JPH10315412A - Polyester film for laminating metal plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film for laminating a metal plate having high impact resistance or particularly scarcely crazing due to impact at low temperature while holding molding processability, heat resistance, retort resistance and perfume retentivity. SOLUTION: The polyester film obtained by laminating an isophthalate copolymer polyester layer (A layer) having a melting point of 210 to 245 deg.C and a polyester composition layer (B layer) made of polyester composition obtained by melt mixing 99 to 50 wt.% of copolymer polyester (I) having a main repeating unit of ethylene terephthalate having a melting point of 210 to 245 deg.C and 1 to 50 wt.% of polyester (II) having a main repeating unit of butylene terephthalate having a melting point of 180 to 223 deg.C. In this case, transesterification rate of the polyester composition for constituting the composition layer (B layer) is 3.0% or more, thereby improving impact resistance or particularly craze at the time of low temperature.

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 a metal plate, and more particularly, it shows excellent moldability when laminating to a metal plate and performing can forming such as drawing. The present invention relates to a polyester film for metal plate laminating processing capable of producing metal cans, such as beverage cans and food cans, which are excellent in retort resistance, fragrance preserving property, impact resistance and the like.

[0002]

2. Description of the Related Art Metal cans are generally coated to prevent corrosion on the inner and outer surfaces, but recently, for the purpose of simplifying the process, improving hygiene, and preventing pollution, rust prevention is achieved without using organic solvents. The development of a method for obtaining a resin has been promoted, and as one of the methods, coating with a thermoplastic resin film has been attempted. That is, a method of laminating a thermoplastic resin film on a metal plate of tin, tin-free steel, aluminum, or the like, followed by drawing, etc., has been studied. 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, especially polyethylene terephthalate films, have attracted attention as having balanced properties, and several 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 (Japanese Patent Application Laid-Open No. 56-10451).
JP, JP-A-1-192546). (B) An amorphous or extremely low-crystalline aromatic polyester film is laminated on a metal plate and used as a material for producing a can (JP-A-1-192545, JP-A-2-5-5).
No. 7339). (C) A biaxially oriented polyethylene terephthalate film, which is heat-set with low orientation, is laminated on a metal plate and used as a can-making material (JP-A-64-22530).

However, the present inventors have studied and found that no satisfactory characteristics can be obtained in any case, and the following problems have been found. Regarding (A), the biaxially oriented polyethylene terephthalate film is excellent in heat resistance and fragrance retention, but is insufficient in moldability and whitening of the film (generation of microcracks) in canning with large deformation. Breakage occurs. Regarding (B), since it is an amorphous or extremely low-crystalline aromatic polyester film, the moldability is good, but the fragrance retention is inferior, and after printing after can-making and retort sterilization, etc. There is a possibility that the film may be easily embrittled by the treatment and further long-term storage, 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 a low orientation applicable to can processing, Even if it can be processed in a small area, the subsequent printing, other retort treatment to sterilize the contents of the can become brittle, and it is likely to be transformed into a film that is easily broken by an impact from the outside of the can. Same as (B).

[0005] In order to solve such a problem, the present inventors have considered using 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 this film is bonded is dropped at a low temperature to give an impact, the film tends to crack. 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.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to improve impact resistance while maintaining excellent molding workability, heat resistance, retort resistance, and fragrance retention. An object of the present invention is to provide a polyester film for laminating a metal plate, which hardly occurs.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result, have found that a laminated polyester film is used as a film and one layer thereof is a copolymerized polyester containing ethylene terephthalate as a main repeating unit. And a polyester composition layer consisting of polyester having butylene terephthalate as a main repeating unit,
By finding that the transesterification rate of the polyester composition is in a specific range, the impact resistance at low temperatures is remarkably improved, and the present invention has been completed.

That is, the present invention has a melting point of 210 to 24.
Isophthalic acid copolymerized polyester layer at 5 ° C (A)
And a copolymer polyester (I) containing ethylene terephthalate having a melting point of 210 to 245 ° C. as a main repeating unit.
A polyester film obtained by laminating a polyester composition layer (B) comprising 99 to 50% by weight and 1 to 50% by weight of a polyester (II) having butylene terephthalate having a melting point of 180 to 223 ° C. as a main repeating unit. The polyester composition constituting the polyester composition layer (B) has a transesterification ratio of 3.0% or more.

In the present invention, the isophthalic acid copolymerized polyester layer (A) is a layer exhibiting excellent fragrance retention and is composed of an isophthalic acid copolymerized polyester, a representative of which is isophthalic acid copolymerized polyethylene terephthalate. An example is given. This isophthalic acid-copolymerized polyethylene terephthalate is used in a range in which a copolymer component or a copolymer alcohol component other than isophthalic acid does not impair its properties, for example, in a proportion of 3 mol% or less based on all acid components or all alcohol components. It may be polymerized. Examples of the copolymerized acid component include phthalic acid, aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and 1,10-decanedicarboxylic acid. Can be illustrated,
As the alcohol component, 1,4-butanediol,
Examples thereof include aliphatic diols such as 1,6-hexanediol and neopentyl glycol, and alicyclic diols such as 1,4-cyclohexanedimethanol. These can be used alone or in combination of two or more.

The proportion of isophthalic acid and other copolymer components is such that the polymer has a melting point of 210-245 ° C., preferably 2
It is a ratio falling within a range of 15 to 235 ° C. Melting point 210
If the temperature is lower than ℃, the heat resistance is inferior. On the other hand, the melting point is 24
If it exceeds 5 ° C., the crystallinity of the polymer is too high, and the moldability is impaired.

Here, the melting point of the isophthalic acid copolymerized polyester was measured by Du Pont Instrument.
A method in which a melting peak is determined at a heating rate of 20 ° C./min using s910 DSC. The sample amount is about 20
mg.

The intrinsic viscosity of the isophthalic acid copolymerized polyester is preferably 0.52 to 0.80,
More preferably, it is 0.54 to 0.70, particularly preferably 0.57 to 0.65.

In the present invention, the copolymer polyester (I) constituting the polyester composition layer (B) is a copolymer polyester containing ethylene terephthalate as a main repeating unit. This copolymer component may be an acid component or an alcohol component. Examples of the copolymerized acid component include isophthalic acid, phthalic acid, aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, adipic acid, azelaic acid, and the like.
Examples thereof include aliphatic dicarboxylic acids such as sebacic acid and 1,10-decanedicarboxylic acid, and examples of the alcohol component include aliphatic diols such as 1,4-butanediol, 1,6-hexanediol, and neopentyl glycol. And alicyclic diols such as 1,4-cyclohexanedimethanol. These can be used alone or in combination of two or more. Of these, isophthalic acid is preferred.

The proportion of the copolymer component depends on the type thereof, but is a proportion that results in a polymer melting point of 210 to 245 ° C., preferably 215 to 235 ° C. If the melting point is lower than 210 ° C., the heat resistance will be poor. On the other hand, when the melting point exceeds 245 ° C., the melting point of the polymer is too high, and the moldability is impaired.

Here, the melting point of the copolymerized polyester (I) is measured by the same method as that for the isophthalic acid copolymerized polyester. The intrinsic viscosity of the copolymerized polyester (I) is preferably 0.52 to 0.80, more preferably 0.54 to 0.70, and particularly preferably 0.57 to 0.65.

In the present invention, the polyester (II) constituting the polyester composition 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 copolymerizing acid component include aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and 1,10-decanedicarboxylic acid, and aromatic dicarboxylic acids such as isophthalic acid, phthalic acid and 2,6-naphthalenedicarboxylic acid. Examples of the acid component include an aliphatic diol such as 1,6-hexanediol and neopentyl glycol, and an alicyclic diol such as 1,4-cyclohexanedimethanol.
These can be used alone or in combination of two or more.
Among these, adipic acid is preferable, and it is particularly preferable to copolymerize adipic acid in an amount of 5 to 40 mol% with respect to the acid component from the viewpoint of impact resistance.

The proportion of the copolymer component depends on the type thereof, but as a result, the melting point of the polymer is from 180 to 223 ° C, preferably from 200 to 223 ° C, more preferably from 210 to 223 ° C.
It is the ratio in the range of ° 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 method for measuring the melting point of the polyester is as follows.
The measurement is performed in the same manner as in the measurement of the melting point of the isophthalic acid copolymerized polyester.

The intrinsic viscosity of the polyester (II) is preferably from 0.70 to 2.00, more preferably from 0.80 to 1.70, and particularly preferably from 0.85 to 1.70.
1.50.

In the polyester film of the present invention,
The polyester composition layer (B) has a melting point of 210 to 245.
99% to 50% by weight of a copolymerized polyester (I) having ethylene terephthalate as a main repeating unit at a temperature of 180 ° C. and 1 to 50% by weight of polyester (II) having a butylene terephthalate having a melting point of 180 to 223 ° C. as a main repeating unit.
It is necessary to consist of 1% by weight of polyester (II) containing butylene terephthalate as the main repeating unit
When the content is less than 99% by weight and the copolymerized polyester (I) containing ethylene terephthalate as a main repeating unit exceeds 99% by weight, the impact resistance at low temperatures cannot be improved. When the content of the polyester (II) containing butylene terephthalate as a main repeating unit exceeds 50% by weight and the content of the copolymerized polyester (I) containing ethylene terephthalate as a main repeating unit is less than 50% by weight, the heat resistance of the film decreases. In addition, the impact resistance becomes insufficient.

In the present invention, the main repeating units are isophthalic acid copolymerized polyester used in the isophthalic acid copolymerized polyester layer (A) and ethylene terephthalate used in the copolymerized polyester (I) of the polyester composition layer (B). The polyester having butylene terephthalate as a main repeating unit used for the copolymerized polyester and the polyester (II) of the polyester composition layer (B) is not limited by the production method. For example, in the case of a copolyester having ethylene terephthalate as a main repeating unit, 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 copolyester. Alternatively, a method of subjecting dimethyl terephthalate, ethylene glycol and a copolymer component to a transesterification reaction, and then subjecting the resulting reaction product to a polycondensation reaction to obtain a copolymerized polyester is preferably used. In the production of each copolymerized polyester and polybutylene terephthalate homopolymer, other additives such as a fluorescent whitening agent, an antioxidant, a heat stabilizer, and an antistatic agent can be added as necessary.

In the present invention, the transesterification rate of the polyester composition constituting the polyester composition layer (B) needs to be 3.0% or more, and is preferably 3.0 to 9.0%.
It is preferably 0%. The transesterification rate is 3.0%
With the above, the crystallinity of the polyester composition layer (B) is suppressed, and the moldability and impact resistance are significantly improved.
If it exceeds 9%, the film-forming property of the film may be deteriorated due to the deterioration of the polymer. Conversely, if the transesterification rate is less than 3.0%, the crystallinity is increased, so that the moldability and impact resistance are insufficient, which is not preferable.

It is preferable that the copolymerized polyester (I) and the polyester (II) constituting the polyester composition layer (B) are melt-kneaded before film formation.

The transesterification rate can be set according to the conditions for melt-mixing the copolymerized polyester (I) and the polyester (II), for example, the extrusion temperature and the residence time. The transesterification rate can also be adjusted by adjusting the amount of the polyester (II) polymerization catalyst.

The transesterification rate of the polyester composition constituting the polyester composition layer (B) was measured as follows.

About 10 mg of the corresponding polyester composition was scraped off from the film, dissolved in a mixed solvent of CDCl ₃ : CF ₃ COOD, and measured by 600 MHz ¹ H-NMR (FIG. 1). Peaks A, B and C due to transesterification of the detected PET / PBT blend system
Were separated from each other (FIG. 2), the respective integral values were determined, and the transesterification rate was determined by the following equation.

[0028]

## EQU00001 ## Ester exchange rate = SB / (SA + SB + SC) .times.100 [where, SA represents the integrated value of peak A, SB represents the integrated value of peak B, and SC represents the integrated value of peak C. ]

The polyester film of the present invention has a structure in which an isophthalic acid copolymerized polyester layer (A) and a polyester layer composition (B) are laminated, and can be produced by a conventionally known method. it can. For example,
Isophthalic acid copolymerized polyester and polyester composition constituting each layer are separately melted and co-extruded, laminated and fused before solidification, then biaxially stretched, heat-fixed, and isophthalic acid copolymerized polyester. A method in which the polyester composition is separately melted and extruded to form a film, and two films are laminated in an unstretched state or after stretching.

The polyester film of the present invention may be an unstretched film, but is preferably a biaxially stretched film. In this case, the refractive index in the thickness direction of the isophthalic acid copolymerized polyester layer (A) is 1.490 to 1.5.
50, more preferably 1.505.
Over 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. 10-75 μm,
In particular, the thickness is preferably 15 to 50 μm. 6μ thick
If it is less than m, breakage or the like is likely to occur during processing, while 7
Those exceeding 5 μm are excessive quality and uneconomical.

Isophthalic acid copolymerized polyester layer (A)
Is preferably about 0.02 to 1.5, more preferably 0.04 to 0.67, and particularly preferably 0.04 to 0.67, which is the ratio of the thickness TA of the polyester composition layer to the thickness TB of the polyester composition layer (B). 0.04 to 0.25. Specifically, for example, in the case of a polyester film having a thickness of 25 μm, the thickness of the isophthalic acid copolymerized polyester layer (A) is set to 0.5 to 15 μm.
m, preferably 1 to 10 μm, more preferably 1 to 5 μm
m.

As a metal plate to which the polyester film of the present invention is bonded, in particular, 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 methods (A) and (A). (A) The metal plate is heated to a temperature equal to or higher than the melting point of the film, the film is bonded, and then cooled, and the surface layer (thin layer) of the film in contact with the metal plate is made amorphous and adhered. (A) An adhesive is primer-coated on the film in advance, and this surface is bonded to a metal plate. As the adhesive, a known resin adhesive, for example, an epoxy adhesive, an epoxy-ester adhesive, an alkyd adhesive, or the like can be used.

When the polyester film of the present invention is bonded to a metal plate, the polyester layer (B) is bonded to the metal plate. Further, in the polyester film of the present invention, if necessary, another additional layer may be laminated between the isophthalic acid copolymerized polyester layer (A) and the polyester composition layer (B) or on one side. .

[0035]

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

[Examples 1 to 8 and Comparative Examples 1 to 5] Copolymerized polyethylene terephthalate (intrinsic viscosity: 0.64) obtained by copolymerizing the components shown in Table 1 is the copolymerized polyester layer (A). The polyester composition is dried separately at 280 ° C. by a conventional method so that the polyester composition becomes the polyester composition layer (B), then co-extruded from dies adjacent to each other, laminated, fused and quenched and solidified,
An unstretched laminated film was prepared. In addition, the transesterification rate of the polyester composition of the B layer was set by changing the above-mentioned melting temperature.

Next, the unstretched film was longitudinally stretched 3.2 times at 130 ° C., then transversely stretched 3.3 times at 120 ° C., and heat-set at 180 ° 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 composition layer (B) were 5 μm and 20 μm, respectively.

[0039]

[Table 1]

A total of 13 types of films obtained in Examples 1 to 8 and Comparative Examples 1 to 5 were heated at 230 ° C. to a thickness of 0.1 mm.
The polyester layer (B) is stuck on both sides of 25 mm tin-free steel so that the surface of the polyester layer (B) is in contact with the tin-free steel, and after cooling with water, cut into a 150 mm-diameter disc and drawn in four steps using a drawing die and a punch. By deep drawing, a 55 mm-diameter side seamless container (hereinafter abbreviated as can) was prepared. Perform the following observations and tests on this can,
Each was evaluated according to the following criteria.

(1) Deep drawing processability ：: The film was processed without any abnormality, and no whitening or breakage was observed in the film. Δ: Whitening is observed at the top of the film can. X: Film breakage is observed in a part of the film.

(2) Impact resistance For a can which has good deep drawing, pour water and cool to 10 ° C., and 10 cans of each test are 30 cm in height.
Rust prevention test on the film surface in the can (1% NaCl water was put in the can, the electrode was inserted, and the voltage when 6V was applied with the can body as the anode) (Hereinafter referred to as ERV test), and evaluated according to the following criteria. ；: 0.2 mA or less for all 10 samples. Δ: 0.2 mA or more for 1 to 5 pieces. C: The film was 0.2 mA or more for 6 or more pieces, or cracks of the film were already observed after dropping.

(3) Heat Embrittlement Resistance The can which had been subjected to good deep drawing was heated and maintained at 200 ° C. for 5 minutes, and then the impact resistance described in (2) was evaluated. . ：: 0.1 mA or less for all 10 samples. Δ: 0.1 mA or more for 1 to 5 pieces. X: The film was 0.1 mA or more for 6 or more pieces, or cracks of the film were already observed after heating at 200 ° C. for 5 minutes.

(4) Retort Resistance The cans having good deep drawing properties were filled with water, retorted at 120 ° C. for 1 hour in a steam sterilizer, and then stored at 50 ° C. for 30 days. After dropping 10 cans for each test from a height of 1 m onto a PVC tile floor, ERV tests were performed in the cans, and each was evaluated according to the following criteria. ；: 0.2 mA or less for all 10 samples. Δ: 0.2 mA or more for 1 to 5 pieces. C: The film was 0.2 mA or more for 6 or more pieces, or cracks of the film were already observed after dropping.

(5) Flavor Retention The cans having good deep drawability were filled with cider and sealed. After holding at 37 ° C. for 30 days, the can was opened, and the change in fragrance was examined by a sensory test, and each was evaluated according to the following criteria. ；: There was no change in fragrance. Δ: Slight change in fragrance was observed. ×: Change in scent was observed.

(6) Taste retention In the same manner as in (5), the change in taste was examined by a sensory test.
Each was evaluated according to the following criteria. ；: There was no change in taste. Δ: Slight change in taste was observed. X: Change in taste was observed. The results of the above six evaluations are as shown in Table 2.

[0047]

[Table 2]

As is clear from the results in Table 2, cans using the polyester film of the present invention are excellent in deep drawability, heat embrittlement resistance, retort resistance, and fragrance retention, and are also impact resistant. In particular, it has excellent impact resistance at low temperatures, and is good without deteriorating the taste of soft drinks and the like.

[0049]

Industrial Applicability The polyester film for laminating metal sheets of the present invention has excellent moldability, heat resistance, retort resistance, and fragrance retention, as well as impact resistance, especially impact resistance at low temperatures. It is excellent without deteriorating the taste of soft drinks and the like. Therefore, it is particularly suitable to be used by being bonded to a metal can, such as for soft drinks, which is often cooled and handled at a low temperature.

[Brief description of the drawings]

FIG. 1 shows the NM of a polyester composition obtained by melt-kneading a copolymerized polyester (I) and a polyester (II).
It is an R chart.

FIG. 2 is an enlarged NMR chart of peaks A, B and C resulting from the transesterification of the PET / PBT blend system in FIG.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tetsuya Hasegawa 3-37-19 Koyama, Sagamihara City, Kanagawa Prefecture, Sagamihara Research Center, Teijin Limited

Claims (2)

[Claims] 1. An isophthalic acid copolymerized polyester layer (A) having a melting point of 210 to 245 ° C., and a melting point of 210 to 245 ° C.
It is composed of 99 to 50% by weight of a copolymerized polyester (I) having ethylene terephthalate as a main repeating unit at 45 ° C and 1 to 50% by weight of polyester (II) having a butylene terephthalate as a main repeating unit having a melting point of 180 to 223 ° C. A polyester film obtained by laminating a polyester composition layer (B), wherein the polyester composition constituting the polyester composition layer (B) has a transesterification rate of 3.0% or more. Polyester film for board lamination. 2. The polyester (II) has an adipic acid content of 5%.
The polyester film for laminating metal plates according to claim 1, wherein the polyester film is butylene terephthalate copolymerized by 40 mol%.