JPH10120879A - Polyester film for lamination with metallic sheet or plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polyester film for lamination with a metallic sheet or plate, which does not increase an oligomer content after it is laminated with the sheet or plate, is excellent in elution resistance, moldability, impact resistance and taste retention and is desirable for food containers by using a polyester film containing a germanium compound and an antimony compound. SOLUTION: The content of the germanium compound is 0.01-0.1 pt.wt. per 100 pts.wt. polyester resin. The germanium compound is exemplified by germanium oxide or germanium hydroxide. Germanium hydroxide is desirable in respect of taste retention. The antimony compound is exemplified by antimony oxide or ammonium acetate, and antimony trioxide is desirable. The ratio of the content of the germanium compound to that of the antimony compound is desirably 0.01-0.1 in which the film shows improved heat resistance and not lowered taste retention. A metallic sheet or plate laminated with a polyester film made from the composition is desirably used to mold metallic containers such as cans for drinks.

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 to a metal suitable for a food container having excellent adhesiveness, impact resistance, taste characteristics and moldability. The present invention relates to a polyester film for board lamination.

[0002]

2. Description of the Related Art Conventionally, the inner and outer surfaces of a metal food container are coated with a solution in which various thermosetting resins such as epoxy and phenol are dissolved or dispersed in a solvent, and the surface of the metal plate is coated. Coating and preventing corrosion have been widely practiced. However, such a method of coating a thermosetting resin on the surface of a metal plate requires a long time to dry the paint, thereby lowering the productivity. There were problems such as contamination.

In order to solve problems such as a decrease in productivity and environmental pollution due to organic solvents, a polyester film is laminated on a steel plate, an aluminum plate, or a metal plate subjected to various surface treatments such as plating. Forming a metal plate with laminated film, for example,
2. Description of the Related Art A metal container is formed by drawing.
The following characteristics are required for such a polyester film for metal plate lamination.

(1) Even if an impact is applied to a metal container, the polyester film does not peel off, and cracks and pinholes do not occur.

(2) The taste and aroma of beverages are not changed and the flavor is not impaired by components generated from the polyester film.

(3) The scent component of the metal container does not adsorb to the polyester film.

Many studies have been made to satisfy these required performances. For example, as a polymerization condensation catalyst for polyester, an antimony compound is known, but when an antimony compound is used alone as a catalyst for a polycondensation reaction, heat treatment in a step of laminating a polyester film on a metal plate, or a polyester film After processing the laminated metal plate into a metal container, the high temperature heat treatment when printing the surface increases the oligomers in the polyester film. Oligomers generated by these heat treatments are extracted by boiling water treatment after enclosing a beverage such as tea in a metal container, and there is a problem that the taste and aroma of the beverage are deteriorated.

It is also known to use a germanium compound alone as a catalyst for a polyester polycondensation reaction. For example, Japanese Patent Application Laid-Open No. 5-339392 proposes to use a copolymerized polyester film having a melting point of 210 to 245 ° C. produced using a germanium compound as a catalyst for a polycondensation reaction. Further, JP-A-5-339393 discloses that the acetaldehyde content of the copolymerized polyester film is 20 ppm,
Preferably, it has been proposed to use a germanium compound as a catalyst for the polycondensation reaction. However, in the method using such a germanium compound alone,
At the time of polymerization, and the amount of oligomers in the polyester film at the time of film formation decreases, but as in the case of using the antimony compound alone as a catalyst for the polycondensation reaction, when the polyester film is heated again in the film laminating step or the like, There has been a problem that oligomers in the polyester film increase to deteriorate the taste and aroma of the beverage.

[0009]

As described above, the conventional method of using an antimony compound or a germanium compound alone as a catalyst for a polycondensation reaction prevents an increase in oligomers in a polyester film after lamination on a metal plate. I couldn't.

[0010] The present invention prevents the oligomer from increasing after lamination on a metal plate, and has a low elution property and moldability.
An object of the present invention is to provide a polyester film for metal plate lamination suitable for a food container having excellent impact resistance and taste characteristics.

[0011]

Means for Solving the Problems The inventors of the present invention have made intensive studies to achieve the above object, and as a result, a polyester film containing both a germanium compound and an antimony compound has an effect of suppressing an increase in oligomers due to heat treatment. And found the present invention.

That is, the present invention is a polyester film for laminating a metal plate, comprising a germanium compound and an antimony compound.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester film for laminating a metal plate of the present invention contains a germanium compound and an antimony compound, and the germanium compound and the antimony compound preferably act as a catalyst for the polyester polycondensation reaction. .

The polyester in the present invention preferably has a structural unit of 8 to maintain the crystallization characteristics of the film and to prevent the deterioration of impact resistance when processed into a metal container.
0% or more is ethylene terephthalate.

The dicarboxylic acid component to be copolymerized with the polyester in the present invention includes, for example, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfondicarboxylic acid, diphenoxyethanedicarboxylic acid, 5-sodium sulfoisophthalic acid, and phthalic acid. Isoaromatic dicarboxylic acids, oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, aliphatic dicarboxylic acids such as phthalic acid, alicyclic dicarboxylic acids such as cyclohexyne dicarboxylic acid, p-oxybenzoic acid And the like. Of these, isophthalic acid and naphthalenedicarboxylic acid are preferable in terms of impact resistance and taste characteristics.

The glycol component to be copolymerized with the polyester in the present invention includes, for example, propanediol,
Aliphatic glycols such as butanediol, pentanediol, hexanediol and neopentyl glycol;
Examples include alicyclic glycols such as cyclohexanedimethanol, and aromatic glycols such as bisphenol A and bisphenol S.

The dicarboxylic acid component and the glycol component may be used in combination of two or more kinds. If necessary, the copolymerized polyester may be further added to trimellitic acid, trimesic acid, trimethylolpropane or the like. Functional compounds may be copolymerized.

In the present invention, the content of the germanium compound is from 0.01 to 0.1 with respect to 100 parts of the polyester resin.
One part is preferred. When the content of the germanium compound is 0.
When the amount is from 0.1 to 0.1 part, the polymerization reactivity is good, and further,
The germanium compound used in the present invention, which has less terminal groups and less DEG (diethylene glycol) in the polyester film and has good taste characteristics when processed into a metal container, includes germanium oxide, germanium hydroxide, germanium alcoholate, and germanium halide. Examples thereof include germanium compounds having a catalytic ability, and in particular, germanium oxide, and among them, germanium dioxide is preferable from the viewpoint of taste characteristics.

Examples of the antimony compound used in the present invention include antimony compounds such as antimony oxide and antimony acetate, which have a catalytic activity. Antimony oxide is particularly preferable, and among them, antimony trioxide is preferable.

The ratio (B / A) between the content of the germanium compound (A) and the content of the antimony compound (B) (B / A) is from 0.01 to 0.01 because heat resistance is improved and taste characteristics are not reduced.
0.1 is preferred.

These germanium compounds and antimony compounds may be added separately, as a mixture, or may be added after preheating with ethylene glycol or the like. Further, when the germanium compound is activated by an alkali treatment or the like, more excellent effects can be obtained.

The polyester used for the polyester film for laminating a metal plate of the present invention is not particularly limited and can be produced by any known method. Furthermore, the polyester film for metal plate lamination of the present invention can be formed by a known method and any method,
There is no particular limitation. Here, a case where an isophthalic acid component is copolymerized with polyethylene terephthalate will be described as an example.

First, a terephthalic acid component and an isophthalic acid component are transesterified or esterified with ethylene glycol. Then, as a polymerization catalyst, amorphous germanium dioxide and antimony trioxide are treated with ethylene glycol heated to 120 ° C. The mixture is added after mixing at a predetermined rate, and subsequently a polycondensation reaction is carried out at a high temperature and under reduced pressure to obtain a polyester by a direct weight method. Further, it is preferable to reduce the amount of oligomers in the polyester by a solid phase polymerization method, a heat treatment under reduced pressure, and an extraction method.

In the preparation of the polyesters, the already known additives such as phosphorous acid, trimethyl phosphate,
Triphenyl phosphate, polysiloxane and the like can be used as needed. In producing the polyester of the present invention, if necessary, an antioxidant,
Additives such as plasticizers, antistatic agents and weathering agents can also be used as appropriate.

The polyester (isophthalic acid 16 mol% copolymerized polyethylene terephthalate ([η] = 0.69, melting point 215 ° C.)) thus obtained was subjected to a biaxial venting method in which the extrusion temperature was set to the melting point + 20 ° C. And melted. Next, after discharging from a normal T-die, it is cooled and solidified by a cooling drum to obtain an amorphous film.

The above-mentioned polyester amorphous film is
Simultaneous or sequential biaxial stretching can be performed. In the case of sequential biaxial stretching, stretching in the longitudinal direction or width direction of the film can be performed twice or more. The stretching ratio in the longitudinal direction and the width direction of the film is set according to the desired degree of orientation of the film.
It is 0 times. Either the stretching ratio in the longitudinal direction or the width direction may be large, but the ratio of the stretching ratio in the width direction to the longitudinal direction is preferably 0.7 to 1.3, and more preferably 0.8 to 1.2. And The stretching temperature is set in accordance with the desired degree of orientation of the film, but is often set to 20 ° C. to 50 ° C. higher than the glass transition temperature of the polyester. In the case of the present invention, the preheating temperature before stretching is preferably set at 2 ° C. to 10 ° C. higher than the stretching temperature. Usually, it is preferable that the preheating temperature is 100 to 150 ° C and the stretching temperature is 90 to 130 ° C.

The stretched film is further subjected to a heat treatment. The heat treatment temperature at this time is set to a temperature equal to or higher than the crystallization temperature of the polyester and equal to or lower than the softening point so that the target average refractive index is obtained. Normally, the melting point of the film is 20 to
The heat treatment is often performed at a temperature lower by 80 ° C. Although the heat treatment time is optional, it is usually preferable to perform the treatment for 5 to 120 seconds. Further, the heat treatment may be performed while relaxing the film in the longitudinal direction and / or the width direction.

In the polyester film for laminating a metal plate in the present invention, the amount of oligomer after laminating on the metal plate and heat-treating for 5 minutes in a temperature range of melting point (Tm) to (Tm-20 ° C.) is 0.5 wt% or less. It is preferred that

The polyester film for laminating a metal plate in the present invention is preferably a uniaxially or biaxially stretched film. The thickness of the metal film laminate polyester film of the present invention is not particularly limited,
In consideration of the moldability, impact resistance, and taste characteristics of the metal container, the thickness is preferably 10 to 50 μm, more preferably 1 to 50 μm.
5 to 40 μm.

The polyester film for laminating a metal plate of the present invention has an average refractive index (n _ave ) and a plane orientation coefficient (f).
n) preferably satisfies the following expression.

0.4 ≦ n _ave −fn × 10 ≦ 0.6 where the plane orientation coefficient (fn) and the average refractive index (n _ave )
Is defined by the following equation.

[0032] _{fn = (n md + n td} ) / 2-n zd n ave = (n md + n td + n zd) / 3 ( where, n _md is the refractive index in the longitudinal direction of the film, n _td
Is the refractive index in the width direction of the film, and _nzd is the refractive index in the thickness direction of the film.) Prevents wrinkles due to shrinkage of film when laminating film to metal plate,
The difference between n _ave and fn × 10 is to keep the impact resistance of the film, and to prevent the film from cracking after processing into a metal container and iron to dissolve into the contents and the taste characteristics to be reduced.
0.4 or more and 0.6 or less are preferable. Further, in order to maintain the moldability when processing the film into a metal container and to prevent the film from being broken during the molding, the average refractive index of the film (n
_ave ) is preferably from 1.590 to 1.610, and more preferably from 1.595 to 1.60.
5 or less. Further, a preferable range of the plane orientation coefficient (fn) is 0.099 or more and 0.121 or less.

The type of metal plate on which the polyester film for laminating a metal plate of the present invention is laminated is not particularly limited, but a metal plate made of iron, aluminum, or the like is preferable in terms of moldability. Further, in the case of a metal plate made of iron, an inorganic oxide coating layer, for example, chromic acid treatment, phosphoric acid treatment, chromic acid / phosphoric acid treatment, for the purpose of improving adhesion and corrosion resistance on the surface, etc. And a chemical conversion coating layer represented by electrolytic chromic acid treatment, chromate treatment and the like. In particular, when performing treatment using a chromium compound, 6.5 to 150 mg / m as chromium in terms of chromium metal.
^The hydrated chromium oxide of 2 is preferred, and a spreadable metal plating layer such as nickel, tin, zinc, aluminum, gunmetal, brass, etc. may be provided. A metal plate having a plating amount of 0.5 to 15 mg / m ² for tin plating and 1.8 to 20 g / m ² for nickel or aluminum is preferred.

The polyester film for laminating a metal plate of the present invention can be suitably used for coating the inner or outer surface of a two-piece metal can manufactured by drawing or ironing. In addition, the polyester film for laminating a metal plate of the present invention has good adhesion and moldability to a metal plate.
It can be used for covering the body, lid and bottom of piece cans.

Furthermore, a metal can using a polyester film for laminating a metal plate containing a germanium compound and an antimony compound can be used as a food container having excellent impact resistance, taste characteristics and the like. ,
It is suitable as a food can or the like.

[0036]

The present invention will be described below in detail with reference to examples.

The properties of the polyester film were measured by the following methods.

(1) Average refractive index (n _ave ) and plane orientation coefficient (fn) Refractive index in the longitudinal direction (n _md ) of polyester film before lamination on a metal plate, refractive index in the width direction of film ( n _td ) and the refractive index (n _zd ) in the thickness direction of the film were measured with an Abbe refractometer and calculated by the following equation.

[0039] _{fn = (n md + n td} ) / 2-n zd n ave = (n md + n td + n zd) / 3 (2) during a heat moldability 180 to 230 ° C. The metal roll and a silicone rubber roll The polyester film and the tin-plated tin plate are joined together and pressurized and bonded at a pressure of 20 kg / cm ² , and immediately thereafter, rapidly cooled in a water tank to make a polyester film laminated metal plate (hereinafter referred to as a laminated metal plate).
Was prepared.

The laminated metal plate is formed at a temperature of not less than the glass transition temperature of the polyester film and not more than the crystallization temperature at a pressure of 100 kg / cm ² by a press forming machine (VAS-33P type manufactured by Senba Iron Works), and the diameter D is 100 mm. And a cup with a depth h of 130 mm and a draw ratio (h / D) of 1.3. Put 1% saline solution in this cup,
After heating to 7 ° C. and allowing to stand for 7 days, moldability was determined based on the following criteria from the state of rust generated in the can.

A: No rust generated B: Rust of less than 5 mm or less C: Many rusts generated (3) Amount of oligomer in polyester film (2) Polyester laminated metal plate prepared by the method described in (2) Heat treatment is performed for 5 minutes in a hot air oven set at a temperature 10 ° C. lower than the melting point of the film. Next, a laminated metal plate was cut out so that the weight of the polyester film became 100 mg, the polyester film was dissolved in 1 ml of orthochlorophenol, and the cyclic trimer was measured by liquid chromatography (Model 8500 manufactured by Varian). The amount of oligomer was used.

(4) Adsorption amount of d-limonene The laminated metal plate produced by the method described in (2) was
After cutting out to 15 cm × 15 cm and immersing in a perfume aqueous solution (d-limonene 20 ppm aqueous solution) for 5 days, the metal plate was heated at 80 ° C. for 30 minutes in a nitrogen stream, and the emission component was quantified by gas chromatography. The amount of adsorbed d-limonene per gram of the film was determined, and the taste characteristics of the film were evaluated.

Example 1 73 parts of terephthalic acid, ethylene glycol (EG) 38
Parts, 14 parts (16 mol%) of isophthalic acid as a copolymerization component and 0.008 part of triethylamine were charged into a stainless steel autoclave equipped with a stirrer, a distillation column, and a pressure regulator, and after pressurizing with nitrogen, pressurized. 2.5 kg / c pressure
m ² to keep, was continuously removed while the esterification reaction water generated at 240 ° C. from the top of the evaporation column. 120 minutes after the start of the reaction, the pressure was released to obtain a product having an esterification reaction rate of 95%. The esterification product was added to 0.03 parts of germanium dioxide and 0.1 g of antimony trioxide.
0015 parts were added as EG solutions from the respective supply ports, and 0.092 part of phosphoric acid was further added as an EG solution. Then, the mixture was transferred to a 240 ° C. polycondensation reactor and required to reach 280 ° C. in 30 minutes. The pressure of the reaction system was gradually lowered to 0.05 mmHg while raising the temperature, and a polycondensation reaction was further performed at the same temperature and pressure for about 80 minutes. The intrinsic viscosity of the obtained polymer was 0.57, and DEG (diethylene glycol) was 1.0 mol%. Furthermore, this melting point 218
A polyester chip having a intrinsic viscosity of 0.72 was obtained by heat-treating a polyester chip at 188 ° C. for about 15 hours under a nitrogen atmosphere.

This polyester chip was melted in a twin-screw vent type extruder (the temperature of the extruder was set at 248 ° C., the average residence time was 8 minutes), discharged from the T die, cooled with a cooling drum, and cast into a 220 μm cast. I got a film. After the obtained cast film was preheated by a roll heated to 125 ° C, it was stretched 3.1 times in the longitudinal direction by a roll heated to 115 ° C. This uniaxial film is stretched 3.1 times in the width direction at 110 ° C. by using a stenter, and 178 ° C. under a constant length.
For 20 seconds, and wound up in a roll to obtain a polyester film having a thickness of 20 μm.

Table 1 shows the properties of the polyester film thus obtained. The oligomer amount of the polyester film was small, and the moldability and taste characteristics were good.

Example 2 87 parts of terephthalic acid, 38 parts of ethylene glycol and 0.008 part of triethylamine were charged into a stainless steel autoclave equipped with a stirrer, a distillation column and a pressure regulator, and the esterification reaction was carried out in the same manner as in Example 1. Was done. To the esterification product, 0.03 part of germanium dioxide and 0.0015 part of antimony trioxide were added in the same manner as in Example 1, and further, as in Example 1, a polyester chip, and then a 20 μm-thick polyester chip. A polyester film was obtained. The properties of the polyester film thus obtained are shown in Table 1. The oligomer amount of the polyester film was small, and the moldability and taste characteristics were good.

Example 3 A polyester film having a thickness of 20 μm was obtained in the same manner as in Example 2 except that the addition amount of germanium dioxide was increased to 0.05 part. The properties of the polyester film thus obtained are shown in Table 1. The oligomer amount of the polyester film was small, and the moldability and taste characteristics were good.

Example 4 Instead of isophthalic acid, 10 mol% of cyclohexane dimethanol (CHDM) was used as a copolymer component, 0.05 part of germanium dioxide and 0.0 part of antimony trioxide were used.
035 parts and a thickness of 20 μm in the same manner as in Example 1.
m polyester film was obtained. The properties of the polyester film thus obtained are shown in Table 1. The oligomer amount of the polyester film was small, and the moldability and taste characteristics were good.

Comparative Example 1 A polyester film was obtained in the same manner as in Example 2 except that the polymerization catalyst was antimony trioxide alone. Table 1 shows the results. The amount of oligomer in the polyester film increased.

Comparative Example 2 A polyester film was obtained in the same manner as in Example 2, except that germanium dioxide was used alone as the polymerization catalyst. Table 1 shows the results. The amount of oligomer in the polyester film increased.

[0051]

[Table 1]

[0052]

The polyester film of the present invention for laminating a metal plate has a small amount of oligomer after heat treatment, and is excellent in low dissolution, moldability, impact resistance, and taste characteristics.
The metal plate obtained by laminating the polyester film of the present invention is suitable as a metal container such as a beverage can by molding.

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Claims (6)

[Claims] 1. A polyester film for laminating a metal plate, comprising a germanium compound and an antimony compound. 2. The polyester film according to claim 1, wherein the germanium compound is germanium dioxide and the antimony compound is antimony trioxide. 3. The ratio (B / A) of the content (A) of the germanium compound to the content (B) of the antimony compound is as follows:
The polyester film for laminating a metal plate according to claim 1 or 2, wherein the thickness is 0.01 to 0.1. 4. After lamination on a metal plate, a melting point (T
4. The polyester film for laminating a metal plate according to claim 1, wherein the amount of the oligomer after heat treatment at m) to (Tm-20 ° C.) for 5 minutes is 0.5 wt% or less. 5. An average refractive index (n _ave ) and a plane orientation coefficient (f)
n) satisfying the following equation:
5. The polyester film for laminating a metal plate according to 3 or 4. 0.4 ≦ n _ave −fn × 10 ≦ 0.6 6. The method according to claim 1, wherein the average refractive index (n _ave ) is not less than 1.590 and not more than 1.610.
The polyester film for metal plate lamination according to 2, 3, 4 or 5.