JP3391090B2 - Polyester composite film for bonding metal sheets - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polyester composite film for laminating metal sheets, and more specifically,
The present invention relates to a polyester composite film suitable for laminating metal sheets for metal cans such as beverage cans and food cans. The present invention also relates to a laminated metal plate obtained by laminating the above polyester composite film on a metal sheet.

[0002]

2. Description of the Related Art Conventionally, in metal cans for canning containing beverages, foods, etc., metal odor is transferred to the contents (flavor resistance is poor) and the inner surface of the metal can is corroded by the contents. In order to prevent this, various laminated steel sheets obtained by heating and press-bonding a polyester film to a tin-plated steel sheet, a chrome-treated steel sheet, a nickel-plated steel sheet or the like have been studied as the material of the metal can. For example, the contents of the technology are disclosed in Japanese Patent Publication No. 57-23584, Japanese Patent Publication No. 59-34580, Japanese Patent Publication No. 62-61427, and the like.

In these techniques, a single-layer film is used, and when the single-layer film and the steel sheet are laminated and sufficiently adhered at a temperature equal to or higher than the melting point of the polymer forming the film, a can-making process is performed. A local film tear (crack) occurs due to the impact. When laminating at a temperature lower than the melting point, film peeling occurs due to poor adhesion in the can manufacturing process, the subsequent heat treatment process and / or the retort treatment process after filling the contents.

In order to avoid such drawbacks, Japanese Patent Laid-Open Publication No. Hei 2
Japanese Patent Publication No.-81630 discloses that a polyester composite film having a crystallization calorific value between 110 ° C. and 180 ° C. of 0.1 to 1.5 cal / g is used.

However, with this technique, the film may shrink due to the heat history after lamination, and peeling may occur in a remarkable case, which is not yet satisfactory.

[0006]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned conventional problems, and an object thereof is to provide excellent impact resistance when laminated with a metal sheet such as a steel plate,
In addition, it is to provide a polyester composite film that is less likely to shrink and / or peel due to heat history after lamination. Another object of the present invention is a polyester composite film having the above-mentioned excellent properties and suitable for laminating metal sheets for metal cans such as beverage cans and food cans, and a laminated metal obtained by laminating the polyester composite film. To provide a plate.

[0007]

The polyester composite film for laminating metal sheets of the present invention has a melting point of 220 ° C.
A base layer (A layer) made of a polyester composition having a temperature of 235 ° C. or lower and an adhesive layer (B layer) made of a polyester composition having a melting point of 170 ° C. or higher and 215 ° C. or lower, and the B layer with respect to the thickness a of the A layer. The thickness b ratio (b / a) is 1 or more 1
It is 0 or less, and thereby the above-mentioned object is achieved.

In a preferred embodiment, the polyester contained in the A layer and the B layer are respectively
Contains isophthalic acid.

The laminated metal plate of the present invention is obtained by laminating the above polyester composite film on a metal sheet so that the layer B of this film is in close contact.

The present invention will be described in detail below.

The layers A and B are each made of a polyester composition containing a polyester obtained by polycondensation of a dicarboxylic acid and a diol. Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid,
2,6-naphthalene acid, adipic acid, sebacic acid, decanedicarboxylic acid, azelaic acid, dodecanedicarboxylic acid, cyclohexanedicarboxylic acid, dimer acid and the like may be used alone or in combination. As the diol, ethylene glycol, neopentyl glycol, butanediol, hexanediol, cyclohexanedimethanol, decanediol, etc. may be used alone or in combination. A copolymer of two or more kinds of dicarboxylic acids or diols described above, or another monomer such as diethylene glycol, triethylene glycol, polyethylene glycol or polytetramethylene glycol, or a copolymer with a polymer may be used.

The polyesters contained in the A layer and the B layer used in the present invention can be produced by a conventional method. For example, a polyester or a copolyester is prepared by a direct esterification method in which the dicarboxylic acid and the diol are directly reacted; a transesterification method in which the dicarboxylic acid dimethyl ester and the diol are reacted. Each of these methods may be a batch method or a continuous method. Alternatively, solid phase polymerization may be used to increase the molecular weight.

In order to obtain the polyester composition for forming the A layer, the dicarboxylic acid and diol are selected so that the melting point of the obtained polyester composition is 220 ° C. or higher and 235 ° C. or lower. Examples of such polyesters include polyethylene terephthalate isophthalate, polybutylene terephthalate, and the like, with polyethylene terephthalate isophthalate (containing about 10 mol% of repeating units of ethylene isophthalate) being particularly preferable. One or more kinds of these polyesters may be mixed and used, and for example, a mixture of the above-mentioned polyethylene terephthalate isophthalate 80% by weight and polybutylene terephthalate 20% by weight is preferably used.

In order to obtain the polyester constituting the layer B, the dicarboxylic acid and the diol are selected so that the melting point of the obtained polyester is 170 ° C. or higher and 215 ° C. or lower. Examples of such polyesters include polyethylene terephthalate isophthalate and polyethylene terephthalate, with polyethylene terephthalate isophthalate (containing 22 mol% of repeating units of ethylene isophthalate) being particularly preferred. These polyesters may be used as a mixture of one or more kinds, and for example, a mixture of 80% by weight of polyethylene terephthalate isophthalate and 20% by weight of polyethylene terephthalate is preferably used.

If necessary, an antioxidant, a heat stabilizer, an ultraviolet absorber, a plasticizer, inorganic particles, an inorganic lubricant, an organic lubricant, a pigment, an antistatic agent, etc. are dispersed and blended in the above polyester composition. It

Next, an example of the method for producing the polyester composite film of the present invention will be described. An unstretched film is obtained by extruding the polyesters constituting the A layer and the B layer by separate extruders, forming two layers outside or inside the die and then rapidly cooling. This unstretched film is at least uniaxially stretched. The stretching method is not particularly limited. Preferably 70
Stretched 2 to 4 times in the machine direction at ~ 110 ° C, then 80-1
It is stretched 3 to 5 times in the transverse direction at 10 ° C. After that, 120 ~
The polyester composite film of the present invention can be obtained by heat treatment at 230 ° C.

The thickness of the polyester composite film of the present invention is not particularly limited, but is preferably 12 to 75 μm,
More preferably, it is 15 to 25 μm. The ratio (b / a) of the thickness b of the B layer to the thickness a of the A layer of the polyester composite film of the present invention is 1 or more and 10 or less. b / a
When the value of is less than 1, shrinkage and / or peeling of the film due to heat history after lamination is apt to occur.
When it exceeds the above range, the heat resistance of the obtained laminated metal plate is poor, so that a trace of the transport pin is likely to be left during transport in the heat treatment step after can making. The thickness a of the A layer is not particularly limited,
3-60 micrometers is preferable.

The polyester composite film of the present invention is laminated on the surface of a metal sheet such as a steel plate,
Used to produce coated metal sheets. The method for laminating on a metal sheet is not particularly limited, and for example, a dry laminating method, a thermal laminating method or the like can be adopted. Specifically, the layer B side of the polyester composite film of the present invention and the metal sheet are brought into close contact with each other, and the temperature is lower than the melting point of the polyester composition constituting the layer A, preferably the softening point of the polyester composition constituting the layer B. A method in which thermal lamination is carried out by electrically heating at a temperature higher than the melting point of the polyester composition constituting the A layer is higher.

As described above, the melting point of the polyester composition constituting the layer A of the film of the present invention is 220 ° C. or higher and 2
Since the temperature is 35 ° C. or lower, the heat resistance is good, and the shrinkage and / or peeling of the film due to the heat history after lamination hardly occur. Furthermore, the laminated metal plate obtained by using the film of the present invention has excellent impact resistance. When the melting point of the polyester composition is less than 220 ° C., the heat resistance is poor, so that the marks of the transport pins are likely to be left during transport in the heat treatment step after can making. When the melting point of the polyester composition constituting the layer A exceeds 235 ° C, shrinkage and / or peeling of the film due to heat history after lamination is likely to occur.

Since the melting point of the polyester contained in the layer B is 170 ° C. or higher and 215 ° C. or lower, the polyester composite film is laminated with the metal sheet while only the layer B is softened and the impact resistance of the layer A is secured. It is possible to suppress the shrinkage and / or peeling of the film due to the heat history after lamination, and to improve the heat resistance. When the melting point of the polyester is less than 170 ° C., shrinkage and / or peeling of the film due to heat history after lamination are likely to occur. The melting point of polyester is 21
If it exceeds 5 ° C., the impact resistance of the laminated metal sheet after lamination is lowered, and cracks are likely to occur in the can making process.

The film may be laminated on the metal sheet either on one side or on both sides. In the case of double-sided laminating, they may be laminated simultaneously or sequentially. When the polyester composite film of the present invention is laminated with a metal sheet, it is possible to obtain a laminated metal plate which is excellent in impact resistance and is less likely to cause shrinkage and / or peeling of the film. Furthermore, by laminating the polyester composite film of the present invention on both sides of a metal sheet and forming a can, a metal can having not only excellent inner surface protection but also excellent outer appearance can be obtained.

The method for molding a metal container using the above laminated metal plate is also not particularly limited. As the form of the metal container, a so-called three-piece can, in which the top and bottom lid is wound and the contents are filled, is particularly preferable.

[0023]

EXAMPLES The present invention will be described below with reference to examples. The measuring method used in the examples is as follows.

(1) Melting point The polyester composition of each layer was heated and melted at 300 ° C. for 5 minutes, mixed, and then rapidly cooled with liquid nitrogen to obtain a sample of 10 m.
g using a differential scanning calorimeter in N ₂ gas flow at 10 ° C.
The temperature was raised at a rate of / min and the thermograph was measured. The peak temperature of the endothermic peak associated with melting was taken as the melting point.

(2) Impact resistance evaluation The layer B surface, which is the adhesive layer of the polyester composite film 1, was
Tin-free steel sheet (T-1, thickness: 0.
(29 mm) 2 was press-bonded with a water-cooled roll and then rapidly cooled in water to obtain a laminated metal plate 10 (FIG. 1 (a)). This laminated metal plate 10 is coated with the polyester composite film 1
DuPont impact test from the side (impactor tip diameter: 12.7 m
m, impactor weight: 1 kg, impactor drop height: 30 cm)
Shocked by. As shown in FIG. 1 (b), a cylinder 4 in which the tip of the platinum electrode 3 is penetrated from the side is prepared. Then, a 1% sodium chloride aqueous solution 40 was poured so that the platinum electrode 3 was immersed in the space formed by the cylinder. Next, the platinum electrode 3 and the steel plate 2 of the laminated metal plate 10
The side was connected to a 6V DC power source 6 and an ammeter. 6V
The current value was measured 30 seconds after the direct current voltage was loaded. The smaller the current value, the better the impact resistance.

(3) Evaluation of shrinkage amount after heating and presence / absence of peeling A 3 cm × 3 cm cut piece was prepared from a laminated metal plate obtained by the same method as the laminated metal plate used in the above impact resistance evaluation, and a diagonal line shape was formed. A sample (FIG. 2 (a)) in which a film was cut into the film was prepared. The degree of shrinkage of the film (Fig. 2 (b)) after heating this at 230 ° C for 10 minutes
It was evaluated by measuring the gap t between the film pieces, and further, the presence or absence of peeling of the film was evaluated.

(4) Evaluation of heat resistance A 5 cm × 5 cm cut piece was prepared from a laminated metal plate obtained by the same method as the laminated metal plate used for the above impact resistance evaluation, and a 100 g weight was placed on the film surface side. The state was evaluated by the degree of generation of traces of the weight after heating at 220 ° C. for 10 minutes. By visual judgment (n = 3), ○: No trace type △: Partial trace type ×: Overall trace type × ×: Weight adheres and overall trace type ○ and △ are practical is there.

(5) List of polyesters used The polyesters used in the following Examples and Comparative Examples are shown below. Polyester I: Polyethylene terephthalate Polyester II: Polybutylene terephthalate Polyester III: Polyethylene terephthalate isophthalate (Repeating unit of ethylene isophthalate 1
0 mol%) Polyester IV: polyethylene terephthalate isophthalate (repeating unit of ethylene isophthalate 22
Polyester V: A copolymer of terephthalic acid and ethylene glycol with terephthalic acid and neopentyl glycol (copolymerization ratio of terephthalic acid and neopentyl glycol of 30 mol%).

(Example 1) A layer is made of polyester (III)
And the layer B was composed of 20% by weight of polyester (I) and 80% by weight of polyester (IV), and the two layers were formed by die outside bonding using an extruder and then at 290 ° C. It was extruded and rapidly cooled to obtain an unstretched film. This unstretched film was stretched 3.5 times in the longitudinal direction at 100 ° C., then 4.0 times in the transverse direction and then heat-treated at 170 ° C. to have a thickness of 25 μm (b / a = 20 μm / 5 μm =
A polyester composite film of 4.0) was obtained. The characteristics of the obtained polyester composite film were evaluated by the above methods, and the results are shown in Table 1. Table 1 also shows the evaluation results of the following Examples 2 to 5 and Comparative Examples 1 to 7.

(Example 2) A layer is made of polyester (II)
Thickness 2 as in Example 1 except 20% by weight and 80% by weight polyester (III) were used.
A polyester composite film of 5 μm (b / a = 20 μm / 5 μm = 4.0) was obtained and evaluated in the same manner as in Example 1.

(Example 3) The thickness of the polyester composite film was 40 μm (b / a = 35 μm / 5 μm = 7.0).
A polyester composite film was obtained in the same manner as in Example 2 except for the above, and evaluated in the same manner as in Example 1.

Example 4 A polyester composite film having a thickness of 20 μm (b / a = 17 μm / 3 μm = 5.7)
A polyester composite film was obtained in the same manner as in Example 2 except for the above, and evaluated in the same manner as in Example 1.

(Example 5) A layer of polyester (II) 2
20 μm in thickness as in Example 1 except that 0% by weight and 80% by weight of polyester (III) were used and the B layer was formed using only polyester (IV).
A polyester composite film of (b / a = 17 μm / 3 μm = 5.7) was obtained and evaluated in the same manner as in Example 1.

Comparative Example 1 20% by weight of polyester (I) and 80% by weight of polyester (IV) were obtained in the same manner as in Example 1 to obtain a single-layer polyester film having a thickness of 25 μm. evaluated.

(Comparative Example 2) A layer of polyester (I) 2
A thickness of 25 μm (b) was obtained in the same manner as in Example 1 except that 0% by weight and 80% by weight of polyester (IV) were used and the B layer was formed using only polyester (IV).
/ A = 20 μm / 5 μm = 4.0) was obtained and evaluated in the same manner as in Example 1.

Comparative Example 3 A layer having a thickness of 25 μm was prepared in the same manner as in Example 1 except that the layer A was prepared using only the polyester (I) and the layer B was prepared using only the polyester (IV). b / a = 20 μm / 5 μm = 4.0) was obtained and evaluated in the same manner as in Example 1.

(Comparative Example 4) A layer is made of polyester (III)
25 μm in thickness in the same manner as in Example 1 except that the B layer was made using 50% by weight of polyester (I) and 50% by weight of polyester (IV).
Evaluation was performed in the same manner as in Example 1 except that a polyester composite film of (b / a = 20 μm / 5 μm = 4.0) was obtained, and the polyester composite film and the metal sheet were laminated at 240 ° C.

(Comparative Example 5) A layer is made of polyester (III)
A polyester composite having a thickness of 25 μm (b / a = 20 μm / 5 μm = 4.0) prepared by the method described in Example 1, except that the layer B was prepared using only the polyester (V). A film was obtained and evaluated in the same manner as in Example 1.

(Comparative Example 6) A layer is made of polyester (III)
Polyester composite having a thickness of 25 μm (b / a = 3 μm / 22 μm = 0.14) in the same manner as in Example 1 except that the layer B was prepared using only the polyester (IV). A film was obtained and evaluated in the same manner as in Example 1.

Comparative Example 7 The thickness of the polyester composite film was 50 μm (b / a = 48 μm / 2 μm = 24.
A polyester composite film was obtained in the same manner as in Comparative Example 6 except that it was 0), and was evaluated in the same manner as in Example 1.

[0041]

[Table 1]

As is clear from Table 1, all of the polyester composite films of the present invention obtained in Examples 1 to 5 are excellent in impact resistance and heat resistance, and have a thermal history after lamination. It can be said that the amount of shrinkage is small and the film is of high quality and is highly practical as a film for metal bonding. The films obtained in Comparative Examples 1 and 2 were inferior in impact resistance and heat resistance, and the films obtained in Comparative Examples 3 and 6 had a large amount of shrinkage of the film due to the heat history after lamination, and thus were obtained in Comparative Example 4. The resulting film has poor impact resistance,
The films obtained in Comparative Examples 5 and 7 have poor heat resistance,
Moreover, the amount of shrinkage of the film due to the heat history after lamination is large, and both of them are inferior in quality as a film for metal bonding.

[0043]

Industrial Applicability As described above, the polyester composite film of the present invention is at least a uniaxially stretched bikinetic polyester bilayer film of two types, and the melting point of the polyester composition constituting each layer and the adhesion of the polyester composite film. Since the ratio of the thickness of the layer to the base layer is controlled within an appropriate range, it has excellent impact resistance during can making and does not cause shrinkage and / or peeling of the film due to heat history after lamination. Furthermore, it has excellent heat resistance after lamination, and does not leave marks on the transport pins during transport in heat treatment processes and the like. As a result, a metal can having excellent inner surface protection (flavor resistance, corrosion resistance) can be obtained. The metal can obtained by making a laminated metal plate obtained by laminating the polyester composite film of the present invention on both sides of a steel plate has not only excellent inner surface protection but also excellent external appearance, and beverages. It is useful as a can or food can.

[Brief description of drawings]

FIG. 1 (a) is a view showing a laminated metal plate produced to evaluate the impact resistance of the polyester films obtained in Examples and Comparative Examples, and FIG.
FIG. 4 is a diagram showing an apparatus used to evaluate the impact resistance.

FIG. 2 (a) is a diagram showing a sample before heating of a test piece in a test for evaluating the shrinkage amount after heating and the presence or absence of peeling of the polyester composite films obtained in Examples and Comparative Examples. 2 (b) is a diagram showing shrinkage of the polyester composite film after heating in this test.

[Explanation of symbols]

1 Polyester composite film 2 steel plate 3 Platinum electrode 4 cylinders 5 Impact part 6 DC power supply 10 Laminated metal plate 40 1% sodium chloride solution t Contraction amount

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Nagano 344 Maebata, Kizu character, Inuyama City, Aichi Prefecture Toyobushi Co., Ltd.Inuyama Plant (72) Inventor, Kunio Takeuchi 344 Maebata, Kizu character, Inuyama City, Aichi Prefecture Toyobo Inuyama Factory Co., Ltd. (72) Inventor Akira Matsuda 344 Maebata, Kizu, Inuyama City, Aichi Toyobo Co., Ltd. Inuyama Factory (56) Reference JP-A-5-42643 (JP, A) JP-A-56- 10451 (JP, A) JP 4-353443 (JP, A) JP 7-144396 (JP, A) JP 7-276564 JP, A) JP 8-238720 (JP, A) (58 ) Fields surveyed (Int.Cl. ⁷ , DB name) B32B 1/00-35/00

Claims (3)

(57) [Claims] 1. A der melting point of 220 ° C. or higher 235 ° C. or less
And polyethylene terephthalate isophthalate
A base material layer (A layer) made of a polyester composition containing polybutylene terephthalate and an adhesive layer made of a polyester composition having a melting point of 170 ° C. or higher and 215 ° C. or lower and containing polyethylene terephthalate isophthalate and polyethylene terephthalate (B A polyester composite film for laminating metal sheets, wherein the ratio (b / a) of the thickness b of the B layer to the thickness a of the A layer is 1 or more and 10 or less. 2. The polyester composite film for laminating metal sheets according to claim 1, wherein the polyesters contained in the A layer and the B layer each contain isophthalic acid. 3. A laminated metal plate obtained by laminating the polyester composite film according to claim 1 or 2 on a metal sheet so that the B layer of the film is in close contact.