Polyester resin coated seamless can and method for producing the same

Abstract

The present invention relates to a polyester resin coated seamless can and a method for manufacturing the same, which can suppress the occurrence of white spots even when exposed to high temperature and high humidity conditions such as retort sterilization, and can suppress the occurrence of whitening such as white lines even when the can as a whole is exposed to high temperature conditions in a heating process for the purpose of removing lubricants in the canning process and relieving forming deformation, and the resin coating has excellent adhesion. The seamless can is characterized in that, relative to the height of the entire can from the uppermost part of the can body to the bottom of the can, there is a reduced diameter portion achieved by necking within a distance of 0 to 15% from the uppermost part of the can body, and at a distance from the uppermost part of the can body to the bottom of the can body, there is a reduced diameter portion achieved by necking. At a position within a distance of 45% to 60% from the upper part, the maximum value of the peak intensity of the outer surface polyester resin coating between 2θ=15° and 19° obtained by the X-ray diffraction method is divided by the thickness of the outer surface polyester resin coating at the measurement position to obtain a value Im (cps / μm), and at the maximum diameter reduction portion of the diameter reduction portion, the maximum value of the peak intensity of the outer surface polyester resin coating between 2θ=15° and 19° obtained by the X-ray diffraction method is divided by the thickness of the polyester resin coating at the measurement position to obtain a value Iu (cps / μm), and the ratio of the value Im to the value Iu, Im / Iu, is greater than 1.0.

Description

Technical Field

[0001] The present invention relates to a seamless can coated with a polyester resin and a method for manufacturing the same. More specifically, the present invention relates to a seamless can coated with a polyester resin having excellent adhesion of the polyester resin coating layer and excellent corrosion resistance and retort resistance, and a method for manufacturing the same. Background Art

[0002] A seamless can is widely used, which is formed by subjecting a polyester resin-coated metal sheet obtained by coating a polyester resin on a metal sheet to forming processes such as deep drawing, deep drawing / redrawing, deep drawing / ironing, and thin-walled deep drawing / ironing.

[0003] In seamless cans for beverage and food applications, retort sterilization treatment is performed after filling the contents. Since the retort sterilization treatment is carried out under high-temperature and high-humidity conditions, crystallization occurs in parts where water droplets adhere, such as the bottom of the can, and a problem called retort whitening (white spots) occurs, resulting in whitening.

[0004] In order to solve the problem of retort whitening, a copolyester containing polybutylene terephthalate is proposed as the polyester resin film.

[0005] For example, in Patent Document 1 below, a stretched polyester film for metal lamination forming is described as a film having excellent retort resistance. Among them, in a polyester film containing 99 to 60% by weight of a polyester having a melting point of 210 to 245°C and a glass transition temperature of 60°C or higher and 1 to 40% by weight of a polyester mainly composed of polybutylene terephthalate having a melting point of 180 to 223°C, the free monomer is 300 ppm or less.

[0006] In addition, in Patent Document 2 below, a metal laminate is described as a laminated metal sheet for a metal can body and a can lid material that does not cause film whitening even when the film is crystallized. It contains 10 to 70% by weight of a polyethylene terephthalate-based resin and 90 to 30% by weight of a polybutylene terephthalate-based resin and has two or more melting peaks.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Unexamined Patent Publication No. 7-330924

[0010] Patent Document 2: Japanese Unexamined Patent Publication No. 2008-143184 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] However, in the polyester film compounded with polyethylene terephthalate resin (hereinafter sometimes referred to as "PET") and polybutylene terephthalate resin (hereinafter sometimes referred to as "PBT") described in the prior art, when the content of PBT is small, in the case of sterilization treatment such as retort sterilization treatment or retort treatment, and when exposed to high temperature and high humidity conditions after filling the contents, it is impossible to sufficiently suppress whitening such as retort whitening occurring at the bottom of the can of the outer surface resin coating. In addition, in the heating process for the purpose of removing lubricants and alleviating forming deformation in the can manufacturing process, when the whole can is exposed to high temperature conditions, it is impossible to sufficiently suppress the occurrence of appearance defects called white streaks that are linearly whitened at the bottom of the can. On the other hand, if the content of PBT is large, there is a possibility of reducing the resin coating during the ironing process, resulting in metal exposure, or reducing the appearance characteristics after printing. In addition, the adhesion to the metal plate is reduced, and a new problem such as peeling (delamination) of the resin coating from the necking part occurs during retort sterilization, and only containing PBT cannot fully meet the requirements.

[0013] Therefore, an object of the present invention is to provide a seamless can coated with polyester resin and a method for manufacturing the same, which can suppress the occurrence of white spots even when exposed to high temperature and high humidity conditions such as retort sterilization treatment, can suppress the occurrence of whitening such as white streaks even when the whole can is exposed to high temperature conditions in the heating process, and has excellent adhesion of the resin coating.

[0014] Technical solution

[0015] According to the present invention, there is provided a seamless can, characterized in that a polyester resin coating is formed on at least the outer surface of a metal plate, and within a distance of 0 to 15% from the uppermost part of the can body to the bottom of the whole can with respect to the height of the whole can, there is a necking part formed by necking processing, and at a position within a distance of 45% to 60% from the uppermost part of the can body, the maximum value of the peak intensity obtained by X-ray diffraction method between 2θ = 15° and 19° of the outer surface polyester resin coating is divided by the thickness of the outer surface polyester resin coating at the measurement part to obtain a value Im (cps / μm), and at the maximum necking part of the necking part, the maximum value of the peak intensity obtained by X-ray diffraction method between 2θ = 15° and 19° of the outer surface polyester resin coating is divided by the thickness of the polyester resin coating at the measurement part to obtain a value Iu (cps / μm), and the ratio Im / Iu of the value Im to the value Iu is 1.0 or more.

[0016] In the seamless can according to the first aspect of the present invention, preferably,

[0017] (1) The maximum necking part is necked at a necking rate of 6% or less with respect to the diameter of the can body at a position of 15% to 60% from the uppermost part of the can body.

[0018] (2) With respect to the outer surface polyester resin coating, as the main constituent elements, it contains ethylene terephthalate in an amount of 40 to 80% by mass and butylene terephthalate in an amount of 20 to 60% by mass.

[0019] (3) On at least a part of the reduced diameter portion, a printed layer is formed on the outer surface polyester resin coating.

[0020] (4) On the inner surface of the metal plate, a polyester resin coating mainly composed of polyethylene terephthalate is formed as a resin coating.

[0021] (5) The full width at half maximum (FWHM) of the peak near 1730 cm -1 obtained by micro-Raman spectroscopy on the surface of the inner surface polyester resin coating at a position within a distance of 45% to 60% from the uppermost part of the can body is designated as Wm (cm -1 ), and the full width at half maximum (FWHM) of the peak near 1730 cm -1 obtained by micro-Raman spectroscopy on the surface of the inner surface polyester resin coating at the maximum reduced diameter portion is designated as Wu (cm -1 ), and the ratio of Wm to Wu (Wm / Wu) is 0.85 or less.

[0022] (6) The orientation index MOu obtained by micro-Raman spectroscopy on the surface of the inner surface polyester resin coating at the maximum reduced diameter portion is 2.40 or less.

[0023] (7) The ratio (MOm / MOu) of the orientation index MOm obtained by micro-Raman spectroscopy on the surface of the inner surface polyester resin coating at a position within a distance of 45% to 60% from the uppermost part of the can body to the orientation index MOu is 2.10 or more.

[0024] Furthermore, according to the present invention, there is provided a seamless can, characterized in that the seamless can has a polyester resin coating formed on at least the inner surface of a metal plate, has a reduced diameter portion achieved by necking processing within a distance of 0 to 15% from the uppermost part of the can body with respect to the overall height of the seamless can from the uppermost part of the can body to the bottom of the can, the melting point of the polyester resin is 250 °C or higher, and in the state before the seamless can undergoes a sterilization treatment for preventing the deterioration of the contents, the orientation index MOu obtained by micro-Raman spectroscopy on the surface of the inner surface polyester resin coating at the maximum reduced diameter portion is 3.60 or less.

[0025] In the seamless can according to the second aspect of the present invention described above, preferably,

[0026] (1) The maximum diameter-reduced portion is diameter-reduced at a diameter-reduction rate of 15% or more with respect to the diameter of the can body at a position 15% to 60% from the uppermost part of the can body.

[0027] (2) The ratio MOm / MOu of the orientation index MOm obtained by micro-Raman spectroscopy on the surface of the polyester resin coating at a position within a distance of 45% to 60% from the uppermost part of the can body to the orientation index MOu is 1.80 or more.

[0028] (3) In the state where the seamless can has undergone a sterilization treatment for preventing the deterioration of the contents, the orientation index MOu is 4.10 or less.

[0029] (4) The ratio MOm / MOu of the orientation index MOm obtained by micro-Raman spectroscopy on the surface of the polyester resin coating at a position within a distance of 45% to 60% from the uppermost part of the can body to the orientation index MOu is 1.37 or more.

[0030] Furthermore, according to the present invention, there is provided a seamless can, characterized in that a polyester resin coating is formed on at least the inner surface of the metal plate, and within a distance of 0 to 15% from the uppermost part of the can body of the seamless can with respect to the overall height of the seamless can from the uppermost part of the can body to the bottom of the can, there is a diameter-reduced portion achieved by necking processing. The melting point of the polyester resin is 220°C or less. In the state where the seamless can has undergone a sterilization treatment for preventing the deterioration of the contents, the ratio MOm / MOu of the orientation index MOm obtained by micro-Raman spectroscopy on the surface of the polyester resin coating at a position within a distance of 45% to 60% from the uppermost part of the can body to the orientation index MOu on the surface of the inner surface polyester resin coating at the maximum diameter-reduced portion is 1.37 or more.

[0031] In the seamless can of the above third aspect of the present invention, preferably,

[0032] (1) The maximum diameter-reduced portion is diameter-reduced at a diameter-reduction rate of 15% or more with respect to the diameter of the can body at a position 15% to 60% from the uppermost part of the can body.

[0033] (2) The metal plate is an aluminum plate without surface treatment, and the orientation index MOu obtained by micro-Raman spectroscopy on the surface of the inner surface polyester resin coating at the maximum diameter-reduced portion is 3.10 or less.

[0034] Furthermore, according to the present invention, there is provided a method for manufacturing a seamless can, characterized in that the method for manufacturing the seamless can has: a drawing forming step of forming a shallow drawn can by drawing using a polyester resin-coated metal sheet having a polyester resin coating layer formed on the inner surface and / or the outer surface; a redrawing and ironing forming step of forming the shallow drawn can into a redrawn and ironed can by redrawing and ironing; a heating step of heating the whole of the redrawn and ironed can; a printing step of performing printing on the outer surface of the main body portion of the redrawn and ironed can that has undergone the heating step; a drying / baking step of heating the whole of the printed can; and a necking / flanging step of performing necking / flanging on the redrawn and ironed can that has undergone the drying / baking step. Any one of between the drawing forming step and the redrawing and ironing forming step, between the heating step of heating the whole of the redrawn and ironed can and the printing step, or after the necking / flanging step has the following local heating step of locally heating the portion that becomes the necking portion when forming the seamless can to a temperature of 185 to 230 °C.

[0035] In the method for manufacturing a seamless can of the present invention, it is preferable that

[0036] (1) the local heating step is performed after the necking / flanging step,

[0037] (2) the heating in the local heating step is high-frequency induction heating,

[0038] (3) the heating time of the high-frequency induction heating is less than 2 seconds.

[0039] Advantages of the Invention

[0040] In the seamless can with an outer surface resin coating of the first aspect of the present invention, due to the above-mentioned ratio Im / Iu of the outer surface polyester resin coating layer (hereinafter, sometimes referred to as "outer surface resin coating layer") being 1.0 or more, even in the case of being exposed to high-temperature and high-humidity conditions after filling the contents, such as in sterilization treatments such as retort sterilization treatment and steaming treatment, the occurrence of whitening such as retort whitening of the outer surface resin coating layer can be prevented; even in the heating step for the purpose of removing lubricants in the can manufacturing process and relieving forming deformation, when the whole can is exposed to high-temperature conditions, the occurrence of whitening such as white streaks can be prevented, and the occurrence of peeling of the outer surface resin coating layer at the necking portion can also be effectively prevented, and the hot water tightness is excellent.

[0041] In addition, the above-described effects can also be judged by the state of the inner surface polyester resin coating (hereinafter sometimes referred to as the "inner surface resin coating"), and it can also be judged that the state of the outer surface resin coating is good based on the ratio Wm / Wu at the inner surface polyester resin coating being 0.85 or less, the orientation index MOu of the surface of the polyester resin coating at the maximum necking portion being 2.40 or less, and the ratio of the orientation indices MOm / MOu obtained by micro-Raman spectroscopy being 2.10 or more.

[0042] That is, as described above, in order to prevent whitening of the outer surface resin coating such as cooking whitening and white streaks, it is preferable to use a polyester resin with a large amount of PBT. However, since the resin coating with a large amount of PBT has high crystallinity, oriented crystals are generated in the rolling direction of the resin-coated metal sheet, i.e., the can axis direction, during the can manufacturing process, and there is a tendency for the adhesion to the metal sheet to decrease. In addition, if the amount of PBT is large, the amount of PET resin is relatively small. In particular, the amount of PET resin with a large amount of isophthalic acid decreases, resulting in a tendency for the adhesion to the metal sheet to decrease. On the other hand, it is conceivable that in the necking portion where processes such as double-seaming are performed, wrinkles (wrinkle impressions) (defects generated during double-seaming) are likely to occur. If exposed to high-temperature and high-humidity conditions such as cooking sterilization treatment, water vapor penetrates from these wrinkles, causing peeling of the resin coating with poor adhesion (sometimes referred to as "necking delamination"). In addition, it is considered that in the entire seamless can, the necking portion is a region where the compressive deformation of the resin film in the circumferential direction of the can becomes large due to drawing and ironing processes during the can manufacturing process, and there is a tendency for the adhesion between the resin film and the metal sheet to become weak.

[0043] In contrast, it is considered that in the seamless can of the first aspect of the present invention, by destroying the oriented crystals of the outer surface resin coating in the necking portion so that Im / Iu is in the above range, the adhesion of the outer surface resin coating to the metal sheet is improved, and even if wrinkles are formed, the intrusion of water vapor can be effectively suppressed. On the other hand, in the portions other than the necking portion of the seamless can, the oriented crystallization of the outer surface resin coating is maintained, so the barrier properties achieved by the outer surface resin coating are ensured, and it has excellent corrosion resistance, and the occurrence of whitening such as cooking whitening and white streaks is also effectively suppressed.

[0044] On the other hand, sometimes even in an internally resin-coated seamless can, due to the double seaming process being applied to the uppermost part of the can body, or during operations such as when foreign objects are involved, blemishes may occur in the necking portion in the same way as in the externally resin-coated layer. If such blemishes are present during sterilization treatments such as retort sterilization or cooking treatments, peeling of the inner surface resin coating (sometimes referred to as "blemish delamination") may occur in the inner surface resin coating under the influence of internal pressure and the contents, similar to the outer surface resin coating. In addition, compared to other areas of the entire can, the adhesion between the resin coating and the metal sheet tends to be weaker in the necking portion, and the same is true for the inner surface resin film. In particular, when the maximum necking portion with a necking rate of 15% or more relative to the can body is within a distance of 0 to 15% from the uppermost part of the can body with respect to the height of the entire can from the uppermost part of the can body to the bottom, the inner surface polyester resin coating is prone to blemish delamination.

[0045] That is, on the inner surface of the above-mentioned externally resin-coated seamless can, in a seamless can with an inner surface polyester resin coating, the oriented crystals are also destroyed so that the ratio Wm / Wu at the inner surface resin coating is 0.85 or less. Thus, similar to the outer surface resin coating, the adhesion of the inner surface resin coating to the metal sheet is improved. Even when subjected to sterilization treatments or cooking treatments after filling with contents, the generation of peeling of the inner surface resin coating in the necking portion can be effectively prevented, and the inner surface resin coating has excellent hot water adhesion and excellent corrosion resistance.

[0046] In addition, in the internally resin-coated seamless can of the second aspect of the present invention, where the melting point of the polyester resin constituting the inner surface resin coating is 250 °C or higher, in the state before the seamless can is subjected to sterilization treatment to prevent the deterioration of the contents, the orientation index MOu is 3.60 or less, and the ratio MOm / MOu of the orientation index MOm to the orientation index MOu is 1.80 or more. In the state after the seamless can has been subjected to sterilization treatment to prevent the deterioration of the contents, the orientation index MOu is 4.10 or less, and the MOm / MOu is 1.37 or more. Or, in the internally resin-coated seamless can of the third aspect of the present invention, where the melting point of the polyester resin constituting the inner surface resin coating is 220 °C or lower, after the sterilization treatment, the MOm / MOu is 1.37 or more, the metal sheet is an aluminum sheet without surface treatment, and the orientation index MOu is 3.10 or less. Thus, the adhesion of the inner surface resin coating to the metal sheet is improved. Even when the necking rate of the maximum necking portion is as large as 15% or more and during sterilization treatments or cooking treatments after filling with contents, the occurrence of peeling of the inner surface resin coating in the necking portion can be effectively prevented, and the inner surface resin coating has excellent hot water adhesion and excellent corrosion resistance.

[0047] Furthermore, according to the method for manufacturing a seamless can of the present invention, by heating the portion to be the necking portion of the seamless can at a specific time point as mentioned above, the oriented crystals of the portion to be the necking portion of the seamless can can be controlled as described above. Furthermore, if the necking portion is heated under high temperature conditions, only the overlapping portion of the finish varnish of the seamless can will have a poor appearance with multiple tiny concave and convex shapes. By performing the local heating at a temperature in the range of 185 to 230°C, the overlapping portion of the finish varnish of the seamless can will not have a poor appearance, and a seamless can with excellent hot water-resistant adhesion and appearance characteristics can be formed. Brief Description of the Figures

[0048] Figure 1 is a side view showing an example of a seamless can of the present invention, and the right half is a side sectional view. Specific implementation method

[0049] (Seamless Cans)

[0050] Figure 1 This is a diagram showing an example of a seamless can of the present invention, in which the seamless can represented as a whole by 1 has: a main body 2 having a straight body shape with a straight outer surface; and a bottom 3 that closes the lower part of the main body 2. The upper part of the main body 2 is connected to a necked portion (sometimes also referred to as a "reduced diameter portion") 4 that is reduced in diameter by necking processing (reducing diameter processing), and a flange portion 5 is formed at the upper end of the necked portion 4 across the maximum reduced diameter portion 8, which is the portion with the largest reduction ratio in the necked portion. In addition, in this seamless can, as can be seen from the enlarged cross-sectional view of the X portion of the seamless can main body, an outer surface resin coating 11 and an inner surface resin coating 12 are formed on the inner and outer surfaces of the metal plate 10. In addition, a printing layer 13 and a top varnish layer 14 are formed on the outer surface resin coating 11.

[0051] [First Implementation Method]

[0052] In the seamless can of the first embodiment of the present invention, it is important that Figure 1 ​​As shown, at least a part of the position within a distance of 0 to 15% from the uppermost part 6 (0%) of the can body with respect to the overall height of the seamless can from the uppermost part 6 of the can body to the bottom 7 (100%) of the can has a necked portion 4 achieved by necking processing. At the position within a distance of 45% to 60% from the uppermost part 6 of the can body (hereinafter, sometimes the part at least a part of the position within this distance is referred to as the "central part of the can body"), the maximum value of the peak intensity between 2θ = 15° and 19° obtained by X-ray diffraction method of the outer surface resin coating divided by the thickness of the outer surface resin coating at the measurement part gives a value Im (cps / μm). The maximum value of the peak intensity between 2θ = 15° and 19° obtained by X-ray diffraction method of the outer surface resin coating at the maximum necked part 8 of the necked portion divided by the thickness of the outer surface resin coating at the measurement part gives a value Iu (cps / μm). The ratio Im / Iu of the value Im to the value Iu is 1.0 or more, and particularly preferably in the range of 1.0 to 4.5.

[0053] Within 2θ = 15° to 19° obtained by X-ray diffraction method of the polyester resin coating, there are peaks related to the crystallinity of PET and PBT. For example, there are diffraction peaks such as crystal plane index (0-11) and crystal plane index (010). In the seamless can with an outer surface resin coating of the present invention, the maximum value Iu of the peak intensity of the outer surface resin coating near the necked portion is less than the maximum value Im of the peak intensity near the center of the main body portion, and it can be seen that the oriented crystals of the outer surface resin coating at the necked portion are damaged.

[0054] In addition, as described above, the above-mentioned oriented crystal state of the outer surface resin coating can also be judged according to the state of the inner surface resin coating of the seamless can. That is, the full width at half maximum (FWHM) of the peak near 1730 cm -1 obtained by micro-Raman spectroscopy on the surface of the polyester resin coating at the position within a distance of 45% to 60% from the uppermost part of the can body is set as Wm (cm -1 ), and the full width at half maximum (FWHM) of the peak near 1730 cm -1 obtained by micro-Raman spectroscopy on the surface of the inner surface polyester resin coating at the maximum necked part 8 of the inner surface polyester resin coating is set as Wu (cm -1 ). The ratio Wm / Wu of the Wm to the Wu is preferably 0.85 or less, and particularly preferably in the range of 0.59 to 0.70.

[0055] In the PET analysis of the polyester resin coating by micro-Raman spectroscopy, at 1730 cm -1A Raman band attributed to C=O stretching vibration is found nearby. Since PET has a resonance-stabilized planar structure during crystallization, the width of the C=O band measured during crystallization becomes narrower, and the smaller the full width at half maximum (FWHM) is as the oriented crystals progress. In the seamless can of the first embodiment of the present invention, the FWHM Wu of the inner surface resin coating near the necking portion is greater than the FWHM Wm near the center of the main body portion, indicating that the oriented crystals of the inner surface resin coating at the necking portion are damaged.

[0056] Moreover, in the seamless can of the first embodiment of the present invention, the orientation index MOu obtained by micro-Raman spectroscopy on the surface of the inner surface polyester resin coating at the maximum diameter reduction portion 8 is preferably 2.40 or less, particularly preferably in the range of 1.00 to 2.00. The ratio MOm / MOu of the orientation index MOm obtained by micro-Raman spectroscopy on the surface of the polyester resin coating at a position within a distance of 45% to 60% from the uppermost part of the can body to the orientation index MOu is preferably 2.10 or more, particularly preferably in the range of 2.50 to 5.00.

[0057] In the PET analysis by the above micro-Raman spectroscopy, the band at 1615 cm -1 is a peak due to the C=C stretching mode and has the highest correlation with orientation. On the other hand, since the band at 632 cm -1 is not affected by orientation, it can be set as an internal standard band. By dividing the maximum value I -1 of the peak intensity at 1615 cm 1615 by the peak top intensity I -1 at 632 cm 632 , the relative intensity I 1615 / I 632 is obtained. For the can height direction (Y) and the direction perpendicular to the can height direction (X), the relative intensity is measured respectively, and the ratio Ix / Iy of the obtained relative intensities is the above orientation index MO, which represents the orientation of PET including the amorphous part.

[0058] Since the orientation index MOu at the necking portion of the inner surface resin coating is 2.40 or less, and the orientation of the inner surface resin coating at the necking portion in the can height direction (Y) is greater than the orientation in the direction perpendicular to the can (X), and the ratio MOm / MOu of the orientation index MOm at the center of the can body to the orientation index MOu is 2.10 or more, the orientation of the inner surface resin coating at the necking portion is less than that of the inner surface resin coating at the center of the can body, indicating that the orientation of the inner surface resin coating at the necking portion is damaged.

[0059] Therefore, the inner surface resin coating of the seamless can of the first embodiment having such an oriented crystal state, like the seamless cans of the second and third embodiments described later, can effectively prevent the peeling (flaw delamination) of the inner surface resin coating at the necking portion even when subjected to retort sterilization treatment or the like. The inner surface resin coating has excellent hot water tightness and excellent corrosion resistance.

[0060] In the seamless can of the first embodiment of the present invention, it is preferable that the diameter reduction rate of the maximum diameter reduction portion is 6% or less with respect to the diameter at a position 15 to 60% from the uppermost part of the can body. By performing the diameter reduction process below the above value, the state of the oriented crystals of the outer surface resin coating at the necking portion can be appropriately maintained.

[0061] [Second and Third Embodiments]

[0062] An important feature of the seamless can of the second embodiment of the present invention is that the melting point of the polyester resin constituting the inner surface resin coating is 250 °C or higher, and in the state before the seamless can is subjected to sterilization treatment for preventing the deterioration of the contents, the orientation index MOu obtained by micro Raman spectroscopy on the surface of the inner surface polyester resin coating at the maximum diameter reduction portion is 3.60 or less.

[0063] Furthermore, in the second embodiment, with respect to this inner surface resin coating, the ratio MOm / MOu of the orientation index MOm obtained by micro Raman spectroscopy on the surface of the polyester resin coating at a position within a distance of 45% to 60% from the uppermost part of the can body to the orientation index MOu is preferably 1.80 or higher, particularly preferably in the range of 1.90 to 4.50. In the state after the seamless can has been subjected to sterilization treatment for preventing the deterioration of the contents (hereinafter, sometimes referred to as "after sterilization treatment"), the orientation index MOu is preferably 4.10 or less, particularly preferably in the range of 1.00 to 4.00, and the MOm / MOu is preferably 1.37 or higher, particularly preferably in the range of 1.40 to 5.00.

[0064] An important feature of the seamless can of the third embodiment of the present invention is that the melting point of the polyester resin constituting the inner surface resin coating is 220 °C or lower, and the MOm / MOu after sterilization treatment is 1.37 or higher, particularly in the range of 1.40 to 2.00. It should be noted that in the third embodiment, when a multilayer structure is used as the inner surface polyester resin coating, the melting point of the resin constituting the lower layer on the metal plate side may be 220 °C or lower.

[0065] Furthermore, in this embodiment, with respect to the inner surface resin coating, the orientation index MOu is preferably 3.10 or less, particularly preferably in the range of 1.40 to 2.00.

[0066] It should be noted that in this specification, "the state of the seamless can before receiving the sterilization treatment for preventing the deterioration of the content" refers to the state of the empty can after being manufactured by the aforementioned manufacturing method of the present invention until the content is filled, and "the state of the seamless can after receiving the sterilization treatment for preventing the deterioration of the content" refers to the state of the can filled with the content that has received the sterilization treatment such as retort sterilization or pasteurization performed after the content is filled, which is well-known in the art.

[0067] In the seamless cans of the second and third embodiments of the present invention, due to the above-mentioned characteristics of the inner surface resin coating, the adhesion to the metal plate is significantly improved. Therefore, even in the case where the maximum necking portion has a large necking amount with a necking rate of 15% or more, especially 20% or more, or in the case where a metal plate without surface treatment is used, when the content is filled and then subjected to sterilization treatment, cooking treatment, etc. to prevent the deterioration of the content, the peeling (flaw delamination) of the inner surface resin coating at the necking portion is effectively prevented, the hot water tight adhesion of the inner surface resin coating is excellent, and it has excellent corrosion resistance.

[0068] [Metal plate]

[0069] In the present invention, as the metal plate, various surface-treated steel plates used for forming seamless cans in the past, light metal plates such as aluminum, etc. can be used.

[0070] As the surface-treated steel plate, a surface-treated steel plate obtained by annealing a cold-rolled steel plate and then performing temper rolling or secondary cold rolling, and then performing one or more surface treatments such as galvanizing, tin plating, nickel plating, electrolytic chromic acid treatment, chromic acid treatment, zirconium compound treatment, etc. can be used.

[0071] As the light metal plate, in addition to the so-called aluminum plate, an aluminum alloy plate can also be used. Specifically, aluminum alloy plates of the 3000 series, 5000 series, and 6000 series of "JIS H 4000" are preferably used. Ideally, these light metal plates are subjected to inorganic surface treatments such as chromate phosphate treatment, zirconium phosphate treatment, zirconium treatment, etc. However, due to the excellent adhesion of the polyester resin coating of the present invention to the metal plate, untreated aluminum plates without the above-mentioned surface treatment can also be appropriately used.

[0072] The original thickness of the metal plate varies depending on the type of metal, the use or size of the container, but generally it is preferably 0.10 - 0.50 mm thick. Among them, in the case of the surface-treated steel plate, from the viewpoints of the strength and formability of the obtained seamless can, a thickness of 0.10 - 0.30 mm is preferred, and in the case of the light metal plate, a thickness of 0.15 - 0.40 mm is preferably used.

[0073] [Polyester outer surface resin coating]

[0074] In the seamless can of the first embodiment of the present invention, as the polyester resin constituting the outer surface resin coating, from the viewpoint of suppressing the occurrence of cooking whitening and white streaks, it is preferably contained in an amount of 20 to 60% by mass, and particularly preferably contained in an amount of 45 to 55% by mass of polybutylene terephthalate homopolymer resin or a copolymer resin mainly composed of butylene terephthalate units (hereinafter, these may be collectively referred to as "PBT"), and the remaining component is polyethylene terephthalate homopolymer resin (PET) or a copolymer resin mainly composed of ethylene terephthalate units (for example, in the case of PET containing 5 mol% of isophthalic acid, it may be denoted as "PETIA5"). When the content of PBT is less than the above range, there may be whitening such as cooking whitening and white streaks at the bottom of the can, and the appearance characteristics are reduced. On the other hand, if the PBT is more than the above range, as described above, the adhesion of the outer surface is reduced, and due to cooking sterilization treatment or the like, the outer surface resin coating of the necking part may be peeled off. In addition, during the ironing and ironing process, the resin coating may be cut, resulting in metal exposure, and the appearance characteristics after printing may be reduced.

[0075] The copolymer resin of PBT or the copolymer resin of PET preferably contains butylene terephthalate units or ethylene terephthalate units in an amount of 50 mol% or more, and particularly preferably in an amount of 80 mol% or more.

[0076] In addition, as the carboxylic acid component other than the terephthalic acid component as the copolymer component, examples include: isophthalic acid, naphthalenedicarboxylic acid, p-β-oxyethoxybenzoic acid, biphenyl-4,4'-dicarboxylic acid, diphenoxyethane-4,4'-dicarboxylic acid, sodium isophthalate-5-sulfonate, hexahydroterephthalic acid, adipic acid, sebacic acid, trimellitic acid, pyromellitic acid, trimesic acid, 1,1,2,2-ethanetetracarboxylic acid, 1,1,2-ethanetricarboxylic acid, 1,3,5-pentanetricarboxylic acid, 1,2,3,4-cyclopentanetetracarboxylic acid, biphenyl-3,4,3',4'-tetracarboxylic acid, dimer acid, etc., but are not limited thereto.

[0077] On the other hand, as the alcohol component other than 1,4-butanediol or ethylene glycol, examples include: propylene glycol, neopentyl glycol, 1,6-hexanediol, diethylene glycol, triethylene glycol, cyclohexanedimethanol, ethylene oxide adduct of bisphenol A, glycerin, trimethylolpropane, pentaerythritol, dipentaerythritol, sorbitan, etc., but are not limited thereto.

[0078] As the outer surface resin coating, the isophthalic acid (IA) content in polyethylene terephthalate resin is preferably 2 to 15 mol%, particularly preferably 5 to 13 mol%, but is not limited thereto. In addition, it is preferably composed of a mixture of polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) in a mass ratio of PET:PBT = 80:20 to 40:60 in the polyester resin film.

[0079] In addition, in the second and third seamless cans of the present invention, as the outer surface resin coating, the above polyester resin similar to the first embodiment can also be used, but when the diameter reduction rate of the maximum diameter reduction portion is set to 15% or more, a polyester resin containing ethylene terephthalate units in an amount of more than 80 mol% is preferably used. It should be noted that as the copolymerization components other than ethylene glycol and terephthalic acid, the above copolymerization components can be used.

[0080] In the seamless cans of the second and third embodiments, preferably, as in the following examples, the outer surface resin coating is the same as the inner surface resin coating.

[0081] Regarding the polyester resin, the intrinsic viscosity (IV) measured using a phenol / tetrachloroethane mixed solvent as the solvent is preferably in the range of 0.5 to 1.4 dL / g, particularly preferably in the range of 0.65 to 1.4 dL / g. If the intrinsic viscosity is greater than the above range, the melt viscosity when the resin is heated and melted becomes extremely high, making the operation of coating the resin on the metal plate difficult and not preferred. In addition, if the intrinsic viscosity is less than the above range, it is not resistant to severe processing such as deep drawing and thinning, and the flavor and corrosion resistance are also poor, which is not preferred.

[0082] The glass transition temperature (Tg) of the polyester resin is preferably in the range of 30 to 80 °C, particularly preferably in the range of 50 to 65 °C. Especially when the Tg is higher than the above range, the processability may decrease. On the other hand, when the Tg is lower than the above range, the resistance to cooking whitening may decrease.

[0083] In addition, the melting point (Tm) of the polyester resin is preferably in the range of 200 to 260 °C, particularly preferably in the range of 215 to 235 °C. When the melting point is lower than the above range, the resistance to cooking whitening may decrease.

[0084] Moreover, in the polyester resin, resin additives known per se, such as anti-blocking agents such as amorphous silica, pigments such as titanium dioxide, antistatic agents, antioxidants, lubricants, etc., can be blended according to known formulations.

[0085] The thickness of the outer surface resin coating is preferably in the range of 5 to 20 μm, but is not limited thereto. In addition, the outer surface resin coating may be a single layer as shown in Figure 1 or may be a multi-layer of two or more layers. In the case of a multi-layer, it is important that all layers except at least the lowermost layer are the above-mentioned outer surface resin coating containing PBT. In addition, in the case of a multi-layer, the total thickness is preferably in the above range.

[0086] [Polyester inner surface resin coating]

[0087] In the seamless can of the present invention, the inner surface resin coating may also use the same polyester resin as the outer surface resin coating, but from the viewpoints of the processing adhesion and corrosion resistance of the resin coating in the deep drawing and ironing process, a copolymer resin mainly composed of ethylene terephthalate units is preferred.

[0088] Particularly preferably, polyethylene terephthalate homopolymer resin (homo-PET) or a copolymer resin mainly composed of ethylene terephthalate units (copoly-PET) is used, and copolymer-PET containing isophthalic acid in an amount of 1 to 15 mol% can be preferably used.

[0089] In the inner surface resin coating, similar to the outer surface resin coating, the melting point (Tm) of the polyester resin is preferably in the range of 200 to 260 °C, and particularly preferably in the range of 215 to 235 °C. When the melting point is lower than the above range, the resistance to cooking whitening may be reduced.

[0090] It should be noted that in the seamless can of the second embodiment, it is characterized in that a polyester resin having a melting point (Tm) of 250 °C or higher is used as the inner surface resin coating, whereby the container performance with excellent flavor characteristics can be achieved more inexpensively.

[0091] In the inner surface resin coating, the inherent viscosity and glass transition temperature are also in the same range as those of the outer surface resin coating, and conventionally known resin additives can be used.

[0092] In addition, the thickness of the inner surface resin coating is preferably in the range of 10 to 30 μm, but is not limited thereto.

[0093] The inner surface can be either a single layer or a multi-layer. Particularly preferably, PETIA having an isophthalic acid content of 9 to 15 mol% is used for the lower layer, and PETIA having an isophthalic acid content lower than that of the lower layer, i.e., an isophthalic acid content of 9 mol% or less, or homo-PET is used for the surface layer. The thickness ratio of the lower layer to the surface layer is preferably in the range of 8:2 to 4:6, but is not limited thereto.

[0094] (Polyester resin-coated metal sheet)

[0095] The polyester resin-coated metal sheet used for manufacturing the resin-coated seamless can of the present invention can be manufactured by coating a polyester resin layer on a metal sheet by a conventionally known method such as an extrusion lamination method, a hot melt bonding method, or a dry lamination method using the above polyester resin. From the viewpoints of processability and the like, lamination by the extrusion lamination method is preferably performed, but a biaxially stretched polyester film excellent in corrosion resistance can also be laminated by the hot melt bonding method or the dry lamination method.

[0096] The resin coating layer formed of the polyester resin is preferably formed on both the inner surface and the outer surface, and a polyester resin coating layer may be formed only on either one, and the other may be provided with a coating film formed of a conventionally known coating composition.

[0097] In order to further improve the adhesion of the polyester resin coating layer to the metal sheet, an adhesion primer may also be used.

[0098] As a primer coating excellent in adhesion and corrosion resistance, conventionally known primers such as an epoxy phenol-based primer coating and a polyester phenol-based primer coating can be used, but from the viewpoint of hygiene, a polyester phenol-based primer coating composed of a polyester resin and a novolak-type phenolic resin derived from m-cresol as a curing agent is preferably used.

[0099] (Method for manufacturing a seamless can)

[0100] The seamless can of the present invention is formed by using the above metal sheet coated with a polyester resin on the inner surface and / or the outer surface by a conventionally known forming method. For example, in a drawing forming process, it is formed into a shallow drawn can by drawing; in a redrawing and ironing process, the shallow drawn can is formed into a redrawn and ironed can by redrawing and ironing, and it is formed through the following processes: a heating process for heating the whole of the obtained redrawn and ironed can; a printing process for printing the outer surface of the main body of the redrawn and ironed can that has undergone the heating process; a drying / baking process for heating the whole of the printed can; and a necking / flanging process for necking / flanging the redrawn and ironed can that has undergone the drying / baking process. As described above, in the present invention, an important feature is that at any time point among (a) between the drawing forming process and the redrawing and ironing process, (b) between the heating process and the printing process, and (c) after the necking / flanging process, there is a local heating process for locally heating the portion that becomes the necking part when the seamless can is formed to a temperature in the range of 185 to 230 °C, particularly 190 to 210 °C.

[0101] Accordingly, it is possible to reduce the oriented crystals of the polyester resin coating in the portions other than the necking part, reduce the oriented crystals of the polyester resin coating in the portion that becomes the necking part, adjust Im / Iu, Wm / Wu, MOm / MOu, etc. to the aforementioned ranges, and prevent the occurrence of whitening such as retort whitening even when exposed to high-temperature and high-humidity conditions such as retort sterilization treatment; even when the entire can is exposed to high-temperature conditions in the heating process for the purpose of removing lubricants in the can manufacturing process and alleviating forming deformation, it is possible to prevent the occurrence of whitening such as white streaks, and effectively prevent the peeling of the resin coating in the necking part.

[0102] [Drawing forming process / Redrawing and ironing process]

[0103] The drawing forming process and the redrawing and ironing process can be carried out by conventionally known methods.

[0104] In the drawing forming process, a drawing punch and a die are used to perform stretch forming so that the drawing ratio (=blank diameter / punch diameter) is 1.4 to 1.8 to obtain a shallow drawn can, and this shallow drawn can is then supplied to the redrawing and ironing process. In the present invention, as described above, before being supplied to the redrawing and ironing process, the portion of this shallow drawn can that becomes the necking part of the seamless can, that is, the position 0 to 25% from the uppermost part of the can body of the shallow drawn can with respect to the can height, can be locally heated (the time point (a): the heating method will be described later).

[0105] Subsequently, in the redrawing and ironing process that follows, the redrawing process can be omitted according to the drawing ratio of the shallow drawn can, etc., and thinning processing can be directly carried out. In addition, bending and stretching processing (stretch processing) of redrawing can also be carried out. Preferably, the side wall portion is thinned by redrawing and thinning processing. The thinning is preferably carried out in such a way that the thickness of the base plate of the resin-coated metal sheet becomes 30 to 65%, and particularly preferably 34 to 42%.

[0106] [Heating process]

[0107] The seamless can obtained by drawing forming and redrawing and ironing is, after trimming the uppermost part of the can body, supplied to heat treatment in order to remove the lubricant used during forming and alleviate the forming deformation of the polyester resin coating. This heat treatment is usually carried out at a temperature of Tm - 5°C or higher, particularly in the temperature range of Tm - 5°C to Tm + 20°C, based on the melting point (Tm) of the resin coating. The heating time varies depending on the heating method and cannot be generally specified, but it is usually preferably in the range of 30 to 60 seconds.

[0108] As the heating method, for example, conventionally known heating units such as a hot air circulation furnace, an infrared heating furnace, a high-frequency induction heating device, and a dielectric heating device can be used.

[0109] The seamless can that has undergone the heating process and has been cooled is then fed to the printing process. However, in the present invention, as described above, before being fed to the printing process, the part that becomes the necking part of the seamless can after the heating treatment (the position from 0 to 15% of the height of the seamless can after heating, starting from the uppermost part of the can body) can be locally heated (the timing (b): the heating method will be described later).

[0110] [Printing Process and Necking / Flanging Processing]

[0111] The seamless can that has been subjected to the heating treatment is then printed on the can body part by a conventionally known printing method such as gravure printing, offset printing, flexographic printing, inkjet printing, etc., and then a printing layer is formed by baking and drying. In addition, in order to prevent damage to the printed image, etc., a varnish layer is formed on the printing layer. It should be noted that from the viewpoint of design, it is preferable that the printing layer is formed not only in the center of the can body part but also in the necking processed part.

[0112] The seamless can on which the printing layer and the varnish layer are formed is then necked (necking down processing) to form a necking part, and a flange part is formed by flanging processing, and it is completed as a seamless can.

[0113] The necking rate of the necking processing is usually in the range of 5% to 25%. In the seamless can of the first embodiment having an outer surface resin coating layer, it is preferably 6% or less. In the second and third seamless cans having an inner surface resin coating layer, the necking rate can also be set to 15% or more. It should be noted that the necking rate in this specification is calculated according to the following formula.

[0114] Necking rate (%) = (D 0 - D 1 ) / D 0 ×100

[0115] In the formula, D 0 is the inner diameter of the can body at a position from 15% to 60% starting from the uppermost part of the can body, and D 1 is the inner diameter of the can body at the maximum necking part.

[0116] In the present invention, as described above, the part at a position from 0 to 15% of the height of the seamless can starting from the uppermost part of the can body can be heated to make a finished product (the time point (c): the heating method will be described later). It should be noted that at least a part of the area where the necking processing is performed includes the printing layer and the varnish layer. In particular, if a flaw occurs just below the double seam on the outer surface of the can printed with pigments, it is likely to peel off starting from this flaw during retort sterilization.

[0117] [Local Heating Process]

[0118] As described above, in the present invention, by locally heating the portion that becomes the necking part when forming a seamless can to a temperature of 185 to 230°C, particularly 190 to 210°C, at any time point among the above (a) to (c), the values of Im / Iu of the outer surface resin coating, Wm / Wu, MOu, and MOm / MOu of the inner surface resin coating can be adjusted to the above values.

[0119] The local heating process can be carried out at any time point among the above (a) to (c). However, by directly heating the necking part, which is the part where the adhesion to the metal plate is to be improved, in the state of the finished product, the oriented crystals can be efficiently controlled. Therefore, it is particularly preferably carried out in the state of the seamless can after the necking / flanging process, at the time point (c).

[0120] The heating time cannot be generally specified according to the heating temperature and heating method, but it is preferably in the range of 0.05 to 40 seconds. Particularly in the case of high-frequency induction heating, it is preferably less than 2.0 seconds, and particularly preferably in the range of 0.1 to 0.6 seconds.

[0121] The heating method is not limited as long as the above temperature conditions are satisfied, but high-frequency induction heating is particularly preferred. As the advantages over other heating methods such as an oven, in high-frequency induction heating, since the interface between the metal plate and the resin coating is heated by heating the metal plate, the following can be cited: the adhesion between the resin coating and the metal plate can be efficiently improved, the space required for the installation of the equipment is small, a high temperature can be reached in a short time, and only a specific part can be heated.

[0122] It should be noted that in the case of local heating by high-frequency induction in the present invention, only the portion of the seamless can that becomes the necking part is selectively heated. The above temperature is the reaching temperature of the interface between the metal plate and the film, and the time until this reaching temperature is reached is set as the heating time. In addition, in the case of oven heating, the above temperature is the highest reaching temperature in the oven, and the holding time of this highest reaching temperature is set as the heating time.

[0123] High-frequency induction uses high-frequency heating with a frequency of 10 to 200 KHz, but it is not limited thereto. In high-frequency induction heating, a heating device having a high-frequency induction heating coil, which is well-known per se, can be used. This heating device generally includes a high-frequency induction heating coil, an electrode for connecting the coil to a power source, a magnetic member for enhancing the electromagnetic coupling between the coil and the seamless can and restricting the heating part of the seamless can, and a cooling mechanism for cooling the coil.

[0124] The seamless can of the present invention thus completed, as described above, can suppress the occurrence of whitening such as retort whitening even when exposed to high-temperature and high-humidity conditions such as retort sterilization treatment; even when the entire can is exposed to high-temperature conditions in a heating process for the purpose of removing lubricants in the can manufacturing process and alleviating forming deformation, it can suppress the occurrence of whitening such as white streaks, and can effectively prevent the peeling of the resin coating layer at the necking portion.

[0125] Examples

[0126] The present invention will be described in more detail by the following examples, but the present invention is not limited to the following examples.

[0127] (Examples 1 to 12, Comparative Examples 1 to 5)

[0128] An aluminum plate (grade A3104) with a thickness of 0.26 mm was used, and a polyester resin (glass transition temperature 56 °C, melting point I: 218 °C, melting point II: 232 °C) was obtained by mixing polybutylene terephthalate resin (PBT) and polyethylene terephthalate resin (PETIA11) copolymerized with 11 moles of isophthalic acid in a mass ratio of 60:40. A film with a thickness of 10 μm formed from this polyester resin was used as the outer surface resin coating layer, and two layers of films with a thickness of 12 μm formed from polyethylene terephthalate resin containing isophthalic acid (IA) (surface layer: glass transition temperature 79 °C, melting point 247 °C; lower layer: glass transition temperature 75 °C, melting point 215 °C) were used as the inner surface resin coating layer. The outer surface resin coating layer and the inner surface resin coating layer were thermocompression bonded to the above-mentioned aluminum plate heated to 250 °C through a laminating roller to obtain an aluminum plate coated with resin on both inner and outer surfaces.

[0129] The resin-coated aluminum plate obtained was blanked into a circular blank with a diameter of 126.5 mm by a deep drawing forming machine to form a shallow drawn cup body with an average height of 38 mm for the main body wall portion (deep drawing forming process). Then, the thinning process of the shallow drawn cup body was carried out (redrawing and thinning forming process), and the drawn and thinned can obtained was heated in an oven at a set temperature of 190 - 210 °C for 30 - 60 seconds (heating process). Then, a printing layer and a topcoat varnish layer for the can main body were formed (printing process). After that, a necking process was carried out to change the diameter of the can main body with a diameter of 54.0 mm to a diameter of 50.8 mm (necking amount 5.9%), forming a necking portion, and then a flange portion was formed (necking / flange processing process) to produce a seamless can with a can height of 133.215 mm.

[0130] It should be noted that the local heating process is carried out at any time point between the drawing forming process and the redrawing and thinning forming process (denoted as "a" in Table 1), between the heating process and the printing process (denoted as "b" in Table 1), and after the necking / flanging process (denoted as "c" in Table 1). Under the temperature conditions shown in Table 1, it is heated for 0.30 seconds with a high-frequency induction heating device.

[0131] (Examples 13 - 15, Comparative Examples 6 - 7)

[0132] An aluminum plate with a thickness of 0.27 mm (material number A3104) was used, and a film with a thickness of 12 μm formed from polyethylene terephthalate resin (glass transition temperature 80°C, melting point 254°C) was thermocompression bonded to the inner and outer surface sides of the above-mentioned aluminum plate heated to 290°C through a laminating roller, obtaining an aluminum plate with resin coatings on both inner and outer surfaces.

[0133] The obtained resin-coated aluminum plate was blanked into a circular blank with a diameter of 142.0 mm by a drawing forming machine to form a shallow drawing cup with an average height of the main body wall of 33.5 mm (drawing forming process). Then, the thinning process of the shallow drawing cup was carried out (redrawing and thinning forming process), and the obtained drawn and thinned can was heated in an oven at a set temperature of 190 - 210°C for 30 - 60 seconds (heating process). Then, a printing layer and a topcoat varnish layer were formed on the can main body (printing process). After that, a necking process was carried out to change the diameter of the can main body with a diameter of 68.3 mm to a diameter of 54.0 mm (necking amount 20.9%), and after forming a necking part, a flange part was formed (necking / flanging process), manufacturing a seamless can with a can height of 122.2 mm.

[0134] The local heating process is carried out after the necking / flanging process (denoted as "c" in Table 4), and under the temperature conditions shown in Table 4, high-frequency induction heating is carried out in the same manner as in Example 1.

[0135] (Examples 16 - 19, Comparative Examples 8 - 9)

[0136] An aluminum plate with a thickness of 0.27 mm (material number A3104) was used, and a double-layer film with a thickness of 12 μm formed from polyethylene terephthalate resin containing isophthalic acid (IA) (surface layer: glass transition temperature 79°C, melting point 247°C; lower layer: glass transition temperature 75°C, melting point 215°C) was thermocompression bonded to the inner and outer surface sides of the above-mentioned aluminum plate heated to 250°C through a laminating roller, obtaining an aluminum plate with resin coatings on both inner and outer surfaces.

[0137] The obtained aluminum plate with an inner surface resin coating was blanked into a circular blank with a diameter of 142.0 mm by a drawing forming machine, and a shallow drawing cup with an average height of the main body wall of 33.5 mm was formed (drawing forming process). Next, the drawing cup was subjected to a thinning process (redrawing and thinning forming process), and the obtained redrawn and thinned can was heated in an oven at a set temperature of 190 to 210 °C for 30 to 60 seconds (heating process). Next, a printed layer and a topcoat varnish layer were formed on the can main body (printing process). After that, a necking process was performed to change the diameter of the can main body from 68.3 mm to 54.0 mm (necking amount 20.9%), and after forming a necking portion, a flange portion was formed (necking / flange processing process), and a seamless can with a can height of 122.2 mm was produced.

[0138] After the necking / flange processing (indicated by "c" in Table 5), a local heating process was performed, and under the temperature conditions shown in Table 5, high-frequency induction heating was performed in the same manner as in Example 1.

[0139] (Production of specimens)

[0140] For the seamless cans obtained through Examples 1 to 19 and Comparative Examples 1 to 9, specimens were cut out from the maximum necking portion of the seamless can and the position about 53% (central portion of the can main body) from the uppermost part of the can main body in the following manner. The short side of the specimen was set in the height direction of the can, approximately 4 mm × 20 mm in width. It should be noted that the specimens were cut out in such a way that the 0° direction of the rolling of the plate was the center of the long side of the specimen.

[0141] (Maximum peak intensity between 2θ = 15° and 19° obtained by X-ray diffraction method)

[0142] Using a fully automatic multi-functional horizontal X-ray diffractometer, the specimens of Examples 1 to 12 and Comparative Examples 1 to 5 cut out by the above method were placed horizontally on the stage, with the short side facing the X-ray source and the detector side. For the long side, the upper side of the can height direction was oriented towards the inside of the device for measurement. It should be noted that the outer surface resin coating was set as the upper side, and for the specimens, the measurement was performed near the center of the specimen while retaining the aluminum plate. The measurement conditions are as follows.

[0143] Device: Rigaku Corporation's fully automatic multi-functional horizontal X-ray diffractometer SmartLab.

[0144] X-ray tube: Target... Cu, Output... 9 kW.

[0145] Tube voltage: 40 kV.

[0146] Tube current: 20 mA.

[0147] Scanning axis: 2θ / θ.

[0148] Scanning range: 15° to 30°.

[0149] Step size: 0.02 deg.

[0150] For the outer surface resin coating, while maintaining the X-ray diffraction angle 2θ of the polyester resin in the range of 15° to 19° in such a way that the incident angle and the reflection angle are always equal, the diffraction angle 2θ is scanned between 15° and 30°, and the X-ray diffraction spectrum is measured using the reflection method. Here, with respect to the diffraction angle 2θ, the incident angle and the reflection angle of the X-ray are θ respectively. It should be noted that during the measurement, if oil adheres to the sample, it may not be possible to analyze correctly. Therefore, use forceps (pincet), etc., to fix the sample on the stage.

[0151] Connect the peak intensities at 2θ = 15° and 2θ = 30° with a straight line and set it as the background. Find the maximum value of the peak intensity between 2θ = 15° and 19° of the outer surface resin coating at the necking part obtained by X-ray diffraction method after subtracting the background. Divide this value by the thickness of the outer surface resin coating at the measurement part to obtain the value Iu (cps / μm), and calculate this value Iu. Similarly, find the maximum value of the peak intensity between 2θ = 15° and 19° of the outer surface resin coating at the center of the can body obtained by X-ray diffraction method after subtracting the background. Divide this value by the thickness of the outer surface resin coating at the measurement part to obtain the value Im (cps / μm), and calculate this value Im. Based on these results, calculate the ratio Im / Iu. The measurement is carried out before and after retort sterilization at 125°C for 30 minutes. The results are shown in Tables 1 and 2.

[0152] (Measurement of the inner surface resin coating by micro-Raman spectroscopy)

[0153] Place the samples of Examples 4, 9, 12 to 19 and Comparative Examples 1, 4, 6 to 9 cut out by the above method horizontally on the stage, with the inner surface resin film on the upper side. For the samples, perform the measurement near the center of the sample while retaining aluminum.

[0154] A. Measurement of the full width at half maximum

[0155] The device and its measurement conditions are as follows.

[0156] Device: DXR2xi Raman imaging microscope manufactured by Thermo Fisher Scientific.

[0157] Laser, spectrometer: wavelength 532 nm, 5 mW non-polarized, full-band grating.

[0158] Aperture: 25 μm confocal pinhole.

[0159] Analyzer: None.

[0160] Objective lens: ×100.

[0161] Measurement position: Sample surface (measurement within 2μm in depth from the focal position on the outermost surface).

[0162] Under the above conditions, find 1730cm -1 The half-height width W of the peak near . In addition, when calculating the half-height width (FWHM) and peak intensity, the peak intensity after subtracting the background is used. The measurement was carried out before and after retort sterilization at 125°C for 30 minutes. The results are shown in Tables 3 to 5.

[0163] B. Determination of orientation index MO

[0164] When the laser polarization is aligned with the analyzer in the height direction of the sample and when it is aligned in the vertical direction of the sample, calculate 1615cm -1 The peak intensity near 632cm -1 The ratio of the peak intensity near I 1615 / I 632 , the ratio of the height direction to the vertical direction (I 1615 / I 632 )yy / (I 1615 / I 632 ) xx is set as the orientation index MO, and the same method as A is performed. The results are shown in Tables 3 to 5.

[0165] (Delamination evaluation of the necking portion of the outer surface resin coating)

[0166] After filling water into each seamless can obtained in Examples 1 to 12 and Comparative Examples 1 to 5, the can was sealed with a cap and sterilized by retorting at a sterilization temperature of 130°C for 30 minutes.

[0167] For seamless cans after retort sterilization, regardless of the size of the peeling, the case where the film lifts up just below the roll seal is evaluated as peeling, and the number of cans with peeling among 90 cans was investigated. The evaluation criteria are as follows. The results are set in Table 1 (the values ​​in () in the table are the number of cans with peeling).

[0168] ◎: 0 cans with peeling occurred

[0169] 〇: 1 to 3 cans peeled off

[0170] ×: peeling occurred in more than 4 cans

[0171] (Evaluation of delamination of the necking defect of the inner surface resin coating)

[0172] On the inner surface resin coating of the necking part of each seamless can obtained in Examples 4, 9, 12 to 19 and Comparative Examples 1, 4, 6 to 9, after cutting a circumferential incision with a cutter, retort sterilization treatment was carried out under the conditions of a sterilization temperature of 125 °C and a sterilization time of 30 minutes. The evaluation criteria are as follows. The results are shown in Tables 3 to 5.

[0173] 〇: The number of cans with film warping among 10 cans is 0 can

[0174] ×: The number of cans with film warping among 10 cans is 1 can or more

[0175] (Appearance evaluation of the overcoating varnish overlapping part)

[0176] The appearance of the overlapping part of the overcoating varnish of each seamless can obtained in Examples 1 to 12 and Comparative Examples 1 to 5 was observed visually. The evaluation criteria are as follows. The results are shown in Table 1.

[0177] 〇: No abnormality

[0178] ×: Appearance defect occurs

[0179] (Comprehensive evaluation)

[0180] The criteria for the comprehensive evaluation in Table 1 are as follows.

[0181] 〇: Both the appearance evaluation of the overlapping part and the delamination evaluation of the necking part of the resin coating after retorting are 〇

[0182] ×: At least one of the appearance evaluation of the overlapping part or the delamination evaluation of the necking part of the resin coating after retorting is ×

[0183]

[0184]

[0185]

[0186]

[0187]

[0188] Industrial applicability

[0189] Even when the seamless can of the present invention is exposed to high-temperature and high-humidity conditions such as retort sterilization treatment, the occurrence of retort whitening can be effectively suppressed; even when the whole can is exposed to high-temperature conditions in a heating process for the purpose of removing lubricants in the can manufacturing process and alleviating forming deformation, whitening such as white streaks can be effectively suppressed, and peeling of the resin coating at the necking part can also be effectively prevented. Therefore, it can be preferably used as a container for filling contents that require retort sterilization treatment, retort treatment, etc.

[0190] Explanation of Reference Numerals

[0191] 1: Seamless tank;

[0192] 2: Main body part;

[0193] 3: Bottom;

[0194] 4: Necking part;

[0195] 5: Flange part;

[0196] 6: Uppermost part of tank main body;

[0197] 7: Tank bottom;

[0198] 8: Maximum diameter reduction part;

[0199] 10: Metal plate;

[0200] 11: Outer surface resin coating;

[0201] 12: Inner surface resin coating;

[0202] 13: Printing layer;

[0203] 14: Topcoat varnish layer.

Claims

1. A seamless can, characterized in that: The seamless can has a polyester resin coating formed on at least the outer surface of the metal plate. The seamless tank has a reduced diameter portion formed by necking within a distance of 0 to 15% from the top of the tank body relative to the overall height of the tank from the top of the tank body to the tank bottom. At a position within a distance of 45% to 60% from the top of the tank body, the maximum value of the peak intensity of the outer surface polyester resin coating between 2θ=15° and 19° obtained by the X-ray diffraction method is divided by the thickness of the outer surface polyester resin coating at the measuring position to obtain a value Im, and at the maximum reduced diameter portion of the reduced diameter portion, the maximum value of the peak intensity of the outer surface polyester resin coating between 2θ=15° and 19° obtained by the X-ray diffraction method is divided by the thickness of the polyester resin coating at the measuring position to obtain a value Iu, and the ratio of the value Im to the value Iu, Im / Iu, is greater than 1.0, and the units of Im and Iu are cps / μm.

2. The seamless can according to claim 1, wherein: The maximum diameter reduction portion is reduced in diameter at a reduction rate of 6% or less relative to the diameter of the tank body at a position 15% to 60% from the uppermost portion of the tank body.

3. The seamless can according to claim 1 or 2, wherein: The outer surface polyester resin coating layer contains 40 to 80% by mass of ethylene terephthalate and 20 to 60% by mass of butylene terephthalate as main components.

4. The seamless can according to claim 1 or 2, wherein: A printed layer is formed on the outer surface polyester resin coating in at least a portion of the reduced diameter portion.

5. The seamless can according to claim 1 or 2, wherein: A polyester resin coating layer containing polyethylene terephthalate as a main component is formed on the inner surface of the metal plate as a resin coating layer.

6. The seamless can according to claim 5, wherein: The 1730 cm-1 peak of the inner polyester resin coating surface at a position within 45% to 60% of the distance from the uppermost portion of the tank body obtained by micro-Raman spectroscopy -1 The half maximum width FWHM of the peak near the maximum diameter reduction portion is set to Wm, and the 1730 cm -1 The half maximum width FWHM of the peak near is set to Wu, the ratio Wm to Wu Wm / Wu is less than 0.85, and the units of Wm and Wu are cm -1 .

7. The seamless can according to claim 5, wherein: The orientation index MOu of the inner surface polyester resin coating surface at the maximum diameter reduction portion obtained by micro-Raman spectroscopy is 2.40 or less.

8. The seamless can according to claim 7, wherein: The ratio MOm / MOu of the orientation index MOm obtained by micro-Raman spectroscopy to the orientation index MOu of the inner surface polyester resin coating surface at a position within 45% to 60% of the distance from the uppermost portion of the tank body is 2.10 or more.

9. A seamless can, characterized in that: The seamless can has a polyester resin coating formed on at least the inner surface of the metal plate. The seamless tank has a reduced diameter portion formed by necking within a distance of 0 to 15% from the top of the tank body relative to the overall height of the tank from the top of the tank body to the tank bottom. The melting point of the polyester resin is 250° C. or higher, and the orientation index MOu of the inner surface polyester resin coating surface at the maximum diameter reduction portion obtained by micro-Raman spectroscopy is 3.60 or lower in the state before the seamless can is sterilized for preventing the deterioration of the contents. The ratio MOm / MOu of the orientation index MOm obtained by micro-Raman spectroscopy to the orientation index MOu of the surface of the polyester resin coating layer at a position within a distance of 45% to 60% from the uppermost portion of the can body is 1.80 or more.

10. The seamless can according to claim 9, wherein: The maximum diameter reduction portion is reduced in diameter at a reduction rate of 15% or more relative to the diameter of the tank body at a position 15% to 60% from the uppermost portion of the tank body.

11. The seamless can according to claim 9 or 10, wherein: The orientation index MOu is 4.10 or less in a state where the seamless can has been sterilized to prevent deterioration of the contents.

12. The seamless can according to claim 11, wherein: The ratio MOm / MOu of the orientation index MOm obtained by micro-Raman spectroscopy to the orientation index MOu of the surface of the polyester resin coating at a position within a distance of 45% to 60% from the uppermost portion of the can body is 1.37 or more.

13. A seamless can, characterized in that: The seamless can has a polyester resin coating formed on at least the inner surface of the metal plate. The seamless tank has a reduced diameter portion formed by necking within a distance of 0 to 15% from the top of the tank body relative to the overall height of the tank from the top of the tank body to the tank bottom. The melting point of the polyester resin is below 220°C. When the seamless tank has been sterilized to prevent deterioration of the contents, the ratio of the orientation index MOm obtained by micro-Raman spectroscopy on the surface of the polyester resin coating at a distance of 45% to 60% from the top of the tank body to the orientation index MOu obtained by micro-Raman spectroscopy on the surface of the inner surface polyester resin coating at the maximum diameter reduction portion (MOm / MOu) is greater than 1.

37.

14. The seamless can according to claim 13, wherein: The maximum diameter reduction portion is reduced in diameter at a reduction rate of 15% or more relative to the diameter of the tank body at a position 15% to 60% from the uppermost portion of the tank body.

15. The seamless can according to claim 13 or 14, wherein: The metal plate is an aluminum plate that has not been subjected to surface treatment, and the orientation index MOu of the inner surface polyester resin coating surface at the maximum diameter reduction portion obtained by micro-Raman spectroscopy is 3.10 or less.

16. A method for manufacturing a seamless can according to any one of claims 1 to 15, characterized in that: The method for manufacturing a seamless can comprises: a drawing process, in which a polyester resin-coated metal plate having a polyester resin coating formed on the inner surface and / or the outer surface is formed into a shallow drawn can by drawing; a re-drawing and ironing process, in which the shallow drawn can is formed into a drawn and ironed can by re-drawing and ironing; a heating process, in which the entirety of the drawn and ironed can is heated; a printing process, in which the outer surface of the main body of the drawn and ironed can that has undergone the heating process is printed; a drying / baking process, in which the entirety of the printed can is heated; and a necking / flange processing process, in which the drawn and ironed can that has undergone the drying / baking process is necked / flange processed. Between the drawing process and the re-drawing and thinning process, between the heating process for heating the entire drawn and thinned can and the printing process, or after the necking / flange processing process, there is a local heating process for locally heating the portion that becomes the necking portion when the seamless can is made to a temperature of 185 to 230°C.

17. The method for manufacturing a seamless can according to claim 16, wherein: The local heating process is performed after the necking / flange processing process.

18. The method for manufacturing a seamless can according to claim 16 or 17, wherein: The heating in the local heating step is high frequency induction heating.

19. The method for manufacturing a seamless can according to claim 18, wherein: The heating time based on the high frequency induction heating is less than 2 seconds.

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