JPH05154971A - Polyester film for metal plate laminate molding processing - Google Patents

Abstract

PURPOSE:To obtain a polyester film excellent in deep drawing processability and also excellent in impact resistance, heat resistance, retort resistance and corrosion resistance after can manufacturing in molding a metal can by subjecting a polyester film laminated metal plate to can manufacturing processing, for example, deep drawing process. CONSTITUTION:A polyester film for metal plate laminate molding processing is constituted by laminating a copolyester resin layer (B) having an m.p. of 210-245 deg.C and glass transition temp. of above 60 deg.C to at least the single surface of a copolyester resin layer (A) with an m.p. of 210-245 deg.C and glass transition temp. of 60 deg.C or lower.

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 and forming metal plates, and more particularly, it shows excellent forming processability when it is laminated with a metal plate to perform can-making processing such as drawing, and heat resistance. The present invention relates to a polyester film for laminating and processing metal plates, which can be used for producing metal cans, such as beverage cans and food cans, having excellent properties, retort resistance and aroma retention.

[0002]

2. Description of the Related Art Metal cans are generally painted to prevent corrosion on the inside and outside, but recently, for the purpose of simplifying the process, improving hygiene, and preventing pollution, rust prevention without the use of organic solvents The development of a method for obtaining the property has been advanced, and as one of them, coating with a thermoplastic resin film has been attempted. That is,
Studies have been conducted on a method of forming a can by laminating a thermoplastic resin film on a metal plate such as tin plate, tin-free steel, or aluminum, and then drawing it. Polyolefin films and polyamide films have been tried as the thermoplastic resin films, but they do not satisfy all of the molding processability, heat resistance, and aroma retention.

On the other hand, a polyester film, particularly a polyethylene terephthalate film, has been noted as having balanced properties, and several proposals based on this have been made. That is,

(A) A biaxially oriented polyethylene terephthalate film is laminated on a metal plate through an adhesive layer of low melting point polyester and used as a can-making material (JP-A-56).
-10451, JP-A-1-192546). (B) An amorphous or extremely low crystalline aromatic polyester film is laminated on a metal plate and used as a can-making material (JP-A-1-192545 and JP-A-2-573).
39). (C) A low orientation, heat-set, biaxially oriented polyethylene terephthalate film which is heat-fixed is laminated on a metal plate and used as a can-making material (Japanese Patent Laid-Open No. 64-22530).

However, the investigations by the present inventors have revealed that none of them has sufficient characteristics, and each has the following problems.

Regarding (A), the biaxially oriented polyethylene terephthalate film is excellent in heat resistance and aroma retention,
Molding processability is insufficient, and whitening of the film (generation of microcracks) and breakage occur in a can-making process that involves large deformation.

As for (B), since it is an amorphous or extremely low crystalline aromatic polyester film, the moldability is good, but the aroma retention is inferior, and printing after can making and retort sterilization treatment are carried out. After treatment such as the above, and further storage for a long period of time, the film is liable to become brittle, and there is a possibility that the film may deteriorate due to an impact from the outside of the can.

Regarding (C), although it is intended to exert its effect in the intermediate region between the above (A) and (B), it has not yet reached the low orientation applicable to can manufacturing, and Even if it can be processed in a region with a low degree of deformation, subsequent printing,
As in the case of (B), another retort treatment for sterilizing the contents of the can can easily cause embrittlement and change the film into a film that is easily cracked by an impact from the outside of the can.

[0009]

DISCLOSURE OF THE INVENTION The present inventors arrived at the present invention as a result of intensive research to develop a polyester film for can manufacturing which does not have these problems.

[0010]

That is, the present invention has a polymer melting point of 210 to 245 ° C. and a glass transition temperature of 60.
Copolymerized polyester resin layer (B) having a polymer melting point of 210 to 245 ° C and a glass transition temperature of more than 60 ° C on at least one surface of the copolymerized polyester resin layer (A) having a temperature of ℃ or less.
It is a polyester film for laminating and forming metal plates, characterized by being laminated.

Typical examples of the copolymer polyester resin layer (A) in the present invention include copolymer polyethylene terephthalate having a polymer melting point of 210 to 245 ° C. and a glass transition temperature of 60 ° C. or less. The copolymerization component may be an acid component or an alcohol component. The copolymerization acid component that simultaneously satisfies both the polymer melting point and the glass transition temperature is preferably an aliphatic dicarboxylic acid such as adipic acid, azelaic acid, sebacic acid or decanedicarboxylic acid, and the alcohol component is butane. Diol,
Aliphatic diols such as pentanediol and hexanediol, and polyalkylene glycols such as polyethylene glycol and polypropylene glycol are preferable. These may be used alone or in combination of two or more.

The proportion of the copolymerization component depends on the kind thereof, but as a result, the melting point of the polymer is in the range of 210 to 245 ° C., preferably 215 to 240 ° C. When the melting point of the polymer is less than 210 ° C., the heat resistance is poor, so that it cannot withstand the heating during printing after can making. On the other hand, when the melting point of the polymer exceeds 245 ° C., the crystallinity of the polymer is too large and the moldability is impaired.

At the same time, the proportion of the copolymerization component is such that the glass transition temperature of the polymer is in the range of 60 ° C. or lower, preferably 55 ° C. or lower, depending on the kind. If the glass transition temperature of the polymer exceeds 60 ° C,
Molding processability is insufficient, and the film is liable to break due to impact from the outside of the can after molding.

Therefore, it is necessary to determine the kind and amount of the copolymerization component in consideration of both the melting point and the glass transition temperature of the polymer.

Typical examples of the copolymer polyester resin layer (B) in the present invention include copolymer polyethylene terephthalate having a polymer melting point of 210 to 245 ° C. and a glass transition temperature of more than 60 ° C. The copolymerization component may be an acid component or an alcohol component. An aromatic dicarboxylic acid such as isophthalic acid, phthalic acid or naphthalene dicarboxylic acid is preferable as the acid component of the copolymerization that simultaneously satisfies both the polymer melting point and the glass transition temperature, and the alcohol component is diethylene glycol, propylene glycol or neo. Pentyl glycol and the like are preferable. These may be used alone or in combination of two or more.

The proportion of the copolymerization component depends on its kind, but as a result, the melting point of the polymer is in the range of 210 to 245 ° C., preferably 215 to 240 ° C. When the melting point of the polymer is less than 210 ° C., the heat resistance is poor, so that it cannot withstand the heating during printing after can making. On the other hand, when the melting point of the polymer exceeds 245 ° C., the crystallinity of the polymer is too large and the moldability is impaired.

At the same time, depending on the kind of the copolymerization component, the glass transition temperature of the polymer is 60 as a result.
It is a ratio that exceeds ℃, preferably 65 ℃ or more.
When the glass transition temperature is 60 ° C. or lower, the water vapor permeability of the film increases, and the metal plate easily rusts.

Therefore, the proportion of the copolymerization component is determined in consideration of both the melting point and the glass transition temperature of the polymer,
You need to decide the amount.

Here, the melting point of the copolyester is measured by using Du Pont Instruments 910 DSC, and the heating rate is 2
According to a method of obtaining a melting peak at 0 ° C./minute. The sample amount is about 20 mg.

The copolyester in the present invention preferably contains a lubricant having an average particle size of 2.5 μm or less. This lubricant may be inorganic or organic, but is preferably inorganic. Examples of the inorganic lubricant include silica, alumina, titanium dioxide, calcium carbonate, barium sulfate and the like, and examples of the organic lubricant include silicone particles and the like. It is preferable that the average particle diameter of each is 2.5 μm or less. If the average particle size of the lubricant exceeds 2.5 μm, coarse particles (particles with a size of 10 μm or more) in the portion deformed by processing such as deep-drawing can will be the starting point and cause pinholes, or in some cases fracture Therefore, it is not preferable.

Particularly preferred from the viewpoint of pinhole resistance is a monodispersed lubricant having an average particle size of 2.5 μm or less and a particle size ratio (major axis / minor axis) of 1.0 to 1.2. is there. Examples of such a lubricant include true spherical silica and true spherical silicone particles.

The amount of the lubricant in the copolyester may be determined depending on the winding property in the film manufacturing process.
Generally, it is preferable to add a small amount of particles having a large particle size and a large amount of particles having a small particle size. For example, it is preferable to add about 0.05% by weight in the case of silica having an average particle size of 2.0 μm and about 0.3% by weight in the case of titanium dioxide having an average particle size of 0.3 μm.
The film can also be made opaque by intentionally adjusting the pigment of the lubricant. For example, a white film can be obtained by adding 10 to 15% by weight of titanium dioxide.

As the lubricant, in addition to the above-mentioned externally-added particles, it is also possible to use internally-precipitated particles obtained by precipitating a part or all of the catalyst used in the polyester synthesis in the reaction step. Further, it is of course possible to use the externally added particles and the internally precipitated particles in combination.

The copolyester used in the present invention is not limited by its production method. For example, a method in which terephthalic acid, ethylene glycol, and a copolymerization component are subjected to an esterification reaction, and then the resulting reaction product is subjected to a polycondensation reaction to form a copolymerized polyester, or dimethyl terephthalate, ethylene glycol, and a copolymerization component are transesterified. Then, the resulting reaction product is subjected to a polycondensation reaction to obtain a copolyester, which is preferably used. In the production of the copolyester, other additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber and an antistatic agent may be added if necessary.

The polyester film of the present invention is a laminated film in which the copolyester resin layer (B) is laminated on at least one surface of the above-mentioned copolyester resin layer (A). As a method for laminating, for example, a method in which the polyester resins (A) and (B) are independently melted and coextruded from an adjacent die, or a copolymerized polyester resin film (A) and a copolymerized polyester film (B) are used.
And the like.

The polyester film of the present invention may be an unstretched film, but a biaxially stretched and heat-fixed oriented film is preferred. And it is more preferable that this film has the following requirements (1) and (2).

(1) The refractive index in the thickness direction of the film is 1.
It is 505 or more and 1.550 or less, preferably more than 1.510 and 1.540 or less. If the refractive index is less than 1.505, the moldability becomes insufficient, while if it exceeds 1.550 (that is, if the orientation is excessively low), the structure is close to amorphous, resulting in heat resistance. Is often insufficient.

The refractive index in the film thickness direction is measured as follows.

A polarizing plate analyzer is attached to the eyepiece side of the Abbe refractometer, and the refractive index of each is measured with a monochromatic NaD ray. Methylene iodide was used as the mount solution, and the measurement temperature was 25 ° C.

(2) The intrinsic viscosity of the polymer portion of the film is 0.52 or more and 0.80 or less, preferably 0.54 or more and 0.70 or less, and particularly preferably, the copolyester resin layers (A) and (B) respectively. It is 0.57 or more and 0.65 or less. If the intrinsic viscosity is less than 0.52, other physical properties are suitable, for example, even if the product is laminated to a metal plate or can be processed by deep drawing well, the retort can be sterilized after filling the can contents. The film is apt to be embrittled by treatment or long-term storage thereafter, and is easily broken by an impact from the outside of the can. On the other hand, those with an intrinsic viscosity of more than 0.80 are uneconomical because they are of excessive quality and the productivity of the raw material polymer is reduced.

Here, the intrinsic viscosity is a value measured at 25 ° C. using orthochlorophenol as a solvent.

The polyester film of the present invention preferably has a total thickness of 6 to 75 μm. 10-75μ
m, particularly preferably 15 to 50 μm. If the total thickness is less than 6 μm, breakage or the like is likely to occur during processing, while if it exceeds 75 μm, it is uneconomical because of excessive quality.

The ratio of the thickness T _B of the thickness T _A copolymerized polyester resin layer of the copolyester resin layer in the polyester film of the present invention (A) (B) (T B /
0.1-5 are preferable and, as for T _A ), 0.3-2 are especially preferable.

As the metal plate for can-making to which the polyester film of the present invention is laminated, a plate of tin plate, tin-free steel, aluminum or the like is suitable. For attaching the polyester film to the metal plate, for example, the following (1),
It can be performed by the method (2).

(1) The metal plate is heated above the melting point of the film, the films are laminated and then rapidly cooled, and the surface layer (thin layer) of the film in contact with the metal plate is made amorphous and adhered.

(2) The film is pre-coated with an adhesive layer as a primer, and this surface is bonded to a metal plate. As the adhesive layer, a known resin adhesive such as an epoxy adhesive,
Epoxy-ester adhesives, alkyd adhesives, etc. can be used.

When laminating the polyester film of the present invention to a metal plate, in the case of a two-layer type film, it is preferable to laminate the copolyester resin layer (A) on the metal plate side.

[0038]

EXAMPLES The present invention will be further described below with reference to examples. In addition, the measurement of each characteristic value in the Example followed the following method.

(1) Deep drawing workability-1 ○: The film was processed without any abnormality, and no whitening or breakage was observed on the film inside and outside the can. Δ: Whitening was found on the top of the film can. ×: One of the films. Film breakage is observed

(2) Deep drawing workability-2 ○: Processed without any abnormality, rust prevention test of film surface in can (1% NaCl water was put in the can, the electrode was inserted, and the can body was used as an anode. The current value when a voltage of 6 V is applied is measured.
In the following, abbreviated as ERV test) 0.2 mA or less x: There is no abnormality in the film, but the current value is 0.2 mA or more in the ERV test. Hole-like cracks are observed

(3) Impact crack resistance With respect to cans with good deep-drawing, water was fully poured, and 10 pieces for each test were dropped from a height of 1 m onto the PVC tile floor surface, and then the ERV test in the cans was carried out. I went. ◯: 0.1 mA or less for all 10 pieces Δ: 0.1 mA or more for 1 to 5 pieces: 0.1 mA or more for 6 or more pieces, or cracks of the film are already observed after dropping

(4) Heat embrittlement resistance The cans, which had been well-formed by deep drawing, were heated and held at 210 ° C. for 5 minutes, and then the impact crack resistance described in (3) was evaluated. ◯: 0.1 mA or less for all 10 pieces: Δ: 0.1 mA or more for 1 to 5 pieces: 0.1 mA or more for 6 or more pieces, or after heating at 210 ° C. for 5 minutes Cracks are observed

(5) Retort resistance The cans which were well formed by deep drawing were fully filled with water, retort-treated at 130 ° C. for 1 hour in a steam sterilizer, and then stored at 50 ° C. for 30 days. Ten of the obtained cans were dropped from the height of 1 m on each floor of the PVC tile for each test, and then an ERV test in the cans was performed. ◯: 0.1 mA or less for all 10 pieces Δ: 0.1 mA or more for 1 to 5 pieces: 0.1 mA or more for 6 or more pieces, or cracks of the film are already observed after dropping

(6) Rust-preventing property A can having good deep-drawing was filled with a 5% aqueous solution of acetic acid and held at 50 ° C. for 7 days, and then the rust generation of the metal plate was evaluated. ◯: Rust generation was not observed for all 10 pieces Δ: Rust generation was found for 1 to 5 pieces ×: Rust generation was found for 6 or more pieces

[0045]

Examples 1 to 4 Polyethylene terephthalate polymers (A) and (B) obtained by copolymerizing the components shown in Table 1 were independently dried, melted, coextruded from adjacent dies, and rapidly solidified to form unstretched laminated films. Obtained.

The unstretched film was then heated at 115 ° C. for 3 hours.
The film was longitudinally stretched twice and then transversely stretched three times at 130 ° C., followed by heat setting at 190 ° C. to obtain a biaxially oriented film. The thickness of the film was 25 μm, and the thicknesses of the polymer (A) layer and the polymer (B) layer were 15 μm and 10 μm, respectively.

Subsequently, the plate thickness 0.25 heated to 260 ° C.
The polymer (A) layer side was pasted on a mm free tin-free steel and quenched with water.

Further, the laminated metal plates are cut into a disc shape having a diameter of 150 mm, and deep drawing is carried out in three steps using a drawing die and a punch so that the inside is a polyester film bonding surface, and there is no side surface having a diameter of 55 mm. A seam container (hereinafter abbreviated as a can) was created.

Various evaluations were performed on this can. The results are shown in Table 2, which were all good.

[0050]

Comparative Examples 1 to 3 Cans were produced in the same manner as in Example 1 except that the polymer (A) and the polymer (B) were changed.

Various evaluations were carried out on this can, but any one had a defect and was defective. Particularly, in Comparative Example 3, the moldability was insufficient, and it was not possible to obtain one that could withstand the characteristic evaluation.

[0052]

[Table 1]

[0053]

[Table 2]

[0054]

EFFECTS OF THE INVENTION The polyester film for laminating and forming a metal plate of the present invention has a deep drawing workability and a post-can making resistance when a metal can is formed by, for example, deep drawing and then forming into a can. It has excellent impact resistance, heat resistance, retort resistance and rust resistance, and is extremely useful for metal containers.

Claims (1)

[Claims] 1. A polymer melting point of 210-2 on at least one side of a copolyester resin layer (A) having a polymer melting point of 210-245 ° C. and a glass transition temperature of 60 ° C. or less.
A polyester film for metal sheet laminating and forming, comprising a copolyester resin layer (B) laminated at 45 ° C. and a glass transition temperature of more than 60 ° C.