JP2010168432A - Polyester film for metal plate lamination - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat lamination film that is excellent in a heat lamination property to a metal plate as well as high-order processability after heat-laminated to the metal plate, suppresses a hairing phenomenon at a cut portion, causes no deterioration in impact resistance of a molded can and prevents corrosion of a metal plate. <P>SOLUTION: The polyester film for metal plate lamination is composed of a biaxially oriented polyester film, where the polyester is a copolyester containing 0.15-0.40 mol% of a trihydric or higher-hydric carboxylic acid component in the acid component and has a melting point of the film of 210-235&deg;C and an intrinsic viscosity of 0.70-0.85 dl/g. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a polyester film for laminating metal plates.

  Metal cans formed by processing metal plates are used for packaging foods, beverages, and the like. However, the metal plate is excellent in workability, but is easily corroded. Conventionally, in order to prevent the metal plate from being corroded, a solvent-type paint mainly composed of a thermosetting resin has been applied to the surface of the metal plate. .

  However, the method of applying the solvent-type paint has a problem in safety in terms of work and environment because it is necessary to volatilize the solvent in the paint at a high temperature after applying the solvent-type paint to the metal plate. . Therefore, as a method for preventing corrosion of a metal plate without using a solvent, for example, a method of laminating a thermoplastic resin on the metal plate has been proposed. Among thermoplastic resins, polyester resins are particularly excellent in heat resistance, processability to metal plates, and the like, and therefore, development of polyester films for metal plate lamination using polyester resins as raw materials has been studied.

  As a method of laminating a film on a metal plate, for example, a method in which a thermoplastic resin is melted and extruded directly onto a metal plate, a thermoplastic resin film is directly applied, or a metal is bonded via an adhesive between the film and the metal plate. There is a method of thermocompression bonding with a plate. Among them, the method using a thermoplastic resin film is regarded as an effective method because it is easy to handle the resin, is excellent in workability, and is excellent in the uniformity of the resin film thickness when laminated on a metal plate. In addition, since the method of using an adhesive between the film and the metal plate has environmental problems and cost problems, the method of directly thermocompressing the film is advantageous and attracts attention.

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

  The thermoplastic resin film used for such applications has (1) good thermal laminating property with a metal plate, (2) excellent workability during can molding, specifically can molding. Occasionally peeling, cracking, and scratching of a film laminated with a metal plate does not occur, and pinholes do not occur in the heat laminated metal plate. (3) Excellent workability and stability after can molding Specifically, it has excellent printability on the film surface after can-molding using a heat-laminated metal plate, and the inner and outer surface films of the can do not become brittle during the heat sterilization treatment. (4) Can The characteristics such as excellent flavor retention and long-term storage stability of the contents filled in are required.

  As such a polyester film for laminating metal plates, several methods have been proposed, such as mixing or copolymerizing with other components for the purpose of imparting heat laminating properties and improving moldability of the can. Yes.

  For example, Patent Documents 1 to 3 disclose polyester films obtained by copolymerizing polyethylene terephthalate (PET) and other components.

  Patent Documents 4 to 6 disclose polyester films containing 99 to 60% by weight of PET having a melting point of 210 to 245 ° C. and 1 to 40% by weight of polybutylene terephthalate (PBT) or a copolymer thereof.

  Patent Documents 7 and 8 disclose polyester films containing PET as a main component with emphasis on the moldability of cans and the taste and flavor retention of the contents filled in the cans.

  Patent Document 9 discloses a method for suppressing a hair-ring phenomenon in which a film at an end of a metal plate laminated with a polyester film becomes a thread-like hair.

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 JP-A-10-128935 JP 2000-186161 A JP 2000-211083 A

  Patent Documents 1 to 3 are methods for improving workability by increasing the adhesion between a metal plate and a film during thermal lamination by copolymerizing PET with other components to lower the melting point and lower crystallization. In addition to the heat laminating film surface becoming brittle during heat treatment and heat sterilization after can molding, there were problems in that the impact resistance of the molded can was reduced.

  The methods of Patent Documents 4 to 6 use a film in which PET and PBT having a melting point of 210 to 245 ° C are blended or a film in which a copolymer of PBT and other components is blended with PET having a melting point of 210 to 245 ° C. , The embrittlement of the heat-laminated film is suppressed, and the impact resistance of the molded can is improved, but the heat laminating property and adhesiveness between the metal plate and the film are insufficient, so that especially the drawing molding and ironing molding etc. There was a problem that the high-order workability was not sufficient.

  The methods of Patent Documents 7 and 8 are intended to impart processability by controlling the crystallinity of the polyester film, but high-order processability such as drawing or ironing during can molding is sufficient. However, especially for the heat laminating property, a temperature higher than the melting point of the film is required, or an adhesive must be applied.

  More recently, the demand for increased can manufacturing speed, increased capacity of cans, and thinner cans has been advancing, and the ratio of metal deformation during drawing and ironing is further increasing. Because the friction with the jig is further increased, even if the above film is used in the body of a can that is particularly severely deformed, depending on the subtle fluctuations in the manufacturing conditions of the laminated metal plate and the molding processing conditions of the final can, the film There has been a new problem of whitening and microcracks.

  In addition, in order to increase the processing ratio, in the case of the remelt method in which the film is heat-treated at a temperature equal to or higher than the melting point and made into an amorphous state and then subjected to processing, the film's deformation followability increases, but the film surface is smoothed. Along with this, the slipperiness with the jig was lowered, and the film was damaged or even ruptured.

  In addition, when the ironing molding is a punching die, when the unnecessary portion of the laminated metal plate is trimmed and removed, the film portion of the trimming end face cannot be cut cleanly, and the peeled film residue remains in a hair shape. In some cases, the phenomenon occurs, and when it is remarkable, film scraps that are torn off in the form of hair are scattered in the process, causing operational troubles.

  Patent Document 9 proposes a method for improving the hair generation of such a film. Here, the polyester on the side in contact with the metal is low crystallized to improve the hair ring by increasing the adhesion with the metal, and further imparting formability by the remelt method, Insufficient or, particularly, low-crystalline polyester is subjected to a remelt treatment, but the adhesion is improved, but the hair ringability is lowered.

  In addition to being excellent in heat laminating properties with a metal plate, the present invention is also superior in high-order workability when can molding is performed after heat laminating. It aims at providing the polyester film for metal plate lamination which suppresses a property fall.

  As a result of intensive studies to solve the above problems, the present inventors have used a biaxially stretched polyester film obtained by forming a copolymerized polyester film containing a specific amount of a trivalent or higher carboxylic acid component in the acid component. By making the melting point and intrinsic viscosity of the film within a specific range, it is excellent in heat laminating properties with metal plates, and also in high-order workability when can-molding after heat laminating. It has been found that a polyester film for metal laminate can be obtained in which the generation of hair at the cut portion is suppressed and the impact resistance of the molded can is not lowered.

That is, the gist of the present invention is as follows.
It is composed of a biaxially stretched polyester film, and the polyester is a copolyester containing 0.15 to 0.40 mol% of a trivalent or higher carboxylic acid component in the acid component, and the melting point of the film is 210 to 235 ° C. A polyester film for laminating metal plates, characterized in that the intrinsic viscosity is 0.70 to 0.85 dl / g.

  The polyester film for laminating a metal plate according to the present invention is suitable for remelt treatment and has high heat laminating property with a metal plate, and has an appropriate intrinsic viscosity, so that it has a high degree of deformation during molding. Excellent in properties. Moreover, since the said polyester film for metal plate lamination is comprised by the copolyester using the carboxylic acid component more than trivalence, since it has moderate hardness and waist, the cut surface of a heat laminate board has a sharp cross section Therefore, the hair generation of the film is suppressed. Furthermore, since the polyester film for metal plate lamination has an appropriate melting point, it does not need to be remelted at a high temperature, so that the strength of the metal plate is not lowered. Since the polyester film for metal plate lamination of the present invention has the above-described characteristics, it can be suitably used as a heat laminate film for preventing corrosion of the metal plate.

Hereinafter, the present invention will be described in detail.
The polyester film for metal plate lamination of the present invention is composed of a biaxially stretched polyester film, and the polyester is a copolymerized polyester containing 0.15 to 0.40 mol% of a trivalent or higher carboxylic acid component in the acid component. The melting point of the film is 210 to 235 ° C., and the intrinsic viscosity is 0.70 to 0.85 dl / g.

  Acid components used in the synthesis of the copolyester include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid , Dodecanedioic acid, dimer acid, maleic anhydride, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, cyclohexanedicarboxylic acid and other dicarboxylic acid components, 4-hydroxybenzoic acid, ε-caprolactone, lactic acid, etc. It is done. In addition, in the present invention, a trivalent or higher carboxylic acid component such as trimellitic acid, trimesic acid, and pyromellitic acid is an essential acid component.

  The dicarboxylic acid component, which is an acid component, is used as a main raw material or a secondary raw material when a copolyester is synthesized by polycondensation with an alcohol component. Among the dicarboxylic acid components, terephthalic acid is preferably used as a main raw material when synthesizing the copolyester because the glass transition point is hardly lowered. On the other hand, among the dicarboxylic acid components, isophthalic acid is suitably used as an auxiliary material for adjusting the melting point and the like of the copolyester having terephthalic acid as the main raw material.

  Conventionally, the terephthalic acid or isophthalic acid was mainly used as the acid component for synthesizing the copolyester. However, the acid component of the present invention has a trivalent or higher carboxylic acid as an auxiliary material in addition to the acid component. Use ingredients. Since the trivalent or higher carboxylic acid component is used as a crosslinking agent when synthesizing the copolymer polyester, the copolyester obtained by three-dimensionally cross-linking the trivalent or higher carboxylic acid component with the copolymer during synthesis. The polyester film made of the material has flexibility as a film and has appropriate hardness and waist. As a result, the effect of suppressing hair at the time of trimming of the heat-laminated plate in which the film and the metal plate are heat-laminated becomes sufficient, so that the generation of hair by the film is suppressed. Among the trivalent or higher carboxylic acid components, trimellitic acid is particularly preferably used from the viewpoint of polymerization stability when synthesizing the copolyester, film formability, and workability of a heat laminated plate obtained by heat lamination. It is done.

  The trivalent or higher carboxylic acid component needs to be contained in the acid component in an amount of 0.15 to 0.40 mol%. When the amount of the trivalent or higher carboxylic acid component in the acid component is less than 0.15 mol%, the effect of suppressing the hair during the trimming step of cutting the heat laminated plate to adjust the shape becomes insufficient.

  On the other hand, when the amount of trivalent or higher carboxylic acid component exceeds 0.40 mol%, the copolyester is likely to gel during synthesis, which causes operational troubles. Moreover, when synthesizing by suppressing gelation, since polymerization does not proceed sufficiently, it becomes impossible to obtain a copolyester having a high intrinsic viscosity.

  Examples of the alcohol component used for the polycondensation reaction with the acid component during the synthesis of the copolyester include ethylene glycol, diethylene glycol, 1,3-propanediol, 1-4 butanediol, neopentyl glycol, 1,6-hexanediol, Examples include polyols such as cyclohexanedimethanol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, ethylene oxide adducts of bisphenol A and bisphenol S.

  The polyester film for metal plate lamination of the present invention is a biaxially stretched film. Biaxial stretching imparts slipperiness to the film, and the laminate property of the metal plate and the moldability of the can can be controlled by the degree of heat treatment after stretching. As the stretching method, sequential biaxial stretching, simultaneous biaxial stretching, and a stretching method combining them are used. The draw ratio is preferably 9 times or more in terms of surface magnification in terms of film thickness uniformity and productivity.

  Melting | fusing point of the polyester film for metal plate lamination of this invention needs to be 210-235 degreeC, and it is preferable that it is the range of 220-230 degreeC.

  When the melting point is less than 210 ° C., the crystallinity of the polyester film for metal plate lamination is lowered, and troubles such as film scratches and breakage due to a decrease in slipperiness with a jig when drawing and ironing, The heat treatment after the molding process may cause whitening or white spots on the polyester film, or decrease the impact resistance.

  On the other hand, if the melting point exceeds 235 ° C., the heat laminating property between the metal plate laminating polyester film and the metal plate is lowered, or if the remelt treatment is performed thereafter, the metal plate needs to be treated at a high temperature. When the counterpart is an aluminum plate, the strength of the aluminum is reduced, and when an impact is applied to the molded can, pinholes are likely to occur.

  A copolyester having a desired melting point is synthesized by appropriately controlling the molecular weight of a polymer produced at the time of synthesis under known synthesis conditions (reaction temperature, time, pressure, etc.) using known raw materials and known synthesis methods. be able to.

  The intrinsic viscosity of the polyester film for metal plate lamination of the present invention needs to be 0.70 to 0.85 dl / g, and preferably in the range of 0.70 to 0.80 dl / g.

  If the intrinsic viscosity is less than 0.70 dl / g, the metal film and the heat-laminated polyester film are easily broken during the high-order processing of the molded can, and the scratches are likely to occur, so that the productivity is extremely deteriorated. In particular, if the capacity of the can increases and the deformation of the film increases during the process of drawing and squeezing from the laminated metal plate to the can, it will not be possible to follow the degree of deformation and the polyester film that has been heat-laminated with the metal plate will not be able to follow. Voids and cracks are generated, and even a slight impact from the outside promotes peeling of the film layer and growth of cracks. As a result, when the heat-laminated film surface is used inside the molded can, the heat-laminated plate from which the polyester film is peeled or the heat-laminated plate with voids or cracks on the film surface comes into direct contact with the contents. Therefore, the flavor-retaining property of the contents is lowered, and there is a problem in flavor properties. In addition, when the heat-laminated film surface is used on the outside of a molded can, voids and scratches are likely to occur on the surface of the heat-laminated film, resulting in a decrease in printed appearance and voids on the surface of the heat-laminated film during long-term storage. There is a risk that the metal plate may corrode from the scratched area.

  On the other hand, when the intrinsic viscosity exceeds 0.85 dl / g, when the polyester film is produced, the load applied to the extruder increases, so the production speed must be sacrificed, and the thickness control of the film becomes difficult. , Film productivity decreases. In addition, the polymerization time and the polymerization process of the copolyester become longer, and it becomes a factor that increases costs due to operational troubles due to the formation of the gel and deterioration of the yield.

  The intrinsic viscosity 0.70 to 0.85 dl / g defined in the present invention is substantially determined by the intrinsic viscosity of the copolyester constituting the polyester film for metal plate lamination of the present invention. In addition, since the intrinsic viscosity of the copolyester generally reflects the molecular weight, known molecular weight control techniques (copolymerization ratio of raw materials used during synthesis, catalyst amount, etc., reaction time during synthesis, temperature, pressure, etc.) ) Can be used appropriately to obtain a copolyester having a desired intrinsic viscosity.

  It is preferable that the glass transition temperature of the polyester film for metal plate lamination of this invention is 60-85 degreeC, and it is especially preferable that it is 70-80 degreeC.

  When the glass transition temperature is less than 60 ° C., the surface of the heat-laminated film is easily damaged at the time of squeezing and ironing. Therefore, when the molded can is filled and stored, the corrosion resistance of the heat-laminated metal plate is lowered. In addition, the flavor of the contents is reduced. Furthermore, in the case of ironing using a punching die, the film is stretched at the cut surface at the upper part of the molding, so that hair tends to be generated. On the other hand, when the glass transition temperature exceeds 85 ° C., the process followability at the time of can molding may be inferior.

  Moreover, 6-50 micrometers is preferable and, as for the thickness of the polyester film for metal plate laminations of this invention, if it is 8-25 micrometers, it is more preferable.

  If the thickness of the film is less than 6 μm, film breakage or the like tends to occur when a heat-laminated metal plate is processed.

  On the other hand, if the thickness of the film exceeds 50 μm, more than the necessary amount is thermally laminated on the metal plate, which is uneconomical due to excessive quality.

  If necessary, an additive such as an antioxidant, a heat stabilizer, an ultraviolet absorber, an antistatic agent and the like can be added to the copolyester. 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.

  Especially in the case of the remelt method in which a film laminated on a metal plate is heat-treated at a temperature equal to or higher than the melting point to make it amorphous and then processed, the slippage with the jig decreases as the film surface is smoothed. In some cases, scratches may break into the surface, or even breakage, but by adding an antioxidant and suppressing a decrease in intrinsic viscosity after remelting, scratch properties such as scratches and breakage can be improved.

  In order to improve the productivity of the polyester film for laminating a metal plate of the present invention or the processability at the time of canning, a small amount of inorganic lubricant such as silica, alumina, kaolin or the like is added to the copolymer polyester, and the film surface is slippery. Is desirable.

  The content of the inorganic lubricant in the film is preferably 0.001 to 0.5% by mass, and more preferably 0.08 to 0.3% by mass. In order to cover the smoothing of the film by remelt treatment, it is effective to increase the amount of addition, but when the amount of inorganic lubricant exceeds 0.5% by mass, the slip property of the film surface is improved. If too much is added, it may cause cracks during molding.

  On the other hand, when the added amount of the inorganic lubricant is less than 0.001% by mass, the slip property of the film is deteriorated, so that the workability at the time of can molding cannot be improved.

  In addition, in order to further improve the slip property of the film surface during film formation, it is effective to incorporate a low molecular weight polymer that is incompatible with the copolymerized polyester. Examples of the low molecular weight polymer include polyethylene, polypropylene, polystyrene, polyamide, and the like, and polyolefin resins such as polyethylene and polypropylene are desirable from the viewpoint of stability and compatibility when blended with the copolymer polyester. The blending amount of the low molecular weight polymer with respect to the copolyester is preferably 0.01 to 1.0% by mass.

  The polyester film for laminating a metal plate of the present invention is thermally laminated to a metal plate such as a steel plate or an aluminum plate. The metal plate to be laminated includes chromic acid treatment, phosphoric acid treatment, electrolytic chromic acid treatment, chromate treatment, etc. Metal plates subjected to chemical conversion treatment, nickel, tin, zinc, aluminum, gun metal, brass, and other various plating treatments can be used.

  As a method of laminating the metal plate laminating polyester film of the present invention and a metal plate, for example, the metal plate is preheated to 200 to 250 ° C. in advance, and the preheated metal plate and film are 30 ° C. from the metal plate, Is a method in which a metal plate and a film are press-contacted with a roll controlled at a temperature as low as 50 ° C. or more and thermally laminated, and then continuously cooled by cooling to room temperature.

  Examples of the preheating method for the metal plate include a heater roll heat transfer method, an induction heating method, a resistance heating method, a hot air transfer method, etc. Especially, when considering the equipment cost and simplification of the equipment, the heater roll heat transfer method is used. It is preferable to use it.

  As a cooling method after heat laminating the metal plate and the polyester film, a method of immersing the heat-laminated metal plate in a coolant such as water or a method of contacting the heat laminate plate with a cooling roll can be used.

  The metal plate on which the film is heat-laminated may be processed as it is, but can be given higher workability by performing the remelt process. That is, after the obtained film is bonded to a metal plate preheated at a temperature 2 to 30 ° C. higher than the melting point of the film and then rapidly cooled, the film laminated with the metal plate is in an amorphous state. Thereby, since the adhesiveness of the heat laminated film and a metal plate becomes high, still higher workability can be provided. In particular, the polyester film for laminating a metal plate of the present invention exhibits a great effect when it is in an amorphous state.

  An adhesive layer may be provided between the metal plate and the polyester film for laminating metal plates by coextrusion, laminating, or coating for the purpose of further improving the heat laminating property and subsequent adhesion to the metal plate. it can. The thickness of the adhesive layer is preferably 1 μm or less in terms of dry film thickness. The resin used for the adhesive layer is not particularly limited, but is preferably an epoxy resin, a polyurethane resin, a polyester resin, or a thermosetting resin layer made of these various modified resins.

  In addition, on the opposite surface of the metal plate to be heat-laminated, one or more resin layers are provided to improve the appearance and printability of the metal can body and to improve the heat resistance and retort resistance of the film. Can be provided. These resin layers can be provided on the metal plate by a coextrusion method, lamination, or coating.

  The heat-laminated metal plate can be used, for example, as a metal container that has been sufficiently processed until it can be filled with food and drink and used for use and a part thereof. As such a metal container, a metal container 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 formed into a shape that can be wound In particular, when 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 and ironing The excellent processability of the film of the present invention is exhibited.

  The metal container using the film of the present invention has coffee, green tea, black tea, oolong tea, beer, particularly highly corrosive acidic beverages (fruit juice beverages) and milky beverages because of its excellent retort resistance, flavor properties, and corrosion resistance. Suitable for filling contents such as various processed foods.

  The method for synthesizing the copolymer polyester constituting the polyester film for metal plate lamination of the present invention is not particularly limited, and examples thereof include a transesterification method and a direct polymerization method. Examples of catalysts used for transesterification include oxides and acetates of Mg, Mn, Zn, Ca, Li, and Ti. Examples of catalysts used for direct polymerization include Sb, Ti, Ge oxide, and acetate. And the like.

  In order to remove the acid component, alcohol component, and oligomers produced by reaction with the acid component and alcohol component, and by-products such as acetaldehyde or tetrahydrofuran, the synthetic product at the time of synthesizing the copolyester It is preferable to carry out solid phase polymerization at a temperature of 200 ° C. or higher under reduced pressure or inert gas flow.

  The manufacturing method of the polyester film for metal plate lamination of this invention is described below. The polyester film for laminating a metal plate of the present invention is obtained by melt-mixing a copolymer polyester containing 0.15 to 0.40 mol% of a trivalent or higher carboxylic acid component in an acid component with an extruder, and then forming a sheet through a T die It is manufactured by performing biaxial stretching and heat setting on the obtained unstretched film after extruding the film onto a cooling drum and winding it while cooling. For example, in the sequential biaxial stretching method, after winding an unstretched film extruded into a sheet shape through a T-die while cooling, it is first 2.5 to 3.6 times in the longitudinal direction and then 2.7 in the lateral direction. Biaxial stretching is performed to obtain a stretching ratio of ˜4.0 times. After being biaxially stretched, the stretched film is subjected to heat fixing treatment at 130 to 170 ° C. for several seconds continuously, and several percent relaxation treatment is performed to adjust the heat shrinkage characteristics of the stretched film. Then, the biaxially stretched film is obtained by cooling the stretched film which performed the relaxation process to the temperature below Tg of a film.

  Next, the present invention will be specifically described with reference to examples.

  Evaluation methods of characteristics in the following examples and comparative examples are shown below.

A. 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. Melting point (Tm)
Using a Perkin Elmer DSC, the melting point at elevated temperature was measured at 20 ° C./min. The measurement sample used was a film which was melted and then rapidly cooled at a rate of 100 ° C./min or more to be in an amorphous state.

C. Thermal laminating property A sample film and an aluminum plate having a thickness of 0.3 mm are superposed and supplied between a metal roll heated to 220 ° C. and a silicon rubber roll, the speed is 20 m / min, and the linear pressure is 4.9 × 10 ^4. Heat-bonded at N / m, immersed in ice water after 2 seconds, and cooled to obtain a laminated aluminum plate. From the obtained laminated aluminum plate, a strip-shaped test piece having a width of 18 mm (the end portion is not laminated and the laminated portion is ensured to be 8 cm or more in the MD direction (flow direction)) in the TD direction (width) 11 sheets were cut out in the direction). 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.
X: The peel strength of 7 or more test pieces is less than 2.9N.

D. Formability With the film side of the laminated aluminum plate obtained by the method described in C above as the outer surface of the can body, after remelting at the temperature shown in Table 2, squeezing and ironing is performed at a speed of 200 cans / minute, equivalent to 500 ml 100 cans of each of the two-piece cans were molded. The outer surface of the obtained can was visually observed and the moldability was evaluated according to the following criteria.
(I) Scratch property ○: The number of cans with scratches on the film surface is less than 5 cans.
Δ: 5 or more cans but less than 10 cans with scratches observed on the film surface.
X: 10 or more cans with scratches observed on the film surface.
(B) Hair generation O: No film elongation of 3 mm or more in width at the cut surface of the upper part of the molded can is observed.
(Triangle | delta): 1 or more cans but less than 10 cans by which film elongation of width 3mm or more in the cut surface of a shaping | molding can upper part is recognized.
X: 10 or more cans in which film elongation of 3 mm or more in width at the cut surface of the upper part of the formed cans is observed.

E. Pinhole Resistance Ten cans obtained by filling the cans obtained by the method described in D above were wound and joined with tabs, and 10 2-piece beverage cans corresponding to 500 ml were prepared. After this beverage can was heated at 65 ° C for 20 minutes with warm water, a strike core (tip R1 / 16 inch) was set at the center of the can body in an atmosphere of 20 ° C, and a 300 g weight was shot from a height of 10 cm. After dropping on the core and applying an impact, the presence or absence of aluminum pinholes was visually examined, and the pinhole resistance was evaluated according to the following criteria.
○: No pinhole generated ×: One pin or more generated pinhole

Preparation method of copolyester (I) A slurry of terephthalic acid (TPA) and ethylene glycol (EG) is continuously supplied to an esterification reaction vessel in which bis (β-hydroxyethyl) terephthalate and its low polymer are present. Then, the reaction was carried out under the conditions of a temperature of 250 ° C. and a pressure of 50 hPaG to continuously obtain a PET oligomer having an esterification reaction rate of 95%. On the other hand, a slurry composed of isophthalic acid (IPA) and EG was charged into another esterification reaction can and subjected to esterification at a temperature of 200 ° C. to obtain a reaction solution of IPA and EG. A PET oligomer is charged into a polymerization reactor, followed by IPA and EG reaction solution, trimellitic acid, and silicon dioxide with an average particle size of 2.5 μm as a lubricant, 0.1% by mass of the theoretical polymer amount, and a hinder as an antioxidant. Add 0.02 mass% of the theoretical polymer amount of dophenol antioxidant (Irganox 1010 manufactured by Ciba Specialty), 0.01 mass% of the theoretical polymer amount of germanium dioxide as a catalyst, and reduce the pressure in the polymerization reactor. Finally, a polycondensation reaction was performed at a temperature of 280 ° C. and a pressure of 0.9 hPaG. Adjust the copolymerization ratio of terephthalic acid, isophthalic acid, and trimellitic acid to the values shown in Table 1, and adjust the melting point and intrinsic viscosity to the values shown in Table 1, Polymerized polyesters (I) A1 to A14 were obtained.

Preparation of master batch (II) containing a low molecular weight polymer As an auxiliary material, 98.6% by mass of the copolyester (I) A1 in Table 1 and 1.4% by mass of the following polyethylene, which is a low molecular weight polymer, are biaxially vented. The mixture was melt-kneaded at 260 ° C. using a machine to obtain a master batch (II) containing a low molecular weight polymer.
Low molecular weight polymer: polyethylene (Lycowax PE190 manufactured by Clariant)
Number average molecular weight Mn5500 Melting point 128 ° C

Examples 1-6, Comparative Examples 1 and 4-8
96.43% by mass of copolymer polyesters (I) A1 to A7 and A10 to A14 of Table 1 and 3.57% by mass of a low molecular weight polymer-containing masterbatch (II) were mixed, and each ranged from 255 to 280 ° C. After melt kneading with an extruder, the film extruded from the T-die was rapidly cooled and solidified to obtain an unstretched polyester film.

  The obtained unstretched polyester film was stretched 3.4 times in the MD direction by a preheating roll at 70 ° C. and a stretching roll at 90 ° C., and then gripped by a clip in the tenter, and traveled through a preheating zone at 80 ° C. Thereafter, the film was stretched 3.7 times in the TD direction at 100 ° C. Thereafter, the relaxation rate in the TD direction was set to 3%, heat treated at 155 ° C. for 4 seconds, cooled to room temperature, wound up, and the polyester films B1 to B7, B10 for metal plate lamination in Table 2 having a thickness of 12 μm -B14 was obtained.

  Using the obtained polyester films B1 to B7 and B10 to B14 for metal plate lamination in Table 2, laminated aluminum plates were obtained by the method described in C above, and the thermal laminating properties were evaluated.

  The can moldability of laminated aluminum plates obtained by heat laminating polyester films B1 to B7 and B10 to B14 for metal plate lamination in Table 2 obtained by the method described in C above was evaluated by the method described in D above.

  A molded can obtained by processing a laminated aluminum plate obtained by heat laminating polyester films B1 to B7 and B10 to B14 for metal plate lamination in Table 2 obtained by the method described in D above was filled with water. The pinhole resistance was evaluated by the method.

  Table 2 shows various physical properties and various evaluation results of the polyester films B1 to B7 and B10 to B14 for metal plate lamination obtained in the above test.

  In Example 1, copolymer polyester (I) A1 of Table 1 synthesized while appropriately controlling the reaction by a known synthesis method was used as a main raw material, and the melting point was 224 ° C. and the intrinsic viscosity was 0.71 dl / g. A polyester film B1 for laminating metal plates was prepared. As shown in Table 2, the obtained polyester film B1 for laminating metal plates has good adhesion to the aluminum plate during thermal lamination, and the generation of scratches on the film surface and the generation of hair on the cut surface are suppressed. It was. Furthermore, a molded can obtained by processing a laminated aluminum plate obtained by heat laminating the above film was excellent in pinhole resistance and maintained sufficient aluminum strength.

  In Example 2, compared with the copolymer polyester (I) A1 of Table 1 used in Example 1, the ratio of TPA in the acid component was reduced, and the copolymer polyester (I) A2 having a higher IPA ratio was used. The polyester film B2 for metal plate lamination shown in Table 2 was prepared under the same film forming conditions as in Example 1. The evaluation result of the obtained polyester film B2 for metal plate lamination was the same as in Example 1.

  In Example 3, copolymer polyester (I) A3 in which the proportion of trimellitic acid in the acid component was decreased and the proportion of TPA was increased compared to copolymer polyester (I) A1 in Table 1 used in Example 1. The polyester film B3 for metal plate lamination of Table 2 was created on the same film-forming conditions as Example 1 using this. The evaluation result of the obtained polyester film B3 for metal plate lamination was the same as in Example 1.

  In Example 4, copolymer polyester (I) A4 in which the proportion of trimellitic acid in the acid component was increased and the proportion of TPA was decreased as compared with copolymer polyester (I) A1 in Table 1 used in Example 1. The polyester film B4 for metal plate lamination of Table 2 was created on the same film-forming conditions as Example 1 using this. The evaluation results of the obtained polyester film B4 for metal plate lamination were the same as in Example 1.

  In Example 5, compared with the copolymer polyester (I) A1 of Table 1 used in Example 1, the ratio of TPA in the acid component was increased, and the copolymer polyester (I) A5 was used in which the ratio of IPA was decreased. The polyester film B5 for metal plate lamination shown in Table 2 was prepared under the same film forming conditions as in Example 1. The evaluation results of the obtained polyester film B5 for metal plate lamination were the same as in Example 1.

  In Example 6, compared with the copolymerized polyester (I) A1 of Table 1 used in Example 1, the time required for synthesis was lengthened, and the copolymerized polyester (I) was increased in intrinsic viscosity to 0.84 dl / g. Using A6, a polyester film B6 for metal plate lamination in Table 2 was prepared under the same film-forming conditions as in Example 1. The evaluation result of the obtained polyester film B6 for metal plate lamination was the same as in Example 1.

  In Comparative Example 1, using the copolyester (I) A7 in which the time required for the synthesis was shortened compared with the copolyester (I) A1 of Table 1 used in Example 1, the same film-forming conditions as in Example 1 were used. Polyester film B7 for metal plate lamination of Table 2 was created. The obtained polyester film B7 for metal plate lamination had an intrinsic viscosity of 0.62 dl / g, which was lower than the intrinsic viscosity of 0.70 to 0.85 dl / g specified in the present invention. Therefore, the polyester film heat-laminated with the aluminum plate was more likely to cause scratches on the film surface as compared with Example 1.

  In Comparative Example 2, the time required for synthesis was longer than that of the copolyester (I) A1 in Table 1 used in Example 1, and the copolyester (I) was increased in intrinsic viscosity to 0.88 dl / g. A8 was used, but a large amount of gel-like material was generated, causing a trouble with polymerization. Therefore, preparation and evaluation of the polyester film for metal plate lamination were not performed.

  In Comparative Example 3, copolymer polyester (I) A9 in which the proportion of trimellitic acid in the acid component was increased and the proportion of TPA was decreased as compared with copolymer polyester (I) A1 in Table 1 used in Example 1. Was used. However, the copolymerized polyester (I) A9 has a remarkable formation of a gel-like product, and the intrinsic viscosity cannot be sufficiently increased. Therefore, preparation and evaluation of the polyester film for metal plate lamination were not performed.

  In Comparative Example 4, copolymer polyester (I) A10 in which the proportion of trimellitic acid in the acid component was decreased and the proportion of TPA was increased as compared with copolymer polyester (I) A1 in Table 1 used in Example 1. The polyester film B10 for metal plate lamination of Table 2 was produced on the same film-forming conditions as Example 1 using this. Since the obtained polyester film B10 for laminating metal plates did not have appropriate hardness and waist, the hair improving effect on the cut surface was insufficient.

  In Comparative Example 5, copolymer polyester (I) A11 in which the proportion of IPA in the acid component was reduced and the proportion of TPA was increased compared to copolymer polyester (I) A1 in Table 1 used in Example 1 was used. The polyester film B11 for metal plate lamination shown in Table 2 was prepared under the same film forming conditions as in Example 1. The resulting polyester film B11 for laminating metal plates had a melting point higher than 210 to 235 ° C. defined in the present invention, and therefore it was necessary to perform a remelt treatment at a high temperature. The pinhole resistance of the can decreased.

  In Comparative Example 6, a copolymer polyester (I) A12 in which the proportion of IPA was further reduced and the proportion of TPA was increased compared with the copolymer polyester (I) A11 of Table 1 used in Comparative Example 5 was used. A polyester film B12 for metal plate lamination shown in Table 2 was prepared under the same filming conditions as in 1. The obtained polyester film B12 for laminating a metal plate had a melting point that was higher than that of Comparative Example 5 and greatly exceeded the range of 210 to 235 ° C. defined in the present invention. Therefore, it became necessary to perform the remelt treatment at a higher temperature, the strength of the aluminum plate was lowered, and the pinhole resistance of the molded can was lowered. Moreover, the heat laminating property also decreased.

  In Comparative Example 7, compared with the copolymer polyester (I) A1 of Table 1 used in Example 1, the proportion of IPA in the acid component was increased, and the copolymer polyester (I) A13 having a decreased TPA ratio was used. A polyester film B13 for laminating a metal plate was prepared under the same filming conditions as in Example 1. Since the obtained polyester film B13 for metal plate lamination became lower than melting | fusing point 210 degreeC-235 degreeC prescribed | regulated by this invention, scratch property deteriorated and the improvement effect of hair was also impaired.

  In Comparative Example 8, copolymer polyester (I) A14 in which the proportion of trimellitic acid in the acid component was decreased and the proportion of TPA was increased as compared with copolymer polyester (I) A1 in Table 1 used in Example 1. Was used to form a polyester film B14 for laminating metal plates under the same filming conditions as in Example 1. As shown in Table 2, the obtained polyester film B14 for laminating a metal plate had a good scratch property because gelation at the time of synthesis was suppressed and the intrinsic viscosity could be increased to 0.86 dl / g. Although it was able to be obtained, since the intrinsic viscosity was raised too much from the range of the present invention, the result of the hair generation was inferior.

  The polyester film for laminating a metal plate of the present invention is excellent in heat laminating property with a metal plate, excellent in high-order workability after heat laminating with a metal plate, and further suppressing the generation of hair in a cut portion and a molded can Therefore, it can be suitably used as a heat laminate film for preventing corrosion of the metal plate.

Claims (1)

  It is composed of a biaxially stretched polyester film, and the polyester is a copolyester containing 0.15 to 0.40 mol% of a trivalent or higher carboxylic acid component in the acid component, and the melting point of the film is 210 to 235 ° C. A polyester film for laminating metal plates, characterized in that the intrinsic viscosity is 0.70 to 0.85 dl / g.