JP6358945B2 - Can lid for canning - Google Patents

Description

  The present invention relates to a can lid for canned foods and the like using a resin-coated metal plate.

  Conventionally, a solvent-type paint mainly composed of a thermosetting resin has been applied to the inner and outer surfaces of metal cans such as beverage foods. The purpose of this is to maintain the flavor of the contents, to prevent corrosion of the metal that is the can body material for canning, or to improve the design of the outer surface of the can body for canning and to protect the printing surface. However, solvent-based paints require heating at a high temperature to form a coating film, and a large amount of solvent is generated during heating, which has problems in terms of work safety and environmental impact. . Therefore, recently, metal coating with a thermoplastic resin that does not use a solvent has been proposed. In particular, among thermoplastic resins, polyester resins are excellent in processability and heat resistance, and therefore, development of metal laminate films based on polyester resins has been underway.

  When a laminated metal plate (resin-coated metal plate) laminated with a resin film such as polyester is applied to a can lid material for canned foods, etc., the can lid can be When tightening, there was a problem that film cracking or film scraping occurred on the outer surface of the can lid. In addition, the cyclic trimer in the polyester resin is deposited on the surface of the resin film during high-temperature sterilization such as retort treatment, and the design properties are impaired, or the resin film layer itself is discolored so as to become cloudy white during the retort treatment. There were problems such as occurrence of a phenomenon (whitening phenomenon). On the other hand, the resin used for the inner surface of the can lid is required to have corrosion resistance (content resistance) with respect to the contents and adhesion upon long-term contact with the contents.

  As a method for improving such a problem, Patent Document 1 covers both sides of a metal plate with a thermoplastic resin film, and the amorphous ratio of the thermoplastic resin film layer on the outer side of the can lid is 60% or more. A technique for providing a double-sided film laminate can lid having a good anti-winding property by leaving an oriented crystal layer in a part of the thermoplastic resin film layer on the inner surface of the can lid is disclosed.

  Patent Document 2 is a polyester in which a polyester having ethylene terephthalate as a main repeating unit is blended on the outer surface side of the can body in a ratio of 30 to 50% by mass and polyester having butylene terephthalate as a main repeating unit in a proportion of 50 to 70% by mass. A metal plate coated with a film is described. As a result, the shortest half crystallization time is set to 100 seconds or less to crystallize using the heat of retort treatment, and the crystallization speed is increased to prevent white spots (whitening) from occurring on the film. . This metal plate has a polyester resin layer having a two-layer structure on the inner surface of the container, and the upper polyester resin layer is polyethylene terephthalate or a copolymerized polyethylene terephthalate copolymerized with isophthalic acid at a ratio of 6 mol% or less as an acid component. It is also described that. In addition, the upper polyester resin layer contains 0.1 to 5% by mass of an olefinic wax, and the lower polyester resin layer is copolymerized with isophthalic acid as an acid component at a ratio of 10 mol% to 22 mol%. 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 outer film.

  Patent Document 7 discloses a polyester composition containing 30 to 50% by mass of a polyester mainly composed of ethylene terephthalate and 50 to 70% by mass of a polyester mainly composed of butylene terephthalate. This describes a technique for suppressing discoloration during retort processing. 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 processing.

  Further, in Patent Document 10, a polyester film having a contact angle 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 so as to have whitening resistance. Techniques for improving the performance are described.

JP 2002-193256 A JP 2005-342911 A Japanese Patent Laid-Open No. 5-331302 JP 2000-313755 A JP 2001-335682 A JP-A-6-155660 Japanese Patent Laid-Open No. 10-110046 JP 09-012743 A JP 07-145252 A JP 2004-168365 A

  However, although the can lid described in Patent Document 1 has a good anti-clamping property of the outer film, it uses an ethylene terephthalate / isophthalate copolymer, and the crystallization speed is insufficient, so that the retort treatment is performed. The whitening resistance of was insufficient. Moreover, although the effect of improving the whitening resistance of an outer surface film is seen by the technique of patent documents 2-6, since a crystallization state is not taken into consideration, even if it winds up at high speed, a film does not scrape However, it has not improved the abrasion resistance. Further, since the copolymer component is present on the inner surface side, the copolymer component is eluted and there is a concern that the content resistance is inferior.

  In the techniques described in Patent Documents 7 to 9, the steel plate used in the can needs to be heat-sealed simultaneously on both sides, but only one side is described, and there is no disclosure about the resin on the opposite side. As described above, since the performance required for the inner and outer surfaces of the can body is different in the steel plate for cans, it is necessary to combine different types of resins. Considering the productivity of products using different types of resins, it is preferable to heat-seal at the same time, and resins having melting points almost equal by copolymerization have been combined, but it is necessary to add copolymerization components There will be an increase in cost. When the melting points differ greatly, it is necessary to heat the resin on the high melting point side to the high melting point in order to thermally fuse it, but there is a concern that the resin on the low melting point side may exceed the melting point and adhere to a roll or the like to hinder productivity. is there. In the above technology, since these viewpoints are not taken into consideration, there is a concern that the film adhesion is inferior, the product is not competitive, or the productivity is inferior.

  Although the technique described in Patent Document 10 is excellent in whitening resistance, since the crystal structure of the resin is not controlled, the anti-winding property is insufficient. Moreover, since the resin on the inner surface side is isophthalic acid-based copolymerized PET, there is a concern that the copolymer component is eluted and the content resistance is inferior.

  The present invention was made in order to solve the above-mentioned problems, and even if it is fastened at a high speed, it does not cause film scraping or film cracking and is excellent in anti-winding resistance. 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 film.

  The inventors of the present invention diligently studied the combination and crystal structure of the inner and outer surface films of can lids for canned foods and the like, and found that the above problems can be solved by controlling the crystal structure of the inner and outer surfaces.

The can lid for canning according to the present invention is a can lid using a resin-coated metal plate in which both surfaces of the metal plate are coated with a thermoplastic resin film, wherein the resin-coated metal plate is a can lid of the metal plate. A thermoplastic resin film A mainly composed of polybutylene terephthalate (PBT) and polyethylene terephthalate (PET) is heat-sealed on the outer surface, and polyethylene terephthalate (PET) is mainly formed on the inner surface of the can lid. The thermoplastic resin film B was thermally fused, and the composition ratio (wt%) of PBT / PET of the resin film A on the outer surface side was (PBT / PET) = (40/60) to (80 / 20), the resin film B on the inner surface side is not less than 95 mol%, and the melting point derived from PET of the inner surface side resin film B is not less than 250 ° C. and not more than 265 ° C. And, wherein the outer surface side resin film higher 25 ° C. or higher than the melting point of from PBT in A, the outer surface side resin film A, laser Raman spectroscopy 1615 ± 10 cm on the resin film surface was measured by the polarization plane is horizontal ^-1 The Raman band intensity ratio (I ₉₀ / I ₀ ) between the Raman band intensity (I ₀ ) and the Raman band intensity (I ₉₀ ) of 1615 ± 10 cm ⁻¹ measured with a perpendicular polarization plane is 0.60 or more The inner side resin film B has a half band width of 1730 ± 10 cm ⁻¹ measured by a laser Raman spectroscopy with a polarization plane that is horizontal with respect to the resin film surface, and is 15 to 20 cm ^−1. It is characterized by.

  According to the present invention, even if the can lid is tightened at a high speed, no film scraping or film scratches are generated, and the anti-winding resistance is excellent, the appearance design after retort processing is excellent, and the content resistance is excellent. The can lid | cover for cans which can maintain adhesiveness can be provided.

FIG. 1 is an explanatory diagram of laser Raman spectroscopy applied to the present invention. FIG. 2 is an explanatory diagram of a resin film thermal fusion method applied to the present invention. FIG. 3 is an explanatory view of a can lid formed from a resin film laminated metal plate. 4 is a cross-sectional view taken along the line II of the can lid of FIG. 3. FIG. 5 is an explanatory diagram of a can body in which a can lid is wound around a can body.

  Hereinafter, a can lid for forming a can body of the present invention will be described in detail with reference to the drawings as an embodiment. In addition, this invention is not limited by this embodiment.

<Laser Raman spectroscopy>
First, with reference to FIG. 1, the measuring method of the laser Raman spectroscopy applied to this invention is demonstrated. As shown in FIG. 1, in a resin-coated metal plate 10 in which a resin film 2 is laminated on both surfaces of a metal plate 1, a laser beam 4 oscillated from a laser oscillator 3 is incident on the resin film 2 on one surface. Then, the scattered Raman scattered light 5 is split by the spectroscope 6. The beam diameter of the laser beam 4 irradiated by the laser Raman spectroscopy is variable by the lens 7, and the crystallinity can be evaluated with a necessary measurement region size. And the crystallinity degree in the micro area | region of the resin film 2 can be evaluated by restrict | squeezing the beam diameter of the laser beam 4 irradiated. In this Embodiment, the crystallinity degree in arbitrary site | parts of the thickness direction cross section of the resin film 2 was evaluated with the measuring method of the laser Raman spectroscopy shown in FIG.

Here, it is known that the peak half-value width of the Raman band in the vicinity of 1730 cm ⁻¹ (derived from C═O stretching vibration) obtained from laser Raman spectroscopy is inversely proportional to the density of the resin film 2. On the other hand, it is known that there is a relationship of the following formula (1) between the density of the resin film 2 and the volume fraction crystallinity.

Therefore, the density of the resin film 2 in the portion irradiated with the laser beam 4 can be obtained by measuring the peak half-value width of the Raman band (derived from C = O stretching vibration) in the vicinity of 1730 cm ⁻¹ . Furthermore, according to the above formula (1), the volume fraction crystallinity (hereinafter referred to as crystallinity) of the resin film 2 can be obtained.

Further, 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. For C = C stretching vibration, the ratio of the Raman band intensity measured on the polarization plane that is horizontal to the surface of the resin film 2 and the Raman band intensity measured on the polarization plane that is perpendicular to the surface of the resin film 2 by polarizing the irradiated laser beam 4. It is possible to measure the crystallinity from

<Metal plate>
A surface-treated steel plate or an aluminum plate used as a metal material for a can lid or can body of a can body can be used for the metal plate 1 as a base of the resin-coated metal plate 10 used in the present invention. The metal plate 1 is preferably tin-free steel (hereinafter referred to as TFS), which is a surface-treated steel sheet having a two-layer coating in which the lower layer is metallic chromium and the upper layer is chromium hydroxide, but is not limited thereto. It is possible to use a chromium-free surface-treated steel plate replaced with the above metal. In the case of TFS, the amount of metal chromium and chromium hydroxide layer deposited is not particularly limited, but from the viewpoint of workability and corrosion resistance, the metal chromium layer is 70 to 200 mg / m ² , and the chromium hydroxide layer is 10 to 30 mg. / M ² is preferable.

<Resin film coated on metal plate>
In the resin-coated metal plate 10 used in the present invention, of the two surfaces of the metal plate 1, when the can lid is formed from the resin-coated metal plate 10, it is heat-sealed to the surface on the outer surface side of the can lid. The resin film 2 is composed of a thermoplastic resin film A mainly composed of polybutylene terephthalate (PBT) and polyethylene terephthalate (PET). The resin film 2 that is heat-sealed to the inner surface of the can lid is composed of a thermoplastic resin film B mainly composed of polyethylene terephthalate (PET).

  The PBT / PET composition ratio (wt%) of the resin film A on the outer surface side is (PBT / PET) = (40/60) to (80/20), and the resin film B on the inner surface side is 95% by mole or more of PET. The melting point derived from PBT in the thermoplastic resin film A is 25 ° C. or more lower than the melting point derived from the PET of the thermoplastic resin film B.

The resin film A on the outer surface side was measured with a Raman band intensity (I ₀ ) of 1615 ± 10 cm ⁻¹ measured by a laser Raman spectroscopy with a polarization plane horizontal to the surface of the resin film 2 and a polarization plane perpendicular to the surface. The Raman band intensity ratio (I ₉₀ / I ₀ ) to the Raman band intensity (I ₉₀ ) of 1615 ± 10 cm ⁻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 that is horizontal to the surface becomes larger as the crystal component in the surface direction increases. On the other hand, the Raman band intensity (I ₉₀ ) of 1615 ± 10 cm ⁻¹ measured on the vertical polarization plane increases as the crystal component in the thickness direction increases. Therefore, if the Raman band intensity ratio (I ₉₀ / I ₀ ) becomes a large value, it means that the crystal component in the surface direction decreases and the crystal component in the thickness direction increases.

  When the can lid 13 is double-rolled onto the edge flange portion of the can body 19 to form the winding portion 20, the winding roll pressurizes the surface of the resin film A on the outer surface of the can lid, Move at high speed along the direction. The stretched resin film A has a large crystal component in the surface direction during the stretching process. When tightening is performed in this state, the bonds between the weak molecules are easily broken and the resin film A is damaged. Therefore, a crystal component in the direction perpendicular to the resin film A is required. The ratio should just be a Raman band intensity ratio 0.60 or more. Furthermore, the Raman band intensity ratio is preferably 0.70 or more. When the Raman band intensity ratio is less than 0.60, since there are many crystal components in the surface direction, the resin film A is scraped during high-speed winding. Further, the crystallinity of the resin film B on the inner surface side of the can lid 13 which is simultaneously heat-sealed changes, and the adhesion of the resin film B deteriorates.

On the other hand, the resin film B on the inner surface side of the can lid 13 has a half-width of a Raman band of 1730 ± 10 cm ⁻¹ measured by a laser Raman spectroscopy with a polarization plane horizontal to the surface of the resin film B of 15 to 20 cm ^{−. 1} , preferably 16-19 cm ⁻¹ . When the half-value width of this Raman band is smaller than 15 cm ⁻¹ , the resin film A on the outer surface side having a low melting point adheres to Ramirol or the like during the production process, thereby impairing the productivity. If the half-value width of this Raman band is larger than 20 cm ⁻¹ , crystallization is insufficient, so that the adhesiveness of the resin film B on the inner surface side is insufficient, and the content resistance is inferior.

  When the resin-coated metal plate 10 used for the can lid is manufactured, the resin film A on the outer surface side of the can lid 13 and the resin film B on the inner surface side are simultaneously heat-sealed. In order to achieve such crystallinity, it is necessary to appropriately select the resin film B on the inner surface side. As a result of the examination, it was found that it is appropriate that the melting point derived from PET of the inner surface side resin film B is 250 ° C. or higher and 265 ° C. or lower, which is 25 ° C. higher than the melting point derived from PBT in the outer surface side resin film A. When the difference in melting point is less than 25 ° C., the crystallinity of the resin film A on the outer surface cannot be lowered, and the Raman band intensity ratio cannot be 0.60 or more. In order to make the melting point difference 25 ° C. or higher, the melting point derived from PET needs to be 250 ° C. or higher. On the other hand, if the melting point derived from PET exceeds 265 ° C., the melting point of the resin film A on the outer surface side may be greatly exceeded, and a trouble may occur that the resin film 2A adheres to a lami roll described later during production.

  Here, with reference to FIG. 2, a method for heat-sealing the inner and outer resin films 2 will be described. For example, as shown in FIG. 2, after the metal plate 1 is heated to a certain temperature or more by a metal band heating device 11, the resin film 2 is heated by a pressure-bonding roll 12 (hereinafter referred to as a lami roll 12). Pressure contact. Thereby, the resin film 2 can be manufactured by thermally fusing the resin film 2 to the surface of the metal plate 1 (hereinafter sometimes referred to as “laminate”). In this case, it is necessary that the lami roll 12 is pressed against the metal plate 1 and thermally fused.

  Details of the lamination conditions will be described below. 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 film 2. In order to ensure the adhesion between the metal plate 1 and the resin film 2 by the thermal fusion method, it is necessary to heat the polyester resin at the adhesion interface. By setting the temperature of the metal plate 1 to a temperature of + 5 ° C. or higher based on the melting point of the resin film 2, the resin in each layer is thermally fluidized, the wettability at the interface is mutually good, and excellent adhesion Can be obtained. Even if the temperature of the metal plate 1 is higher than + 40 ° C., further improvement in adhesion cannot be expected, the resin film 2 is excessively melted, the surface is roughened by the embossing of the surface of the lami roll 12, and the melt to the lami roll 12 is not melted. Due to concerns about problems such as transfer, the temperature is preferably set to + 40 ° C. or lower.

  The heat history received by the resin film 2 at the time of laminating is preferably not less than the melting point of the resin film 2 and not less than 5 msec. This is because the wettability at the interface becomes good. The resin film 2 melts from the vicinity of the interface of the metal plate 1 with heat during the time of contact with each other. Since the thermal conductivity of the resin film 2 is extremely small, the surface layer of the resin film 2 does not reach the melting point in 5 to 40 msec. . Also from this viewpoint, it is desirable to set it to 40 msec or less. Furthermore, 10 to 25 msec is more preferable.

  In order to achieve such lamination conditions, in addition to high-speed operation of 150 mpm or more, cooling during heat sealing is also necessary. For example, the lami roll 12 in FIG. 2 is an internal water cooling type, and it can suppress that the resin film 2 is heated too much by letting a cooling water pass. Furthermore, it is preferable because the heat history of the resin film 2 can be controlled by independently changing the cooling water temperatures of the inner and outer surface resin films 1 and 2 respectively. Since the resin film 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 is preferably adjusted appropriately in the range of 50 ° C to 130 ° C.

The pressure of the lami roll 12 is desirably 9.8 to 294 N / cm ² (1 to 30 kgf / cm ² ) as the surface pressure. When the pressure of 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 film 2, Since the force which spreads the resin film 2 on one surface is weak, sufficient coverage cannot be obtained. As a result, performance such as adhesion and corrosion resistance (content resistance) may be affected. In addition, if the pressure of the Lami roll 12 exceeds 294 N / cm ² , there will be no inconvenience in the performance of the resin-coated metal plate 10, but the equipment is increased in size because the force applied to the Lami roll 12 is large and the apparatus needs strength. This is uneconomical. Therefore, the pressure of the lami roll 12 is preferably 9.8 to 294 N / cm ² .

  The resin film A on the outer surface side is mainly composed of polybutylene terephthalate (PBT) and polyethylene terephthalate (PET), and the PBT / PET resin composition ratio (wt%) is (PBT / PET) = (40/60) to (80 / 20). When the PBT ratio is less than this range, whitening occurs during retort processing, which is not preferable. Whitening during retort processing will be described later. When the PBT ratio increases, the adhesion and the like deteriorate due to heating in a steam atmosphere, which is not preferable.

  The composition of the resin film B used on the inner surface side is 95 mol% or more of polyethylene terephthalate. If it is less than 95 mol%, other components including the copolymer component are mixed in and eluted into the contents, and the resistance to physical properties deteriorates. Moreover, melting | fusing point falls by addition of another component, and the heat-fusability (adhesion) with the metal plate 1 deteriorates.

  In addition, other dicarboxylic acid components, glycol components, and other resin components may be copolymerized with the material of the resin film 2 on the inner and outer surface sides within a range not impairing workability, heat resistance, and corrosion resistance (on the inner surface side, 5 mol). %). Dicarboxylic acid components 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 aliphatic glycols such as butanediol, propanediol, pentanediol, hexanediol and neopentylglycol, alicyclic glycols such as cyclohexanedimethanol, aromatic glycols such as bisphenol A and bisphenol S, Examples include diethylene glycol. Two or more dicarboxylic acid components and glycol components may be used in combination.

  If necessary, an optical brightener, 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. For example, if a disazo pigment is used for the resin film A on the outer surface side, since it has excellent transparency and strong coloring power and is excellent in spreadability, an appearance with a brilliant color can be obtained even after the lid is made. When adding a pigment, it is preferable to make it 30 PHR or less. Here, the addition amount of the pigment is a ratio (external ratio to the resin amount) with respect to the resin layer to which the pigment is added (when added to the lower resin layer, with respect to the lower resin layer). As the disazo pigment, at least one of pigment yellow 12, 13, 14, 16, 17, 55, 81, 83, 180, and 181 is used as the color index (CI registered name). it can. In particular, it has a high molecular weight and poor solubility in PET resin from the viewpoints 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). C. A pigment having a benzimidazolone structure having a molecular weight of 700 or more is desirable. I. Pigment Yellow 180 is more preferably used.

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

(1) A method of esterifying terephthalic acid, ethylene glycol, and a copolymer component, and then polycondensing the resulting reaction product to obtain a copolymer polyester.
(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 copolymer polyester.

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

  In the polyester resin used in the present invention, the weight average molecular weight of the polyester is preferably in the range of 5,000 to 100,000, more preferably in the range of 10,000 to 80,000 from the viewpoint of improving mechanical properties, laminating properties, and flavor properties. The thickness of the polyester resin of the present invention is preferably 5 μm or more and 50 μm or less, more preferably 8 μm or more and 30 μm or less, particularly preferably 10 μm or more and 25 μm or less.

<About whitening during retort>
In many cases, when the can lid 18 manufactured by using the metal plate 10 coated with the polyester resin film 2 is wound around the end portion of the can body 19 with the retort sterilization treatment, the outer surface side The phenomenon that the resin film A is whitened is observed. This is because fine bubbles are formed in the resin film A, and light is scattered by these bubbles, resulting in a white turbid appearance. In addition, the bubbles formed in the resin film A have the following characteristics. First, these bubbles are not formed even when the can 18 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. The bubbles are not observed over the entire thickness direction of the resin film A on the outer surface side, but are observed in the vicinity of the interface in contact with the metal plate 1. From the above characteristics, it is considered that the formation of bubbles in the outer surface side resin film A accompanying the retort sterilization treatment is caused by the following mechanism.

  The can body is exposed to high-temperature steam from the beginning of the retort sterilization treatment, and part of the steam enters the inside of the outer surface side resin film A and reaches the vicinity of the interface with the metal plate 1. Since the vicinity of the interface between the outer surface side resin film A and the metal plate 1 is cooled from the inner surface by the contents at the beginning of the retort sterilization treatment, the water vapor that has entered the interface becomes condensed water. Next, with the passage of time for the retort sterilization treatment, the temperature of the contents also rises, and the condensed water at the interface with the metal plate 1 is re-vaporized. The vaporized water vapor escapes again through the resin film A, but it is presumed that the trace of condensed water at this time becomes bubbles. The reason why the bubbles are observed only in the vicinity of the interface with the metal plate 1 is considered that the place where the condensed water is formed is in the vicinity of the interface. 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 resin film A on the outer surface side of the can during the retort sterilization treatment, the amorphous polyester layer is quickly crystallized with the heat of the retort sterilization treatment. It is effective to increase the strength of the amorphous layer.

  As described above, according to the can 18 using the can lid 13 using the resin-coated metal plate 10 of the present embodiment as the bottom lid of the can body 19, the outer surface side of the can lid 13 can be used. Even when the resin film A is wound on the resin-coated metal plate 10 at a high speed, the film is not scraped or cracked, and is excellent in anti-winding properties. The resin film B on the inner surface side of the container is excellent in content resistance, and can maintain the adhesion even if the retort treatment is performed in contact with the content.

  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, examples, operational techniques, and the like made by those skilled in the art based on this embodiment are all included in the scope of the present invention.

(Example)
Examples of the present invention will be described below. 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, and then chrome-plated to produce a chromium-plated steel plate (TFS) as the metal plate 1. 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 resin film is laminated (heat-sealed) on both sides of the chrome-plated steel sheet with a lami roll. (Laminated steel sheet) 10 was manufactured. The lamellar roll was an internal water-cooling type, and cooling water was forcibly circulated during lamination to cool the laminated steel sheet 10 while the resin film 2 was adhered. The Raman band intensity ratio by laser Raman spectroscopy was adjusted by changing the lamination conditions to the metal band.

  The properties of the used resin film (biaxially stretched polyester film) 2 were measured and evaluated by the following method (1). Moreover, the characteristic of the laminated steel plate 10 manufactured by the above method was measured and evaluated by the following methods (2) to (6). Table 1 shows the characteristics of the laminated resin film, the lamination conditions, and the evaluation results of each laminated steel sheet 10.

(1) Measurement by laser Raman spectroscopy (1-1) Raman band intensity ratio (I ₉₀ / I ₀ ) of resin film A on the lid outer surface side
A cross-section polished sample of the laminated steel sheet 10 was prepared, and a Raman band intensity of 1615 ± 10 cm ⁻¹ for each 1 μm was measured on the laser polarization plane perpendicular to the cross-sectional direction of the resin film A on the lid outer surface side 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, on the laser polarization plane parallel to the cross-sectional direction of the resin film A, the Raman band intensity of 1615 ± 10 cm ⁻¹ is measured every 1 μm from the surface layer side, and the average value of the measured values of 5 μm from the surface layer side is determined as the Raman band intensity ( I ₉₀ ), and the above-described Raman band intensity ratio (I = I ₉₀ / I ₀ ) was obtained.

(1-2) Raman band half-width of resin film B on the inner surface side of the lid A cross-sectional polished sample of the laminated steel sheet 10 was prepared, and the laser polarization plane parallel to the cross-sectional direction of the resin film B on the inner surface side of the lid under the following measurement conditions Then, the half-value width of the Raman band of 1730 ± 10 cm ⁻¹ was measured every 1 μm, and the average value of the measured values of 5 μm was obtained from the surface layer side.

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

(2) Anti-clamping property The laminated steel sheet 10 is punched into a can lid shape using a press device and processed in a well-known process, and a chuck wall 15 is formed on the outer peripheral portion of the flat panel portion 14. A can lid shape having a curved seaming panel 16 is formed, and a known sealing material 17 is applied and dried on the inner side of the seaming panel 16 to form a can lid (bottom lid) 13 having a common name shown in FIG. did. Next, the can lid 13 was wound around the edge flange portion of the welded can body 19 at a speed of 800 cans per minute. The state of the (outer surface side) resin film A of the can lid tightening portion 20 was observed, and the tightening resistance was evaluated according to the following ratings.

(Score)
A: No occurrence of film shaving out of 50 lid materials.
○: Film scraping occurs in 1 to 5 of 50 lid materials.
(Triangle | delta): Film scraping generate | occur | produced in 6-10 sheets among 50 cover materials.
X: Film scraping occurs in 11 or more of 50 lid materials.

(3) Retort whitening resistance The retort whitening resistance of the resin film A on the lid outer surface side was evaluated. Specifically, after filling can body 18 in which can lid 13 of the present invention is tightened as a bottom lid of welded can body 19 with normal temperature tap water, upper lid 21 is separately wound and sealed, and FIG. The can body shown in FIG. Thereafter, the bottom of the water-filled can was faced down and placed in a steam retort kettle, and retort treatment was performed at 125 ° C. for 30 minutes. After the retort treatment, the appearance change of the outer surface side resin film A of the can lid 13 was visually observed, and the retort whitening resistance was evaluated according to the following scores.

(Score)
A: No change in appearance.
○: Faint cloudy appearance (less than 5% of the film surface area) occurs.
Δ: Faint cloudy appearance (from 5% to less than 10% of the film surface area).
X: The appearance is cloudy (whitening occurs at 10% or more of the film surface area).

(4) Adhesion (wet adhesion)
A flat plate sample (width 15 mm, length 120 mm) of the laminated steel sheet 10 was cut out. A part of the resin film 2 is peeled off from the long side end of the cut sample. The peeled resin film 2 was opened in a direction opposite to the peeled direction (angle: 180 °), a 50 g weight was fixed, and a retort treatment (125 ° C., 30 minutes) was performed. The peel length of the resin film 2 after the retort treatment was measured, and the film wet adhesion before molding (secondary adhesion) was evaluated as adhesion according to the following rating.

(Score)
◎: Less than 10 mm ○: 10 mm or more, less than 20 mm ×: 20 mm or more

(5) Resistance to contents (coverability of the resin film on the inner surface of the lid)
Similarly to the above (2), the can lid 13 of the present invention was wound around the bottom of the welded can body 19 to produce a can body 18 (with an internal capacity of 180 ml) having the shape shown in FIG. After filling with tap water, the upper lid 21 was wound and sealed on the upper part of the can 18, and retort treatment (125 ° C., 30 minutes) was performed. After the retort treatment, when the water-filled can 18 reaches room temperature, the lid on the top of the container is opened, 50 ml of electrolyte (NaCl 1% solution) is injected into the can, and a voltage of 6 V is applied between the can and the electrolyte. The current value measured at this time was evaluated. According to the following scores, the covering property of the resin film B on the inner surface side of the lid was evaluated as content resistance.

(Score)
◎: 0.01 mA or less ○: 0.01 mA or more, 0.1 mA or less △: 0.1 mA or more, 1 mA or less ×: 1 mA or more

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

(Score)
○: No film attached ×: Film attached

  From Table 1, it was found that, within the scope of the present invention, all of the anti-winding resistance, anti-retort whitening resistance, adhesion, content resistance, and manufacturability were excellent.

From Comparative Examples 1 and 2, it was found that in the outer surface side resin composition, when the PBT ratio is low, the whitening resistance is poor, and when the PBT ratio is high, the adhesion is poor. Further, from Comparative Examples 3 to 5, it was found that when the Raman band intensity ratio of the outer surface side resin film A is less than 0.60, the crystal structure is inadequate, so that the anti-clamping property is inferior. Moreover, from the comparative examples 6 and 7, when the half width of the Raman band of the inner surface side resin film B is smaller than 15 cm ⁻¹ , the resin film adhesion on the inner surface side is inferior and the productivity is also inferior, but higher than 20 cm ^−1. In some cases, the content resistance was inferior.

DESCRIPTION OF SYMBOLS 1 Metal plate 2 Resin film 3 Laser oscillator 4 Laser light 5 Raman scattered light 6 Spectrometer 7 Lens 10 Resin-coated metal plate 11 Metal belt heating device 12 Crimp roll (Rami roll)
13 Can lid 14 Flat panel portion 15 Chuck wall 16 Seaming panel 17 Sealing material 18 Can body 19 Can body 20 Tightening portion 21 Upper lid

Claims (1)

In a can lid for canning using a resin-coated metal plate in which both surfaces of a metal plate are coated with a thermoplastic resin film,
In the resin-coated metal plate, a thermoplastic resin film A mainly composed of polybutylene terephthalate (PBT) and polyethylene terephthalate (PET) is heat-sealed on the surface of the metal plate that is the outer surface side of the can lid, and the can lid The thermoplastic resin film B mainly composed of polyethylene terephthalate (PET) is heat-fused on the inner surface side of
The composition ratio (wt%) of PBT / PET of the outer surface side resin film A is (PBT / PET) = (40/60) to (80/20), and the inner surface side resin film B is 95% by mole or more of PET,
The melting point derived from PET of the inner surface side resin film B is 250 ° C. or higher and 265 ° C. or lower, and 25 ° C. higher than the melting point derived from PBT in the outer surface side resin film A,
The outer surface side resin film A was measured with a Raman band intensity (I ₀ ) of 1615 ± 10 cm ⁻¹ measured by a laser Raman spectroscopy with a polarization plane horizontal to the resin film surface, and a measurement plane 1615 measured with a perpendicular polarization plane. The Raman band intensity ratio (I ₉₀ / I ₀ ) to the Raman band intensity (I ₉₀ ) of ± 10 cm ⁻¹ is 0.60 or more,
The inner surface side resin film B is characterized in that a half band width of a Raman band of 1730 ± 10 cm ⁻¹ measured by a laser Raman spectroscopy with a polarization plane horizontal to the resin film surface is 15 to 20 cm ^−1. Can lid for canning.

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