JPH07290666A - Polyester composite film for laminating metal - Google Patents

Abstract

PURPOSE:To provide a polyester composite film for laminating metal which has excellent heat resistance, defomtation resistance, impact resistance and adhesive properties and in which no wrinkle occurs even at the time of heat treating. CONSTITUTION:A polyester composite' film for laminating metal comprises a laminated structure of an A layer, a B layer, a C layer and a D layer, wherein the A layer is made of polyester having a crystallization temperature Tc2 is 150 deg.C or higher, the B layer is formed of polyester having a melting point Tm of 190-225 deg.C and a glass transition temperature Tg of 50 deg.C or higher, and the C layer is formed of polyester having Tg of 30-50 deg.C.

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, it is used for the inner surface coating of metal cans such as beer cans, beverage cans and aerosol cans having a long can wall. Laminated film.

[0002]

2. Description of the Related Art For metal cans, steel materials such as tin and tin-free steel and metal materials such as aluminum are used because of their excellent strength, heat resistance and cold resistance. These metal cans, especially when used for food applications,
It is necessary to prevent so-called flavor defects in which a metallic odor is transferred to foodstuffs and beverages that are the contents, deterioration of the contents and corrosion of the metal can itself 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, Japanese Patent Publication Nos. 57-23584 and 59-34580 disclose coated metal structures 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. For this reason, especially when laminated with a steel plate at a melting point of the polyester used or higher, a local crack may be generated on the film, especially on the bottom of the can, due to the impact at the time of high-speed collision with a stopper provided in the can manufacturing process line. There is. 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.

Therefore, it has been attempted to secure deformation resistance and impact resistance by using a substantially amorphous polyester to improve the flexibility of the film. However, such an amorphous film, when being processed by a die and a punch during the can making process, adheres to the punch due to frictional heat generated during processing, and as a result, the film on the can wall is torn and torn. It often happened. Further, there is a problem that the mark of the carrier pin is left in the heat treatment step after the can manufacturing process, and the commercial value of the metal can is reduced.

For the purpose of improving these heat resistance deficiencies, it has been attempted to use a laminated film satisfying both strength and adhesiveness as a laminated film.
No. -81630 discloses a polyester composite film having a crystallization calorific value in the range of 110 to 180 ° C. of 0.1 to 1.5 cal / g. However, this film has a poor balance between the surface layer that secures heat resistance and the lower layer that secures adhesion, and the problem that the film after lamination shrinks due to various heat histories in the can making process, or wrinkles occur, and metal. In particular, the adhesiveness to tin is poor, and there remains a problem that film peeling and cracks are likely to occur on the can wall and the bottom.

[0006]

Therefore, the present invention provides a polyester composite film for metal laminating which is excellent in heat resistance, deformation resistance, impact resistance and adhesion and does not cause wrinkles during heat treatment. To aim.

[0007]

The polyester composite film for metal laminating of the present invention is a polyester composite film having a structure in which three layers of A layer, B layer and C layer are laminated,
The A layer is made of polyester having a crystallization temperature Tc ₂ of 150 ° C. or higher, and the B layer has a melting point Tm of 190 to 225 ° C.
The glass transition temperature Tg is made of polyester having a temperature of 50 ° C. or higher, and the C layer is made of polyester having a Tg of 30 to 50 ° C. It is a preferred embodiment of the present invention that the polyester constituting the A layer is a polyester using only terephthalic acid as the acid component, and the polyester constituting the B layer and the C layer includes a polyester using isophthalic acid as the acid component. is there.

[0008]

The composite polyester film of the present invention comprises an A layer for imparting heat resistance to the composite film, a B layer for imparting impact resistance and deformation resistance, and a C layer having excellent adhesion to metal.
The point is that the layer structure is used and the temperature characteristics of the polyester constituting each layer are specified.

First, the layer A is the layer that becomes the outermost surface after being laminated with a metal. The layer A is a polyester layer having excellent heat resistance and needs to have a crystallization temperature Tc ₂ of 150 ° C. or higher. When Tc ₂ is less than 150 ° C., defects such as sticking of the punch and the film during can making and traces of the transport pin left on the film during the heat treatment may result in insufficient heat resistance. The higher the Tc ₂ heat resistance will be more improved, no longer can accommodate deformation during rigidity is increased can-processing film when Tc ₂ exceeds 200 ° C., cracks in the can wall. Further, Tc ₂ is preferably set to 200 ° C. or lower because the film forming property is remarkably lowered. The thickness of the layer A is not particularly limited, but is preferably 1 to 10 μm. If it is thinner than 1 μm, it cannot fulfill its role as a heat resistance ensuring layer, and if it is too thick, the deformation resistance deteriorates. A more preferable thickness is 2 to 7 μm.

The B layer has a function of ensuring both the deformation resistance and the impact resistance. The melting point Tm of the B layer is 190 to 225.
The glass transition point Tg must be 50 ° C. or higher. When polyester within this range is used for the B layer, cracks do not occur in the can wall and the can bottom, and the impact resistance is also excellent. However, if the melting point Tm exceeds 225 ° C., the deformation resistance during can manufacturing is reduced and the frequency of cracks increases, which is not preferable. Tm of layer B is 190 ° C
When the temperature is lower or Tg is lower than 50 ° C., cracking does not occur, but when the balance of thermal properties with the A layer is poor and the film is laminated with a steel sheet,
Wrinkles are easily formed on the film during the heat treatment after can making. Therefore, the commercial value of the metal can is significantly reduced, which is not preferable. The thickness of the B layer is 5 in order to exert impact resistance.
It is preferably at least μm. However, if it exceeds 100 μm, the deformation resistance deteriorates. More preferably, it is 20 to 50 μm.

The C layer is a layer provided for exhibiting adhesion with a metal, and it is essential that the polyester constituting the C layer has a Tg of 30 to 50 ° C. If the Tg of the C layer is too high, the adhesion to the metal steel sheet, especially the tin plate is deteriorated, and film peeling occurs on the wall of the can, causing cracks starting from this peeled portion. The lower the Tg of the C layer, the more flexible the film is, so the adhesion is improved, but when the Tg is less than 30 ° C, the A layer and the B layer are
Since the thermal properties of the layers are poorly balanced, wrinkles are easily formed on the film in the heat treatment step after the can-making process. C
Although the thickness of the layer is not particularly limited, it is preferably about 1 to 10 μm.

A layer used in the composite film of the present invention,
Polyethylene terephthalate (PET) obtained by polycondensing ethylene glycol and terephthalic acid has a high crystallization temperature and a high melting point, and thus the polyester constituting the B layer and the C layer can be used as a constituent component of the A layer. Polyesters containing terephthalic acid as an acid component, such as polybutylene terephthalate composed of butylene glycol and terephthalic acid, and polyester composed of butanediol and terephthalic acid, are useful as A layer constituents which have high crystallinity and can exhibit heat resistance. Is. In addition, other dicarboxylic acid components and diol components described later may be used in combination as long as the crystallization temperature Tc ₂ does not deviate from the specified range.

It is known that polyethylene terephthalate isophthalate, which is composed of ethylene glycol, terephthalic acid, and isophthalic acid, has a higher molecular chain mobility and a lower melting point than PET. Therefore, by increasing the copolymerization ratio of the isophthalic acid component, a copolymerized polyester having a lowered melting point or Tg can be obtained. These polyesters may be used alone or in a mixture with the above-mentioned terephthalic acid-based polyester to form a B layer or a C layer.
The polyester forming the layers can be obtained. Other usable acid components include 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, decanedicarboxylic acid, azelaic acid, dodecanedicarboxylic acid, cyclohexanedicarboxylic acid, dimer acid and the like, and the diol component includes 1,4-butanediol, neopentyl glycol, hexanediol, cyclohexanedimethanol, decanediol, di-, tri- and polyethylene glycol, tetramethylene glycol and the like can be used.

The above polyester is obtained by directly reacting a dicarboxylic acid with a glycol and then subjecting the alkyl ester of the dicarboxylic acid to the glycol with an ester exchange reaction followed by polycondensation, or polycondensing the diglycol ester of the dicarboxylic acid. It can be produced by a known method such as.

As the method for producing the composite film of the present invention, the polyesters constituting the A layer, the B layer and the C layer are extruded by independent extruders, respectively, and three layers are formed outside or inside the die. Since an unstretched composite film is obtained by the above, 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, stretching at 70 to 110 ° C. in the longitudinal direction by 2 to 4 times, and then at 80 to 110 at 3 to 4 in the transverse direction.
The film can be stretched 5 times, but the conditions can be appropriately changed depending on the stretching method. It is preferable to perform heat treatment after stretching, preferably at 120 to 240 ° C.

The polyester composite film for metal laminating 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 laminating temperature is preferably higher than the melting point of the polyester of the B layer from the viewpoint of exhibiting the characteristics of each layer.

The polyester composite film of the present invention comprises:
If necessary, known additives, antioxidants, heat stabilizers, ultraviolet absorbers, plasticizers, inorganic particles, inorganic / organic lubricants,
It is also possible to disperse and blend pigments, antistatic agents, and the like.

[0018]

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 and evaluation methods used in the examples and comparative examples are as follows. 1) Crystallization temperature A polyester composition for the layer A was heated and melted at 300 ° C. for 5 minutes and then rapidly cooled with liquid nitrogen to obtain 10 mg of a sample, which was used in a nitrogen stream using a differential scanning calorimeter (DSC). When the exothermic / endothermic curve (DSC curve) was measured at a temperature rising rate of 10 ° C./min, the peak temperature of the exothermic peak accompanying crystallization was taken as the crystallization temperature Tc ₂ (° C.).

2) Melting point and glass transition point A polyester composition for layers B and C was prepared at 300 ° C. for 5 hours.
After heating and melting for 10 minutes, 10 mg of a sample obtained by quenching with liquid nitrogen was used, and a differential scanning calorimeter (DS
C) is used to measure the exothermic / endothermic curve (DSC curve) at a temperature rising rate of 10 ° C./min, the apex temperature of the endothermic peak associated with melting is defined as the melting point Tm (° C.), and 0 to 100 ° C. Two tangents were drawn on the endothermic change curve, and the intersection was taken as the glass transition point Tg (° C).

3) Evaluation of state after can making The polyester composite films obtained in Examples 1 to 6 and Comparative Examples 1 to 7 described below were heated to 220 ° C. tinplate (T-).
1, # 25 / # 25, thickness 0.29 mm) was pressure-bonded with a water-cooled roll and then rapidly cooled in water to produce a laminated steel plate. This laminated steel sheet was drawn and ironed to produce 10 metal cans with a diameter of 211 mm, and the state of adhesion between the punch and the film, film peeling, and the state of cracks in the can wall and can bottom were visually observed. .

4) Evaluation of wrinkle generation state after heat treatment The wrinkle generation state was visually observed after heating the above 10 metal cans at 200 ° C. for 5 minutes in a hot air dryer. 5) Heat resistance (presence or absence of traces of weight) 100 g of weight is placed on a sample obtained by cutting a laminated steel plate into 5 cm x 5 cm, and the generation state of traces of weight is visually observed after heating at 200 ° C for 5 minutes. I observed.

The abbreviations and contents of the polyesters used in the following examples and comparative examples are as follows. PET: Polyethylene terephthalate PBT: Polybutylene terephthalate PETI15: Polyethylene terephthalate / isophthalate (15 mol% repeating units of ethylene isophthalate) PETI22: Ethylene terephthalate / isophthalate (22 mol% repeating units of ethylene isophthalate) PETI50: Polyethylene terephthalate Isophthalate (repeating unit of ethylene isophthalate: 50 mol%) PTIAB: terephthalic acid / isophthalic acid / adipic acid (mol% ratio 65/10/25) and butanediol (1
Copolyester with PDB: terephthalic acid / dimer acid (molar ratio 9
Copolymerized polyester of 1/9) and butanediol (100 mol%) PENT: terephthalic acid (100 mol%) and ethylene glycol / neopentyl glycol (molar ratio 70)
/ 30)

Example 1 PET alone as the A layer, PETI15 alone as the B layer,
70% by weight of PETI22 and 3 of PTIAB as C layer
Using 0% by weight of polyester, each layer-constituting polyester was formed into three layers by die outside bonding, and then 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 95 ° C., then 4.0 times in the transverse direction at 95 ° C., and then heat-treated at 180 ° C. to give a polyester composite film having a total thickness of 30 μm. Obtained. At this time, the A layer was 3 μm, the B layer was 25 μm, and the C layer was 2 μm. Table 1 shows the characteristic results evaluated by the measurement method.

Example 2 As in Example 1, except that PBT alone was used as the A layer, the total thickness was 30 μm (A layer / B layer / C layer = 3/2).
A polyester composite film of 5/2 μm) was obtained. The characteristic results are shown in Table 1.

Example 3 The total thickness was 30 μm (A layer / B layer / C layer = 3/2) in the same manner as in Example 1 except that PDB alone was used as the A layer.
A polyester composite film of 5/2 μm) was obtained. The characteristic results are shown in Table 1. Example 4 A polyester composite film having an overall thickness of 30 μm (A layer / B layer / C layer = 3/25/2 μm) was obtained in the same manner as in Example 1 except that PETI22 was used alone as the B layer. The characteristic results are shown in Table 1.

Example 5 The total thickness was 30 μm (A layer / B layer / C layer = 3 /) in the same manner as in Example 1 except that polyester containing 80% by weight of PETI22 and 20% by weight of PBT was used as the B layer. Two
A polyester composite film of 5/2 μm) was obtained. The characteristic results are shown in Table 1. Example 6 80% by weight of PETI22 as a C layer, PTIAB2
The total thickness was 30 μm (A layer / B layer / C layer = 3) in the same manner as in Example 1 except that 0% by weight of polyester was used.
/ 25/2 μm) of a polyester composite film was obtained.
The characteristic results are shown in Table 1.

Comparative Example 1 A layer having a thickness of 30 was prepared in the same manner as in Example 1 except that the C layer was not provided.
A two-layer polyester film of μm (A layer / B layer = 3/27 μm) was prepared. The characteristic results are shown in Table 1. Comparative Example 2 A layer having a thickness of 30 was prepared in the same manner as in Example 1 except that the B layer was not provided.
A two-layer polyester film having a thickness of μm (A layer / C layer = 3/27 μm) was prepared. The characteristic results are shown in Table 1.

Comparative Example 3 A layer having a thickness of 30 was prepared in the same manner as in Example 1 except that the layer A was not provided.
A two-layer polyester film having a thickness of μm (B layer / C layer = 28/2 μm) was prepared. The characteristic results are shown in Table 1. Comparative Example 4 The total thickness was 30 μm (A layer / B layer / C layer = 3/25 /) in the same manner as in Example 1 except that the C layer was PENT alone.
A polyester composite film of 2 μm) was obtained. The characteristic results are shown in Table 1.

Comparative Example 5 The whole thickness was 30 μm (A layer / B layer / C layer = 3 /) in the same manner as in Example 1 except that polyester containing 50% by weight of PET and 50% by weight of PETI22 was used as the B layer. Two
A polyester composite film of 5/2 μm) was obtained. The characteristic results are shown in Table 1.

Comparative Example 6 The entire thickness was 25 μm (B layer / A layer = 3 μm / 22 μm) in the same manner as in Example 1 except that PENT alone was used as the B layer.
To obtain a polyester composite film of 0.14). The characteristic results are shown in Table 1. Comparative Example 7 The total thickness was 30 μm (A layer / B layer / C layer = 3/2) in the same manner as in Example 1 except that PET containing 60% by weight of PET and 40% by weight of PETI50 was used as the A layer.
A polyester composite film of 5/2 μm) was obtained. The characteristic results are shown in Table 1.

[0032]

[Table 1]

The polyester composite films of Examples 1 to 6 of the present invention were excellent in heat resistance and had no punch adhesion and no trace of weight. In addition, film peeling after can making, cracking at the can wall and can bottom, and generation of wrinkles after heat treatment were not observed, indicating that this is a high-performance laminated steel sheet.

On the other hand, in Comparative Example 1, since there was no C layer, the adhesion to tin was poor, and film peeling and cracking of the can wall were observed in 50% of metal cans. In Comparative Example 2 in which the B layer was not provided and only the A layer and the C layer had a two-layer structure, wrinkles were observed to be generated during heat treatment in 60% of the metal cans because the balance of the thermal properties of the two layers was poor. In Comparative Example 3 without the A layer, defects such as punch adhesion and trace weight adhesion due to insufficient heat resistance occurred.

Although Comparative Examples 4 to 7 have a three-layer structure, none of them satisfy the thermal characteristics of each layer defined by the present invention. In Comparative Example 4, the Tg of the C layer for ensuring the adhesion is Is too high, film peeling and can wall cracking occurred in all metal cans. Comparative Example 5 in which the Tm of layer B is too high
Has poor deformation resistance, so that cracking is particularly remarkable at the can wall. On the contrary, Comparative Example 6 in which the Tm of the B layer is too low
Was observed in 80% of the metal cans during the heat treatment.
In Comparative Example 7, it is clear that the crystallization temperature Tc ₂ of the A layer is too low to ensure heat resistance.

[0036]

EFFECT OF THE INVENTION Since the polyester composite film for metal laminating of the present invention is constituted as described above, it is to provide a laminated steel sheet excellent in heat resistance, deformation resistance, impact resistance and adhesion. You can In addition, since the thermal properties of the respective layers are well balanced, wrinkles do not occur on the film even in the heat treatment step after can making. Therefore, the laminated steel sheet using the film of the present invention does not cause defects in the actual line, such as sticking to the punch during can manufacturing and trace-shaped adhesion of the transport pin. Further, since it has good adhesion and deformation resistance even in a can having a long can wall portion, it was possible to provide a very high-performance and useful film as an internal protective film for a metal can.

 ─────────────────────────────────────────────────── ─── 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 (2)

[Claims] 1. A polyester composite film having a structure in which three layers, an A layer, a B layer and a C layer, are laminated, wherein the A layer is made of polyester having a crystallization temperature Tc ₂ of 150 ° C. or higher. Has a melting point Tm of 190 to 225 [deg.] C. and a glass transition temperature Tg of 50 [deg.] C. or higher, and the layer C comprises a polyester having a Tg of 30 to 50 [deg.] C. . 2. The polyester constituting the layer A is a polyester using only terephthalic acid as an acid component, and the polyester constituting the layers B and C is a polyester using terephthalic acid and isophthalic acid as acid components. The composite film according to claim 1.