JP2908159B2 - Polyester film for metal plate lamination processing - Google Patents

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 exhibits excellent formability when laminating to a metal plate and performing can forming such as drawing. Polyester film for metal plate lamination that can be used to produce metal cans having good heat resistance, and excellent heat resistance, retort resistance, fragrance preservation and flavor, impact resistance, etc., such as beverage cans and food cans About.

[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, rust prevention is performed without using an organic solvent. Development of a method for obtaining the property has been advanced, and as one of the methods, coating with a thermoplastic resin film has been attempted. That is,
Studies have been made on a method of laminating a thermoplastic resin film on a metal plate such as tin, tin-free steel, or aluminum, and then forming the can by drawing or the like. Polyolefin films and polyamide films have been tried as this thermoplastic resin film, but they do not satisfy all of moldability, heat resistance, fragrance retention and impact resistance.

On the other hand, polyester films, particularly polyethylene terephthalate films, have been attracting attention as having balanced properties, and some proposals based on these have been made. That is, (A) a biaxially oriented polyethylene terephthalate film is laminated on a metal plate via a low-melting-point polyester adhesive layer and used as a can-making material (JP-A-56-1045).
No. 1, JP-A-1-192546). (B) Amorphous or extremely low-crystalline aromatic polyester film is laminated on a metal plate and used as a can-forming material (JP-A-1-192545, JP-A-2-57).
339). (C) A biaxially oriented polyethylene terephthalate film having a low orientation and thermally fixed is laminated on a metal plate and used as a can-making material (Japanese Patent Application Laid-Open No. 64-22530).

[0004] However, the present inventors' studies have revealed that no satisfactory characteristics can be obtained in any case, and that each has the following problems.

Regarding (A), a biaxially oriented polyethylene terephthalate film is excellent in heat resistance and fragrance retention,
In the process of making cans with insufficient molding workability and large deformation, whitening (generation of minute cracks) and breakage of the film occur.

As for (B), since it is an amorphous or extremely low-crystalline aromatic polyester film, the moldability is good, but the fragrance retention is inferior, and the printing and retort sterilization after can-making are performed. Such a film may be easily embrittled by post-treatments or storage for a long period of time, and may be changed to a film which is easily broken by an impact from the outside of the can.

As for (C), the effect is not exhibited in the intermediate region between the above (A) and (B), but it has not yet reached the low orientation applicable to can processing. Even if it can be processed in a region with a small degree of deformation, subsequent printing,
As in the case of (B), there is a possibility that the retort treatment for sterilizing the contents of the can makes the film brittle easily and the film is likely to be broken by an impact from the outside of the can.

In order to solve such a problem, the present inventors have considered various uses of a film made of a copolymerized polyester and have made various studies. As a result, the copolymerized polyester film is excellent in molding workability, heat resistance, retort resistance, and fragrance retention, but has an impact resistance, particularly
It has been found that the impact resistance at a low temperature of 5 ° C. or less is insufficient, and that when the metal can to which the film is bonded is dropped at a low temperature to give an impact, the film is likely to crack. Poor impact resistance at low temperatures poses a major problem when handled in a cooled state, such as metal cans for juices and soft drinks.

Further, it has been found that when a copolymerized polyester film is used, the fragrance retention is generally good, but when used in soft drinks and the like, there arises a problem that the taste of the contents deteriorates. .

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to improve the impact resistance of a copolymerized polyester film while maintaining the excellent moldability, heat resistance, retort resistance and fragrance retention. Another object of the present invention is to provide a polyester film for laminating a metal plate which is hardly cracked by an impact at a low temperature and does not deteriorate the taste of soft drink and the like.

[0011]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, have made a film a copolymerized polyester laminated film, one surface layer of which contains a large amount of filler. Constructed of a copolyester, and by limiting the surface roughness of both surface layers to specific ranges respectively, the impact resistance and taste retention at low temperatures are improved, and the deterioration of winding properties can be avoided. Heading that
The present invention has been completed.

That is, the present invention has a melting point of 210-245 ° C.
And a copolyester layer (A) containing 5 to 30% by weight of a filler having an average particle size of 2.5 μm or less and a melting point of 210 to 245 ° C. The isophthalic acid copolymerized polyester layer (A) has a surface roughness (Ra) of 15 nm or less;
A polyester film for laminating and processing a metal plate, wherein the polyester layer (B) has a surface roughness of 15 nm or more.

In the present invention, copolymerized polyethylene terephthalate is a representative example of the copolymerized polyester used in the copolymerized polyester layer (B). The copolymer component may be an acid component or an alcohol component. Examples of the acid component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid and naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decane dicarboxylic acid, and alicyclic groups such as cyclohexanedicarboxylic acid. Examples of the dicarboxylic acid include aliphatic alcohols 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 type thereof, and as a result, the melting point of the polymer is in the range of 210 to 245 ° C., preferably 215 to 235 ° C. Melting point 2
If it is lower than 10 ° C., the heat resistance will be poor. On the other hand, when the melting point exceeds 245 ° C., the crystallinity of the polymer is 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 about 20 mg.

The intrinsic viscosity of the copolymerized polyester is preferably 0.52 to 0.80, more preferably 0.54 to 0.70, and particularly preferably 0.57 to 0.70.
0.65.

In the present invention, the copolymer polyester used for the isophthalic acid copolymer polyester layer (A) is
Among the above-mentioned copolyesters used in the copolyester layer (B), because of their excellent fragrance retention,
A copolymerized polyester containing an isophthalic acid component in the acid component, and a typical example is a copolymerized polyethylene terephthalate obtained by copolymerizing the isophthalic acid component (isophthalic acid copolymerized polyethylene terephthalate). This isophthalic acid copolymerized polyethylene terephthalate has a copolymerization component other than isophthalic acid, such as the copolymerization component of the copolymerized polyester of the copolymerized polyester layer (B), as long as the copolymerizable component does not impair its properties. It may be copolymerized at a ratio of 3 mol% or less based on all the acid components or all the alcohol components.

The proportion of isophthalic acid and other copolymer components is such that the polymer has a melting point of 210-245 ° C., preferably 2
It is a ratio falling within a range of 15 to 235 ° C. Melting point 210
If the temperature is lower than ℃, the heat resistance is inferior. On the other hand, the melting point is 24
If the temperature exceeds 5 ° C., the crystallinity of the polymer is too large and the moldability is impaired.

In the present invention, the copolyester constituting the copolyester layer (B) enhances the adhesive strength when laminated and bonded to the isophthalic acid copolyester layer (A), and improves the impact resistance. The melting point difference between the isophthalic acid copolymerized polyester (A) and the isophthalic acid copolymerized polyester (A) is ± 10 ° C or less, preferably ± 7 ° C or less, more preferably ± 5 ° C or less.

Further, the copolymerized polyester layer (B) contains 5 to 30% by weight of a filler having an average particle size of 2.5 μm or less. The filler may be inorganic or organic, but is preferably inorganic. Preferred examples of the inorganic pigment include alumina, titanium dioxide, calcium carbonate, barium sulfate and the like. In the case of the present invention, titanium dioxide is particularly optimal.

Each of these fillers has an average particle size of 2.
It needs to be 5 μm or less. When the average particle size of the filler exceeds 2.5 μm, coarse particles (for example, particles having a size of 10 μm or more) of a portion deformed by processing such as a deep drawing can serve as a starting point, and pinholes may be generated. It is not preferable because it breaks. The average particle size of the filler is preferably from 0.05 to 1.5 μm, particularly preferably from 0.1 to 0.5 μm.

The content of the filler needs to be 5 to 30% by weight, particularly preferably 10 to 20% by weight.
If the content of the filler exceeds 30% by weight, it is difficult to form a film. If the content is less than 5% by weight, the effect of improving the impact resistance at low temperatures cannot be recognized.

Before the filler is contained in the copolymerized polyester forming the layer (B), it is preferable to adjust the particle size and remove coarse particles using a purification process. Industrial means of the refining process include, for example, a jet mill and a ball mill as pulverizing means, and examples of the classifying means include a dry or wet centrifuge. Of course, these means may be used in combination of two or more, and may be purified stepwise.

Various methods can be used for incorporating a filler into the copolymerized polyester forming the layer (B). A typical method is as follows. (A) A method of adding before the end of transesterification or esterification reaction at the time of synthesizing the copolyester, or adding before starting the polycondensation reaction. (A) A method of adding to the copolymerized polyester and melt-kneading. (C) The method of (a) or (b), wherein a master pellet containing a large amount of an additive is produced, kneaded with a copolymer polyester containing no particles, and a predetermined amount of the additive is contained.

When the method (a) of adding an additive during the synthesis of the polyester is used, it is preferable to add the additive to the reaction system as a slurry in which the additive is dispersed in glycol.

In the present invention, the copolyester layer (B) has a surface roughness (Ra) of 15 nm or more, preferably 15 to 100 nm, more preferably 15 to 80 n.
m. This surface roughness (Ra) is 15
When the thickness is less than nm, the handling property (winding property) of the film deteriorates, which is not appropriate.

The copolyester layer (B) is a layer to be bonded to the metal plate when the laminated film is molded into a metal plate and formed into a can, and does not directly contact the contents of the can. Even if the surface roughness (Ra) is 15 nm or more, the taste of the contents does not deteriorate.

In the case of the copolyester (B), the desired surface roughness (Ra) can be obtained by appropriately selecting the average particle size and the amount of the filler to be added to the copolyester within the above ranges. Can be obtained.

On the other hand, the isophthalic acid copolymerized polyester layer (A) must have a surface roughness (Ra) of 15 nm or less, preferably 12 nm or less, and more preferably 2 to 10 nm. The isophthalic acid copolymerized polyester layer (A) is a layer located on the side in contact with the contents of the can when molded into a can bonded to a metal plate, and has a surface roughness (Ra) of 15 nm or less. Thereby, it is possible to prevent the taste of the contents, especially soft drinks such as carbonated drinks, from being deteriorated, and to improve the impact resistance at low temperatures. If the surface roughness (Ra) is less than 2 nm, the surface of the film is easily damaged.

In order to reduce the surface roughness (Ra) to 15 nm or less, the average particle size and the amount of the lubricant to be added to the isophthalic acid copolymerized polyester may be appropriately selected. The lubricant is
It does not matter whether it is inorganic or organic, but inorganic is preferred.
Examples of the inorganic lubricant include silica, alumina, kaolin, titanium dioxide, calcium carbonate, and barium sulfate. Examples of the organic lubricant include silicone particles, crosslinked polystyrene particles, and crosslinked acrylic resin particles. In particular, a lubricant which is preferable in terms of pinhole resistance is a monodispersed lubricant having a particle size ratio (major axis / minor axis) of 1.0 to 1.2. Examples of such a lubricant include spherical silica and spherical silicone particles.

The amount of addition may be selected according to the size of the lubricant. For example, for spherical silica having an average particle size of 1.5 μm, 0.04% by weight or less may be added, and for spherical silica having an average particle size of 0.8 μm, 0.36% by weight or less may be added. When the addition amount is 0.2% by weight, the average particle diameter of the spherical silica is 0.95 μm or less, and the addition amount is 0.05% by weight.
In this case, the average particle size of the spherical silica may be set to 1.33 μm or less.

The film has a surface roughness (Ra) of J
This is the center line average roughness determined according to IS-B0601, and a portion of the measured length L is extracted from the film surface roughness curve in the direction of the center line, the center line of the extracted portion is defined as the X axis, and the longitudinal magnification Is the Y axis, and the roughness curve is Y =
When represented by f (x), the value (R
a: nm) is defined as the film surface roughness.

[0033]

(Equation 1)

In the present invention, when the reference length is 2.5 mm, 5
The number is measured, and Ra is represented as an average of four values excluding one from the larger value.

The isophthalic acid copolymerized polyester and the copolymerized polyester in the present invention are not limited by the production method. For example, a method in which terephthalic acid, ethylene glycol and isophthalic acid or a copolymer component is subjected to an esterification reaction, and then the obtained reaction product is subjected to a polycondensation reaction to obtain an isophthalic acid copolymerized polyester or a copolymerized polyester, or dimethyl terephthalate, A method of subjecting ethylene glycol and isophthalic acid or a copolymer component to a transesterification reaction and then subjecting the resulting reaction product to a polycondensation reaction to obtain an isophthalic acid copolymerized polyester or a copolymerized polyester is preferably used. In the production of the isophthalic acid copolyester or copolyester, other additives such as a fluorescent whitening agent, an antioxidant, a heat stabilizer, an ultraviolet absorber, an antistatic agent and the like can be added, if necessary. .

In the present invention, the polyester has a structure in which an isophthalic acid copolymerized polyester layer (A) and a copolymerized polyester (B) are laminated. The isophthalic acid copolymerized polyester and the copolymerized polyester are separately melted, co-extruded from a die, laminated and fused before solidification, then biaxially stretched, and heat-fixed. And then extruded into a film, in an unstretched state or after stretching, and then laminating and fusing them.

The polyester film of the present invention may be an unstretched film, but is usually used in a state of being biaxially stretched and heat set. In this case, the refractive index in the thickness direction of the isophthalic acid copolymerized polyester layer (A) is 1.49.
It is preferably 0 to 1.550, and more preferably more than 1.505 and not more than 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.

[0038] The polyester film of the present invention preferably has a thickness of 6 to 75 µm. 10-75μ
m, particularly preferably 15 to 50 μm. If the thickness is less than 6 μm, breakage or the like is likely to occur during processing, while if it exceeds 75 μm, the quality is excessive and uneconomical.

Isophthalic acid copolymerized polyester layer (A)
The thickness T _B of the thickness T _A, copolyester layer (B)
The ratio of the (T _A / T _B) is preferably about 0.02 to 1.5, more preferably 0.04 to 0.67, particularly preferably 0.04 to 0.25. Specifically, for example, in the case of a polyester film having a thickness of 25 μm, the thickness of the isophthalic acid copolymerized polyester layer (A) is set to 0.5 to 15 μm.
μm, preferably 1 to 10 μm, more preferably 1 to 5
μm.

As the 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, and the surface layer (thin layer) of the film in contact with the metal plate is made amorphous and adhered.

A film is preliminarily coated with an adhesive layer by a primer, and this surface is bonded to a metal plate. As the adhesive layer, a known resin adhesive, for example, an epoxy-based adhesive,
Epoxy-ester adhesives, alkyd adhesives and the like can be used.

When the polyester film of the present invention is bonded to a metal plate, the polyester layer (B) is bonded to the metal plate.

Furthermore, in the polyester film of the present invention, if necessary, another additional layer may be laminated between the isophthalic acid copolymerized polyester layer (A) and the polyester layer (B).

[0045]

The present invention will be further described with reference to the following examples.

[0046]

Examples 1 to 6 and Comparative Examples 1 to 5 Polyethylene terephthalate copolymerized with the components shown in Table 1 (intrinsic viscosity 0.6
4, containing 0.1% by weight of spherical silica having a particle size ratio of 1.1 and an average particle size of 0.3 μm) is a copolymerized polyester layer (A),
Similarly, polyethylene terephthalate (containing 18% by weight of titanium dioxide having an intrinsic viscosity of 0.64 and an average particle size of 0.27 μm) obtained by copolymerizing the components shown in Table 1 is separately formed so as to form the copolymerized polyester layer (B). After being dried and melted by a conventional method, they were co-extruded from dies adjacent to each other, laminated, fused and quenched and solidified to prepare an unstretched laminated film.

Next, the unstretched film was longitudinally stretched 3.0 times at 110 ° C., and then transversely stretched 3 times at 120 ° C.
It was heat-set at 190 ° C. to obtain a biaxially oriented laminated film.

The thickness of the obtained film was 25 μm, and the thicknesses of the copolymerized polyester layer (A) and the polyester layer (B) were 5 μm and 20 μm, respectively. The surface roughness (Ra) was 5 nm and 58 nm, respectively.
Met.

The surface roughness (Ra) was measured by a stylus type surface roughness meter (SURFCORDER S, manufactured by Kosaka Laboratory Co., Ltd.).
E-30C) using a stylus radius of 2 μm and a measurement pressure of 0.0
The measurement was performed under the conditions of 3 g and a cutoff value of 0.25 mm.

[0050]

[Table 1]

[0051]

Comparative Examples 6 and 7 In Example 2, only the isophthalic acid copolymerized polyester layer (A) (Comparative Example 6) and the copolymerized polyester layer (B) alone (Comparative Example 7) were not used as the two-layer laminated structure. Was prepared as a single-layer film having a thickness of 25 μm.

[0052]

Examples 7 to 9 and Comparative Examples 8 to 9
The amount of titanium dioxide contained in the copolymerized polyester layer (B) was changed as shown in Table 2, and the other conditions were as in Example 2.
In the same manner as in the above, a biaxially oriented laminated film was obtained. Table 2 also shows the surface roughness (Ra) of the polyester layer (B).

[0053]

[Table 2]

[0054]

Examples 10 to 11 and Comparative Examples 10 to 11 In Example 2, the average particle size and content of spherical silica contained in the isophthalic acid copolymerized polyester layer (A) and contained in the copolymerized polyester layer (B) were used. The average particle size and content of the titanium dioxide to be produced were changed as shown in Table 3, and the respective surface roughnesses (Ra) were changed as shown in Table 3, and other conditions were the same as in Example 2. A biaxially oriented laminated film was obtained.

[0055]

[Table 3]

A total of 22 kinds of films obtained in the above Examples 1 to 11 and Comparative Examples 1 to 11 were coated on both sides of a 0.25 mm thick tin-free steel heated to 230 ° C. with a copolymerized polyester layer (B). ) Is bonded to the tin-free steel so that the surface is in contact with the tin-free steel, water-cooled, cut into a disk having a diameter of 150 mm, deep-drawn in four stages using a drawing die and a punch, and a side-seamless container having a diameter of 55 mm ( Hereinafter, it is abbreviated as can).

The following observations and tests were performed on the cans, and the cans were evaluated according to the following standards.

(1) Deep drawing processability -1 ：: The film was processed without any abnormality, and no whitening or breakage was observed in the film. Δ: Whitening was observed in the upper part of the film. ×: The film was partially broken in the film. Is recognized

(2) Deep drawing processability-2 ○: Processed without any abnormality, rust prevention test on film surface in can (1% NaCl water was put in the can, electrodes were inserted, and the can body was used as an anode. The current value when a voltage of 6 V is applied is measured.
X: No abnormality in the film, but the current value was 0.1 mA or more in the ERV test, and when the energized portion was enlarged and observed, a pin starting from a coarse lubricant was found on the film. Hole-shaped cracks are observed

(3) Impact resistance For cans that had good deep drawing, plenty of water was added, and after cooling to 10 ° C., 10 pieces of each test were 30 cm in height.
ERV test was performed in the can after dropping on a PVC tile floor surface from the test results. A: 0.3 mA or less for all 10 pieces. Δ: 1 mA or more was 0.3 mA or more. X: 0.3 mA or more for 6 or more pieces, or cracks of the film were already observed after dropping.

(4) Heat embrittlement resistance After the can which had been subjected to good deep drawing was heated and maintained at 200 ° C. for 5 minutes, the impact resistance evaluation described in (3) was performed. Was 0.3 mA or less. Δ: 1 mA or more was 0.3 mA or more. C: Cracks were already observed in the film after heating for 6 or more at 0.3 mA or more or at 200 ° C. for 5 minutes.

(5) Retort Resistance The cans having good deep drawing properties were filled with water, retorted in a steam sterilizer at 120 ° C. for 1 hour, and then stored at 50 ° C. for 30 days. After dropping 10 cans obtained for each test from a height of 1 m onto a PVC tile floor, an ERV test in the cans was performed. ：: 0.3 mA or less for all 10 pieces Δ: 0.3 mA or more for 1 to 5 pieces ×: 0.3 mA or more for 6 pieces or more, or cracks of the film were already observed after dropping Was

(6) Scent Retention A can having good deep drawing was filled with cider and sealed. After being kept at 37 ° C. for 30 days, the can was opened and the change in fragrance was examined by sensory test. ：: no change in scent Δ: slight change in scent was observed ×: change in scent was observed

(7) Taste preservation In the same manner as in (6), changes in taste were examined by a sensory test. ：: No change in taste. Δ: Slight change in taste was observed. ×: Change in taste was observed.

The results of the above seven evaluations and the winding properties are as shown in Table 3.

[0066]

[Table 4]

As is clear from the results shown in Table 4, the cans using the polyester film of the present invention are excellent in deep drawing workability, heat embrittlement resistance, retort resistance, fragrance retention and impact resistance. It has excellent impact resistance, especially at low temperatures, and without deteriorating the taste of soft drinks, etc.
The winding property is also good.

[0068]

The film for laminating and processing metal sheets of the present invention has excellent moldability, heat resistance, retort resistance, and fragrance retention, and also has impact resistance, especially impact resistance at low temperatures. Is improved, the taste of soft drinks and the like is not deteriorated, and the winding property is also good. Therefore, it is particularly suitable for being used after being cooled and stuck to a metal can for soft drinks and the like which is often handled at a low temperature.

Continuation of front page (56) References JP-A-5-338103 (JP, A) JP-A-6-172556 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B32B 1 / 00-35/00

Claims (1)

(57) [Claims] 1. An isophthalic acid copolymerized polyester layer (A) having a melting point of 210 to 245 ° C. and an average particle size of 2.5
5 to 30% by weight of a filler having a melting point of 21 μm or less.
The isophthalic acid copolymerized polyester layer (A) has a surface roughness (Ra) of 15 nm or less, and a surface roughness of the polyester layer (B). Having a thickness of 15 nm or more.