Resin-coated metal sheet for containers, metal container, and method for manufacturing a resin-coated metal sheet for containers

Abstract

The present invention provides a resin-coated metal plate for containers which has excellent workability, film adhesion, and retort whitening resistance. A resin-coated metal plate 1 for containers according to the present invention has a polyester resin coating layer 3, not less than 90 mol% of which is an ethylene terephthalate unit, wherein: the half-width of a peak in the vicinity of 1730 cm-1 as measured by causing linearly polarized laser light to be incident on a thickness direction cross-section of the resin coating layer 3 such that the plane of polarization is perpendicular to the thickness direction of the resin coating layer 3 is 14.0-18.5 cm-1 at a position which is 1.0 μm from the interface between the resin coating layer 3 and a metal plate 2, and is 14.0-18.0 cm-1 at a position which is 1.0 μm from the surface of the resin coating layer 3; and the value A / B, which is obtained by dividing a half-width A by a half-width B is 0.80-1.10, the half-width A being that of a peak in the vicinity of 1730 cm-1 as measured by causing the light to be incident such that the plane of polarization is parallel to the thickness direction of the resin coating layer 3, at a position which is 1.0 μm from the interface between the resin coating layer 3 and the metal plate 2, the half-width B being that of said peak at a position which is 1 / 2 the thickness of the resin coating layer 3.

Description

Technical Field

[0001] The present invention relates to a resin-coated metal sheet for containers having a polyester resin coating layer on at least one side of a metal sheet, a metal container using the resin-coated metal sheet for containers, and a method for manufacturing the resin-coated metal sheet for containers.

Background Art

[0002] Conventionally, metal sheets such as Tin Free Steel (TFS) and aluminum used as materials for metal containers have been coated for the purpose of improving corrosion resistance and weather resistance. However, the technology for applying this coating requires a large amount of processing time in complex coating and baking processes, and further has a problem of discharging a large amount of solvents. Therefore, a resin-coated metal sheet for containers in which a thermoplastic film is coated on the surface of a metal sheet has been developed and is currently widely used industrially mainly as a material for beverage cans.

[0003] For resin-coated metal sheets for metal containers, performance such as workability and film adhesion is required, and designability and color tone stability are also required. In conventional resin-coated metal sheets using a polyester resin, when the resin coating layer is used on the outer surface side of the container, a whitening phenomenon occurs in which the resin coating layer turns white in the retort sterilization treatment process. When the whitening phenomenon occurs, the designability of the container is greatly impaired, so several improvement studies have been made on suppressing the whitening phenomenon, that is, retort whitening resistance.

[0004] In Patent Document 1, "a resin-coated metal sheet having polyester resin layers mainly composed of polyethylene terephthalate on both sides, and in the cross section in the thickness direction of the polyester resin layer, the half-width of the peak caused by the C=0 stretching vibration in the vicinity of 1730 cm -1 is in the range of 16.0 cm -1 to 24.0 cm -1 characterized resin-coated metal sheet for containers" is described.

[0005] In Patent Document 2, "it has an unstretched thermoplastic polyester resin layer, and the thermoplastic polyester resin layer has, on the interface side with the metal material, a half-width of the Raman shift peak of the thermoplastic polyester resin due to the C=O stretching vibration in the vicinity of 1730 cm -1 being 20 cm -1 or more and 24 cm -1 or less in the first region, and having, on the surface side opposite to the metal material, a half-width of the Raman shift peak being 14 cm -1 or more and 18 cm -1 or less in the second region, a thermoplastic polyester resin-coated metal plate characterized by this" is described.

Prior Art Document

Patent Document

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the prior art, it has been difficult to achieve all of processability, film adhesion, and retort whitening resistance. In Patent Document 1, heat treatment is performed for 5 to 15 seconds, but since it is a short time, depending on the lamination conditions before heat treatment, crystallization of the resin coating layer becomes insufficient, and retort whitening resistance cannot be sufficiently obtained. In Patent Document 2, since an unstretched resin coating layer is used, the resin chains constituting the resin coating layer are not arranged in the plane direction of the resin coating layer. Therefore, the water barrier property of the resin coating layer is inferior, and retort whitening resistance cannot be sufficiently obtained. Further, a resin coating layer without orientation is brittle, and there is a risk of cracking of the resin coating layer due to processing.

[0008] Therefore, in view of the above problems, an object of the present invention is to provide a resin-coated metal plate for containers, a method for manufacturing the same, and a metal container using the metal plate, which are excellent in processability, film adhesion, and retort whitening resistance.

Means for Solving the Problems

[0009] As a result of intensive studies to solve the above problems, the present inventors have obtained the following findings. When the resin coating layer has a layer having an appropriate crystallinity and orientation in the vicinity of the metal plate side and a layer having an orientation perpendicular to the thickness direction in the vicinity of the surface side, it is excellent in processability, film adhesion, and retort whitening resistance. At this time, the vicinity of the metal plate side of the resin coating layer is a molten resin layer with low crystallinity in order to obtain film adhesion to the metal plate, but by strictly controlling the crystallinity and orientation, excellent film adhesion and retort whitening resistance can be achieved simultaneously. In addition, by having an orientation perpendicular to the thickness direction in the vicinity of the surface side of the resin coating layer, a resin coating layer excellent in processability can be obtained. The appropriate indices of crystallinity and orientation can be represented by the peak half-width measured by laser Raman spectroscopy.

[0010] The gist of the present invention completed based on the above findings is as follows.

[0011] [1] A resin-coated metal plate for containers having a polyester resin coating layer on at least one side of a metal plate, wherein 90 mol% or more of the constituent units are ethylene terephthalate units, In the cross-section in the thickness direction of the polyester resin coating layer, the half-width of the peak caused by the C=O stretching vibration in the vicinity of 1730 cm -1 obtained from laser Raman spectroscopy measured by incident linearly polarized laser light so that the polarization plane is perpendicular to the thickness direction of the polyester resin coating layer is (I) 14.0 cm at a position 1.0 μm thick from the interface of the polyester resin coating layer with the metal plate -1 or more and 18.5 cm -1 or less, and (II) 14.0 cm at a position 1.0 μm thick from the surface of the polyester resin coating layer-1 More than 18.0cm -1 The following: The measurement obtained by laser Raman spectroscopy, in which linearly polarized laser light is incident on the cross-section in the thickness direction of the polyester resin coating layer so that its plane of polarization is parallel to the thickness direction of the polyester resin coating layer, is 1730 cm². -1 The value A / B obtained by dividing the half-width A of the peak caused by nearby C=O stretching vibration at a position 1.0 μm thick from the interface between the polyester resin coating layer and the metal plate by the half-width B of the polyester resin coating layer at a position half the thickness of the polyester resin coating layer is 0.80 or more and 1.10 or less. Resin-coated metal sheet for containers.

[0012] [2] In the polyester resin coating layer, the diffraction peak intensity of the (100) plane by X-ray diffraction is 100 Diffraction peak intensity I of the (110) plane 110 Ratio I 100 / I 110 A resin-coated metal plate for containers as described in [1] above, wherein the ratio is 2.00 or more and 8.50 or less.

[0013] [3] A metal container formed by molding a resin-coated metal plate for containers as described in [1] or [2] above, wherein the polyester resin coating layer is located on the outer surface side of the container.

[0014] [4] A lamination step to obtain a resin-coated metal plate in which a stretched polyester resin coating having 90 ml or more of its constituent units as ethylene terephthalate units is heat-pressed onto a metal plate using a laminating roll, thereby forming a polyester resin coating layer on at least one side of the metal plate. A heat treatment step to obtain a resin-coated metal plate for containers, comprising: holding the resin-coated metal plate at 80°C to 165°C for 10 minutes or more; A method for manufacturing a resin-coated metal plate for containers having the following properties.

[0015] [5] The method for manufacturing a resin-coated metal sheet for a container according to [4] above, wherein the temperature of the metal sheet during the heat-pressing process is 260°C or higher and 279°C or lower in the laminating process. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a resin-coated metal sheet for containers that has excellent processability, film adhesion, and resistance to retort whitening, a method for manufacturing the same, and a metal container using the metal sheet. [Brief explanation of the drawing]

[0017] [Figure 1] This is a cross-sectional view showing the structure of a resin-coated metal plate for a container according to one embodiment of the present invention. [Figure 2] This figure shows the polarization direction of a laser in laser Raman spectroscopy. [Modes for carrying out the invention]

[0018] The following describes a resin-coated metal plate for containers according to one embodiment of the present invention. The embodiments described below are examples that embody the present invention, and these specific examples do not limit the configuration of the present invention. Furthermore, unless otherwise specified, "%" in the following refers to "mass%".

[0019] Figure 1 shows a cross-sectional view of a resin-coated metal plate for containers according to one embodiment of the present invention. The resin-coated metal plate for containers 1 comprises a metal plate 2 and a polyester resin coating layer 3 (hereinafter also referred to as the "resin coating layer"). In Figure 1, an example is shown in which the resin-coated metal plate for containers 1 has the resin coating layer 3 on one side of the metal plate 2, but the resin coating layer 3 may be provided on both sides of the metal plate 2.

[0020] [Metal plate] For the resin-coated metal sheet, tinplate and tin-free steel (TFS) sheets can be used. For tinplate, the plating amount should be 0.5 g / m². 2 More than 15g / m 2 The following ranges are preferable: The amount of tin-free steel should be 50 mg / m². 2 More than 200g / m 2The following is the metal Cr layer, and the amount of adhesion is 3 mg / m² in terms of metal Cr layer. 2 More than 30g / m 2 Preferably, the surface has a Cr oxide layer as described below.

[0021] The type of metal sheet is not particularly limited as long as it can be formed into the desired shape, but steel sheets with the following component composition and manufacturing method are preferred. (1) A steel sheet obtained by recrystallization annealing using low-carbon steel with a carbon content of 0.010% or more and 0.10% or less, through continuous annealing. (2) A steel sheet obtained by using low-carbon steel with a carbon content of 0.010% or more and 0.10% or less, and performing recrystallization annealing and overaging treatment by continuous annealing. (3) A steel sheet obtained by recrystallizing annealing using box annealing with low carbon steel having a carbon content of 0.010% or more and 0.10% or less. (4) A steel sheet obtained by using low-carbon steel with a carbon content of 0.010% or more and 0.10%, recrystallizing annealing by continuous annealing or box annealing, and then secondary cold rolling (DR (Double Reduced) rolling). (5) A steel sheet obtained by recrystallizing annealing through continuous annealing using IF (Interstitial Free) steel, which is made by adding elements that fix dissolved carbon, such as Nb and Ti, to ultra-low carbon steel with a carbon content of 0.003% or less.

[0022] The mechanical properties of the metal sheet are not particularly limited, as long as they allow it to be formed into the desired shape. It is preferable to use a metal sheet with a yield point (YP) of 220 MPa to 580 MPa in order to maintain sufficient strength without impairing workability. Furthermore, the Rankford value (r-value), an indicator of plastic anisotropy, is preferably 0.8 or higher. In addition, the absolute value of the in-plane anisotropy Δr of the r-value is preferably 0.7 or lower.

[0023] The composition of the metal sheet is not particularly limited, but for example, a steel sheet containing elemental elements such as Si, Mn, P, S, Al, and N may be used. The Si content is preferably 0.001% or more, and preferably 0.1% or less. The Mn content is preferably 0.01% or more, and preferably 0.6% or less. The P content is preferably 0.002% or more, and preferably 0.05% or less. The S content is preferably 0.002% or more, and preferably 0.05% or less. The Al content is preferably 0.005% or more, and preferably 0.100% or less. The N content is preferably 0.0005% or more, and preferably 0.020% or less. Furthermore, the composition may also contain elements such as Ti, Nb, B, Cu, Ni, Cr, Mo, and V. The total content of these elemental elements is preferably 1.0% or less.

[0024] The thickness of the metal plate is not particularly limited, but it may be, for example, 0.01 mm or more, or 0.35 mm or less.

[0025] [Resin coating layer] The resin coating layer is a polyester resin coating layer in which 90 mol% or more of the polyester's constituent units are ethylene terephthalate units. Preferably, 95 mol% or more of the polyester's constituent units are ethylene terephthalate units. If the proportion of ethylene terephthalate units in the constituent units is less than 100 mol%, the remainder may be various dicarboxylic acid units or glycol units as shown below.

[0026] Dicarboxylic acid units can include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfondicarboxylic acid, diphenoxyethanedicarboxylic acid, 5-sodium sulfisophthalic acid, and phthalic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, and fumaric acid; alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; and units derived from oxycarboxylic acids such as p-oxybenzoic acid.

[0027] Glycol units can include aliphatic glycols such as ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, and neopentyl glycol; alicyclic glycols such as cyclohexanedimethanol; aromatic glycols such as bisphenol A and bisphenol S; and units derived from diethylene glycol, etc.

[0028] Furthermore, the dicarboxylic acids and glycols mentioned above may be used in combination in multiple quantities, as long as they do not impair the processability.

[0029] The resin material used to form the resin coating layer is not limited by its manufacturing method. Furthermore, in the production of polyester resin coatings, additives such as fluorescent whitening agents, antioxidants, heat stabilizers, ultraviolet absorbers, antistatic agents, and lubricants may be added as needed.

[0030] The thickness of the resin coating layer is not particularly limited, but it may be, for example, 0.01 mm or more, or 0.10 mm or less.

[0031] The inventors have found that excellent resistance to retort whitening can be obtained by setting the crystallinity and orientation of the resin coating layer within an appropriate range. The inventors believe that the whitening phenomenon during retort sterilization occurs through the following mechanism: In the initial stages of retort sterilization, water vapor that has permeated through the resin coating layer is cooled by the low-temperature contents near the metal plate interface within the resin coating layer and condenses within the resin coating layer. As the temperature of the contents rises, the condensed water vaporizes, forming bubbles near the metal plate interface within the resin coating layer, causing the whitening phenomenon. Therefore, by setting the crystallinity and orientation of the resin coating layer near the metal plate interface within an appropriate range, the hardness of the resin coating layer is maintained, and the expansion of bubbles is suppressed, thereby suppressing the whitening phenomenon.

[0032] The degree of crystallinity and orientation of the resin coating layer were determined by laser Raman spectroscopy at 1730 cm². -1 The half-width of the peak based on nearby C=O stretching vibrations can be used as an indicator for evaluation. 1730cm -1 The full width at half maximum of the peak based on nearby C=O stretching vibrations is known to correlate with the density of the polyester resin (A.J. Melverger, "Laser-Raman Study of Crystallinity Changes in Poly(ethylene Terephtalate)", Journal of Polymer Science Part A2 (Polymer Physics) vol.10, published February 1972, pp. 317-322). Furthermore, a correlation is known between the density of the resin and the volume fraction crystallinity (The Polymer Society of Japan, Editorial Committee of Polymer Experiments, "Solid Structure of Polymers II", Kyoritsu Shuppan Co., Ltd., published 1984). Therefore, 1730 cm -1 By measuring the full width at half maximum of the peaks based on nearby C=O stretching vibrations, the degree of crystallinity of the polyester resin can be determined through its density.

[0033] Figure 2 shows directions 4 perpendicular to the thickness direction of the resin coating layer 3 and direction 5 parallel to it. Conventionally, laser Raman spectroscopy values ​​obtained by incidenting linearly polarized laser light onto the thickness-direction cross-section of the resin coating layer with the polarization plane set to direction 5 have been used. However, such average values ​​in the thickness direction of the resin coating layer 3 alone cannot accurately evaluate the crystallinity near the metal plate side or the orientation state near the surface side. Therefore, in the present invention, the half-width of the peak obtained by incidenting linearly polarized laser light onto the thickness-direction cross-section of the resin coating layer 3 with the polarization plane set to direction 4 (i.e., the direction parallel to the surface of the metal plate 2) is also used. This makes it possible to evaluate the degree of crystallinity of the resin coating layer 3 near the metal plate and near the surface.

[0034] The measurement, obtained from laser Raman spectroscopy, is performed by irradiating a linearly polarized laser beam onto a cross-section of the polyester resin coating layer in the thickness direction, such that the plane of polarization is perpendicular to the thickness direction of the polyester resin coating layer. The result is 1730 cm². -1 The full width at half maximum of the peak caused by the nearby C=O stretching vibration is 14.0 cm at a position 1.0 μm thick from the interface between the polyester resin coating layer and the metal plate. -1 Over 18.5cm -1 The following applies: Peak half-width is 14.0 cm. -1 If the value is less than 18.5 cm², the degree of crystallinity of the resin coating layer near the metal plate interface is excessive, resulting in poor film adhesion. -1 In the case of excessive crystallinity, the degree of crystallinity of the resin coating layer is insufficient, the resin coating layer does not harden sufficiently, the expansion of air bubbles cannot be suppressed, and the resistance to retort whitening is poor. From the viewpoint of crystallinity, the peak width at half maximum is 15.0 cm. -1 It is preferable that the above values ​​are met. Furthermore, the peak width at half maximum is 16.5 cm. -1 The following is preferable: The peak width at half maximum is 15.0 cm. -1 More than 16.5cm -1 The following is more preferable:

[0035] The measurement, obtained from laser Raman spectroscopy, is performed by irradiating a linearly polarized laser beam onto a cross-section of the polyester resin coating layer in the thickness direction, such that the plane of polarization is perpendicular to the thickness direction of the polyester resin coating layer. The result is 1730 cm². -1 The full width at half maximum of the peak caused by nearby C=O stretching vibrations is 14.0 cm at a distance of 1.0 μm from the surface of the polyester resin coating layer. -1 More than 18.0cm -1 The following applies: The peak half-width is 14.0 cm. -1 If the value is less than 18.0 cm, excessive crystallization has occurred, resulting in brittleness and poor workability. On the other hand, if the peak half-width is 18.0 cm, -1 If it exceeds this value, the amount of crystals is small, and the blocking resistance, as described later, is poor. The peak half-width mentioned above is 15.0 cm. -1 It is preferable that the above values ​​are met. Furthermore, the peak width at half maximum is 17.0 cm. -1 The following is preferable: The peak width at half maximum is 15.0 cm. -1 More than 17.0cm -1 The following is more preferable:

[0036] The measurement, obtained from laser Raman spectroscopy, is performed by irradiating a linearly polarized laser beam onto a cross-section of the polyester resin coating layer in the thickness direction, such that the plane of polarization is parallel to the thickness direction of the polyester resin coating layer. The result is 1730 cm². -1The value A / B, obtained by dividing the half-width A of the peak caused by nearby C=O stretching vibration at a position 1.0 μm thick from the interface between the polyester resin coating layer and the metal plate by the half-width B of the polyester resin coating layer at a position half the thickness of the polyester resin coating layer, should be between 0.80 and 1.10. If A / B exceeds 1.10, the adhesion between the metal plate and the resin coating layer is impaired, and processability cannot be obtained. On the other hand, if A / B is less than 0.80, the film adhesion is excellent, but retort whitening resistance cannot be obtained. A / B is preferably 1.05 or less, and more preferably 1.03 or less. Furthermore, A / B is preferably 0.85 or more, and more preferably 0.90 or more. A / B is even more preferably 0.85 to 1.05, and most preferably 0.90 to 1.03. Furthermore, from the viewpoint of suppressing bubble expansion, the half-width value A should be 20.5 cm. -1 The following is preferable:

[0037] The full width at half maximum and A / B ratio of the peaks mentioned above can be measured as follows: A linearly polarized laser beam is incident on the thickness-direction cross-section of the resin coating layer to be measured, such that its plane of polarization is perpendicular to the thickness-direction cross-section of the resin coating layer, and laser Raman spectroscopy is performed. This results in 1730 cm². -1 The full width at half maximum (FHA) of the peak caused by nearby C=O stretching vibrations is obtained. The measurement positions are 1.0 μm thick from the interface between the resin coating layer and the metal plate, and 1.0 μm thick from the surface of the resin coating layer. Similarly, laser Raman spectroscopy is performed on the thickness-direction cross-section of the manufactured resin-coated metal plate for the container, with linearly polarized laser light positioned so that its polarization plane is parallel to the thickness-direction cross-section of the resin coating layer. This results in 1730 cm⁻¹. -1 The full width at half maximum (FWHM) of the peak caused by the nearby C=O stretching vibration is obtained. Let A be the FWHM measured at a position 1.0 μm thick from the interface between the resin coating layer and the metal plate, and B be the FWHM measured at a position half the thickness of the resin coating layer. The FWHM ratio A / B is then calculated. For laser Raman spectroscopy, a Nanophoton RAMAN force can be used. The laser wavelength can be 532 nm, a 100x objective lens can be used, the aperture diameter can be 25 μm, and the diffraction grating can be 600 gr / mm.

[0038] Diffraction peak intensity of the (100) plane by X-ray diffraction I 100 Diffraction peak intensity I of the (110) plane 110 Ratio I 100 / I 110 The ratio is preferably 2.00 or higher, and preferably 8.50 or lower. When a resin-coated metal plate heated above the glass transition temperature of the resin coating layer is compressed under high load, such as in a coil, there is a risk of the resin surface fusing and sticking together (blocking). By preventing blocking, it is possible to easily remove the coil and improve the surface performance of the product. The inventors have revealed that the crystallinity of the entire resin coating layer, not just the outermost layer where the resins come into contact, affects the blocking resistance. Furthermore, the intensity ratio of the diffraction peaks between the (100) plane and the (110) plane obtained by X-ray diffraction of the resin coating layer is 100 / I 110 It was found that when the strength ratio is in the range of 2.00 or more and 8.50 or less, the resistance to blocking is particularly excellent. 100 / I 110 If the strength ratio is 2.00 or higher, the crystallinity of the entire resin coating layer is sufficiently high, which effectively prevents the resin coating layer from melting and fusing during heating and pressing. Regarding blocking resistance, the higher the crystallinity of the resin coating layer, the better the performance; however, for typical resin-coated metal sheets, the strength ratio is effectively limited to 8.50. 100 / I 110 It is more preferable that the intensity ratio I 100 / I 110 It is more preferable that the intensity ratio is 8.00 or less. 100 / I 110 It is even more preferable that it be between 3.50 and 8.00.

[0039] The diffraction peak intensity for each direction can be measured as follows. X-ray diffraction is performed on the resin-coated metal plate of the container to be measured using Rigaku's Smart Lab. The X-ray tube can be set to CuKα, the measurement angle range to 2θ = 10° to 30°, and the scan speed to 80 seconds / degree. The peak present at the measurement angle 24° to 29° is taken as the peak of the (100) plane, and the intensity I 100 The peaks present at measurement angles of 22° to 24° are defined as the peaks on the (110) plane, and the intensity I 110 Measure the peak intensity ratio I from each obtained intensity. 100 / I 110 We seek.

[0040] By using the resin-coated metal sheet for containers described above, a metal container with excellent processability, coating adhesion, and resistance to retort whitening can be provided. In one example, the metal container comprises a member formed by molding a resin-coated metal sheet for containers, and the member has a polyester resin coating layer on the outer surface of the container. The metal container and member can be manufactured by conventional methods.

[0041] [Manufacturing method] Next, a method for manufacturing a resin-coated metal sheet for containers will be described. The resin coating layer having the above-mentioned properties can be achieved through a two-step process: (1) heat-pressing a stretched polyester resin film onto a metal sheet while controlling the thermal history (laminating process), and then (2) heating and aging the metal sheet (heat treatment process).

[0042] First, an unstretched polyester resin coating is manufactured using a polyester resin in which 90 mol% or more of the constituent units are ethylene terephthalate units. As the polyester resin constituting the polyester resin coating, a polyester resin in which 90 mol% or more of the constituent units are ethylene terephthalate units can be used, as described above in the explanation of the resin coating layer. Additives and the like are also as described above in the explanation of the resin coating layer.

[0043] The method for manufacturing a polyester resin coating is not particularly limited, but in one example, it can be manufactured as follows. First, the polyester resin is heated and dried under vacuum as needed, then put into an extruder and heated and melted in the extruder. The heated and melted polyester resin is extruded through a filter or the like. At this time, foreign matter and modified resin can be removed by the filter. The extruded polyester resin is formed into a sheet shape with a T-die and discharged onto a cooling body such as a cast drum. By cooling and solidifying the extruded sheet, an unstretched polyester resin coating can be obtained.

[0044] Next, the unstretched polyester resin coating is stretched to obtain a stretched polyester resin coating. Preferably, the method for obtaining the stretched polyester resin coating is a sequential biaxial stretching method, in which the material is stretched in one direction (longitudinal or widthwise) and then in the other direction, or a simultaneous biaxial stretching method, in which the material is stretched simultaneously in both the longitudinal and widthwise directions. The stretched polyester resin coating is preferably a biaxially stretched polyester resin coating.

[0045] Next, a lamination process is performed in which the stretched polyester resin coating is heat-pressed onto the metal plate. The stretched polyester resin coating is heated to a temperature above the melting point and heat-pressed onto the metal plate using a laminating roll (heat-pressure film lamination method). In order to control the properties of the resin coating layer, it is preferable that the resin coating layer after heat-pressing is melted near the interface with the metal plate and oriented near the opposite surface.

[0046] Furthermore, the temperature of the metal plate during thermocompression bonding is preferably 279°C or lower in order to control the X-ray diffraction intensity ratio. If the temperature of the metal plate during thermocompression bonding is 279°C or lower, the diffraction peak intensity of the (100) plane due to X-ray diffraction is I 100 Diffraction peak intensity I of the (110) plane 110 Ratio I 100 / I 110This can be set to 2.00 or higher. Furthermore, the temperature of the metal plate during heat-pressure bonding is preferably 260°C or higher, and more preferably 265°C or higher. When the temperature of the metal plate during heat-pressure bonding is 260°C or higher, suitable wettability between the stretched polyester resin coating and the metal plate can be obtained. The temperature of the metal plate during heat-pressure bonding is even more preferably 260°C to 279°C, and most preferably 265°C to 279°C.

[0047] To control the orientation of the resin coating layer near its surface to an appropriate degree, it is preferable to maintain the orientation formed during the manufacturing of the stretched polyester resin coating without melting the area near the surface of the stretched polyester resin coating. For this purpose, it is preferable to set the temperature of the laminating roll used to press the stretched polyester resin coating onto the metal plate during heat compression to (melting point of the resin coating layer - 100)°C or lower. This effectively suppresses the surface of the stretched polyester resin coating from being heated above its melting point during heat compression, making it possible to maintain the orientation of the stretched polyester resin coating. The temperature of the laminating roll is more preferably (melting point of the resin coating layer - 120°C) or lower, and even more preferably (melting point of the resin coating layer - 140°C) or lower. Furthermore, the temperature of the laminating roll is preferably (melting point of the resin coating layer - 200°C) or higher. The temperature of the laminate roll is preferably between (melting point of the resin coating layer - 200°C) and (melting point of the resin coating layer - 100°C), more preferably between (melting point of the resin coating layer - 200°C) and (melting point of the resin coating layer - 120°C), and even more preferably between (melting point of the resin coating layer - 200°C) and (melting point of the resin coating layer - 140°C).

[0048] The time during which the stretched polyester resin coating is heat-pressed onto the metal plate by the laminating roll (hereinafter referred to as the heat-pressing time) is preferably short in order to maintain the orientation. The heat-pressing time is preferably 5 msec or longer, and preferably 40 msec or shorter. By setting the heat-pressing time to 5 msec or longer, sufficient time is secured for the stretched polyester resin coating to flow due to heat, resulting in better wetting to the metal plate and improved coating adhesion. Furthermore, by setting the heat-pressing time to 40 msec or shorter, the retention of the orientation is more favorable. The heat-pressing time is more preferably 5 msec or longer and 40 msec or shorter.

[0049] Next, the metal plate after the lamination process is subjected to heat treatment (heat treatment process). In the heat treatment process, the metal plate side of the resin coating layer is appropriately crystallized, and the degree of crystallinity of the resin coating layer is adjusted to within the range specified by the present invention. The method of heat treatment is not particularly limited; for example, a method of heating from the surface side of the resin coating layer by raising the ambient temperature to a high temperature using a hot air furnace may be used. Alternatively, an induction heater or a method of heating with near-infrared radiation may be used.

[0050] The heat treatment temperature shall be between 80°C and 165°C. This temperature range is the temperature range from the glass transition temperature to the cold crystallization peak temperature of a polyester resin in which 90 ml or more of the constituent units are ethylene terephthalate units. Preferably, the heat treatment temperature shall be 90°C or higher. Also preferably, the heat treatment temperature shall be 120°C or lower. More preferably, the heat treatment temperature shall be between 90°C and 120°C. By setting the heat treatment temperature to 90°C or higher and 120°C or lower, suitable resistance to retort whitening can be obtained while suppressing a decrease in film adhesion due to excessive crystallization. After reaching the predetermined temperature, the temperature shall be controlled to be maintained within this temperature range. The heat treatment temperature shall be based on the temperature of the metal plate.

[0051] The heat treatment processing time should be 10 minutes or more. If the processing time is less than 10 minutes, crystallization of the resin coating layer near the metal plate will be insufficient, making it difficult to obtain retort whitening resistance. Furthermore, it is preferable that the heat treatment processing time be 48 hours or less. When the processing time is 48 hours or less, crystallization of the resin coating layer near the metal plate is suitable, and suitable adhesion between the metal plate and the resin coating layer is obtained. The heat treatment processing time should preferably be 1 hour or more, and more preferably 5 hours or more. Furthermore, it is preferable that the heat treatment processing time be 24 hours or less. The heat treatment processing time should preferably be 1 hour or more and 48 hours or less, and more preferably 5 hours or more and 24 hours or less.

[0052] Furthermore, manufacturing conditions other than those mentioned above can be met by conventional methods. [Examples]

[0053] The metal plate is 0.22 mm thick TFS (metal Cr layer: 120 mg / m²). 2 Cr oxide layer: 10 mg / m² in terms of metallic Cr 2 A polyester resin with a temper grade of T3CA was used. The polyester resin shown in Table 1 (percentage of ethylene terephthalate units: 100 mol%) was put into an extruder, heated and melted, then extruded through a filter, and cooled and solidified to obtain a polyester resin coating. The polyester resin coating was stretched in the longitudinal direction and then in the width direction to obtain a biaxially oriented polyester resin coating. The thickness of the polyester resin coating was 12 μm. For sample No. 25, the process was carried out without stretching.

[0054] [Table 1] TIFF0007868683000002.tif223115

[0055] A biaxially oriented polyester resin coating (or, in the case of No. 25, an unoriented polyester resin coating) was applied to a metal plate using a film lamination method (film thermocompression method). The metal plate was heated to the temperatures shown in Table 1, and the biaxially oriented polyester resin coating (or, in the case of No. 25, an unoriented polyester resin coating) was thermocompressed onto both sides of the metal plate using a laminating roll. The melting point of the resin coating layer (PET) was approximately 260°C. The temperature of the laminating roll was kept below 160°C, and the thermocompression was performed within the range of 5 msec to 40 msec. After thermocompression, the metal plate was cooled with water for 1 second to produce a resin-coated metal plate with both sides covered by the resin coating layer. Next, the resin-coated metal plate was heat-treated under the conditions shown in Table 1 to obtain a resin-coated metal plate for containers.

[0056] Laser Raman spectroscopy and X-ray diffraction were performed using the methods described above. The results of each measurement are shown in Table 1. In Table 1, the direction of the polarization plane is described as follows: "horizontal polarization" refers to the case where the polarization plane is perpendicular to the cross-section in the thickness direction of the resin coating layer, with the direction of the metal plate surface as the reference; and "perpendicular polarization" refers to the case where the polarization plane is parallel to the cross-section in the thickness direction of the resin coating layer.

[0057] The resin-coated metal plates of the inventive example and comparative example were evaluated for retort whitening resistance, coating adhesion, processability, and blocking resistance using the methods described below. Table 1 shows the evaluation results for each.

[0058] (1) Evaluation of resistance to whitening in retort A container was fabricated using a resin-coated metal sheet for containers, with the resin coating layer to be evaluated facing the outside of the can. After filling the inside of the can with distilled water, the lid was sealed. Then, the can was placed in a retort apparatus with the bottom facing downwards and subjected to retort sterilization at 125°C for 90 minutes. After that, the retort apparatus was filled with 20°C water and the can was rapidly cooled. The bottom of the can after rapid cooling was observed and evaluated according to the following criteria. Rating "4": No bleaching. Rating "3": Slight whitening is observed in areas of 3% or less of the surface area. No practical problems. Rating "2": Whitening is observed in areas with a surface area percentage between 3% and 50%. No practical problems. Rating "1": Whitening is observed in areas exceeding 50% of the surface area. This poses a practical problem.

[0059] (2) Evaluation of coating adhesion A resin-coated metal plate for containers was coated with paraffin wax. Next, a 200 mm diameter disc was punched out. The disc was then drawn into a cup with a drawing ratio of 2.00 using a cupping press so that the resin coating layer to be evaluated was on the outer surface of the can. Next, the resulting cup was subjected to two stages of redrawing to achieve drawing ratios of 2.20 and 2.50. A redrawn can was obtained by trimming the can flange. The resulting can body was subjected to retort sterilization treatment at 125°C for 90 min using a retort apparatus. The trimmed part of the can body after retort sterilization was observed around its entire circumference and evaluated according to the following criteria. Rating "4": No peeling. Rating "3": Peeling of up to 1mm or less is observed. No practical problems. Rating "2": Peeling is observed in areas exceeding 1mm but not exceeding 3mm. No practical problems. Rating "1": Peeling exceeding 3mm in some areas is observed. This presents a practical problem.

[0060] (3) Evaluation of processability A resin-coated metal sheet for containers was coated with paraffin wax. Next, a 200 mm diameter disc was punched out. The disc was then drawn into a cup with a drawing ratio of 2.00 using a cupping press so that the resin coating layer to be evaluated would face the outside of the can. Next, the resulting cup was subjected to two stages of redrawing to achieve drawing ratios of 2.20 and 2.50. A panel was applied to the bottom of the can. The panelized bottom section of the resulting can was observed and evaluated according to the following criteria. Rating "4": No damage to the polyester resin coating layer after molding. Rating "3": Minor damage is partially visible in the polyester resin coating layer after molding. No practical problems. Rating "2": Partial damage is observed in the polyester resin coating layer after molding. No practical problems. Rating "1": Minor damage is observed all around the polyester resin coating layer after molding. This presents a practical problem.

[0061] (4) Evaluation of blocking resistance Multiple 20mm square pieces of resin-coated metal sheet were cut before heat treatment and stacked. 200kg / cm 2 Under the specified pressure, heat treatment was performed at the heat treatment temperatures and times shown in the table. The stacked resin-coated metal plates were peeled apart with tweezers to evaluate whether they could be separated from each other without resistance. The surfaces of the separated resin-coated metal plates were also observed using a scanning electron microscope to check for surface damage, and evaluated according to the following criteria. Rating "4": No resistance at all during peeling, and no damage to the resin coating layer. Rating "3": There is slight resistance during peeling, but no damage to the resin coating layer. Rating "2": Resistance during peeling is relatively strong, but there is no damage to the resin coating layer. Rating "1": Strong resistance during peeling. The resin coating layer fuses together, and damage is visible on the surface.

[0062] In the resin-coated metal plate for containers of the invention example, the retort whitening resistance, film adhesion, and processability were all good (evaluation "2" or higher). On the other hand, in the comparative examples, the evaluation results for at least one of the retort whitening resistance, film adhesion, and processability were insufficient (evaluation "1"). No. 1 has a large full width at half maximum of the C=O peak at 1.0 μm from the metal plate surface and a small amount of crystals, resulting in poor retort whitening resistance. Also, no crystal peaks were observed in X-ray diffraction, resulting in poor blocking resistance. No. 2 also has a large full width at half maximum of the C=O peak at 1.0 μm from the metal plate surface and a small amount of crystals, resulting in poor retort whitening resistance. Nos. 23 and 24 have high heat treatment temperatures and excessive crystallization, resulting in an excessive full width at half maximum ratio A / B, and thus poor film adhesion, processability, and blocking resistance. Because No. 25 uses an unstretched polyester resin coating, it has a low crystal content and inferior resistance to retort whitening, processability, and blocking. Therefore, the effects of the present invention are clear.

[0063] Among the examples of inventions, the X-ray diffraction peak intensity ratio I100 / I 110 Materials with a ratio of 2.00 to 8.50 exhibited good resistance to retort whitening, coating adhesion, and processability, as well as good resistance to blocking (rating of "2" or higher). This clearly demonstrates that by setting the X-ray diffraction peak intensity ratio within the preferred range of the present invention, a resin-coated metal plate for containers with excellent resistance to blocking can be obtained. [Industrial applicability]

[0064] According to the present invention, it is possible to provide a resin-coated metal sheet for containers that has excellent processability, film adhesion, and resistance to retort whitening, a method for manufacturing the same, and a metal container using the metal sheet. [Explanation of symbols]

[0065] 1. Resin-coated metal plate for containers 2 metal plate 3. Resin coating layer 4. Direction perpendicular to the thickness direction of the resin coating layer 5. Direction parallel to the thickness direction of the resin coating layer

Claims

1. A resin-coated metal plate for containers having a polyester resin coating layer on at least one side of the metal plate, wherein 90 mol or more of the constituent units are ethylene terephthalate units, The measurement, obtained from laser Raman spectroscopy, is performed by irradiating the cross-section of the polyester resin coating layer in the thickness direction with linearly polarized laser light, such that its plane of polarization is perpendicular to the thickness direction of the polyester resin coating layer. The result is 1730 cm². －１ The full width at half maximum of the peak caused by nearby C=O stretching vibrations is (I) 14.0 cm at a position 1.0 μm thick from the interface of the polyester resin coating layer with the metal plate －１ 18.5cm or more －１ The following, and, (II) 14.0 cm at a position 1.0 μm thick from the surface of the polyester resin coating layer －１ 18.0cm or more －１ The following: The measurement, obtained from laser Raman spectroscopy, is performed by irradiating the cross-section of the polyester resin coating layer in the thickness direction with linearly polarized laser light, such that its polarization plane is parallel to the thickness direction of the polyester resin coating layer. The result is 1730 cm². －１ The value A / B obtained by dividing the half-width A of the peak caused by nearby C=O stretching vibration at a position 1.0 μm thick from the interface between the polyester resin coating layer and the metal plate by the half-width B at a position half the thickness of the polyester resin coating layer is 0.80 or more and 1.10 or less. Resin-coated metal sheet for containers.

2. In the polyester resin coating layer, the diffraction peak intensity I of the (100) plane by X-ray diffraction １００ and the diffraction peak intensity I of the (110) plane １１０ The ratio I of １００ / I １１０ is 2.00 or more and 8.50 or less. The resin-coated metal plate for containers according to claim 1

3. A metal container formed by molding a resin-coated metal plate for containers according to claim 1 or 2, wherein the polyester resin coating layer is located on the outer surface side of the container.

4. A lamination step is performed to obtain a resin-coated metal plate in which a stretched polyester resin coating, in which 90 mol or more of the constituent units are ethylene terephthalate units, is heat-pressed onto a metal plate at a temperature of 265°C or higher using a laminating roll, thereby forming a polyester resin coating layer on at least one side of the metal plate. A heat treatment step to obtain a resin-coated metal plate for containers, comprising: holding the resin-coated metal plate at 80°C to 165°C for 10 minutes or more; A method for manufacturing a resin-coated metal sheet for a container, comprising having the characteristics described in claim 1.

5. The method for manufacturing a resin-coated metal sheet for a container according to claim 4, wherein the temperature of the metal sheet during the heat-pressing process in the lamination step is 279°C or lower.

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