JP2018140542A - Can lid for canned food - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a can lid for canned food, using a resin coated metal plate causing no damage of a resin layer when seaming or molding a can lid at high speed, excellent in designability of an external appearance and content resistance after retort sterilization, and capable of retaining adhesion of the resin layer.SOLUTION: A can lid for canned food is such that: a thermoplastic resin layer A of a resin coated metal plate used for the can lid for canned food is constituted of two or more layers; a weight ratio of PBT/PET of an A1 layer as a layer in contact with the metal plate is in a range of (40/60)-(80/20); a PET weight ratio in an A2 layer as the outermost surface layer is larger than a PBT weight ratio in the A2 layer; a thickness d(μm)of the A2 layer satisfies prescribed mathematical formula; and 95 mol% or more of thermoplastic resin in a thermoplastic resin layer B is polyethylene terephthalate.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a can lid for canning using a resin-coated metal plate.

  Conventionally, solvent-based paints mainly composed of thermosetting resins have been applied to the inner and outer surfaces of metal beverage cans and food cans. This is to maintain the flavor of the contents, to prevent the corrosion of the metal that is the base material of beverage cans and food canned containers, or to improve the design and printing surface of the outer surface of beverage cans and food canned containers This is for the purpose of protection. However, in order to form a solvent-based paint film, heat treatment at a high temperature is necessary, and a large amount of solvent is generated during the heat treatment, which causes problems in terms of work safety and environmental impact. there were. For this reason, recently, a metal coating with a thermoplastic resin has been proposed as a corrosion prevention method without using a solvent. In particular, among thermoplastic resins, polyester resins are excellent in processability and heat resistance, and therefore, development of films for metal laminates based on polyester resins has been underway.

  When a resin-coated metal plate coated with a resin film such as a polyester resin film is applied to a beverage can or a food canned container, if the lid is wound at a high speed to increase productivity, the resin on the outer surface side The film may be cracked or scraped. In addition, the cyclic trimer in the resin film precipitates on the surface of the resin film during high temperature sterilization such as retort sterilization, and the design property is impaired, or the resin film itself appears white and cloudy during the retort sterilization The phenomenon of discoloration (whitening phenomenon) may occur. On the other hand, the resin film used on the inner surface side is required to have corrosion resistance (content resistance) with respect to the contents and adhesion when in contact with the contents for a long time.

  As a method for improving such a problem, Patent Document 1 discloses that a thermoplastic resin film layer is coated on both surfaces of a metal plate, and the amorphization ratio of the thermoplastic resin film layer on the outer side of the can lid is 60% or more. And a double-sided film laminate can lid in which an oriented crystal layer is left in a part of the thermoplastic resin film layer on the inner surface side of the can lid. Further, Patent Document 2 discloses a film which is a polyester containing 30 to 50% by mass of a polyester having ethylene terephthalate as a main repeating unit and 50 to 70% by mass of a polyester having butylene terephthalate as a main repeating unit. A metal plate coated on the outer surface side is described.

  Furthermore, in Patent Document 2, a polyester resin layer having a two-layer structure is coated on the inner surface of a metal plate, and the upper polyester resin layer is copolymerized with polyethylene terephthalate or isophthalic acid as an acid component at a ratio of 6 mol% or less. It is also described that it is a copolymerized polyethylene terephthalate. In Patent Document 2, the upper polyester resin layer contains 0.1 to 5% by mass of olefin wax, and the lower polyester resin layer contains isophthalic acid as an acid component in a ratio of 10 to 22 mol% or less. It is also described that it is a copolymerized polyethylene terephthalate. Similarly, Patent Documents 3 to 6 describe techniques for improving the whitening resistance of the resin film on the outer surface side.

  Patent Document 7 describes a polyester composition containing 30 to 50% by mass of a polyester having ethylene terephthalate as a main repeating unit and 50 to 70% by mass of a polyester having butylene terephthalate as a main repeating unit. . Patent Document 7 also describes a technique for melting the interface when the melting point of the resin is defined and heat-sealed. Patent Documents 8 and 9 also describe techniques for suppressing discoloration during retort sterilization. In Patent Document 10, a polyester film having a contact angle in the range of 70 to 120 ° is used on the inner surface of the can, and PET-PBT having a crystallization temperature of 120 ° C. or less is bonded to the outer surface of the can to make it white. Techniques that improve performance are described.

JP 2002-193256 A JP 2005-342911 A Japanese Patent Laid-Open No. 5-331302 JP 2001-335682 A JP 2002-88233 A JP 2003-238780 A Japanese Patent Laid-Open No. 10-110046 JP 09-012743 A JP 07-145252 A JP 2004-168365 A

  However, the double-sided film laminate can lid described in Patent Document 1 uses an ethylene terephthalate / isophthalate copolymer, although the outer thermoplastic resin film layer has good anti-clamping properties, and is crystallized. Since the speed is insufficient, the whitening resistance at the time of retort sterilization is insufficient. In addition, in the techniques described in Patent Documents 2 to 6, although the effect of improving the whitening resistance of the resin film on the outer surface side is seen, the crystallization state is not taken into consideration, so that the winding and molding are performed at high speed. It has not yet been improved against damage to the resin film. Further, since the copolymer component is present in the resin film on the inner surface side, the copolymer component may be eluted and the content resistance may be poor.

  Moreover, in the techniques described in Patent Documents 7 to 9, it is necessary to heat-seal the resin film on both sides at the same time for the metal plate used in the container, there is only a description on the resin film on one side, and the opposite side There is no description regarding the resin film on the surface. As described above, since the performance required for the inner and outer surfaces of the can is different in the metal plate for cans, it is necessary to combine different types of resin films. In consideration of the productivity of using different types of resin films, it is preferable to heat-bond the resin films on both sides simultaneously, and resin films having substantially the same melting point by copolymerization have been combined. However, in this case, it is necessary to add a copolymerization component, leading to an increase in cost. In addition, when the melting points of the resin films are greatly different, it is necessary to heat the high melting point resin film to the high melting point in order to heat-seal, but the low melting point resin film exceeds the melting point and adheres to a roll or the like. There is a concern of hindering productivity. In the above technology, since these viewpoints are not taken into consideration, there is a concern that the adhesiveness of the resin film is inferior, the product is not competitive, or the productivity is inferior.

  Further, although the technology described in Patent Document 10 is excellent in whitening resistance, the crystallization state is not taken into consideration, so that it has not led to an improvement against damage to the resin film when performing winding and molding at high speed. Further, since the resin film on the inner surface side is isophthalic acid-based copolymerized polyethylene terephthalate, there is a concern that the copolymer component is eluted and the content resistance is inferior.

  The present invention has been made in view of the above problems, and its purpose is to prevent the resin layer from being damaged when wound or molded at a high speed, and to have a design appearance after retort sterilization and An object of the present invention is to provide a can lid for canning using a resin-coated metal plate that has excellent content resistance and can maintain the adhesion of a resin layer.

The can lid for canning according to the present invention is a thermoplastic mainly composed of polybutylene terephthalate (PBT) and polyethylene terephthalate (PET) provided on a metal plate and a surface of the metal plate on the outer surface side of the can lid. The resin layer A and a thermoplastic resin layer B mainly composed of polyethylene terephthalate (PET) provided on the inner surface side of the can lid of the metal plate, the thermoplastic resin layer A being 2 In the A2 layer that is the outermost layer, the weight ratio of PBT / PET of the A1 layer that is composed of layers or more and is in contact with the metal plate is in the range of (40/60) to (80/20) The PET weight ratio is larger than the PBT weight ratio in the A2 layer, the thickness d (μm) of the A2 layer satisfies the following formula (1), and 95 mol% or more of the thermoplastic resin in the thermoplastic resin layer B is poly A Chi terephthalate, the thermoplastic in the resin layer A, Raman band intensity (I ₀₎ of the laser Raman spectroscopy 1615 ± 10 cm ^-1, measured in a horizontal plane of polarization with respect to the resin layer surface using a resin layer surface The ratio (I ₉₀ / I ₀ ) to the Raman band intensity (I ₉₀ ) of 1615 ± 10 cm ⁻¹ measured with a polarization plane perpendicular to the above is 0.60 or more. In the thermoplastic resin layer B, the laser The half-value width of a Raman band of 1730 ± 10 cm ⁻¹ measured with a plane of polarization parallel to the surface of the resin layer using Raman spectroscopy is 22 cm ⁻¹ or more.

  The thermoplastic resin of the thermoplastic resin layer A is preferably polyethylene terephthalate or a copolymerized polyethylene terephthalate having a copolymer component of 10 mol% or less and polybutylene terephthalate or a copolymerized polybutylene terephthalate having a copolymer component of 10 mol% or less. .

  In the thermoplastic resin layer A, the copolymer component of the polyethylene terephthalate of the A1 layer is preferably isophthalic acid.

  In the thermoplastic resin layer A, the melting point of the thermoplastic resin layer A is preferably in the range of 235 to 245 ° C.

  According to the can lid for cans according to the present invention, when the can lid is wound or molded at high speed, the resin layer is not damaged, and the appearance of the resin layer after the retort sterilization treatment is excellent. A can lid for canning using a resin-coated metal plate capable of maintaining adhesion can be provided.

FIG. 1 is a schematic diagram for explaining the measurement principle of laser Raman spectroscopy. FIG. 2 is a schematic diagram for explaining a method for heat-sealing a resin layer. FIG. 3 is a plan view showing the configuration of the can lid. FIG. 4 is a cross-sectional view showing the configuration of the can lid. FIG. 5 is a diagram showing the configuration of the can body. FIG. 6 is a graph showing the relationship between PBT / (PET / PBT) and thickness d of the A2 layer.

  Hereinafter, a can lid for canning according to the present invention will be described in detail with reference to the drawings.

[Laser Raman spectroscopy]
First, the measurement principle of laser Raman spectroscopy applied to the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram for explaining the measurement principle of laser Raman spectroscopy. As shown in FIG. 1, in the laser Raman spectroscopy, the resin layer 2 on one surface side of the resin-coated metal plate 10 for can lid according to the present invention in which the resin layer 2 is coated on both surfaces of the metal plate 1. The laser light 4 oscillated from the laser oscillator 3 is incident, and the scattered Raman scattered light 5 is dispersed by the spectroscope 6. The beam diameter of the laser beam 4 is variable by the lens 7, and the crystallinity in a minute region of the resin layer 2 can be evaluated by reducing the beam diameter of the laser beam 4. In the present invention, the crystallinity at an arbitrary position in the cross section in the thickness direction of the resin layer 2 is evaluated based on the measurement principle of the laser Raman spectroscopy shown in FIG.

Here, it is known that the half-value width of a Raman band (derived from C = O stretching vibration) in the vicinity of 1730 cm ⁻¹ obtained from laser Raman spectroscopy is inversely proportional to the density of the resin layer 2. On the other hand, it is known that there is a relationship represented by the following formula (2) between the density of the resin layer 2 and the volume fraction crystallinity (hereinafter abbreviated as crystallinity). From these things, the state of crystallization can be grasped from the half width of the Raman band.

Furthermore, the Raman band seen in the vicinity of 1615 cm ⁻¹ by laser Raman spectroscopy is derived from the benzene ring C═C stretching vibration. Regarding the benzene ring C = C stretching vibration, the laser beam 4 to be irradiated is polarized, and the Raman band intensity measured with the polarization plane horizontal to the surface of the resin layer 2 and the polarization plane perpendicular to the surface of the resin layer 2 are used. The state of crystallization can also be grasped from the ratio with the measured Raman band intensity.

[Metal plate]
A steel plate or an aluminum plate that is widely used as a material for canned containers can be used for the metal plate 1 that is the base of the resin-coated metal plate 10 for can lids according to the present invention. The metal plate 1 may be subjected to various surface treatments, and in particular, tin-free steel (hereinafter referred to as TFS) which is a surface-treated steel plate with a two-layer coating in which the lower layer is made of metal chromium and the upper layer is made of chromium hydroxide. And the like are preferred. The amount of adhesion of the metal chromium and chromium hydroxide layer in TFS is not particularly limited, but from the viewpoint of workability and corrosion resistance, the amount of adhesion of the metal chromium layer is within the range of 70 to 200 mg / m ² . The amount of adhesion is desirably in the range of 10 to 30 mg / m ² .

[Resin layer coated on metal plate for can lid]
In the resin-coated metal plate 10 for a can lid according to the present invention, the resin layer 2 that is heat-sealed to the outer surface side of the can lid when being molded into the can lid among the two surfaces of the metal plate 1 is And a thermoplastic resin layer A mainly composed of polybutylene terephthalate (PBT) and polyethylene terephthalate (PET). The resin layer 2 that is heat-sealed to the lid surface that is the inner surface side of the can lid is composed of a thermoplastic resin layer B mainly composed of polyethylene terephthalate (PET).

  The thermoplastic resin layer A is composed of two or more layers. When the layer in contact with the metal plate 1 is the A1 layer and the outermost layer is the A2 layer, the composition ratio (wt%) of PBT / PET in the A1 layer is (40 / 60) to (80/20). When the PBT ratio in the A1 layer is less than this range, whitening occurs during the retort sterilization treatment, which is not preferable. The whitening during the retort sterilization process will be described later. On the other hand, when the PBT ratio in the A1 layer is larger than this range, the adhesion and the like deteriorate due to heating in a water vapor atmosphere, which is not preferable.

The thermoplastic resin of the thermoplastic resin layer A is mainly composed of polyethylene terephthalate and polybutylene terephthalate, and it is necessary to make the polyethylene terephthalate and polybutylene terephthalate have a certain relationship, but within the range not impairing the performance. The thermoplastic resin may be included. For example, it is good also as copolymerization polyethylene terephthalate whose copolymerization component is 10 mol% or less, and copolymerization polybutylene terephthalate whose copolymerization component is 10 mol% or less. In particular, as a copolymerization component of polyethylene terephthalate, it is more preferable to copolymerize 10% by mole or less of isophthalic acid. By reducing the melting point of the A1 layer by copolymerization of isophthalic acid, the Raman band intensity (I ₉₀ ) of 1615 ± 10 cm ⁻¹ measured in the polarization plane perpendicular to the resin layer surface is increased, resulting in In addition, the intensity ratio (I ₉₀ / I ₀ ) by laser Raman spectroscopy is increased. Details of the laser Raman spectroscopy will be described later. When the copolymerization ratio of isophthalic acid is larger than 10 mol%, the melting point is lowered, and although it is not in direct contact with the roll, there is a concern about welding, which is not preferable. When the copolymerization ratio of isophthalic acid is less than 2 mol%, the effect of increasing the Raman band strength (I ₉₀ ) is small. Moreover, in the thermoplastic resin layer A, it is preferable that melting | fusing point of the thermoplastic resin layer A exists in the range of 235-245 degreeC.

  The PET ratio in the A2 layer is made larger than the PBT ratio in the A2 layer. This is because, when the resin layers 2 on both sides are simultaneously heat-sealed, the thermoplastic resin layer B on the inner surface side of the can having a high PET ratio has a high melting point, so there is a concern that the thermoplastic resin layer A is welded to the roll. It is. If the ratio of PET with a high melting point in the A2 layer in direct contact with the roll is larger than the ratio of PBT, regardless of the resin component when there is an intermediate layer between the lower A1 layer or the A1 layer and the A2 layer It is possible to suppress operability deterioration due to welding. In addition, although the component of an intermediate | middle layer is not specifically limited, From a viewpoint on manufacture, it is preferable that melting | fusing point is near and it is preferable that the difference of melting | fusing point with an upper and lower layer shall be 10 degrees C or less.

  The thickness d (μm) of the A2 layer satisfies the following formula (1). The inventors of the present invention have studied various compositions of the A2 layer that can suppress whitening during the retort sterilization treatment within a favorable range of the composition of the A1 layer, and obtained the results of FIG. From the results, it was confirmed that there was a correlation between the PBT ratio of the surface layer and the thickness d. The relationship of Formula (1) was obtained by plotting the relationship between the minimum surface layer thickness to be whitened and PBT / (PBT + PET) and performing regression calculation. Bubbles at the time of retort sterilization are likely to be formed in the vicinity of the interface in contact with the metal plate 1, but they are also formed at the outermost layer and may cause whitening. However, it has been found that bubbles are not formed if the outermost layer thickness and the PBT ratio with a high crystallization rate are within the range shown in Equation (1). This is because the formation of bubbles in the outermost layer is mild because the outermost layer is in contact with steam and the temperature difference during retort sterilization is small compared to the interface with the steel plate close to the contents side. It is considered that the thickness and the PBT ratio were improved when they were in the range shown in the mathematical formula (1).

  The content of PET in the thermoplastic resin in the thermoplastic resin layer B is 95 mol% or more. When the content of PET is less than 95 mol%, other components including a copolymer component are mixed in and eluted into the content, resulting in deterioration of the content resistance. Moreover, melting | fusing point falls by addition of another component, and the heat-fusability (adhesion) with the metal plate 1 deteriorates.

In the thermoplastic resin layer A, the Raman band intensity (I ₀ ) of 1615 ± 10 cm ⁻¹ measured using a laser Raman spectroscopy with a polarization plane horizontal to the resin layer surface and a polarization plane perpendicular to the resin layer surface The intensity ratio (I ₉₀ / I ₀ ) with respect to the Raman band intensity (I ₉₀ ) of 1615 ± 10 cm ⁻¹ measured in ( ¹ ) is 0.60 or more, preferably 0.70 or more. Here, the Raman band intensity (I ₀ ) of 1615 ± 10 cm ⁻¹ measured with a polarization plane horizontal to the resin layer surface becomes larger as the crystal component in the in-plane direction on the resin layer surface increases. On the other hand, the Raman band intensity (I ₉₀ ) of 1615 ± 10 cm ⁻¹ measured with a polarization plane perpendicular to the resin layer surface increases as the crystal component in the thickness direction of the resin layer increases. Therefore, if the intensity ratio (I ₉₀ / I ₀ ) becomes a large value, it means that the crystal component in the in-plane direction of the resin layer decreases and the crystal component in the thickness direction of the resin layer increases.

The film for the thermoplastic resin layer A stretched at the time of production has a large crystal component in the in-plane direction of the resin film during the stretching process. When winding is performed in this state, the bonds between weak molecules are easily broken, and the thermoplastic resin layer A is damaged. Therefore, a crystal component in the thickness direction of the thermoplastic resin layer A is required. Its proportion is the intensity ratio _(I 90 / I ₀₎ need only be equal to or greater than 0.60. Furthermore, the intensity ratio (I ₉₀ / I ₀ ) is preferably 0.70 or more. When the strength ratio (I ₉₀ / I ₀ ) is less than 0.60, there are many crystal components in the in-plane direction of the resin film, and therefore the thermoplasticity when wound at high speed or molded at high speed. The resin layer A is shaved.

On the other hand, in the thermoplastic resin layer B, the half-value width of the Raman band of 1730 ± 10 cm ⁻¹ measured with a plane of polarization parallel to the surface of the resin layer using laser Raman spectroscopy is 22 cm ⁻¹ or more, preferably 24 cm ^{−. 1} or more. When the half-value width of the Raman band is smaller than 22 cm ⁻¹ , the thermoplastic resin layer B breaks without following the molding when molding with a high workability. Although there is no upper limit of the half band width of the Raman band, there is no problem in manufacturing unless the thermoplastic resin layer A is welded to the roll.

  During the production of the can-covered resin-coated metal plate 10, the thermoplastic resin layer A and the thermoplastic resin layer B are heat-sealed simultaneously or substantially simultaneously. In this case, it is necessary to appropriately select the thermoplastic resin layer B in order to bring the thermoplastic resin layer A into a crystalline state as described above. Here, with reference to FIG. 2, a method of thermally fusing the resin layer 2 will be described.

  FIG. 2 is a schematic diagram for explaining a method of thermally fusing a resin film as an example of a method for forming the resin layer 2. As shown in FIG. 2, when the resin film is heat-sealed to form the resin layer 2, the metal plate 1 is heated to a certain temperature or higher by the metal band heating device 11, and then the pressure roll ( The resin layer 2 is press-contacted to both surfaces of the metal plate 1 using 12). Thereby, the resin layer 2 can be heat-seal | fused on both surfaces of the metal plate 1, and the resin-coated metal plate 10 for can lids which concerns on this invention can be manufactured. In this case, the heat-bonding of the resin layer 2 to the metal plate 1 can be made uniform by pressing the lami roll 12 against the metal plate 1 through the resin layer 2.

  Hereinafter, the details of the heat sealing conditions will be described. The temperature of the metal plate 1 at the start of heat fusion is preferably in the range of + 5 ° C. to + 40 ° C. based on the melting point of the resin layer 2. In order to ensure the adhesion between the metal plate 1 and the resin layer 2 by the heat fusion method, it is necessary to heat the polyester resin at the interface. By setting the temperature of the metal plate 1 to a temperature range of + 5 ° C. or higher based on the melting point of the resin layer 2, the resin heat-flows at the interface, the wettability at the interface becomes good, and excellent adhesion is achieved. can get. Even if the temperature of the metal plate 1 exceeds + 40 ° C., further improvement in adhesion cannot be expected, the resin layer 2 is excessively melted, the surface is roughened by embossing on the surface of the lami roll 12, and the melt is transferred to the lami roll 12. Therefore, the temperature of the metal plate 1 at the start of thermal fusion is preferably + 40 ° C. or less based on the melting point of the resin layer 2.

  At the time of heat-sealing, it is desirable that the metal plate 1 is pressure-welded by a lami roll 12 for a time of 5 msec or more in a state where the temperature is equal to or higher than the melting point of the resin layer 2. This is because the wettability at the interface becomes good. When in contact with each other, the resin layer 2 is melted from the vicinity of the interface with the metal plate 1 by heat. Since the thermal conductivity of the resin layer 2 is extremely small, the surface layer of the resin layer 2 does not reach the melting point in a time of 5 to 40 msec. However, when this time becomes long, the temperature rises to a temperature close to the melting point and is welded to the lami roll 12. There are concerns. Also from this viewpoint, it is desirable that the pressure contact time is 40 msec or less. Furthermore, it is more preferable if the pressure contact time is within a range of 10 to 25 msec.

  In order to achieve such heat fusion conditions, temperature control during heat fusion is necessary in addition to high-speed operation of 150 mpm or more, and the temperature of the lami roll 12 may be controlled. For example, it can suppress that the resin layer 2 is heated too much by making the lami roll 12 in FIG. 2 into an internal water cooling type, and allowing cooling water to pass through. Furthermore, it is preferable because the heat history of the resin layer 2 on the inner surface side and the outer surface side can be controlled by independently changing the resin layer 2 on the inner surface side and the outer surface side when the temperature of the cooling water is a can lid. It is. Since the resin layer 2 on the inner surface side has a higher melting point, it is preferable that the temperature of the Lami roll 12 is set higher and the temperature of the Lami roll 12 on the outer surface side is set lower. For example, it is preferable to provide a temperature difference such that the temperature of the inner side lami roll 12 is 120 ° C. and the temperature of the outer side lami roll 12 is 80 ° C. The temperature of the lami roll 12 may be adjusted as appropriate within the range of 50 ° C to 130 ° C.

The pressurization with the lami roll 12 is preferably 9.8 to 294 N / cm ² (1 to 30 kgf / cm ² ) as the surface pressure. In the case where the pressure applied by the lami roll 12 is less than 9.8 N / cm ² , even if the temperature at the start of thermal fusion is + 5 ° C. or higher with respect to the melting point of the resin layer 2, Since the force which spreads the resin layer 2 on the surface of the plate 1 is weak, sufficient coverage cannot be obtained. As a result, there is a possibility of affecting performance such as adhesion and corrosion resistance (content resistance). In addition, when the pressure applied by the Lami roll 12 exceeds 294 N / cm ^2, although there is no inconvenience in the performance of the resin-covered metal plate 10 for can lids, the force applied to the Lami roll 12 is large, and the equipment needs strength. It is uneconomical due to the increase in size of the equipment. Therefore, the pressurization with the lami roll 12 is preferably within a range of 9.8 to 294 N / cm ² .

  Other dicarboxylic acid components, glycol components, and other resin components may be copolymerized with the material of the resin layer 2 on the inner and outer surfaces in a range that does not impair the workability, heat resistance, and corrosion resistance (however, the resin on the inner surface side The content in layer 2 is less than 5 mol%). Examples of the dicarboxylic acid component include isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfone dicarboxylic acid, diphenoxyethanedicarboxylic acid, 5-sodium sulfoisophthalic acid, aromatic dicarboxylic acid such as phthalic acid, oxalic acid, succinic acid, Examples thereof include aliphatic dicarboxylic acids such as adipic acid, sebacic acid, dimer acid, maleic acid and fumaric acid, alicyclic carboxylic acids such as cyclohexanedicarboxylic acid, and oxycarboxylic acids such as p-oxybenzoic acid.

  Examples of the glycol component include ethylene glycol or butanediol, propanediol, pentanediol, hexanediol, neopentylglycol and other aliphatic glycols, cyclohexanedimethanol and other alicyclic glycols, bisphenol A and bisphenol S and other aromatic glycols, Examples include diethylene glycol. Two or more dicarboxylic acid components and glycol components may be used in combination.

  If necessary, a low molecular weight polymer, a fluorescent brightening agent, an antioxidant, a heat stabilizer, an ultraviolet absorber, a plasticizer, a pigment, an antistatic agent, a crystal nucleating agent, and the like can be blended. The low molecular weight polymer has, for example, a number average molecular weight of about 1000 to 10,000, and examples thereof include polyolefin, polystyrene, and polyamide. Since these low molecular weight polymers are incompatible with the polyester constituting the film, if they are present on the surface layer, an effect of imparting lubricity can be expected by forming appropriate irregularities. In addition, it is possible to impart design properties by adding pigments. For example, if a disazo pigment is used for the thermoplastic resin layer A, it is excellent in transparency but has strong coloring power and excellent spreadability. A bright appearance can be obtained even after the lid is closed. The additive components other than the resin may be added by appropriately calculating the necessary amount based on the weight ratio with respect to the total amount of the coating, but when the pigment is added, the addition amount is preferably 30 PHR or less. Here, the addition amount of the pigment is a ratio (excluding the resin amount in the resin layer in the lower layer when added to the lower resin layer) with respect to the resin amount in the resin layer to which the pigment is added. Means. Examples of the disazo pigment include CI Pigment Yellow 12, 13, 14, 16, 17, 55, 81, 83, 180, 181 and the like as color indexes (CI registered names). These may be used alone or in combination of two or more. In particular, pigments with high molecular weight and poor solubility in PET resin from the standpoints of vividness of color tone (bright color) and bleeding resistance in retort sterilization environment (inhibition ability against the phenomenon that pigment is deposited on the film surface). And having a benzimidazolone structure having a molecular weight of 700 or more. I. Pigment Yellow 180 is more preferably used.

  The resin material which forms the resin layer 2 which is the thermoplastic resin layer A and the thermoplastic resin layer B is not limited by the manufacturing method. For example, the resin material can be formed using the following methods (1), (2), and the like.

(1) A method of esterifying terephthalic acid, ethylene glycol, and a copolymer component, and then polycondensing the resulting reaction product to obtain a thermoplastic resin.
(2) A method in which dimethyl terephthalate, ethylene glycol, and a copolymer component are subjected to a transesterification reaction, and then a reaction product obtained is subjected to a polycondensation reaction to obtain a thermoplastic resin.

  In the production of the thermoplastic resin, additives such as a fluorescent brightener, an antioxidant, a heat stabilizer, an ultraviolet absorber, and an antistatic agent may be added as necessary.

  For the polyester resin, the thermoplastic resin layer A and the thermoplastic resin layer B used in the present invention have a weight average molecular weight of 5,000 to 100,000 in terms of improving mechanical properties, laminating properties and taste properties. Those within the range are preferable, and those within the range of 10,000 to 80,000 are more preferable. The thicknesses of the thermoplastic resin layer A and the thermoplastic resin layer B of the present invention are preferably in the range of 5 μm to 50 μm, more preferably in the range of 8 μm to 30 μm, particularly in the range of 10 μm to 25 μm. It is preferable to be within. Moreover, when forming several resin layers with a film, it is preferable that each layer shall be 0.3 micrometer or more from a viewpoint of film thickness uniformity.

[Whitening during retort sterilization]
When a retort sterilization treatment is performed on a can body produced by tightening a can lid manufactured using a resin-coated metal plate 10 for a can lid coated with a resin layer 2, a phenomenon in which the thermoplastic resin layer A is whitened is observed. There is. This is because fine bubbles are formed in the thermoplastic resin layer A, and light is scattered by these bubbles, resulting in a white turbid appearance. In addition, the bubbles formed in the thermoplastic resin layer A have the following characteristics. First, these bubbles are not formed even when the can is heated in a dry heat environment. Moreover, even if a retort sterilization process is performed with an empty can without filling the can, no bubbles are formed. From the above characteristics, it is considered that the formation of bubbles in the thermoplastic resin layer A accompanying the retort sterilization treatment occurs by the following mechanism.

  The can body is exposed to high-temperature steam from the beginning of the retort sterilization treatment, and a part of the steam enters the interior of the thermoplastic resin layer A and reaches the vicinity of the interface with the metal plate 1. Since the vicinity of the interface between the thermoplastic resin layer A and the metal plate 1 is cooled from the inner surface of the can lid by the contents at the beginning of the retort sterilization treatment, the water vapor that has entered the interface becomes condensed water. Next, the temperature of the contents rises with the lapse of time for the retort sterilization treatment, and the condensed water at the interface with the metal plate 1 is re-vaporized. The vaporized water vapor escapes again through the thermoplastic resin layer A, but it is estimated that the trace of condensed water at this time becomes bubbles. In addition, the resin in the vicinity of the interface melted by contact with the heated metal plate 1 is an amorphous resin that is mechanically soft and highly deformable even after cooling and solidification, and is easily deformed and forms bubbles. It is thought to be easy. Therefore, in order to suppress whitening without forming bubbles in the thermoplastic resin layer A during the retort sterilization treatment, the amorphous polyester layer is quickly crystallized with the heat of the retort sterilization treatment with respect to the thermoplastic resin layer A. It is effective to increase the strength of the amorphous layer.

  As described above, according to the resin-coated metal plate 10 for a can lid according to the present invention, when the resin layer 2 is manufactured by heat-sealing, the thermoplastic resin layer A on the outer surface side is welded to the lami roll. The thermoplastic resin layer A of the can lid made of the present metal plate can be stably manufactured without any damage when being fastened or molded at high speed, and the appearance after the retort sterilization treatment The thermoplastic resin layer B is excellent in content resistance, and can retain adhesion even if it is subjected to a retort sterilization process in contact with the content.

Examples of the present invention will be described below. In this example, a steel plate having a thickness of 0.18 mm and a width of 977 mm subjected to cold rolling, annealing, and temper rolling was degreased, pickled, chrome plated, and a chrome plated steel plate (TFS) as a metal plate 1. Manufactured. Chromium plating was performed by chromium plating in a chromium plating bath containing CrO ₃ , F ⁻ , SO ₄ ²⁻ , intermediate rinsing, and then electrolyzed with a chemical conversion treatment solution containing CrO ₃ and F ⁻ . At that time, the electrolysis conditions (current density, amount of electricity, etc.) were adjusted so that the metal chromium adhesion amount and the chromium hydroxide adhesion amount were 120 mg / m ² and 15 mg / m ² in terms of Cr, respectively.

  Next, using a metal strip laminator, the chrome-plated steel sheet obtained above is heated with a metal strip heater, and a biaxially stretched polyester film is heat-sealed as a resin film on both sides of the chrome-plated steel sheet with a lamin roll. A resin-coated metal plate 10 for a lid was produced. The lami roll was an internal water-cooling type, and cooling water was forcibly circulated during heat fusion, thereby cooling the resin-coated metal plate 10 for can lids during heat fusion. The Raman band intensity ratio by laser Raman spectroscopy was adjusted by changing the lamination conditions to the metal band.

  The characteristics of the resin layer 2 were measured and evaluated by the following method (1). Moreover, the characteristic of the resin-coated metal plate 10 for can lids manufactured by the above method was measured and evaluated by the following methods (2) to (6). Tables 1 to 4 show the characteristics of the laminated resin layer 2 and the heat-sealing conditions and the evaluation results of the resin-coated metal plate 10 for each can lid.

(1) Measurement by laser Raman spectroscopy (1-1) Raman band intensity ratio of thermoplastic resin layer A (I ₉₀ / I ₀ )
A cross-section polished sample of the resin-coated metal plate 10 for can lids was prepared, and a Raman band intensity of 1615 ± 10 cm ⁻¹ for each 1 μm on the laser polarization plane horizontal to the cross-sectional direction of the thermoplastic resin layer A under the following measurement conditions. The average value of the measured values of 5 μm from the surface layer side was taken as the Raman band intensity (I ₀ ). Further, the Raman band intensity of 1615 ± 10 cm ⁻¹ is measured every 1 μm from the surface layer side on the laser deflection surface perpendicular to the cross-sectional direction of the thermoplastic resin layer A, and the average value of the measured values of 5 μm from the surface layer side is determined as the Raman band intensity. The Raman band intensity ratio (I = I ₉₀ / I ₀ ) was determined as (I ₉₀ ).

(1-2) Raman band half-value width of thermoplastic resin layer B A cross-sectional polished sample of the resin-coated metal plate 10 for can lids was prepared, and the laser deflection horizontal in the cross-sectional direction of the thermoplastic resin layer B under the following measurement conditions The half width of the Raman band of 1730 ± 10 cm ⁻¹ was measured every 1 μm on the surface, and the average value of the measured values of 5 μm was determined from the surface layer side.

(Measurement condition)
Excitation light source: Semiconductor laser (λ = 532 nm)
Microscopic magnification: x100
Aperture: 25μmφ

(2) Measurement of melting | fusing point Melting | fusing point was measured on 20 degreeC / min temperature rising conditions using DSC8500 made from Perkin Elmer. For the measurement, a resin layer was melted and then rapidly cooled in liquid nitrogen as a measurement sample.

(3) Anti-clamping property The resin-coated metal plate 10 for can lids is punched into a can lid shape using a press device, and is processed by a well-known process to obtain a can lid (bottom name) shown in FIGS. Lid) 21 was formed. Specifically, a chuck wall 23 is formed on the outer peripheral portion of the flat panel portion 22 and a seaming panel 24 curved outward is formed, and a well-known seal is formed inside the seaming panel 24. The material 25 was applied and dried. Next, the can lid 21 was wound around the end flange portion of the welded can body 27 (see FIG. 5) at a speed of 800 cans per minute. The state of the thermoplastic resin layer A in the tightening portion 28 of the can lid 21 was observed, and the anti-winding property was evaluated according to the following score.

(Score)
(Double-circle): There is no generation | occurrence | production of resin layer abrasion among 50 cover materials.
○: Resin layer scraping occurred in 1 to 5 of 50 lid materials.
(Triangle | delta): Resin layer abrasion generate | occur | produced in 6-10 sheets among 50 cover materials.
X: Resin layer scraping occurs in 11 or more of 50 lid materials.

(4) Retort whitening resistance Retort whitening resistance of the thermoplastic resin layer A of the can lid 21 was evaluated. Specifically, after filling the can body 26 with the can lid 21 wound as the bottom lid of the welding can body 27 with normal temperature tap water, the upper lid 29 is wound and sealed, and the can body 26 shown in FIG. Formed. After that, the bottom of the can body 26 was placed face down and placed in a steam retort sterilization furnace, and retort sterilization was performed at 125 ° C. for 30 minutes. After the retort sterilization treatment, the appearance change of the thermoplastic resin layer A of the can lid 21 was visually observed, and the retort whitening resistance was evaluated according to the following ratings.

(Score)
○: No change in appearance.
X: The appearance is cloudy.

(5) Adhesion (wet adhesion)
A flat plate sample (width 15 mm, length 120 mm) before making the lid of the resin-coated metal plate 10 for can lids was cut out. A part of the resin layer 2 was peeled off from the end portion on the long side of the cut sample. The peeled resin layer (film) 2 was opened in a direction opposite to the peeled direction (angle: 180 °), a 50 g weight was fixed, and retort sterilization treatment (125 ° C., 30 minutes) was performed. The peel length of the resin layer 2 after the retort sterilization treatment was measured, and the film wet adhesion before molding (secondary adhesion) was evaluated as adhesion according to the following rating. Although this test method is a test that simulates the adhesion after retort sterilization, the content resistance on the inner surface of the can lid is also largely due to the deterioration of the adhesion, so both the inner and outer surfaces of the can lid are subject to the same conditions. Tested.

(Score)
A: Less than 10 mm.
○: 10 mm or more and less than 20 mm.
X: 20 mm or more.

(6) Manufacturability The resin-coated metal plate 10 for can lids was manufactured as described above, the presence or absence of the resin layer 2 being welded to the lami roll 12 or the like was observed, and the manufacturability was evaluated according to the following ratings.

(Score)
○: No film welding.
X: There exists film welding.

From Tables 3 and 4, it was confirmed that the resin-coated metal plate for can lids according to the present invention was excellent in anti-winding property, anti-retort whitening property, adhesion, content resistance property, and manufacturability. On the other hand, in Comparative Examples 1 and 2, it was confirmed that in the thermoplastic resin layer A, when the PBT ratio is low, the whitening resistance is poor, and when the PBT ratio is high, the adhesion is poor. In Comparative Example 3, it was confirmed that when the PBT ratio of the A2 layer was high, welding occurred and the manufacturability deteriorated. Moreover, in the comparative example 4, when the PBT ratio and thickness in A2 layer were outside the range shown to Numerical formula (1), it was confirmed that it is inferior to whitening resistance. In Comparative Example 5, it was confirmed that when the Raman band intensity ratio of the thermoplastic resin layer A was less than 0.60, the crystal structure was inadequate, so that the anti-winding resistance was poor. In Comparative Example 6, when the PET ratio in the thermoplastic resin layer B was low, it was confirmed that the adhesion was poor. In Comparative Example 7, when the half band width of the Raman band of the thermoplastic resin layer B was smaller than 22 cm ⁻¹ , it was confirmed that the adhesiveness of the thermoplastic resin layer B was inferior.

1 Metal plate 2 Resin layer (film)
DESCRIPTION OF SYMBOLS 3 Laser oscillator 4 Laser beam 5 Raman scattered light 6 Spectrometer 7 Lens 10 Resin-coated metal plate for can lid 11 Metal band heating device 21 Can lid 22 Flat panel part 23 Chuck wall 24 Seaming panel 25 Sealing material 26 Can body 27 Welding can body 28 Tightening part 29 Upper lid

Claims (4)

A metal plate,
A thermoplastic resin layer A mainly composed of polybutylene terephthalate (PBT) and polyethylene terephthalate (PET), provided on the outer surface of the metal plate can lid;
A thermoplastic resin layer B mainly composed of polyethylene terephthalate (PET) provided on the inner surface of the metal plate can lid;
With
The thermoplastic resin layer A is composed of two or more layers, and the weight ratio of PBT / PET of the A1 layer that is in contact with the metal plate is within the range of (40/60) to (80/20). Yes, the PET weight ratio in the outermost A2 layer is larger than the PBT weight ratio in the A2 layer, and the thickness d (μm) of the A2 layer satisfies the following formula (1):
95 mol% or more of the thermoplastic resin in the thermoplastic resin layer B is polyethylene terephthalate. In the thermoplastic resin layer A, 1615 ± measured in a plane of polarization horizontal to the surface of the resin layer using laser Raman spectroscopy. the ratio of the Raman band intensity of 10 cm ^-1 Raman band intensity _{(I 90)} of _{(I 0)} and 1615 ± 10 cm were measured in the polarization plane perpendicular to the surface of the resin layer ^-1 _(I 90 / I ₀₎ is 0 .60 or more,
The thermoplastic resin layer B is characterized in that the half-value width of a Raman band of 1730 ± 10 cm ⁻¹ measured with a plane of polarization parallel to the surface of the resin layer using laser Raman spectroscopy is 22 cm ⁻¹ or more. Can lid for canning.

  The thermoplastic resin of the thermoplastic resin layer A is polyethylene terephthalate, copolymerized polyethylene terephthalate and polybutylene terephthalate having a copolymer component of 10 mol% or less, or copolymer polybutylene terephthalate having a copolymer component of 10 mol% or less. The can lid for canning according to claim 1, wherein the can lid is a can.   The can lid for canning according to claim 1 or 2, wherein in the thermoplastic resin layer A, the copolymer component of the polyethylene terephthalate of the A1 layer is isophthalic acid.   The can lid for canning according to any one of claims 1 to 3, wherein in the thermoplastic resin layer A, the melting point of the thermoplastic resin layer A is in a range of 235 to 245 ° C.

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