Aluminum surface treatment bath

Abstract

To provide an aluminum surface treatment bath capable of suppressing a brown spot and improving appearance and dry efficiency.SOLUTION: An aluminum surface treatment bath used for the surface treatment of aluminum includes 10-1000 mg / L of polyoxyethylene alkyl ether and 1-50 mg / L of phosphoric acid compound being at least one kind selected from a group consisting of a phosphoric acid, condensed phosphoric acid and the salt thereof in terms of phosphate ions. The phosphoric acid compound preferably includes at least one kind of sodium salt, potassium salt and ammonium salt of phosphoric acid or condensed phosphoric acid.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aluminum surface treatment bath. [Background technology]

[0002] Conventionally, aluminum products such as seamless aluminum cans are widely used as containers for food and beverages such as beer and carbonated drinks. In order to form a good chemical conversion coating on the surface of the aluminum product, surface treatment is carried out using a surface treatment bath containing a surfactant, an etching agent, etc. For example, a technology has been proposed relating to a surface treatment agent for metal cans that contains phosphate esters, alcohols, and a water-soluble organic substance (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 01-085292 Summary of the Invention [Problem to be solved by the invention]

[0004] The technology disclosed in Patent Document 1 involves surface-treating aluminum cans to impart slipperiness to the can surface, thereby improving mobility on a production line. However, the surface of aluminum products such as aluminum cans may develop a defect in appearance known as brown spots. Furthermore, after surface treatment of aluminum products, they are washed and dried, and there is a need to improve the efficiency of the drying process after the washing. Until now, no research has addressed these issues.

[0005] The present invention has been made in view of the above problems, and has as its object to provide an aluminum surface treatment bath that can suppress brown spots, improve the appearance, and increase drying efficiency. [Means for solving the problem]

[0006] (1) The present invention relates to an aluminum surface treatment bath used for treating the surface of aluminum, which contains 10 to 1000 mg / L of polyoxyethylene alkyl ether and 1 to 50 mg / L, calculated as phosphate ions, of a phosphate compound that is at least one selected from the group consisting of phosphoric acid, condensed phosphoric acid, and salts thereof.

[0007] (2) The aluminum surface treatment bath according to (1), wherein the polyoxyethylene alkyl ether has an EO addition mole number of 3 to 11 and a carbon chain length of 8 to 14.

[0008] (3) The aluminum surface treatment bath according to (1) or (2), which is used for treating the surface of aluminum cans.

[0009] (4) An aluminum surface treatment agent used to prepare the aluminum surface treatment bath according to any one of (1) to (3), which is an aqueous solution containing at least one of the polyoxyethylene alkyl ether in an amount of 1 to 20 mass % and the phosphoric acid compound in an amount of 1 to 20 mass % calculated as phosphate ions.

[0010] (5) The aluminum surface treatment agent according to (4), wherein the phosphoric acid compound includes at least one of a sodium salt, a potassium salt, and an ammonium salt of phosphoric acid or condensed phosphoric acid. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an aluminum surface treatment bath and an aluminum surface treatment agent that can suppress brown spots, improve appearance, and improve drying efficiency. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the description of the following embodiments.

[0013] <Aluminum surface treatment bath> The aluminum surface treatment bath according to this embodiment is used to form a chemical conversion coating on the surface of an aluminum product to be treated. The aluminum surface treatment bath contains a polyoxyethylene alkyl ether and a phosphate compound.

[0014] (Polyoxyethylene alkyl ether) Polyoxyethylene alkyl ethers are compounds in which a polyoxyethylene chain and an alkyl group are bonded via an ether bond. The polyoxyethylene alkyl ether of this embodiment is a monoalkyl compound in which one alkyl group is bonded to a polyoxyethylene chain. Polyoxyethylene alkyl ethers are used as surfactants that impart slipperiness to aluminum surfaces. The hydrophilic groups of the polyoxyethylene alkyl ether adsorb to the aluminum surface, resulting in hydrophilic and hydrophobic groups arranged on the surface side. The hydrophilic groups arranged on the surface side impart hydrophilicity to the aluminum surface. This allows the amount of moisture adhering to the aluminum surface during the water washing process to be removed and reduced before the drying process. This allows the drying temperature in the drying process to be reduced. Furthermore, the combined use of a phosphoric acid compound and a polyoxyethylene alkyl ether improves the brown spot suppression effect compared to using a phosphoric acid compound alone. Furthermore, the hydrophobic groups improve the slipperiness of the aluminum surface after drying, thereby improving the transportability of aluminum cans, for example, when the treated object is an aluminum can.

[0015] The concentration of polyoxyethylene alkyl ether in the aluminum surface treatment bath is 10 to 1000 mg / L. If the concentration is less than 10 mg / L, the above-mentioned effect as a surfactant cannot be obtained. If the concentration is more than 1000 mg / L, the polyoxyethylene alkyl ether may remain on the aluminum surface after drying, causing whitening and impairing the appearance characteristics of the aluminum surface. The concentration of polyoxyethylene alkyl ether is preferably 50 to 1000 mg / L, and more preferably 100 to 400 mg / L.

[0016] The number of moles of EO added, which is the number of repeating oxyethylene units in polyoxyethylene alkyl ether, is preferably 3-11.

[0017] The HLB value of the polyoxyethylene alkyl ether is preferably 8 to 14. Here, the HLB value is the hydrophilic-lipophilic balance, which is a measure of the degree of hydrophilicity and lipophilicity (hydrophobicity). The stronger the hydrophilicity, the higher the HLB value.

[0018] The number of carbon chains in the polyoxyethylene alkyl ether is preferably 8 to 14. Here, the number of carbon chains means the number of carbon chains in the alkyl group of the polyoxyethylene alkyl ether.

[0019] If the number of EO molar additions of the polyoxyethylene alkyl ether exceeds 11, if the HLB value exceeds 14, or if the carbon chain length is less than 8, the aluminum surface treatment bath will foam more, reducing workability. Furthermore, if the number of EO molar additions of the polyoxyethylene alkyl ether is less than 3, if the HLB value is less than 8, or if the carbon chain length is more than 14, the bath dispersibility of the aluminum surface treatment bath will decrease, making components in the bath more likely to float and separate. This can result in uneven adhesion of the conversion coating, resulting in poor appearance. Furthermore, the effectiveness of reducing the amount of moisture adhering to the aluminum surface will decrease.

[0020] The polyoxyethylene alkyl ether may be used alone or in combination of two or more. When two or more polyoxyethylene alkyl ethers are used in combination, it is preferable to use a main component having an EO addition mole count of 3 to 8, an HLB value of 8 to 12, and a carbon chain length of 10 to 14 in combination with a subcomponent having an EO addition mole count of 6 to 10, an HLB value of 12 to 14, and a carbon chain length of 8 to 12 in combination. When the main component and subcomponent are used in combination, it is preferable that the molar ratio of the subcomponent to the main component is 5:1 to 1:1.

[0021] (phosphate compounds) Phosphate compounds function as film-forming treatment agents that inactivate aluminum surfaces. When aluminum, the target of treatment in an aluminum surface treatment bath, reacts with the pure water used in the cleaning process, an oxide film called a boehmite film grows significantly, resulting in the formation of brown spots. The occurrence of brown spots can cause unevenness when printing or painting the aluminum surface, resulting in poor appearance. Phosphate compounds react with the aluminum to form aluminum phosphate, which forms a film with excellent corrosion resistance on the aluminum surface. This chemically inactivates the aluminum surface, preventing the formation of brown spots without the need for acid treatment or other procedures.

[0022] The phosphate compound is a compound having a phosphate group and is at least one selected from the group consisting of phosphoric acid, condensed phosphoric acid, and salts thereof. The condensed phosphoric acid is a general term for linear polymeric phosphoric acids produced by dehydration condensation of orthophosphoric acid, and examples thereof include pyrophosphoric acid, tripolyphosphoric acid, trimetaphosphoric acid, tetrametaphosphoric acid, and ultraphosphoric acid. The salt of the phosphoric acid or condensed phosphoric acid preferably includes at least one of sodium salt, potassium salt, and ammonium salt. The phosphate compound may be used alone or in combination of two or more.

[0023] Phosphate compounds consist of phosphate ions (PO4 3- The concentration in the aluminum surface treatment bath is 1 to 50 mg / L in terms of phosphate ions. If the concentration in terms of phosphate ions is less than 1 mg / L, the formation of an oxide film on the aluminum surface may not be sufficiently suppressed. If the concentration in terms of phosphate ions exceeds 50 mg / L, the effect of suppressing brown spots cannot be obtained. The concentration in terms of phosphate ions can be calculated, for example, by converting the number of moles of phosphorus atoms measured by ICP (inductively coupled plasma) atomic emission spectrometry into phosphate ions. The concentration in terms of phosphate ions is preferably 3 to 10 mg / L, and more preferably 5 to 10 mg / L.

[0024] (Other ingredients) The aluminum surface treatment bath according to this embodiment may optionally contain other components such as an antibacterial agent, a surfactant, an anticorrosive agent, etc. In addition to the above, the bath may optionally contain a silane coupling agent, colloidal silica, amines, a phenolic water-soluble organic compound including a phenolic resin, etc. for the purpose of improving adhesion.

[0025] Examples of antibacterial agents include alcohols such as ethanol and isopropanol, guanidine group-containing compounds such as polyhexamethylene biguanidine hydrochloride, benzimidazole antibacterial agents such as 2-(4-thiazolyl)-benzimidazole and methyl-2-benzimidazole carbamate, phenol antibacterial agents such as p-chloro-m-xylenol and p-chloro-m-cresol, and nitrile antibacterial agents such as 2,4,5,6-tetrachloroisophthalonitrile and 1,2-dibromo-2,4-dicyanobutane. Examples of antibacterial agents include pyridine-based antibacterial agents such as sodium (2-pyridylthio-1-oxide) and zinc bis(2-pyridylthio-1-oxide); isothiazolone-based antibacterial agents such as 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one; quaternary ammonium salts such as benzalkonium chloride and benzethonium chloride; benzoic acid, ethyl p-hydroxybenzoate, sorbic acid, potassium sorbate, sodium dehydroacetate, and sodium propionate.

[0026] The surfactant is not particularly limited, and examples thereof include nonionic surfactants other than the above-mentioned polyoxyethylene alkyl ethers, cationic surfactants, anionic surfactants, etc. The rust inhibitor is not particularly limited, and examples thereof include tannic acid, imidazoles, triazines, guanines, hydrazines, biguanides, etc.

[0027] The pH of the aluminum surface treatment bath according to this embodiment is preferably from 3 to 10. When the pH of the aluminum surface treatment bath according to this embodiment is in this range, excessive etching of the aluminum surface can be suppressed, and damage to the appearance of the aluminum surface can be prevented.

[0028] The aluminum to be treated with the aluminum surface treatment bath according to this embodiment is not particularly limited, and examples thereof include aluminum, aluminum-copper alloy, aluminum-manganese alloy, aluminum-silicon alloy, aluminum-magnesium alloy, aluminum-magnesium-silicon alloy, aluminum-zinc alloy, and aluminum-zinc-magnesium alloy. Furthermore, the shape of the aluminum substrate to be treated is not particularly limited, and treatment targets of any shape, such as plates, rods, and cans, can be chemically treated. For example, aluminum beverage cans are manufactured by a drawing process known as drawing and ironing (DI) processing, and brown spots are likely to occur due to the accumulation of pure water in uneven areas. However, the use of the aluminum surface treatment bath according to this embodiment can suppress brown spots that tend to occur on aluminum beverage cans.

[0029] <Aluminum surface treatment agent> The aluminum surface treatment agent according to this embodiment can be used to prepare the aluminum surface treatment bath or to supply various components to the aluminum surface treatment bath. The aluminum surface treatment agent is an aqueous solution containing 1 to 20% by mass of polyoxyethylene alkyl ether and at least one of a phosphoric acid compound in an amount of 1 to 20% by mass, calculated as phosphate ions. The phosphoric acid compound is a compound having a phosphoric acid group and is preferably at least one selected from the group consisting of phosphoric acid, condensed phosphoric acid, and salts thereof. The condensed phosphoric acid is a general term for linear polymeric phosphoric acids generated by dehydration condensation of orthophosphoric acid, and examples thereof include pyrophosphoric acid, tripolyphosphoric acid, trimetaphosphoric acid, tetrametaphosphoric acid, and ultraphosphoric acid. The salt of the phosphoric acid or condensed phosphoric acid preferably includes at least one of sodium salt, potassium salt, and ammonium salt. The phosphoric acid compound may be used alone or in combination of two or more.

[0030] The surface treatment agents may be used alone or in combination of two or more. For example, two or more aqueous solutions may be used in combination when preparing or replenishing an aluminum surface treatment bath, or they may be used alone.

[0031] The aluminum surface treatment bath according to this embodiment can be prepared by diluting the aluminum surface treatment agent with water. The aluminum surface treatment bath is prepared so that the polyoxyethylene alkyl ether concentration is 10 to 1000 mg / L and the phosphate compound concentration, calculated as phosphate ions, is 1 to 50 mg / L. Furthermore, adding the aluminum surface treatment agent to the surface treatment bath allows for the replenishment of various components to the aluminum surface treatment bath. It is preferable to replenish the components so that the concentrations of the polyoxyethylene alkyl ether and the phosphate compound are within the above-mentioned ranges.

[0032] The aluminum surface treatment agent may optionally contain other components contained in the aluminum surface treatment bath, such as antibacterial agents, surfactants, rust inhibitors, silane coupling agents, colloidal silica, amines, and phenolic water-soluble organic compounds including phenolic resins.

[0033] <Aluminum surface treatment method> The aluminum surface treatment method using the aluminum surface treatment bath according to this embodiment includes, for example, a water-rinsing step, a surface treatment step, and a drying step. Furthermore, the method may include a degreasing step and a pre-cleaning step before the surface treatment step.

[0034] The degreasing process is a process in which, for example, aluminum powder called smut and components such as lubricating oil that adhere to the surface of aluminum cans produced by DI processing are removed using a degreasing agent. The degreasing process also removes the aluminum oxide film formed on the aluminum surface. Known commercially available degreasing agents can be used.

[0035] The preliminary cleaning step is a step in which dirt adhering to the surface of the aluminum is removed by spraying cleaning water or the like.

[0036] The water washing step is a step in which dirt adhering to the surface of the aluminum or the degreasing agent adhering to the surface of the aluminum in the degreasing step is washed away by spraying pure water or the like.

[0037] The surface treatment step is a step of forming a surface treatment film on the surface of aluminum by immersing aluminum in the aluminum surface treatment bath according to this embodiment, or by spraying or applying the aluminum surface treatment bath to the aluminum.

[0038] The drying step is a step of drying the aluminum after the surface treatment step to remove moisture. In this embodiment, the surface treatment step allows a highly hydrophilic surface treatment film to be formed on the aluminum surface, making it possible to remove and reduce the amount of moisture adhering to the surface treatment film before the drying step. Therefore, the drying step according to this embodiment can be performed at a drying temperature of 140°C to 220°C for a drying time of 80 seconds to 4 minutes. The drying temperature and drying time can be, for example, a combination of a drying temperature of 140°C for 4 minutes and a drying temperature of 220°C for 80 seconds. A conventional heating and drying device such as an oven can be used as the drying means in the drying step. Conventional drying conditions require high energy costs, and high drying temperatures can reduce the strength of the aluminum, potentially resulting in deformation. The drying step according to this embodiment can solve the above problems by reducing the drying temperature and drying time compared to conventional methods. [Example]

[0039] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0040] <Examples 1 to 15 and Comparative Examples 1 to 5> Aluminum surface treatment baths for the Examples and Comparative Examples were prepared at the concentrations and compound types shown in Table 1. An aqueous solution containing 5% by mass of polyoxyethylene alkyl ether and an aqueous solution containing 2% by mass of a phosphoric acid compound, calculated as phosphate ions, were used, and the aluminum surface treatment baths were diluted with water to the concentrations shown in Table 1. DI-processed aluminum cans were used as the treatment target. A degreaser (Surf Cleaner NHC260A, manufactured by Nippon Paint Surf Chemicals Co., Ltd.) was used. The cans were degreased by spraying a 40 g / L bath of the degreaser at 75°C for 60 seconds, followed by a 10-second rinse with water, a further 10 seconds of pure water spray, and then spraying with the aluminum surface treatment bath prepared above for 10 seconds. The drying time, brown spots, and appearance after surface treatment were evaluated under the following conditions.

[0041] [Drying property evaluation] The aluminum cans treated in the aluminum surface treatment baths of the Examples and Comparative Examples were dried at 160°C and 200°C for 3 minutes, respectively, and visually evaluated according to the following criteria. The results are shown in Table 1. 3: No water droplets 2: Very small amount of water droplets 1: Water droplets

[0042] [Brown spot evaluation] The aluminum cans treated with the aluminum surface treatment baths according to the Examples and Comparative Examples were dried at 200°C for 3 minutes, and the presence or absence of brown spots (areas discolored to a brownish reddish-red) in the center of the inner surface was visually evaluated according to the following criteria. The results are shown in Table 1. 3: No occurrence 2: Slight occurrence 1: Occurred

[0043] [Appearance evaluation] The aluminum cans treated in the aluminum surface treatment baths of each Example and Comparative Example were dried at 200°C for 3 minutes, and the presence or absence of whitening in the center of the outer surface was visually evaluated according to the following criteria. The results are shown in Table 1. 3: No whitening 2: Slightly whitened 1: Whitening

[0044] [Table 1]

[0045] The results in Table 1 confirm that the surface treatment using the aluminum surface treatment bath according to each example can improve the drying properties of aluminum and suppress brown spots.

Claims

1. An aluminum surface treatment bath used for surface treatment of aluminum, comprising: Contains 10 to 1000 mg / L of polyoxyethylene alkyl ether, containing 1 to 50 mg / L of at least one phosphate compound selected from the group consisting of phosphoric acid, condensed phosphoric acid, and salts thereof, calculated as phosphate ions; The aluminum surface treatment bath comprises a polyoxyethylene alkyl ether having an EO addition mole number of 3 to 11, a carbon chain length of 8 to 14, and an HLB value of 8 to 14.

2. 2. The aluminum surface treatment bath according to claim 1, which is used for treating the surface of aluminum cans.

3. An aluminum surface treatment agent used to prepare the aluminum surface treatment bath according to claim 1 or 2, The aluminum surface treatment agent is an aqueous solution containing at least one of the polyoxyethylene alkyl ether in an amount of 1 to 20 mass % and the phosphoric acid compound in an amount of 1 to 20 mass % in terms of phosphate ions.

4. The aluminum surface treatment agent according to claim 3 , wherein the phosphate compound includes at least one of a sodium salt, a potassium salt, and an ammonium salt of phosphoric acid or a condensed phosphoric acid.

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