JP4532137B2 - Film for laminating metal plates, film laminated metal plates, and metal cans - Google Patents

Description

  The present invention relates to a film for laminating a metal plate, and in particular, a film laminated metal plate obtained by laminating this film on a metal plate can be useful as a material used for drawing or ironing, The present invention relates to a metal plate laminating film.

  Conventionally, a solvent-type paint mainly composed of a thermosetting resin has been applied to prevent corrosion of the inner and outer surfaces of a metal can. However, solvent-based paints need to be heated at a high temperature in order to form a coating film, and a large amount of solvent is generated at that time, which causes problems in terms of work safety and environment. Therefore, recently, a metal coating with a thermoplastic resin has been proposed as a corrosion prevention method that does not use a solvent, and among polyester resins, polyester is particularly excellent in processability and heat resistance. The development of film is being promoted.

  As a method for coating a film on a metal plate, there are a method in which a thermoplastic resin is melted and extruded directly onto a metal, and a method in which a thermoplastic resin film is thermocompression bonded directly or via an adhesive. Among them, the method using a thermoplastic resin film is considered to be an effective method because it is easy to handle the resin, has excellent workability, and is excellent in the uniformity of the resin film thickness. In addition, since the method using an adhesive has environmental problems and cost problems, a method of directly thermocompression bonding a film has attracted attention.

  Metal cans coated with a thermoplastic resin film are manufactured by laminating a thermoplastic resin film on a metal plate such as a steel plate or aluminum plate (including those subjected to surface treatment such as plating), and molding the laminated metal plate Is done.

  The thermoplastic resin film used in such applications has good heat laminating properties with metal plates, excellent can moldability, that is, film peeling, cracks, pinholes, etc. during can molding A number of characteristics are required at the same time, such as no occurrence of odor, printing after can-molding, retort sterilization treatment, no embrittlement during long-term storage, and excellent content and flavor retention.

  As such a polyester film for laminating a metal plate, methods for mixing or copolymerizing other components have been proposed for the purpose of imparting heat laminating properties and improving moldability of cans.

  For example, (a) those obtained by copolymerizing other components with PET are disclosed in Patent Documents 1 to 3, and the like. In addition, (b) a copolymerized PET blended with PBT or a copolymer thereof (Patent Documents 4 to 6), (c) a PET or copolymer thereof blended with PBT or a copolymer thereof, A limited can lid film (Patent Documents 7 and 8) is disclosed.

  However, in (A), although PET is copolymerized to lower its melting point and crystallize, its heat laminating properties and moldability are improved. However, it becomes brittle during heat treatment and retort sterilization after can molding, and is impact resistant. There was a problem that decreased. In (b), by adding a PBT-based resin, the heat laminating property and the embrittlement and impact resistance, which are the disadvantages of (a) above, are being improved in a balanced manner. Laminating properties and adhesiveness are not sufficient, and particularly high workability such as drawing and ironing is not sufficient. In (c), whitening and white spots after heat treatment at relatively low temperatures such as retort sterilization can be improved by limiting crystallinity, but formability under severe conditions such as drawing or ironing (high processing) Property) was not considered, and sufficient moldability was not imparted.

  On the other hand, the present inventors have previously proposed a biaxially stretched film made of polyethylene terephthalate or polyester mainly composed of this and polybutylene terephthalate or polyester mainly composed of this (Patent Document 9, 10). Even if this film has a high degree of crystallinity, it can be thermocompression bonded at a relatively low temperature, and the obtained laminated metal plate is excellent in workability, and does not become brittle during retort sterilization treatment and long-term storage. It also has excellent impact resistance. Recently, however, there has been a demand for an increase in can manufacturing speed, an increase in can size, and a thinner can, and further improvements in impact resistance particularly at low temperatures have been desired.

In order to improve impact resistance at a low temperature, a method of coating a metal plate in a substantially unoriented state by blending an olefin component with a polyester resin (Patent Document 11) is disclosed. Must be extruded directly onto the metal or thermocompression bonding of the unstretched film is inferior in the uniformity of the resin film thickness, easily galling in drawing or ironing, etc. Met. Further, when heat sterilization treatment is performed, there is a problem that impact resistance at low temperatures is lowered.
Japanese Patent Publication No. 8-19245 Japanese Patent Publication No. 8-19246 Japanese Patent No. 2528204 Japanese Patent No. 2851468 JP-A-5-186612 JP-A-5-186613 Japanese Patent Laid-Open No. 5-331302 JP 7-145252 A JP-A-9-194604 Japanese Patent Laid-Open No. 10-110046 JP 2002-347178 A

  The object of the present invention is for metal laminating suitable for a film laminating metal can body excellent in heat laminating property with a metal plate, moldability of a can and heat shock sterilization treatment even at low temperatures. The object is to provide a film, a laminated metal plate, and a metal can body using the same.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that an ethylene-based terpolymer is added to a substantially incompatible polyester, that is, a polybutylene terephthalate-based polyester and a polyethylene terephthalate-based polyester. The blended film was found to be excellent in impact resistance at low temperatures after heat sterilization in addition to can moldability, and reached the present invention. That is, the gist of the present invention is as follows.
(1) A biaxially stretched film comprising polybutylene terephthalate or polyester (I) mainly composed of this, polyester (II) mainly composed of polyethylene terephthalate, and ethylene terpolymer (P). The polyester (I) has a mass ratio (I / II) of 80/20 to 40/60, and the polyester (II) is substantially composed of polyethylene terephthalate (IIA) having a copolymerization amount of 5 mol% or less. Is a mixture with an amorphous copolymerized polyethylene terephthalate (IIB), and its mass ratio (IIA / IIB) is 50/50 to 90/10, and the ethylene-based terpolymer (P) is Ethylene terpolymer (95 to 50% by mass, maleic anhydride 0.5 to 10% by mass, unsaturated carboxylic acid alkyl ester 4.9 to 40% by mass, P) is blended in an amount of 5 to 20 parts by mass with respect to a total of 100 parts by mass of polyester (I) and (II), and the film has a melting point of polyester (I) of 200 to 223 ° C and 230 to 256 ° C. A metal plate laminating film characterized by having a melting point of polyester (II).
(2) The film for laminating a metal plate according to the above (1), wherein the crystallization peak temperature of the film is 60 to 100 ° C. and the heat of crystal fusion is 20 to 40 J / g.
(3) A film laminated metal plate obtained by laminating the metal plate laminating film according to the above (1) or (2) directly through heat bonding or an adhesive.
(4) A metal can formed using the film-laminated metal plate according to (3).

  According to the present invention, a metal having excellent heat laminating properties, moldability, particularly high workability such as drawing and ironing, and excellent impact resistance at low temperature even after being subjected to heat sterilization after molding. A can and a metal plate laminated with a film for forming the metal can can be provided.

  Hereinafter, the present invention will be described in detail. The polybutylene terephthalate (PBT) or the polyester (I) mainly composed of the polybutylene terephthalate according to the present invention is obtained by copolymerizing PBT or other components with a melting point of 200 to 223 ° C. When the melting point is lower than 200 ° C., the heat resistance is lowered.

  The copolymerization ratio may be such that the melting point is within the above range, and 1,4-butanediol is preferably at least 80 mol%, particularly preferably at least 90 mol%, based on all alcohol components. When 1,4-butanediol is less than 80 mol%, the crystallinity, particularly the crystallization rate, is lowered, and the impact resistance after the retort treatment is lowered.

  The copolymer component is not particularly limited, but the acid component is isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, Examples include dodecanedioic acid, dimer acid, maleic anhydride, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, and dicarboxylic acids such as cyclohexanedicarboxylic acid, 4-hydroxybenzoic acid, ε-caprolactone, and lactic acid.

  The alcohol component includes ethylene glycol, diethylene glycol, 1,3-propanediol, neopentyl glycol, 1,6-hexanediol, cyclohexanedimethanol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, bisphenol. Examples thereof include ethylene oxide adducts of A and bisphenol S.

  Further, a small amount of trifunctional compounds such as trimellitic acid, trimesic acid, pyromellitic acid, trimethylolpropane, glycerin, pentaerythritol, and the like may be used. Two or more of these copolymer components may be used in combination.

  The polyester (II) mainly composed of polyethylene terephthalate (PET) in the present invention is a mixture of polyethylene terephthalate (IIA) having a copolymerization amount of 5 mol% or less and a substantially amorphous copolymerized polyethylene terephthalate (IIB). It is necessary to be.

  Polyethylene terephthalate (IIA) is obtained by copolymerizing PET or other components thereto, and is not particularly limited as a component that can be copolymerized with PET, and examples thereof are the same as those of polyester (I). it can. The copolymerization amount of other components copolymerized with PET must be 5 mol% or less. When the copolymerization amount exceeds 5 mol%, the crystallinity is lowered and the heat resistance is lowered, which is not preferable.

  On the other hand, polyethylene terephthalate (IIB) needs to be a substantially amorphous copolymerized PET. The term “substantially amorphous” means that no crystallization peak is observed when the temperature is raised at 20 ° C./min during DSC, and therefore no crystal melting peak is observed. The substantially amorphous copolymer polyethylene terephthalate (IIB) is not particularly limited. For example, when isophthalic acid is copolymerized, 22 mol% or more of 1,4-cyclohexanedimethanol or neopentyl glycol is copolymerized. In the case of polymerization, polyethylene terephthalate copolymerized at 15 mol% or more can be mentioned.

  In the polyester (II), the mass ratio (IIA / IIB) of polyethylene terephthalate (IIA) to polyethylene terephthalate (IIB) needs to be 50/50 to 90/10, and further 60/40 to 80 / 20 is preferable. If the polyethylene terephthalate (IIA) exceeds 90% by mass, the crystallinity may be too high and the impact resistance after the heat treatment may be inferior, whereas if it is less than 50% by mass, the heat resistance and the corrosion resistance may be inferior. In the present invention, by blending highly crystalline (IIA) and amorphous (IIB) within a certain range, heating is maintained while maintaining higher heat resistance as compared with a single copolymer polyethylene terephthalate. Impact resistance after the treatment can be improved.

  In the present invention, the melting point of polyester (II) obtained by mixing polyethylene terephthalate (IIA) and (IIB) is preferably 230 to 256 ° C. When the melting point is less than 230 ° C., the crystallinity is lowered, whitening or vitiligo occurs after the retort treatment, or the impact resistance after the retort treatment is inferior.

  The intrinsic viscosity of the polyesters (I) and (II) used for producing the film of the present invention is 0.6 to 1.6 for the polyester (I) and 0.5 to 0.9 for the polyester (II). Preferably, the intrinsic viscosity after melt mixing is preferably 0.6 to 1.0. If the intrinsic viscosity is less than the above range, the practical performance of the film is insufficient, and if it exceeds the above range, the productivity is inferior, and the heat laminating property of the film to the metal plate is also impaired.

  The polymerization method of the raw material polyesters (I) and (II) is not particularly limited, and can be polymerized by, for example, a transesterification method or a direct polymerization method. Examples of the transesterification catalyst include Mg, Mn, Zn, Ca, Li, Ti oxides, acetates, and the like. Examples of the polycondensation catalyst include compounds such as Sb, Ti, Ge oxide, and acetate.

  Since the polyester after polymerization contains monomers, oligomers, by-products such as acetaldehyde and tetrahydrofuran, it is preferable to perform solid-phase polymerization at a temperature of 200 ° C. or higher under reduced pressure or through an inert gas flow.

  In the polymerization of the polyester, additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber, and an antistatic agent can be added as necessary. Examples of the antioxidant include hindered phenol compounds and hindered amine compounds, examples of the heat stabilizer include phosphorus compounds, and examples of the ultraviolet absorber include benzophenone compounds and benzotriazole compounds. Can be mentioned.

The ethylene-based terpolymer (P) in the present invention comprises ethylene, maleic anhydride , and an alkyl ester of an unsaturated carboxylic acid . Maleic anhydride is most preferred from the standpoint of affinity for polyester and cost performance.

  Moreover, the alkyl ester of unsaturated carboxylic acid in ethylene terpolymer (P) is C1-C4 alkyl ester of unsaturated carboxylic acid, for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl Examples thereof include acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate and the like, and n-butyl acrylate, ethyl acrylate, and methyl acrylate are particularly preferable.

The constituent ratio of each component constituting the ethylene terpolymer (P) is 95 to 50% by weight of ethylene, 0.5 to 10% by weight of maleic anhydride , and 4.9 to 40 of alkyl ester of unsaturated carboxylic acid. More preferably, they are ethylene 89.5-60 mass%, maleic anhydride 0.5-5 mass%, and alkyl ester of unsaturated carboxylic acid 10-35 mass%.

When the copolymerization ratio of maleic anhydride is less than the above range, the affinity of the resulting copolymer with the polyester becomes insufficient, and the film- forming property of the film is deteriorated, as well as the ethylene ternary in the polyester. The dispersibility of the copolymer (P) becomes insufficient, and the impact improving effect may be inferior. On the other hand, if this range is exceeded, the melt viscosity of the resulting copolymer will extremely increase, making it difficult to knead with the polyester, or excessive reaction with the polyester during melt kneading to reduce the heat resistance of the polyester There is. In addition, when the copolymerization ratio of the unsaturated carboxylic acid alkyl ester is less than the above range, the resulting film is inferior in flexibility, and the impact resistance at low temperature becomes insufficient. In this polymerization apparatus, it is difficult to obtain a terpolymer.

  Examples of the polymerization method of the ethylene-based terpolymer (P) include methods such as bulk, solution, suspension, or emulsion polymerization. The most common method is a bulk copolymerization method, using a compound that generates free radicals as an initiator, such as an organic peroxide, at a temperature of 100 to 300 ° C. under a pressure of 700 to 3000 atm. By polymerization, an ethylene-based terpolymer (P) can be obtained.

  The melt flow rate MFR (based on JIS K6760) of the ethylene-based terpolymer (P) is preferably in the range of 0.1 to 60 g / 10 minutes, and more preferably in the range of 1 to 50 g / 10 minutes. If it is out of this range, kneading with polyester may be difficult.

  In the present invention, the polyesters (I) and (II) are melt-mixed at a specific blending ratio, and the blending ratio is (I) / (II) = 80/20 to 40/60, preferably 70/30. ~ 50/50. When the blending ratio of the polyester (I) exceeds 80% by mass, the characteristics of the polyester (I) having high crystallinity are remarkably exhibited and not only the moldability is inferior but also the impact resistance is deteriorated. Moreover, when the compounding ratio of polyester (I) is less than 40 mass%, the crystallization speed | rate falls and the physical property after a retort process falls.

  In the present invention, 5 to 20 parts by mass, preferably 8 to 20 parts by mass, and more preferably 10 to 10 parts by mass of the ethylene terpolymer (P) with respect to 100 parts by mass in total of polyesters (I) and (II). It is necessary to add 17 parts by mass. When the amount is less than 5 parts by mass, the effect of addition is not observed and the impact resistance at low temperatures is poor. When the amount is more than 20 parts by mass, ballast is generated and film formation becomes difficult.

  The mixing method of the polyester (I), (II) and the ethylene terpolymer (P) is not particularly limited, but the dispersibility of the ethylene terpolymer (P) incompatible with the polyester is improved. Therefore, after melt-mixing using a highly kneading apparatus such as a twin-screw extruder or kneader to prepare a master chip having a concentration higher than a predetermined value in advance, a polyester ( It is preferable to melt and mix I) and (II). The method of melt mixing is not particularly limited, and examples thereof include a method in which the blended raw material chips are melt-mixed with the same extruder, and a method in which each is mixed after being melted in separate extruders. When mixing for a long time at a high melting temperature or high shear as the melt mixing condition, the transesterification reaction or decomposition reaction of the polyesters (I) and (II) proceeds and the characteristics of the mixture change greatly. In particular, if the transesterification proceeds too much, the melting point and glass transition temperature decrease, the excellent properties of the film due to polyester (I) and (II) disappear, and the heat resistance and moldability decrease, so the melt mixing conditions Is preferably set to a melting point of (II) + 20 ° C. or lower and a residence time of 15 minutes or shorter.

  The film of the present invention must have at least one melting point of polyester (I) in the temperature range of 200 to 223 ° C. and one or more melting points of polyester (II) in the temperature range of 230 to 256 ° C. In particular, when the melting point derived from polyester (I) is below 200 ° C., the heat resistance of the film is lowered, and the moldability and impact resistance are poor.

  The film of the present invention preferably has a temperature rising crystallization peak temperature (Tc) from an amorphous state of 60 to 100 ° C, and more preferably in the range of 60 to 95 ° C. When Tc exceeds 100 ° C., crystallization gradually proceeds during the heat sterilization treatment usually performed in the range of 95 ° C. to 125 ° C., and the impact resistance of the film is reduced, whitening and white spots occur. The film may look bad. Moreover, when Tc is less than 60 degreeC, when a shaping | molding temperature is high, the moldability of a laminated metal plate may fall, and the flavor retention property of the content may also fall.

  The film of the present invention preferably has a heat of crystal fusion of 20 to 40 J / g, and more preferably 25 to 35 J / g. If the heat of crystal fusion exceeds 40 J / g, the impact resistance after the heat sterilization treatment is lowered. On the other hand, if it is less than 20 J / g, the impact resistance is excellent, but the corrosion resistance may be inferior.

  The film of the present invention needs to be a biaxially stretched film. By biaxial stretching, the thickness accuracy and dimensional stability of the film are increased, and troubles such as galling and whitening can be reduced in the thermal lamination with a metal plate and the subsequent can manufacturing process.

  Next, an example of film production is shown. Dry-blended polyesters (I) and (II) and an ethylene-based terpolymer (P) are fed to an extruder equipped with a T-die and melt-mixed at a temperature of 250 to 280 ° C. for 3 to 15 minutes to form a sheet. The extruded sheet was closely adhered to a cooling drum whose temperature was adjusted to room temperature or lower and cooled, and the obtained unstretched sheet was about 1 to 1.2 times in the machine direction (MD) as necessary. Pre-stretching, followed by biaxial stretching with a tenter at a temperature of 50 to 150 ° C. in the MD and transverse directions (TD) so that the stretching ratio is about 2 to 4 times, respectively, and further the relaxation rate of TD is several percent As above, it can be manufactured by performing heat treatment at 80 to 220 ° C. for several seconds. As the biaxial stretching method, a sequential or simultaneous biaxial stretching method can be used.

  The heat treatment after stretching is a process necessary for imparting dimensional stability to the film. As the method, known methods such as a method of blowing hot air, a method of irradiating infrared rays, a method of irradiating microwaves, etc. Can be used. Of these, the method of blowing hot air is optimal because it can be heated uniformly and accurately.

  In order to improve the process passability during film production and can making, it is desirable to add a small amount of an inorganic lubricant such as silica, alumina, kaolin or the like to form a film to impart slip properties to the film surface. Furthermore, in order to improve the film appearance and printability, for example, the film can contain a silicone compound or the like.

  The film of the present invention can be provided with an adhesive layer by a coextrusion method, a laminating process, or a coating process for the purpose of further improving the thermocompression bonding property with the metal plate and the subsequent adhesion. The adhesive layer is not particularly limited, but is preferably a polyester resin layer not containing an ethylene-based terpolymer, or a thermosetting resin layer made of an epoxy resin, a polyurethane resin, a polyester resin, or various modified resins thereof. . In particular, it is preferable to laminate a polyester resin layer having a thickness of 1.0 to 10 μm and a thermosetting resin layer having a thickness of 1.0 μm or less.

  In addition, on the opposite side of the metal plate and the film to be thermocompression bonded, one or more resins are used to improve the appearance and printability of the metal can body and to improve the heat resistance and retort resistance of the film. A layer can be provided. These layers can be provided by coextrusion, lamination, or coating.

  In the film of the present invention, it is particularly preferable that a polyester resin layer not containing an ethylene-based terpolymer is laminated on both sides, and further a thermosetting resin layer is laminated if necessary.

  The film of the present invention is laminated on a metal plate such as a steel plate or aluminum directly through heat bonding or an adhesive. The metal plates to be laminated are steel plates that have been subjected to chemical treatments such as chromic acid treatment, phosphoric acid treatment, electrolytic chromic acid treatment, and chromate treatment, as well as nickel, tin, zinc, aluminum, gunmetal, brass, and other various plating treatments. Can be used.

  As a method of laminating a film and a metal plate, the metal plate is preheated to 160 to 250 ° C., and this and the film are pressed by a roll whose temperature is controlled to be 30 ° C. lower than the metal plate by 50 ° C. or more. Then, after being thermocompression bonded, it is continuously manufactured by cooling to room temperature. Heating methods for metal plates include heater roll heat transfer method, induction heating method, resistance heating method, hot air transfer method, etc., especially when considering the equipment cost and simplification of equipment, the heater roll heat transfer method is preferable. Moreover, about the cooling method after lamination, the method immersed in refrigerant | coolants, such as water, and the method of making it contact with a cooling roll can be used.

  The metal plate obtained as described above may be processed as it is, but is rapidly cooled after heat treatment at a temperature 10 to 30 ° C. higher than the melting point of the polyester to make this film in an amorphous state. Further, high workability can be imparted. In particular, the film of the present invention exhibits a great effect when it is in an amorphous state.

  The metal can of the present invention is formed by molding the above laminated metal plate. As a metal can body, a metal can body that has been processed to a form that can be filled with food and drink and used for use, and a part thereof, for example, a can lid that is formed into a shape that can be tightened included. In particular, the film of the present invention is used as a can body member of a three-piece can (3P can) subjected to severe neck-in processing or a can body member of a two-piece can (2P can) manufactured by drawing ironing. Excellent workability is exhibited. The metal can body using the film of the present invention has various processed foods such as coffee, green tea, black tea, oolong tea, particularly highly corrosive acidic beverages (fruit juice beverages) and dairy beverages because of its excellent retort resistance and corrosion resistance. Suitable for filling the contents of

  Next, the present invention will be specifically described by way of examples. The raw materials of the film and the method for measuring the characteristic values in the examples and comparative examples are as follows.

(1) Raw material polyester (I):
PBT: PBT subjected to solid phase polymerization, IV 1.08 dl / g, Tm 223 ° C., Tg 30 ° C., Ti catalyst 40 ppm contained.

Polyester (IIA):
PET: PET subjected to solid phase polymerization, IV 0.75 dl / g, Tm 255 ° C., Tg 74 ° C., containing Ge catalyst 40 ppm.
DA4-PET: PET obtained by copolymerizing 4 mol% of a dimer acid having 36 carbon atoms, and solid phase polymerization is not performed. IV 0.75 dl / g, Tm 244 ° C., Tg 53 ° C., containing 60 ppm of Ge catalyst.
IP12-PET: PET obtained by copolymerization of 12 mol% of isophthalic acid, not subjected to solid phase polymerization. IV0.65 dl / g, Tm226 degreeC, Tg67 degreeC, Sb catalyst 100ppm containing.

Polyester (IIB):
CH30-PET: PET copolymerized with 30 mol% of 1,4-cyclohexanedimethanol, not subjected to solid phase polymerization. IV0.75, Tg80 ° C, Ge catalyst 80ppm, Sb catalyst 100ppm.
NP20-PET: PET obtained by copolymerizing 20 mol% of neopentyl glycol, not subjected to solid phase polymerization. IV 0.78, Tg 70 ° C., Ge catalyst 80 ppm, Sb catalyst 100 ppm contained.

Ethylene terpolymer (P):
P1: It consists of ethylene / methyl acrylate / maleic anhydride, and its composition ratio is 83.4 / 15 / 1.6 (mass%), MFR (190 ° C.) 8 g / 10 min.
P2: It consists of ethylene / ethyl acrylate / maleic anhydride, and the composition ratio is 68.5 / 30 / 2.5 (mass%), MFR (190 ° C.) 9 g / 10 min.
P3: It consists of ethylene / methyl acrylate / maleic anhydride, and its composition ratio is 84.95 / 15 / 0.05 (mass%), MFR (190 ° C.) 10 g / 10 min.
P4: It consists of ethylene / methyl acrylate / maleic anhydride, and its composition ratio is 73/16/11 (mass%), MFR (190 ° C.) 9 g / 10 min.
P5: It consists of ethylene / methacrylic acid, the composition ratio is 88/12 (mass%), MFR (190 degreeC) 7g / 10min.

(2) Measurement method Intrinsic viscosity (IV)
It calculated | required from the solution viscosity measured by the temperature of 20 degreeC and the density | concentration of 0.5 g / dl using the equal mass mixed solvent of phenol / ethane tetrachloride.

B. Crystallization peak temperature (° C), melting point (° C), and heat of crystal fusion (J / g)
Using a Perkin Elmer DSC, the crystallization peak temperature, melting point, and heat of crystal melting during heating were measured at 20 ° C./min. As a measurement sample of the film, a stretched film was heated to 280 ° C. at 100 ° C./min, held for 3 minutes, and then rapidly cooled in liquid nitrogen to be in an amorphous state.

C. Thermal laminating property A sample film and an aluminum plate having a thickness of 0.30 mm are superposed and supplied between a metal roll heated to 200 ° C. and a silicon rubber roll, the speed is 20 m / min, and the linear pressure is 4.9 × 10. Heat bonded at ⁴ N / m, immersed in ice water after 2 sec, and cooled to obtain a laminated metal plate. From the obtained laminate, 11 strip-shaped test pieces having a width of 18 mm (end portions were not laminated and the laminated portion was ensured to be 8 cm or more in MD) were cut out into 11 pieces in TD. Next, an adhesive tape specified in JIS Z-1522 is attached to the film surface of this test piece, and a 180 degree peel test is performed at a speed of 10 mm / min using an autograph manufactured by Shimadzu Corporation. By measuring, the adhesiveness was evaluated according to the following criteria.
A: The peel strength of 10 or more test pieces is 2.9 N or more, or the film is broken at 2.9 N or more.
○: The peel strength of 5 to 9 test pieces is 2.9 N or more, or the film is broken at 2.9 N or more.
Δ: Seven or more test pieces having a peel strength of less than 2.9N.

D. Formability Using the film side of the laminated metal plate obtained in C above as the inner surface of the can body, drawing and ironing was performed to form a two-piece can corresponding to 500 ml. The obtained can was filled with 1% by mass saline, the current value when a voltage of 6 V was applied with the can body as an anode was measured, and the degree of film defects was evaluated. The more current flows, the more defects, and the can quality is preferably 1 mA or less.

E. Impact resistance Eleven of the laminated metal plates obtained in C above were cut out into 10 cm × 10 cm, (a) treated with boiling water at 95 ° C. for 30 seconds, (b) treated with boiling water at 95 ° C. for 30 seconds, and stored at 38 ° C. for 3 months. Later, in an atmosphere of 5 ° C., a 300 g weight (with a tip of R0.75, an opening angle of 60 degrees, and a wedge shape with a length of 30 mm) was dropped from a height of 20 cm onto a metal surface to give an impact. Was immersed in an aqueous solution of sodium hydroxide, the metal surface was used as an anode, and a current value when a direct current of 200 V was applied for 30 seconds was measured and evaluated according to the following criteria.
X: 7 or more sheets are 5 mA or more Measurement value: When 5 sheets or more are 1 mA or more and less than 5 mA Maximum value of current value: 7 to 9 sheets are less than 1 mA ◎: 10 sheets or more are less than 1 mA

Examples 1-7, Comparative Examples 1-11
Equal amounts of PBT and ethylene terpolymer (P) were blended and supplied to a twin screw extruder, and melt kneaded at 250 ° C. to obtain a master chip. To this chip, PBT, polyester (IIA) and (IIB) were blended so as to have the ratio shown in Table 1, and silica having an average particle diameter of 2.5 μm was added so that the total amount was 0.08% by mass. Then, it was supplied to an extruder equipped with a T die, melted in a range of 250 to 290 ° C. for 3 to 10 minutes, extruded into a sheet form from a T die outlet, and rapidly cooled and solidified to obtain an unstretched film. Next, the end of the unstretched film is held by a clip of a tenter type simultaneous biaxial stretching machine, and after running through a preheating zone of 40 to 60 ° C., the temperature is 50 to 80 ° C. and 3.0 times the MD, TD Were simultaneously biaxially stretched by 3.3 times. However, after that, after a TD relaxation rate of 5% and heat treatment for 4 seconds at a temperature of 150 ° C., the film was cooled to room temperature and wound to obtain a biaxially stretched film having a thickness of 25 μm. From the obtained film, a laminated metal plate was obtained by the method described in C and evaluated at the same time. Further, the moldability of the laminated metal plate film obtained in C was evaluated by the method described in D. Further, the impact resistance of the laminated metal plate was evaluated by the method shown in E. Table 1 shows various physical properties and evaluation results of the film obtained in the above test.

The films obtained in Examples 1 to 7 were excellent in heat laminating properties, moldability, and impact resistance, but the films obtained in Comparative Examples 1 to 7, 9, and 11 had all the above performances. I was not satisfied. Further, Comparative Examples 8 and 10 were not evaluated because the film could not be formed due to the ballast phenomenon.

Claims (4)

A biaxially stretched film composed of polybutylene terephthalate or polyester (I) mainly composed of this, polyester (II) mainly composed of polyethylene terephthalate, and ethylene terpolymer (P), The mass ratio (I / II) between I) and (II) is 80/20 to 40/60, and the polyester (II) is substantially amorphous with polyethylene terephthalate (IIA) having a copolymerization amount of 5 mol% or less. A copolymer of high quality copolymerized polyethylene terephthalate (IIB), and its mass ratio (IIA / IIB) is 50/50 to 90/10, and ethylene-based terpolymer (P) is ethylene 95- 50% by mass, maleic anhydride 0.5 to 10% by mass, unsaturated carboxylic acid alkyl ester 4.9 to 40% by mass, ethylene terpolymer (P) It is blended in an amount of 5 to 20 parts by mass with respect to 100 parts by mass in total of polyesters (I) and (II), and the film has a melting point of polyester (I) at 200 to 223 ° C and a polyester ( A film for laminating metal plates, characterized by having a melting point of II). The film for laminating metal plates according to claim 1, wherein the film has a crystallization peak temperature of 60 to 100 ° C and a heat of crystal fusion of 20 to 40 J / g. A film-laminated metal plate obtained by laminating the film for laminating a metal plate according to claim 1 or 2 directly by heat bonding or an adhesive. A metal can body formed using the film-laminated metal plate according to claim 3.