JPH10231413A - Copolyester film for lamination with metallic sheet or plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a film excellent in flavor retention, heat resistance, impact resistance and the evenness of thickness by selecting a film made from a copolyester comprising an aromatic dicarboxylic acid and a glycol, containing a Ge compound and further containing an alkali metal compound and a P compound in a specified ratio. SOLUTION: This film is one made from a copolyester comprising an aromatic dicarboxylic acid and a glycol (e.g. a polyester prepared by copolymerizing isophthalic acid with a polyester obtained from terephthalic acid and ethylene glycol), containing desirably 5-300ppm, more desirably 10-100ppm of a Ge compound (e.g. germanium dioxide) and further containing an alkali metal compound (e.g. KOH) desirably an Na compound and/or a K compound and a P compound (e.g. trimethyl phosphate) in a ratio in the range: 0.1<=M/P<=1.5 [wherein M (ppm) is the amount of the alkali metal, and P (ppm) is the amount of the phosphorus].

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copolyester film for laminating a metal plate. More specifically, the present invention relates to a copolyester film for bonding metal plates, which is excellent in fragrance retention, heat resistance, impact resistance, and thickness uniformity, and is suitable for metal cans produced by molding.

[0002]

2. Description of the Related Art Conventionally, a thermosetting resin has been applied to the inner and outer surfaces of a metal can for the purpose of preventing corrosion.
However, such a thermosetting resin coating has a problem that it takes a long time to dry the coating material, thereby deteriorating the productivity and a large amount of the organic solvent is scattered, which is not preferable in environmental hygiene.

[0003] As a method for solving these problems, a method of laminating a polyester film on a metal plate has been used. When a metal plate laminated with a polyester film is formed into a metal can, the polyester film is required to have the following characteristics.

(1) Excellent adhesion to a metal plate.

(2) The polyester film is not crystallized or deteriorated by heating such as drying and retorting after can making, and the film does not peel off, shrink, crack, pinhole, etc. (heat resistance).

(3) The polyester film does not peel or crack due to impact on the metal can (impact resistance).

(4) The scent component of the contents of the metal can is not adsorbed on the polyester film, and the flavor of the contents is not impaired by the smell of the polyester (fragrance retention).

(5) The thickness unevenness of the polyester film is
Less (thickness uniformity).

There has been a keen need to develop a polyester film that satisfies all of the above-mentioned various required properties.

Many proposals have been made to solve these requirements. For example, Japanese Patent Application Laid-Open No. Sho 64-22530 discloses a polyester film having a specific density and plane orientation coefficient. However, although this polyester film is excellent in adhesion to a metal plate and the like, it does not satisfy other properties such as fragrance retention and is insufficient.

Japanese Patent Application Laid-Open No. 6-116376 discloses that an alkali metal compound is contained to improve the fragrance retention. However, simply containing an alkali metal compound deteriorates thermal stability and does not satisfy the requirement of heat resistance.

On the other hand, in order to improve the film forming speed and the uniformity of the thickness of a polyester film, a method of incorporating various metal compounds into the film is known (Japanese Patent Laid-Open No. Sho 5).
9-108058, JP-A-62-236722, JP-A-55-89329, and the like. For example,
Japanese Patent Application Laid-Open No. 55-89329 discloses a metal element content (M / P) with respect to phosphorus element in order to improve the thickness uniformity. Sufficient properties of the film were not obtained, and in particular, the fragrance retention and heat resistance were insufficient.

[0013]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems, and it is an object of the present invention for bonding metal sheets, which is excellent in fragrance retention, heat resistance, impact resistance and thickness uniformity. An object of the present invention is to provide a copolymerized polyester film.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to provide a copolymerized polyester film containing aromatic dicarboxylic acid and glycol as constituents, containing a germanium compound, and further comprising an alkali metal compound and a phosphorus compound. It can be achieved by a copolymerized polyester film for bonding a metal plate, characterized in that it is contained so as to satisfy the following formula. 0.1 ≦ M / P ≦ 1.5 where M indicates the amount (ppm) of the alkali metal element and P indicates the amount (ppm) of the phosphorus element.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The copolymerized polyester in the present invention refers to a polyester comprising an aromatic dicarboxylic acid component and a glycol component, and an aromatic dicarboxylic acid component, a dicarboxylic acid component other than the glycol component, and / or A polyester obtained by copolymerizing a glycol component.

Examples of the polyester comprising an aromatic dicarboxylic acid component and a glycol component include conventionally known polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyhexamethylene terephthalate, polycyclohexylene dimethylene terephthalate, and polyethylene naphthalate. Of these, polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate are particularly preferred in terms of heat resistance, impact resistance, and fragrance retention.

Examples of the dicarboxylic acid component copolymerized with the polyester include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfondicarboxylic acid, and phthalic acid, oxalic acid, and succinic acid. Acid, adipic acid,
Examples thereof include aliphatic dicarboxylic acids such as sebacic acid, dimer acid, maleic acid, and fumaric acid, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid. Of these dicarboxylic acid components, isophthalic acid and naphthalenedicarboxylic acid are particularly preferred in terms of impact resistance and fragrance retention. These dicarboxylic acid components may be alkyl esters and the like. Further, as the glycol component copolymerized with the polyester, for example, ethylene glycol,
Aliphatic glycols such as propanediol, butanediol, pentanediol, hexanediol and neopentyl glycol, bisphenol A, bisphenol S
And the like, and alicyclic glycols such as cyclohexane dimethanol. Among these glycol components, neopentyl glycol and cyclohexane dimethanol are particularly preferable in view of impact resistance and fragrance retention. The above dicarboxylic acid component and glycol component may be used alone or in combination of two or more. These copolymer components are 1 to 30 m with respect to all acid components and / or all glycol components constituting the copolymerized polyester.
ol% is preferable from the viewpoints of adhesion to a metal plate, impact resistance and heat resistance, and more preferably 5 to 20 mol.
%, Particularly preferably 7 to 15 mol%.

The copolymerized polyester of the present invention needs to contain a germanium compound in order to improve the fragrance retention. The content of the germanium element is not particularly limited, but is preferably 5 to 300 ppm, more preferably 1 to 300 ppm.
0 to 100 ppm. The method for incorporating the germanium element into the polyester may be any conventionally known method, and is not particularly limited.In general, at any stage before the completion of the production of the polyester, a germanium compound is added as a polycondensation catalyst. Is preferred. Examples of such a method include a method of adding a germanium compound powder as it is, a method of dissolving a germanium compound in a glycol component and adding the same. As the germanium compound, for example, germanium dioxide, germanium hydroxide containing crystal water, or germanium alkoxide compound such as germanium tetramethoxide, germanium tetrabutoxide, germanium ethylene glycoloxide, germanium phenolate, germanium phenoxide compound such as germanium β-naphtholate And germanium acetate.

The copolymerized polyester in the present invention needs to contain an alkali metal compound and a phosphorus compound.
m), when the content of phosphorus element is P (ppm), M
The value of / P needs to be in the range of 0.1 to 1.5, preferably 0.2 to 1.0. When no alkali metal compound is contained, a film having a uniform thickness cannot be obtained. Further, when the phosphorus compound is not contained, the thermal stability of the polyester is deteriorated, the heat resistance and the impact resistance are reduced, and the coloring is further increased. When the value of M / P is less than 0.1, the effect of thickness uniformity is not sufficient,
When the ratio exceeds 1.5, the effect of the above-mentioned phosphorus compound is impaired, and thermal stability is deteriorated, coloring occurs, and defects such as pinholes of the film occur.

The content of the alkali metal compound is preferably from 1 to 50 ppm, more preferably from 3 to 30 ppm, particularly preferably from 5 to 20 ppm, as the amount of the metal element.
m. The method of incorporating the alkali metal compound into the polyester is not particularly limited, and any conventionally known method can be employed. As the alkali metal compound,
Examples include lithium acetate, sodium acetate, potassium acetate, lithium benzoate, sodium benzoate, potassium benzoate, lithium carbonate, sodium carbonate, potassium carbonate, lithium hydroxide, sodium hydroxide, potassium hydroxide, and the like. Among these alkali metal compounds, a sodium compound and a potassium compound are preferred from the viewpoints of fragrance retention and heat resistance.

The method for incorporating the phosphorus compound into the polyester is not particularly limited, and any conventionally known method can be employed. As the phosphorus compound, for example, phosphoric acid, phosphorous acid, trimethyl phosphate, triethyl phosphate,
Examples include triphenyl phosphate, methyl acid phosphate, ethyl acid phosphate, methylphosphonic acid, and ethylphosphonic acid. Of these phosphorus compounds, phosphoric acid and trimethyl phosphate are particularly preferred from the viewpoints of fragrance retention and heat resistance.

The copolymerized polyester in the present invention requires at least three compounds of a germanium compound, a phosphorus compound and an alkali metal compound. The combination of these three compounds provides excellent thickness uniformity, fragrance retention, impact resistance, and the like. A copolymer film having good heat resistance can be obtained. Further, a metal element other than the germanium element and the alkali metal element may be contained as long as the effects of the present invention are not impaired.

The production of the copolymerized polyester of the present invention can be carried out by any conventionally known method, and is not particularly limited. For example, a method in which terephthalic acid, isophthalic acid, and ethylene glycol are used as production raw materials and an esterification reaction is performed by adding potassium hydroxide, and then a polycondensation reaction is performed by adding phosphoric acid and germanium dioxide. Further, after the transesterification or esterification reaction, a polycondensation reaction is performed until a certain degree of polymerization is reached, and then the resulting low polymer is further subjected to a polycondensation reaction under a reduced pressure or an inert gas stream at a temperature lower than its melting point. Solid phase polymerization may be used.

The copolymerized polyester of the present invention contains 0.001 to 5 μm of inorganic particles and / or organic particles having an average particle diameter of 0.01 to 5 μm in order to improve the handleability of the film and the moldability of the metal can. 10% by weight, more preferably 0.05 to 3
0.005 μm of inorganic and / or organic particles
Preferably, it is contained at 3% by weight.

The copolyester film in the present invention may be an unstretched sheet-like film or a uniaxially or biaxially stretched film, and is formed by any conventionally known method. be able to. For example, in the case of a biaxially stretched film, the above-mentioned copolymerized polyester is sufficiently dried and then supplied to an extruder, and is melt-extruded onto a casting drum to form an unstretched film. A method of axial stretching may be used. In the case of sequential biaxial stretching, the stretching order may be such that the film is oriented in the longitudinal direction, the width direction, or vice versa. Further, in sequential biaxial stretching, stretching in the longitudinal direction or the width direction can be performed twice or more. The stretching ratio in the longitudinal direction and the width direction of the film can be arbitrarily set according to the degree of orientation, strength, elastic modulus and the like of the target film, but is preferably 2.5 to 5.0.
It is twice. Either of the stretching ratio in the longitudinal direction and the stretching ratio in the width direction may be increased, and may be the same. The stretching temperature can be any temperature as long as it is in the range of the glass transition temperature or higher of the polyester and the crystallization temperature or lower.
150 ° C. is preferred. Further, after biaxial stretching, heat treatment of the film can be performed. This heat treatment can be performed by any conventionally known method such as in an oven or on a heated roll. The heat treatment temperature can be any temperature not lower than the crystallization temperature of the polyester and not higher than the softening point, but is preferably from 120 to 240 ° C. Although the heat treatment time is not particularly limited, it is generally preferable to perform the heat treatment for 1 to 60 seconds. The heat treatment may be performed while the film is stretched or relaxed in the longitudinal direction and / or the width direction.

Further, the thickness of the copolymerized polyester film of the present invention is not particularly limited, but is 5 to 100 μm in consideration of the lamination property to a metal plate and the moldability of a metal can.
Is preferably, more preferably, 10 to 80 μm, and particularly preferably, 15 to 50 μm. Further, the copolymerized polyester film in the present invention may be a laminated film composed of the same kind or two or more kinds of polyesters.

[0027]

The present invention will be described in detail with reference to the following examples. The properties of the polyester film were measured and evaluated by the following methods.

(1) Content of Metal Element in Polyester Film The content of the alkali metal element was determined by atomic absorption spectrometry, and the content of other metal elements was determined by X-ray fluorescence measurement from the calibration curve of each element.

(2) Perfume-retaining property of polyester film A perfume aqueous solution (d-limonene 20 ppm aqueous solution) was put into a metal can formed from a laminated plate obtained by laminating a polyester film and a metal plate, and left for 1 month after sealing. The package was opened and a change in odor was evaluated by a sensory test according to the following criteria. First grade: No change in odor. Second grade: Little change in odor is seen. Grade 3-Change in odor is seen.

(3) Heat resistance of polyester film A metal can formed from a laminated plate obtained by laminating a polyester film and a metal plate was heated at 210 ° C. for 20 minutes, and the state of the film bonded to the metal can was observed. The heat resistance was evaluated according to the following criteria, and a grade of 2 or higher was judged to be acceptable. First class: No film peeling occurs. Class 2: The rate of occurrence of film peeling is less than 1% of the area bonded to the metal can. Class 3: The rate of film peeling is 1% or more and less than 5% of the area bonded to the metal can. Grade 4: The rate of film peeling is 5% or more of the area bonded to the metal can.

(4) Impact Resistance of Polyester Film A metal can formed from a laminated plate obtained by laminating a polyester film and a metal plate was filled with water, and the metal can was dropped on marble from a height of 1 m. Drop 10 metal cans and conduct an electricity test (ERV) for each metal can.
Test), the impact resistance was evaluated based on the following criteria, and the second or higher grade was judged as passing. The energization test is a test in which a dropped metal can is filled with a 1% aqueous solution of sodium chloride, and the value of a current flowing when a voltage of 6 V is applied to the electrode and the metal can provided in the aqueous solution is measured. First class: 9 or more metal cans with a current value of 0.2 mA or less. Class 2: 7 to 8 metal cans with a current value of 0.2 mA or less. Class 3: Less than 7 metal cans with a current value of 0.2 mA or less.

(5) Thickness uniformity of polyester film An electronic microfilm thickness gauge (K-306) manufactured by Anritsu Corporation
C-type) along the length of the film
m was measured, and thickness unevenness was defined by the following equation.
The measurement was performed 10 times, and those having an average thickness unevenness of 10% or less were accepted. The average film thickness was measured from the weight of ten films having a length of 6 m and a width of 6 m, and the density of the film was determined to be 1.41 g / cm ³ .

[0033]

(Equation 1) Example 1 110 parts by weight of terephthalic acid, 15 parts by weight of isophthalic acid,
96 parts by weight of ethylene glycol and 0.0035 parts by weight of potassium hydroxide as an alkali metal compound were charged into a reaction vessel to carry out an esterification reaction. Subsequently, 0.042 parts by weight of trimethyl phosphate and 0.025 parts by weight of germanium dioxide were added as phosphorus compounds. Thereafter, the pressure of the reaction system was gradually reduced to 0.5 mmHg, and a polycondensation reaction was performed to obtain a copolyester chip.

After the copolyester chips were dried, they were melt-extruded on a casting drum using an extruder to obtain an unstretched film. The unstretched film is 3.0 times at 90 ° C. in the longitudinal direction and 3.times.
It was stretched 0 times. Further, this film was heat-treated at 190 ° C. for 3 seconds to obtain a polyester film having a thickness of 25 μm. Perfume retention, thickness uniformity of this polyester film,
Table 1 shows the evaluation results of the heat resistance and impact resistance of the film when formed into a metal can.

Examples 2 to 4 The amounts of the isophthalic acid component, alkali metal compound, alkali metal compound and phosphorus compound were changed as shown in Table 1,
The copolymerized polyester was polymerized in the same manner as in Example 1 to obtain a biaxially stretched film. Table 1 shows the evaluation results of the film.

Comparative Example 1 A copolyester was polymerized in the same manner as in Example 1 except that no alkali metal compound was added to obtain a biaxially stretched film. Table 1 shows the evaluation results of the film.

Comparative Example 2 A copolyester was polymerized in the same manner as in Example 1 except that no phosphorus compound was added to obtain a biaxially stretched film.
Table 1 shows the evaluation results of the film.

Comparative Examples 3 and 4 Copolymerized polyesters were polymerized in the same manner as in Example 1 except that the amounts of alkali metal compounds and phosphorus compounds were changed as shown in Table 1, to obtain biaxially stretched films. Table 1 shows the evaluation results of the film.

Comparative Example 5 Antimony trioxide was added in place of germanium dioxide to a concentration of 0.1%.
Except for adding 019 parts by weight, the copolymerized polyester was polymerized in the same manner as in Example 1 to obtain a biaxially stretched film. Table 1 shows the evaluation results of the film.

[0040]

[Table 1]

[0041]

The copolyester film for metal bonding according to the present invention is excellent in fragrance retention, heat resistance, impact resistance and thickness uniformity, and is manufactured by molding a film-metal laminate plate. It can be used particularly preferably for metal cans.

Claims (3)

[Claims] 1. A copolymerized polyester film comprising an aromatic dicarboxylic acid and a glycol, comprising a germanium compound, further comprising an alkali metal compound,
A copolyester film for bonding a metal plate, comprising a phosphorus compound so as to satisfy the following formula. 0.1 ≦ M / P ≦ 1.5 where M indicates the amount (ppm) of the alkali metal element and P indicates the amount (ppm) of the phosphorus element. 2. The copolyester film for laminating metal plates according to claim 1, wherein the alkali metal compound is a sodium compound, a potassium compound, or both. 3. The copolyester film for bonding metal plates according to claim 1, wherein the alkali metal compound is contained in an amount of 1 ppm to 50 ppm as an alkali metal element.