JP5811116B2 - Laminated metal plate for 2-piece can and 2-piece laminated can - Google Patents

Description

  The present invention relates to a laminated metal plate for a two-piece can and a two-piece laminated can.

  Conventionally, the inner and outer surfaces of metal cans for foods have the purpose of preventing the corrosion of metal can materials at the same time as maintaining the flavor of the contents, or improving the design of the outer surface and protecting the printed surface. As described above, a solvent-type paint mainly composed of a thermosetting resin was applied. However, in order to form a coating film with a solvent-type paint, heating at a high temperature is required, and a large amount of solvent volatilizes during the heating, which causes problems in terms of work safety and environment. Therefore, recently, a metal can laminate using a thermoplastic resin has been proposed as a corrosion prevention method that does not use a solvent-based paint. Among them, polyester resins are excellent in processability and heat resistance, and therefore, development of films for laminating metal plates based on polyester resins is underway.

  However, in metal cans laminated with polyester resin, during high-temperature sterilization treatment such as retort sterilization treatment, the cyclic trimer in the polyester resin precipitates on the resin surface and impairs the design, and the polyester resin itself becomes white and cloudy. Thus, there are problems such as occurrence of a retort whitening phenomenon that changes color. For this reason, in order to solve these problems, in Patent Document 1, as a polyester resin layer that becomes an outer surface side when molded into a container, 30 to 50% by mass of a polyester resin having ethylene terephthalate as a main repeating unit, A polyester composition containing 50 to 70% by mass of a polyester resin whose main repeating unit is butylene terephthalate is described.

  By the way, in addition to basic characteristics such as processability and adhesion, food canned materials have various functions such as deep drawability, adhesion after processing and retorting, corrosion resistance, and designability for 2-piece can applications. Desired. As a method of making the film laminated metal plate multifunctional, (1) a method of adding a modifier having a function to be added to the film to make the film itself multifunctional, or (2) without modifying the film Any of the methods of coating a modifier having a function desired to be added to the film surface or a resin containing the modifier can be selected.

  The method (1) is a method with high production efficiency and high profitability when a film having a certain function is produced in large quantities. However, since canned foods have a wide variety of shapes and types of contents, and different functions are required for each type, it is not appropriate to use the method (1). The reason is that every time the function to be applied to the film is changed, it is necessary to clean the devices such as the resin extrusion device, casting drum, and cooling roll, and the production line must be stopped for a long time. It is because it will fall remarkably.

  On the other hand, since the method (2) can easily change the function added to the film, it can meet various needs for food canning. The reason is that the function change can be quickly dealt with by washing and replacing the tank containing the coating liquid containing the modifier. In addition, as a method of coating the film surface with a resin containing a modifier, for example, there is a method described in Patent Document 2. In the method described in Patent Document 2, a resin layer containing an epoxy resin as a main component and containing a melamine resin, a blocked isocyanate compound, and a colorant is formed between a metal plate and a film.

On the other hand, the intensity ratio of the Patent Document 3, the film is laminated on the inner surface side of the food canning, and 3085cm ^-1 Raman band intensity near (I3085) and 2968cm ^-1 Raman band intensity near (I2968) by laser Raman It is described that a biaxially stretched polyester film in which the film crystal structure is highly controlled so that (I2968 / I3085) is in the range of 0.2 to 1.0 is excellent in content takeout property.

JP 2005-342911 A JP 2007-185915 A JP 2006-205575 A JP 05-331302 A JP 2002-88233 A JP 2001-335682 A JP 2004-58402 A JP 2004-249705 A Japanese Patent Laid-Open No. 04-266984 Japanese Patent Laid-Open No. 08-199147 Japanese Patent Laid-Open No. 10-183095 JP 2002-206079 A

  However, the techniques described in Patent Documents 1 to 3 have the following problems.

  That is, the polyester resin layer described in Patent Document 1 has poor deep drawability and cannot be applied to a two-piece can. Patent Document 4 describes that the retort whitening phenomenon can be suppressed by increasing the crystallization speed of the polymer. However, the mechanism of the retort whitening phenomenon is not completely understood, and the problem of the retort whitening phenomenon has not been fundamentally solved. Patent Documents 5 to 8 describe a metal plate laminating film used for laminating a film made of butylene terephthalate and ethylene terephthalate on an aluminum plate and drawing and ironing (DI). . However, such a smooth laminated metal plate has insufficient processability when used in containers such as food cans, and may cause defects such as film tearing. In particular, when a metal plate having a strength higher than that of an aluminum plate is used as a base, the film is damaged during molding and cannot be used as a can.

  On the other hand, although epoxy resin is rich in reactivity and excellent in adhesion to a metal plate, it has a drawback that deep drawability is inferior, so a film that can be used as a two-piece can material cannot be obtained. In other words, even if the resin-coated metal plate described in Patent Document 2 is formed into a deep drawing (DRD: Drawn and ReDrawn) can, the epoxy resin cannot follow the elongation deformation in the can height direction and restrains the deformation of the material. Therefore, the material is broken in the drawing process. Note that Patent Documents 9 to 12 disclose a method of coating a film with a resin for the purpose of improving adhesion. However, the resins described in Patent Documents 9 to 12 are mainly composed of a composite system of a polyester resin and an epoxy resin or an epoxy resin. For this reason, the resins described in Patent Documents 9 to 12 have difficulty in deep-drawing moldability, as in the case of the polyester resin layer described in Patent Document 1, and cannot be applied to 2-piece can applications. Moreover, since the example which evaluated can manufacturing process and deep drawing formability is not disclosed in the example of invention described in patent documents 9-12, these require deep drawing processing 2 It is clear that the piece can application is not considered.

  Moreover, when manufacturing a metal container combining the biaxially stretched polyester film described in Patent Document 3, the melting point difference between the inner surface side film and the outer surface side film is large, and the crystal structure after lamination of the inner surface side film is within a desired range. When controlled, the crystal structure of the outer film cannot be controlled. For this reason, when manufacturing DRD cans and DI cans using these film-laminated metal plates, the film surface is reduced in scratch resistance due to a decrease in slipperiness with a jig, or the film is ruptured due to insufficient film deformability. Along with this, a broken cylinder occurs.

  The present invention has been made in view of the above-mentioned problems, and its purpose is excellent in design of the appearance of the can body after retort sterilization, and excellent in moldability applicable to a two-piece laminated can. Another object of the present invention is to provide a laminate metal plate for use and a two-piece laminate can manufactured using the laminate metal plate for two-piece cans.

  In order to solve the above problems and achieve the object, a laminated metal plate for a two-piece can according to the present invention includes a metal plate and a first polyester film laminated on at least one surface of the metal plate. The first polyester film contains 45 to 65% by mass of polybutylene terephthalate, 25 to 52% by mass of polyethylene terephthalate copolymerized with 5 to 8% by mol of isophthalic acid, and 3 to 10% by mass of polyethylene terephthalate. The higher melting point of the melting point of the first polyester film is higher than the melting point of polyethylene terephthalate copolymerized with 5 to 8 mol% of isophthalic acid.

  The first polyester film preferably contains 2000 to 6000 ppm of low molecular weight polyethylene having a number average molecular weight in the range of 1000 to 8000.

  The first polyester film is laminated on the surface of the metal plate which becomes the outer surface of the container after molding the container, and the polyethylene plate which is copolymerized with 10 to 14 mol% of isophthalic acid is formed on the surface of the metal plate which becomes the inner surface of the container after molding the container. The second polyester film containing terephthalate is preferably laminated.

  It is preferable that the residual crystal orientation after lamination of the first polyester film and the second polyester film is less than 20%.

  The difference between the heat of crystallization and the heat of fusion after lamination of the first polyester film and the second polyester film is preferably greater than at least 0 J / g in terms of unit weight.

  In order to solve the above problems and achieve the object, a two-piece laminated can according to the present invention is manufactured using the laminated metal plate for a two-piece can according to the present invention.

  According to the present invention, a laminate metal plate for a two-piece can excellent in design of the can body appearance after retort sterilization treatment and excellent in moldability applicable to a two-piece laminate can, and the laminate metal plate for the two-piece can It is possible to provide a two-piece laminated can manufactured using the same.

  Hereinafter, the structure of the laminated metal plate for 2 piece cans which is one embodiment of the present invention will be described.

[Overall configuration of laminated metal plate for 2-piece cans]
A laminated metal plate for a two-piece can according to an embodiment of the present invention includes a metal plate, a can outer surface film laminated on the surface side of the metal plate that becomes the outer surface of the container after forming the container, and a metal that becomes the inner surface of the container after forming the container. A can inner surface film laminated on the surface side of the plate.

[Composition of metal plate]
As the metal plate, a steel plate or an aluminum plate widely used as a can material can be used. As the metal plate, in particular, tin-free steel (TFS), which is a surface-treated steel sheet having a two-layer coating in which the lower layer and the upper layer are formed of metal chromium and chromium hydroxide, respectively, is suitable. The amount of metal chromium and chromium hydroxide deposited in TFS is not particularly limited, but from the viewpoint of workability and corrosion resistance, the amount of metal chromium deposited is within the range of 70 to 200 mg / m ² , and the amount of chromium hydroxide deposited is It is preferable to be within the range of 10 to 30 mg / m ² .

[Composition of the film of the present invention]
The film of the present invention particularly suitable for the outer surface of the can is a polyester film containing three components of polybutylene terephthalate (B), isophthalic acid copolymerized polyethylene terephthalate (C), and polyethylene terephthalate (D). The can outer film functions as the first polyester film according to the present invention.

  Polybutylene terephthalate (B), isophthalic acid copolymerized polyethylene terephthalate (C), and polyethylene terephthalate (D) may be copolymerized with other monomers as long as the effects of the present invention are not impaired. The acid components to be copolymerized include 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 acids, 4-hydroxybenzoic acid, ε-caprolactone, lactic acid and the like.

  Examples of the alcohol component to be copolymerized include ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, cyclohexanedimethanol, triethylene glycol, polyethylene glycol, polypropylene Examples include glycol, polytetramethylene glycol, ethylene oxide adducts of bisphenol A and bisphenol S, and the like. As the copolymer component, a small amount of a trifunctional compound such as trimellitic acid, trimesic acid, pyromellitic acid, trimethylolpropane, glycerin, pentaerythritol, or the like may be used. Two or more of these copolymer components may be used in combination.

  Isophthalic acid copolymerized polyethylene terephthalate (C) is obtained by copolymerizing polyethylene terephthalate with isophthalic acid, and the copolymerization ratio of isophthalic acid is required to be 5 to 8 mol%, and 5 to 7 mol%. More preferably. When the copolymerization ratio of isophthalic acid is less than 5 mol%, the crystallinity after lamination thermocompression bonding becomes high, and the adhesion to the metal plate is not good. On the other hand, when the copolymerization ratio of isophthalic acid exceeds 8 mol%, the heat resistance decreases.

  The melting point of isophthalic acid copolymerized polyethylene terephthalate (C) is preferably in the range of 225 to 238 ° C, and more preferably in the range of 228 to 235 ° C. When the melting point is less than 225 ° C., whitening or white spots occur due to the heat treatment after molding, and the impact resistance is poor. On the other hand, if the melting point exceeds 238 ° C., the degree of crystallinity after lamination thermocompression bonding increases, and the adhesion to the metal plate decreases. Furthermore, in order to give sufficient adhesiveness, it is necessary to raise the temperature of the melting point near or above the melting point to melt the crystal of the film, which is inferior in productivity. If the isophthalic acid copolymerization ratio is as described above, the melting point of isophthalic acid copolymerized polyethylene terephthalate (C) is often within the above range, but a monomer other than isophthalic acid is used so that the melting point does not deviate from the above range. The copolymerization ratio may be adjusted as appropriate.

  The intrinsic viscosity of the polybutylene terephthalate (B) is preferably in the range of 0.75 to 1.60, and more preferably in the range of 0.90 to 1.40. The intrinsic viscosity of isophthalic acid copolymerized polyethylene terephthalate (C) and polyethylene terephthalate (D) is preferably in the range of 0.70 to 0.85, and is preferably in the range of 0.70 to 0.80. Is more preferable.

  If the intrinsic viscosity is less than the above range, the film may be broken during high-order processing of the can, and productivity may be extremely reduced. In particular, when the capacity of the can is large, the degree of deformation of the film increases in the process of DI processing of the laminated metal plate, so that the film cannot follow it, and voids or cracks occur. Even a slight impact from the outside promotes the peeling of the film layer and the growth of cracks, and the printed appearance becomes poor at the portion where the film is whitened by the void. In addition, there is a risk that the can corrodes during long-term storage due to voids and cracks. On the other hand, if the intrinsic viscosity exceeds the above range, the load on the resin melt extruder increases in the film production process, and the production rate decreases, making it difficult to control the film thickness, etc. Decreases. In addition, a material having a high intrinsic viscosity has a long polymerization time and a long polymerization process, which increases the cost.

  The film of the present invention contains 45 to 65% by mass of polybutylene terephthalate (B), 25 to 52% by mass of isophthalic acid copolymerized polyethylene terephthalate (C), and 3 to 10% by mass of polyethylene terephthalate (D). In the present invention, the total amount of these components is 100% by mass, and the other additive components are shown in an extra amount.

  When content of polybutylene terephthalate (B) is less than 45 mass%, the crystallinity degree of the film in the state of the can finally obtained becomes low, and it whitens at the time of a retort sterilization process. When the content of polybutylene terephthalate (B) exceeds 65% by mass or when the content of isophthalic acid copolymerized polyethylene terephthalate (C) is less than 25% by mass, the crystallinity of the film after lamination becomes high, Formability is reduced.

  Even when the content of isophthalic acid copolymerized polyethylene terephthalate (C) exceeds 52% by mass, the addition concentration of polybutylene terephthalate (B) is less than 45% by mass, so the crystallinity of the can film is lowered. A retort whitening phenomenon may occur. Even if the content of polybutylene terephthalate (B) is an appropriate amount, when the content of polyethylene terephthalate (D) is less than 3% by mass, the film melting point described later is lowered and the crystallinity of the film is lowered. Retort whitening resistance decreases. When content of a polyethylene terephthalate (D) exceeds 10 mass%, the crystallinity after lamination becomes high and adhesiveness with a metal plate falls.

  Polybutylene terephthalate (B), isophthalic acid copolymerized polyethylene terephthalate (C), and polyethylene terephthalate (D) undergo transesterification with each other during film production. For this reason, when the melting point of the film is measured, a melting point different from that of polybutylene terephthalate (B), isophthalic acid copolymerized polyethylene terephthalate (C), and polyethylene terephthalate (D) itself is observed. That is, the melting point derived from polybutylene terephthalate (PBT) is observed as the lower melting point of the melting points of the film. Also, since the melting point of isophthalic acid copolymerized polyethylene terephthalate (C) is close to the melting point of polyethylene terephthalate (D), the melting point derived from polyethylene terephthalate (PET) is one melting point regardless of the presence or absence of isophthalic acid copolymerization. The higher melting point of the melting point of the film is observed.

  In the present invention, the melting point derived from PET, which is the higher melting point of the melting points of the film, needs to be higher than the melting point of isophthalic acid copolymerized polyethylene terephthalate (C). When the melting point derived from PET of the film is lower than the melting point of isophthalic acid copolymerized polyethylene terephthalate (C), polybutylene terephthalate (B), isophthalic acid copolymerized polyethylene terephthalate (C) and polyethylene terephthalate (D) are excessive. Transesterification has occurred, and substantially the same effect as a decrease in the content of polybutylene terephthalate (B) is exhibited, and whitening may occur during retort. By adding polyethylene terephthalate (D), it is possible to suppress a decrease in the melting point of the film.

  The film of the present invention is formed by adding a small amount of an inorganic lubricant such as silica, alumina, kaolin or the like in order to improve the process passability at the time of film production or can making, and imparts slip properties to the film surface. Is desirable. The content of the inorganic lubricant in the film is preferably in the range of 0.001 to 0.5% by mass, and more preferably in the range of 0.05 to 0.3% by mass. Further, in combination with the function of the lubricant, titanium dioxide can be added up to about 20% by mass for the purpose of concealment. In particular, in simultaneous biaxial stretching, a stretched film can be obtained even if titanium dioxide exceeding 40% by mass is added. Furthermore, in order to improve the film appearance and printability, for example, the film can contain a silicone compound or the like.

  The polymerization method of polybutylene terephthalate (B), isophthalic acid copolymerized polyethylene terephthalate (C), and polyethylene terephthalate (D) (hereinafter referred to as polyester) is not particularly limited. For example, transesterification or direct polymerization Can be polymerized. 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.

  Polybutylene terephthalate after polymerization, polyester such as isophthalic acid copolymerized polyethylene terephthalate, and polyethylene terephthalate contain monomers, oligomers, by-products such as acetaldehyde, tetrahydrofuran, etc. It is preferable to perform solid phase polymerization at a temperature of at least ° C. In the polymerization of polyester, additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber, and an antistatic agent can be added as necessary. Examples of antioxidants include hindered phenol compounds and hindered amine compounds, examples of heat stabilizers include phosphorus compounds, and examples of ultraviolet absorbers include benzophenone compounds and benzotriazole compounds. Can be illustrated.

  The film of the present invention preferably contains 2000 to 6000 ppm of low molecular weight polyethylene that is incompatible with the polyester. When the content of the low molecular weight polyethylene is less than 2000 ppm, the effect of improving the slipperiness is not sufficient, and when the content of the low molecular weight polyethylene exceeds 6000 ppm, the slipperiness of the film surface becomes an excessive quality. In addition, as the amount of incompatible resin increases, the film may become brittle, or the finished can may be inferior in impact properties and may have reduced flavor properties.

  In the present invention, the low molecular weight polyethylene preferably has a number average molecular weight in the range of 1000 to 8000, and particularly preferably in the range of 2000 to 6000. By incorporating low molecular weight polyethylene in the above molecular weight range into an incompatible polymer, the surface of the stretched film can be roughened to improve slipperiness, and also when the film is laminated to a metal plate, it moves to the surface. Thus, the rough film surface can be retained. If the number average molecular weight is less than 1000, the molecular weight is too low, and when the film is processed or when the film is laminated, it may be deposited on the surface of the film and peeled off, and the jig may be soiled in the can processing process. Conversely, the film itself may be scratched. On the other hand, when the number average molecular weight exceeds 8000, the effect of roughening the film surface after making the film amorphous is not sufficient, and the slipperiness during can processing is inferior.

  In the present invention, the low molecular weight polyethylene preferably has a softening point of 95 ° C. or higher, particularly preferably in the range of 100 to 200 ° C. When the softening point is less than 95 ° C., the film softens within the range of 60 to 90 ° C. which is a normal can molding temperature, and the slipping property at the time of can molding may be inferior. Although the addition method of low molecular weight polyethylene is not particularly limited, a master chip containing about 0.5 to 5% by mass in polybutylene terephthalate, copolymerized polyester, or a mixture thereof is prepared in advance and added by the master chip. The method is preferred.

[Composition of can inner film]
The inner surface film of the can is laminated on the surface of the metal plate that becomes the inner surface side after forming the container. Although it is possible to apply the first polyester film of the present invention suitable for the outer surface side of the can to the inner surface side of the can, the exposure environment differs between the inner surface side and the outer surface side of the canned container, so that it is suitable for the inner surface side of the can. It is preferable to apply the second polyethylene film of the present invention. That is, the inner surface side of the canned container is not directly exposed to high-temperature water vapor during the retort sterilization treatment, so it is not necessary to use a resin having a lower crystallization temperature as the outer surface side, and the processability is resistant to DI molding. Anything is acceptable. The can inner film is preferably polyethylene terephthalate copolymerized with isophthalic acid. Although terephthalic acid as an acid component is essential from the viewpoint of mechanical strength, heat resistance, chemical resistance, etc., further, copolymerization with isophthalic acid improves flexibility and tear strength. By copolymerizing the isophthalic acid component with respect to the terephthalic acid component in an amount of 10 to 14 mol%, it is preferable because deep drawability and post-processing adhesion are improved. When a film containing polyethylene terephthalate having an isophthalic acid copolymerization amount outside the above range is used on the inner surface side of the metal container, deep drawability and post-processing adhesion may be inferior.

  On the other hand, you may copolymerize another dicarboxylic acid component and a glycol component in the range which does not impair the said characteristic. Dicarboxylic acid components include diphenylcarboxylic acid, 5-sodium sulfoisophthalic acid, aromatic dicarboxylic acid such as phthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, fumaric acid and the like Examples thereof include aliphatic dicarboxylic acids such as dicarboxylic acid and cyclohexanedicarboxylic acid, and oxycarboxylic acids such as p-oxybenzoic acid. Further, as other glycol components, aliphatic glycols such as propanediol, butanediol, pentanediol, hexanediol and neopentylglycol, finger ring glycols such as cyclohexanedimethanol, aromatic glycols such as bisphenol A and bisphenol S, Examples include diethylene glycol and polyethylene glycol. These dicarboxylic acid components and glycol components may be used in combination of two or more. Moreover, as long as the effect of this invention is not inhibited, you may copolymerize polyfunctional compounds, such as trimellitic acid, trimesic acid, a trimethylol propane.

[Thickness of can outer film and can inner film]
The thickness of the outer surface film of the can and the inner surface film of the can is preferably in the range of 3 to 50 μm in terms of formability after being laminated to the metal plate, coatability to the metal plate, impact resistance, and taste characteristics. More preferably, it exists in the range of 8-30 micrometers.

[Remaining oriented crystal amount of film after lamination]
A major characteristic of polyethylene terephthalate-based laminate films is that the amount of oriented crystals greatly affects the properties. Taking advantage of this feature, a laminated metal plate having a desired basic performance can be produced by controlling the amount of oriented crystals to an appropriate amount according to the required performance. As a specific method, a biaxially oriented crystal film is used, the lamination conditions in the heat fusion method are precisely controlled, and the residual amount of oriented crystals is controlled. This method is very convenient industrially, and it is possible to make various varieties that meet the required performance using the same raw materials. In general, the formability is improved by reducing the degree of residual crystal orientation, and the impact resistance can be increased by increasing the degree of residual crystal orientation. In the present invention, the residual crystal orientation of the biaxially oriented polyester resin layer is controlled within a range of less than 20% in accordance with the degree of processing for a two-piece can application. The residual crystal orientation is a value determined by X-ray diffraction and is defined as follows.

(1) For the oriented polyester resin (or oriented polyester film) before lamination and the resin (or film) after lamination, the X-ray diffraction intensity is measured in the range of 2θ = 20 to 30 °.
(2) The X-ray diffraction intensity at 2θ = 20 ° and 2θ = 30 ° is connected by a straight line to be a base line.
(3) The height of the highest peak appearing in the vicinity of 2θ = 22 to 28 ° is measured from the baseline.
(4) When the height of the highest peak of the film before lamination is P1, and the highest peak of the film after lamination is P2, P2 / P1 × 100 is the residual crystal orientation (%).

  The residual crystal orientation after the polyester film is laminated on the metal plate is preferably in the range of less than 20%. When the residual crystal orientation is 20% or more, problems such as film peeling after processing occur due to the occurrence of broken cylinders during can making due to poor film formability and decreased adhesion. When the biaxially stretched polyester film is heat-sealed, heat is input from the metal plate to break the oriented crystals, and the resin layer becomes an amorphous polyester resin. If the heat input at the time of heat fusion is small, the resin layer at the interface with the metal plate is not sufficiently melted, and the adhesion between the metal plate and the resin layer becomes weak. Proportion of amorphous polyester resin layer with excellent deformability laminated to a metal plate by ensuring the adhesive strength of the resin layer required when applied to food containers and further reducing the residual crystal orientation to a certain level or less Therefore, it is necessary to ensure workability by increasing the number.

  In view of the above, the residual crystal orientation after the can outer film and the can outer film are laminated on the metal plate is preferably less than 20%, more preferably 10% or less. Further, from the viewpoint of film formability, it is desirable to reduce the degree of residual crystal orientation according to the degree of processing.

[Difference between heat of crystallization and heat of fusion of film after lamination]
The outer surface film of the can and the inner surface film of the can are laminated so that the difference between the heat of crystallization and the heat of fusion after lamination is in a range larger than at least 0 J / g in terms of unit weight. The amount of heat of crystallization and the amount of heat of fusion can be measured using a differential scanning calorimetry (DSC). The difference between the heat of crystallization and the heat of fusion is an indicator of the crystallinity of the film after lamination. The biaxially stretched film has a high degree of crystallinity until film formation and is poor in deformability. However, by contacting with a metal plate heated during lamination, the crystal component in the film melts and the crystallinity of the film decreases. Taking advantage of the characteristics of this biaxially stretched film, a laminated metal plate having a desired basic performance can be produced by controlling the crystallinity to an appropriate amount according to the required performance.

  As a specific method, a biaxially oriented crystal film is used, the lamination conditions in the heat fusion method are precisely controlled, and the crystallinity is controlled. This method is very convenient industrially, and it is possible to make various varieties that meet the required performance using the same raw materials. Generally, the lower the film crystallinity, the better the moldability of the film, and the higher the film crystallinity, the higher the impact resistance. When the difference between the heat of crystallization and the heat of fusion is 0 J / g, it indicates that the laminated film is in an amorphous state, and the crystallinity becomes 0, which is not preferable from the viewpoint of impact resistance.

[Method for producing film]
As a manufacturing method of the 1st polyester film of this invention, the manufacturing method of a well-known polyester film is applicable. For example, a mixture of polybutylene terephthalate (B), isophthalic acid copolymerized polyethylene terephthalate (C) and polyethylene terephthalate (D) is put into an extruder, and melt mixed at a temperature of 270 to 300 ° C. for 3 to 15 minutes. After that, the sheet is extruded through a T die. The sheet was cooled by bringing it into close contact with a cooling drum whose temperature was adjusted to room temperature or lower, and the resulting unstretched film was then guided to a simultaneous biaxial stretching machine, and each of MD and TD was 2 to 4 at a temperature of 40 to 120 ° C. The first polyester film of the present invention can be produced by biaxially stretching so as to obtain a draw ratio of about twice, and further performing heat treatment at 140 to 190 ° C. for several seconds with a TD relaxation rate of several percent. it can. Moreover, the 2nd polyester film of this invention can be manufactured similarly except a component.

  The film of the present invention can also be produced by a sequential stretching method. The outline of the method is as follows. An unstretched film similar to that described in the simultaneous biaxial method is heated by roll heating, infrared rays or the like, and stretched in the longitudinal direction to obtain a longitudinally stretched film. Stretching preferably uses a difference in peripheral speed of two or more rolls and is 2.5 times or more and 3.6 times or less in a temperature range of 40 ° C. higher than the glass transition point (Tg) to Tg of polyester. Subsequently, the longitudinally stretched film is successively subjected to lateral stretching, heat setting, and thermal relaxation to form a biaxially oriented film. The transverse stretching starts at a temperature 40 ° C. higher than the Tg to Tg of the polyester, and the maximum temperature is preferably a temperature lower by (100 to 40) ° C. than the melting point (Tm) of the polyester. The transverse stretching ratio is adjusted depending on the required physical properties of the final film, but is preferably 2.7 times or more, more preferably 3.0 times or more, and more preferably 3.6 times or more. . Although an elongation of 2 to 20% may be applied in the film width direction during the heat setting treatment following the stretching, the stretching ratio is preferably included in the total stretching ratio. After the heat setting treatment, a relaxation treatment is performed to adjust the heat shrink property of the film, and then the film is cooled to Tg or less of the film to obtain a biaxially stretched film.

  The heat treatment after stretching is a process necessary for imparting dimensional stability of the film, and as its 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.

  The film of the present invention is laminated to a metal plate such as a steel plate or aluminum by a thermocompression bonding method, and the metal plate to be laminated is a chemical conversion treatment such as chromic acid treatment, phosphoric acid treatment, electrolytic chromic acid treatment, chromate treatment, Nickel, tin, zinc, aluminum, gun metal, brass, and other metal plates subjected to various plating treatments can be used.

  The film of the present invention can be provided with an adhesive layer by a coextrusion method, a lamination process, or a coating process for the purpose of further improving the thermocompression bonding property with the metal plate and the subsequent adhesion. The thickness of the adhesive layer is preferably 1 μm or less in terms of dry film thickness. Although an adhesive layer is not specifically limited, It is preferable that it is a thermosetting resin layer which consists of an epoxy resin, a polyurethane resin, a polyester resin, and these various modified resins.

[Method for producing film-laminated metal plate]
As a method of laminating the film of the present invention on a metal plate, the metal plate is preheated up to 200 to 250 ° C., and this and the film are temperature-controlled at 30 ° C. and further 50 ° C. lower than the metal plate. After being pressure-welded and thermocompression bonded, it is continuously manufactured by cooling to room temperature. Examples of the method for heating the metal plate include a heater roll heat transfer method, an induction heating method, a resistance heating method, and a hot air transfer method. 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 laminating conditions are appropriately set so that the resin layer defined in the present invention can be obtained. For example, it is preferable that the temperature at the start of lamination is at least equal to or higher than the melting point of the film, and the temperature history received by the film at the time of lamination is within the range of 1 to 35 msec. In order to achieve such lamination conditions, in addition to high-speed lamination, cooling during fusion is also necessary. The pressurization at the time of laminating is not particularly specified, but the surface pressure is preferably in the range of 9.8 to 294 N / cm ² (1 to 30 kgf / cm ² ). If this value is too low, even if the temperature reached by the resin interface is equal to or higher than the melting point, the time is short, so the melting is insufficient and it is difficult to obtain sufficient adhesion. In addition, if the pressure is large, there is no problem in the performance of the laminated metal plate, but the force applied to the laminate roll is large and equipment strength is required, resulting in an increase in the size of the apparatus, which is uneconomical.

[Invention Example]
Degreased and pickled steel sheet (tempered grade T3CA) subjected to cold rolling, annealing, and temper rolling with a thickness of 0.20 to 0.27 mm, and then subjected to chrome plating treatment to obtain a chrome plated steel sheet (TFS). Manufactured. In the chrome plating treatment, chrome plating was performed in a chromium plating bath containing CrO ₃ , F ⁻ , and SO ₄ ²⁻ , and after intermediate rinsing, electrolysis was performed using a chemical conversion treatment solution containing CrO ₃ and F ⁻ . At that time, the electrolysis conditions (current density, amount of electricity, etc.) were adjusted to adjust the metal chromium adhesion amount and the chromium hydroxide adhesion amount to 120 mg / m ² and 15 mg / m ² in terms of Cr, respectively.

  Next, the chrome-plated steel sheet is heated using a metal plate laminating apparatus, a can outer film is laminated on the side of the chrome-plated steel sheet on the outer surface after making one can with a laminating roll, and the other inner surface after making the other can The inner surface film of the can was laminated on the side. The laminating roll was an internal water cooling type, and cooling water was forcibly circulated during laminating to perform cooling during film adhesion. Methods, measurements, and evaluation methods for the properties of the film used, the laminated metal plate produced by the above method, and the properties of the film on the laminated metal plate are shown below.

In DI molding, 50 mg / m ² of paraffin wax with a melting point of 45 ° C. was applied to both surfaces of a laminated metal plate, and a 123 mmφ blank was punched out. Molded. Next, this cup was inserted into a commercially available DI molding apparatus, and at a punch speed of 200 mm / s and a stroke of 560 mm, a total reduction rate of 50% (reduction of 20% and 19% respectively) was obtained by redrawing and three-stage ironing. %, 23%), and finally a can having a can inner diameter of 52 mm and a can height of 90 mm was formed. During DI molding, tap water was circulated at a temperature of 50 ° C.

(1) Raw material for film

(1-1) Polybutylene terephthalate (B)
Solid-phase polymerization product, intrinsic viscosity 1.08 dl / g, Tm 223 ° C, Ti catalyst 40ppm

(1-2) Isophthalic acid copolymerized polyethylene terephthalate (C)
(C-1): Solid phase polymerization product, isophthalic acid copolymerization amount 6 mol%, limiting viscosity 0.75 dl / g, Tm233 ° C., Ge catalyst 40 ppm (C-2): Solid phase polymerization product, isophthalic acid copolymerization 4 mol%, intrinsic viscosity 0.75 dl / g, Tm 239 ° C., Ge catalyst 40 ppm contained (C-3): solid phase polymerized product, isophthalic acid copolymerization amount 10 mol%, intrinsic viscosity 0.75 dl / g, Tm 226 ° C. , Ge catalyst 40ppm
(C-4): Solid phase polymerized product, isophthalic acid copolymerization amount 12 mol%, limiting viscosity 0.75 dl / g, Tm 224 ° C., Ge catalyst 40 ppm contained (C-5): Solid phase polymerized product, isophthalic acid copolymerized 14 mol%, intrinsic viscosity 0.75 dl / g, Tm 221 ° C., containing Ge catalyst 40 ppm (C-6): solid phase polymerized product, isophthalic acid copolymerization amount 5 mol%, intrinsic viscosity 0.75 dl / g, Tm 236 ° C. , Ge catalyst 40ppm (C-7): solid state polymerized product, isophthalic acid copolymerization amount 8mol%, intrinsic viscosity 0.75dl / g, Tm229 ° C, Ge catalyst 40ppm

(1-3) Polyethylene terephthalate (D)
Solid phase polymerized product, intrinsic viscosity 1.08 dl / g, Tm255 ° C, Ti catalyst 40ppm

(1-4) Low molecular weight polyethylene (E):
(E-1): Clariant Japan Co., Ltd. Lycowax PE190 Number average molecular weight 5500
(E-2): Sanyo Chemical Industries, Ltd. Sun Wax 171P Number average molecular weight 1500
(E-3): Clariant Japan Co., Ltd. Lycowax PED136 Number average molecular weight 900

(2) Measurement method (2-1) Melting point (Tm)
Using a DSC manufactured by Perkin Elmer, the temperature was raised at 20 ° C./min, and the temperature at which the peak of the rapid heating amount was reached was taken as the melting point. As a measurement sample of the film, a stretched film was melted and then rapidly cooled at a rate of 100 ° C./min or more to be in an amorphous state. Two melting points were observed in each invention example and comparative example, and the lower (Tm1) was derived from polybutylene terephthalate, and the higher (Tm2) was derived from isophthalic acid copolymerized polyethylene terephthalate and polyethylene terephthalate.

(2-2) Intrinsic Viscosity 0.25 g of a measurement sample was dissolved in 50 ml of phenol / tetrachloroethane = 5/5 (mass ratio) and measured at 25 ° C. using an Ubbelohde viscosity tube.

(2-3) Amount of heat of crystallization and heat of fusion The resin coating layer was peeled from the laminated metal plate with diluted hydrochloric acid, and the resin coating layer was sufficiently washed with distilled water and dried. Then, using a differential scanning calorimeter, an exothermic peak and an endothermic peak were measured when the temperature of the resin coating layer was increased from −50 ° C. to 290 ° C. at a rate of temperature increase of 10 ° C./min. The amount of heat of crystallization was calculated from the area of the exothermic peak observed in between, and the amount of heat of fusion was calculated from the area of the endothermic peak observed between 200 ° C. and 280 ° C.

(2-4) Residual crystal orientation degree The polyester film before lamination and the polyester film after lamination were recovered by dissolving them with a metal plate with hydrochloric acid, and the X-ray diffraction intensity was measured in the range of 2θ = 20 to 30 °. = 20 °, 2θ = 30 ° X-ray diffraction intensity (cps) was connected by a straight line to be a baseline. The height of the highest peak appearing in the vicinity of 2θ = 22 to 28 ° was measured from the baseline, and the highest peak height of the polyester film before lamination was P1, and the highest peak of the polyester film after lamination was P2. At that time, P2 / P1 × 100 was defined as the residual crystal orientation degree (%).

(2-5) Adhesiveness before forming A flat plate sample (width 15 mm, length 120 mm) before making a laminated metal plate was cut out. Part of the film is peeled off from the long side end of the cut sample. The peeled film is opened in the direction opposite to the peeled direction (angle: 180 °), and using a tensile tester, a tensile speed of 30 mm / min. A peel test was conducted to evaluate the adhesion per 15 mm width.

(Score)
A: 10.0 (N) / 15 (mm) or more B: 5.0 (N) / 15 (mm) or more, less than 10.0 (N) / 15 (mm) x: 5.0 (N) / Less than 15 (mm)

(2-6) Scratch resistance In the DI molding, first, 50 mg / m 2 of paraffin wax having a melting point of 45 ° C. was applied to both surfaces of a laminated metal plate, and then a 123 mmφ blank was punched out. It was drawn into a 36 mm high cup. Next, this cup was inserted into a commercially available DI molding apparatus, and at a punch speed of 200 mm / s and a stroke of 560 mm, a total reduction rate of 50% (reduction of 20%, 19%, 23%), and finally a can having an inner diameter of 52 mm and a height of 90 mm was formed. During DI molding, tap water was circulated at a temperature of 50 ° C.

(Score)
◎: Cans without scratches ○: Surface scratches occur less than 5% of the can body △: Surface scratches occur 5% or more but less than 15% of the can bodies ×: Surface scratches occur 15% or more of the can bodies XX: Cans made Sometimes film peeling or broken

(2-7) Retort whitening resistance The bottom (can outer surface side) of the can that was moldable (other than xx) in the above scratch resistance evaluation was targeted. After filling the can with room temperature tap water, the lid was wrapped and sealed. Then, the bottom of the can was turned downward and placed in a steam retort sterilization furnace, and retort sterilization was performed at 125 ° C. for 90 minutes. After the treatment, the change in the appearance of the outer surface of the bottom of the can was visually observed.

(Score)
○: No change in appearance Δ: Faint cloudy appearance (less than 5% in film surface area) ×: White turbidity in appearance (whitening occurs at 5% or more in film surface area)

(2-8) Adhesion after molding 1
Cans that were moldable (other than XX) in the scratch resistance evaluation were used. A sample for peel test (width 15 mm, length 120 mm) was cut out from the can body. Part of the film is peeled off from the long side end of the cut sample. The peeled film is opened in the direction opposite to the peeled direction (angle: 180 °), and using a tensile tester, a tensile speed of 30 mm / min. A peel test was conducted to evaluate the adhesion per 15 mm width. The evaluation object is the can body part on the outer surface of the can.

(Score)
A: 10.0 (N) / 15 (mm) or more B: 6.0 (N) / 15 (mm) or more, less than 10.0 (N) / 15 (mm) Δ: 3.0 (N) / 15 (mm) or more, less than 6.0 (N) / 15 (mm) x: less than 3.0 (N) / 15 (mm)

(2-9) Adhesion after molding 2
Cans that were moldable (other than XX) in the scratch resistance evaluation were used. A sample for peel test (width 15 mm, length 120 mm) was cut out from the can body. Part of the film is peeled off from the long side end of the cut sample. The peeled film is opened in the direction opposite to the peeled direction (angle: 180 °), and using a tensile tester, a tensile speed of 30 mm / min. A peel test was conducted to evaluate the adhesion per 15 mm width. The evaluation object is the can body part on the inner surface of the can.

(Score)
A: 10.0 (N) / 15 (mm) or more B: 6.0 (N) / 15 (mm) or more, less than 10.0 (N) / 15 (mm) Δ: 3.0 (N) / 15 (mm) or more, less than 6.0 (N) / 15 (mm) x: less than 3.0 (N) / 15 (mm)

(2-10) Impact resistance Cans that were moldable (other than XX) in the scratch resistance evaluation were used. After making the can, the water is fully filled, and for each test, 10 pieces are dropped from a height of 1.25 m onto the PVC tile floor, then a voltage of 6 V is applied to the electrode and the metal can, and the current value after 3 seconds is read. The average value after 10 cans was measured.

(Score)
A: Less than 0.01 mA B: 0.01 mA or more and less than 0.1 mA X: 0.1 mA or more

[Evaluation]
As is clear from Tables 1 and 2, No. Nos. 1 to 28 were confirmed to have good performance with respect to moldability, retort whitening resistance, post-mold adhesion, and impact resistance required for food canned materials. On the other hand, the comparative example No. It was confirmed that 29 to 40 were inferior in any of the characteristics. From the above, No. which is an invention example. 1 to 28, a laminated metal plate for a two-piece can excellent in design of the can body appearance after retort sterilization treatment and excellent in moldability applicable to a two-piece laminated can, and the laminated metal plate for the two-piece can A two-piece laminated can manufactured using can be provided.

  Although the embodiment to which the invention made by the present inventor is applied has been described above, the present invention is not limited by the description and the drawings that form a part of the disclosure of the present invention according to this embodiment. That is, other embodiments, invention examples, operation techniques, and the like made by those skilled in the art based on the present embodiment are all included in the scope of the present invention.

Claims (6)

A metal plate,
A first polyester film laminated on at least one surface of the metal plate;
With
The first polyester film includes 45 to 65% by mass of polybutylene terephthalate, 25 to 52% by mass of polyethylene terephthalate copolymerized with 5 to 8% by mol of isophthalic acid, and 3 to 10% by mass of polyethylene terephthalate,
A laminated metal plate for a two-piece can, wherein the higher melting point of the melting points of the first polyester film is higher than the melting point of polyethylene terephthalate copolymerized with 5 to 8 mol% of isophthalic acid.   The laminated metal sheet for a two-piece can according to claim 1, wherein the first polyester film contains 2000 to 6000 ppm of low molecular weight polyethylene having a number average molecular weight in the range of 1000 to 8000.   The first polyester film is laminated on the surface of the metal plate which becomes the outer surface of the container after molding the container, and the polyethylene plate which is copolymerized with 10 to 14 mol% of isophthalic acid is formed on the surface of the metal plate which becomes the inner surface of the container after molding the container. The laminated metal plate for a two-piece can according to claim 1 or 2, wherein a second polyester film containing terephthalate is laminated.   The laminated metal plate for a two-piece can according to claim 3, wherein the degree of residual crystal orientation after lamination of the first polyester film and the second polyester film is less than 20%. The calorific difference of the heat of fusion with respect to the amount of heat of crystallization after laminating the first polyester film and the second polyester film is at least greater than 0 J / g in terms of unit weight. Laminated metal plate for 2-piece cans.   A two-piece laminated can manufactured using the laminated metal plate for a two-piece can according to any one of claims 1 to 5.