Resin-coated seamless aluminum can, resin-coated aluminum sheet, and drawn-ironed can

Abstract

[Problem] To provide a resin-coated seamless aluminum can that has both resin adhesiveness and a color tone. [Solution] This resin-coated seamless aluminum can is characterized by comprising an aluminum base material, a surface treatment layer formed on at least one surface of the aluminum base material, and a resin layer formed on the surface treatment layer, and is characterized in that the surface treatment layer contains aluminum hydroxide, and exhibits, in an infrared absorption spectrum thereof measured by FT-IR, a Pa / Pb value of 0.13-3.00 when the height of an absorbance peak at a wave number of 850-1000 cm-1 is defined as Pa and the height of an absorbance peak at a wave number of 1000-1200 cm-1 is defined as Pb.

Description

Resin-coated aluminum seamless cans, resin-coated aluminum sheets, drawn and ironed cans

[0001] The present disclosure relates to a resin-coated aluminum seamless can, a resin-coated aluminum sheet, and a drawn and ironed can.

[0002] Conventionally, aluminum sheets, which are lightweight and easy to form, have been suitably used as metal materials for containers such as food cans and beverage cans. Resin-coated aluminum sheets, which are aluminum sheets coated with a resin, have long been known as can-making materials, and it is also well known that these resin-coated aluminum sheets are subjected to drawing or drawing and ironing processes to form seamless cans for filling beverages, etc. For example, resin-coated aluminum sheets having a thermoplastic resin film as a resin layer made of a crystalline polyester resin primarily composed of ethylene terephthalate units are used as can-making materials for seamless cans.

[0003] Furthermore, the aluminum sheets used in such resin-coated aluminum sheets for seamless can applications are generally surface-treated aluminum sheets that have been subjected to a surface treatment such as a chemical conversion treatment in order to ensure corrosion resistance and adhesion to the resin layer. One example of such surface treatment is chromate phosphate treatment. Surface-treated aluminum sheets that have been subjected to chromate phosphate treatment have been widely used due to their excellent adhesion to the resin layer. However, from the viewpoint of environmental protection, there is an increasing demand for chromium-free surface treatments. For example, Patent Documents 1 to 4 listed below disclose chromium-free surface treatments in which aluminum hydroxide is formed on the surface of an aluminum substrate. They also disclose that containers and the like are formed using aluminum substrates that have been subjected to these treatments.

[0004] Japanese Patent Application Laid-Open No. 2003-013253 Japanese Patent Application Laid-Open No. 2004-216801 Japanese Patent Application Laid-Open No. 2007-176072 Japanese Patent Application Laid-Open No. 11-012762

[0005] The aluminum hydroxide coating formed on the surface of an aluminum substrate is thought to be a coating primarily composed of alumina monohydrate (AlO(OH)), known as boehmite. Boehmite is primarily used for sealing pores in anodized aluminum coatings and is known as a corrosion-resistant substance. It is also known to have an acicular structure with irregularities on the surface, and it is thought that this acicular structure exerts an anchoring effect on resin layers such as paint films and films, improving resin adhesion.

[0006] However, when this aluminum hydroxide coating treatment is applied to a resin-coated aluminum sheet for seamless cans that are formed by severe forming processes such as drawing and ironing, the following problems arise. That is, depending on the conditions of the coating formation treatment, when the can body is subjected to a sterilization process such as retort treatment after forming the seamless can and filling it with contents, the resin layer may peel off due to insufficient adhesion between the aluminum hydroxide coating layer and the resin layer (hereinafter also referred to as "resin adhesion"). Furthermore, the inner surface of the seamless can may have insufficient corrosion resistance against the contents due to the above-mentioned insufficient resin adhesion.

[0007] On the other hand, when aluminum sheets are formed into containers such as seamless cans, designs are often applied that take advantage of the excellent color tones of the aluminum substrate, such as the beautiful silvery-white color and metallic luster. However, when a resin-coated aluminum sheet that has been treated with an aluminum hydroxide coating as described above is subjected to severe forming processes such as drawing and ironing, the silvery-white color and metallic luster inherent to the aluminum substrate are lost, mainly in the processed areas, depending on the conditions of the coating formation process, resulting in a dull white appearance and a loss of color tone.

[0008] The above-mentioned patent documents do not fully consider the resin adhesion when the above-mentioned sterilization treatment such as retort treatment is performed, and further, they do not provide any knowledge about the deterioration of the color tone of the aluminum substrate caused by the aluminum hydroxide coating, and therefore do not solve such problems.

[0009] The present disclosure has been made in consideration of solving such problems, and has an object to provide a resin-coated aluminum seamless can that combines resin adhesion and color tone, and a resin-coated aluminum sheet for producing resin-coated aluminum seamless cans that combines resin adhesion and color tone.

[0010] In order to solve the above-mentioned problems, one embodiment of the present invention provides a resin-coated aluminum seamless can comprising an aluminum substrate, a surface treatment layer formed on at least one surface of the aluminum substrate, and a resin layer formed on the surface treatment layer, wherein the surface treatment layer contains aluminum hydroxide, and in an infrared absorption spectrum measured by FT-IR, the can exhibits a wavelength of 850 to 1000 cm. －１ The height of the absorbance peak is defined as Pa, and the wave number is 1000 to 1200 cm －１ When the height of the absorbance peak is defined as Pb, the value of Pa / Pb is 0.13 to 3.00.

[0011] In order to solve the above-mentioned problems, a resin-coated aluminum sheet according to one embodiment of the present invention comprises an aluminum substrate, a surface treatment layer formed on at least one surface of the aluminum substrate, and a resin layer formed on the surface treatment layer, wherein the surface treatment layer contains aluminum hydroxide, and in an infrared absorption spectrum measured by FT-IR, the surface treatment layer has a wavelength of 850 to 1000 cm. －１ The height of the absorbance peak is defined as Pa, and the wave number is 1000 to 1200 cm －１ When the height of the absorbance peak is defined as Pb, the value of Pa / Pb is 0.13 to 3.00.

[0012] According to the present disclosure, it is possible to provide a resin-coated aluminum seamless can that combines resin adhesion and color tone.

[0013] Fig. 1a is a schematic diagram of a resin-coated aluminum seamless can according to an embodiment, and Fig. 1b is a schematic diagram of a resin-coated aluminum seamless can according to another embodiment. Fig. 3a is a schematic diagram of a resin-coated aluminum plate according to an embodiment, and Fig. 3b is a schematic diagram of a resin-coated aluminum plate according to another embodiment. Fig. 4 is a diagram showing an example of an infrared absorption spectrum.

[0014] Hereinafter, an embodiment of a resin-coated aluminum seamless can according to the present disclosure will be described with reference to the drawings. In this disclosure, the term "resin adhesion" basically refers to the adhesion between the surface treatment layer and the resin layer after the retort treatment following the molding process, as described above. Furthermore, the term "color tone" refers to the color difference (ΔE) and brightness (L) described below. ＊ value).

[0015] <Resin-coated aluminum seamless can 100> Fig. 1 is a diagram schematically illustrating one embodiment of a resin-coated aluminum seamless can. As shown in Fig. 1, the resin-coated aluminum seamless can 100 has a bottomed, cylindrical shape in which the can body and the can bottom are integrated. However, the shape of the resin-coated aluminum seamless can 100 of this embodiment is not limited to the shape shown in Fig. 1, and it can be any known shape used for beverage cans, food cans, etc.

[0016] More specifically, the resin-coated aluminum seamless can 100 may have a shape such as a tapered container 120 in which the diameters of the bottom and top (opening) of the can are different and the sidewalls are inclined (see FIG. 2). The tapered portion may have a step (not shown). Furthermore, the resin-coated aluminum seamless can 100 may have a roughly rectangular shape with rounded corners and a shallow bottom (for example, the shape of canned seafood such as sardines), or a square shape (not shown).

[0017] The height of the resin-coated aluminum seamless can 100 can be adjusted appropriately depending on the application.

[0018] The resin-coated aluminum seamless can 100 includes an aluminum substrate 10 , a surface treatment layer 20 formed on at least one surface of the aluminum substrate 10 , and a resin layer 30 formed on the surface treatment layer 20 .

[0019] Although the resin-coated aluminum seamless can 100 shown in FIG. 1a has a surface treatment layer 20 and a resin layer 30 on the outer surface of the can, this is not limited thereto. That is, the resin-coated aluminum seamless can 100 may also have a surface treatment layer 20 and a resin layer 30 on the inner surface of the can (not shown). Furthermore, as shown in FIG. 1b, this embodiment may also be a resin-coated aluminum seamless can 110 having a surface treatment layer 20 and a resin layer 30 on both the inner and outer surfaces, in that order from the aluminum substrate 10. In this case, the surface treatment layer 20 and the resin layer 30 on the inner and outer surfaces of the can may be the same or different in type and thickness. Furthermore, although the surface treatment layer 20 and the resin layer 30 are not shown in the tapered container 120 in FIG. 2, the surface treatment layer 20 and the resin layer 30 are formed on at least one of the inner and outer surfaces of the container, as in FIG. 1.

[0020] <Aluminum substrate 10> In the resin-coated aluminum seamless can 100, a pure aluminum plate or an aluminum alloy plate can be used as the aluminum substrate 10. The thickness of the aluminum substrate 10 is generally preferably 0.10 mm to 1.00 mm, and particularly preferably 0.15 mm to 0.40 mm. The alloy type of the aluminum substrate 10 is selected depending on the application. For example, from the viewpoints of workability, strength, and corrosion resistance, a JIS 3000 series or 5000 series aluminum alloy plate is used.

[0021] <Surface Treatment Layer 20> The surface treatment layer 20 contains aluminum hydroxide. Aluminum hydroxide is alumina monohydrate (AlO(OH)) or alumina trihydrate (Al(OH) ３ The aluminum hydroxide in the surface treatment layer 20 has a wavelength of 1000 to 1200 cm in the infrared absorption spectrum measured by FT-IR.－１ A peak appears in the range of (more specifically, 1070 cm －１ This can be confirmed by the peak in the vicinity of this wave number. －１ It is known that the peak appearing in this range is an absorbance peak of Al-OH deformation vibration derived from aluminum hydroxide.

[0022] The surface treatment layer 20 contains amorphous alumina (Al ２ O ３ The amorphous alumina in the surface treatment layer 20 has a wavelength of 850 to 1000 cm in the infrared absorption spectrum measured by FT-IR. －１ A peak appears in the range (more specifically, 950 cm －１ This can be confirmed by the peak in the vicinity of this wave number. －１ It is known that the peak appearing in this range is an absorbance peak derived from the Al—O stretching vibration of amorphous alumina.

[0023] The infrared absorption spectrum measured by FT-IR can be measured, more specifically, by a high-sensitivity reflection method (Reflection Absorption Spectroscopy (RAS) method) using a known Fourier transform infrared spectrophotometer (FT-IR).

[0024] The absorbance peak was measured at a wave number of 1200 cm in the infrared absorption spectrum. －１ Absorbance and wave number 850 cm －１ The absorbances at these points are connected by a straight line, which is used as the baseline. The peaks at wave numbers of 850 to 1000 cm are derived from the Al—O stretching vibration of amorphous alumina. －１ Within the range (950 cm －１ The highest point from the baseline at the wavenumber of 1000 to 1200 cm is the absorbance peak height Pa. －１ Within the range (1070 cm －１ The highest point from the baseline at the point (near the base line) is taken as the absorbance peak height Pb. The peak ratio "Pa / Pb" is calculated from the obtained value.

[0025] As described above, in the resin-coated aluminum seamless can 100 of this embodiment, in the infrared absorption spectrum of the surface treatment layer 20 measured by FT-IR, the wavelength range is 850 to 1000 cm －１ The height of the absorbance peak derived from amorphous alumina is defined as "Pa", and the wave number is 1000 to 1200 cm －１ When the height of the absorbance peak derived from aluminum hydroxide is defined as "Pb," the peak ratio "Pa / Pb" is 0.13 to 3.00.

[0026] In the infrared absorption spectrum measured by FT-IR, the absorbance of the surface treatment layer is considered to be proportional to the amount of infrared-active chemical species present in the surface treatment layer. Therefore, the peak ratio "Pa / Pb" of the height of the absorbance peak attributable to amorphous alumina "Pa" to the height of the absorbance peak attributable to aluminum hydroxide "Pb" is a measure of the quantitative ratio of amorphous alumina to aluminum hydroxide, and the larger this value, the greater the abundance ratio of amorphous alumina / the smaller the abundance ratio of aluminum hydroxide. Conversely, the smaller this value, the smaller the abundance ratio of amorphous alumina / the larger the abundance ratio of aluminum hydroxide.

[0027] The reason why the inventors focused on the peak ratio "Pa / Pb" in the surface treatment layer 20, i.e., the abundance ratio of amorphous alumina to aluminum hydroxide, in order to obtain the desired resin-coated aluminum seamless can is as follows.

[0028] First, we will explain from the viewpoint of resin adhesion. The aluminum hydroxide coating such as boehmite can contain amorphous alumina (Al ２ O ３ ), but unlike the hardly soluble aluminum hydroxide, amorphous alumina is known to dissolve in hot water in a short time.

[0029] Therefore, if the aluminum hydroxide coating between the aluminum substrate and the resin layer contains a high proportion of water-soluble amorphous alumina, the coating's insoluble or poorly soluble properties cannot be maintained, and the adhesive surface with the resin layer dissolves during hot water treatment such as retort treatment, making it impossible to obtain sufficient resin adhesion. Therefore, the inventors believed that it was necessary to control the proportion of amorphous alumina in the coating to obtain resin adhesion, and after extensive research, they found that by setting the peak ratio "Pa / Pb" to 3.00 or less, the coating's insolubility or poorly soluble properties in hot water could be maintained and sufficient resin adhesion could be obtained.

[0030] Next, we will explain the color tone. When an aluminum hydroxide coating is formed on an aluminum substrate by the method described below, as the growth of acicular structures such as boehmite progresses, the unevenness of the coating tends to scatter light. It is believed that excessive growth of the acicular structures leads to a whiter color due to light scattering. Furthermore, when a seamless can is formed from a resin-coated aluminum sheet by drawing and ironing or other processes, excessive growth of the acicular structures is thought to make the coating more susceptible to cohesive failure during processing. This creates gaps (voids) in the coating, which then scatter light, resulting in an increased whiteness, a loss of metallic luster, and a deterioration in color tone. Therefore, the present inventors have intensively investigated the need to control the growth of the acicular structures to suppress color tone changes from the perspective of light scattering and cohesive failure of the coating during processing. As a result, they have found that a peak ratio "Pa / Pb" of 0.13 or more can achieve an appropriate growth state of the acicular structures and maintain a good color tone even after processing.

[0031] For these reasons, in this embodiment, it is important that the peak ratio "Pa / Pb" of the surface treatment layer (aluminum hydroxide coating) is within the range of 0.13 to 3.00. This makes it possible to obtain a resin-coated aluminum seamless can that has both the required resin adhesion and color tone.

[0032] In the surface treatment layer of this embodiment, the value of the peak ratio "Pa / Pb" is preferably in the range of 0.13 to 3.00, preferably 0.14 to 2.50, more preferably 0.20 to 2.00, and particularly preferably 0.30 to 1.50. If the value of the peak ratio "Pa / Pb" is larger than the above range, the resin adhesion will be poor. If it is smaller, the color tone will be poor.

[0033] Furthermore, in the surface treatment layer formed on the outer surface of the can, it is desirable that the value of the peak ratio "Pa / Pb" mentioned above is in the range of 0.13 to 3.00, preferably 0.14 to 2.50, more preferably 0.20 to 2.00, and particularly preferably 0.30 to 1.50. If the value of the peak ratio "Pa / Pb" is larger than the above range, the resin adhesion will be poor. If it is smaller, the color tone will be poor.

[0034] On the other hand, in terms of resin adhesion and corrosion resistance, it is desirable that the surface treatment layer formed on the inner surface of the can have the aforementioned peak ratio "Pa / Pb" value in the range of 0.30 to 3.00, preferably 0.35 to 2.00. If the peak ratio "Pa / Pb" value is greater than the above range, resin adhesion will be poor, resulting in poor corrosion resistance to the contents. On the other hand, if the peak ratio "Pa / Pb" value is less than the above range, the acicular structure will have grown excessively, which is presumably why the coating is prone to cohesive failure during processing when a seamless can is formed from a resin-coated aluminum sheet by drawing and ironing or other processes. This creates gaps (voids) in the coating, which allow the contents to penetrate, making it more susceptible to corrosion under the resin layer, known as under-film corrosion (UFC), and resulting in poor corrosion resistance.

[0035] In this embodiment, the thickness (film thickness) of the surface treatment layer 20 is preferably 2 nm or more in the case of a seamless can from the viewpoint of resin adhesion of the resin-coated aluminum seamless can 100. On the other hand, the upper limit of the thickness of the surface treatment layer 20 is preferably less than 100 nm from the viewpoints of color tone and corrosion resistance. The optimal thickness of the surface treatment layer 20 depends on the target can shape, etc., but is more preferably 5 nm or more but less than 100 nm, even more preferably 8 to 90 nm, particularly preferably 10 to 80 nm, and most preferably 12 to 45 nm. If the film thickness is larger than the above range, color tone and corrosion resistance may be deteriorated, and if it is smaller, resin adhesion may be deteriorated.

[0036] In the case of a drawn and ironed seamless can, as will be described later, the can is formed from a resin-coated aluminum sheet by drawing and ironing, and therefore the thickness of the surface treatment layer located in the can body is thinned by the process, similar to that of the aluminum base material, and the thickness of the surface treatment layer in the center of the can body (the thinnest part near the center in the height direction) is preferably 20 to 85%, preferably 20 to 75%, more preferably 20 to 60%, even more preferably 20 to 50%, particularly preferably 30 to 45%, and most preferably 30% to less than 40% of the thickness of the surface treatment layer in the center of the can bottom. The thickness of the surface treatment layer in the center of the can bottom is more preferably 5 nm to less than 100 nm, even more preferably 8 to 90 nm, particularly preferably 10 to 80 nm, and most preferably 12 to 45 nm.

[0037] In this embodiment, a known method can be applied as a method for measuring the thickness of the surface treatment layer 20. Examples of methods for measuring the thickness of the surface treatment layer 20 include X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS), with TOF-SIMS being particularly preferable.

[0038] TOF-SIMS is a method for mass analysis in which a primary ion beam from a primary ion gun is irradiated onto the surface of a solid sample to be analyzed, and secondary ions sputtered and emitted from the sample surface are mass-separated using their time-of-flight difference (time-of-flight is proportional to the square root of their mass). By detecting the intensity of the secondary ions while sputtering is progressing, the concentration distribution of the target element in the depth direction of the sample surface can be determined by converting the transition time into depth for data on the transition time of the ion intensity of the secondary ions, i.e., the target element ions or molecular ions bonded to the target element.

[0039] In the present disclosure, etching is performed using TOF-SIMS from the surface side of the surface treatment layer 20 (the surface side opposite to the aluminum substrate) until the aluminum substrate is reached, and the depth at which the secondary ion intensity of the metallic aluminum derived from the aluminum substrate becomes half of the maximum intensity (the secondary ion intensity of the metallic aluminum when it reaches the aluminum substrate) is defined as the film thickness of the surface treatment layer. ２ O ３ This is the depth of conversion.

[0040] As described above, the surface treatment layer 20 of this embodiment contains alumina monohydrate and alumina trihydrate as aluminum hydroxide. ２ O ３ The surface treatment layer 20 of this embodiment may contain trace amounts of compounds present in the treatment solution, such as silicon dioxide (SiO ２ ), magnesium oxide (MgO), manganese oxide (MnO), iron oxide (FeO), calcium oxide (CaO), phosphoric acid, etc. may be contained within a range that does not impair performance.

[0041] <Resin layer 30> The resin layer 30 is formed directly or indirectly on the surface treatment layer 20 on the side opposite to the aluminum substrate 10. In this embodiment, a known adhesive layer (adhesive primer layer) or the like may be present between the surface treatment layer 20 and the resin layer 30.

[0042] In this embodiment, the resin layer 30 may be made of a known thermoplastic or thermosetting resin that is typically used to coat a metal substrate. Examples of thermoplastic resins include one or more resins such as polyolefin resin, polyester resin, polycarbonate resin, acrylic resin, polystyrene resin, ABS resin, polyamide resin, fluororesin, and polyvinyl chloride resin. Examples of thermosetting resins include one or more resins such as acrylic resin, unsaturated polyester resin, phenol resin, urea resin, polyurethane resin, silicone resin, polyimide resin, melamine resin, and epoxy resin. Thermoplastic resins are more preferred for the resin layer 30.

[0043] Among the thermoplastic resins, polyolefin resins or polyester resins, and mixtures thereof are more preferably applicable.

[0044] Examples of polyolefin resins that can be preferably used include unsaturated carboxylic acid-modified polyolefin resins such as polyethylene resin, polypropylene resin, ethylene-propylene copolymer resin, ethylene-acrylic acid ester copolymer resin, ethylene-methacrylic acid ester copolymer resin, and ethylene-methacrylic acid copolymer resin, and ionomer resins, and one or more resins thereof.

[0045] As an example of a polyester resin, a polyester resin primarily composed of ethylene terephthalate units is preferred. Specifically, it may be a polyethylene terephthalate resin, but it may also be a copolymerized polyester or a blend thereof containing an acid component other than terephthalic acid in an amount of 35 mol% or less, based on the acid component, and an alcohol component other than ethylene glycol in an amount of 35 mol% or less, based on the alcohol component. Examples of acid components other than terephthalic acid include isophthalic acid, naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, p-β-oxyethoxybenzoic acid, diphenoxyethane-4,4'-dicarboxylic acid, 5-sodium sulfoisophthalic acid, hexahydroterephthalic acid, succinic acid, adipic acid, sebacic acid, dodecanedioic acid, dimer acid, trimellitic acid, and pyromellitic acid. Examples of alcohol components other than ethylene glycol include glycol components such as propylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexylene glycol, diethylene glycol, triethylene glycol, cyclohexanedimethanol, an ethylene oxide adduct of bisphenol A, trimethylolpropane, and pentaerythritol. Examples of polyester resins other than those mainly composed of ethylene terephthalate units include polyester resins mainly composed of butylene terephthalate units and polyester resins mainly composed of ethylene naphthalate units, and blends of these polyester resins may also be used.

[0046] Polyester resin is more preferably used as the resin layer 30, and one or more crystalline polyester resins selected from the group consisting of polyethylene terephthalate resin, polybutylene terephthalate resin, polyethylene terephthalate resin copolymerized with isophthalic acid, and polybutylene terephthalate resin copolymerized with isophthalic acid are particularly preferably used, with polyethylene terephthalate resin copolymerized with isophthalic acid being the most preferred. More specifically, the resin layer 30 is desirably a crystalline polyester resin primarily composed of ethylene terephthalate units containing 2 mol % to 25 mol % of isophthalic acid.

[0047] The resin layer 30 may be a multilayer resin layer, for example, a multilayer polyester resin layer having two or more layers in which isophthalic acid is copolymerized at different ratios. More specifically, the resin layer 30 may include a lower layer having a relatively high isophthalic acid copolymerization ratio and a surface layer having a relatively low isophthalic acid copolymerization ratio. More specifically, the lower layer may be a polyester resin primarily composed of ethylene terephthalate units containing 1 mol% to 20 mol% isophthalic acid, and the surface layer may be a polyethylene terephthalate resin or a polyester resin primarily composed of ethylene terephthalate units containing 15 mol% or less of isophthalic acid, preferably 1 mol% to 10 mol% isophthalic acid. In this case, the lower layer is the layer closest to the aluminum substrate 10, and the surface layer is the layer farthest from the aluminum substrate 10 compared to the lower layer. In this case, the thickness ratio (layer ratio) of the surface layer to the lower layer is preferably in the range of surface layer:lower layer=20:1 to 1:20, and more preferably in the range of surface layer:lower layer=10:1 to 1:10.

[0048] Furthermore, the resin layer 30 may be a resin layer in which a plurality of different resins are blended, such as a resin layer in which polyethylene terephthalate resin is blended with an ionomer resin, an ethylene-propylene copolymer resin, or an unsaturated carboxylic acid-modified polyolefin resin, or a resin layer in which polyethylene terephthalate resin or polyethylene terephthalate resin copolymerized with isophthalic acid is blended with polybutylene terephthalate resin, etc. In the case of a resin in which polyethylene terephthalate resin or polyethylene terephthalate resin copolymerized with isophthalic acid is blended with polybutylene terephthalate resin, it is preferable that the polybutylene terephthalate resin is blended in the range of 10 to 50% with the polyethylene terephthalate resin or polyethylene terephthalate resin copolymerized with isophthalic acid.

[0049] The thermoplastic resin such as the crystalline polyester resin may be formed into a film and then laminated onto an aluminum substrate, or may be formed by direct lamination in which a heated and melted thermoplastic resin is extruded into a film shape through a narrow slit of an extrusion molding machine and then laminated directly onto an aluminum substrate. When the film is formed and then laminated, the film is not particularly limited and may be, for example, an unstretched film, a uniaxially stretched film, or a biaxially stretched film.

[0050] The resin layer 30 can be compounded with known compounding agents for resins, for example, antiblocking agents such as amorphous silica, inorganic fillers such as calcium carbonate, magnesium carbonate, talc, and glass, various fibers such as glass fiber, carbon fiber, and aramid fiber, antistatic agents, antioxidants such as tocopherol, and ultraviolet absorbers, according to known methods.

[0051] The thermoplastic resin layer 30 may be formed on the surface treatment layer 20 via a conventional adhesive primer layer, such as an epoxy phenolic or polyester phenolic adhesive primer. The adhesive primer layer exhibits excellent adhesion to both the surface treatment layer and the resin layer. However, providing an adhesive primer layer on the inner surface of the seamless can suppresses metal exposure and provides excellent impact resistance (dent resistance) even when the can body is dented (defective) by external impact, such as being dropped, causing defects (cracks) in the resin layer. This prevents corrosion at the dented area, even when the contents are highly corrosive, such as acidic beverages. From the standpoint of adhesion and dent resistance, epoxy phenolic adhesive primers are preferably formed from paints containing epoxy resin and phenolic resin in a weight ratio of 50:50 to 99:1, particularly 60:40 to 95:5. From the viewpoint of adhesion and dent resistance, polyester phenol-based adhesive primers are preferably formed from paints containing polyester resin and phenol resin in a weight ratio of 50:50 to 99:1, and particularly 60:40 to 95:5. The adhesive primer layer is generally preferably formed to a thickness of 0.1 to 10 μm.

[0052] When the resin layer 30 is a crystalline resin such as polyethylene terephthalate, it is preferable that the resin layer 30 has oriented crystals therein, but it is not necessary that the resin layer 30 does not have oriented crystals therein. That is, when the resin-coated aluminum seamless can 100 is a drawn and ironed can, the resin layer 30 in the can body is given a processing orientation in the drawing and ironing process, and oriented crystals are formed inside the resin layer 30. On the other hand, the resin layer 30 in the can bottom is given a lower degree of processing orientation in the drawing and ironing process, and therefore the amount of oriented crystals therein is relatively smaller than that in the can body.

[0053] In this way, when the resin-coated aluminum seamless can 100 is a drawn and ironed can, it is preferable that the amount of oriented crystals contained in the resin layer 30 is greater in the can body than in the can bottom. The presence or absence of oriented crystals inside the resin layer 30 and their amount can be confirmed by a known method such as peak intensity using X-ray diffraction. In the case where a resin layer made of a crystalline resin such as polyethylene terephthalate is formed on the inner surface of the resin-coated seamless can of this embodiment, the X-ray diffraction intensity I from the (100) plane parallel to the surface of the resin layer 30 on the inner surface side is 1. （１００） and the X-ray diffraction intensity I from the parallel (1-10) plane （１－１０） X-ray diffraction intensity ratio (R) = I （１００） / I （１－１０） is preferably 1.8 or more in the can body and less than 1.8 in the can bottom. That is, to explain this point, the X-ray diffraction intensity ratio (R) of the resin layer on the inner surface of the can body characterizes the orientation structure of the crystals to the film surface, and the greater the X-ray diffraction intensity of the (100) plane relative to the X-ray diffraction intensity of the (1-10) plane, the more the plane orientation to the film surface is indicated.

[0054] When the resin-coated seamless can of this embodiment is a drawn and ironed can, it is desirable that the X-ray diffraction intensity ratio (R) of the resin layer of a crystalline resin such as polyethylene terephthalate on the inner surface of the can body be 1.8 or more, more preferably 2.2 or more, even more preferably 2.4 or more, and particularly preferably 2.6 or more, with the (100) plane preferentially oriented. This allows oriented crystals to form within the resin layer to a certain extent in the can height direction through drawing / thinning and / or ironing, thereby suppressing corrosion beneath the resin layer, known as under-film corrosion (UFC), when acidic contents are filled into the seamless can, and improving the impact resistance (dent resistance) of the resin layer. Furthermore, this prevents flavor components of the contents from adsorbing to the resin layer during storage as a canned product, thereby suppressing changes in the flavor of the contents. On the other hand, if the X-ray diffraction intensity ratio (R) of the can body is less than 1.8, UFC is more likely to occur, resulting in poor corrosion resistance. Furthermore, the impact resistance (dent resistance) also decreases, which is undesirable.

[0055] When the resin-coated seamless can of this embodiment is a drawn and ironed can, the X-ray diffraction intensity ratio (R) of the resin layer in the can bottom is preferably less than 1.8. That is, the orientation state of the resin layer in the can bottom exhibits the same orientation state as the resin layer before processing, so in order to accommodate the severe processing of the can body, it is desirable that the orientation state of the resin layer in the can bottom be substantially close to unoriented. Since the can bottom is not severely processed and is substantially preserved in the form of the resin-coated aluminum sheet before processing, corrosion resistance and impact resistance can be satisfied even in a nearly unoriented state.

[0056] On the other hand, when the resin-coated aluminum seamless can 100 is a drawn can, there is not much difference between the can body and the can bottom in the degree of processing orientation imparted to the resin layer 30. Therefore, the amount of oriented crystals contained in the resin layer 30 is approximately the same in the can body and the can bottom.

[0057] The thickness of the resin layer 30 is not particularly limited and can be the same as that of known seamless cans. More specifically, the thickness of the resin layer 30 is preferably in the range of 0.5 to 200 μm, more preferably 1 to 40 μm, even more preferably 2 to 30 μm, and particularly preferably 5 to 20 μm. When the seamless can is a drawn and ironed can, the thickness of the resin layer at the center of the can body (the thinnest portion near the center in the can height direction) is preferably 20 to 85%, preferably 20 to 75%, more preferably 20 to 60%, even more preferably 20 to 50%, particularly preferably 30 to 45%, and most preferably 30% or more but less than 40% of the thickness of the resin layer at the center of the can bottom. The thickness of the resin layer 30 at the center of the can bottom is preferably in the range of 0.5 to 200 μm, more preferably 1 to 40 μm, even more preferably 2 to 30 μm, and particularly preferably 5 to 20 μm.

[0058] On the other hand, when the resin-coated aluminum seamless can 100 is a drawn and ironed can, the thickness of the resin layer 30 in the can body is relatively thinner than the thickness of the resin layer 30 in the can bottom. This is because the can side wall is thinned overall in the drawing and ironing process.

[0059] On the other hand, when the resin-coated aluminum seamless can 100 is a drawn can, the resin layer 30 in the can body is compressed in the thickness direction by a mold during the drawing process. Therefore, when the resin-coated aluminum seamless can 100 is a drawn can, the thickness of the resin layer 30 in the can body is relatively thicker than that in the can bottom.

[0060] In this embodiment, the resin-coated aluminum seamless can 100 preferably has a lightness L* value of 85 or more on the can exterior surface. In this embodiment, the lightness L* value can be measured using a spectrophotometer in accordance with JIS Z 8781-4:2013. When measuring the lightness L* value, the can body of the resin-coated aluminum seamless can 100 is cut out and flattened, and the lightness L* value can be measured and evaluated at a portion with a can height of 60 mm and a rolling angle of 0°. In this embodiment, if the resin layer on the exterior surface of the seamless can is printed or if the resin layer itself is colored or has low transparency, it is desirable to remove the resin layer 30 by a known method and measure the lightness L* value of the can exterior surface, leaving only the aluminum substrate and the surface treatment layer.

[0061] The lightness L* value of the outer surface of the can is preferably 85 or more, more preferably 86 or more, and even more preferably in the range of 87 to 92. When the resin layer 30 is removed by a known method and the lightness L* value of the outer surface of the can is measured in a state in which only the aluminum base material and the surface treatment layer remain, the lightness L* value is preferably 86 or more, more preferably 87 or more, and even more preferably in the range of 88 to 93.

[0062] The chromaticity a* and b* values ​​of the outer surface of the resin-coated aluminum seamless can 100 are not particularly limited, but are preferably in the range of -5 or more and 5 or less, more preferably -3 or more and 3 or less.

[0063] In this embodiment, the resin-coated aluminum seamless can 100 has a color difference (ΔE) on the outer surface thereof from a reference can not having the surface treatment layer 20 of preferably less than 5, more preferably less than 4, and even more preferably less than 3.

[0064] The color difference (ΔE) is an index indicated using the L*a*b* color system defined in JIS Z8730:2009, and is calculated using the following formula based on the difference in CIE lightness L* and the difference in chromaticity a*, b* between two object colors. Lightness, chromaticity, and color difference can be measured using a colorimeter or the like.

[0065] An example of a specific method for calculating the color difference (ΔE) in this embodiment is as follows. The can body of the resin-coated aluminum seamless can 100 is cut out and flattened, and the lightness (L ＊ value) and chromaticity (a ＊ value and b ＊ In addition, the lightness (L value) of a can (reference product) manufactured in the same manner except that it does not have the surface treatment layer 20 is also measured. ＊ value) and chromaticity (a ＊ value and b ＊ Then, the color difference (ΔE) between the resin-coated aluminum seamless can 100 and the reference product is calculated using the following formula (1): ΔE=((ΔL*) ２ + (Δa*) ２ +(Δb*) ２ ) １／２ ...(1) ΔL*=L* １ -L* ０ , Δa*=a* １ -a* ０ , Δb*=b* １ -b* ０ ΔL*: Change in L* value, L* ０ : L* value of standard product, L* １ : L* value of this embodiment Δa*: change in a* value, a* ０ : a* value of the standard product, a* １ : a* value of this embodiment Δb*: change in b* value, b* ０ : b* value of standard product, b* １ : b* value of this embodiment

[0066] <Method for manufacturing resin-coated aluminum seamless can> The following describes a method for manufacturing the resin-coated aluminum seamless can 100. Note that the manufacturing method described in this embodiment is merely an example, and is not limited to this method.

[0067] The method for producing the resin-coated aluminum seamless can 100 includes at least (I) a step of producing a resin-coated aluminum plate, and (II) a can-making step of forming the obtained resin-coated aluminum plate into a seamless can.

[0068] (II) The can-making process for forming seamless cans will be described in detail below. (I) The manufacturing process for resin-coated aluminum sheets will be described later. Known forming methods can be used in the can-making process. For example, the resin-coated aluminum sheet is punched into a predetermined shape and size, and then formed into various containers using a press die. Conventionally known forming methods such as drawing, drawing and redrawing, drawing and ironing, deep drawing, and drawing, bending, stretching, and ironing can be used as the forming method. However, drawing and ironing is particularly preferred in this embodiment. The resin-coated aluminum sheet used in this embodiment has excellent adhesion between the resin layer and the surface treatment layer, and therefore can be formed into seamless cans by severe processes such as drawing, drawing and deep drawing, drawing and ironing, and drawing, bending, stretching, and ironing without causing breakage or peeling of the resin layer in the flange-forming portion. Furthermore, in this embodiment, by using a resin-coated aluminum plate on which a resin layer 30 has been formed in advance, it is possible to reduce the coefficient of friction of the surface against the processing tool, and processing can be performed under dry conditions without using a coolant (coolant / lubricant). Furthermore, the amount of cleaning water used in the container manufacturing process can be reduced, and the painting and baking processes performed after container molding can be omitted, thereby realizing container manufacturing with a low environmental impact.

[0069] In the can-making process for forming the seamless can of this embodiment, the can body of the seamless can is preferably thinned by bending and stretching by drawing and redrawing the resin-coated aluminum sheet, or by drawing and ironing, so that the thickness of the central part of the can body is 20 to 85%, preferably 20 to 75%, more preferably 20 to 60%, even more preferably 20 to 50%, still more preferably 25 to 45%, and most preferably 30 to 40% of the thickness of the can bottom. If the thickness is greater than the above range, the can body is not sufficiently thinned and is not fully satisfactory from the standpoint of economy. On the other hand, if the thickness is less than the above range, the resin layer cannot follow the processing, and there is a risk of metal exposure.

[0070] In the can-making process for forming seamless cans according to this embodiment, the resulting seamless cans are preferably subjected to at least one heat treatment to remove residual stresses in the resin layer caused by processing. Removing the residual stresses in the resin layer improves adhesion between the resin layer and the surface-treated layer after processing, and, when the resin layer is a crystalline resin such as polyethylene terephthalate, heat-sets oriented crystals in the can body. This heat treatment is generally performed at a temperature of Tg + 50°C or higher, based on the glass transition point (Tg) of the resin layer, and preferably within a range of Tg + 100 to the melting point (Tm) - 5°C. Temperatures lower than this range tend to insufficiently relieve the residual stresses in the resin layer, resulting in poor post-processing, such as necking-in. Temperatures higher than this range tend to dissolve the oriented crystals formed during can forming, resulting in poor corrosion resistance and impact resistance (dent resistance) of the can body. In the case of a multi-layer structure having two or more resin layers, it is preferable to perform heat treatment so that the temperature of the bottommost resin layer is within the above range. This heat treatment improves the heat resistance of the resin layer, improves adhesion to the aluminum substrate, and also improves processability in post-processing such as necking-in and flanging, as well as corrosion resistance, impact resistance (dent resistance), and flavor.

[0071] <Resin-coated aluminum sheet> A resin-coated aluminum sheet 300 that can be used to manufacture the resin-coated aluminum seamless can 100 is described below. FIG. 3 is a schematic diagram illustrating a resin-coated aluminum sheet 300 according to this embodiment. As shown in FIG. 3, the resin-coated aluminum sheet 300 includes an aluminum substrate 10′, a surface treatment layer 20′ formed on at least one surface of the aluminum substrate 10′, and a resin layer 30′ formed on the surface treatment layer 20′. While the resin-coated aluminum sheet 300 shown in FIG. 3a has the surface treatment layer 20′ and the resin layer 30′ on one surface thereof, the present disclosure is not limited thereto. As shown in FIG. 3b, a resin-coated aluminum sheet 310 having the surface treatment layer 20′ and the resin layer 30′ on both surfaces of the aluminum substrate 10′ may also be used. The aluminum substrate 10′, the surface treatment layer 20′, and the resin layer 30′ correspond to the aluminum substrate 10, the surface treatment layer 20, and the resin layer 30, respectively, included in the resin-coated aluminum seamless can 100 described above. Therefore, only the differences will be described below, and a description of the common configuration will be omitted.

[0072] In this embodiment, the thickness of the surface treatment layer 20' is preferably 2 nm or more from the viewpoint of resin adhesion. On the other hand, the upper limit of the thickness of the surface treatment layer 20' is preferably less than 100 nm from the viewpoint of color tone and corrosion resistance. The optimal thickness of the surface treatment layer 20' depends on the target can shape, etc., but is more preferably 5 nm or more but less than 100 nm, even more preferably 8 to 90 nm, particularly preferably 10 to 80 nm, and most preferably 12 to 45 nm.

[0073] In this embodiment, the thickness of the resin layer 30' is not particularly limited, but is preferably in the range of 0.5 to 200 μm, more preferably in the range of 1 to 40 μm, and even more preferably in the range of 2 to 20 μm. Generally, the thicker the resin layer, the better the corrosion resistance, but the lower the resin adhesion, so there is an optimal thickness range depending on the application.

[0074] The Pa / Pb ratio does not change due to forming processes such as drawing, drawing and ironing, etc. Therefore, the Pa / Pb ratio of the surface treatment layer 20′ in the resin-coated aluminum sheet 300 is characterized by being 0.13 to 3.00, similar to that of the resin-coated aluminum seamless can 100.

[0075] In this embodiment, when the resin layer 30' of the resin-coated aluminum sheet 300 is a crystalline resin such as polyethylene terephthalate, it is preferably unoriented from the viewpoint of processability, because this provides excellent drawing and thinning drawing and / or ironing processability, allowing the can body to be highly thin-walled, and also facilitating the increase in the height of seamless cans.

[0076] <Method for manufacturing resin-coated aluminum sheet> Next, a method for manufacturing the resin-coated aluminum sheet 300 in this embodiment (the above-mentioned (I) manufacturing process of the resin-coated aluminum sheet) will be described below. Note that the manufacturing method described here in this embodiment is merely one example, and is not limited to this method.

[0077] The method for producing a resin-coated aluminum sheet in this embodiment includes a surface treatment step of forming a surface treatment layer 20' containing aluminum hydroxide on an aluminum substrate 10', and a resin coating step of forming a resin layer 30'. Note that the surface treatment step is performed to detect a wavenumber of 850 to 1000 cm, which is mainly derived from the Al-O stretching vibration of amorphous alumina, in an infrared absorption spectrum measured by FT-IR. －１ The height of the absorbance peak is defined as Pa, and the wavenumber of 1000 to 1200 cm is mainly due to the Al-OH deformation vibration of aluminum hydroxide. －１ When the height of the absorbance peak is defined as Pb, the surface treatment layer 20' is formed so that the value of Pa / Pb is 0.13 to 3.00.

[0078] The surface treatment step is not particularly limited as long as it can set the peak ratio Pa / Pb to a value of 0.13 to 3.00. Examples of the surface treatment step include a method of immersing the aluminum base 10′ in a solution (treatment agent) at 20 to 100°C and pH 6 to 13 for 0.1 to 30 seconds, or a method of contacting the aluminum base 10′ with water vapor (treatment agent) at 100 to 140°C for 0.1 to 120 seconds.

[0079] That is, the treating agent for the surface treatment can be a solution at 20° C. to 100° C. or water vapor at 100° C. to 140° C. The higher the temperature of the treating agent, the shorter the time required to form the surface treatment layer 20′.

[0080] When treating the aluminum substrate 10′ by immersing it in a solution (treatment agent), the pH of the treatment agent can be in the range of 6 to 13. Aluminum hydroxide is hardly formed in an acidic solution with a pH of less than 6, but a stable coating can be formed in water with a pH of 7 or higher or an alkaline solution with a pH of 8 to 13.

[0081] The reason for using an alkali in the surface treatment solution is to dissolve, in an extremely short time, the naturally formed oxide film present on the surface of the aluminum substrate before treatment. Generally, the naturally formed oxide film on an aluminum substrate is a coating primarily composed of aluminum oxide, and can be dissolved in an alkaline solution in an extremely short time. However, the higher the pH of the solution, the higher the proportion of amorphous alumina in the surface treatment layer 20', so a more preferable pH range is pH 8 to 10.

[0082] The surface treatment solution used in the surface treatment step is preferably pure water. Ion-exchanged water with an electrical conductivity of 10 μS / cm or less may also be used. The reason why pure water or ion-exchanged water is preferred is that the proportion of amorphous alumina contained in the surface treatment layer 20′ increases as the phosphorus concentration, calcium concentration, silicon concentration, magnesium concentration, and iron concentration in the surface treatment solution increase. If any of the phosphorus concentration, calcium concentration, silicon concentration, magnesium concentration, and iron concentration exceeds 1 ppm, the proportion of amorphous alumina contained in the surface treatment layer 20′ increases sharply, so it is preferable to control the concentrations of these elements to 1 ppm or less. More preferably, it is 0.1 ppm or less.

[0083] When the surface treatment solution used in the surface treatment step is alkaline (pH 8 to 13), preferred solutions include an aqueous solution of sodium carbonate, an aqueous solution of sodium aluminate, an aqueous solution of sodium hydroxide, an aqueous solution of potassium hydroxide, etc. The water used in the alkaline solution is preferably the above-mentioned pure water or ion-exchanged water.

[0084] Specific examples of gases that can be used as the treatment agent include water vapor and superheated steam. In this case, the temperature of the water vapor is preferably 100°C to 140°C. Furthermore, the temperature of the superheated steam is preferably 120°C to 350°C. The higher the temperature, the shorter the treatment time required to form a surface treatment layer 20' suited to the application. In the case of superheated steam, the aluminum substrate surface becomes wet with condensation the moment it is placed in the superheated steam furnace, or a process is required in which the aluminum substrate 10', which has been previously wet with water, is placed in the superheated steam furnace and dried. This is because a coating containing aluminum hydroxide is rapidly formed when the moisture on the aluminum substrate surface evaporates.

[0085] The manufacturing method of this embodiment may include a pretreatment step prior to the surface treatment step. The pretreatment step is carried out as a step of removing a natural oxide film present on the surface of the aluminum base material 10'. Specific examples of the pretreatment step include immersion treatment using an alkaline solution and cathodic electrolysis treatment. Specific examples of immersion treatment conditions include an alkaline solution with a pH of 8 to 13, a solution temperature of 20°C to 90°C, and an immersion time of 0.1 to 10 seconds. Specific examples of cathodic electrolysis treatment conditions include an alkaline solution with a pH of 8 to 13, a solution temperature of 20°C to 90°C, a cathodic electrolysis time of 0.1 to 10 seconds, and a current density of 1 to 10 A / dm ２ The above pretreatment step removes the native oxide film present on the surface of the aluminum substrate and suppresses local dissolution of the aluminum substrate, thereby forming a more uniform surface treatment layer 20' containing aluminum hydroxide. In particular, from the viewpoint of homogenizing the surface treatment layer 20', cathodic electrolysis is preferable to immersion treatment because it can remove the native oxide film more uniformly. Furthermore, if necessary, a known degreasing treatment may be performed before the pretreatment step as a surface cleaning to remove rolling oil, rust-preventive oil, etc. The degreasing agent is not particularly limited, and known degreasing agents such as organic solvent-based degreasing agents and acidic or alkaline aqueous degreasing agents can be used.

[0086] Next, the resin coating process may involve forming a resin layer 30' on the surface-treated layer 20' formed as described above. The resin layer 30' can be formed by any method. For example, when the resin layer 30' is a thermoplastic resin, the resin may be directly laminated in a molten state onto the surface-treated aluminum plate, or a film formed on a separate line may be thermocompressed onto a surface-treated aluminum plate heated on a lamination line. Furthermore, as mentioned above, an adhesive primer layer may be formed between the surface-treated layer 20' and the resin layer 30' to enhance dent resistance. The adhesive primer layer may be previously formed on the surface-treated layer on the surface-treated aluminum plate, or may be previously formed on a resin layer such as a thermoplastic resin film. When the resin layer 30' is a thermosetting resin, the resin may be applied using a roll coater followed by drying in an oven, or may be spray-coated and then dried in an oven.

[0087] <Examples> The present disclosure will be described in more detail below with reference to examples. First, the measurement methods used in the examples will be described.

[0088] [Calculation of absorbance peak ratio (Pa / Pb)] The absorbance in the infrared absorption spectrum of the surface treatment layer 20 of the resin-coated aluminum seamless can 100 was calculated from the surface-treated aluminum plate using a Fourier transform infrared spectrophotometer (FT-IR) by a high-sensitivity reflection method (Reflection Absorption Spectroscopy (RAS) method) under the following conditions. A gold-deposited mirror was used as the background. A polarizer was used to detect only parallel polarized light.

[0089] Equipment: JASCO Corporation FTIR-6600 type A Measurement conditions: Measurement method: RAS method Accessories used: PIKE Advanced Grazing Angle Detector: MCT Wavenumber resolution: 4 cm －１ Number of measurements: 64 Measurement temperature: room temperature Measurement atmosphere: air Measurement wave number range: 4000 to 500 cm －１

[0090] The absorbance peak was measured on a surface-treated aluminum plate. First, as shown in Figure 4, the infrared absorption spectrum was measured at a few 1200 cm －１ Absorbance and wave number 850 cm －１ The absorbances at these points are connected by a straight line, which is used as the baseline. The peaks at wave numbers of 850 to 1000 cm are derived from the Al—O stretching vibration of amorphous alumina. －１ The highest point from the baseline within this range was taken as the absorbance peak height Pa. In addition, the peak originating from the Al-OH deformation vibration of aluminum hydroxide was taken as the peak height Pa within the wavenumber range of 1000 to 1200 cm. －１ Within this range, the highest point from the baseline was taken as the absorbance peak height Pb. The absorbance peak ratio (Pa / Pb) was calculated from the measured Pa and Pb. The values ​​are shown in Table 1 together with the calculated absorbance peak ratio (Pa / Pb). The absorbance peak ratio value obtained by the above-mentioned measurement method coincides with the absorbance peak ratio value obtained by measuring the resin-coated aluminum seamless can 100 after removing the resin layer 30 by a known method. An example of measuring the absorbance peak ratio value from the resin-coated aluminum seamless can 100 is shown below.

[0091] A 350 mL drawn and ironed can (resin-coated aluminum seamless can) obtained from the resin-coated aluminum plate of Example 4 produced by the method (ii) described below was heat-treated in an oven at 200° C. for 90 seconds. Next, a can wall portion having a height of 60 mm was cut into a 6 cm × 6 cm piece, and the resin layers 30 on the inner and outer surfaces were removed by a known method, leaving only the aluminum substrate 10 and the surface treatment layer 20. The absorbance peak and the absorbance peak ratio were measured by the method described above, and the results were Pa: 0.0045, Pb: 0.030, and Pa / Pb: 0.15.

[0092] [Calculation of the film thickness of the surface treatment layer] The film thickness of the surface treatment layer was calculated from the surface-treated aluminum plate using a time-of-flight secondary ion mass spectrometer (TOF-SIMS) under the following conditions. Mass analysis of the coating constituents was performed while repeatedly soft-etching at a constant rate using a Cs (cesium) ion gun from the surface side of the surface treatment layer of the surface-treated aluminum plate. Etching was continued until the aluminum substrate was reached, and the depth at which the secondary ion intensity of metallic aluminum derived from the aluminum substrate was half of the maximum intensity (secondary ion intensity of metallic aluminum when it reached the aluminum substrate) was taken as the film thickness of the surface treatment layer. The depth is the depth in terms of alumina.

[0093] Equipment: ION TOF, TOF. SIMS5 Measurement conditions: Primary ion type: Bi Etching gun type: Cs Measurement area: 50 μm × 50 μm

[0094] [Retort Adhesion Evaluation] Resin adhesion in a humid environment was tested and evaluated using the following method using drawn and ironed cans (resin-coated seamless aluminum cans) obtained from resin-coated aluminum sheets produced by method (i) described below. First, a cutter was used to make a slit in the film (resin layer) on the outer surface of the produced 350 mL drawn and ironed can at a height of 90 mm from the can bottom. The can was placed in a retort oven while immersed in tap water and subjected to retort treatment at 125°C for 45 minutes. The maximum film peel length below the cutter-made part of the removed can was measured and evaluated as follows: ⊚: Film peel length 10 mm or less; ◯: Film peel length more than 10 mm but not more than 20 mm; Δ: Film peel length more than 20 mm but not more than 30 mm; ×: Film peel length more than 30 mm

[0095] [Color Tone Evaluation] The can body of a 350 mL drawn and ironed can (resin-coated aluminum seamless can) obtained from the resin-coated aluminum sheet produced by the method (ii) described below was cut out and flattened. The color tone of the outer surface was measured at a can height of approximately 60 mm and at a rolling angle of 0°. The measuring instrument used was a portable integrating sphere spectrophotometer Ci64 manufactured by X-Rite. Specifically, the lightness (L ＊ value) and chromaticity (a＊ value and b ＊ After measuring the color difference (ΔE) from the reference product (Comparative Example 1), the color difference (ΔE) was calculated using the following formula (1).

[0096] ΔE = ((ΔL*) ２ + (Δa*) ２ +(Δb*) ２ ) １／２ ...(1) ΔL*=L* １ -L* ０ , Δa*=a* １ -a* ０ , Δb*=b* １ -b* ０ ΔL*: Change in L* value, L* ０ : L* value of Comparative Example 1, L* １ : L* value of the example Δa*: change in a* value, a* ０ : a* value of Comparative Example 1, a* １ : a* value of the example Δb*: change in b* value, b* ０ : b* value of Comparative Example 1, b* １ : b* value of Example Based on the obtained ΔE, the following evaluation was made: ⊚: ΔE is less than 3 ◯: ΔE is 3 or more but less than 4 △: ΔE is 4 or more but less than 5 ×: ΔE is 5 or more

[0097] In the 350 mL drawn and ironed cans (resin-coated aluminum seamless cans) obtained from the resin-coated aluminum sheets of Examples 3, 4, and 5 produced by the method (ii) described below, the can wall portion at a can height of approximately 60 mm and at a rolling angle of 0° was cut out to a size of 6 cm x 6 cm and flattened. Next, the outer resin layer 30 was removed by a known method, leaving only the aluminum substrate 10 and the surface treatment layer 20. After that, the lightness (L ＊ The L value of the drawn and ironed can of Example 3 was measured. ＊ Value: 90.31 L of the squeezed and ironed can of Example 4 ＊ Value: 88.29 L of the squeezed and ironed can of Example 5 ＊ Value: 86.97

[0098] [Corrosion Resistance Evaluation] First, a 350 mL drawn and ironed can (resin-coated aluminum seamless can) obtained from the resin-coated aluminum sheet prepared by the method (ii) described below was heat-treated at 200°C for 90 seconds in an oven. Next, a 4 cm x 4 cm test piece was cut from the inner surface of the can body at a height of 60 mm and at a 90° angle to the rolling direction. Two cross-cuts reaching the base material were made in the test piece with a cutter at a 45° angle to the rolling direction. The test piece was then immersed in a corrosion model solution (aqueous solution containing 1.0% and 0.5% sodium chloride and anhydrous citric acid by mass concentration, respectively) at 37°C for 2 weeks. The test piece was then removed from the model solution, and the cross-cut area and its surroundings were visually observed for peeling of the film (resin layer) or discoloration due to the generation of corrosion products. The maximum width of discoloration or film peeling around the cross-cut area was evaluated as follows: ◎: The maximum width is less than 1 mm per side. ○: The maximum width is 1 mm or more but less than 2 mm per side. △: The maximum width is 2 mm or more but less than 3 mm per side. ×: The maximum width is 3 mm or more per side.

[0099] [Dent Resistance Evaluation] The following method was used to evaluate 350 mL drawn and ironed cans (resin-coated aluminum seamless cans) obtained from resin-coated aluminum sheets prepared by the method (ii) described below and resin-coated aluminum sheets with an adhesive primer prepared by the method (iii) described below. The surface-treated aluminum sheets used were those of Example 2. First, the open edge of the drawn and ironed can was trimmed, followed by heat treatment at 200°C for 90 seconds in an oven. The open edge was then necked and flanged, after which 350 g of Coca-Cola (trademark) was filled into the can, and the lid was tightened in the usual manner. The can was then placed horizontally, and a 1 kg metal weight was dropped vertically from a height of 30 mm onto the underside of the sidewall (near the bottom) of the can to create a dent. The cans were then stored at 37°C for 1.5 months with the lids facing up, after which the state of corrosion in the dented areas on the inner surface of the cans was visually inspected to evaluate dent resistance. The results are shown below. Wrought and ironed cans of Example 2 (without adhesive primer): Corrosion present Wrought and ironed cans of Example 2 (with adhesive primer): No corrosion

[0100] [Calculation of X-ray diffraction intensity ratio (R)] A 350 mL drawn and ironed can (resin-coated aluminum seamless can) obtained from a resin-coated aluminum plate prepared by the method (ii) described below was subjected to heat treatment at 200°C for 90 seconds using an oven. Next, a 3 cm x 3 cm piece was cut out from the center of the can bottom, and the aluminum substrate was dissolved by a known method to leave only the inner resin layer. This was then fixed to a flat aluminum alloy plate with double-sided tape to prepare a measurement sample. Also, a 60 mm high can wall was cut out to a 3 cm x 3 cm piece, and the aluminum substrate was dissolved by a known method to leave only the inner resin layer. This was then fixed to a flat aluminum alloy plate with double-sided tape to prepare a measurement sample. The X-ray diffraction intensity ratio (R) of the (100) plane and the (1-10) plane was measured under the following measurement conditions, and the X-ray diffraction intensity ratio (R) of the can bottom and can wall (R = I （１００） / I （１－１０） was calculated.

[0101] X-ray diffraction apparatus: Rigaku Corporation, RINT-2500 X-ray: CuKα X-ray (wavelength λ=0.1542 nm) Tube voltage: 45 kV Tube current: 200 mA Divergence slit: 1 / 2° Receiving slit: 0.15 mm

[0102] The maximum X-ray diffraction intensity observed in the range of 2θ = 25.0 to 27.0° was used for the (100) plane. The maximum X-ray diffraction intensity observed in the range of 2θ = 22.0 to 24.0° was used for the (1-10) plane. The background was removed by the Sonneveld-Visser method.

[0103] The drawn and ironed can of Example 1 using the resin-coated aluminum plate produced by the method (ii) above was subjected to a heat treatment at 200°C for 90 seconds, and then the X-ray diffraction intensity ratio (R) of the inner resin layer of the can bottom and can wall was measured. （１００） / I （１－１０） The X-ray diffraction intensity ratio (R) of the can bottom was 1.7, and the X-ray diffraction intensity ratio (R) of the can wall was 2.9.

[0104] Example 1 An aluminum substrate having an alloy type of A3104, temper type of H19, and a thickness of 0.27 mm was prepared. After the rolling oil on the aluminum substrate was degreased by a known method, the aluminum substrate was immersed in a treatment liquid (ion-exchanged water at 95°C) (surface treatment step). The treatment time was 8 seconds. The water was removed with a roller, and the substrate was dried with a dryer to obtain a surface-treated aluminum plate having a surface treatment layer containing aluminum hydroxide formed on both sides in the same manner. The film thickness and absorbance peak ratio (Pa / Pb) of the surface treatment layer of the obtained surface-treated aluminum plate were calculated and are shown in Table 1.

[0105] Next, a resin layer was thermocompression bonded onto the surface-treated layer of the obtained surface-treated aluminum plate to prepare a resin-laminated plate (resin-coated aluminum plate). Specifically, the resin-laminated plate was prepared by the following three methods (i) to (iii).

[0106] (i) A non-stretched two-layer polyethylene terephthalate film (20 μm thick) was laminated on both sides of a heated surface-treated aluminum plate, and then quenched in water to obtain a resin-laminated plate. The two-layer polyethylene terephthalate film used was a film consisting of a surface layer of polyethylene terephthalate copolymerized with 2 mol % of isophthalic acid (IA) and a bottom layer of polyethylene terephthalate copolymerized with 15 mol % of isophthalic acid (IA), laminated in a layer ratio of 4:1 for the surface layer:bottom layer.

[0107] (ii) Stretched polyethylene terephthalate films were laminated on both sides of a heated surface-treated aluminum plate, and the plate was quenched in water to obtain a resin laminate. The surface that would become the inner surface of the can was a polyethylene terephthalate film (thickness 19 μm) copolymerized with 11 mol% isophthalic acid (IA). The surface that would become the outer surface of the can was a stretched two-layer polyethylene terephthalate film (thickness 12 μm) consisting of a surface layer of polyethylene terephthalate copolymerized with 7.5 mol% isophthalic acid (IA) and a bottom layer of polyethylene terephthalate copolymerized with 15 mol% isophthalic acid (IA), laminated in a layer ratio of 1:5 for the surface layer:bottom layer. X-ray diffraction confirmed that the films on the inner and outer surfaces after lamination were unoriented.

[0108] (iii) Stretched polyethylene terephthalate films were laminated on both sides of the heated surface-treated aluminum plate, and the plate was quenched in water to obtain a resin laminate. The surface that would become the inner surface of the can was a polyethylene terephthalate film (19 μm thick) copolymerized with 11 mol% isophthalic acid (IA), with a polyester phenol-based adhesive primer pre-applied to a thickness of 1 μm on the laminated surface. The surface that would become the outer surface of the can was a stretched two-layer polyethylene terephthalate film (12 μm thick) consisting of a surface layer of polyethylene terephthalate copolymerized with 7.5 mol% isophthalic acid (IA) and a bottom layer of polyethylene terephthalate copolymerized with 15 mol% isophthalic acid (IA) in a layer ratio of 1:5. X-ray diffraction confirmed that the inner and outer films after lamination were unoriented.

[0109] The resin laminate sheet was coated on both sides with 50 mg / m ２ The first cup was then punched out to a blank diameter of 142 mm to prepare a first cup. This first cup was then processed into a 350 mL drawn and ironed can with a reduction rate of 65% using a can-making machine (BodyMaker). Can body diameter: approximately 66 mm, Can body height: approximately 130 mm, Thickness near the center of the can body relative to the original plate thickness (can bottom): approximately 35%

[0110] The drawn and ironed cans thus obtained were evaluated for retort adhesion on the exterior of the can, color tone on the exterior of the can, and corrosion resistance on the interior of the can. The results of each evaluation are shown in Table 1.

[0111] (Examples 2 to 5) The immersion time in the treatment solution (treatment time) in the surface treatment step was as shown in Table 1. Other than that, the same procedures as in Example 1 were carried out. The results are shown in Table 1.

[0112] (Comparative Example 1) An aluminum substrate having an alloy type of A3104, temper type of H19, and a thickness of 0.27 mm was prepared. After the rolling oil on the aluminum substrate was degreased by a known method, the aluminum substrate was evaluated in the same manner as in Example 1 without undergoing any surface treatment. The results are shown in Table 1. The coating that formed naturally after degreasing was a coating mainly composed of amorphous alumina, and the absorbance peak ratio (Pa / Pb) was 13.98. The results are shown in Table 1.

[0113] (Comparative Examples 2 to 5) The immersion time in the treatment solution (treatment time) in the surface treatment step was as shown in Table 1. Other than that, the same procedures as in Example 1 were carried out. The results are shown in Table 1.

[0114] (Reference Example) Using an aluminum alloy plate having a phosphate chromate treatment film, cans were drawn and ironed and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0115]

[0116] From the above examples and comparative examples, it was confirmed that by setting the Pa / Pb value of the surface treatment layer to 0.13 to 3.00, it was possible to obtain a resin-coated aluminum seamless can that combines resin adhesion and color tone on the outer surface of the can after retort treatment. It was also confirmed that by setting the Pa / Pb value to 0.30 to 3.00, it was possible to obtain a resin-coated aluminum seamless can that also combines excellent corrosion resistance on the inner surface of the can.

[0117] The resin-coated aluminum seamless can of the present disclosure is suitable for use as a beverage can or a beverage cup.

[0118] 100 Resin-coated aluminum seamless can 10 Aluminum substrate 20 Surface treatment layer 30 Resin layer

Claims

1. An aluminum substrate, a surface treatment layer formed on at least one surface of the aluminum substrate, and a resin layer formed directly or indirectly on the surface treatment layer, wherein the surface treatment layer contains aluminum hydroxide, and has an infrared absorption spectrum measured by FT-IR with a wave number of 850 to 1000 cm. －１ The height of the absorbance peak is defined as Pa, and the wave number is 1000 to 1200 cm －１ wherein, when the height of the absorbance peak of the resin-coated aluminum seamless can is defined as Pb, a value of Pa / Pb is 0.13 to 3.

00.

2. The resin-coated aluminum seamless can according to claim 1, wherein the thickness of the surface treatment layer is 2 nm or more and less than 100 nm.

3. The resin-coated aluminum seamless can according to claim 1 or 2, wherein the L* value in the can body is 85 or more.

4. The resin-coated aluminum seamless can according to claim 1 or 2, wherein the resin layer contains a crystalline polyester resin.

5. The resin-coated aluminum seamless can according to claim 1 or 2, which is a drawn and ironed can.

6. The resin-coated aluminum seamless can according to claim 5, wherein the thickness of the central portion of the can body is 20 to 85% of the thickness of the central portion of the can bottom.

7. The resin-coated aluminum seamless can according to claim 1 or 2, wherein the amount of oriented crystals contained in the resin layer is greater in the can body than in the can bottom.

8. The resin-coated aluminum seamless can according to claim 1 or 2, wherein the resin layer contains a crystalline polyester resin, and the crystalline polyester resin is a polyester resin mainly composed of ethylene terephthalate units and containing 2 mol % to 25 mol % of isophthalic acid.

9. X-ray diffraction intensity I from the (100) plane parallel to the surface of the resin layer （１００） and the X-ray diffraction intensity I from the parallel (1-10) plane （１－１０） X-ray diffraction intensity ratio (R) = I （１００） / I （１－１０） 3. The resin-coated aluminum seamless can according to claim 1, wherein the can body has a viscosity of at least 1.8 and the can bottom has a viscosity of less than 1.

8.

10. The resin-coated aluminum seamless can according to claim 1 or 2, wherein the resin layer is a multi-layer resin layer, and the thickness ratio of the surface layer to the lower layer is surface layer:lower layer=20:1 to 1:

20.

11. The resin-coated aluminum seamless can according to claim 1 or 2, which has the surface treatment layer and the resin layer on the outer surface side of the can, and the Pa / Pb value of the surface treatment layer is 0.13 to 3.

00.

12. The resin-coated aluminum seamless can according to claim 1 or 2, which has the surface treatment layer and the resin layer on the inside surface of the can, and the Pa / Pb value of the surface treatment layer is 0.30 to 3.

00.

13. An aluminum substrate, a surface treatment layer formed on at least one surface of the aluminum substrate, and a resin layer formed on the surface treatment layer, wherein the surface treatment layer contains aluminum hydroxide, and has an infrared absorption spectrum measured by FT-IR with a wave number of 850 to 1000 cm. －１ The height of the absorbance peak is defined as Pa, and the wave number is 1000 to 1200 cm －１ wherein, when the height of the absorbance peak of the resin-coated aluminum sheet is defined as Pb, the value of Pa / Pb is 0.13 to 3.

00.

14. A resin-coated aluminum seamless can comprising the resin-coated aluminum sheet according to claim 13.

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