JP3095891B2 - Polyester film for metal plate lamination processing - Google Patents

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 a metal plate, and more particularly, it shows excellent formability when laminating a metal plate to form a can, such as drawing. The present invention relates to a metal film that can be used to produce metal cans, such as beverage cans, food cans, and the like, having excellent properties, retort resistance, fragrance retention, impact resistance, rust resistance, and the like.

[0002]

2. Description of the Related Art Metal cans are generally coated to prevent corrosion of the inner and outer surfaces. Recently, for the purpose of simplifying the process, improving hygiene, and preventing pollution, rust prevention is performed without using an organic solvent. Development of a method for obtaining the property has been advanced, and as one of the methods, coating with a thermoplastic resin film has been attempted. That is,
Studies have been made on a method of laminating a thermoplastic resin film on a metal plate such as tin, tin-free steel, or aluminum, and then forming the can by drawing or the like. Polyolefin films and polyamide films have been tried as this thermoplastic resin film, but they do not satisfy all of moldability, heat resistance, fragrance retention and impact resistance.

On the other hand, polyester films, particularly polyethylene terephthalate films, have been attracting attention as having balanced properties, and some proposals based on these have been made. That is, (A) a biaxially oriented polyethylene terephthalate film is laminated on a metal plate via a low-melting-point polyester adhesive layer and used as a can-making material (JP-A-56-1045).
No. 1, JP-A-1-192546). (B) Amorphous or extremely low-crystalline aromatic polyester film is laminated on a metal plate and used as a can-forming material (JP-A-1-192545, JP-A-2-57).
339). (C) A biaxially oriented polyethylene terephthalate film having a low orientation and thermally fixed is laminated on a metal plate and used as a can-making material (Japanese Patent Application Laid-Open No. 64-22530).

[0004] However, the present inventors' studies have revealed that no satisfactory characteristics can be obtained in any case, and that each has the following problems.

Regarding (A), a biaxially oriented polyethylene terephthalate film is excellent in heat resistance and fragrance retention,
In the process of making cans with insufficient molding workability and large deformation, whitening (generation of minute cracks) and breakage of the film occur.

As for (B), since it is an amorphous or extremely low-crystalline aromatic polyester film, the moldability is good, but the fragrance retention is inferior, and the printing and retort sterilization after can-making are performed. Such a film may be easily embrittled by post-treatments or storage for a long period of time, and may be changed to a film which is easily broken by an impact from the outside of the can.

As for (C), the effect is not exhibited in the intermediate region between the above (A) and (B), but it has not yet reached the low orientation applicable to can processing. Even if it can be processed in a region with a small degree of deformation, subsequent printing,
As in the case of (B), there is a possibility that the retort treatment for sterilizing the contents of the can makes the film brittle easily and the film is likely to be broken by an impact from the outside of the can.

In order to solve such a problem, the present inventors have considered various uses of a film made of a copolymerized polyester and have made various studies. As a result, the copolymerized polyester film is excellent in molding workability, heat resistance, retort resistance, and fragrance retention, but has an impact resistance, particularly
It has been found that the impact resistance at a low temperature of 5 ° C. or less is insufficient, and when the metal can to which the film is bonded is dropped at a low temperature to give an impact, the film is easily cracked. Poor impact resistance at low temperatures poses a major problem when handled in a cooled state, such as metal cans for juices and soft drinks.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to improve the impact resistance of a copolymerized polyester film while maintaining the excellent moldability, heat resistance, retort resistance and fragrance retention. Another object of the present invention is to provide a polyester film for laminating and forming a metal plate, which is less likely to crack due to an impact at a low temperature.

[0010]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, have found that a film is made of a copolyester containing ethylene as a main repeating unit and a polyester containing butylene terephthalate as a main repeating unit. The present inventors have found that the impact resistance at low temperatures can be remarkably improved by comprising two layers including a layer of a polyester composition in which the present invention is blended.

That is, the present invention has a melting point of 210 to 245.
C., a copolymerized polyester layer (A) having a glass transition temperature of 60 ° C. or more, a copolymerized polyester (I) having a melting point of 210 to 245 ° C. and having ethylene terephthalate as a main repeating unit, 99 to 60% by weight, and a melting point of 180. ~ 223 ° C
And a polyester layer (B) comprising a polyester composition containing 1 to 40% by weight of a polyester (II) containing butylene terephthalate as a main repeating unit. It is a polyester film.

In the present invention, a typical example of the copolymerized polyester used for the copolymerized polyester (I) of the copolymerized polyester layer (A) and the polyester layer (B) is copolymerized polyethylene terephthalate. The copolymer component may be an acid component or an alcohol component. Examples of the acid component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid and naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decane dicarboxylic acid, and alicyclic groups such as cyclohexanedicarboxylic acid. Examples of the dicarboxylic acid include aliphatic alcohols such as butanediol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These can be used alone or in combination of two or more.

Although the proportion of the copolymer component depends on the type, it results in a melting point of 210 to 245 ° C., preferably 215 ° C.
It is the ratio which becomes the range of -235 ° C. If the melting point is lower than 210 ° C., the heat resistance will be poor. On the other hand, the melting point is 245 ° C
If it exceeds, the crystallinity of the polymer is too large and the molding processability is impaired.

Here, the melting point of the copolyester was measured by Du Pont Instruments 910.
A method in which a melting peak is determined at a heating rate of 20 ° C./min using DSC. The sample amount is about 20 mg.

The intrinsic viscosity of the copolymerized polyester is preferably 0.52 to 0.80, more preferably 0.54 to 0.70, and particularly preferably 0.57 to 0.70.
0.65.

Further, the copolymerized polyester constituting the copolymerized polyester layer (A) in the present invention needs to have a glass transition temperature of 60 ° C. or higher, preferably 70 ° C. or higher. When the secondary transition point is lower than 60 ° C., satisfactory scent retention cannot be obtained. As such a copolymerized polyester, a copolymerized polyester having a high glass transition temperature can be obtained, and thus isophthalic acid copolymerized polyethylene terephthalate is particularly preferable.

In the present invention, the polyester (II) contained in the polyester layer (B) is a polyester having butylene terephthalate as a main repeating unit, and may be a homopolymer or a copolymer.

The copolymer component in the copolymer may be an acid component or an alcohol component. Examples of the copolymeric acid component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decane dicarboxylic acid, and fatty acids such as cyclohexanedicarboxylic acid. Examples of the cyclic dicarboxylic acid include aliphatic diols such as ethylene glycol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These can be used alone or in combination of two or more.

The proportion of the copolymer components depends on the type thereof, but as a result, the melting point is from 180 to 223 ° C., preferably from 200 to 223 ° C.
To 223 ° C, more preferably 210 to 223 ° C. If the melting point is lower than 180 ° C., the heat resistance will be poor. The melting point of the polybutylene terephthalate homopolymer is 223 ° C.

The measurement of the melting point of the polyester was carried out in the same manner as in the measurement of the copolymerized polyester.
Performed using Instruments 910 DSC.

In the polyester film of the present invention,
The polyester layer (B) is composed of 99 to 60% by weight of a copolymer polyester mainly composed of polyethylene terephthalate and having a melting point of 210 to 245 ° C, and having a melting point of mainly polybutylene terephthalate or polybutylene terephthalate of 1%.
It is necessary to be composed of 1 to 40% by weight of a copolyester at 80 to 223C. If the amount of the polybutylene terephthalate or the polybutylene terephthalate copolymerized polyester is less than 1% by weight and the amount of the polyethylene terephthalate copolymerized polyester is more than 99% by weight, the impact resistance at low temperatures cannot be improved. When the content of the polybutylene terephthalate or the polybutylene terephthalate copolymerized polyester exceeds 40% by weight and the content of the polyethylene terephthalate copolymerized polyester is less than 60% by weight, the heat resistance of the film decreases and the impact resistance becomes insufficient.

In the present invention, the copolyester used for the copolyester (I) of the copolyester layer (A) and the polyester layer (B) and the polyester used for the polyester (II) of the polyester layer (B) are: It is not limited by the manufacturing method.
For example, in the case of a copolymerized polyester mainly composed of polyethylene terephthalate, a method in which terephthalic acid, ethylene glycol and a copolymer component are subjected to an esterification reaction, and then the obtained reaction product is subjected to a polycondensation reaction to form a copolymerized polyester, or Preferably, a method is used in which dimethyl terephthalate, ethylene glycol and a copolymer component are subjected to a transesterification reaction, and then the obtained reaction product is subjected to a polycondensation reaction to obtain a copolymerized polyester. In the production of each of the copolymerized polyester and polybutylene terephthalate, other additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber, and an antistatic agent can be added as necessary.

In the present invention, the copolymer polyester constituting the copolymer polyester layer (A) and the polyester composition constituting the polyester layer (B) are usually
In order to improve the handling property (winding property) in the film manufacturing process, the composition contains 1% by weight or less of a lubricant.

The lubricant may be inorganic or organic, but inorganic is preferred. Examples of the inorganic lubricant include silica, alumina, titanium dioxide, calcium carbonate, barium sulfate and the like, and examples of the organic lubricant include cross-linked polystyrene particles,
Examples include silicone particles. In any case, the average particle diameter is desirably 2.5 μm or less. When the average particle diameter of the lubricant exceeds 2.5 μm, coarse lubricant particles (for example, 10 μm or more) of a portion deformed by processing such as deep drawing cans and the like are used. Is a starting point, and pinholes are formed or broken in some cases, which is not preferable.

In particular, a lubricant which is preferable from the viewpoint of pinhole resistance is a monodisperse lubricant having an average particle diameter of 2.5 μm or less and a particle diameter ratio (major axis / minor axis) of 1.0 to 1.2. It is a lubricant. Examples of such a lubricant include spherical silica, spherical tatatin oxide, spherical zirconium, and spherical silicone particles.

The polyester film of the present invention has a structure in which a copolymerized polyester layer (A) and a polyester layer (B) are laminated, and such a two-layered film constitutes, for example, each layer. The copolymerized polyester and the polyester composition are separately melted, co-extruded, laminated and fused before solidification, then biaxially stretched, a method of heat setting, the copolymerized polyester and the polyester composition are separately melted and extruded. It can be manufactured by a method of forming a film, unstretched state or after stretching, and laminating and fusing them.

When the polyester film is composed only of the copolymerized polyester layer (A), the impact resistance at low temperatures becomes insufficient. Conversely, when the polyester film is composed solely of the polyester layer (B), the protection is insufficient. It is not suitable because fragrance and rust prevention deteriorate.

The polyester film of the present invention may be an unstretched film, but is usually used in a state of being biaxially stretched and heat set. In this case, the refractive index in the thickness direction of the copolymerized polyester layer (A) is 1.505 to 1.55.
It is preferably 0, more preferably more than 1.510 and not more than 1.540. If the refractive index is too low, the moldability will be insufficient, while if it is too high, the structure will be close to amorphous and the heat resistance may decrease.

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

The thickness T of the copolymerized polyester layer (A)
The ratio of the _A, and the thickness T _B of the polyester layer (B) (T _A /
T _B) is preferably about 0.02 to 0.67, more preferably 0.04 to 0.43, particularly preferably 0.04
０．２0.25. Specifically, for example, the thickness is 25 μm
Polyester layer (B)
Is 0.5 to 10 μm, preferably 1 to 7.5 μm.
m, more preferably 1 to 5 μm.

As a metal plate to which the polyester film of the present invention is bonded, particularly a metal plate for can making, a plate of tin, tin-free steel, aluminum or the like is suitable.
The bonding of the polyester film to the metal plate can be performed, for example, by the following method.

The metal plate is heated to a temperature equal to or higher than the melting point of the film, the film is laminated, and then cooled, and the surface layer (thin layer) of the film in contact with the metal plate is made amorphous and adhered.

[0033] The film is preliminarily coated with an adhesive layer with a primer, and this surface is bonded to a metal plate. As the adhesive layer, a known resin adhesive, for example, an epoxy-based adhesive,
Epoxy-ester adhesives, alkyd adhesives and the like can be used.

When the polyester film of the present invention is bonded to a metal plate, it is necessary to improve the impact resistance.
It is preferable to bond together such that the polyester layer (B) is located on the side receiving the impact. For example, when the polyester film of the present invention is bonded to the inside of a can, the polyester layer (B) may be bonded to the can.

Further, in the polyester film of the present invention, if necessary, both polyester layers (A),
(B) Another additional layer may be laminated between or on one side.

[0036]

The present invention will be further described with reference to the following examples.

[0037]

Examples 1 to 7 and Comparative Examples 1 to 8 Polyethylene terephthalate copolymerized with the components shown in Table 1 (intrinsic viscosity 0.6
4. 0.3% by weight of titanium dioxide having an average particle diameter of 0.3 μm
(A) and a copolyester layer (A), and the polyester compositions shown in Table 1 are each dried and melted by a conventional method so as to become the polyester layer (B). Then, the resultant was laminated, fused and quenched and solidified to prepare an unstretched laminated film.

Next, the unstretched film was longitudinally stretched 3.1 times at 110 ° C., and then transversely stretched 3 times at 125 ° C.
It was heat-set at 190 ° C. to obtain a biaxially oriented laminated film.

The thickness of the obtained film was 25 μm, and the thicknesses of the copolymerized polyester layer (A) and the polyester layer (B) were 5 μm and 20 μm, respectively.

[0040]

[Table 1]

[0041]

Comparative Examples 9 to 10 In Example 6, instead of having a two-layer laminated structure, a single layer of the polyester layer (A) (Comparative Example 9) and the polyester layer (B) (Comparative Example 10) were used. A film was made.

A total of 17 kinds of films obtained in the above Examples 1 to 7 and Comparative Examples 1 to 10 were laminated on both surfaces of tin-free steel heated to 250 ° C. and having a plate pressure of 0.25 mm.
After cooling with water, the plate was cut into a disk having a diameter of 150 mm and deep-drawn in four stages using a drawing die and a punch to prepare a side-seamless container (hereinafter abbreviated as can) having a diameter of 55 mm.

The following observations and tests were performed on the cans, and the cans were evaluated according to the following standards.

(1) Deep drawing processability -1 ○: The film was processed without any abnormality, and no whitening or breakage was observed in the film. Δ: Whitening was observed in the upper part of the film can. ×: The film was partially broken in the film. Is recognized

(2) Deep drawing processability-2 ○: Processed without any abnormality, rust prevention test on film surface in can (1% NaCl water was put in the can, electrodes were inserted, and the can body was used as an anode. The current value when a voltage of 6 V is applied is measured.
X: No abnormality in the film, but the current value was 0.1 mA or more in the ERV test, and when the energized portion was enlarged and observed, a pin starting from a coarse lubricant was found on the film. Hole-shaped cracks are observed

(3) Impact resistance For cans having good deep drawing, pour water thoroughly and cool to 10 ° C., and 10 cans of each test were 30 cm in height.
After the ERV test was carried out in the can after dropping on a PVC tile floor surface from, ：: 0.1 mA or less for all 10 pieces Δ: 0.1 mA or more for 1 to 5 pieces ×: 6 More than 0.1 mA or more, or cracking of the film was already observed after dropping

(4) Heat Embrittlement Resistance The cans which had been subjected to good deep drawing were heated and maintained at 200 ° C. for 5 minutes, and then subjected to the impact resistance evaluation described in (3). Δ: 0.1 mA or more for 1 to 5 pieces ×: 0.1 mA or more for 6 or more pieces, or already cracked in the film after heating at 200 ° C. for 5 minutes Was

(5) Retort Resistance The cans having good deep drawing properties were filled with water and retorted at 120 ° C. for 1 hour with a steam sterilizer, and then stored at 50 ° C. for 30 days. After dropping 10 cans for each test from a height of 30 cm on a PVC tile floor, 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 were already observed after dropping Was

(6) Rust Prevention A 1% NaCl aqueous solution was fully poured into cans having good deep drawability, and kept at 50 ° C. for 10 days. In each test, the state of rust on the metal plate was visually observed and evaluated for ten cans. ：: No rust was observed for all 10 △: Rust was observed for 1 to 5 ×: Rust was observed for 6 or more

(7) Aroma Retention A can with good deep drawing was filled with orange juice and sealed. After being kept at 37 ° C. for 30 days, the can was opened and changes in aroma and taste were examined by sensory tests. ：: no change in fragrance and taste △: slight change in fragrance and taste was observed ×: change in fragrance and taste was observed

The results of the above seven evaluations are as shown in Table 2.

[0052]

[Table 2]

As is clear from the results shown in Table 2, the cans using the polyester film of the present invention are excellent in deep drawing workability, heat embrittlement resistance, retort resistance, fragrance retention and rust prevention. And also has excellent impact resistance, especially at low temperatures.

[0054]

The film for laminating and processing metal sheets of the present invention has excellent moldability, heat resistance, retort resistance, and fragrance retention, and also has impact resistance, especially impact resistance at low temperatures. Is remarkably improved, and rust prevention is also good. Therefore, it is particularly suitable to be used by bonding it to a metal can often cooled and used at a low temperature, such as for juices and soft drinks.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoji Murakami 3-37-19 Koyama, Sagamihara City, Kanagawa Prefecture Inside the Sagamihara Research Center Teijin Limited (56) References JP-A-56-10451 (JP, A) (58) ) Field surveyed (Int. Cl. ⁷ , DB name) B32B 1/00-35/00

Claims (2)

(57) [Claims] 1. A copolymerized polyester layer (A) having a melting point of 210 to 245 ° C. and a glass transition temperature of 60 ° C. or higher,
Copolyester (I) having a repeating unit of ethylene terephthalate having a melting point of 210 to 245 ° C. as a main repeating unit.
Polyester (II) containing 60% by weight of butylene terephthalate having a melting point of 180 to 223 ° C. as a main repeating unit
A polyester film for laminating and processing a metal plate, comprising laminating a polyester layer (B) made of a polyester composition containing 1 to 40% by weight. 2. The polyester film according to claim 1, wherein the copolymerized polyester layer (A) is made of isophthalic acid copolymerized polyethylene terephthalate.