JP2002241517A - Film for laminating metal container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film for laminating a metal container, capable of keeping the taste of a food or beverage well and also having an impact resistance on processing it as a metal container after being laminated with a metal plate. SOLUTION: This film for laminating the metal container is characterized by using a resin obtained by blending (A) a copolyester resin consisting mainly of ethylene terephthalate and having 200-250 deg.C melting point with (B) 5-25 wt.% of polyamide resin containing aromatic rings and having 200-250 deg.C melting point.

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 a metal container, and more particularly to a polyester film for a metal container. And a film for laminating a metal container having excellent impact resistance.

[0002]

2. Description of the Related Art Conventionally, various types of thermosetting resins, such as epoxy-based resins and phenol-based resins, dissolved or dispersed in a solvent have been applied to the inner and outer surfaces of a metal food container for the purpose of preventing corrosion. Coating metal surfaces has been widely practiced. However, such a method of coating a thermosetting resin requires a long time to dry the paint, and thus lowers productivity,
There are undesirable problems such as environmental pollution due to a large amount of organic solvent.

As a method for solving these problems, a method has been proposed in which a polyester film is bonded to a steel plate, an aluminum plate, or a steel plate which has been subjected to various surface treatments, such as plating, as a material of a metal container. . When a metal plate to which a film is attached is drawn and ironed to produce a metal container, the polyester film is required to have the following characteristics.

(1) The film must not be damaged by contents, especially carbonated beverages, fruit juices, etc., so that carbonic acid does not come off or taste deteriorates. (2) The film does not break when subjected to an impact. (3) The taste of the contents does not deteriorate when kept at a high temperature.

[0005] Many proposals have been made to satisfy these requirements. That is, (A) JP-A-5-269
No. 819 discloses a film made of a copolyester having a melting point of 140 to 200 ° C., which is excellent in adhesion to metal, moldability, and impact resistance, and is not deteriorated in the taste of the contents even after long-term storage. On top of that, a film made of a polymer mainly composed of polybutylene terephthalate having a glass transition temperature Tg of 45 ° C. or higher has been proposed.

(B) Also, in Japanese Patent Application Laid-Open No. Hei 5-30198, when forming a can such as drawing by laminating a metal plate, excellent moldability is exhibited, and after the can is made, an impact is applied from outside the can. In order to make it hard to be broken even when it is received, a copolymerized polyester having a specific composition and physical properties, that is, terephthalic acid containing 80 to 95 mol% of an acid component constituting the polymer, and 20
-5 mol% of isophthalic acid and / or sebacic acid, the main glycol component being trimethylene glycol, melting point 200-235 ° C, secondary transition point 50 ° C
A film using the following copolyester and using a copolyester containing particles having an average particle size of 2.5 μm or less has been proposed.

However, in the method (A), if the degree of drawing or ironing after the lamination to the metal plate becomes large, the laminated portion peels off and the film is broken by impact, so that the quality of the contents cannot be maintained.

In the method (B), since the glass transition temperature is low, a hot bender such as a vending machine uses a 50 ° C.
In the case where the film is stored as described above, the metal component contained in the film dissolves together with the low-molecular-weight material, thereby deteriorating the taste of the content.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and when processed into a metal container after being bonded to a metal plate, a food or beverage product is produced. An object of the present invention is to provide a film for laminating a metal container which has good taste and further has impact properties.

[0010]

As a result of intensive studies to solve the above problems, a copolymer polyester resin having a specific range of melting point and a polyamide resin having an aromatic ring having a specific range of melting point have been mixed. The present inventors have found that it is only necessary to use the obtained resin, and have reached the present invention. That is, the film for laminating a metal container according to the present invention has a melting point of 200-2.
It is characterized by comprising a resin obtained by mixing 5 to 25% by weight of a polyamide resin (B) having an aromatic ring having a melting point of 200 to 250 ° C with a copolymerized polyester resin (A) having ethylene terephthalate as a main component at 50 ° C. Consisting of

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with preferred embodiments. The copolymer polyester resin (A) containing ethylene terephthalate as a main component and having a melting point of 200 to 250 ° C., which constitutes the film in the present invention, uses terephthalic acid as a dicarboxylic acid in an amount of 80 mol% to 95%, It is a copolymer resin obtained by condensation. As the acid component to be copolymerized, for example, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, 5-sodium sulfoisophthalic acid, aromatic dicarboxylic acids such as phthalic acid, oxalic acid, Succinic acid, adipic acid, sebacic acid, dimer acid,
Examples thereof include aliphatic dicarboxylic acids such as maleic acid and phthalic acid, alicyclic dicarboxylic acids such as cyclohexyne dicarboxylic acid, and oxycarboxylic acids such as p-oxybenzoic acid. Of these dicarboxylic acid components, isophthalic acid and naphthalenedicarboxylic acid are preferred. Examples of the glycol component include aliphatic glycols such as ethylene glycol, propanediol, butanediol, pentanediol, hexanediol and neopentyl glycol; alicyclic glycols such as cyclohexanedimethanol; aromatic glycols such as bisphenol A and bisphenol S; Is mentioned. Note that two or more of these dicarboxylic acid components and glycol components may be used in combination.
If the melting point is lower than 200 ° C., it cannot withstand heating in the printing step after can making. On the other hand, when the temperature exceeds 250 ° C., the crystallinity of the polymer becomes too large, and the film peels off from the metal plate during the molding process. The copolymer component is adjusted and selected so that the glass transition temperature Tg is 50 ° C. or higher, preferably 60 ° C. or higher. If the Tg is less than 50 ° C, the metal component contained in the film will dissolve together with the low molecular weight material when stored at 50 ° C or more in a hot vender such as a vending machine, and the taste of the contents will be reduced. make worse.

Further, the resin constituting the film according to the present invention needs to be mixed with a polyamide resin (B) having an aromatic ring having a melting point of 200 to 250 ° C. in an amount of 5 to 25% by weight. If it is less than 5%, the carbon dioxide permeability increases, and the content retention of the carbonated beverage deteriorates. 25%
If it exceeds 300, the thermal adhesion to the metal plate will deteriorate.

The film according to the present invention preferably has a carbon dioxide gas permeability of 6 cc.mm/m ² .day.atm or less. If it exceeds 6 cc · mm / m ² · day · atm, the amount of carbon dioxide gas permeation increases, and the content retention of carbonated beverages such as beer deteriorates.

The film according to the present invention may be an unstretched sheet such as a cast film, or a stretched film obtained by uniaxially or biaxially stretching the cast film as required. The polyester film according to the present invention can be formed by a conventionally known method.

As an example of a method for producing the film according to the present invention which satisfies the above-mentioned requirements, a method by biaxial stretching, in particular, a sequential biaxial stretching will be described below. However,
The method for producing a film according to the present invention is not limited to this.

The above-mentioned copolymerized polyester (A) and polyamide resin (B) are mixed at a specified ratio, dried at 150 ° C. for 4 hours in a nitrogen atmosphere, and then supplied to a single screw extruder to be melted. After discharging from a normal T-die, it is cooled and solidified by a cooling drum to obtain an amorphous film. Further, as a method of mixing the resin (A) and the resin (B), in order to improve the dispersibility of the resin (B), besides the above-described method, the resin (A) is kneaded with the resin (B) in advance, and then the master is mixed. It is desirable to prepare a chip and mix the master chip and the resin (A) such that the concentration of the resin (B) is within a specified range. Further, in order to improve the handleability in the film production process, it is preferable to contain a lubricant. The lubricant may be inorganic or organic. Examples of the inorganic lubricant include silicon dioxide, alumina, titanium dioxide, calcium carbonate, and barium sulfate. Examples of the organic lubricant include cross-linked polystyrene particles and silicone resin particles. In any case, the average particle diameter is desirably in the range of 0.1 to 5 μm. If the average particle diameter of the lubricant exceeds 5 μm, the lubricant particles become a starting point in a portion deformed by deep drawing or the like, and a pinhole is formed. It is not preferable because the film is broken. If less than 0.1 μm,
Does not contribute to improvement in handling in the film manufacturing process.

Next, the above-mentioned polyester amorphous film is biaxially stretched simultaneously or successively. Here, 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 can be appropriately set according to the accuracy of the thickness of the intended film, the degree of orientation, the strength, the elastic modulus,
Each is preferably 2 to 4 times. Either the stretching ratio in the longitudinal direction or the width direction may be large, but preferably the ratio of the stretching ratio in the width direction to the longitudinal direction is 0.7 to
1.3, more preferably in the range of 0.8 to 1.2.
It is desirable that the lubricant is previously dispersed in the polymerization step of the resin (A).

The stretching temperature may be any temperature as long as it is in the range from the glass transition temperature of the polyester to the crystallization temperature, but is usually from 80 to 150 ° C.
Is preferred. After the biaxial stretching, the film can be subjected to a heat treatment. The heat treatment temperature can be any temperature from the crystallization temperature of the polyester to the softening point, but is preferably from 120 to 220 ° C. Further, the heat treatment time can be arbitrarily set, but it is usually preferable to perform the treatment for 5 to 120 seconds. The heat treatment may be performed while relaxing the film in the longitudinal direction and / or the width direction.

The metal plate to be used in the present invention is not particularly limited, but a metal plate made of iron, aluminum, or the like is preferable in terms of cost and formability. Further, in the case of a metal plate made of iron, an inorganic oxide coating layer on the surface of the metal plate to improve adhesion and corrosion resistance, for example, chromic acid treatment, phosphoric acid treatment, chromic acid / phosphoric acid treatment, electrolytic chromic acid treatment ,
A chemical conversion coating layer represented by chromate treatment or the like may be provided. In particular, in terms of chromium metal, 6.5 to chrome
150 mg / m ² chromium hydrated oxide is preferred, and further a spreadable metal plating layer such as nickel, tin, zinc,
Aluminum, gunmetal, brass, or the like may be provided. It is preferable that tin plating has a plating amount of 0.5 to 15 mg / m ² , and nickel or aluminum has a plating amount of 1.8 to 20 g / m ² .

The film for laminating a metal container according to the present invention can be suitably used for coating a metal can produced by drawing or ironing. Also a three-piece can body,
It can be used preferably for covering the lid and the bottom, because it has good adhesiveness and moldability to a metal plate.

The film can be attached to the metal plate by, for example, the following method. (1) A metal plate is heated to a temperature equal to or higher than the melting point of the film, the films are stacked and bonded, and then rapidly cooled. (2) Laminate between the film and the metal plate via an adhesive. As the adhesive, a known resin adhesive, for example, an epoxy adhesive, an epoxy-ester adhesive, an alkyd adhesive, or the like can be used.

[0022]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. Example 1 Polyester resin (A) obtained by copolymerizing 10% by mole of isophthalic acid (intrinsic viscosity: 0.67, 0.1% by weight of silicon dioxide having an average particle size of 0.5 μm was added, and germanium dioxide was used as a polymerization catalyst. Manufactured by direct polymerization method) 95
Parts by weight and aromatic polyamide (melt index:
2) 5 parts by weight of the resin (B) were mixed and stirred until uniform, then dried under a nitrogen flow at 150 ° C. until the water content became 50 ppm, and then discharged from a T-die with a single screw extruder to obtain 40 parts.
The resulting mixture was cooled and solidified by a cooling drum at ℃ to obtain a 215 μm thick unoriented film. 105 ° C.
And stretched 2.8 times in the longitudinal direction. This uniaxially stretched film is stretched 3.2 times in the width direction at 100 ° C. using a stenter, and heat-treated at 185 ° C. for 20 seconds under constant length, and then relaxed by 1% at 170 ° C. simultaneously in the length and width directions. After the treatment, the film was wound into a roll. In this way, thickness 25
A μm target film was obtained.

Example 2 A target film was obtained in the same manner as in Example 1 except that 85 parts of the copolymerized polyester resin (A) and 15 parts of the resin (B) were used.

Example 3 A target film was obtained in the same manner as in Example 1 except that 75 parts of the copolymerized polyester resin (A) and 25 parts of the resin (B) were used.

Example 4 A target film was obtained in the same manner as in Example 2 except that the copolymerization component was changed to 15 mol% of hexanediol.

Example 5 A target film was obtained in the same manner as in Example 2 except that the copolymer component was changed to 5 mol% of naphthalenedicarboxylic acid.

Comparative Example 1 A film was obtained in the same manner as in Example 2 except that the polymerization catalyst for the resin (A) was changed from germanium dioxide to antimony trioxide.

Comparative Example 2 Example 2 except that the resin (A) did not contain a copolymer component.
A film was obtained in the same manner as above.

Comparative Example 3 A film was obtained in the same manner as in Example 1 except that only the resin (A) was used without mixing the resin (B).

Comparative Example 4 A film was obtained in the same manner as in Example 1 except that 65 parts of the copolymerized polyester resin (A) and 35 parts of the resin (B) were used.

Comparative Example 5 A film was obtained in the same manner as in Example 2 except that nylon 6 was used as the resin (B).

Comparative Example 6 A film was obtained in the same manner as in Example 2 except that nylon 66 was used as the resin (B).

Comparative Example 7 A film was obtained in the same manner as in Example 2, except that polybutylene terephthalate was used as the resin (B).

In the present invention, the method for measuring each characteristic of the film is as follows. (1) Carbon dioxide gas permeability Measured by a high vacuum gas permeability measurement method.

(2) Melting point of resin Differential scanning calorimeter (DSC7 manufactured by PerkinElmer)
Using a mold) at a sample amount of 10 mg and a heating rate of 20 ° C./min, and read from the obtained melting peak value.

(3) Amount of metal component contained in the film Using a fluorescent X-ray analyzer (RIGAKU3270)
The content of the metal component was determined from a calibration curve measured in advance.

Also, the film formability, impact resistance,
The scent retention was evaluated by the following method. The obtained film was bonded to one side of an aluminum plate having a thickness of 0.20 mm heated to 260 ° C., cooled with water, punched into a disk having a diameter of 150 mm, deep-drawn in two steps using a drawing die and a punch, and subjected to 65 mm deep drawing. A side seamless container having a diameter (hereinafter, referred to as a can) was produced. The following observations and tests were performed on the cans, and evaluated according to the following criteria.

(4) Deep drawing processability ：: The film on the inner surface of the can is processed without any abnormality, and no whitening or breakage is observed on the film on the inner or outer surface of the can. Δ: Whitening or peeling is observed on the film on the inner surface of the can. X: A part of the film on the inner surface of the can is broken.

(5) Impact Resistance Cans having good moldability were filled with 1% saline solution, plugged, cooled in a refrigerator at 5 ° C. for 7 days, and 10 cans of each level were obtained. From height 1m to 30 on one side
After dropping on the plane of a cm cube iron block, open it,
Using the can as the anode, insert the cathode into 1% saline solution in the can,
A voltage of 6 V was applied, and a current value after 30 seconds was measured. Good: 0.1 mA or less for all 10 cans. Δ: There were 1 to 3 cans of 0.1 mA or more. ×: 4 to 10 cans of 0.1 mA or more.

(6) Taste and Aroma Retention For cans with good deep drawability, beer and mineral water were each filled with 10 bottles each, plugged, stored at 50 ° C. for 1 month, and then changed in aroma and taste. Was subjected to a sensory test. ：: No change in aroma and taste. Δ: There are 1-3 cans whose aroma and taste have changed. X: There are 4 to 10 cans whose fragrance and taste have changed.

The evaluation results of the films obtained in each of the above Examples and Comparative Examples are summarized in Tables 1 to 4.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

[Table 4]

[0046]

As described above, according to the present invention,
After bonding to a metal plate, it has excellent carbon dioxide gas transmission rate, and exhibits good moldability and impact resistance when and after processing into a metal container, and also has excellent taste and aroma retention A achievable film for metal container lamination can be obtained.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // B65D 1/12 B65D 1/12 Z (C08L 67/02 (C08L 67/02 77:00) 77: 00) B29K 67:00 B29K 67:00 B29L 7:00 B29L 7:00 (72) Inventor Yoshihiro Yoshikawa 4845, Mishima-shi, Shizuoka (No town, chome display) Toray Co., Ltd. Mishima Plant F-term (reference) 3E033 AA04 BA07 FA01 3E086 AB01 BA04 BA13 BA15 BB03 BB85 CA01 4F071 AA46 AA56 AA84 AF23 AH04 BB06 BB07 BB08 BC01 4F210 AA24K AA30 AG01 QC06 QG01 QG18 4J002 CF061 CL002 CL062 DE096GG

Claims (4)

[Claims] 1. A copolymer polyester resin (A) containing ethylene terephthalate having a melting point of 200 to 250 ° C. as a main component and a polyamide resin (B) having an aromatic ring having a melting point of 200 to 250 ° C. in an amount of 5 to 25% by weight. %. A film for laminating a metal container, characterized by being made of a resin mixed with the same. 2. A carbon dioxide gas transmission rate of 6 cc · mm / m ² · day · a
2. The film for laminating a metal container according to claim 1, wherein the thickness is not more than tm. 3. The resin has a metal component content of 200 ppm.
The film for laminating a metal container according to claim 1 or 2, characterized in that: 4. The film for laminating a metal container according to claim 1, wherein the film is stretched in at least one direction.