives. Of these, ethylene glycol is preferred. The butylene terephthalate copolymer used in the present invention has a butylene terephthalate unit content of 90 mol% or more. A copolymer having a butylene terephthalate unit content of less than 90 mol% has a problem that it has poor heat resistance and is economically disadvantageous. The butylene terephthalate copolymer preferably has a butylene terephthalate unit content of 95 mol% or more.

In the present invention, the adhesive layer (B layer) is made of polyester having a melting point of 180 to 240 ° C. When the melting point of the polyester is less than 180 ° C, the heat resistance of the polyester is low, and wrinkles may occur during laminating,
When the laminated metal plate is subjected to heat treatment such as retort treatment, the laminated film becomes white and peels off, which is not preferable. On the other hand, when the temperature exceeds 240 ° C., the thermal adhesiveness of polyester is deteriorated, and it is necessary to laminate with an adhesive other than polyester. As a result, the organic solvent contained in the adhesive remains and adversely affects the taste and smell of the food product. The preferable melting point range of polyester is 190 to 23.
It is 5 ° C. The control of the melting point of the polyester can be set by selecting the type and amount of the copolymerization component of the polyester described below.

The polyester used for the adhesive layer is mainly obtained by polycondensing a polycarboxylic acid and a polyhydric alcohol. Examples of the polycarboxylic acid component constituting the polyester for the adhesive layer include dicarboxylic acid, for example, terephthalic acid, isophthalic acid, phthalic acid,
Aromatic dicarboxylic acids such as naphthalenedicarboxylic acid and diphenyldicarboxylic acid, adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid,
Examples thereof include aliphatic dicarboxylic acids such as dimer acid and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid. Examples of the polyhydric alcohol component constituting the above polyester include glycols, for example, aliphatic diols such as ethylene glycol, diethylene glycol, triethylene glycol, propanediol, butanediol, hexanediol, dodecane methylene glycol and neopentyl glycol. Alicyclic diols such as cyclohexanedimethanol, aromatic diols such as ethylene oxide adducts of bisphenol derivatives, and the like.

In the present invention, it is preferable to use, as the polyester for the adhesive layer, a copolymer obtained by copolymerizing polyethylene terephthalate with an isophthalate component from the viewpoint of economy. In this case, the molar ratio of terephthalate units to isophthalate units is generally 94/6 to 69/31 terephthalate / isophthalate. In the present invention, the use of other copolymerization components is not limited. The polyester preferably has an intrinsic viscosity of 0.5 or more for reasons such as adhesive strength.

In the present invention, the polyester for forming the base material layer and the adhesive layer may be, if necessary, an antioxidant, a heat stabilizer, an ultraviolet absorber, a plasticizer, a pigment, an antistatic agent, a lubricant. There is no limitation on compounding agents, crystal nucleating agents and the like.

The method for producing the polyester for the base layer and the adhesive layer is not particularly limited, and may be produced by either the transesterification method or the direct polymerization method. Further, it may be produced by a solid phase polymerization method to increase the molecular weight. The use of the solid phase polymerization method is a preferable method in the sense that the content of the ethylene terephthalate cyclic trimer described below is lowered.

In the present invention, the content of the ethylene terephthalate cyclic trimer (oligomer) produced in the polymerization step or the film forming step in the above composite film is 0.7% by weight or less based on the total amount of polyester. Is more preferable, 0.6% by weight or less is more preferable, and 0.5% by weight or less is particularly preferable. This can further suppress the elution of the oligomer. When the content of the oligomer exceeds 0.7% by weight, when a food product is filled in a metal container formed by laminating the polyester-based composite film, a heat treatment such as a retort treatment is performed. However, the amount of oligomers eluted from the film is increased, and when the laminate film is a can inner surface laminate film, the oligomer migrates to the food product and adversely affects the taste and odor of the food product, which is not preferable. Further, in the case of a can outer surface laminated film, oligomers are deposited on the film surface and the appearance is impaired, which is not preferable.

There is no particular limitation on the method for adjusting the content of the oligomer in the polyester film to 0.7% by weight or less. For example, after the polyester film is formed, water or an organic solvent is used to form an ethylene terephthalate cyclic trihydrate. This can be achieved by extracting and removing the monomer. Further, it can be achieved by using a polyester having a small content of ethylene terephthalate cyclic trimer as a raw material. It is economical and recommended to use the latter method. There is no limitation on the method for producing a polyester raw material having a low ethylene terephthalate cyclic trimer content, and a reduced pressure heat treatment method, a solid phase polymerization method, an extraction method with water or an organic solvent and a method combining these methods, etc. Can be mentioned. In particular, after reducing the amount of ethylene terephthalate cyclic trimer by the solid phase polymerization method, the method of further reducing the cyclic trimer by water extraction, the content of the cyclic trimer in the raw material polyester is low, and This is the most preferable method because the amount of the cyclic trimer produced in the film forming step can be suppressed.

The thickness of the base material layer of the polyester composite film of the present invention is generally 3 to 50 μm, preferably 5 to 2
It is 0 μm. If it is less than 3 μm, the film is difficult to handle, the laminating processability is deteriorated, and there is a risk that the corrosion resistance is deteriorated due to the occurrence of defects such as pinholes and cracks in the can manufacturing process and the like, which is not preferable. On the other hand, when it exceeds 50 μm, the protective effect such as corrosion resistance of the metal plate is saturated, which is not economical, and the internal stress of the film itself increases, which may adversely affect the adhesiveness, which is not preferable. On the other hand, the thickness of the adhesive layer of the polyester-based composite film of the present invention is generally 1 to 15 μm, preferably 2 to 10 μm. If it is less than 1 μm, the adhesion to the metal plate becomes insufficient, which is not preferable. On the other hand, when it exceeds 15 μm, the adhesion to the metal plate is saturated and the heat resistance is lowered, which is not preferable.

The method for producing a polyester-based composite film in which an adhesive layer is laminated on at least one surface of the base material layer of the present invention is not particularly limited as long as a film satisfying the above requirements can be formed, and for example, a multi-layer extrusion method or extrusion. It is manufactured by a laminating method or the like. In the present invention, the multi-layer extrusion method is preferred for economical reasons.

The laminated metal plate of the present invention is obtained by laminating the above polyester-based composite film on one side or both sides of the metal plate so that the adhesive layer of the film and the metal plate are in contact with each other. Examples of the metal plate used include tin plate, tin-free steel, aluminum and the like.

When laminating the above polyester-based composite film on a metal plate, it is important that the adhesive layer surface of the composite film and the metal plate surface are in contact with each other. With the combination, the effects of the present invention can be exhibited for the first time. As a laminating method, a conventionally known method can be applied and is not particularly limited, but in the present invention, it is preferable to carry out by a thermal laminating method which can achieve organic solvent-free and can avoid an adverse effect on the taste and smell of food products due to residual solvent. . Among them, the thermal laminating method in which a metal plate is electrically processed is particularly recommended. In the case of double-sided laminating, they may be laminated at the same time or sequentially.

In the present invention, it goes without saying that the composite film can be laminated on the metal plate using an adhesive.

The metal container of the present invention can be obtained by molding using the above laminated metal plate. The method for forming this metal container is not particularly limited. Further, the shape of the metal container is not particularly limited, but it is preferably applied to a so-called two-piece can, which is formed by a forming process such as drawing, drawing and ironing, and stretch draw molding. The present invention is also applicable to a so-called three-piece can in which the contents are filled by winding a top lid suitable for filling food items such as coffee drinks.

[0023]

EXAMPLES Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the examples below, and the present invention can be carried out within a range not departing from the above-mentioned gist. Both are within the technical scope of the present invention.

Various measurement and evaluation methods used in the examples are as follows. (1) Melting point The composition of each layer was heated and melted at 300 ° C. for 5 minutes, mixed, and then rapidly cooled with liquid nitrogen.
The temperature was raised at a rate of 10 ° C./min in a N ₂ gas flow using a differential scanning calorimeter to measure a thermograph, and the peak temperature of the endothermic peak associated with melting was taken as the melting point.

(2) Impact resistance evaluation A ten-free steel plate (T-
(1, 0.29 mm) so that the polyester adhesive layer surface adheres to both surfaces thereof, the product was pressure-bonded with a water-cooled roll and then rapidly cooled in water to obtain a laminated steel plate. An impact was applied to the laminated steel sheet from one film surface side of the steel sheet by a DuPont impact test (impactor tip diameter 12.7 mm, impactor weight 1 kg, impactor drop height 30 cm). Then, by the method shown in FIG. 1, the current value passing through the impact portion was measured.
That is, referring to FIG. 1, the laminated steel plate (1) on which the impact portion (2) is formed is used as a bottom plate with the film (1a) surface side where the impact portion (2) is concave facing up. Then, a polyvinyl chloride cylinder (3) having an inner diameter of 20 mm and a height of 60 mm was placed on the steel plate (1). A Pt electrode (4) is horizontally provided at the center of the height of the cylinder (3). Then, as shown in FIG. 1, a 1% sodium chloride aqueous solution (5) was poured onto the Pt electrode (4). Between the other film (1b) surface of the impact part (2) and the Pt electrode (4), a Pt electrode (4) was used as a negative electrode and a 6 V DC power source was loaded, and the current value after 30 seconds was measured with an ammeter. Measured in (6). The smaller the current value, the better the impact resistance. Here, a double-sided laminated steel sheet is shown, but a single-sided laminated steel sheet can be similarly measured.

(3) Evaluation of shrinkage amount after heating Laminated steel sheet obtained by the same method as used for impact resistance evaluation
A cut piece of 3 cm × 3 cm was prepared from (1), and FIG.
As shown in, the width (L1) on the film (1a) surface side of this cut piece
A sample having two 0.3 mm cuts (7) was prepared. Then, after heating this sample at 230 ° C. for 10 minutes, as shown in FIG. 2 (B), the width (L2) of the cut (7)
Was measured. As a result, the amount of film shrinkage (L2-L1)
Was evaluated.

(4) Quantification of ethylene terephthalate cyclic trimer A polyester composite film was dissolved in hexafluoroisopropyl alcohol / chloroform = 2/3 (V / V), the polyester was precipitated with methanol, and the precipitate was filtered off. To do. The filtrate is evaporated to dryness and the evaporated dry matter is dissolved in dimethylformamide. The solution was developed by liquid chromatography to quantify the ethylene terephthalate cyclic trimer in the composite film.

(5) Judgment of Elution of Oligomer A 10 cm square laminated steel plate is subjected to retort treatment at 120 ° C. for 30 minutes together with 500 cc of distilled water. The treated laminated steel sheet was air-dried, the state of the film surface was observed with a loupe, and the presence or absence of oligomer elution was determined based on the following criteria. Present: Oligomer crystals are observed on the film surface. None: No oligomer crystals are observed on the film surface.

[Example 1] As a resin for a base material layer (A layer), 0.10% by weight of spherical silica having an average particle size of 1.5 µm was contained, and the intrinsic viscosity was reduced to 0.70 by an extraction method to obtain an intrinsic viscosity of 0.70,
A blended product of 80 parts by weight of polyethylene terephthalate having an ethylene terephthalate cyclic trimer content of 0.30% by weight and 20 parts by weight of polybutylene terephthalate having an intrinsic viscosity of 0.85 was used. On the other hand, as the resin for the adhesive layer (B layer), 0.08% by weight of spherical silica having an average particle diameter of 1.5 μm was contained, and the intrinsic viscosity was 0.7 which was oligomerized by the extraction method.
0, ethylene terephthalate cyclic trimer content 0.28
% Terephthalic acid / isophthalic acid (molar ratio 8
Copolymerized polyester (melting point 225 ° C.) of 8/12) and ethylene glycol was used. The resin for layer A and the resin for layer B were melted by separate extruders respectively, and these melts were merged between the dies, and then extruded on a cooling drum to form an amorphous sheet, and then longitudinally at 100 ° C. Was stretched 3.5 times in the transverse direction and 4.0 times in the transverse direction and heat-set at 180 ° C. to obtain a polyester-based composite film having an A layer thickness of 22 μm and a B layer thickness of 3 μm (total thickness 25 μm). The composite film was pressure-bonded with a water-cooling roll so that the B layer surface was bonded to both surfaces of a ten-free steel plate (T-1, 0.29 mm) heated to 225 ° C. and then rapidly cooled in water to obtain a laminated steel plate. It was Table 1 shows the properties of the obtained polyester-based composite film and the laminated steel sheet. The laminated steel sheet laminated with the polyester-based composite film obtained in this example has good impact resistance, and the shrinkage amount of the film due to the history of thermal covering after lamination is small, and further, the amount of oligomer discharged is There were few, and it was high quality as a laminated steel plate. Thus, the polyester-based composite film obtained in this example was of high quality as a film for metal laminating. When the laminated steel sheet (double-sided laminate) obtained in this example was formed into a two-piece can by drawing, the composite film was not cracked during the can-making process and could be made at high speed. In addition, the molding can was filled with oolong tea and subjected to retort treatment, but it was of high commercial value with no change in taste or odor without migration of oligomers or organic solvents from the composite film. Further, no oligomer was deposited on the outer surface of the bottom lid even after the retort treatment.

[Comparative Example 1] A polyester-based composite film and a laminated steel sheet were prepared in the same manner as in Example 1 except that polybutylene terephthalate was not used as the resin for the layer A and only polyethylene terephthalate was used. Obtained. These characteristics are shown in Table 1. The laminated steel sheet obtained in this comparative example was inferior in impact resistance, had a large amount of shrinkage of the film due to the thermal covering history after lamination, and was not practical. As described above, the polyester-based composite film obtained in this comparative example had low practicability as a film for metal laminating. Further, a laminated steel sheet (double-sided laminate) was made in the same manner as in Example 1, but the film was cracked in the molding process and only a product having a low commercial value was obtained.

[Comparative Example 2] A polyester type resin was prepared in the same manner as in Example 1 except that the resin for the layer A was changed to a compounding ratio of polyethylene terephthalate and polybutylene terephthalate of 60/40 (weight ratio). A composite film and a laminated steel plate were obtained. These characteristics are shown in Table 1. The laminated steel sheet obtained in this comparative example was inferior in impact resistance, and the polyester-based composite film was low in practicality as a film for metal lamination.

[Comparative Example 3] A polyester-based composite film was obtained in the same manner as in Example 1 except that the resin for A layer in Example 1 was used as the resin for B layer. The obtained film was laminated on a ten-free steel plate in the same manner as in Example 1, but the adhesive strength was low, and the film was not practical as a metal laminating film.

[Comparative Example 4] A polyester-based composite film and a laminated steel sheet were obtained in the same manner as in Example 1, except that the resin for layer B of Example 1 was used as the resin for layer A. These characteristics are shown in Table 1. The laminated steel sheet obtained in this comparative example was inferior in impact resistance, and the polyester-based composite film was low in practicality as a film for metal lamination.

[Comparative Example 5] In Example 1, 40 parts by weight of polyethylene terephthalate used as the resin for the A layer in Example 1 as the resin for the B layer, and an intrinsic viscosity of 0.70 which was oligomerized by the extraction method, Blend of terephthalic acid / isophthalic acid (molar ratio 90/10) with an ethylene terephthalate cyclic trimer content of 0.29% by weight and 60 parts by weight of a copolyester of ethylene glycol (after melt extrusion of the blend Melting point 240 ° C.)
A polyester-based composite film was obtained in the same manner as in Example 1. The obtained film was laminated on a ten-free steel sheet in the same manner as in Example 1, but the adhesive strength was low. Although the bonding strength was improved by increasing the laminating temperature to 240 ° C and laminating, the resulting laminated steel sheet was inferior in impact resistance and had a large amount of shrinkage of the film due to the thermal covering history after laminating. , Was of low practicality. As described above, the polyester-based composite film of this comparative example had low practicability as a film for metal laminating.

[Comparative Example 6] In Example 1, as the resin for the layer B, terephthalic acid and ethylene glycol / neopentyl glycol (70/30 molar ratio) having an ethylene terephthalate cyclic trimer content of 0.30% by weight were used. Example 1 except that a copolymer resin with a melting point of 160 ° C. was used.
A polyester-based composite film was obtained in the same manner as in. The obtained film was laminated on a ten-free steel plate in the same manner as in Example 1, but the amount of shrinkage due to the history of thermal covering after lamination was large and wrinkles were generated, which is of low practicality as a film for metal lamination. Met.

[Comparative Example 7] In Comparative Example 6, the contents of the ethylene terephthalate cyclic trimer in the resin for layer A and the resin for layer B were 1.0% by weight and 0.72, respectively.
A polyester-based composite film was obtained in the same manner as in Comparative Example 6 except that the weight percentage was changed. The obtained film was laminated on a ten-free steel sheet in the same manner as in Example 1, but the amount of shrinkage due to the history of thermal covering after lamination was large and wrinkles were generated. Moreover, the amount of oligomers eluted was large, and the quality of the laminated steel sheet was low. As described above, the polyester-based composite film obtained in this comparative example had a low quality as a film for metal laminating.

[Example 2] As the resin for the layer A, 0.15% by weight of spherical polymethylmethacrylate particles crosslinked with trimethylolpropane trimethacrylate having an average particle diameter of 3.0 µm was contained, and a low oligomer was prepared by the extraction method. Polyethylene terephthalate 8 with a modified intrinsic viscosity of 0.70 and an ethylene terephthalate cyclic trimer content of 0.33% by weight
A blend of 5 parts by weight and 15 parts by weight of a copolyester of terephthalic acid / isophthalic acid (molar ratio 95/5) having an intrinsic viscosity of 0.80 and 1,4 butanediol was used. On the other hand, the resin for layer B has an average particle size of 3.
Spherical polymethylmethacrylate particles cross-linked with 0 μm trimethylol propylene trimethacrylate 0.1% by weight, low-oligomerized by extraction method, intrinsic viscosity 0.70, ethylene terephthalate cyclic trimer content 0.28 A copolymerized polyester (melting point 215 ° C.) of terephthalic acid / isophthalic acid (molar ratio 83/17) by weight and ethylene glycol was used. A polyester-based composite film and a laminated steel sheet were obtained in the same manner as in Example 1 except that the resin for layer A and the resin for layer B were changed as described above. These characteristics are shown in Table 1. Also,
A laminated steel sheet (double-sided laminate) was manufactured in the same manner as in Example 1. The polyester film, the laminated steel plate and the metal can obtained in this example were of high quality as in Example 1.

[Third Embodiment] In the first embodiment, the layers A and B are used.
A polyester-based composite film and a laminated steel plate were obtained in the same manner as in Example 1 except that the layer thicknesses were 12 μm and 8 μm, respectively. These characteristics are shown in Table 1. Further, a laminated steel sheet (double-sided laminate) was manufactured in the same manner as in Example 1. The polyester film, the laminated steel plate and the metal can obtained in this example were of high quality as in Example 1.

Example 4 A polyester-based composite was prepared in the same manner as in Example 1 except that the mixing ratio of polyethylene terephthalate and polybutylene terephthalate of the resin for layer A was 85/15 (weight ratio). A film and a laminated steel plate were obtained. These characteristics are shown in Table 1. Further, a laminated steel sheet (double-sided laminate) was manufactured in the same manner as in Example 1. The polyester film, the laminated steel plate and the metal can obtained in this example were of high quality as in Example 1.

[0040]

As described above, the polyester-based composite film of the present invention can be heat-bonded without using an adhesive agent, and the shrinkage amount of the film due to the history of thermal covering after lamination is small and the occurrence of wrinkles does not occur. Therefore, it is very suitable as a film for metal laminating.

Further, since the laminated metal plate of the present invention has excellent impact resistance, by using this as a metal container material, the film will not crack even if it is subjected to forming processing such as drawing or stretch draw molding. Cans can be produced at high speed, and cans with excellent corrosion resistance can be obtained.
Further, since the laminated metal plate is produced without using an adhesive, there is no elution of residual solvent due to the adhesive, and the metal container produced from this laminated metal plate is
Filling a food item does not have an adverse effect on the taste or smell of the food item. Further, even when the filled foodstuff is subjected to heat treatment such as retort treatment, the elution amount of the ethylene terephthalate cyclic trimer (oligomer) from the polyester-based composite film is suppressed, so that the oligomer may be transferred to food. , It does not deposit on the film surface and the surface appearance does not deteriorate.

As described above, the polyester-based composite film of the present invention can be heat-bonded to a metal plate, has excellent moldability, and suppresses the elution of oligomers even when heated, It is extremely useful as a laminating metal plate or a metal container, particularly as a laminating film for a metal container for filling retort food.

[0043]

[Table 1]

[Brief description of drawings]

FIG. 1 is a diagram for explaining a method of evaluating impact resistance of a laminated metal plate.

FIG. 2 is a diagram for explaining a shrinkage evaluation method after heating a film on a laminated metal plate.

[Explanation of symbols]

 (1) ... Laminated steel plates (1a) (1b) ... Film (2) ... Impact part (3) ... Cylinder (4) ... Pt electrode (5) ... Sodium chloride aqueous solution (6) ... Ammeter (7) ... Break ( L1)… Width of cut (7) before treatment (L2)… Width of cut (7) after treatment

Front page continuation (72) Inventor Tsutomu Isaka 2-8 Dojimahama, Kita-ku, Osaka Toyobo Co., Ltd.

Claims (5)

[Claims] 1. Polyethylene terephthalate 70 to 98
The composition has a melting point of 180 to 240 ° C. on at least one surface of a base material layer made of a composition containing 2 wt% to 30 wt% of polybutylene terephthalate or a butylene terephthalate copolymer having a polybutylene terephthalate unit of 90 mol% or more.
A polyester-based composite film for metal laminating, wherein an adhesive layer made of the above polyester is laminated. 2. The polyester-based composite film according to claim 1, wherein the content of the ethylene terephthalate cyclic trimer in the composite film is 0.7% by weight or less. 3. The polyester-based composite film according to claim 1, wherein the content of the ethylene terephthalate cyclic trimer in the composite film is 0.5% by weight or less. 4. The method according to claim 1, which is provided on at least one surface of the metal plate.
4. A laminated metal plate obtained by laminating the polyester composite film according to any one of 3 above so that the adhesive layer of the film and the metal plate are in contact with each other. 5. A metal container formed by molding the laminated metal plate according to claim 4.