JPH10278205A - Polyester film for metal plate laminating molding processing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the polyester film holding excellent molding processability, heat resistance, retort resistance and impact resistance though being inexpensive and not changing taste of mineral water severely requiring flavor and taste holding properties. SOLUTION: This film is obtained by laminating a copolyester layer (A) having an m.p. of 210-245 deg.C and a glass transition temp. of 60 deg.C or higher and produced by using a germanium compd. as a polycondensation catalyst and a copolyester layer (B) having an m.p. of 210-245 deg.C and produced by using an antimony compd. as a polycondensation catalyst and the total amt. of an alkali metal element contained in the copolyester layer (A) is 5 ppm or less.

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 moldability when laminating to a metal plate for can making such as drawing. Metal cans with excellent taste retention and impact resistance, heat resistance, and good retort resistance, such as beverage cans,
The present invention relates to a polyester film for laminating and processing metal plates capable of producing food cans 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, coating with a thermoplastic resin film has been attempted as a method of imparting rust prevention without using an organic solvent.

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.

[0004] As such a thermoplastic resin film, a copolymerized polyester film is suitable in terms of moldability, heat resistance, impact resistance, fragrance and flavor, and the like, and there have been some proposals using this. Have been. However, these films do not necessarily exhibit sufficient fragrance and taste when used as beverages, such as green tea, in which beverages with extremely delicate taste are important, and mineral water, which is required to be tasteless and odorless. There was a problem that a change to was perceived.

On the other hand, Japanese Patent Application Laid-Open No. Hei 6-116376 proposes a polyester film for forming a metal plate having an improved flavor made of a copolyester containing a specific amount of an alkali metal element and a germanium element. I have.

However, germanium compounds are very expensive, and when all copolymerized polyesters constituting the film are produced using the germanium compound, there is a problem that the film production cost increases.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a mineral which is inexpensive, retains excellent moldability, heat resistance, retort resistance, impact resistance, and has strict requirements for flavor and taste. An object of the present invention is to provide a polyester film for laminating and processing a metal plate without changing the taste of water or the like.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, the film has a two-layer structure, and the layer on the side in contact with the beverage has an effect on flavor and taste. The present inventors have found that by using a certain polyester and using a general polyester for the layer on the side to be bonded to the metal, it is possible to realize sufficient flavor and taste retention and low cost, and have reached the present invention.

That is, the present invention has a melting point of 210 to 24.
5 ° C., a glass transition temperature of 60 ° C. or higher, a copolymerized polyester layer (A) produced using a germanium compound as a polycondensation catalyst, and a melting point of 210 to 245 ° C., and an antimony compound as a polycondensation catalyst. And laminating the copolymerized polyester layer (B) produced by using the above method, wherein the total amount of alkali metal elements contained in the copolymerized polyester layer (A) is 5 ppm or less. It is a polyester film for molding.

In the present invention, the copolymerized polyester used for the copolymerized polyester layer (A) and the copolymerized polyester layer (B) includes copolymerized polyethylene terephthalate, copolymerized polyethylene-2,6-naphthalenedicarboxylate, and copolymerized polyester. A representative example is polymerized polybutylene terephthalate. These copolymer components may be acid components or alcohol components. Examples of the 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, and cyclohexanedicarboxylic acid. Examples of the alcohol component include aliphatic diols such as butanediol 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 component depends on the kind thereof, but is a proportion that results in a polymer melting point in the range of 210 to 245 ° C., preferably 215 to 235 ° C. If the melting point is lower than 210 ° C., the heat resistance deteriorates, which is not preferable. On the other hand, if the melting point is higher than 245 ° C., the crystallinity of the polymer becomes too large and the moldability 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 20 mg.

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 less than 60 ° C., satisfactory flavor and flavor cannot be obtained. As such a copolymerized polyester, a copolymerized polyester having a high glass transition temperature can be obtained, and therefore, especially preferred is isophthalic acid copolymerized polyethylene terephthalate or 2,6-naphthalenedicarboxylic acid copolymerized polyethylene terephthalate.

The copolyester in the present invention can be produced by a known method. For example, as a method for producing a copolymerized polyethylene terephthalate, a method in which terephthalic acid, ethylene glycol and a copolymer component are subjected to an esterification reaction, and then the resulting reaction product is subjected to a polycondensation reaction to obtain a copolymerized polyethylene terephthalate (direct polymerization method) Or 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 polyethylene terephthalate (ester exchange method).
Are preferred. In the case of the transesterification method, it is preferable to use a manganese compound (for example, manganese acetate) or a titanium compound (for example, titanium acetate, titanium tetrabutoxide, etc.) as the transesterification catalyst.

The catalyst used for the polycondensation reaction of the copolymerized polyester constituting the copolymerized polyester layer (A) must be a germanium compound. If a germanium compound is not used for the copolymerized polyester of the layer (A) which is in direct contact with the beverage, the fragrance and flavor will be significantly inferior.

The germanium compound used in the polycondensation reaction includes (a) amorphous germanium oxide,
(B) fine crystalline germanium oxide, (iii) a solution of germanium oxide dissolved in glycol in the presence of an alkali metal or alkaline earth metal or a compound thereof,
(D) A solution obtained by dissolving germanium oxide in water is preferred. The amount of the germanium compound is as follows:
It is preferably from 10 to 200 ppm, more preferably from 30 to 150 ppm, per germanium element.

For the polycondensation reaction of the polyester constituting the copolymerized polyester layer (B), use is made of an antimony compound which is inexpensive and does not significantly impair the flavor and taste retention. Preferred examples of the antimony compound include antimony oxide and antimony acetate. The amount of the antimony compound is 12 per antimony element.
0 to 600 ppm is preferable, and 180 to 450 ppm is more preferable.

The intrinsic viscosity (orthochlorophenol, 35 ° C.) of the copolyester used in the copolyester layer (A) and the copolyester layer (B) is 0.1.
It is preferably from 52 to 1.50, more preferably from 0.57 to 1.00, particularly preferably from 0.60 to 0.10.
80. When the intrinsic viscosity is less than 0.52, the impact resistance of the film may be insufficient, while when the intrinsic viscosity is more than 1.50, the formability may be impaired. The intrinsic viscosity may be adjusted only by melt polymerization, or may be further adjusted by a polymerization method in a solid state (solid state polymerization) after the melt polymerization. If necessary, additives such as an antioxidant, a heat stabilizer, a viscosity modifier, a plasticizer, a hue improver, a nucleating agent, and an ultraviolet absorber can be added.

Further, the total amount of the alkali metal elements contained in the copolymerized polyester constituting the copolymerized polyester layer (A) in the present invention must be 5 ppm or less.

Here, the total amount of the alkali metal elements means the pp of Li, Na and K elements determined by atomic absorption analysis.
m represents the sum of the concentrations. If the total amount of the alkali metal elements in the copolymerized polyester layer (A) exceeds 5 ppm, the change in taste of the beverage is detected because the change in taste when the alkali metal elutes into the beverage exceeds the threshold value of human taste. It is not preferable because it comes to be.

A lubricant can be added to the copolymerized polyester layer (A) and the copolymerized polyester layer (B) for the purpose of improving the film winding property. 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, barium sulfate, and the like, and examples of the organic lubricant include crosslinked 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 crosslinked silicone resin particles, and spherical crosslinked polystyrene resin particles. When selecting the lubricant used for the copolymerized polyester layer (A), it is necessary to pay attention to the content of the alkali metal contained in the lubricant.

The particle size and amount of the lubricant to be added may be determined in consideration of the winding property of the film, the pinhole resistance, and the flavor and flavor. For example, in the copolymerized polyester layer (A), 0.04% by weight or less for silica having an average particle size of 1.5 μm, and 0.36% for silica having an average particle size of 0.8 μm.
% By weight or less, and the copolymerized polyester layer (B)
By adding 0.06% by weight or more for silica having an average particle size of 1.5 μm and 0.42% by weight or more for silica having an average particle size of 0.8 μm, the scent can be obtained without impairing the flavor and flavor retention. It is possible to ensure ease of use.

The lubricant is not limited to the above-mentioned 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.

In order for the polyester film of the present invention to be particularly suitable for use in food cans or beverage cans, it is preferable that the amount of substances eluted or scattered from the film is as small as possible.
It is virtually impossible to eliminate these substances at all. Therefore, for use in food cans or beverage cans, for example, the amount of extraction per 1 inch ² of the film when extracted with ion-exchanged water at 121 ° C. for 2 hours is preferably 0.5 mg or less, and 0.1 mg or less. It is more preferred that:

The polyester film of the present invention has a structure in which a copolymerized polyester layer (A) and a copolymerized polyester layer (B) are laminated. The copolyesters constituting are separately melted and co-extruded, laminated and fused before solidification, then biaxially stretched, heat-fixed, the copolyesters constituting each layer are separately melted and extruded. The film can be manufactured by a method of laminating and fusion-bonding the two into an unstretched state or after stretching.

When the polyester film is composed only of the copolymerized polyester layer (A), it becomes expensive and uneconomical. It is not suitable because the taste retention deteriorates and the taste of the contents of the can deteriorates.

The polyester film of the present invention may be an unstretched film, but is preferably in the form of a biaxially oriented film that has been biaxially stretched and heat set. In this case, the refractive index in the thickness direction of the copolymerized polyester layer (A) is 1.5.
It is preferably from 0.05 to 1.550, and more preferably from 1.510 to 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 75
Those exceeding μm are excessive quality and uneconomical.

The thickness T of the copolymerized polyester layer (A)
The ratio of the _A, and the thickness T _B of the copolymerized polyester layer (B) (T
_A / T _B ) is preferably from 0.02 to 0.67, more preferably from 0.04 to 0.47, and particularly preferably from 0.04 to 0.47.
0.39. Specifically, for example, in the case of a polyester film having a thickness of 25 μm, the thickness of the copolymerized polyester layer (A) is set to 0.5 to 10 μm, preferably 1 to 8 μm.
m, more preferably 1 to 7 μm.

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.

When the polyester film of the present invention is bonded to a metal plate, it is necessary to bond the copolymerized polyester layer (A) so as to be in contact with the contents such as a beverage.
That is, when the film of the present invention is bonded to the inside of a metal can, the side of the copolymerized polyester layer (B) is bonded to the can.

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

[0033]

The present invention will be further described with reference to the following examples.
In addition, each characteristic was measured and evaluated by the following methods. (1) Intrinsic viscosity of polyester Measured in orthochlorophenol at 35 ° C.

(2) Melting point of polyester Using Du Pont Instruments 910 DSC, heating rate 20 ° C.
/ Min to determine the melting peak. The sample amount was 20 mg.

(3) Glass Transition Temperature (Tg) of Polyester Film A 20 mg film sample was placed in a pan for DSC measurement, heated and melted for 5 minutes on a 290 ° C. heating stage, and the sample pan was quickly spread on ice. Rapid solidification on foil, heating rate 2 using Du Pont Instruments 910 DSC
The glass transition point was determined by measuring at 0 ° C./min.

(4) Total amount of alkali metal elements in polyester A film sample was dissolved in orthochlorophenol,
The extraction operation was performed with 0.5N hydrochloric acid. This extract was subjected to atomic absorption spectrometry to determine the amounts of Na, K, and Li for each element, and was determined from the sum of them.

(5) Deep drawability The film was heated at a temperature equal to or higher than the melting point of the polyester.
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 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 having good deep drawing, pour water fully and cool to 10 ° C., and 10 cans of 30 cm in height for each test.
Was dropped on a PVC tile floor, and an ERV test was performed in the can, and evaluated according to the following criteria. ：: 0.2 mA or less for all 10 samples. Δ: Exceeded 0.2 mA for 1 to 5 pieces. X: More than 6 pieces exceeded 0.2 mA, or cracking of the film was already observed after dropping.

(7) Heat Embrittlement Resistance The can which had good deep drawing was heated and maintained at 200 ° C. for 5 minutes, and then subjected to the impact resistance evaluation described in (6), and evaluated according to the following criteria. ：: 0.2 mA or less for all 10 samples. Δ: Exceeded 0.2 mA for 1 to 5 pieces. ×: More than 6 pieces exceeded 0.2 mA, or cracking of the film was already observed after heating at 200 ° C. for 5 minutes.

(8) Retort resistance The cans having good deep drawability were filled with water, retorted in a steam sterilizer at 120 ° C. for 1 hour, and then heated to 50 ° C.
For 30 days. The cans obtained were 10 for each test.
After dropping from the height of 50 cm to the PVC tile floor,
An ERV test in the can was performed and evaluated according to the following criteria. ：: 0.2 mA or less for all 10 samples. Δ: Exceeded 0.2 mA for 1 to 5 pieces. X: More than 6 pieces exceeded 0.2 mA, or cracking of the film was already observed after dropping.

(9) Taste preservation A can having good deep drawing was filled with ion-exchanged water and stored at room temperature (20 ° C.) for 30 days. A tasting test was 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 8 and Comparative Examples 1 to 5] Copolymerized polyethylene terephthalate (intrinsic viscosity 0.64, particle size ratio) produced by using the components shown in Table 1 as copolymerization components and using germanium dioxide as a polycondensation catalyst 1.1, average particle size 0.3
μm spherical silica (containing 0.1% by weight) is a copolymerized polyester layer (A), which is a copolymerized polyethylene terephthalate produced using the components shown in Table 1 as copolymerization components and diantimony trioxide as a polycondensation catalyst. Particle size ratio 1.1,
Each of them is dried and melted by a conventional method so that the copolyester layer (B) contains spherical silica having an average particle size of 1.5 μm (containing 0.1% by weight of true spherical silica), and then co-extruded from dies adjacent to each other. And laminate, fused, quenched and solidified,
An unstretched laminated film was prepared. The total amount of the alkali metal elements contained in the copolymerized polyethylene terephthalate constituting the copolymerized polyester layer (A) was 2
ppm or less.

Next, the unstretched film was longitudinally stretched 3.2 times at 110 ° C., then transversely stretched 3.3 times at 115 ° C., and heat-set at 180 ° C. to obtain a biaxially oriented laminated film. .

[0044] The thickness of the obtained film was 25 [mu] m, and the thickness T _A copolyester layer (A), the ratio between the thickness T _B of the copolymerized polyester layer _{(B) (T A / T} B) is 0 .25. The properties of these films are shown in Tables 1 and 2.

Comparative Example 6 Copolyester Layer (A)
A single-layer film was prepared in the same manner as in Example 1 except that no was laminated. The properties of this film are shown in Tables 1 and 2.

Example 9 and Comparative Example 7 In Example 1, sodium acetate was added to the copolymerized polyethylene terephthalate used in the copolymerized polyester layer (A) in an amount of 4 ppm (Example 9) and 6 ppm (Comparative Example 7) in terms of Na element. ) A biaxially oriented laminated film was prepared in the same manner as in Example 1 except that it was contained. The properties of these films are shown in Tables 1 and 2.

[0047]

[Table 1]

[0048]

[Table 2]

As is clear from the evaluation results in Table 2, the cans using the polyester film of the present invention have good deep drawing workability, heat embrittlement resistance, retort resistance, impact resistance and good fragrance retention. It was excellent in taste retention.

[0050]

The polyester film for laminating and processing a metal plate of the present invention is obtained by laminating a metal plate and then forming a can.
For example, when forming a metal can by deep drawing, it has good moldability, heat resistance, retort resistance, impact resistance, and flavor retention, and can be manufactured at low cost. Very useful for processing.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI // B29K 67:00 B29L 9:00

Claims (5)

[Claims] 1. A copolymerized polyester layer (A) having a melting point of 210 to 245 ° C., a glass transition temperature of 60 ° C. or higher, and produced using a germanium compound as a polycondensation catalyst.
And a copolyester layer (B) having a melting point of 210 to 245 ° C. and produced using an antimony compound as a polycondensation catalyst, and an alkali contained in the copolyester layer (A). The total amount of metal elements is 5ppm
A polyester film for laminating a metal plate, comprising: 2. The polyester film according to claim 1, wherein the copolymerized polyester layer (A) comprises isophthalic acid copolymerized polyethylene terephthalate or 2,6-naphthalenedicarboxylic acid copolymerized polyethylene terephthalate. 3. The polyester film according to claim 1, wherein the copolymer polyester layer (A) has a refractive index in the thickness direction of 1.505 to 1.550. 4. The thickness T _A of the copolyester layer (A)
When the ratio between the thickness T _B of the copolymerized polyester layer (B) (T _A
The polyester film for metal plate lamination processing according to claim 1, wherein (/ T _B ) is 0.02 to 0.67. 5. The film is treated with ion-exchanged water at 121 ° C. for 2 hours.
0.5 mg / inc extract amount after time extraction
h ² or less is claim 1 or 2 metal plates bonded polyester film for combined molding according.