JPH07290665A - Polyester composite film for laminating metal - Google Patents

Abstract

PURPOSE:To provide a polyester composite film for laminating metal which has excellent impact resistance and excellent adhesive properties to metal without shrinkage and peeling due to heat history after laminating. CONSTITUTION:A polyester composite film for laminating metal is obtained by laminating a base material layer (A layer) made of polyester having a melting point of 240 deg.C or higher and an adhesive layer (B) made of polyester having a melting point of 200-235 deg.C in such a manner that a ratio (B/A) of a thickness of the A layer to a thickness of the B layer is 0.1-1.0 and a crystallization heat generation amount of the film at 110-180 deg.C is less than 0.1cal/g.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester composite film for metal laminating, and more particularly to a laminate film used for the inner surface coating of metal cans such as beverage cans and food cans.

[0002]

2. Description of the Related Art Food cans and beverage cans, in which foods and liquid contents are sealed in cans, have excellent strength, heat resistance and cold resistance. A metal material is used. When these metal cans are used for foods in particular, it is necessary to prevent so-called flavor defects in which a metallic odor is transferred to foodstuffs and beverages, which are the contents, deterioration of the contents and corrosion of the metal cans due to the contents. For this reason, laminated steel sheets obtained by heating and pressure-bonding a polyester film to a tin plate (tin-plated steel sheet), a chrome-treated steel sheet (tin-free steel), a nickel-plated steel sheet, etc. have characteristics such as strength of metal and plastic film. Has been researched as satisfying both the corrosion resistance and the barrier property of.

For example, JP-B-57-23584 and JP-B-59-34580 disclose a coated metal structure in which a specific polyester layer is formed on a metal substrate. However, these prior arts have relatively good thermal adhesiveness but poor heat resistance, relatively weak polyester layer and poor impact resistance. Therefore, especially when laminated with a steel plate at a melting point of the polyester used or higher, a local crack is generated on the film, especially on the bottom of the can, due to the impact at the time of high-speed collision with the stopper provided in the can manufacturing process line. Sometimes. On the other hand, if the temperature at the time of lamination is insufficient, cracks are unlikely to occur even when subjected to high-speed impact, but film breakage tends to occur when large deformation occurs in the can wall portion. Further, there is a problem that delamination between the can and the film occurs due to poor adhesion in the can manufacturing process and the heat treatment process before and after filling the contents.

The above problems are caused by the fact that these polyester layers for laminated steel sheets are single layers. From this point of view, it has been attempted to use a laminated film satisfying both strength and adhesiveness as a laminate film. For example, in JP-A-2-81630, a crystallization calorific value between 110 and 180 ° C. is 0.1 to 180 ° C. A polyester composite film that is 1.5 cal / g has been disclosed. However, this film has a serious problem that the film after lamination shrinks due to various heat histories in the can making process and peels from the metal material when the shrinkage is remarkable.

[0005]

SUMMARY OF THE INVENTION In the present invention, therefore, a metal having good impact resistance during can-making processing and having good adhesion without shrinkage or peeling due to heat history after lamination. An object is to provide a polyester composite film for laminating.

[0006]

The polyester composite film for metal laminating of the present invention comprises a base material layer (A layer) made of polyester having a melting point of 240 ° C. or higher and a melting point of 200 to 2
A polyester composite film in which an adhesive layer (B layer) made of polyester at 35 ° C. is laminated, and the ratio (B / A) of the thickness of the adhesive layer B layer to the thickness of the A layer which is the base layer is 0.1. ˜1.0, and 110 to 110 of the composite film.
The gist is that the crystallization heat value at 180 ° C. is less than 0.1 cal / g.

In the present invention, it is preferable that the impact resistance current value, which is an index for expressing the crack generation state with high accuracy, is 1 mA or less. It is a preferred embodiment of the present invention that the polyester constituting the base material layer contains 30 to 90% by weight of polyethylene terephthalate and the polyester constituting the adhesive layer contains 0 to 20% by weight of polyethylene terephthalate.

[0008]

Function: Melting point 240 used in the composite film of the present invention
A base material layer (A layer) made of polyester having a melting point of 200 ° C. or higher and an adhesive layer (B made of polyester having a melting point of 200 to 235 ° C.)
The layer) may be a homopolyester, a mixture thereof, or a copolyester. Polyethylene terephthalate (PET) obtained by polycondensing ethylene glycol and terephthalic acid has a high crystallinity and a high melting point around 260 ° C. Therefore, the polyester containing a large amount of PET can be used as the main constituent component of the A layer having a melting point of 240 ° C. or higher. PET is preferably contained in the layer A in an amount of 30 to 90% by weight.

Other polyester constitutional units which can be introduced by blending or copolymerization with polyethylene terephthalate include butylene terephthalate consisting of butylene glycol and terephthalic acid, ethylene isophthalate consisting of ethylene glycol and isophthalic acid, neopentyl glycol and terephthalate. Examples thereof include neopentyl terephthalate composed of an acid.

Since these constitutional units lower the crystallinity and lower the melting point, these constitutional units are copolymerized with polyethylene terephthalate (ethylene glycol and terephthalic acid), or the above constitutional units are homopolymerized or plural. When polyethylene terephthalate is blended in the form of a copolymer of structural units, the resulting polyester has a low melting point and can be used as a B layer having a melting point of 200 to 235 ° C. PET is 20 in the B layer.
It is preferably contained in an amount of not more than wt% (including 0).

In addition, 2,6-dicarboxylic acid component
Naphthalenedicarboxylic acid, adipic acid, sebacic acid, decanedicarboxylic acid, azelaic acid, dodecanedicarboxylic acid, cyclohexanedicarboxylic acid, dimer acid and the like can be used. The diol component is 1,4
-Butane diol, neopentyl glycol, hexane diol, cyclohexane dimethanol, decane diol, di, tri and polyethylene glycol, tetramethylene glycol and the like can be used. Polyester is known in the art, such as direct reaction of dicarboxylic acid and glycol, and then polycondensation after transesterification of alkyl ester of dicarboxylic acid and glycol, or polycondensation of diglycol ester of dicarboxylic acid. It can be manufactured by a method.

In the present invention, the melting point of the base material layer (A layer) is 24.
The melting point of the adhesive layer (B layer) is 200 to 235 at 0 ° C. or higher.
Must be ℃. If the melting point of the base material layer is lower than 240 ° C., the impact resistance will be poor and cracks will occur during can manufacturing. Further, if the melting point of the adhesive layer exceeds 235 ° C., the adhesion to the metal becomes poor, so that cracks and peeling also increase. When the melting point of the adhesive layer is lower than 200 ° C., the difference in melting point between the adhesive layer and the base material layer becomes large, and shrinkage due to heat history in the can manufacturing process easily occurs.

Ratio (B / A) of the thickness of the adhesive layer B layer to the thickness of the layer A which is the base material layer in the composite film of the present invention.
Is important to be 0.1 to 1.0. Within this range, the layer A can secure sufficient impact resistance, the layer B has good adhesion to metal, and the thicknesses of both layers are well balanced. No shrinkage or peeling occurs. When B / A is smaller than 0.1, the layer A is too thick or the layer B is too thin, so that shrinkage or peeling due to thermal history occurs. Also, B / A is 1.
If it exceeds 00, the thickness of the B layer becomes thicker than that of the A layer.
This is not preferable because the impact resistance of the composite film is lowered and cracks are likely to occur in the can making process. In addition, A
The preferred thickness of the layer is 5-60 μm. If it is thinner than 5 μm, it is difficult to secure impact resistance, and if it exceeds 60 μm, the whole composite film is too thick, and it tends to cause shrinkage or peeling due to heat history during can making.

In the present invention, the impact resistance current value is adopted to grasp invisible cracks. The impact resistance current value is a value obtained by laminating a film on a metal plate, then performing an impact resistance test (Dupont type), and measuring the amount of electricity passed in salt water. Specifically, the adhesive layer B layer side of the composite film was heated to 225 ° C., a tin-free steel plate (T-1,
(0.29 mm) with a water-cooled roll, and then rapidly cooled in water to form a laminated steel plate, with a tip diameter of 12.7 m.
An impactor having a weight of 1 m and a weight of 1 kg was used to apply an impact at a drop distance of 30 cm, and then the presence or absence of fine cracks generated was checked with the current-carrying device shown in FIG. In the current-carrying device, the bottom of a cylinder having a diameter of 20 mm was used as the anode by closely contacting the sample laminated steel plate after the impact test with the film surface facing upward.
Using a platinum electrode provided in the container as a cathode, a 1% sodium chloride aqueous solution was filled, and then a direct current of 6 V was applied,
The amount of current flowing is measured, and the impact resistance current value is 1 mA.
In the following cases, more preferably 0, the film has little or no cracks generated by impactors, and shows good impact resistance.

In the present invention, the composite film in which the base material layer (A layer) and the adhesive layer (B layer) are laminated is at 110 to 180 ° C.
The calorific value of crystallization must be less than 0.1 cal / g. The crystallization calorific value is a calorific value associated with crystallization, and a DSC curve was measured at a temperature rising rate of 10 ° C./min in a nitrogen stream using a differential scanning calorimeter (DSC),
The value (cal / g) obtained by dividing the heat generation amount converted from the heat generation peak area associated with crystallization at 180 ° C. by the sample weight is used as the crystallization heat generation amount. If the amount of heat generated by crystallization within the above temperature range exceeds 0.1 cal / g, shrinkage or peeling may occur due to the heat history after lamination with a metal, which is not preferable.

As the method for producing the composite film of the present invention, polyester constituting the base material layer A and the adhesive layer B are used.
Since the unstretched composite film can be obtained by extruding the polyesters constituting the layers by independent separate extruders and forming two layers outside or inside the die, a known stretching step may be performed thereafter. The unstretched film is at least uniaxially formed by a known stretching method such as a roll stretching method between rolls having a speed difference, a tenter stretching method in which a clip is held and expanded by a clip, or an inflation method in which the film is expanded in the circumferential direction by air pressure. It is oriented. The stretching conditions include, for example, 70 to 110 ° C. and 2 to 4 times in the machine direction, and then 80
Although it can be stretched 3 to 5 times in the transverse direction at 110,
The conditions can be changed appropriately according to the stretching method. Further, in the present invention, it is preferable to perform heat treatment at 120 to 230 ° C. after stretching.

The metal-bonded polyester composite film of the present invention can be manufactured through the above steps. The metal to be bonded is not particularly limited, but examples thereof include tin plates (tin-plated steel plates) for metal cans, chrome-treated steel plates (tin-free steel), and nickel-plated steel plates. The lamination temperature is preferably 240 ° C. or lower, which is lower than the melting point of the polyester of the base material layer A, because the impact resistance of the layer A can be secured.

The polyester composite film for metal laminating of the present invention secures impact resistance by the presence of the high melting point base material layer A layer, and exhibits good adhesion to metal by the presence of the adhesive layer B layer. In addition, since the amount of heat generated by crystallization when the composite film is formed is less than 0.1 cal / g, shrinkage or peeling does not occur due to thermal history even after lamination with the steel sheet. In the composite film, known additives, antioxidants, heat stabilizers, ultraviolet absorbers, plasticizers, inorganic particles, inorganic / organic lubricants, pigments, antistatic agents, etc. may be added as necessary. It may be dispersed and mixed.

[0019]

The present invention will be described in more detail with reference to the following examples, but the following examples do not limit the present invention.
All modifications and implementations that do not depart from the spirit of the description below are included in the technical scope of the present invention.

The measurement / evaluation methods used in the examples are as follows. 1) Melting point The composition of each layer was heated and melted at 300 ° C. for 5 minutes, mixed, and then rapidly cooled with liquid nitrogen.
10 using a differential scanning calorimeter (DSC) in a nitrogen stream
The DSC curve was measured at a temperature rising rate of ° C / min, and the peak temperature of the endothermic peak associated with melting was taken as the melting point.

2) Crystallization calorific value A DSC curve was measured in the same manner as in the above melting point measurement using a film state sample as a sample, and the calorific value converted from the exothermic peak area accompanying crystallization at 110 to 180 ° C. The value obtained by dividing by the sample weight was taken as the heat value for crystallization (cal / g).

3) Impact resistance evaluation The adhesive layer B side of the composite film was pressure-bonded to a tin-free steel plate (T-1, 0.29 mm) heated to 225 ° C. with a water-cooled roll, and then rapidly cooled in water to obtain a laminated steel plate. Was prepared, and a DuPont type impact test was performed using this as a sample. Using an impactor having a tip diameter of 12.7 mm and a weight of 1 kg, after applying an impact at a drop distance of 30 cm, the presence or absence of fine cracks generated was checked with the current-carrying device shown in FIG. A sample laminated steel plate after the impact test was adhered to the bottom of the cylinder with a diameter of 20 mm with the film surface facing upwards to serve as an anode, and a platinum electrode provided in the container was used as a cathode, and a 1% sodium chloride aqueous solution was filled, and then a direct current of 6 V was applied. A current was applied and the amount of current that flowed was measured. The smaller the amount of current, the smaller the number of cracks caused by impactors in the film, and the better the impact resistance.

4) Shrinkage due to heating and presence / absence of peeling Laminated steel sheets similar to those used in the above impact resistance evaluation were cut into a film surface of a sample cut into 3 cm × 3 cm,
A diagonal line was cut with a cutter, and the shrinkage state of the film after heating at 230 ° C. for 10 minutes was evaluated at the distance shown in FIG. Further, the presence or absence of peeling was visually evaluated.

The abbreviations and contents of the polyesters used in the following examples and comparative examples are as follows. PET: Polyethylene terephthalate PBT: Polybutylene terephthalate PETI10: Ethylene terephthalate / ethylene isophthalate copolymer (10 mol% repeating units of ethylene isophthalate) PETI22: Ethylene terephthalate / ethylene isophthalate copolymer (22 mol% repeating units of ethylene isophthalate) PENPT : Terephthalic acid and ethylene glycol / neopentyl glycol copolymer (neopentyl glycol content in the glycol component is 30 mol%)

EXAMPLE 1 85% by weight of PET and 15% of PETI10 were added to the base layer A layer.
Polyester containing weight% of PETI as the adhesive layer B layer
Only 10 was used. After making both layers by die outside bonding,
It was extruded at 290 ° C. and rapidly cooled to obtain an unstretched film. This unstretched film was stretched 3.5 times in the longitudinal direction at 100 ° C.,
Then, the film was stretched in the transverse direction by 4.0 times and then heat-treated at 200 ° C. to obtain a polyester composite film having an overall thickness of 25 μm. At this time, the A layer is 22 μm and the B layer is 3 μm.
μm, and the ratio of B layer / A layer was 0.14. Table 1 shows the characteristic results evaluated by the measurement method.

EXAMPLE 2 40% by weight of PET and 60% of PETI10 were added to the base layer A layer.
The total thickness is 25 μm (B layer / A layer = 3 μm / 22) in the same manner as in Example 1 except that the polyester containing the weight% is used.
A polyester composite film of μm = 0.14) was obtained.
The characteristic evaluation results are shown in Table 1.

Example 3 In the same manner as in Example 1 except that polyester containing 80% by weight of PET and 20% by weight of PBT was used for the base layer A,
Overall thickness 25 μm (B layer / A layer = 3 μm / 22 μm =
A polyester composite film of 0.14) was obtained. The characteristic evaluation results are shown in Table 1. Example 4 A total thickness of 20 μm was obtained by combining the layers A and B of Example 1.
A polyester composite film of (B layer / A layer = 10 μm / 10 μm = 1.0) was obtained. The characteristic evaluation results are shown in Table 1.

Example 5 40 wt% of PET and 60 of PETI10 were added to the base layer A layer.
Polyester containing 2% by weight is used, and PET2 is used for the adhesive layer B layer.
The total thickness is 20 μm in the same manner as in Example 1 except that a polyester containing 0% by weight and 80% by weight of PETI 22 is used.
m (B layer / A layer = 10 μm / 10 μm = 1.0) to obtain a polyester composite film. The characteristic evaluation results are shown in Table 1.

Comparative Example 1 Only PETI 10 was manufactured in the same manner as in Example 1 and had a thickness of 25 μm.
m as a single-layer polyester film. The characteristic evaluation results are shown in Table 1. Comparative Example 2 The base layer A layer was PETI10 alone, and the adhesive layer B layer was PE.
An overall thickness of 2 was obtained in the same manner as in Example 1 except that a polyester containing 50% by weight of T50 and 50% by weight of PETI22 was used.
A polyester composite film of 5 μm (B layer / A layer = 3 μm / 22 μm = 0.14) was obtained. Table 1 shows the characteristic evaluation results.
It was shown to.

COMPARATIVE EXAMPLE 3 The entire thickness was 25 μm (B layer / A layer = 3 μm / 22 μm) in the same manner as in Example 1 except that polyester containing 40% by weight of PET and 60% by weight of PETI was used for the B layer of the adhesive layer.
A polyester composite film having m = 0.14) was obtained. The characteristic evaluation results are shown in Table 1.

Comparative Example 4 The entire thickness was 25 μm (B layer / A layer = 3 μm / 2) in the same manner as in Example 1 except that the adhesive layer B layer was made of PENPT only.
A polyester composite film having a thickness of 2 μm = 0.14) was obtained. The characteristic evaluation results are shown in Table 1.

Comparative Example 5 An overall thickness of 25 was obtained in the same manner as in Example 1 except that the adhesive layer B layer was 10 wt% PET and the PETI 22 was 90 wt%.
A polyester composite film of μm (B layer / A layer = 15 μm / 10 μm = 1.5) was obtained. The characteristic evaluation results are shown in Table 1.

Comparative Example 6 Same as Example 1 except that the base layer A layer was PET alone, the adhesive layer B layer was 20 wt% PET, PETI 22 was 80 wt% and the heat treatment temperature after transverse stretching was 240 ° C. Total thickness 25 μm (B layer / A layer = 3 μm / 22 μm = 0.
A polyester composite film of 14) was obtained. The characteristic evaluation results are shown in Table 1.

[0034]

[Table 1]

It can be seen that the composite films of Examples 1 to 5 have excellent impact resistance and do not shrink or peel even when heated. In Comparative Example 1, the A layer defined in the present invention was not present, and in Comparative Example 2, the melting point of the A layer was low, and thus the impact resistance was poor. In Comparative Example 3, since the B layer has a high melting point, the rigidity of the entire film is high, the adhesion to metal is poor, and the impact resistance is poor. Further, it can be seen that the amount of shrinkage after heating is large. In Comparative Example 4, since the melting point of the B layer is low, the amount of shrinkage due to heating is large. Comparative Example 5 is A
Since the thickness of the B layer is too large compared to the layer, the impact resistance is poor and the shrinkage amount after heating is large. In Comparative Example 6, since the melting point of the B layer was low and the amount of heat generated by crystallization was large, both impact resistance and the amount of shrinkage after heating were poor.

[0036]

EFFECT OF THE INVENTION Since the polyester composite film for metal laminating of the present invention is constituted as described above, it is excellent in impact resistance and shrinks or peels off even if heat history after lamination is applied. It is a film having good adhesiveness to metal, which has no The polyester composite film of the present invention is used by being stuck to a metal for beverage cans and food cans, and has an effect of protecting the inner wall of the can, preventing flavor defects inside the can, corrosion of metal, and denaturation of contents. It is also a high-performance composite film that can withstand heat sterilization (retort) treatment after can making.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a current-carrying test device in a shock resistance test.

FIG. 2 is an explanatory diagram showing measurement points of a heat shrinkage amount.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nagano 344 Maebata, Kizu character, Inuyama City, Aichi Prefecture Inuyama Plant, Toyobo Co., Ltd. (72) Inventor Akira Matsuda 344 Maebata, Kizu character, Inuyama City, Aichi Prefecture Toyobo Co., Ltd. Inuyama Factory

Claims (3)

[Claims] 1. A polyester composite film in which a base material layer (A layer) made of polyester having a melting point of 240 ° C. or higher and an adhesive layer (B layer) made of polyester having a melting point of 200 to 235 ° C. are laminated. The ratio (B / A) of the thickness of the adhesive layer B layer to the thickness of the layer A that is the base material layer is 0.1 to 1.
0, and the calorific value of crystallization at 110 to 180 ° C. of the composite film is less than 0.1 cal / g. 2. The composite film according to claim 1, which has an impact resistance current value of 1 mA or less. 3. The composite film according to claim 1, wherein the polyester constituting the substrate layer contains 30 to 90% by weight of polyethylene terephthalate, and the polyester constituting the adhesive layer contains 0 to 20% by weight of polyethylene terephthalate.