JPH0542643A - Film for metal laminate - Google Patents

Abstract

PURPOSE:To obtain a film for metal laminate improved in adhesive properties with metal plates, molding properties, and heat resistance. CONSTITUTION:A title film is composed of at least two layers and laminated on a metal at one surface thereof for use. This film is made of a biaxially oriented polyester film. A melting point (TmA) of a surface layer (A) at which the film is to be laminated on the metal is determined to be 170-220 deg.C. A melting point (TmB) of a surface layer (B) at which the film is not to be laminated on the metal is 220-255 deg.C.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a film for metal laminating. More specifically, it relates to a biaxially stretched polyester film which can withstand squeezing and ironing for forming a metal can after being laminated with a polyester film and a metal plate.

[0002]

2. Description of the Related Art A paint is generally applied to prevent corrosion of the inner and outer surfaces of a metal can, and a thermosetting resin is used as the paint.

Furthermore, there is a method using a thermoplastic resin. For example, it has been attempted to laminate a polyolefin film on a heated tein-free steel or a polypropylene resin. Further, it has been studied to laminate a biaxially oriented polyethylene terephthalate film having better heat resistance on a metal plate.

[0004]

The thermosetting resin coating composition is coated with a coating suitable for the intended use, but most of them are solvent-based coatings, and it takes a long time of several minutes to form the coating film and 150 coatings.
Heating at a high temperature of up to 250 ° C is required, and a large amount of organic solvent is scattered during baking. Further, it is necessary to pay attention to cracks, corrosion resistance and pinholes during severe processing.

When a thermoplastic resin film is used, these problems can be solved, but when laminating with an adhesive, the problems of solvent scattering and residual solvent remain as in the coating method. In some cases, no adhesive is used. For example, there is a method of laminating a polyethylene film on a heated tin-free steel, but polyethylene has a low melting point and may be whitened and peeled off when subjected to retort treatment.

In this respect, the biaxially oriented polyester film is excellent in mechanical properties and heat resistance and therefore has no problem even if it is subjected to retort treatment, and thus has been recently studied.

As a method of laminating, (1) a method of laminating an oriented polyester film on a metal plate and at the same time thermocompression bonding at a temperature of glass transition point of polyester + 80 ° C. to melting point, (2) adhesion start temperature of thermoplastic resin film A method of temporarily adhering to a metal plate heated to a temperature (T1) higher by 20 to 80 ° C., reheating at a temperature of T1 +20 to 80 ° C. to completely fuse and then quenching, (3) polyester film Method of laminating on a metal plate heated to a melting point to a melting point + 160 ° C. and quenching (Japanese Patent Laid-Open No. 58-82).
717) and so on.

The biaxially oriented polyester film laminated metal sheet laminated by these methods has poor formability and the adhesion between the metal sheet and the film is insufficient.

[0009]

Means for Solving the Problems As a result of intensive studies to solve this problem, the present invention has been achieved. That is, the present invention is a film made of a polyester resin stretched in a biaxial direction, which is used by laminating at least two layers on one side of a metal, and is used on the side of the side to be laminated on the metal. The melting point (TmA) of the surface layer (A) is 170 ° C. or higher and 220 ° C. or lower, and the melting point (TmB) of the surface layer (B) on the side not laminated to the metal.
) Is 220 ° C. or higher and 255 ° C. or lower, a film for metal laminating.

The film of the present invention must have at least a two-layer structure. Unless it has at least a two-layer structure, the adhesiveness to the metal plate and the heat resistance of the outer layer, that is, the surface not in contact with the metal plate are not compatible. Further, if the heat resistance is emphasized in a single-layer film, the moldability will deteriorate, which is not preferable.

The melting point (TmA) of the surface layer (A) to be laminated on the metal is in the range of 170 to 220 ° C, preferably 180 to 210 ° C. When the temperature is lower than 170 ° C., the heat treatment temperature is correspondingly lowered and the heat shrinkage ratio is increased, which is inconvenient when laminating with a metal.
If it exceeds 220 ° C, the adhesiveness to a metal deteriorates, leading to coating film defects caused by this.

The melting point (Tm B) of the surface layer (B) on the side not laminated with metal is therefore 220 to 255.
It is a polyester resin in the range of ° C. If it is less than 220 ° C, it tends to be a defect such as softening and scratches when added in post-processing. In addition, the moldability of the mold from the molded product deteriorates during molding. If it exceeds 255 ° C, the moldability is not good.

The thickness (tA) of the surface layer (A) on the side to be laminated on the metal and the thickness (tB) of the surface layer (B) on the side not to be laminated are preferably tA> tB, More preferably, tA> 2tB. t
If A ≦ tB, the moldability tends to deteriorate.

The glass transition temperature (Tg) of each of the polyester (A) and the polyester (B) constituting the layer (A) and the layer (B) is preferably 55 to 80 ° C.
If the temperature is below 55 ° C, the workability during film formation is poor, and 80 ° C
If it exceeds, the moldability will be poor.

The polyester used in the present invention is represented by polyethylene terephthalate obtained by condensation polymerization of dicarboxylic acid and diol.

Examples of the dicarboxylic acid used herein include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, decanedicarboxylic acid, azelaic acid, dodecadicarboxylic acid, cyclohexanedicarboxylic acid, etc. It is a mixture, and as the diol, ethylene glycol, butane diol, hexane diol, neopentyl glycol, 1,4 cyclohexane dimethanol, decane diol, 2-ethyl-2-butyl-1. -Propanediol or the like, either alone or as a mixture. Further, copolymers of two or more kinds of dicarboxylic acids and diols, and other monomers such as diethylene glycol, triethylene glycol and polyethylene glycol.
Alternatively, a copolymer with a polymer or the like may be used. If necessary, additives such as antioxidants, heat stabilizers, ultraviolet absorbers, plasticizers, inorganic particles, organic particles, organic lubricants, pigments and antistatic agents can be dispersed and blended.

The conventional biaxially oriented polyester film is very excellent in mechanical properties, heat resistance and dimensional stability as represented by polyethylene terephthalate film. However, in order to laminate the polyester film to the metal, the metal plate is heated to a temperature around the melting point of the film, and the film is laminated to this, so if the melting point of the film is high, the adhesion between the film and the metal is poor and this is formed. Property and defects after molding.

The film of the present invention can be manufactured at once by one continuous process as described below, but is not necessarily limited thereto.

The polyester (A) on the surface to be adhered to the metal surface and the polyester (B) on the surface not to be adhered are supplied to different extruders to be melted and merged in a pipe,
The polymer melt is extruded from the die and cooled and solidified on a cooling drum. If necessary, it may be stretched in the longitudinal direction or the width direction and heat-treated. Polyester (A)
As (B), those obtained by copolymerizing diol such as butanediol and hexanediol and dicarboxylic acid such as adipic acid and isophthalic acid are very effective. The unstretched film which has been cooled and solidified on the cooling drum is stretched, but its magnification is 2 to 6 times, preferably 3 to 5 times. The heat treatment after stretching is carried out if necessary, but is appropriately selected depending on the kind and melting point of the polymer. The film thickness is preferably 6 to 250 μm, but the frequently used range is 12 to 50 μm, and more preferably 1
It is 6 to 35 μm. If it is less than 12 μm, it becomes thinner after molding, resulting in defects such as pinholes and cracks, and there is a risk that the corrosion resistance deteriorates. If it exceeds 50 μm, there is no such risk, but it is not economical and the internal stress of the film itself becomes larger than the adhesive force with the metal plate, and the adhesive property with the metal plate becomes a concern.

The metal plate is made of tin metal, aluminum, steel or the like which is commonly used for canning. The thickness of the metal plate is generally 0.20 to 0.50 mm, further 0.22
0.35 mm is desirable.

[0021]

EXAMPLES The characteristic values of the present invention are based on the following measuring methods.

(1) Melting point (Tm), glass transition temperature (T
g) Obtained using a differential scanning calorimeter DSC2 (manufactured by Perkin Elmer). In the measurement, 10 mg of a sample is melted and held under a nitrogen stream at 280 ° C. for 5 minutes, and then cooled at a cooling rate of 320 ° C./minute. 1 for the sample thus obtained
When the temperature was raised at a heating rate of 0 ° C./min, the change in specific heat due to the transition from the glass state to the rubber state was read, and this temperature was taken as the glass transition temperature (Tg). Further, the endothermic peak temperature based on crystal melting was taken as the melting point (Tm).

(2) Adhesive property A rubber roll was press-bonded to a heatable metal roll, and a polyester film and a metal plate were superposed between them and passed at a pressure of 20 kg / cm and a speed of 3 m / min. The temperature of the metal roll was 180 ° C. The adhesive strength (lamination strength) of the laminated product of the film and the metal plate after passing was measured by Tensilon. ◯: Laminate strength is 200 g / cm or more ×: Laminate strength is less than 200 g / cm

(3) Heat resistance The heat resistance was judged by measuring the friction coefficient according to ASTM-D1894. That is, the surface of the 80 × 150 mm sample film that does not come into contact with the metal (the B surface) and the chrome-plated steel heated to 120 ° C. are superposed on each other, and 200 is placed thereon.
The coefficient of friction is the value obtained by dividing the tension when the lower steel is pulled at 200 mm / min by applying a load of g and dividing the tension by 200 g of load. ◯: Friction coefficient is less than 5 ×: Friction coefficient is 5 or more

(4) Moldability A laminate of a polyester film and a metal plate was press-molded with a molding machine (VAS-33P type manufactured by Semba Iron Works Co., Ltd.) at a pressure of 100 kg / cm ² , and the diameter was 1
A cup of 00 mm and a depth of 70 mm was obtained. The cracked state of the film on the inner surface of the cup was visually and microscopically observed. ◯: No cracks are found in the film Δ: Some cracks are found but the metal substrate is not shown ×: Cracks are found in the film and the metal substrate is shown

Example 1 As polyester A, terephthalic acid / isophthalic acid (molar ratio 70/30) and a copolymerized polyester (Tm = 190 ° C.) from ethylene glycol, and as polyester B terephthalic acid / isophthalic acid (molar ratio) 92/8) and ethylene glycol copolymer polyester (Tm = 2
And 47 ° C.) were melted by separate extruders, and the melts were combined in a pipe and then extruded onto a cooling drum for cooling to obtain an unstretched film. The unstretched film was first stretched 3.3 times at 90 ° C in the machine direction and then at 110 ° C in the cross direction at 3.3 times.
After stretching 4 times, heat treatment is performed at 160 ° C. for 6 seconds to give a total thickness of 30 μm (thickness of the layer made of polyester A is 25 μm.
m, and a layer of polyester B having a thickness of 5 μm) was obtained. A laminated product was obtained by passing the polyester film A side, a 0.27 mm tin plate and a 170 ° C. metal roll. The adhesiveness, moldability, and heat resistance of this product were good as shown in Table 1.

Example 2 As polyester A, terephthalic acid / isophthalic acid (molar ratio 80/20) and a copolymerized polyester (Tm = 211 ° C.) from ethylene glycol, and as polyester B terephthalic acid / adipic acid (molar ratio) 90/10) and ethylene glycol copolymer polyester (Tm = 2
36 ° C.) are melted in separate extruders, and the melts are combined in a pipe and then extruded onto a cooling drum to be cooled to obtain an unstretched film, which is stretched in the same manner as in Example 1,
Heat treatment was performed at 180 ° C. for 5 seconds to give a total thickness of 25 μm (thickness of the layer consisting of polyester A: 20 μm, polyester B:
To obtain a polyester film having a layer thickness of 5 μm). The polyester film was evaluated in the same manner as in Example 1. As a result, the adhesiveness, moldability, and heat resistance of this product were good as shown in Table 1.

Example 3 As polyester A, terephthalic acid and ethylene glycol were used.
/ 1,4 cyclohexane dimethanol (molar ratio 75 /
25) Copolymerized polyester (Tm = 203 ° C.)
And terephthalic acid / isophthalic acid (molar ratio 90/10) as polyester B and a copolyester (Tm = 242 ° C.) from ethylene glycol are melted in separate extruders, and the melt is placed in a pipe. After merging with each other, it is extruded on a cooling drum to be cooled to obtain an unstretched film, which is stretched in the same manner as in Example 1 and then heat-treated at 170 ° C. for 10 seconds to give a total thickness of 30 μm (thickness of the layer consisting of polyester A is 27 μm , Thickness of layer consisting of polyester B 3 μm)
To obtain a polyester film. The polyester film was evaluated in the same manner as in Example 1. As a result, the adhesiveness, moldability, and heat resistance of this product were good as shown in Table 1.

Example 4 As polyester A, terephthalic acid / isophthalic acid / sebacic acid (molar ratio 75/20/5) and ethylene glycol were used.
And a terephthalic acid / isophthalic acid (molar ratio 87/13) as polyester B and a copolymerized polyester from ethylene glycol (Tm = 235 ° C.) are separated from each other. After being melted by an extruder, the melts are combined in a pipe, then extruded onto a cooling drum and cooled to obtain an unstretched film, which is stretched in the same manner as in Example 1 and then heat treated at 165 ° C. for 5 seconds, Total thickness 35 μm (thickness of layer consisting of polyester A 27 μm
m, and the thickness of the layer consisting of polyester B was 8 μm) to obtain a polyester film. The polyester film was evaluated in the same manner as in Example 1. As a result, the adhesiveness of this product,
The moldability and heat resistance were good as shown in Table 1.

Example 5 As polyester A, terephthalic acid and ethylene glycol were used.
/ 1,4 cyclohexane dimethanol (molar ratio 75 /
25) Copolymerized polyester (Tm = 203 ° C.)
And terephthalic acid / isophthalic acid (molar ratio 90/10) as polyester B and a copolyester (Tm = 242 ° C.) from ethylene glycol are melted in separate extruders, and the melt is placed in a pipe. After being merged with each other, it is extruded on a cooling drum to be cooled to obtain an unstretched film, which is stretched in the same manner as in Example 1 and then heat-treated at 170 ° C. for 10 seconds to give a total thickness of 30 μm (the thickness of the layer made of polyester A is 8 μm. , The thickness of the layer made of polyester B 22 μm)
To obtain a polyester film. The polyester film was evaluated in the same manner as in Example 1. As a result, the adhesiveness of this product was good and the moldability was good, but some cracks were formed on the film surface.

Comparative Example 1 As polyester A, terephthalic acid / isophthalic acid (molar ratio 80/20) and a copolymerized polyester (Tm = 211 ° C.) from ethylene glycol, and as polyester B, polyethylene terephthalate (Tm =). (260 ° C.) are melted by separate extruders, the melts are merged in a pipe and then extruded on a cooling drum to be cooled to obtain an unstretched film, which is stretched in the same manner as in Example 1 and then heat treated. 1
85 ℃, 5 seconds, total thickness 25μm (Polyester A
A polyester film having a layer thickness of 20 μm and a layer thickness of polyester B of 5 μm) was obtained. The polyester film was evaluated in the same manner as in Example 1. As a result, although the film was molded, the film had cracks.

Comparative Example 2 As polyester A, terephthalic acid / isophthalic acid (molar ratio 70/30) and a copolymerized polyester (Tm = 190 ° C.) from ethylene glycol, and as polyester B terephthalic acid / isophthalic acid (molar ratio) 82/18) and a copolymerized polyester (Tm =
215 ° C.) are melted in separate extruders, and the melts are merged in a pipe and then extruded on a cooling drum to be cooled to obtain an unstretched film, which is stretched in the same manner as in Example 1 and then heat treated. At 160 ℃ for 5 seconds, total thickness 25μm
A polyester film having a thickness of 20 μm for the layer made of polyester A and a thickness of 5 μm for the layer made of polyester B was obtained. The polyester film was evaluated in the same manner as in Example 1. As a result, the adhesiveness and moldability of this product were good, but the heat resistance was poor and the mold did not come off easily during molding.

Comparative Example 3 As polyester A, terephthalic acid / sebacic acid (molar ratio 88/12) and a copolymerized polyester (Tm = 234 ° C.) from ethylene glycol, and as polyester B terephthalic acid / isophthalic acid (molar ratio) 90/10) and ethylene glycol copolymer polyester (Tm = 2
42 ° C.) are melted in separate extruders, and the melts are combined in a pipe and then extruded onto a cooling drum to cool to obtain an unstretched film, which is stretched in the same manner as in Example 1,
Heat treatment was carried out at 205 ° C. for 5 seconds to give a total thickness of 35 μm (layer thickness of polyester A: 27 μm, polyester B:
A polyester film having a layer thickness of 8 μm) was obtained. The polyester film was evaluated in the same manner as in Example 1. As a result, the adhesiveness of this product was poor and it could not withstand the subsequent evaluation.

Comparative Example 4 As a polyester, terephthalic acid / isophthalic acid (molar ratio 82/18) and a copolymerized polyester (Tm = 215 ° C.) from ethylene glycol were melted in an extruder, and this melt was placed on a cooling drum. And then cooled to obtain an unstretched film, which was stretched in the same manner as in Example 1 and then heat-treated at 180 ° C.
This was carried out at 5 ° C. for 5 seconds to obtain a polyester film having a thickness of 30 μm. The polyester film was evaluated in the same manner as in Example 1. As a result, the adhesiveness and moldability of this product were good, but the heat resistance was poor and the mold did not come off easily during molding.

Comparative Example 5 Polyethylene terephthalate (Tm = 260) comprising terephthalic acid and ethylene glycol as polyester
(° C) in the same manner as in Comparative Example 4 to obtain an unstretched film, which is further stretched and then heat-treated at 225 ° C for 10 seconds to give a thickness of 30.
A single layer film having a thickness of μm was obtained. The polyester film was evaluated in the same manner as in Example 1. As a result, the adhesiveness to metal was not good, and evaluation after molding could not be achieved.

[0036]

[Table 1]

[0037]

EFFECTS OF THE INVENTION The film of the present invention has a structure of two or more layers, and by applying a polyester film in which the characteristics of both surface layers are within specific ranges, the adhesiveness to a metal plate is improved, and the film is formed into a can. Since the film has good moldability, and the film surface layer has good heat resistance even after being formed into a can, it can withstand post-processing such as printing. That is, the single-layer film cannot simultaneously satisfy the adhesiveness, moldability, and heat resistance, but the present invention can satisfy all of them.

Claims (2)

[Claims] 1. A film comprising a biaxially stretched polyester resin having at least a two-layer structure, one surface of which is laminated with a metal, the film comprising:
The melting point (T) of the surface layer (A) on the side to be laminated on the metal
mA) is 170 ° C. or higher and 220 ° C. or lower, and the melting point (Tm B) of the surface layer (B) on the side that is not laminated to metal is 220 ° C. or higher and 255 ° C. or lower. 2. The film for metal laminating according to claim 1, wherein the thickness (tA) of the layer (A) and the thickness (tB) of the layer (B) are tA> tB.