ALUMINUM CAN LIDS WITH PLASTIC COATING AND ALUMINUM SHEETS WITH PLASTIC COATING

Abstract

The invention proposes a resin-coated aluminum can lid with resin adhesion, corrosion resistance, and harmonious color. The resin-coated aluminum can lid comprises an aluminum substrate, a surface treatment layer formed on at least one side of the aluminum substrate, and a resin layer formed on the surface treatment layer. The surface treatment layer contains aluminum hydroxide, and has a Pa / Pb value of 0.14 to 3.50 where, in the FT-IR infrared absorption spectrum, the height of the absorption peak at wavelengths from 850 to 1000 cm-1 is determined as Pa and the height of the absorption peak at wavelengths from 1000 to 1200 cm-1 is determined as Pb.

Description

Resin-coated aluminum can lids, resin-coated aluminum sheets

[0001] The present disclosure relates to a resin-coated aluminum can lid and a resin-coated aluminum sheet.

[0002] Conventionally, aluminum sheets, which are lightweight and easy to form, have been suitably used as metal materials for food cans, beverage cans, etc. Resin-coated aluminum sheets, which are aluminum sheets on which a coating film or a resin layer such as a thermoplastic resin film is formed, have long been known as can materials, and it is also well known that these resin-coated aluminum sheets are processed to form can lids for beverage cans, etc.

[0003] The aluminum sheets used for such resin-coated aluminum sheets for can lid 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 after the formation of a resin layer. An example of such a surface treatment is chromate phosphate treatment. Surface-treated aluminum sheets that have been subjected to chromate phosphate treatment have been widely used because they have excellent adhesion and corrosion resistance after the formation of a resin layer, but there is an increasing demand for chromium-free surface treatments from the perspective of environmental protection.

[0004] 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, and disclose that containers and the like are formed using aluminum substrates that have been subjected to these treatments.

[0005] 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

[0006] The aluminum hydroxide coating formed on the surface of an aluminum substrate is thought to be 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 for its 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.

[0007] However, when this aluminum hydroxide coating treatment is applied to surface-treated aluminum sheets for can ends, the following problems arise: Surface-treated aluminum sheets for can ends are used in combination with a wide variety of coatings and thermoplastic resin films depending on the application, but when an aluminum hydroxide coating treatment is combined with a specific coating or thermoplastic resin film, the corrosion resistance and / or resin adhesion may be poor, and the aluminum hydroxide coating treatment has not been usable in a wide range of applications like phosphate chromate treatment.

[0008] On the other hand, many can ends made of aluminum plate have an appearance that makes use of the excellent color tone of the aluminum base material, such as a beautiful silvery-white color and metallic luster. However, when the above-mentioned aluminum hydroxide coating treatment is applied, depending on the treatment conditions for forming the coating, the inherent silvery-white color and metallic luster of the aluminum base material may be lost, resulting in a loss of color tone.

[0009] The above-mentioned patent documents do not fully consider the adhesion to the wide variety of coating films and thermoplastic resin films, or the corrosion resistance after the formation of a resin layer. Furthermore, they do not provide any knowledge about the deterioration in color tone of the aluminum substrate caused by an aluminum hydroxide coating, and therefore do not provide a solution to these problems.

[0010] The present disclosure has been made in view of solving the above problems, and has as its object to provide a resin-coated aluminum can closure that can ensure adhesion and corrosion resistance even when combined with a wide range of coatings and thermoplastic resin films and also has an excellent color tone. It is also an object to provide a resin-coated aluminum sheet for producing the resin-coated aluminum can closure.

[0011] In order to solve the above-mentioned problems, one embodiment of the present invention provides a resin-coated aluminum can lid, which includes 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 of the sample is defined as Pb, the value of Pa / Pb is 0.14 to 3.50.

[0012] 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 coating film 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 of the sample is defined as Pb, the value of Pa / Pb is 0.14 to 3.50.

[0013] According to the present disclosure, it is possible to provide a resin-coated aluminum can lid that combines resin adhesion, corrosion resistance, and color tone.

[0014] FIG. 1 is a schematic plan view of a resin-coated aluminum can lid according to an embodiment. FIG. 2 is a schematic cross-sectional view of a resin-coated aluminum can lid according to an embodiment. FIG. 3 is a schematic cross-sectional view of a resin-coated aluminum can lid according to an embodiment. FIG. 4 is a schematic cross-sectional view of a resin-coated aluminum plate according to an embodiment. FIG. 5 is a diagram showing an example of an infrared absorption spectrum. FIG. 6 is a diagram showing a schematic view of a test piece used for evaluating paint adhesion. FIG. 7 is a diagram showing a schematic view of a test piece and a test method used for evaluating resin adhesion. FIG. 8 is a diagram showing a schematic view of a test piece used for evaluating openability. FIG. 9 is a diagram showing a schematic view of a test piece used for evaluating corrosion resistance after can lid processing.

[0015] Hereinafter, an embodiment of a resin-coated aluminum can lid according to the present disclosure will be described with reference to the drawings. In the present disclosure, the term "color tone" refers to the color difference (ΔE) and brightness (L ＊ value).

[0016] <Resin-coated aluminum can lid 100> Fig. 1 is a plan view schematically showing a resin-coated aluminum can lid 100 according to this embodiment. Fig. 2 is a view schematically showing a cross section taken along the line A-A in Fig. 1. As shown in the figure, the resin-coated aluminum can lid 100 is a stay-on type easy-open can lid in which the rear end of a tab fixed to the top plate of the can lid at a position outside the opening flap is pulled up, thereby pressing the front end of the tab firmly against the upper surface of the opening flap to break the score line surrounding the opening flap and push the opening flap into the can body.

[0017] 1 and 2 , the resin-coated aluminum can lid 100 includes a central panel portion 4, a reinforcing annular groove 5, and a seaming portion on the outermost periphery. The central panel portion 4 has an intended opening portion 7 surrounded by scores 6, and a tear-opening tab 8 fixed thereto via a rivet 9. The tear-opening tab 8 includes a gripping ring 11, a pushing tip 12, and a rivet fixing tongue 13, and the pushing tip 12 is attached so as to overlap the intended opening portion 7.

[0018] As shown in FIG. 2 , the reinforcing annular groove 5 comprises an inner wall portion 14, a radius portion 15, and an outer wall portion (chuck wall) 16. The outer wall portion 16 is connected to a seaming panel portion 17 and a curl portion 18. The backside of the seaming panel portion 17 and the curl portion 18 forms a groove 19, which is lined with a sealing rubber composition (not shown) and forms a double-seamed seal between the can body flange (not shown). However, the shape of the resin-coated aluminum can end 100 of this embodiment is not limited to the shape shown in FIG. 1 and can be any known shape for can ends used for beverage cans, food cans, etc. That is, it includes so-called full-open type can ends, can ends that are seamed to the can body and opened with a can opener, and bottom ends for three-piece cans, etc.

[0019] Fig. 3 is an enlarged cross-sectional view of part B in Fig. 2. As shown in Fig. 3, the resin-coated aluminum can lid 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.

[0020] In Fig. 3(A), the resin-coated aluminum can lid 100 has a surface treatment layer 20 and a resin layer 30 on the outer surface side thereof, but the present invention is not limited to this. That is, the resin-coated aluminum can lid 100 may have a surface treatment layer 20 and a resin layer 30 on the inner surface side thereof (not shown). Furthermore, as shown in Fig. 3(B), the surface treatment layer 20 and the resin layer 30 may be provided on both the inner surface side and the outer surface side thereof in this order from the aluminum base material 10. In addition, when the resin layer 30 is provided on both surfaces thereof as shown in Fig. 3(B), the type and thickness of the resin layer on the inner surface side and the outer surface side of the can lid may be the same or different.

[0021] <Aluminum substrate 10> In the resin-coated aluminum can lid 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 5000 series or 3000 series aluminum alloy plate according to the JIS standard is used.

[0022] <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. －１It is known that the peak appearing in this range is an absorbance peak of Al-OH deformation vibration derived from aluminum hydroxide.

[0023] 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.

[0024] 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).

[0025] 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.

[0026] As described above, in the resin-coated aluminum can lid 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 －１The 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 0.14 to 3.50. This is for the following reasons.

[0027] 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.

[0028] 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 can lid is as follows.

[0029] First, we will explain from the viewpoint of resin adhesion. When an aluminum hydroxide coating is formed on an aluminum substrate by the method described below, as the growth of the acicular structure of boehmite or the like progresses, the coating changes from being mainly amorphous, and the proportion of aluminum hydroxide in the coating increases. However, if the growth of this acicular structure is insufficient, it becomes difficult to exert an anchoring effect on a resin layer such as a coating film or a thermoplastic resin film. Therefore, the present inventors have considered the need to control the degree of growth of the acicular structure from the viewpoint of resin adhesion, and as a result of extensive research, have found that by setting the peak ratio "Pa / Pb" to 3.50 or less, a state in which the acicular structure has grown sufficiently can be achieved, and good resin adhesion can be obtained.

[0030] Next, the corrosion resistance will be explained. The aluminum hydroxide coating such as boehmite can contain amorphous alumina (Al ２ O ３ ), but unlike aluminum hydroxide, which is hardly soluble, amorphous alumina is water-soluble and may dissolve when it comes into contact with acidic contents, etc.

[0031] Therefore, if the aluminum hydroxide coating between the aluminum substrate and the resin layer contains a high proportion of water-soluble amorphous alumina, it is believed that the coating's insoluble or poorly soluble properties cannot be maintained. Therefore, if a defect occurs in the resin layer for some reason, causing the contents to come into contact with the aluminum hydroxide coating, a portion of the coating will dissolve, making it more susceptible to corrosion beneath the resin layer, known as under-film corrosion (UFC), and making it difficult to achieve sufficient corrosion resistance. Therefore, the inventors believed that controlling the proportion of amorphous alumina in the coating was necessary to achieve corrosion resistance, and after extensive research, they discovered that by setting the peak ratio "Pa / Pb" to 3.50 or less, the coating's insoluble or poorly soluble properties in the contents can be maintained and sufficient corrosion resistance can be achieved.

[0032] Next, we will explain from the perspective of color tone. When an aluminum hydroxide coating is formed on an aluminum substrate, as the growth of an acicular structure such as boehmite progresses, the unevenness of the coating tends to scatter light. It has been found that if the acicular structure grows excessively, the color gradually changes from silvery white to white due to light scattering, and the metallic luster also weakens. Therefore, the inventors of the present invention have intensively investigated the need to control the degree of growth of the acicular structure in order to suppress changes in color tone due to coating formation. As a result, they have found that by setting the peak ratio "Pa / Pb" to 0.14 or more, the acicular structure can be grown appropriately, resulting in a good color tone.

[0033] For these reasons, it is important in the present invention that the peak ratio "Pa / Pb" of the surface treatment layer (aluminum hydroxide coating) be within the range of 0.14 to 3.50. This makes it possible to obtain a resin-coated aluminum can lid that has the required resin adhesion, corrosion resistance, and color tone.

[0034] In the surface treatment layer of the present invention, the aforementioned peak ratio "Pa / Pb" is preferably in the range of 0.14 to 3.50, preferably 0.15 to 3.30, more preferably 0.20 to 3.00, even more preferably 0.30 to 2.50, and particularly preferably 0.40 to 2.30. If the peak ratio "Pa / Pb" is greater than the above range, resin adhesion and corrosion resistance will be poor for the reasons described above. On the other hand, if the peak ratio "Pa / Pb" is less than the above range, color tone will be poor for the reasons described above. Furthermore, because the acicular structure has grown excessively, it is presumed that the coating is prone to cohesive failure during processing. This creates gaps (voids) in the coating at the processed area, which allows the content liquid to penetrate, making under-film corrosion (UFC) more likely to occur and resulting in poor corrosion resistance. Furthermore, depending on the type of resin layer, the coating may be prone to cohesive failure, resulting in reduced resin adhesion.

[0035] In this embodiment, the thickness (film thickness) of the surface treatment layer 20 is preferably 2 nm or more from the viewpoint of resin adhesion to the resin-coated aluminum can lid 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 viewpoint of color tone and corrosion resistance. The optimal thickness of the surface treatment layer 20 depends on the target can lid shape, etc., but is more preferably 5 nm or more and less than 70 nm, even more preferably 6 to 60 nm, particularly preferably 7 to 50 nm, and most preferably 8 to 35 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 and corrosion resistance may be deteriorated.

[0036] In this embodiment, the thickness of the surface treatment layer 20 can be measured, for example, by using time-of-flight secondary ion mass spectrometry (TOF-SIMS). TOF-SIMS involves irradiating the surface of a solid sample to be analyzed with a primary ion beam from a primary ion gun, and then mass-separating and mass-analyzing secondary ions emitted by sputtering from the sample surface 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 data for the ion intensity of the secondary ions, i.e., the target element ions or molecular ions bonded to the target element.

[0037] 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 the conversion.

[0038] 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.

[0039] <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.

[0040] In this embodiment, the resin layer 30 may be made of a known coating film or thermoplastic resin film that is used to coat a metal substrate.

[0041] <Resin Layer (Coating Film)> Examples of the coating film include coating films formed from coating compositions containing thermosetting resins, such as amino resins such as urea resins (urea resins), melamine resins, and benzoguanamine resins, phenolic resins, furan resins, xylene resins, ketone resins, alkyd resins, unsaturated polyester resins, epoxy resins, epoxy acrylic resins, epoxy phenolic resins, bismaleimide resins, triallyl cyanurate resins, thermosetting acrylic resins, silicone resins, and oil-based resins, or thermoplastic resins, such as vinyl chloride organosols, vinyl chloride-vinyl acetate copolymers, partially saponified vinyl chloride-vinyl acetate copolymers, vinyl chloride-maleic acid copolymers, vinyl chloride-maleic acid-vinyl acetate copolymers, acrylic resins, polyester resins (saturated polyester resins), and polyolefin resins. These resins can be used alone or in combination as components of the coating composition. Of these resins, the above-mentioned amino resins, phenol resins, epoxy resins, epoxy acrylic resins, epoxy phenolic resins, vinyl chloride organosols, acrylic resins, saturated polyester resins and polyolefin resins are preferred, and coating films formed from coating compositions containing one or more of these, specifically epoxy coating films, epoxy acrylic coating films, epoxy phenolic coating films, epoxy urea coating films, polyester phenolic coating films, polyester amino coating films, vinyl chloride organosol coating films and polyolefin coating films are more preferred, with epoxy acrylic coating films, polyester phenolic coating films, polyester amino coating films and vinyl chloride organosol coating films being even more preferred.Furthermore, as the inner coating film formed on the inner surface of the can lid, an epoxy acrylic coating film, an epoxy phenolic coating film, an epoxy urea coating film, a polyester phenolic coating film, a polyester amino coating film, a vinyl chloride organosol coating film, or a polyolefin coating film is preferred, and an epoxy acrylic coating film, an epoxy phenolic coating film, a polyester phenolic coating film, or a vinyl chloride organosol coating film is more preferred, while as the outer coating film formed on the outer surface of the can lid, an epoxy acrylic coating film, an epoxy urea coating film, a polyester amino coating film, or a polyolefin coating film is more preferred, and an epoxy acrylic coating film or a polyester amino coating film is more preferred. The coating composition for forming the coating film can be in the form of either an aqueous coating film in which the coating constituents are dissolved in an aqueous solvent, or a solvent-based coating film in which the coating constituents are dissolved in an organic solvent.

[0042] <Resin Layer (Thermoplastic Resin Film)> As the thermoplastic resin constituting the thermoplastic resin film, 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 can be preferably used.

[0043] Among the thermoplastic resins, polyolefin resins or polyester resins, and mixtures thereof are more preferably applicable. Examples of polyolefin resins 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 are preferably applicable. Examples of polyester resins include polyester resins primarily composed of ethylene terephthalate units. Specifically, polyethylene terephthalate resin may be used, but it may also be a copolymer polyester resin alone 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 are also acceptable.

[0044] 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.

[0045] The resin layer 30 may be a multi-layer resin layer, for example, two or more polyester resin layers in which isophthalic acid is copolymerized at different ratios. More specifically, the resin layer 30 may include a lower layer in which the copolymerization amount of isophthalic acid is relatively high and a surface layer in which the copolymerization amount of isophthalic acid is relatively low. More specifically, the lower layer may be a polyester resin mainly 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 mainly 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 relatively 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 20:1 to 1:20, more preferably 10:1 to 1:10.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] Furthermore, the resin layer 30 made of a thermoplastic resin film 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. For epoxy phenolic adhesive primers, a paint containing an epoxy resin and a phenolic resin in a weight ratio of 50:50 to 99:1, particularly a weight ratio of 60:40 to 95:5, is preferred from the standpoint of adhesion and corrosion resistance. For polyester phenolic adhesive primers, a paint containing a polyester resin and a phenolic resin in a weight ratio of 50:50 to 99:1, particularly a weight ratio of 60:40 to 95:5, is preferred from the standpoint of adhesion and corrosion resistance. The adhesive primer layer is generally formed to a thickness of 0.1 to 10 μm, preferably 0.3 to 3 μm.

[0050] When the resin layer 30 is made of a crystalline resin such as polyethylene terephthalate, it is preferable that the resin layer 30 has oriented crystals therein from the viewpoint of opening properties, but it is not necessary that the resin layer 30 has oriented crystals therein.

[0051] The thickness of the resin layer 30 is not particularly limited, and can be the same as that of known can lids. More specifically, the thickness of the resin layer 30 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. Furthermore, when the resin layer 30 is a coating, the upper limit of the thickness is particularly preferably 15 μm. Furthermore, when the resin layer 30 is a coating, the coating amount is 10 to 200 mg / dm ２ The range is preferably 30 to 150 mg / dm ２ The range is more preferable.

[0052] In the present disclosure, the resin-coated aluminum can lid 100 preferably has a lightness L* value of 85.5 or more on the outer surface side. Furthermore, in the present disclosure, the lightness L* value can be measured using a spectrophotometer in accordance with JIS Z 8781-4:2013. In the present disclosure, if the resin layer itself on the outer surface of the can lid 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 outer surface of the can lid, leaving only the aluminum substrate and the surface treatment layer.

[0053] The lightness L* value of the outer surface of the can lid is preferably 85.5 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 lid 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.

[0054] The chromaticity a* and b* of the outer surface of the resin-coated aluminum can lid 100 are not particularly limited.

[0055] In the present disclosure, the resin-coated aluminum can lid 100 preferably has a color difference (ΔE) on the outer surface from a reference can lid that does not have a surface treatment layer 20 of less than 3, more preferably less than 2.

[0056] 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.

[0057] A specific example of a method for calculating the color difference (ΔE) in this embodiment is as follows. The resin-coated aluminum can lid 100 is cut out, and the lightness (L ＊ value) and chromaticity (a ＊ value and b ＊ In addition, the lightness (L value) of a can lid (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 can lid 100 and a reference product is calculated using the following formula (1).

[0058] 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

[0059] In the present disclosure, the resin-coated aluminum can lid 100 preferably has a specular gloss on the outer surface, as measured in 60° gloss according to JIS Z 8741:1997, of 85 or more, and more preferably 90 or more. When the specular gloss is 85 or more, the metallic luster characteristic of an aluminum substrate is felt, and dullness and whitishness are suppressed, resulting in a lid with a desirable appearance. Note that the specular gloss in the present disclosure is measured according to the measurement method specified in JIS Z 8741:1997.

[0060] <Method for manufacturing resin-coated aluminum can lid> The following describes a method for manufacturing the resin-coated aluminum can lid 100. Note that the manufacturing method described here in this embodiment is merely an example, and is not limited to this method.

[0061] The method for manufacturing the resin-coated aluminum can lid 100 includes at least (i) a resin-coated aluminum plate manufacturing step, and (ii) a lid-making step of forming the obtained resin-coated aluminum plate into a can lid.

[0062] (ii) The can lid forming process will be described in detail below. (i) The resin-coated aluminum sheet manufacturing process will be described later. Known forming methods, such as press forming, can be used in the lid forming process. First, a resin-coated aluminum sheet or coil is punched into a predetermined shape and size, and then, or simultaneously, formed into a lid using a press mold. This method is generally applied to stay-on-tab type easy-open lids and full-open type easy-open lids.

[0063] <Resin-coated aluminum sheet> A resin-coated aluminum sheet 300 that can be used to manufacture the resin-coated aluminum can lid 100 is described below. FIG. 4 is a schematic diagram illustrating the resin-coated aluminum sheet 300 according to this embodiment. As shown in FIG. 4, 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′. The resin-coated aluminum sheet 300 shown in FIG. 4( a) has the surface treatment layer 20′ and the resin layer 30′ on one surface thereof, but is not limited thereto. 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′ as shown in FIG. 3( b) 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 can lid 100 described above. Therefore, only the differences will be described below, and a description of the common configuration will be omitted.

[0064] 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 lid shape, etc., but is more preferably 5 nm or more but less than 70 nm, even more preferably 6 to 60 nm, particularly preferably 7 to 50 nm, and most preferably 8 to 35 nm.

[0065] 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. Furthermore, when the resin layer 30 is a coating film, the upper limit of the thickness is particularly preferably 15 μm. Furthermore, when the resin layer 30 is a coating film, the coating amount is 10 to 200 mg / dm ２ The range is preferably 30 to 150 mg / dm ２ Generally, the thicker the resin layer, the better the corrosion resistance, but the resin adhesion may decrease, so there is an optimum thickness range depending on the application.

[0066] The Pa / Pb ratio does not change during the forming process into a can lid. Therefore, the Pa / Pb ratio of the surface treatment layer 20′ in the resin-coated aluminum sheet 300 is characterized by being 0.14 to 3.50, similar to that of the resin-coated aluminum can lid 100.

[0067] <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 step 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.

[0068] 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 0.14 to 3.50.

[0069] The surface treatment step is not particularly limited as long as it can set the peak ratio Pa / Pb to a value of 0.14 to 3.50. 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.

[0070] 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′.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] Next, examples of the resin coating process include a method of 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, in the case of a coating film, a coating composition can be applied using a roll coater and then dried in an oven, or a spray coating can be applied and then dried in an oven. In the case of a thermoplastic resin film, a method of directly laminating a molten resin onto the surface-treated aluminum plate, or a method of processing a film on a separate line and then thermocompressing it onto a heated surface-treated aluminum plate on a lamination line, can be used. Furthermore, as mentioned above, an adhesive primer layer may be formed between the surface-treated layer 20' and the resin layer 30' to enhance resin adhesion. 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.

[0078] <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.

[0079] [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 can lid 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.

[0080] 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

[0081] The absorbance peak was measured on a surface-treated aluminum plate prepared by the method described below. First, as shown in FIG. 5, the absorbance peak was measured at several 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. This is shown together with the calculated absorbance peak ratio (Pa / Pb) in Table 1. The absorbance peak ratio value obtained by the above-mentioned measurement method matches the absorbance peak ratio value obtained by measuring the resin-coated aluminum can lid 100 after removing the resin layer 30 by a known method.

[0082] [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.

[0083] Equipment: ION TOF, TOF. SIMS5 Measurement conditions: Primary ion type: Bi Etching gun type: Cs Measurement area: 50 μm × 50 μm

[0084] [Coating Adhesion Evaluation (T-Peel Evaluation)] The coating adhesion when coated with a coating film was evaluated by the following method (T-peel evaluation) using a resin-coated aluminum plate prepared by the method described below. First, two resin-coated aluminum plates cut to 5 mm x 100 mm were prepared, and the coated inner surfaces were placed face to face with a nylon film of the same width sandwiched between them and hot-pressed. The substrate at the position where the film was not present was bent 90° to form a T shape, to obtain the test specimen shown in Figure 6. Using a tensile tester, the bent portion was chucked and pulled in the direction of the arrow in the figure, and the adhesive strength (coating adhesion) was measured. The measurement results were evaluated as follows. Note that the evaluation surface of the test specimen after evaluation was observed, and if the coating on the evaluation surface was completely peeled off from the aluminum substrate, it was determined that the coating had undergone interfacial peeling. Furthermore, if the coating or nylon film remained on the evaluation surface, it was determined that the coating or nylon film had undergone cohesive failure. ◎: Cohesive failure or interfacial peeling with strength of 17N or more ○: Interfacial peeling with strength of 15N or more but less than 17N △: Interfacial peeling with strength of 13N or more but less than 15N ×: Interfacial peeling with strength of less than 13N

[0085] [Resin Adhesion Evaluation (180° Peel Evaluation)] Resin adhesion when coated with a thermoplastic resin film was evaluated by the following method (180° peel evaluation) using a resin-coated aluminum plate prepared by the method described below. First, a T-shaped sample with the dimensions shown in Figure 7a was cut out from the resin-coated aluminum plate, and a 180° peel test shown in Figure 7b was performed at a tensile speed of 20 mm / min to measure the adhesive strength (resin adhesion) per 15 mm width. The measurement results were evaluated as follows: ◯: Maximum tensile strength is 10 N / 15 mm or more ×: Maximum tensile strength is less than 10 N / 15 mm

[0086] [Evaluation of Openability (Feathering Evaluation)] The openability was evaluated by the following method (feathering evaluation) using a resin-coated aluminum plate prepared by the method described below. First, the resin-coated aluminum plate was cut into 40 mm × 130 mm pieces, and scores were made with a cutter at positions 5 mm from both ends to prepare test pieces as shown in Figure 8. Using the test pieces, one piece of the sample was chucked using a tensile tester and pulled at 500 mm / min. The sample was torn along the scores, and feathering (peel length of the coating film) occurring along the scores was measured on the coating film surface (surface to be evaluated) that would become the inner surface of the lid. Evaluation was performed according to the type of coating on the inner surface as follows.

[0087] In the case of epoxy acrylic paints, ◯: The peeling length of the coating film was 0.3 mm or less. △: The peeling length of the coating film was more than 0.3 mm and 0.4 mm or less. ×: The peeling length of the coating film was more than 0.4 mm.

[0088] In the case of polyester phenolic paints, ◯: Peeling length of paint film is 0.2 mm or less △: Peeling length of paint film is more than 0.2 mm and 0.4 mm or less ×: Peeling length of paint film is more than 0.4 mm

[0089] In the case of vinyl chloride organosol paints, ◯: Peeling length of coating film is 1.0 mm or less △: Peeling length of coating film is more than 1.0 mm and less than 2.0 mm ×: Peeling length of coating film is more than 2.0 mm

[0090] [Corrosion Resistance Evaluation (Coated Plate)] The corrosion resistance of resin-coated aluminum plates (coated plates) was evaluated by the following method using resin-coated aluminum plates prepared by the method described below. First, the resin-coated aluminum plate was cut into 50 mm x 50 mm pieces, and DuPont impact (½ inch, 300 g, 30 cm) was applied with the inner coating surface facing outward (convex). Next, two cross-cuts (5 cm each) were made with a cutter, reaching the substrate, so that the apexes of the convex parts of the DuPont impact parts intersected. The plate 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) and left at 37°C for 2 weeks. Thereafter, the test piece was removed from the model solution, and the corrosion state of the DuPont impact parts was evaluated as follows: ○: No or slight corrosion; △: Partial corrosion; ×: Corrosion occurred over the entire surface.

[0091] [Corrosion Resistance Evaluation (Can Lid)] The corrosion resistance after can lid processing was evaluated using the following method using resin-coated aluminum sheets prepared by the method described below. First, a can was formed using a lid processing mold, and rivets and scores were added to the inner coating surface to prepare a test specimen (Figure 9). The prepared test specimen was immersed in a corrosion model solution (aqueous solution containing 1.0% sodium chloride and 0.5% anhydrous citric acid by mass concentration) so that it was in contact with the inner coating surface, and left at 37°C for two weeks. The test specimen was then removed from the model solution, and the corrosion state of the rivet and score areas was evaluated as follows.

[0092] In the case of rivets: ○: No or slight corrosion △: Corrosion has occurred in parts ×: Corrosion has occurred over the entire surface

[0093] In the case of the scored area: ○: No corrosion accompanied by blisters occurred ×: Corrosion accompanied by blisters occurred

[0094] [Color Tone Evaluation] Color tones were measured using resin-coated aluminum sheets prepared by the method described below. Specifically, first, the brightness (L ＊ value) and chromaticity (a ＊ value and b ＊After measuring the color difference (ΔE) between the sample and a reference sample (Comparative Example 1 or 3) using the following formula (1), the color difference (ΔE) from the reference sample was calculated. Note that since the color tone differs depending on the aluminum substrate, calculations were performed for separate reference samples for each alloy type. A spectrophotometer CM-5 manufactured by Konica Minolta was used as the measuring instrument.

[0095] 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 or 3, L* １ : L* value of the example Δa*: change in a* value, a* ０ : a* value of Comparative Example 1 or 3, a* １ : a* value of the example Δb*: change in b* value, b* ０ : b* value of Comparative Example 1 or 3, b* １ : b* value of Example Based on the obtained ΔL* and ΔE, the following evaluation was made: ◯: ΔL* is less than 3.0 and ΔE is less than 4.0 ×: ΔL* is 3.0 or more or ΔE is 4.0 or more

[0096] [Gloss Evaluation] The gloss was measured using a resin-coated aluminum plate prepared by the method described below. Specifically, a gloss meter was used to measure specular gloss based on the method for measuring specular gloss (JIS Z 8741), and calibration was performed using black glass as a primary standard surface. The incident angle and reflection angle were both set to 60°. Next, the gloss of the coating surface on the outer surface of the resin-coated aluminum plate was measured and evaluated as follows. A gloss meter (VG7000) manufactured by Nippon Denshoku Industries Co., Ltd. was used as the gloss meter.

[0097] ◯: Gloss (60°) is 88 or more △: Gloss (60°) is less than 88, 85 or more ×: Gloss (60°) is less than 85

[0098] Example 1 An aluminum substrate having an alloy type of A3104, temper type of H19, and a thickness of 0.27 mm was prepared. The rolling oil on the aluminum substrate was degreased by a known method, and the aluminum substrate was then 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 on the obtained surface-treated aluminum plate were calculated and are shown in Table 1.

[0099] Next, when the resin layer was a coating film, an epoxy acrylic paint, a polyester phenolic paint, and a vinyl chloride organosol paint were applied as the inner surface coating material to the surface treatment layer of the obtained surface-treated aluminum plate using a bar coater, and an epoxy acrylic paint (exterior clear paint) was applied as the outer surface coating material, and the resulting plate was baked in a drying oven under conditions of 260°C x 90 seconds to produce a coated plate (resin-coated aluminum plate). The coating amount of the inner surface coating material was about 120 mg / dm ２ (approximately 10 μm), the coating amount of the outer surface paint is 50 mg / dm ２ (approximately 4 μm).

[0100] On the other hand, when the resin layer was a thermoplastic resin film, a resin layer was thermocompression bonded onto the surface-treated layer of the obtained surface-treated aluminum plate to produce a resin-laminated plate (resin-coated aluminum plate). Specifically, the resin-laminated plate was produced by the following two methods (i) and (ii).

[0101] (i) A stretched two-layer polyethylene terephthalate film (20 μm thick) was laminated on the surface of the heated surface-treated aluminum plate that would become the inner surface of the lid, and then quenched in water to obtain a resin-laminated plate. The two-layer polyethylene terephthalate film used was a film in which two layers were laminated: a surface layer of polyethylene terephthalate copolymerized with 2 mol% isophthalic acid (IA) and a bottom layer of polyethylene terephthalate copolymerized with 18 mol% isophthalic acid (IA) in a layer ratio of 4:1. Next, an epoxy urea-based paint (exterior clear paint) was applied to the surface that would become the outer surface of the lid using a bar coater, and baked in a drying oven at 185°C for 10 minutes to produce a resin-coated aluminum plate. The coating amount of the paint on the outer surface was 50 mg / dm ２ (approximately 4 μm).

[0102] (ii) A stretched polyethylene terephthalate film was laminated onto one side of the heated surface-treated aluminum plate, which would become the inner surface of the lid, and then quenched in water to obtain a resin-laminated plate. The film used was a polyethylene terephthalate film (thickness: 30 μm) copolymerized with 11 mol% isophthalic acid (IA), with a polyester phenol-based adhesive primer pre-coated to a thickness of 1 μm on the laminated surface. Next, an epoxy urea-based paint (exterior clear paint) was applied to the surface that would become the outer surface of the lid using a bar coater, and the paint was baked in a drying oven at 185°C for 10 minutes to produce a resin-coated aluminum plate.

[0103] The obtained resin-coated aluminum sheets were evaluated for coating adhesion (T-peel evaluation), resin adhesion (180° peel evaluation), openability (feathering evaluation), corrosion resistance (coated sheet, can lid), and the color tone and gloss of the outer surface of the lid. The evaluation results are shown in Tables 2, 3, and 4.

[0104] (Example 2) The immersion time in the treatment solution (treatment time) in the surface treatment step was as shown in Table 1. Other than that, the procedure was the same as in Example 1. The results are shown in Tables 2, 3 and 4.

[0105] Example 3 An aluminum substrate having an alloy type of A5182, temper grade of H19, and a thickness of 0.235 mm was prepared. The rolling oil on the aluminum substrate was degreased by a known method, and then the aluminum substrate was immersed in a treatment liquid (ion-exchanged water at 95°C) (surface treatment step). The treatment time was 5 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. The film thickness and absorbance peak ratio (Pa / Pb) of the surface treatment layer on the obtained surface-treated aluminum plate were calculated and are shown in Table 1. The remaining procedures were the same as in Example 1. The results are shown in Tables 2, 3, and 4.

[0106] (Example 4) The immersion time in the treatment solution (treatment time) in the surface treatment step was as shown in Table 1. Other than that, the procedure was the same as in Example 1. The results are shown in Tables 2, 3 and 4.

[0107] (Example 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 procedure was the same as in Example 1. The results are shown in Tables 2, 3 and 4.

[0108] (Comparative Example 1) An aluminum substrate having an alloy type of A3104, temper type of H18, 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 Tables 2, 3, and 4. 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.

[0109] (Comparative Example 2) The immersion time in the treatment solution (treatment time) in the surface treatment step was as shown in Table 1. Other than that, the procedure was the same as in Example 1. The results are shown in Tables 2, 3 and 4.

[0110] (Comparative Example 3) An aluminum substrate having an alloy type of A5182, temper type of H19, and a thickness of 0.235 mm was prepared. The rolling oil on the aluminum substrate was degreased by a known method, and then the aluminum substrate was evaluated in the same manner as in Example 1 without being subjected to any surface treatment. The results are shown in Tables 2, 3, and 4. The coating that formed naturally after degreasing was a coating mainly composed of amorphous alumina, and the absorbance peak ratio (Pa / Pb) was 8.523. The results are shown in Table 1.

[0111] (Comparative Example 4) The immersion time (treatment time) in the treatment solution in the surface treatment step was as shown in Table 1. Other than that, the procedure was the same as in Example 1. The results are shown in Tables 2, 3 and 4.

[0112] (Reference Example) Using an aluminum alloy plate having a phosphate chromate treatment film, evaluation was carried out in the same manner as in Example 1. The results are shown in Tables 2, 3 and 4.

[0113]

[0114]

[0115]

[0116]

[0117]

[0118]

[0119]

[0120]

[0121] From the above examples and comparative examples, it was confirmed that by setting the Pa / Pb value of the surface treatment layer to 0.14 to 3.50, resin adhesion, corrosion resistance, and color tone were all achieved in an evaluation assuming a resin-coated aluminum can lid.

[0122] The resin-coated aluminum can lid of the present disclosure is suitable for use as a lid for beverage cans, food cans, etc.

[0123] 100 Resin-coated aluminum can lid 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 can lid is defined as Pb, a value of Pa / Pb is 0.14 to 3.

50.

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

3. A resin-coated aluminum can end according to claim 1 or 2, wherein the L* value on the outer surface of the can end is 85.5 or more.

4. The resin-coated aluminum can end according to claim 1 or 2, wherein the outer surface of the can end has a specular gloss of 85 or more in terms of 60° gloss value in accordance with JIS Z 8741:1997.

5. The resin-coated aluminum can end according to claim 1 or 2, wherein the resin layer is a coating film.

6. The resin-coated aluminum can end according to claim 5, wherein the coating film is at least one selected from the group consisting of epoxy acrylic coating films, polyester phenol coating films, polyester amino coating films, and vinyl chloride organosol coating films.

7. The resin-coated aluminum can end according to claim 1 or 2, wherein the resin layer is a thermoplastic resin film.

8. The resin-coated aluminum can end according to claim 7, wherein the thermoplastic resin film is a crystalline polyester.

9. The resin-coated aluminum can end according to claim 7 or 8, wherein the thermoplastic resin film is formed on the surface treatment layer via an adhesive primer layer.

10. An aluminum substrate, a surface treatment layer formed on at least one surface of the aluminum substrate, and a coating film 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 wave number is 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 0.14 to 3.

50.

11. A resin-coated aluminum can lid comprising the resin-coated aluminum sheet according to claim 10.