JPH1149873A - Copolyester film and laminate metal plate of the film and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject film capable of exhibiting excellent impact resistance, excellent hydrolysis resistance, excellent thermal decomposition resistance and good metal plate laminability and useful for metal containers, etc., by limiting the melting point, thickness and reducing viscosity difference of film in specific ranges, respectively. SOLUTION: This copolyester film (e.g. a polyester film comprising a copolyester obtained by copolymerizing ethylene terephthalate units with ethylene dicarboxylic acid component or neopentyl glycol component) has a melting point of 150-250 deg.C and a thickness of 3-50 μm. A difference between a reducing viscosity after thermally treated at the melting point +30 deg.C for 60 sec and a reducing viscosity before thermally treated is <=0.05 deciliter/g. The film has preferably a reducing viscosity of 0.4-1.0 deciliter/g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a copolyester film, a laminated metal plate and a method for producing the same.
More specifically, the present invention relates to a copolymerized polyester film, a laminated metal plate, and a method for producing the same, which are excellent in impact resistance, hydrolysis resistance, and heat decomposition resistance.

[0002]

2. Description of the Related Art Conventionally, at least the inner surface of a metal can is coated with a resin paint for the purpose of corrosion protection. This paint is inefficient because it can be applied to each can by spray coating after can making, and it requires a lot of energy to bake the paint at high temperatures. There's a problem.

[0003] In recent years, in order to solve such disadvantages, a technique of pre-coating a metal plate with paint before forming a can (pre-coating technique) or a technique of laminating a film (pre-laminating technique) has been proposed. ) Is being developed. However, in these techniques, the organic resin layer formed by coating or laminating suffers severe deformation and heat history during the can-making process, so that defects easily occur after can-making, and it is difficult to exhibit sufficient corrosion resistance. It is.

As a film applied to the above-mentioned prelaminating technique, a polyester film mainly composed of polyethylene terephthalate is used because of its excellent hygiene and fragrance retention properties. However, when the pre-laminated polyester film is stretch-oriented, the laminated metal plate cannot follow the deformation during can-making, the film cracks, the corrosion resistance deteriorates, and the appearance of the can also worsens. .

Therefore, a method of laminating the above polyester film on a metal plate, heating it to a temperature equal to or higher than the melting point of the laminated film, and then quenching it to make it amorphous and non-oriented (remelting method) has been studied. When making a can using a laminated metal plate manufactured by this method, the laminated film easily follows the deformation during can making, so that the film does not crack or peel after the can is made, and good outer parent and corrosion resistance are obtained. Can be

However, the above-mentioned laminated metal sheet produced by the remelt method has poor impact resistance after can production, and when the can is dropped, the film is liable to crack and the corrosion resistance cannot be maintained. In order to improve the impact resistance, attempts have been made to increase the reduced viscosity of the polyester. However, when the film is remelted, the reduced viscosity of the polyester is greatly reduced, and the above problem has not been solved.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the conventional polyester film and laminated metal plate and provides a metal container excellent in impact resistance, hydrolysis resistance, heat decomposition resistance and can processability. An object of the present invention is to provide a laminate film that can be manufactured.

[0008]

In order to achieve the above object, the copolymerized polyester film of the present invention has a melting point of 15
A reduced viscosity of a copolymerized polyester film obtained by heat-treating a film at 0 to 250 ° C and a thickness of 3 to 50 µm for 60 seconds at a temperature of the melting point of the film + 30 ° C and a reduced viscosity of the copolymerized polyester before the heat treatment. Is not more than 0.05 deciliter / g.

[0009] The copolymerized polyester film having the above constitution is excellent in impact resistance, hydrolysis resistance and thermal decomposition resistance, so that a laminated metal plate suitable for producing a container by laminating with a metal plate can be easily prepared. Obtainable.

[0010] The laminated metal sheet of the present invention is characterized in that the above-mentioned copolymerized polyester film is laminated on at least one side.

[0011] The laminated metal plate having the above structure is excellent in impact resistance, hydrolysis resistance and thermal decomposition resistance, and is suitable for manufacturing containers.

Further, the method for producing a laminated metal according to the present invention is characterized in that a heat treatment is performed at a temperature higher than the melting point of the film in a state where the above-mentioned copolymerized polyester film is laminated on the surface of a metal plate.

The method for producing a laminated metal sheet having the above-described structure is excellent in impact resistance, hydrolysis resistance and heat decomposition resistance, and is suitable for obtaining a laminated metal sheet suitable for producing a container. .

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

The copolyester referred to in the present invention is a saturated polyester comprising a dicarboxylic acid component and a diol component, and has a melting point in the range of 150 ° C. to 250 ° C. Particularly preferred is a copolymerized polyester obtained by copolymerizing an ethylene terephthalate unit with a naphthalenedicarboxylic acid component or a neopentyl glycol component.

The dicarboxylic acid component includes terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, maleic acid,
Examples thereof include dimer acid, indandicarboxylic acid, diphenylcarboxylic acid, and metal salts of sulfoisophthalic acid.

The diol components include ethylene glycol, propanediol, butanediol, pentanediol, neopentyl glycol, hexanediol, cyclohexanedimethanol, ethylene oxide adduct of bisphenol A, and ethylene oxide adduct of bisphenol S. , Polyethylene glycol, polytetramethylene glycol and the like.

The proportion of the copolymer component depends on the type, but as a result, the melting point of the polyester is 150 ° C. to 250 ° C.,
Preferably from 210 ° C. to 240 ° C., more preferably 215 ° C.
It is the ratio which falls in the range of ° C to 235 ° C. If the melting point of the polyester is less than 150 ° C., the heat resistance is poor. On the other hand, if the melting point of the polyester exceeds 250 ° C., the crystallinity of the polyester is too large and the moldability is impaired.

The copolymerized polyester used in the present invention is not limited by the production method. For example, it can be obtained by polycondensation under melting by a transesterification method or a direct polymerization method.

In the production of the above-mentioned copolymerized polyester, additives such as white pigments, lubricants, antiblocking agents, heat stabilizers, antioxidants, antistatic agents, light stabilizers, impact modifiers and the like may be used as necessary. Known additives may be blended.

The copolymerized polyester film of the present invention comprises:
The melting point is 150 ° C. to 250 ° C., the thickness is 3 to 50 μm, and the reduced viscosity of the copolymerized polyester after the film is heat-treated at the temperature of the melting point of the film + 30 ° C. for 60 seconds and the reduced viscosity of the copolymerized polyester before the heat treatment. 0.05 difference
The film is less than deciliter / g.

The above-mentioned copolymerized polyester film can be obtained by melting, extruding and cooling polyester by a known method, and can be obtained by further uniaxially or biaxially stretching. And the thickness of the film is 3-50
μm, preferably 10 to 20 μm, but if the thickness of the film is less than 3 μm, pinholes are easily formed in the film, resulting in poor corrosion resistance. The film thickness is 50μ.
If it exceeds m, the moldability tends to be impaired.

The copolymerized polyester film of the present invention comprises:
The reduced viscosity is preferably 0.4 to 1.0 deciliter /
g, more preferably 0.5 to 0.8 deciliter / g. When the reduced viscosity is less than 0.4 deciliter / g, the impact resistance of a metal container manufactured from a laminated metal plate obtained by laminating the obtained copolymerized polyester film on a metal plate tends to be insufficient. When the reduced viscosity exceeds 1.0 deciliter / g, a large amount of energy is required for polymerization of the copolymerized polyester, film formation, production of a laminated metal plate, and the like, and the cost tends to increase.

In the present invention, the melting point of the film + 30 ° C.
Is performed by placing the film in a hot-air oven set at the temperature. However, if the film is directly put into a hot-air oven, it will fly or stick in the hot-air oven. Therefore, heat treatment is performed after laminating the film on an aluminum plate having a thickness of 100 μm. After the heat treatment, an aluminum plate on which the film is laminated in 10% hydrochloric acid is put, only the aluminum portion is melted, the heat-treated film is taken out, and the reduced viscosity is measured.

When a copolymerized polyester film having a difference in reduced viscosity before and after heat treatment exceeding 0.05 deciliters / g is laminated on a metal plate by a remelt method, the resistance of the metal container formed from the obtained laminated metal plate is reduced. Impact strength is not enough. In addition, when the obtained metal container is used as a beverage can, flavor properties are deteriorated.

The remelting method is a method in which a copolymerized polyester film is laminated on a metal plate, heated to a temperature higher than the melting point and then rapidly cooled. At this time, the obtained laminate film is preferably in a substantially non-oriented amorphous state. By making the film substantially non-oriented amorphous, it is possible to improve the followability of the laminate film in the can-making process.

The material of the metal plate on which the copolymerized polyester film is laminated is not particularly limited, and examples thereof include iron, steel, tinplate, tin-free steel, brass, copper, aluminum, and aluminum alloy.

The metal plate used in the present invention may be subjected to a surface treatment. Examples of the surface treatment include an electrochemical treatment, an inorganic chemical treatment, an organic chemical treatment, and the like, such as a chromate treatment, a phosphoric acid chromate treatment, a zinc chromate treatment, and an alumite treatment.

Further, the copolymerized polyester film used in the present invention may be subjected to corona treatment, coating treatment, flame treatment, etc., if necessary, in order to improve the adhesiveness and wettability.

The method of laminating the copolymerized polyester film on the metal plate includes a method of pressing the film on a metal plate heated to a temperature higher than the softening point of the film, and a method of applying an adhesive to the metal plate in advance and placing it on the metal plate. Compression bonding method and the like can be mentioned.

The film laminated on the metal plate is further melted completely to make it non-oriented, and then quenched and solidified to obtain an amorphous non-oriented laminate layer. preferable. Examples of a heating method for completely melting the laminated film include hot air heating, roll heating, electric heating, dielectric heating, and high-frequency heating. For example, in the case of hot air heating, usually the melting point of the film ~
The film can be completely melted by heating at a temperature of melting point + 40 ° C. for 15 to 120 seconds, preferably at a temperature of melting point + 5 ° C. to melting point + 20 ° C. for 30 to 60 seconds.

Examples of the method of quenching and solidifying include immersion in water and spraying with cold air. Here, quenching is a cooling operation having a cooling rate sufficient to prevent the formation of crystals when the molten film solidifies, and is usually 10 ° C.
The object can be achieved by cooling at a rate of at least 50 ° C./sec, preferably at least 50 ° C./sec.

The laminated metal sheet of the present invention can be used in a shallow drawing container manufactured by a drawing method, a deep drawing container manufactured by a drawing re-drawing method, a thinned drawing container manufactured by a drawing stretching and stretching method, and a drawing ironing method. It is formed into a drawn ironing container manufactured by the DI method (DI method). In performing such a forming process, it is preferable that the temperature of the laminated metal plate is set near the glass transition point of the film.

[0034]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

The method for evaluating characteristics in the present invention is as follows.

(1) Melting Point The melting point was measured using an external heating type differential scanning calorimeter (DSC) manufactured by Rigaku Corporation at a sample amount of 10 mg and a heating rate of 20 ° C./min. Here, the detected endothermic peak temperature of the melting was defined as the melting point.

(2) Reduced viscosity before heat treatment Using a mixed solvent of phenol / tetrachloroethane in a weight ratio of 6/4, the polyester is dissolved at a solution transfer rate of 0.4 g / deciliter. Then, the temperature was measured at 30 ° C. using an Ubbelohde type viscosity tube.

(3) Reduced Viscosity After Heat Treatment (Heat Treatment) A copolymer polyester film was fused to one side of a phosphoric acid chromate-treated aluminum plate having a thickness of 100 μm and a width of 20 cm using a roll laminator.
Here, the aluminum plate is supplied at room temperature, the rubber roll temperature is 180 to 250 ° C., and the passage speed is 25 to 100 cm /
The gauge pressure was 6 kg / cm ² .

Next, the aluminum plate on which the copolymerized polyester film was fused was heated in a hot air oven at a temperature of the melting point of the film + 30 ° C. for 60 seconds to completely melt the film. This was taken out of the oven and blown with cold air at 5 ° C. within 5 seconds to be rapidly cooled and solidified. The heat-treated laminated metal plate was immersed in 10% hydrochloric acid, and only the aluminum plate was dissolved to obtain a heat-treated film.

The reduced viscosity of this film was measured by the above method (2).

(4) ERV value of the can immediately after making the can The manufactured metal container was filled with 350 cc of 1% by weight saline solution, and the ERV (enamel rating value) was measured with an enameler. The voltage is DC 6 volts, a metal exposed part is made on the outside of the bottom of the can, and it is connected to the anode.
The current value after 30 seconds was measured. In ERV measurement,
As the current flows more, the film serving as an insulator has defects and the metal is exposed, so that corrosion is likely to occur, and the ERV value immediately after can making is preferably 10 mA or less.

(5) ERV value of can after drop impact The manufactured metal container is subjected to a baking treatment condition corresponding to 20 times.
After performing heat treatment at 0 ° C. for 15 minutes, the produced metal container was filled with 350 cc of water, dropped from a height of 1 m with the can bottom facing down, and the water was removed. Fill and measure ERV. The ERV value after a drop impact is desirably 20 mA or less.

(Examples 1 to 3, Comparative Examples 1 to 3) Preparation of copolymerized polyester (a) 30 mol% of isophthalic acid copolymerized polyethylene terephthalate, (b) 10 mol% of naphthalenedicarboxylic acid
Chips of copolymerized polyethylene terephthalate, (c) 30 mol of neopentyl glycol copolymerized polyethylene terephthalate, and (d) 30 mol of cyclohexanedimethanol copolymerized polyethylene terephthalate were obtained by a direct weight method.

The reduced viscosities of the copolymerized polyesters were (a) 0.68 deciliter / g and (b) 0.63
Deciliter / g, (c) 0.67 deciliter / g,
(D) It was 0.67 deciliter / g. For all polyesters, a fine silica gel powder having an average particle size of 1.8 μm was added to the film in an amount of 0.06 to secure an appropriate sliding property.
% By weight.

B. Production of biaxially stretched film The copolymerized polyester ((a) to
(D)) Chip and reduced viscosity 0.65 deciliter / g
And polyethylene terephthalate chips of the formula (1) and (2) were blended in such a manner that the composition becomes as shown in Tables 1 and 2, and dried under vacuum to a moisture content of 0.01% by weight or less, and then extruded from a T-die with an extruder.
It was melt-extruded at 70 ° C and taken up by a cooling roll at 30 ° C to obtain an unstretched sheet. Immediately, the film is stretched 3.5 times in the longitudinal direction at 90 to 100 ° C. with a roll stretching machine, and further stretched 4 times in the transverse direction at 90 to 100 ° C. with a tenter stretching machine.
While being relaxed by 10%, the film was heat-set at a temperature lower by 15 to 30 ° C. than the melting point to obtain a 15 μm thick stretched film.

C. Manufacture of DI can The biaxially stretched film obtained in the above section B was fused to both surfaces of a phosphoric acid chromate-treated aluminum plate having a thickness of 300 µm and a width of 20 cm using a roll laminator. Here, the aluminum plate is supplied at room temperature, the rubber roll temperature is 180 to 250 ° C., the passing speed is 25 to 100 cm / min,
The gauge pressure was 6 kg / cm ² .

Next, the aluminum plate to which the biaxially stretched film was fused was placed in a hot air oven and the melting point of the film +
The film was heated at a temperature of 30 ° C. for 60 seconds to completely melt the film. Take this out of the oven and within 5 seconds 5 ℃
And then rapidly cooled and solidified.

The obtained laminated metal plate is 150 m in diameter.
cut out into a circle with a diameter of m
m, a height of 125 mm and a wall thickness of 0.12 mm were prepared.

Tables 1 and 2 show the characteristics of the copolymerized polyester film laminated on the laminated metal plate and the characteristics of the DI can using the same.

As shown in Table 1, the films of Examples 1 to 3 had a difference in reduced viscosity before and after heat treatment of 0.05 or less.
As a result, the DI can produced using this film was less likely to have defects and cracks even when subjected to a drop impact, and had a low ERV value.

On the other hand, the films of Comparative Examples 1 to 3 shown in Table 2 showed a large decrease in reduced viscosity after heat treatment, and the DI cans produced using these films could have defects or cracks when subjected to a drop impact. It was easy and the ERV value was high.

[0052]

[Table 1]

[0053]

[Table 2]

[0054]

The copolymerized polyester film of the present invention is excellent in impact resistance, hydrolysis resistance and thermal decomposition resistance, and particularly, the generation of oligomers due to hydrolysis and thermal decomposition in the lamination and heat treatment steps. And excellent in flavor resistance.

Further, the laminated metal sheet of the present invention maintains an appropriate reduced viscosity even after the laminating and heat-treating steps, and thus has excellent can-making processability. Excellent corrosion resistance, in particular, it is unlikely to be embrittled by heat treatment such as baking coating or retort treatment,
Generation of cracks and the like in the laminate film can be suppressed.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideto Ohashi 2-1-1 Katata, Otsu-shi, Shiga Prefecture Toyobo Co., Ltd. Research Institute (72) Inventor Shigetsugu Konagaya 2-1-1 Katata, Otsu-shi, Shiga Prefecture No. 1 Toyobo Co., Ltd. Research Institute (72) Inventor Masao Yamashita Kirin Brewery Co., Ltd. 2-1-1 Shinkawa, Chuo-ku, Tokyo

Claims (3)

[Claims] 1. A melting point of 150 to 250 ° C. and a thickness of 3 to 50 μm.
m, wherein the difference between the reduced viscosity of the copolyester after heat treatment of the film at the temperature of the melting point of the film + 30 ° C for 60 seconds and the reduced viscosity of the copolyester before heat treatment is 0.05 deciliters. /
g or less. 2. A laminated metal sheet, wherein the copolymerized polyester film according to claim 1 is laminated on at least one side. 3. A method for producing a laminated metal sheet, wherein a heat treatment is performed at a temperature equal to or higher than the melting point of the film while the copolymerized polyester film according to claim 1 is laminated on the surface of the metal sheet.