JP3552059B2 - Polyester composite film for metal lamination - Google Patents

Description

【図面の簡単な説明】
【図１】図１は鋼板にフイルムを接着した後、耐衝撃性の程度を評価するための装置の略図である。
【符号の説明】
１．フイルム
２．鋼 板
３．白金電極
４．１％塩化ナトリウム
５．電流計
６．直流電源[0001]
[Industrial applications]
The present invention relates to a polyester composite film for metal lamination, and more particularly to a polyester composite film suitable as a constituent material of a laminated steel sheet for obtaining a metal can such as a beverage can or a food can.
[0002]
[Prior art]
Conventionally, in metal cans, tin-plated steel sheets, chrome-treated steel sheets, nickel-plated steel sheets, etc. have been used to prevent metal odor from migrating to the contents (defective flavor) and prevent the contents from corroding the inner surface of the metal cans. Various laminated steel sheets obtained by bonding a film under heat and pressure have been studied. For example, the technical contents are disclosed in JP-B-57-23584, JP-B-59-34580, and JP-B-62-61427.
However, in this technique, it is premised that a single-layer film is used. Therefore, when the film is laminated with a steel plate at a temperature equal to or higher than the melting point of the polymer constituting the film and sufficiently adhered, local film tearing due to an impact at the time of can making processing. (Cracks) occur. Also, when laminated at a temperature lower than the melting point, cracks due to impact during can making are unlikely to occur, but poor adhesion occurs in the can making process, the subsequent heat treatment process and / or the retort treatment process after filling the contents. Accompanying film peeling occurs.
To avoid such a drawback, Japanese Patent Application Laid-Open No. 2-81630 discloses the use of a composite film.
However, in this technique, peeling is often caused by retort treatment, which has not been satisfactory.
[0003]
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned circumstances, and provides a polyester film which ensures impact resistance in a can-making process and has good adhesion (particularly, hardly causes peeling due to retort treatment). It is intended for that purpose.
[0004]
[Means for Solving the Problems]
The polyester film of the present invention that has achieved the above object is a base layer (A layer) made of polyester having a melting point of 220 ° C. or more and an adhesive layer made of polyester having a melting point of 200 ° C. or more and 5 ° C. or more lower than the melting point of the A layer. This is a composite film composed of (B layer), and has a gist in that the heat shrinkage force of the composite film is 40 gf.
[0005]
The polyester composite film of the present invention is obtained by laminating a polyester resin (A layer) having a melting point of 220 ° C. or more and a polyester resin (B layer) having a melting point of 200 ° C. or more and 5 ° C. or more lower than the melting point of the A layer. It is an essential requirement that the film be stretched at least uniaxially. However, the stretching method is not particularly limited.
When laminating the polyester composite film of the present invention with a steel sheet, it is preferable to use the B layer and the steel sheet together at a temperature lower than the melting point of the A layer in order to exhibit the effects of the present invention.
[0006]
In the polyester composite film of the present invention, since the melting point of the layer A is 220 ° C. or higher, the impact resistance after lamination is excellent. As a result, cracks are less likely to occur during the can-making process, so that the corrosion resistance of the inner surface of the obtained metal can is ensured.
Conversely, if the melting point of the layer A is less than 220 ° C., the impact resistance after lamination is reduced, and cracks are liable to occur in the can making process.
[0007]
The thickness of the layer A is not particularly limited, but is preferably 5 to 60 μm.
In addition, since the melting point of the layer B is 200 ° C. or more and (melting point of the layer A−5) ° C. or less, lamination can be performed with the impact resistance of the layer A secured, and peeling due to retort treatment is suppressed. Is done.
Conversely, if the melting point of the layer B exceeds (melting point of the layer A-5) ° C., the impact resistance after lamination is reduced, and cracks are liable to occur in the can-making process. When the melting point of the B layer is less than 200 ° C., peeling is likely to occur due to the retort treatment.
Further, since the heat shrinkage force of the composite film is 40 gf or less, peeling due to the retort treatment is suppressed. Conversely, if the heat shrinkage force of the composite film is greater than 40 gf, peeling due to retort processing is likely to occur.
The polyester composite film of the present invention is a polyester film obtained by polycondensation of a dicarboxylic acid and a diol.
[0008]
As such a dicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 2-6-naphthalene acid, adipic acid, sebacic acid, decanedicarboxylic acid, azelaic acid, dodecanedicarboxylic acid, cyclohexanedicarboxylic acid, a single substance or a mixture of dimer acids, etc. Can be used. As the diol, ethylene glycol, neopentyl glycol, butanediol, hexanediol, cyclohexanedimethanol, decanediol and the like can be used alone or in a mixture. Further, a copolymer of two or more dicarboxylic acids or diols or a copolymer with another monomer or polymer such as diethylene glycol, triethylene glycol, polyethylene glycol, or polytetramethylene glycol may be used. If necessary, antioxidants, heat stabilizers, ultraviolet rays, absorbers, plasticizers, inorganic particles, inorganic lubricants, organic lubricants, pigments, antistatic agents and the like may be dispersed and blended.
Next, an example of the method for producing the polyester composite film of the present invention will be described. The polyester resin constituting the layer A and the layer B is extruded by a separate extruder, formed into two layers outside or inside the die, and then rapidly cooled to obtain an unstretched film. The unstretched film is stretched 2 to 4 times in the machine direction at 70 to 110 ° C., then stretched 3 to 5 times in the transverse direction at 80 to 110 ° C., and then heat-treated at 120 to 240 ° C. to obtain the polyester composite of the present invention. A film is obtained.
[0009]
Hereinafter, the present invention will be described in detail based on examples. The measurement methods and polyesters used in the examples and comparative examples are as follows.
1. Using a 10 mg sample obtained by heating and melting the resin material of each layer at 300 ° C. for 5 minutes and then quenching with liquid nitrogen, using a differential scanning calorimeter to raise the temperature at 10 ° C./min. The peak temperature of the endothermic peak accompanying melting in the endothermic curve was defined as the melting point.
[0010]
2. A sample having a width of 4 mm and a length of 20 to 30 mm was cut out from the heat shrinkable composite film, and the load obtained by using a thermomechanical analyzer at a sample holder interval of 5 mm, an initial load of 5 gf, and heating from 30 ° C at 10 ° C / min. The maximum value (shrinkage force in the longitudinal and transverse directions of the composite film) associated with shrinkage in the curve was determined.
The average value of the longitudinal contraction force and the lateral contraction force was defined as the heat contraction force.
[0011]
3. Using a layer of impact-resistant polyester B as an adhesive layer, a tin-free steel sheet heated to a predetermined temperature was pressure-bonded with a water-cooled roll, and then rapidly cooled in water to obtain a laminated steel sheet. An impact was applied to the laminated steel sheet from the film side by a drop impact test (impactor tip diameter 4 mm, impactor weight 0.4 kg, impactor drop height 30 cm), and the impact portion was as shown in FIG. The current value was measured 30 seconds after the 6V DC power supply load by a suitable method. The smaller the current value, the better the impact resistance.
[0012]
4. Retort adhesion After laminating steel plates (one that had an impact from the film side and one that had an impact from the steel plate side) after the falling cone impact, the film was retorted at 120 ° C. for 30 minutes, and the presence or absence of peeling of the film was visually determined.
[0013]
5. Heat resistance evaluation A sample cut into 5 cm x 5 cm from a laminated steel sheet obtained by the same method as the impact resistance evaluation sample was used as a sample, and heated at 220 ° C for 10 minutes with a 100 g weight placed on the film surface side. The evaluation was based on the degree of trace formation of the weight.
[0014]
6. Polyester used in Examples and Comparative Examples Polyester A: polyethylene terephthalate Polyester B: polyethylene terephthalate isophthalate (repeating unit of ethylene isophthalate 10 mol%)
Polyester C: polyethylene terephthalate isophthalate (22 mol% of repeating units of ethylene isophthalate)
Polyester D: Polybutylene terephthalate Polyester E: Copolymer of terephthalic acid / isophthalic acid / adipic acid // butanediol = 65/10/25 // 100
Example 1
The A layer was made up of 85% by weight of polyester A and 15% by weight of polyester B, and the B layer was made up of 50% by weight of polyester A and 50% by weight of polyester C. After being formed into two layers by die bonding, it was extruded and rapidly cooled at 290 ° C. to obtain an unstretched film. . The unstretched film is stretched 3.5 times in the machine direction at 100 ° C., then stretched 4.0 times in the transverse direction, and then heat-treated at 180 ° C. to obtain a polyester having a thickness of 12 μ (B layer / A layer = 3 μ / 9 μ). I got a film. Table 1 shows the properties of the polyester film.
[0016]
Example 2
A layer was polyester B alone Polyester film having a thickness of 25 μ (B layer / A layer = 3 μ / 22 μ) was obtained by the method described in Example 1 except that the B layer was 20% by weight of polyester A and 80% by weight of polyester C. Table 1 shows the properties of the polyester film.
[0017]
Example 3
A polyester film having a thickness of 25 μ (B layer / A layer = 3 μ / 22 μ) was obtained by the method described in Example 2 except that the heat treatment temperature after the transverse stretching was 210 ° C. Table 1 shows the properties of the polyester film.
[0018]
Example 4
A polyester film having a thickness of 25μ (layer B / layer A = 3μ / 22μ) was obtained by the method described in Example 1 except that the layer A was 80% by weight of polyester A and 20% by weight of polyester D. Table 1 shows the properties of the polyester film.
[0019]
Comparative Examples 1 and 2
85% by weight of polyester A and 15% by weight of polyester B were obtained by the method described in Example 1 to obtain a single-layered polyester film having a thickness of 25 μm. Table 1 shows the properties of the polyester film.
[0020]
Comparative Example 3
Polyester A 50% by weight, Polyester C 50% by weight A single-layer polyester film having a thickness of 25 μm was obtained by the method described in Example 1. Table 1 shows the properties of the polyester film.
[0021]
Comparative Example 4
Except that the layer A is composed of 20% by weight of polyester A and 80% by weight of polyester C, and the layer B is composed of 10% by weight of polyester A and 90% by weight of polyester C, a thickness of 25 μm (B layer / A layer = 3 μ / 22μ) of a polyester film was obtained. Table 1 shows the properties of the polyester film.
[0022]
Comparative Example 5
A polyester film having a thickness of 25 μ (layer B / layer A = 3 μ / 22 μ) was obtained by the method described in Example 1 except that layer A was polyester B and layer B was polyester E. Table 1 shows the properties of the polyester film.
[0023]
Comparative Example 6
Except that A layer is 85% by weight of polyester A, 15% by weight of polyester B, B layer is 15% by weight of polyester A, and 85% by weight of polyester B, a thickness of 25 μm (B layer / A layer = 3 μ / 22 μ) of a polyester film was obtained. Table 1 shows the properties of the polyester film.
After laminating Examples 1 to 4 and Comparative Examples 1 to 4 at the temperatures shown in Table 1, impact resistance and adhesion after retort treatment were evaluated.
As is clear from Table 1, the polyester films obtained in Examples 1 to 4 are excellent in impact resistance and adhesion after retort treatment. Therefore, it is of high quality as a polyester film for metal bonding.
On the other hand, the polyester films of Comparative Examples 2 to 4 are inferior in impact resistance, and the polyester films of Comparative Examples 1, 5, and 6 are remarkably inferior in adhesion after retort treatment, so that the quality is inferior as a polyester film for metal bonding.
[0024]
【The invention's effect】
As described above, the polyester composite film of the present invention is a two-layer, two-layer composite polyester film that is at least uniaxially stretched, and the melting point of each layer and the heat shrinkage of the composite film are controlled in appropriate ranges. It has excellent impact resistance at the time, and does not peel off during retort treatment. As a result, a metal can excellent in inner surface protection (flavor property, corrosion resistance) can be obtained. When the polyester film of the present invention is laminated on the inner surface of a steel sheet, the resulting metal can has not only excellent inner surface protection but also excellent outer surface aesthetics.
[0025]
[Table 1]

[Brief description of the drawings]
FIG. 1 is a schematic view of an apparatus for evaluating the degree of impact resistance after bonding a film to a steel plate.
[Explanation of symbols]
1. 1. Film Steel plate3. 4. platinum electrode 4.1% sodium chloride Ammeter 6. DC power supply

Claims (1)

Polyethylene terephthalate resins and polybutylene terephthalate melting point made of a resin is made of polyester resin composition above 220 ° C. base material layer (A layer) and a polyethylene terephthalate resin and the polyethylene ethylene terephthalate isophthalate mp consisting phthalate resin A layer at 220 ° C. or higher A composite film composed of an adhesive layer (layer B) made of a polyester resin composition having a melting point of at least 5 ° C. lower than the melting point of the composite film, wherein the heat shrinkage of the composite film is 40 gf or less. For polyester composite film.
Here, the heat shrink force means a value obtained by the following measuring method.
A sample having a width of 4 mm and a length of 20 to 30 mm was cut out from the composite film, and contracted in a load curve obtained by using a thermomechanical analyzer at a sample holder interval of 5 mm, an initial load of 5 gf, and raising the temperature from 30 ° C. at 10 ° C./min. (The shrinking force in the longitudinal and lateral directions of the composite film) was calculated, and the average value of the shrinking force in the longitudinal direction and the shrinking force in the lateral direction was calculated.

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