Laminated polyester film for metal sheet lamination molding

Abstract

Provided is a biaxially stretched polyester film for metal sheet lamination molding. With reference to can lid production by thermocompression bonding in a lamination process, this biaxially stretched polyester film exhibits an excellent adhesiveness and an excellent openability free of feathering during opening. This film can also prevent corrosion even for contents that readily cause metal corrosion. The laminated film for metal sheet lamination molding has a layer containing an amorphous polyester resin B provided on one surface of a biaxially stretched polyester film that contains a polyester resin A. In measurement of the laminated film using a dynamic viscoelasticity measurement instrument, the maximum temperature peak temperature Te1 (°C) of the loss elastic modulus of the film and the temperature Te2 (°C) of the peak at the next highest temperature after Te1 satisfy 15 ≤ Te1 (°C) - Te2 (°C) ≤ 90.

Description

Laminated Polyester Film for Metal Plate Laminating Forming Process

[0001] The present invention relates to a laminated polyester film for metal plate laminating forming process.

[0002] Generally, metal cans are coated to prevent corrosion of the inner and outer surfaces. In recent years, as a method of imparting rust prevention without using organic solvents for the purpose of simplifying processes, improving hygiene, preventing pollution, etc., coating with a thermoplastic resin film such as a polyester film has been carried out. That is, a laminate of a thermoplastic resin film on a metal plate such as tinplate, tin-free steel, aluminum, etc. is used for metal cans such as food cans and beverage cans and their lids. In the case of metal lids, in recent years, there has been a tendency to attach a can lid called an easy-open end (EOE) that can be opened by hand without using an opening tool such as a can opener. For this reason, there is a need for an opening property that allows the film to open the can lid without generating feathering.

[0003] In order to achieve good opening properties, the following two requirements are necessary. (i) The film adheres closely to the metal plate and does not peel off from the metal plate during opening. (ii) The film is broken and torn with appropriate stress.

[0004] Regarding (i), in addition to the method of using an adhesive to bond a polyester film to a metal plate or the like, for example, a method of imparting thermoadhesive properties to the polyester film and directly bonding it to the adherend, or further, a method of imparting thermoadhesive properties by forming a laminated structure of a layer having a thermoadhesive layer with a polyester film as a base material.

[0005] Among these, in the case of a laminated polyester film having a thermoadhesive layer, it is excellent in that it is easy to have thermoadhesive properties and film strength and dimensional stability (see, for example, Patent Documents 1 and 2). However, for example, when using a metal plate such as tinplate or aluminum that is difficult to thermoadhere, sufficient adhesiveness cannot be obtained.

[0006] On the other hand, Patent Document 3 describes a laminated polyester film that can be thermoadhered at a low temperature. However, when this film is used for EOE, since the film stretches and is difficult to cut, feathering is likely to occur.

[0007] Furthermore, regarding (ii), Patent Document 4 discloses a biaxially stretched polyester resin film for metal can lids in which the surface orientation coefficient is defined within a certain range. This film is intended to have excellent moldability, impact resistance, and opening properties. However, when this film is used for EOE, corrosion may occur depending on the contents.

[0008] To prevent corrosion of EOE (End of Earth Engraving), Patent Document 5 discloses a technique for coating a metal surface with a film via an adhesive. However, even with the use of an adhesive, it may not be able to adequately follow the lamination process and subsequent molding, and in some cases, corrosion may progress because the adhesion cannot be maintained during retort processing.

[0009] JP 6-340047 JP 7-101015 JP 5-42643 JP 2001-335650 JP 2008-296440

[0010] The present invention was devised to solve the problems of the prior art described above, and its purpose is to provide a laminated polyester film for metal sheet bonding and molding that has excellent adhesion and excellent opening properties that do not cause feathering when opening when a can lid is manufactured by heat pressing in the lamination process, and that can prevent corrosion even with contents that are prone to metal corrosion.

[0011] As a result of diligent research to achieve the above objective, the inventors of the present invention have discovered that by using polyester of a specific composition for the polyester constituting the film, it is possible to manufacture a metal can lid that exhibits excellent adhesion to metal plates and corrosion resistance, while simultaneously having excellent opening properties that prevent feathering when opened, by ensuring that the peak of the film's loss modulus is within a specific temperature range. This has led to the completion of the present invention.

[0012] In other words, the present invention comprises the following configurations (1) to (6): (1) A laminated polyester film for metal plate lamination, wherein a layer containing amorphous polyester resin B is provided on one side of a biaxially oriented polyester film containing polyester resin A, and the highest temperature peak temperature Te1 (°C) and the temperature Te2 (°C) of the loss modulus of the film, measured using a dynamic viscoelasticity measuring device for the laminated film, satisfy the following formula: 15 ≤ Te1 (°C) - Te2 (°C) ≤ 90 (2) The laminated polyester film for metal plate lamination according to (1), wherein the polyester resin B contains 0.5 to 5 mol% of trifunctional or higher polycarboxylic acid components with respect to 100 mol% of the total polycarboxylic acid components constituting the polyester resin B. (3) The laminated polyester film for metal plate lamination according to (1), wherein the polyester resin B consists of a plurality of ester constituent units containing two or more types of polycarboxylic acid components and two or more types of polyol components. (4) A laminated polyester film for metal sheet lamination molding according to (1), wherein the layer containing polyester resin B is a coating layer. (5) A method for manufacturing a metal sheet, comprising the step of heat-pressing a biaxially oriented polyester film for metal sheet lamination molding according to any one of (1) to (4) onto a metal sheet. (6) A method for manufacturing a metal container, comprising the step of molding a metal sheet obtained by the method for manufacturing a metal sheet according to (5).

[0013] The laminated polyester film for metal sheet bonding and molding according to the present invention exhibits excellent adhesion when heat-pressed onto a metal sheet, prevents deterioration of opening performance due to film peeling during opening, and prevents corrosion even with contents prone to metal corrosion. Furthermore, because the film is designed to tear under appropriate stress, it can be opened without feathering, making it suitable for use as a metal can lid.

[0014] This is an explanatory diagram of Te1 and Te2 in the present invention.

[0015] Embodiments of the present invention will be described in detail below. The laminated polyester film for metal plate lamination molding of the present invention is a laminated film in which a layer containing amorphous polyester resin B is provided on one side of a biaxially oriented polyester film containing polyester resin A, and is characterized in that the highest peak temperature Te1 (°C) and the next highest peak temperature Te2 (°C) of the loss modulus of the laminated film satisfy a specific formula.

[0016] <Polyester Resin A> The polyester resin A constituting the biaxially oriented polyester film is not particularly limited as long as it is a polyester resin, but preferably examples include homopolyethylene terephthalate, polyethylene terephthalate copolymer, and polyethylene-2,6-naphthalate copolymer. Homopolyethylene terephthalate is particularly preferred for suppressing feathering when opening.

[0017] Polyester resin A may be a polyester resin copolymerized with a third component to the extent that it does not affect the feathering properties at opening. Such copolymerization component may be a polycarboxylic acid component or a polyol component. Examples of polycarboxylic acid components include aliphatic dicarboxylic acids such as adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, fumaric acid, and maleic acid; aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid; and alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid. Examples of alcohol components include aliphatic diols such as 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, and triethylene glycol; and alicyclic diols such as 1,4-cyclohexanedimethanol. Among these, isophthalic acid, 2,6-naphthalenedicarboxylic acid, fumaric acid, maleic acid, 1,4-cyclohexanedimethanol, and neopentyl glycol are preferred because they have the effect of improving moldability without worsening opening properties. When polyester resin A contains copolymer components as described above, it is preferable that the total amount of copolymer components be less than 10 mol%, when the total amount of all polycarboxylic acid components and all polyol components constituting the polyester is 200 mol%. This makes it easier to improve feathering resistance when opening.

[0018] The layer containing polyester resin A may also contain other resins blended into it. Examples of other resins include polycarbonate, polyethylene, polypropylene, polyamide, polyvinyl chloride, ionomer, and silicone resin.

[0019] Furthermore, it is preferable to include a lubricant in polyester resin A. The lubricant can be inorganic or organic, but inorganic lubricants are preferred. Examples of inorganic lubricants include silica, alumina, titanium dioxide, calcium carbonate, and barium sulfate, while examples of organic lubricants include silicone resin particles and cross-linked polystyrene particles. In particular, a preferred lubricant in terms of pinhole resistance is a monodisperse lubricant with a particle size ratio (long diameter / short diameter) of 1.0 to 1.2. Examples of such lubricants include spherical silica, spherical silicone resin particles, and spherical cross-linked polystyrene particles. When silica is used as a lubricant, it is preferable to add it in the range of 0.01% to 0.3% by mass if the average particle size is 1.5 μm, or in the range of 0.05% to 0.5% by mass if the average particle size is 0.8 μm.

[0020] Polyester resin A may also contain other additives, such as antioxidants, dispersants, viscosity modifiers, fluorescent whitening agents, heat stabilizers, UV absorbers, and antistatic agents.

[0021] <Polyester Resin B> Polyester resin B is an amorphous polyester. Here, amorphous means that, according to the method described in JIS-K-7121, no melting peak is observed when a mass of approximately 10 mg is heated from 20°C at a rate of 20°C / min in DSC measurement. Polyesters are condensates of polycarbonates and polyols. Examples of polycarboxylic acid components include aromatic polycarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, trimellitic acid, and pyromellitic acid; aliphatic polycarboxylic acids such as adipic acid, azelaic acid, sebacic acid, dimer acid, fumaric acid, and maleic acid; and alicyclic polycarboxylic acids such as 1,4-cyclohexanedicarboxylic acid. Examples of polyol components include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, glycerol, pentaerythritol, trimethylolethane, and trimethylolpropane; and alicyclic polyols such as 1,4-cyclohexanedimethanol.

[0022] These can be used individually or in combination of two or more, but it is more preferable to use multiple ester constituent units containing two or more polycarboxylic acid components and two or more polyol components to reduce the crystallinity of the resin. Among these, terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, fumaric acid, maleic acid, and trimellitic acid are preferred as polycarboxylic acid components, and ethylene glycol, 1,2-propanediol, 1,4-cyclohexanedimethanol, and neopentyl glycol are preferred as polyol components. The polycarboxylic acid and polyol components are preferably designed so that the polyester does not have crystallinity, and the most abundant polycarboxylic acid component is preferably 90 mol% or less, more preferably 85 mol% or less, and particularly preferably 80 mol% or less, based on 100 mol% of the total polycarboxylic acid components. Similarly, the most abundant polyol component is preferably 90 mol% or less, more preferably 85 mol% or less, and particularly preferably 80 mol% or less, based on 100 mol% of the total polyol components.

[0023] Furthermore, the Tg of polyester resin B is preferably 25°C or higher and 75°C or lower, more preferably 30°C or higher and 75°C or lower, and even more preferably 50°C or higher and 70°C or lower. If the Tg of polyester is 25°C or higher, blocking is easily suppressed when winding the laminated film, which is made of biaxially oriented polyester film made of polyester resin A and then laminated with polyester resin B, into a roll shape. On the other hand, if it is 75°C or lower, it is easy to laminate without impairing adhesion to metal.

[0024] To achieve a preferred Tg range, for example, when the total polycarboxylic acid component is 100 mol%, it is preferable to include 50-80 mol% of terephthalic acid, 0-30 mol% of isophthalic acid, and 0-30 mol% of 2,6-naphthalenedicarboxylic acid, and when the total polyol component is 100 mol%, it is preferable to include 20-90 mol% of ethylene glycol, 0-80 mol% of 1,2-propanediol, and 0-40 mol% of 1,4-cyclohexanedimethanol.

[0025] Polyester resin B plays a role in improving opening properties and corrosion resistance through its high adhesion to metal plates. When a polycarboxylic acid component with three or more functions, such as trimellitic acid, is included in polyester resin B, the polyester acquires a branched structure, improving cohesive force and thus enhancing adhesion. Adhesion to metal plates is easily improved if the content of a polycarboxylic acid component with three or more functions is 0.5 mol% or more of the total 100 mol% polycarboxylic acid component. Furthermore, if it is 5 mol% or less, the cohesive force is not too high, and opening properties are less likely to be impaired. Additionally, including a dicarboxylic acid component with unsaturated bonds, such as fumaric acid or maleic acid, in polyester resin B can also increase the cohesive force of polyester resin B, thus enhancing adhesion. It is preferable that the content of unsaturated dicarboxylic acids is 5 mol% or more of the total 100 mol% polycarboxylic acid component constituting polyester resin B, as this improves adhesion to metal plates. Side reactions are easily suppressed if the content of unsaturated dicarboxylic acids is 20 mol% or less. In this case, the acid value of polyester resin B is preferably 100 eq / ton or higher, more preferably 200 eq / ton or higher, and particularly preferably 300 eq / ton or higher. Having an acid value above the above lower limit ensures sufficient adhesion of polyester resin B to the metal substrate, and thus improves corrosion resistance.

[0026] It is preferable that polyester resin B is a sufficiently random copolymer polymer, with all its constituent monomer components added during polymerization. There is a method to obtain a polyester of a desired composition by kneading two or more different polyesters, which have been polymerized separately, during melting. In this case, it is preferable that the transesterification reaction proceeds sufficiently during melting so that the resin exhibits amorphous properties, that is, it is preferable that no melting point peak is observed in the DSC measurement described above.

[0027] The reduced viscosity of polyester resin B is preferably 0.2 to 0.6 dl / g, and more preferably 0.3 to 0.5 dl / g. If the reduced viscosity is 0.2 dl / g or higher, sufficient cohesive force is easily achieved, resulting in good adhesion. If it is 0.6 dl / g or lower, it is less likely to stretch too much and hinder opening.

[0028] It is preferable that polyester resin B further contains a catalyst. By including a catalyst, the branching structure formation of polyester resin B can be promoted, and the adhesion to metal can be further improved. Examples of catalysts include acid catalysts such as sulfuric acid, p-toluenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, camphor sulfonic acid, and phosphoric acid, as well as amine blocks (partially neutralized by adding an amine) of these, organotin compounds such as dibutyltin dilaurylate, titanium compounds such as titanium tetrabutoxide, zinc compounds such as zinc acetate, hafnium compounds such as hafnium chloride / THF complex, and rare earth compounds such as scandium triflate. One or more of these can be used in combination. Among these, dodecylbenzenesulfonic acid and its neutralized product are preferred in terms of compatibility with polyester resin B and hygiene.

[0029] The mixing ratio of the catalyst to the polyester resin B is preferably (polyester resin B) / (catalyst) = 100 / 0.01 to 100 / 1 (parts by mass), more preferably 100 / 0.05 to 100 / 0.8 (parts by mass), and most preferably 100 / 0.1 to 100 / 0.5 (parts by mass). Being within this range enhances the adhesion of the polyester resin B to the metal, and when processed into a metal lid, feathering at the time of opening can be more effectively prevented. Side reactions such as gelation are more likely to occur when the amount of catalyst added is large, but it is preferable to add the catalyst after the production of the polyester resin B because this suppresses side reactions.

[0030] Polyester resin B may contain other additives, such as antioxidants, dispersants, viscosity modifiers, fluorescent whitening agents, heat stabilizers, UV absorbers, and antistatic agents. However, it is important that the amount of these additives is kept to a minimum and does not affect the flavor.

[0031] <Film Properties> As shown in Figure 1, the laminated polyester film of the present invention preferably has a difference between Te1 (°C) and Te2 (i.e., Te1 (°C) - Te2 (°C)) of 15 or more and 90 or less, where Te1 (°C) is the highest peak temperature of the loss modulus of the film measured using a dynamic viscoelasticity measuring device, and Te2 (°C) is the next highest peak temperature after Te1. The value of Te1 (°C) - Te2 (°C) is more preferably 20 or more and 85 or less, and particularly preferably 25 or more and 80 or less. If Te1 (°C) - Te2 (°C) is 15 or more, the thermal adhesion to the metal plate in the lamination process is good, and feathering is easily suppressed when the metal lid is opened. On the other hand, if it is 90 or less, feathering caused by excessive stretching of the polyester resin B is easily suppressed.

[0032] In the present invention, Te1 is preferably 90°C to 120°C, and more preferably 95°C to 115°C. If Te1 is 90°C or higher, feathering is less likely to occur when opening the metal lid. On the other hand, if Te1 is higher than 120°C, the molecular orientation and crystallinity of the film become too high, which tends to significantly reduce moldability, even for lid applications where the degree of moldability is low. The value of Te1 depends on the copolymerization components and copolymerization amount, but can be adjusted by the film formation conditions, particularly by the biaxial stretching ratio or stretching temperature and the heat setting temperature. Depending on whether polyester resin A is homopolyethylene terephthalate or copolymerized polyethylene terephthalate, and the type and amount of copolymerized monomer components, the stretching ratio should be approximately 3.3 to 4.2 times in both the longitudinal and transverse directions, the stretching temperature should be approximately 90 to 105°C, and the heat setting temperature should be set to 180 to 220°C. This makes it easier to adjust Te1 to the aforementioned preferred range, and as a result, it becomes easier to appropriately adjust the Te1-Te2 value. The Te1-Te2 value should preferably be adjusted by adjusting Te1 using the method described above, while adjusting the Te2 value using the copolymerized components and amount of copolymerization, and it is preferable to set the Tg of polyester resin B to the aforementioned preferred range.

[0033] Here, Te1 and Te2 are measured using a dynamic viscoelasticity measuring device at a frequency of 10 Hz and a dynamic displacement of ±25 × 10⁻⁶. －４ It can be calculated using cm and a heating rate of 2°C / min.

[0034] <Film Manufacturing Method> The manufacturing method for the laminated polyester film for metal plate lamination molding of the present invention described above is not particularly limited and can be manufactured by conventionally known methods. For example, first, the polyester resin A is thoroughly dried and then melt-extruded using an extruder at a crystal melting peak temperature (Tp) in DSC + 30 to 70°C to create an unstretched laminated sheet.

[0035] Next, the unstretched laminated sheet is manufactured by sequential or simultaneous biaxial stretching and heat fixing. When forming a film by sequential biaxial stretching, the unstretched laminated sheet is heated by roll heating, infrared heating, etc., and first stretched in the longitudinal direction, and then stretched transversely with a tenter. At this time, it is preferable to set the stretching temperature to a temperature 10 to 50°C higher than the Tg of the polyester of layer A, and the longitudinal stretching ratio to be in the range of 3.0 to 4.2 times and the transverse stretching ratio to be in the range of 3.1 to 4.5 times. The heat fixing temperature is preferably determined according to the Tp of polyester resin A, and it is good to adjust it in the range of Tp - 40°C to Tp + 15°C. The thickness of the biaxially oriented polyester film can be changed as needed, but the range of 6 to 75 μm is preferable, and among these, the range of 10 to 75 μm, and especially 15 to 50 μm is preferable. If the thickness is 6 μm or more, tearing etc. is less likely to occur during molding, while if it is 75 μm or less, it is economical.

[0036] The method of laminating a layer containing polyester resin B onto a biaxially oriented polyester film containing polyester resin A manufactured as described above is not particularly limited, but a preferred method is to prepare a coating solution by dissolving or dispersing polyester resin B in water or an organic solvent beforehand, and then coating the biaxially oriented polyester film using a coater.

[0037] Examples of organic solvents used to paint polyester resin B include toluene, xylene, ethyl acetate, butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, methyl cellosolve, butyl cellosolve, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, ethylene glycol monoacetate, methanol, ethanol, butanol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, and Solvesso. One or more of these are selected and used, taking into consideration solubility, evaporation rate, etc.

[0038] Polyester resin B can also be dispersed in an aqueous medium and used as a polyester resin aqueous dispersion. Methods for forming an aqueous dispersion include (a) dissolving polyester resin B in a water-soluble organic solvent in which polyester resin B dissolves, and then sequentially adding a basic compound and water as needed to disperse it; and (b) adding polyester resin B, water, a water-soluble organic solvent in which polyester resin B dissolves, and a basic compound as needed, and then heating and dispersing it. Furthermore, if it is desired to reduce the amount of organic solvent or to completely remove it to form an aqueous dispersion, it is also possible to disperse it using an organic solvent having a boiling point of 100°C or less, and then remove the solvent by heating or under reduced pressure. In the case of polyester resin B of the present invention, the former method (a) is preferred from the viewpoint of film-forming properties.

[0039] The coating manufactured using polyester resin B can be applied to a biaxially oriented polyester film using conventionally known equipment such as a roll coater, bar coater, or knife coater by known methods. Of course, it can also be applied using a spray or other methods. The adhesive is preferably applied to a thickness of 0.1 to 20 μm, preferably 0.5 to 15 μm, and more preferably 1 to 10 μm, in terms of solid content. After drying at 90 to 160°C, the film is wound into a roll.

[0040] As the metal plate to which the laminated polyester film for metal plate lamination molding of the present invention is laminated, particularly as a metal plate for can manufacturing, plates such as tinplate, tin-free steel, and aluminum are preferable. The lamination temperature is preferably a temperature at which both the adhesiveness of the film and the formability into a metal container can be achieved. The metal plate laminated with the film can be formed into a metal can lid by a known forming method.

[0041] The laminated polyester film for metal plate lamination molding of the present invention is intended to protect the metal from the contents when used on the inner surface of a metal container, and it may be used not only for the can lid but also for the can body. Further, it may be used on the outer surface to protect the metal from the external environment.

[0042] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to only these examples. Each characteristic value was measured by the following method.

[0043] (1) Measurement of polyester component content A sample of the polyester resin was dissolved in deuterated chloroform, and 1H-NMR analysis was performed using a VARIAN nuclear magnetic resonance (NMR) apparatus 400-MR. The molar ratio was determined from the integral value ratio.

[0044] (2) Measurement of reduced viscosity (unit: dl / g) 0.1 g of a sample of the polyester resin was dissolved in 25 cc of a mixed solvent of phenol / tetrachloroethane (mass ratio 6 / 4), and the measurement was performed at 30°C.

[0045] (3) Measurement of acid value 0.2 g of a sample of the polyester resin was dissolved in 40 ml of chloroform, and titrated with a 0.01 N potassium hydroxide ethanol solution to obtain the equivalent (eq / ton) per 10 ６ g of the polyester resin. Phenolphthalein was used as the indicator.

[0046] (4) Determination of polyester amorphousness Approximately 10 mg of the polyester was enclosed in a measurement aluminum pan and attached to a differential scanning calorimeter (DSCQ100 manufactured by TA Instruments), and when the temperature was raised from 20°C to 300°C at a rate of 20°C / min, it was confirmed that no crystal melting peak (endothermic peak) was observed.

[0047] (5) Glass transition temperature (Tg) of polyester Approximately 10 mg of polyester was sealed in an aluminum pan for measurement and mounted on a differential scanning calorimeter (DSCQ100 manufactured by TA Instruments). The temperature was raised from 20°C to 250°C at a rate of 20°C / min, held for 3 minutes, cooled to 25°C at a rate of 20°C / min, and then raised from 20°C to 250°C again at a rate of 20°C / min to measure the glass transition temperature.

[0048] (6) Loss elastic modulus peak temperatures (Te1 and Te2) Measured using a dynamic viscoelasticity measuring device (DMA8000 manufactured by PerkinElmer) at a measurement frequency of 10 Hz, a dynamic displacement of ±25 μm, and a heating rate of 2°C / min.

[0049] (7) Thermal adhesiveness On one side of a tin plate with a thickness of 0.3 mm, a film sample was laminated by thermal fusion at 220°C with the side where the polyester resin B was laminated facing the metal plate side. The adhesive strength of the film adhered to the tin plate was evaluated according to the following criteria. 〇: Can be thermally adhered, and the film breaks when trying to peel it off. △: Can be thermally adhered, but can be peeled off without cutting the film. ×: Cannot be thermally adhered (the film peels off from the tin plate immediately after adhesion).

[0050] (8) Moldability and opening property The film laminated on the tin according to the method of (7) was punched out to a diameter of 90 mm in the direction where the laminated surface exists on the inner surface side of the lid. A sealing compound was applied to the part that should be on the inner surface side of the curled part, dried, and then partial opening type score processing (score remaining thickness 150 μm, score width 20 μm), riveting, and attachment of an opening tab were performed on the outer surface side of the lid to produce an easy-open lid. The moldability at this time was evaluated according to the following criteria. 〇: Molded normally. △: Floating of the film less than 1 mm occurred after molding. ×: Floating or peeling of the film of 1 mm or more occurred after molding. Furthermore, an opening test was carried out on this lid in hot water at 50°C and evaluated according to the following criteria. ○: Feathering did not occur during opening. △: Feathering occurred during opening, but the elongation of the film was less than 1 mm. ×: Feathering occurred during opening, and the elongation of the film was 1 mm or more.

[0051] (9) Corrosion resistance The lid prepared in (8) was immersed in 3% acetic acid and retorted at 130°C for 2 hours. After treatment, the lid was observed and evaluated according to the following criteria: ○: No discoloration or corrosion was observed at all △: Some discoloration was observed, but it had not progressed to corrosion ×: There were parts that were discolored black and the metal was corroded

[0052] [Synthesis of Polyester Resins A1 to A3] Monomer raw materials were blended to achieve the compositions shown in Table 1. Manganese acetate was added as a transesterification catalyst at a ratio of 1 part by mass per 2000 parts by mass of monomer raw materials. The mixture was charged into a reactor equipped with a stirrer, a rectification column, and a methanol distillation condenser. The mixture was heated while gradually increasing the temperature from 130°C to 240°C, and the methanol produced as a result of the reaction was distilled out of the system for 3 hours to carry out the transesterification reaction. Next, trimethyl phosphate was added as a stabilizer at a ratio of 2 parts by mass per 2000 parts by mass of monomer raw materials, bulk silica with an average particle size of 2.3 μm was added as a lubricant at a ratio of 1 part by mass per 2000 parts by mass of monomer raw materials, and germanium dioxide was added as a polycondensation catalyst at a ratio of 0.3 parts by mass per 2000 parts by mass of monomer raw materials. The reaction mixture was transferred to a reactor equipped with a stirrer and a glycol distillation condenser, and subjected to a polycondensation reaction while gradually increasing the temperature from 240°C to 285°C and decreasing the pressure from atmospheric pressure to a high vacuum of 1 mmHg to obtain polyester resins A1 to A3. The reduced viscosity of the obtained polyester resins was 0.75 dl / g, and the acid value was 20 eq / ton.

[0053] [Synthesis of Polyester Resins B1 to B5] Monomer raw materials were blended to achieve the compositions shown in Table 1. 0.5 parts by mass of tetra-n-butyl titanate (TBT) (0.03 mol% of the total polycarboxylic acid component) was added as a catalyst to a 3 L four-necked flask, and the transesterification reaction was carried out while gradually increasing the temperature to 240°C over 4 hours. After the reaction, the pressure in the system was gradually reduced, and polymerization was carried out under reduced pressure to 10 mmHg over 1 hour, while the temperature was raised to 245°C. Further polymerization was carried out under a vacuum of 1 mmHg or less for 50 minutes. This was cooled to 210°C under a nitrogen atmosphere. Next, a predetermined amount of trimellitic anhydride was added, and stirring was continued for 30 minutes at 200-230°C under a nitrogen atmosphere. This was then removed to obtain polyester resins B1 to B5. The reduced viscosity of the obtained polyester resins was 0.30 dl / g, and the acid value was 300 eq / ton.

[0054]

[0055] [Examples 1-7, Comparative Examples 1 and 2] After drying and melting the polyester resin A described in Table 2, each was extruded from a die at 280°C and rapidly cooled and solidified to obtain an unstretched laminated film. Next, each of these unstretched films was longitudinally stretched at the temperatures and magnifications shown in Table 2, then transversely stretched at the temperatures and magnifications shown in Table 2, and subsequently heat-set at the temperatures shown in Table 2 to obtain a biaxially oriented polyester film. The thickness of the film was 20 μm. Next, each of the polyester resin B described in Table 2 was dissolved in 100 parts by mass (solids), 0.3 parts by mass of dodecylbenzenesulfonic acid as a catalyst, and methyl ethyl ketone as a solvent to obtain a coating solution with a solids content of 20% by weight. Next, this coating solution was coated onto the aforementioned biaxially oriented polyester film using a roll coater and dried at 120°C to form a coating film with a thickness of 2 μm to prepare the laminated films of Examples 1-7 and Comparative Examples 1 and 2. The evaluation results of the obtained films are shown in Table 2.

[0056] [Comparative Example 3] A biaxially oriented polyester film was manufactured in the same manner as in Example 1 using polyester resin A shown in Table 2, and then the film of Comparative Example 3 was obtained without coating with polyester resin B. The evaluation results of the obtained film are shown in Table 2.

[0057]

[0058] As can be seen from Table 2, the laminated films of Examples 1 to 7 that satisfy the conditions of the present invention obtained good film evaluations, whereas the laminated films of Comparative Examples 1 and 2 that do not satisfy the Te1-Te2 condition, and the film of Comparative Example 3 that does not use polyester resin B, clearly showed inferior film evaluations.

[0059] The biaxially oriented polyester film for metal sheet lamination molding of the present invention exhibits excellent adhesion when heat-pressed to a metal sheet, prevents deterioration of opening performance due to film peeling during opening, and prevents corrosion even with contents that are prone to metal corrosion. Furthermore, because the film is designed to tear under appropriate stress, it can be opened without feathering, making it suitable for use as a metal can lid.

Claims

1. A laminated polyester film for metal plate lamination and molding, comprising a biaxially oriented polyester film containing polyester resin A, with a layer containing amorphous polyester resin B on one side, characterized in that the highest temperature peak temperature Te1 (°C) and the next highest temperature peak temperature Te2 (°C), measured using a dynamic viscoelasticity measuring device for the laminated film, satisfy the following equation: 15 ≤ Te1 (°C) - Te2 (°C) ≤ 90 2. The laminated polyester film for metal plate lamination molding according to claim 1, wherein the polyester resin B contains 0.5 to 5 mol% of trifunctional or higher polycarboxylic acid components with respect to 100 mol% of the total polycarboxylic acid components constituting the polyester resin B.

3. The laminated polyester film for metal plate lamination molding according to claim 1, wherein the polyester resin B comprises a plurality of ester constituent units containing two or more polycarboxylic acid components and two or more polyol components.

4. The laminated polyester film for metal plate bonding and molding according to claim 1, wherein the layer containing polyester resin B is a coating layer.

5. A method for manufacturing a metal sheet, comprising the step of heat-pressing a biaxially oriented polyester film for metal sheet lamination molding according to any one of claims 1 to 4 onto a metal sheet.

6. A method for manufacturing a metal container, comprising the step of shaping a metal sheet obtained by the method for manufacturing a metal sheet described in claim 5.

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