JPH0639981A - Polyester film for metallic sheet laminating fabrication - Google Patents

Abstract

PURPOSE:To provide a polyester film for metallic sheet laminating fabrication wherein shock resistance, especially the shock resistance at low temperature is improved while an excellent fabrication property, heat resistance, retort resistance, and a fragrance-keeping property which a copolymer polyester film had, are being held. CONSTITUTION:A polymer film for metallic sheet laminating fabrication is prepared by laminating a copolymer polyester layer (A) of 210-245 deg.C melting point and at least 60 deg.C glass transition temperature which contains at most 1wt.% of a lubricant of at most 2.5mum mean grain size, and a polyester layer (B) consisting of a polyester composition wherein 99-60wt.% of a copolymer polyester (I) which contains 5-30wt.% of a filler of at most 5mum mean grain size and has ethylene terephthalate of 210-245 deg.C melting point as a principal repetitive unit and 1-40wt.% of polyester (II) having butylene teraphthalate of 180-223 deg.C melting point as a principal repetitive unit are blended.

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 a can forming process such as drawing process and has a high heat resistance. The present invention relates to a polyester film for metal plate laminating and forming which can produce metal cans excellent in resistance, retort resistance, aroma retention, impact resistance, rust resistance, etc., such as beverage cans and food cans.

[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,
A method of making a can by drawing a thermoplastic resin film on a metal plate such as tin plate, tin-free steel, or aluminum is being studied. 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, aroma retention, and impact resistance.

On the other hand, a polyester film, especially 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 via an adhesive layer of low melting point polyester and used as a can-making material (JP-A-56-1045).
No. 1, 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-2-57).
339). (C) A low orientation, heat-set, biaxially oriented polyethylene terephthalate film is laminated on a metal plate and used as a can-making material (Japanese Patent Laid-Open No. 64-22530).

However, the studies by the present inventors have revealed that none of them has sufficient characteristics and have 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 the can-making process involving large deformation.

As for (B), since it is an amorphous or extremely low crystalline aromatic polyester film, it has good moldability, but it is inferior in aroma retention, and printing after can making and retort sterilization treatment. 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 is deteriorated by a shock 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 makes the film more fragile and may be transformed into a film that is easily cracked by an impact from the outside of the can.

In order to solve such a problem, the present inventors have made various studies in consideration of using a film made of a copolyester. As a result, the copolyester film is excellent in molding processability, heat resistance, retort resistance, and aroma retention, but impact resistance, especially 1
It has been found that the impact resistance at a low temperature of 5 ° C. or less is insufficient, and that when a metal can to which this film is bonded is dropped at a low temperature to give an impact, the film is likely to be cracked. Poor impact resistance at low temperatures is a serious problem for those handled in a cooled state such as juice and metal cans for soft drinks.

[0009]

The object of the present invention is to improve impact resistance while maintaining the excellent molding processability, heat resistance, retort resistance and aroma retention which the copolyester film has. Another object of the present invention is to provide a polyester film for metal sheet laminating and forming which is resistant to cracking due to impact at low temperatures, particularly at low temperatures of 10 ° C. or lower.

[0010]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that a film has a copolymerized polyester containing ethylene terephthalate as a main repeating unit and a butylene terephthalate as a main repeating unit. It was found that the impact resistance at a low temperature can be remarkably improved by blending the above-mentioned polyester and a two-layer structure including a layer of a polyester composition containing a large amount of filler. completed.

That is, the present invention contains 1% by weight or less of a lubricant having an average particle size of 2.5 μm or less and a melting point of 210 to 245.
C, a copolymerized polyester layer (A) having a glass transition temperature of 60 ° C. or higher, and 5 to 30% by weight of a filler having an average particle size of 2.5 μm or less, and ethylene terephthalate having a melting point of 210 to 245 ° C. Copolymerized polyester (I) having a main repeating unit of 99 to 60% by weight and a melting point of 180 to 2
Metal plate laminating molding, which comprises laminating a polyester layer (B) made of a polyester composition containing 1 to 40% by weight of polyester (II) containing butylene terephthalate as a main repeating unit at 23 ° C. It is a polyester film for processing.

In the present invention, a typical example of the copolymerized polyester used as the copolymerized polyester (I) of the copolymerized polyester layer (A) and the polyester layer (B) is copolymerized polyethylene terephthalate. The copolymerization 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 decanedicarboxylic acid, and alicyclic compounds such as cyclohexanedicarboxylic acid. Examples thereof include dicarboxylic acid, and examples of the alcohol component include aliphatic diols such as butanediol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. 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 is 210 to 245 ° C., preferably 215.
The ratio is in the range of ˜235 ° C. If the melting point is less 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 moldability is impaired.

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

The intrinsic viscosity of the copolyester is preferably 0.52 to 0.80, more preferably 0.54 to 0.70, and particularly preferably 0.57 to.
It is 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. If the glass transition temperature is lower than 60 ° C,
Satisfactory aroma retention cannot be obtained. As such a copolymerized polyester, isophthalic acid copolymerized polyethylene terephthalate is particularly preferable because a copolymerized polyester having a high glass transition temperature can be obtained.

The copolyester constituting the copolyester layer (A) 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. Both require that the average particle size is 2.5 μm or less. When the average particle size of the lubricant exceeds 2.5 μm, coarse lubricant particles (for example, particles of 10 μm or more) in the portion deformed by the processing such as deep drawing can are used as a starting point to generate pinholes, or in some cases, It is not preferable because it breaks.

In particular, the preferable lubricant in terms of pinhole resistance is a monodisperse 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. It is a lubricant. Examples of such a lubricant include true spherical silica and true spherical silicone particles.

The lubricant of the copolyester layer (A) is necessary for improving the handling property (winding property) in the film manufacturing process, and its content is 1% by weight or less.

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

The copolymerization 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 decanedicarboxylic acid, and fats such as cyclohexanedicarboxylic acid. Examples thereof include cyclic dicarboxylic acids, and examples of the copolymerized alcohol component include aliphatic diols such as ethylene glycol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. 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 180 to 223 ° C, preferably 200 to 223 ° C, more preferably 210 to 223 ° C.
It is the ratio to be in the range of. If the melting point of the polymer is less than 180 ° C, the heat resistance will be poor. The melting point of the polybutylene terephthalate homopolymer is 223 ° C.

The melting point of this polyester is measured in the same manner as the measurement of the copolyester described above by Du Pont.
Performed using Instruments 910 DSC.

In the polyester film of the present invention,
The polyester layer (B) is composed of polyethylene terephthalate as a main component and has a melting point of 210 to 245 ° C. and 99 to 60% by weight of copolymerized polyester, and polybutylene terephthalate or polybutylene terephthalate as a main component and a melting point of 1%.
It must consist of 1-40% by weight of copolyester at 80-223 ° C. When the polybutylene terephthalate or the polybutylene terephthalate copolymerized polyester is less than 1% by weight and the polyethylene terephthalate copolymerized polyester exceeds 99% by weight, the impact resistance at low temperature cannot be improved. If the polybutylene terephthalate or polybutylene terephthalate copolymerized polyester exceeds 40% by weight and 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 in the copolyester (I) of the copolyester layer (A) and the polyester layer (B) and the polyester used in the polyester (II) of the polyester layer (B) are , The manufacturing method is not limited.
For example, in the case of a copolyester mainly composed of polyethylene terephthalate, a method of subjecting terephthalic acid, ethylene glycol and a copolymerization component to an esterification reaction, and then subjecting the resulting reaction product to a polycondensation reaction to obtain a copolyester, or Is preferably a method in which dimethyl terephthalate, ethylene glycol and a copolymerization component are transesterified, and the resulting reaction product is subjected to polycondensation reaction to obtain a copolymerized polyester. In the production of each copolyester and polybutylene terephthalate, other additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber and an antistatic agent may be added, if necessary.

Further, the polyester layer (B) contains 5 to 30% by weight of a filler having an average particle diameter of 2.5 μm or less. This filler may be inorganic or organic, but is preferably inorganic. Preferred examples of the inorganic pigment include alumina, titanium dioxide, calcium carbonate, barium sulfate and the like. In the case of the present invention, titanium dioxide is particularly suitable.

The fillers all have an average particle size of 2.5.
It must be less than μm. The average particle size of the filler is 2.
If it exceeds 5 μm, coarse particles (for example, particles of 10 μm or more) in a portion deformed by processing such as deep drawing can are used as a starting point, and pinholes are generated, or in some cases, it is broken, which is not preferable. The average particle size of the filler is preferably 0.05 to 1.5 μm, particularly preferably 0.1 to 1.5 μm.
It is 0.5 μm.

The content of the filler is 5 to 30% by weight.
It is necessary that the content be 10 to 20% by weight. If the content of the filler exceeds 30% by weight, it is difficult to form the film, and if it is less than 5% by weight, the effect of improving the impact resistance at low temperature cannot be recognized.

In the present invention, the filler is preferably subjected to a particle size adjustment and coarse particle removal using a purification process before being incorporated into the copolyester. As an industrial means of the purification process, for example, a jet mill, a ball mill or the like can be used as a crushing means, and a dry or wet centrifuge or the like can be used as a classification means. Needless to say, these means may be used in combination of two or more and purified stepwise.

Various methods can be used for incorporating the filler into the copolyester. The following method can be given as a typical method. (A) A method of adding before the completion of the transesterification or esterification reaction during the synthesis of the copolyester, or before the start of the polycondensation reaction. (A) A method of adding to the copolyester and melt-kneading. (C) A method in which, in the methods of (a) and (a) above, a master pellet having a large amount of additives added is produced, kneaded with a particle-free copolymerized polyester, and a predetermined amount of additives is contained.

When the method of adding an additive during the polyester synthesis of (a) is used, it is preferable to add it to the reaction system as a slurry in which the additive is dispersed in glycol.

The polyester film of the present invention has a structure in which a copolyester layer (A) and a polyester layer (B) are laminated, and the film having such a two-layer structure constitutes each layer, for example. Melting the copolyester and the polyester composition separately, coextruding from the die, after laminating fusion before solidification, biaxial stretching, a method of heat setting, the copolyester and the polyester composition are melted separately, It can be manufactured by a method of extruding to form a film, and then laminating and adhering the both in an unstretched state or after stretching.

When the polyester film is composed only of the copolyester layer (A), the impact resistance at low temperature becomes insufficient, and conversely when it is composed only of the polyester layer (B), it is not protected. It is not suitable because the fragrance and rust resistance deteriorate.

The polyester film of the present invention may be an unstretched film, but it is usually biaxially stretched and heat-set. In this case, the refractive index in the thickness direction of the copolyester layer (A) is 1.505 to 1.55.
It is preferably 0, more preferably more than 1.510 and 1.540 or less. If this refractive index is too low, moldability becomes insufficient, while if it is too high, the structure becomes 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 tends to occur during processing, while if it exceeds 75 μm, it is uneconomical because of excessive quality.

Thickness T of Copolyester 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 1.5, more preferably 0.04 to 0.67, and particularly preferably 0.04 to.
It is 0.25. Specifically, for example, in the case of a polyester film having a thickness of 25 μm, the thickness of the polyester layer (A) is 0.5 to 15 μm, preferably 1 to 10 μm, more preferably 1 to 5 μm.

As the metal plate to which the polyester film of the present invention is stuck, particularly the metal plate for can manufacturing, tin, tin-free steel, aluminum and the like plates are suitable.
The polyester film can be attached to the metal plate by the following method, for example.

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

An adhesive layer is preliminarily coated on the film with a primer, and this surface is bonded to a metal plate. As the adhesive layer, a known resin adhesive, for example, an epoxy adhesive,
Epoxy-ester adhesives, alkyd adhesives, etc. can be used.

When the polyester film of the present invention is attached to a metal plate, in order to improve impact resistance,
It is preferable that the polyester layer (B) is laminated on the side that receives the impact. For example, when the polyester film of the present invention is attached to the inside of a can, the polyester layer (B) may be attached to the can.

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

[0042]

EXAMPLES The present invention will be further described below with reference to examples.

[0043]

Examples 1 to 7 and Comparative Examples 1 to 8 Polyethylene terephthalate obtained by copolymerizing the components shown in Table 1 (intrinsic viscosity 0.6
4, 0.3% by weight of titanium dioxide with an average particle size of 0.3 μm
So as to form the copolyester layer (A) and the polyester composition shown in Table 1 (containing 18% by weight of titanium dioxide having an average particle size of 0.27 μm) as the polyester layer (B). After being dried and melted by the method, they were co-extruded from dies adjacent to each other, laminated, fused and rapidly cooled and solidified to prepare an unstretched laminated film.

Next, this unstretched film was longitudinally stretched at 100 ° C. to 2.9 times, and then transversely stretched at 120 ° C. to 3 times,
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 copolyester layer (A) and the polyester layer (B) were 5 μm and 20 μm, respectively.

[0046]

[Table 1]

[0047]

[Comparative Examples 9 to 10] In Example 2, only the single layer of the copolyester layer (A) (Comparative Example 9) and the polyester layer (B) (Comparative Example 10) was used without forming a two-layer laminated structure. I made a film.

[0048]

Examples 8 to 10 and Comparative Examples 11 to 12 In Example 2, the amount of titanium dioxide contained in the copolyester layer (B) was changed as shown in Table 2, and other conditions were the same as in Example 2. A biaxially oriented laminated film was obtained in the same manner.

[0049]

[Table 2]

A total of 22 kinds of films obtained in Examples 1 to 10 and Comparative Examples 1 to 12 were laminated on both sides of a tin-free steel plate heated to 250 ° C. and having a plate pressure of 0.25 mm.
After cooling with water, it was cut into a disk shape having a diameter of 150 mm, and deep drawing was performed in four steps using a drawing die and a punch to prepare a side surface seamless container (hereinafter abbreviated as a can) having a diameter of 55 mm.

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

(1) Deep drawing workability-1 ○: The film was processed without any abnormality, and whitening or breakage was not observed on the film. Δ: Whitening was found on the top of the film can. ×: Film breakage was observed on a part of the film. Is recognized

(2) Deep drawing workability-2 ○: Processed without any abnormality, rustproof 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), 0.1 mA or less is shown. ×: There is no abnormality in the film, but the current value is 0.1 mA or more in the ERV test. Hole-like cracks are observed

(3) Impact resistance For cans with good deep drawing, after pouring water into the cans and cooling them to 5 ° C., 10 pieces for each test were dropped from a height of 30 cm onto the PVC tile floor surface. The results of the in-can ERV test were as follows: O: 0.1 mA or less for all 10 B: 0.1 mA or more for 1 to 5 X: 0.1 mA or more for 6 or more Or, cracking of the film was already observed after dropping.

(4) Heat embrittlement resistance After the cans that had been well-formed by deep drawing were heated and held at 200 ° C. for 5 minutes, the impact resistance evaluation described in (3) was carried out. Was 0.1 mA or less. Δ: 0.1 mA or more for 1 to 5 pieces: 0.1 mA or more for 6 or more pieces, or cracks were already observed in the film after heating at 200 ° C. for 5 minutes. Was

(5) Retort resistance The cans, which were well formed by deep drawing, were refilled with water and retorted 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 for each test onto the PVC tile floor surface, 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 in the film were already observed after dropping Was

(6) Rust-preventing property A can with good deep drawing was fully filled with 1% NaCl water and kept at 50 ° C. for 60 days. In each test, 10 cans each were visually observed and evaluated for the occurrence of rust on the metal plate. ◯: Rust generation was not observed in all 10 pieces Δ: Rust generation was found in 1 to 5 pieces ×: Rust generation was found in 6 or more pieces

(7) Aroma Retaining Property A can of good deep drawing was filled with orange juice and sealed. After holding at 37 ° C. for 30 days, the can was opened, and changes in aroma and taste were examined by a sensory test. ◯: No change in aroma or taste Δ: Slight change in aroma or taste was observed ×: Change in aroma or taste was observed

The evaluation results of the above 7 types are as shown in Table 3.

[0060]

[Table 3]

As is clear from the results shown in Table 3, the can using the polyester film of the present invention is excellent in deep-drawing workability, heat embrittlement resistance, retort resistance, and aroma retention, and also has rust resistance. Is also excellent and has excellent impact resistance, especially at low temperatures.

[0062]

EFFECT OF THE INVENTION The metal plate laminating and forming film of the present invention has excellent forming processability, heat resistance, retort resistance, and aroma retention, and also has impact resistance, especially at a low temperature such as 5 ° C. The impact resistance is markedly improved and the rust resistance is also good.
Therefore, it is particularly suitable for being stuck to a metal can that is often cooled and handled at a low temperature such as for juice or soft drink.

Front Page Continuation (72) Inventor Yoji Murakami 3-37-19 Oyama, Sagamihara-shi, Kanagawa Teijin Limited Sagamihara Research Center

Claims (3)

[Claims] 1. A copolyester layer (A) containing 1% by weight or less of a lubricant having an average particle diameter of 2.5 μm or less, a melting point of 210 to 245 ° C. and a glass transition temperature of 60 ° C. or more.
And a melting point of 99 to 60% by weight of a copolymerized polyester (I) containing 5 to 30% by weight of a filler having an average particle diameter of 2.5 μm or less and a main repeating unit of ethylene terephthalate having a melting point of 210 to 245 ° C. Of 180 to 223 [deg.] C. butylene terephthalate as a main repeating unit, and a polyester layer (B) composed of a polyester composition containing 1 to 40% by weight of polyester (II) as a main repeating unit. Polyester film for laminating and forming. 2. The polyester film for laminating and molding metal plates according to claim 1, wherein the copolyester layer (A) comprises isophthalic acid copolyethylene terephthalate. 3. The polyester film for metal plate laminating and forming according to claim 1, wherein the filler contained in the polyester layer (B) is titanium dioxide.