JPH10166440A - Polyester film to be bonded on metal plate for forming processing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film which has improved canning workability after being bonded on a metal plate, e.g. deep drawing property, and improved heat resistance, impact resistance, rust proof, particularly taste retention and smell retention properties after a retort treatment. SOLUTION: In a polyester film comprising copolymer of polyethylene terephthalate having melting point of 210-245 deg.C, a maximum peak temperature Te of loss elastic modulus of the film and glass transition point at DSC measurement satisfy the following equations: Tg>=78, Te-Tg<=30, where Tg is glass transition temperature deg.C at DSC measurement after heating and melting at 290 deg.C and quenching, and Te is maximum peak temperature deg.C of loss elastic modulus of the film.

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 to a metal plate and performing can forming such as drawing. The present invention relates to a polyester for metal plate lamination processing capable of producing metal cans having excellent heat resistance, retort resistance, fragrance retention, impact resistance, rust resistance and the like, such as beverage cans and food cans.

[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 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 film has been attempted.

That is, studies are being made on a method of laminating a thermoplastic resin film on a metal plate such as tinplate, tin-free steel, aluminum or the like, and then forming the can by drawing or the like.

As a thermoplastic resin film, it is gradually becoming clear that a copolyester film is suitable in terms of moldability, heat resistance, impact resistance, fragrance retention and the like. However, this polyester film does not necessarily show sufficient fragrance and taste when used as beverages, such as green teas, which have an extremely delicate taste and mineral water which is required to be tasteless and odorless. Is sensed.

On the other hand, Japanese Patent Application Laid-Open No. Hei 6-116376 proposes a polyester film for forming a metal sheet having an improved flavor, comprising a copolymerized polyester containing a specific amount of an alkali metal element and a germanium element. I have. However, when this film is used, it shows excellent flavor and fragrance retention in the process where heat is not applied at the stage of filling contents such as a cold pack system, but at the stage of filling contents such as retort treatment. In the step in which the heat treatment is performed, it is not always possible to obtain sufficient flavor and fragrance retention.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to overcome the disadvantages of the prior art and to maintain the excellent molding processability, heat resistance and impact resistance of a copolymerized polyethylene terephthalate film while retaining its contents. It is an object of the present invention to provide a polyester film for laminating and processing a metal plate, which has an improved scent-retaining property of a product, particularly, a scent-retaining property after retort treatment.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, using a copolymerized polyethylene terephthalate having a specific melting point and glass transition temperature, with a specific dynamic viscosity. The present inventors have found that a film having elasticity can improve the flavor and fragrance retention after retort treatment without impairing the moldability, and have led to the present invention.

That is, the present invention has a melting point of 210 to 24.
A biaxially stretched film made of copolymerized polyethylene terephthalate having a temperature of 5 ° C., wherein the highest temperature peak temperature (Te) of the loss modulus of the film and the glass transition temperature (Tg) in DSC measurement satisfy the following expressions. Characteristic polyester film for metal plate lamination processing.

[0009]

Tg ≧ 78 (1) Te−Tg ≦ 30 (2) (where, Tg is the glass transition temperature (° C.) in DSC measurement after 290 ° C. heating-quenching, and Te is the loss elasticity of the film. Rate is the highest peak temperature (° C).)

In the present invention, the copolymerization component of the copolymerized polyethylene terephthalate may be a dicarboxylic acid component or a diol component.

Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid and 2,6-naphthalenedicarboxylic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decane dicarboxylic acid; Alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid can be exemplified.
Examples thereof include aliphatic diols such as -butanediol, 1,6-hexanediol, and diethylene glycol; alicyclic diols such as 1,4-cyclohexanedimethanol; and aromatic diols such as bisphenol A. These can be used alone or in combination of two or more.

The proportion of the components of the copolymer depends on the type of the copolymer, but is a proportion that results in a polymer melting point in the range of 210 to 245 ° C., preferably 215 to 240 ° 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 crystallinity of the polymer is too large and the moldability is impaired.

Here, the melting point of the copolymerized polyethylene terephthalate 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 20mg
And

Further, the intrinsic viscosity (orthochlorophenol, 35 ° C.) of the copolymerized polyethylene terephthalate is preferably from 0.52 to 1.50, more preferably from 0.57 to 1.00, particularly preferably from 0.17 to 1.00. 60 ~
0.80. If the intrinsic viscosity is less than 0.52, the impact resistance may be insufficient, which is not preferable. On the other hand,
If the intrinsic viscosity exceeds 1.50, the moldability may be impaired.

The copolymerized polyethylene terephthalate in the present invention is not limited by its production method,
Terephthalic acid, a method of subjecting ethylene glycol and a copolymer component to an esterification reaction, and then subjecting the resulting reaction product to a polycondensation reaction to a desired degree of polymerization to obtain a copolymerized polyethylene terephthalate, or dimethyl terephthalate, Preferable examples include a method of subjecting ethylene glycol and a copolymer component to a transesterification reaction, and then subjecting the obtained reaction product to a polycondensation reaction until a desired degree of polymerization is obtained to obtain a copolymerized polyethylene terephthalate. Further, the copolymerized polyethylene terephthalate obtained by the above method (melt polymerization) can be converted into a polymer having a higher degree of polymerization by a polymerization method in a solid state (solid state polymerization) if necessary.

The copolymerized polyethylene terephthalate may contain, if necessary, an antioxidant, a heat stabilizer, a viscosity modifier,
Additives such as a plasticizer, a hue improver, a lubricant, a nucleating agent, and an ultraviolet absorber can be added.

The catalyst used in the polycondensation reaction includes:
Antimony compounds (Sb compounds), titanium compounds (Ti
Compounds) and germanium compounds (Ge compounds). Among them, titanium compounds and germanium compounds are more preferable from the viewpoint of the fragrance retention of the film. Preferred examples of the titanium compound include titanium tetrabutoxide and titanium acetate. As the germanium compound, (a) amorphous germanium oxide,
(B) Fine crystalline germanium oxide, (c) a solution of germanium oxide dissolved in glycol in the presence of an alkali metal or alkaline earth metal or a compound thereof, and (d) a solution of germanium oxide dissolved in water. Preferred are mentioned. The amount of the catalyst used may be a commonly used amount.

The copolymerized polyethylene terephthalate includes:
It is preferable to add a lubricant for the purpose of improving the winding property of the film. The type of lubricant may be inorganic or organic, but inorganic is preferred. Examples of the inorganic lubricant include silica, alumina, titanium oxide, calcium carbonate, and barium sulfate. Examples of the organic lubricant include silicone resin particles and crosslinked polystyrene particles. Particularly preferred lubricants in terms of pinhole resistance are monodispersed lubricants having a particle size ratio (major axis / minor axis) of 1.0 to 1.2.
Examples of such a lubricant include spherical silica, spherical silicone resin particles, and spherical cross-linked polystyrene.

The particle size and amount of the lubricant may be determined based on the film winding property, pinhole resistance and fragrance retention. That is, in the case of silica having an average particle size of 1.5 μm, 0.06% by weight or more and 0.25% by weight or less, and an average particle size of 0.
In the case of 8 μm silica, the rollability can be secured without impairing the fragrance and flavor retention by adding the silica in the range of 0.1% by weight or more and 0.45% by weight or less.

The lubricant is not limited to the externally added particles. For example, internal precipitated particles obtained by depositing a part or all of the catalyst used in the production of polyester in the reaction step can be used. It is also possible to use externally added particles and internally precipitated particles in combination.

The polyester film of the present invention is suitable for use in food or beverage cans, in particular, in that the less the substance that elutes or scatters from the film, the better. However, it is substantially impossible to eliminate such substances at all. Impossible. Therefore, in order to use it for food cans or beverage cans, for example, the amount of extraction per inch ² of the film when extracted with ion-exchanged water at 121 ° C. for 2 hours is 0.5 mg.
Or less, more preferably 0.1 mg or less.

The polyester film of the present invention is used in a state of being biaxially stretched and heat set. At this time, the highest temperature peak temperature (Te) of the loss modulus of the polyester film
And the glass transition temperature (Tg) in the DSC measurement must satisfy the following expressions (1) and (2).

[0023]

Tg ≧ 78 (1) Te−Tg ≦ 30 (2) (where Tg is the glass transition temperature (° C.) in DSC measurement after heating and melting and quenching at 290 ° C., and Te is the loss elasticity of the film. Rate is the highest peak temperature (° C).)

If the Tg of the film is less than 78 ° C., the heat resistance becomes poor, and the flavor and odor retention after retorting deteriorates. For this reason, as a copolymerization component of the copolymerized polyethylene terephthalate, at least one component, the glass transition temperature does not change when the proportion of the copolymerization component is increased,
Alternatively, it is preferable to use a component that increases.
Preferred examples of the component that increases the glass transition temperature when the proportion of the copolymer component is increased are 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid component, and 1,4-cyclohexanedimethanol as the diol component. it can.

Here, the Tg of the polyester was measured by placing a 20 mg film sample in a pan for DSC measurement,
After heating and melting for 5 minutes on a heating stage, the sample pan was quickly cooled and solidified on an aluminum foil spread on ice,
A method of determining a glass transition point at a heating rate of 20 ° C./min using on Instruments 910 DSC.

Further, when the value of Te-Tg exceeds 30, the molecular orientation and the crystallinity of the film become too high, so that the formability is remarkably reduced. Although the value of Te depends on the copolymerization components and the copolymerization amount, a method of adjusting the film forming conditions, particularly the biaxial stretching ratio or the stretching temperature, is preferably mentioned.

Here, Te is determined at a measurement frequency of 10 Hz and a dynamic displacement of ± 25 × 10 ⁻⁴ cm using a dynamic viscoelasticity measuring device.

The refractive index in the thickness direction of the polyester film is preferably from 1.500 to 1.540, and more preferably from 1.505 to 1.530. If this refractive index is too low, molding processing becomes insufficient,
On the other hand, if it is too high, the structure becomes close to amorphous, so that the heat resistance may decrease.

The polyester film of the present invention preferably has a thickness of 6 to 75 μm. Further, it is preferably from 8 to 75 μm, particularly preferably from 10 to 50 μm. 6 μm thick
If it is less than 75%, breakage or the like tends to occur during processing, while
Those exceeding μm are excessive quality and uneconomical.

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 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. The surface layer (thin layer) of the film in contact with the metal plate is made amorphous and adhered. An adhesive layer is primer-coated on the film in advance, and this surface is bonded to a metal plate. As the adhesive layer, a known resin adhesive, for example, an epoxy adhesive, an epoxy-ester adhesive, an alkyd adhesive, or the like can be used.

[0031]

The present invention will be further described with reference to the following examples.
The characteristics in the examples were measured by the following methods. (1) Intrinsic viscosity of polyester Measured in orthochlorophenol at 35 ° C.

(2) Melting point of polyester Du Pont Instruments 910 D
A method in which a melting peak is determined at a heating rate of 20 ° C./min using SC. The sample amount is 20 mg.

(3) Glass transition temperature of polyester (T
g) 20 mg of a film sample was placed in a pan for DSC measurement, heated and melted for 5 minutes on a 290 ° C. heating stage, and then rapidly cooled and solidified on an aluminum foil spread on ice, and then Du Pont Instruments 910 was prepared.
A method in which the glass transition point is determined at a heating rate of 20 ° C./min using DSC.

(4) Maximum peak temperature of loss elastic modulus of film (Te) The loss elastic modulus was determined at a measurement frequency of 10 Hz and a dynamic displacement of ± 25 × 10 ⁻⁴ cm using a dynamic viscoelasticity measuring apparatus. The peak temperature at this time is shown.

(5) Deep drawing workability The film pressure of the film heated above the melting point of the polyester is 0.1 mm.
Affixed to both sides of 25 mm tin-free steel, water-cooled, cut into a 150 mm diameter disk, deep-drawn in four stages using a drawing die and punch, and a 55 mm diameter side-side seamless container (hereinafter referred to as can and Abbreviated). The following observations and tests were performed on the cans, and the cans were evaluated according to the following criteria. Deep drawing processability-1 ○: No whitening or breakage is observed in the film processed without any abnormality. Δ: Whitening was observed on the upper part of the film can. X: Film breakage is observed in a part of the film. Deep drawing processability-2 ○: Processed without abnormality, rust prevention test of film surface in can (1% NaCl aqueous solution was put in the can, electrodes were inserted, and a voltage of 6 V was applied using the can body as an anode. The current value at that time is measured, and is 0.2 mA or less in the ERV test. ×: There is no abnormality in the film, but the current value is 0.2 mA or more in the ERV test, and pinhole-shaped cracks starting from the coarse lubricant of the film are observed when the energized portion is observed under magnification.

(6) Impact resistance For cans with good deep drawing, pour water thoroughly, cool to 0 ° C., drop 10 pieces for each test from a height of 30 cm onto a PVC tile floor. As a result of the ERV test in the can, the results were as follows: ○: 0.2 mA or less for all 10 samples. C: 0.2 mA or more for 1 to 5 pieces. ×: 0.2 mA or more for 6 or more pieces, or cracks of the film were already observed after dropping.

(7) Heat embrittlement resistance After the can which had been successfully deep drawn was heated and held at 200 ° C. for 5 minutes, the impact resistance evaluation described in (3) was performed. It was 0.2 mA or less. C: 0.2 mA or more for 1 to 5 pieces. X: The film was 0.2 mA or more for 6 or more pieces, or cracking of the film was already observed after heating at 200 ° C. for 5 minutes.

(8) Retort resistance The cans having good deep drawing properties are filled with water and retorted in a steam sterilizer at 120 ° C. for 1 hour.
Stored at 50 ° C. for 30 days. After dropping 10 cans for each test from a height of 50 cm onto a PVC tile floor, an ERV test in the cans was performed. ：: 0.2 mA or less for all 10 samples. C: 0.2 mA or more for 1 to 5 pieces. ×: 0.2 mA or more for 6 or more pieces, or cracks of the film were already observed after dropping.

(9) Taste preservation -1 A can having good deep drawing is filled with ion-exchanged water and stored at normal temperature (20 ° C) for 30 days. A tasting test is carried out by 30 panelists using the immersion liquid, and compared with ion-exchanged water for comparison, and evaluated according to the following criteria. ◎: Three or less out of thirty felt change in taste as compared with the comparative solution. 〇: 4 to 6 persons among 30 persons felt a change in taste as compared with the comparative solution. Δ: 7 to 9 persons among 30 persons felt a change in taste as compared with the comparative solution. ×: 10 or more out of 30 persons felt a change in taste as compared with the comparative solution.

(10) Food preservation property-2 Cans with good deep drawing were filled with ion-exchanged water, retorted in a steam sterilizer at 120 ° C. for 1 hour, and then at room temperature (20 ° C.). Store for 30 days. A tasting test is carried out by 30 panelists using the immersion liquid, and compared with ion-exchanged water for comparison, and evaluated according to the following criteria. ◎: Three or less out of thirty felt change in taste as compared with the comparative solution. 〇: 4 to 6 persons among 30 persons felt a change in taste as compared with the comparative solution. Δ: 7 to 9 persons among 30 persons felt a change in taste as compared with the comparative solution. ×: 10 or more out of 30 persons felt a change in taste as compared with the comparative solution.

Examples 1 to 7 and Comparative Examples 1 to 4
Copolymerized polyethylene terephthalate (intrinsic viscosity 0.64, particle size ratio 1.1, average particle size 0.1).
After drying 5 μm spherical silica (containing 0.2% by weight), the mixture was melt-extruded, quenched and solidified to obtain an unstretched film. Next, the unstretched film was longitudinally stretched at the temperature and magnification shown in Table 1, then transversely stretched at the temperature and magnification shown in Table 1, and heat-set at 180 ° C. to obtain a biaxially stretched polyester film. The thickness of the obtained film was 25 μm. Table 1 shows the glass transition temperature (Tg) and the maximum peak temperature (Te) of the loss modulus of the film, and Table 2 shows the evaluation results.

[0042]

[Table 1]

[0043]

[Table 2]

As is clear from the evaluation results in Table 2, cans using the polyester film of the present invention have good deep drawability, heat embrittlement resistance, retort resistance, impact resistance, and aroma retention. It was excellent in properties, in particular, the preservation of flavor and flavor after retort.

[0045]

The polyester film for laminating and forming a metal plate of the present invention can be formed into a metal can by, for example, deep drawing after laminating with a metal plate. It has good retort resistance and impact resistance, and also has excellent fragrance retention properties, particularly, flavor retention and fragrance retention properties after retort, and is extremely useful for metal containers.

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Claims (4)

[Claims] 1. A biaxially stretched film made of a copolymerized polyethylene terephthalate having a melting point of 210 to 245 ° C., wherein a maximum temperature peak temperature (T
e) and a polyester film for metal plate lamination processing, wherein the glass transition temperature (Tg) in DSC measurement satisfies the following formulas (1) and (2). Tg ≧ 78 (1) Te−Tg ≦ 30 (2) (where Tg is the glass transition temperature (° C.) in DSC measurement after heating and melting and quenching at 290 ° C., and Te is the loss elasticity of the film. Rate is the highest peak temperature (° C).) 2. The polyester film according to claim 1, wherein the copolymerization component of the copolymerized polyethylene terephthalate is naphthalenedicarboxylic acid. 3. The polyester film according to claim 1, wherein the copolymerized polyethylene terephthalate is produced using a germanium compound as a polycondensation catalyst. 4. A film is heated at 121 ° C. with ion-exchanged water.
The amount of extraction when the time extraction process is performed is 0.5 mg / inch
^{2. The} polyester film for laminating and processing a metal plate according to claim 1, which is ² or less.