JP2015086466A - Surface treatment method for aluminum can - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treatment method for an aluminum can, in which an acid treatment solution easy to handle can be used and energy cost is sufficiently low.SOLUTION: The surface treatment method for an aluminum can includes an alkali treatment step of treating an aluminum can with an alkali treatment solution, and an acid treatment step of treating the aluminum can after the alkali treatment step with an acid treatment solution. The amount of etching in the alkali treatment step is less than 50 mg/m. The alkali treatment solution preferably contains at least one kind selected from the group consisting of sodium ions, potassium ions, and ammonium ions.

Description

  The present invention relates to a surface treatment method for an aluminum can.

  Conventionally, an aluminum can such as a beverage can manufactured from aluminum or an aluminum alloy is manufactured by a drawing process called drawing and ironing process (hereinafter referred to as DI process). Aluminum powder (hereinafter referred to as smut) and lubricating oil generated by scraping during drawing are adhered to the surface of an aluminum can manufactured by DI processing.

  Usually, an aluminum can is subjected to chemical conversion treatment and coating treatment. In order to form a strong chemical conversion coating and paint coating, the smut and lubricating oil adhering to the surface of the aluminum can before chemical conversion are sufficiently removed, and then the oxide film formed on the surface of the aluminum can Must be removed by etching.

  When surface-treating an aluminum can, it is common to use an acidic surface treatment liquid (hereinafter sometimes referred to as an acid treatment liquid) that can appropriately etch the surface of the aluminum can. For example, a method of treating the surface of an aluminum can with an acid treatment solution containing trivalent iron ions and having a pH adjusted to 2 or less with sulfuric acid or nitric acid is known (see, for example, Patent Documents 1 and 2). . Further, a method for treating the surface of an aluminum can with an acid treatment solution containing an organic sulfonic acid, trivalent iron ions, and an inorganic acid such as sulfuric acid or nitric acid is also known (for example, Patent Document 3). reference).

  In addition, regarding the surface treatment of aluminum for can lids, not aluminum cans, after performing degreasing with etching by treating the surface of aluminum for can lids formed of a 5000 series alloy with an alkaline solution, A method for acid cleaning is known (see, for example, Patent Documents 4 to 6).

Japanese Patent Publication No. 3-50838 JP 2000-104185 A JP 2007-197775 A JP 2003-119570 A JP 2004-18992 A JP 2008-127625 A

  By the way, when impurities, such as magnesium and copper, remain on the surface of the aluminum can, a chemical conversion film or a paint film cannot be uniformly formed on the surface of the aluminum can, and as a result, the corrosion resistance of the aluminum can decreases.

  In order to avoid such a situation, it is effective to increase the etching amount by increasing the etching rate with the acid treatment liquid. In order to increase the etching amount, it is conceivable to increase the treatment temperature with the acid treatment liquid (for example, 70 ° C.). However, maintaining the treatment temperature with the acid treatment liquid at a high temperature is not preferable because the energy cost increases.

  Patent Document 3 discloses that the treatment temperature of the acid treatment liquid can be lowered by treating the surface of the aluminum can with an acid treatment liquid containing an organic sulfonic acid. However, even when an acid treatment solution containing an organic sulfonic acid is used, etching may not sufficiently proceed at a low temperature.

  In addition, acid cleaning is performed at a relatively low temperature (for example, 50 ° C.) in the base treatment of aluminum for can lids disclosed in Patent Documents 4 to 6. In the base treatment of aluminum for can lids, the surface of the substrate is etched by treatment with an alkaline solution performed before acid cleaning. The acid cleaning in this case is recognized to be aimed at removing magnesium segregated on the aluminum surface or neutralizing the surface of aluminum that has become alkaline by treatment with an alkaline solution before the acid cleaning. Thus, the purpose is completely different between the acid cleaning in the aluminum base treatment for the can lid and the process of etching the substrate surface with the acid treatment liquid performed in the surface treatment of the aluminum can. If the aluminum can is treated under the aluminum base treatment conditions for the can lid, the etching amount on the aluminum can surface is not controlled, and the appearance of the aluminum can may not be controlled. Therefore, it is not possible to apply the technology related to the surface treatment of aluminum for can lids to the technology related to the surface treatment of aluminum cans.

  As described above, an acid treatment solution that can be easily handled can be used, and a surface treatment method for an aluminum can having a sufficiently low energy cost has not been found.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an aluminum can surface treatment method that can use an acid treatment solution that is easy to handle and that has a sufficiently low energy cost. It is.

The present invention has an alkali treatment step of treating an aluminum can with an alkali treatment solution, and an acid treatment step of treating the aluminum can after the alkali treatment step with an acid treatment solution, and the etching amount in the alkali treatment step is , A surface treatment method for an aluminum can that is less than 50 mg / m ² .

  The alkaline treatment liquid preferably contains at least one selected from the group consisting of sodium ions, potassium ions and ammonium ions.

  The alkali treatment liquid is 40 to 70 ° C., and the treatment time of the aluminum can in the alkali treatment step is preferably 1 to 30 seconds.

  The alkaline treatment liquid preferably contains at least one selected from the group consisting of an organic acid, a chelating agent, a dispersant, and a surfactant.

  The acid treatment liquid contains at least one selected from the group consisting of sulfuric acid, nitric acid and phosphoric acid, contains 0.05 to 4 g / L of trivalent iron ions, has a pH of 2 or less, The treatment temperature of the aluminum can in the acid treatment step is preferably 30 to 65 ° C.

  The treatment time of the aluminum can in the acid treatment step is preferably 10 to 90 seconds.

  The present invention relates to an aluminum can that has been surface-treated by the surface treatment method for an aluminum can.

  According to the present invention, an acid treatment liquid that can be easily handled can be used, and a surface treatment method for an aluminum can with a sufficiently low energy cost can be provided.

  Hereinafter, embodiments of the present invention will be described. In addition, this invention is not limited to the following embodiment.

  A surface treatment method for an aluminum can according to the present embodiment (hereinafter sometimes simply referred to as a surface treatment method) includes an alkali treatment step and an acid treatment step. Examples of the aluminum can treated by the surface treatment method according to the present embodiment include an aluminum can formed from a 3000 series alloy or the like.

<Alkali treatment process>
In the alkali treatment step, the aluminum can is treated with an alkali treatment liquid.
The alkaline treatment liquid removes oil and fat components on the surface of the aluminum can. Moreover, when processing the aluminum can after DI processing, the alkaline processing liquid also plays a role of removing the lubricant.

The etching amount of the aluminum can surface in the alkali treatment step is less than 50 mg / m ² . That is, the surface of the aluminum can is hardly etched in the alkali treatment process. When the etching amount in the alkali treatment step is 50 mg / m ² or more, it becomes difficult to control the etching, and the aluminum can surface is whitened. The amount of etching on the surface of the aluminum can in the alkali treatment step is determined by measuring the mass of the aluminum can with a precision balance before and after the alkali treatment step, and dividing the decrease in the mass of the aluminum can before and after the alkali treatment step by the surface area of the aluminum can. Can be obtained.

In the alkali treatment step, in order to make the etching amount of the aluminum can surface less than 50 mg / m ² , the pH of the alkali treatment solution, the concentration of the alkaline substance in the alkali treatment solution, the treatment time of the alkali treatment step, the treatment of the alkali treatment step It is necessary to control the temperature. More specifically, the amount of etching on the surface of the aluminum can can be increased by increasing the concentration of the alkaline substance in the alkali treatment liquid, that is, by increasing the pH of the alkali treatment liquid. Can be reduced. Also, it is possible to increase the etching amount on the surface of the aluminum can by increasing the treatment time of the alkali treatment step or increasing the alkali treatment temperature. Conversely, the treatment time is shortened or the treatment temperature is lowered. By doing so, the etching amount can be reduced. It is not necessary to adjust all of these elements, and the etching amount on the aluminum can surface can be reduced to less than 50 mg / m ² by adjusting some elements.

  The alkaline treatment liquid preferably has a pH of 9-14. By setting the pH of the alkali treatment liquid to 9 to 14, a hydroxide film can be formed on the surface of the aluminum can. The hydroxide film formed on the surface of the aluminum can in the alkali treatment step is dissolved by the acid treatment solution in the acid treatment step described later. In order to suppress the etching amount while efficiently forming a hydroxide film on the surface of the aluminum can in the alkali treatment step, the pH of the alkali treatment liquid is more preferably 10.0 to 13.0.

  The alkaline treatment liquid preferably contains at least one selected from the group consisting of sodium ions, potassium ions and ammonium ions. When the alkali treatment liquid contains these ions, a hydroxide film can be effectively formed on the surface of the aluminum can. As a source of sodium ion, potassium ion and ammonium ion, inorganic substances such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium hydrogen carbonate, ammonium hydrogen carbonate, sodium salts of organic acids such as gluconic acid and citric acid, Organic materials such as potassium salt and ammonium salt can be mentioned. These compounds may be used in combination of two or more. An inorganic substance such as sodium hydroxide is an alkaline substance and serves as a supply source of sodium ions, potassium ions, or ammonium ions, and also as a supply source of hydroxide ions.

  The alkaline treatment liquid is preferably an aqueous solution containing sodium hydroxide. By using a strongly basic sodium hydroxide aqueous solution as the alkali treatment liquid, a hydroxide film can be more effectively formed on the surface of the aluminum can.

  The concentration of an alkaline substance such as sodium hydroxide in the alkaline treatment liquid is preferably 0.01 to 10 g / L. When the concentration of the alkaline substance in the alkaline treatment liquid is smaller than 0.01 g / L, a hydroxide film tends to be hardly formed on the surface of the aluminum can. When the concentration is larger than 10 g / L, the surface of the aluminum can Etching excessively may cause whitening.

  Moreover, it is preferable that an alkali treatment liquid contains at least 1 sort (s) selected from the group which consists of an organic acid, a chelating agent, a dispersing agent, and surfactant. When the alkali treatment liquid contains an organic acid, a chelating agent, a dispersant, or a surfactant, the surface of the aluminum can can be removed even if the alkali treatment step is performed under mild conditions (eg, low temperature and short time). Smut can be efficiently removed to promote the formation of a hydroxide film.

  Examples of the organic acid contained in the alkali treatment liquid include gluconic acid, citric acid, oxalic acid, malic acid, tartaric acid, sorbic acid, succinic acid, and alkali metal salts such as sodium salt and potassium salt thereof. Among these, it is more preferable that the alkali treatment liquid contains at least one selected from the group consisting of gluconic acid, citric acid, oxalic acid, malic acid, and tartaric acid.

  Examples of the chelating agent contained in the alkali treatment liquid include aminocarboxylic acid chelating agents, phosphonic acid chelating agents, and condensed phosphates. Specific examples include ethylenediaminetetraacetic acid (EDTA), sodium 1-hydroxyethylidene-1,1-diphosphonate (HEDP), sodium nitrilotriacetate (NTA), sodium tripolyphosphate (STPP), and the like. Among these, it is more preferable that the alkali treatment liquid contains at least one of ethylenediaminetetraacetic acid (EDTA) and 1-hydroxyethylidene-1,1-diphosphonate sodium (HEDP).

  Examples of the dispersant contained in the alkali treatment liquid include an acrylic acid maleic acid copolymer, a sodium salt thereof, a polycarboxylic acid, and polyethylene glycol. Among these, it is more preferable that the alkali treatment liquid contains an acrylic acid maleic acid copolymer.

  As the surfactant contained in the alkaline treatment liquid, nonionic, cationic, anionic and zwitterionic surfactants are used. Of these, nonionic compounds are particularly preferable. For example, hydrocarbon derivatives, abietic acid derivatives, alcohol ethoxylates, modified polyethoxylated alcohols, and the like are preferably used.

Furthermore, it is more preferable that the alkali treatment liquid contains at least one selected from the group consisting of organic acids, chelating agents, and dispersants, and a surfactant. That is, a preferable combination of additives contained in the alkali treatment liquid is a combination of at least one selected from the group consisting of an organic acid, a chelating agent, and a dispersant and a surfactant.
Since the alkali treatment liquid contains such a combination of additives, the surface of the aluminum can can be smut even if the alkali treatment step is performed under mild conditions (for example, low temperature and short time) as described above. Both the lubricant and the lubricating oil can be efficiently removed to further promote the formation of the hydroxide film. As described above, if the alkali treatment liquid contains at least one selected from the group consisting of an organic acid, a chelating agent, and a dispersant, and a surfactant, even if the alkali treatment is performed under mild conditions, As a result, the desmutability of the aluminum can after the surface treatment can be further improved.

  The treatment time of the aluminum can in the alkali treatment step is preferably 1 to 30 seconds. If the treatment time of the aluminum can in the alkali treatment step is shorter than 1 second, a hydroxide film tends to be hardly formed on the surface of the aluminum can, and if it is longer than 30 seconds, the surface of the aluminum can is excessively etched. As a result, whitening may occur. The treatment time of the aluminum can in the alkali treatment step is more preferably 3 to 20 seconds.

  The treatment temperature of the aluminum can in the alkali treatment step (the temperature of the alkali treatment liquid) is preferably 40 to 70 ° C. If the treatment temperature of the aluminum can in the alkali treatment step is lower than 40 ° C, a hydroxide film tends to be hardly formed on the surface of the aluminum can. If the treatment temperature is higher than 70 ° C, the surface of the aluminum can is excessively etched. As a result, whitening may occur. The treatment temperature of the aluminum can in the alkali treatment step is more preferably 45 to 60 ° C.

  The processing method of the aluminum can in an alkali treatment process is not specifically limited. Examples of the method for treating the aluminum can in the alkali treatment step include a spray method and a dipping method.

In the alkali treatment step, the treatment with the alkali treatment liquid described above may be performed once or a plurality of times.
In the alkali treatment step, when the treatment with the alkali treatment liquid is performed a plurality of times, the treatment conditions (pH of the alkali treatment liquid, treatment temperature, treatment time, etc.) in each treatment may be the same or changed. Good.

<Acid treatment process>
In the acid treatment step, the aluminum can after the alkali treatment step is treated with an acid treatment solution.
On the surface of the aluminum can, a hydroxide film is formed without being passivated in the alkali treatment step described above. Since the hydroxide film is easily dissolved by the acid treatment solution, the surface of the aluminum can can be etched by the low temperature acid treatment solution in the acid treatment step. If the surface of the aluminum can is treated in the acid treatment step without performing the alkali treatment step, the surface of the aluminum can is passivated, so the temperature of the acid treatment solution needs to be increased in order to advance the etching. There is. If the treatment temperature of the aluminum can in the acid treatment step (the temperature of the acid treatment solution) is high, the energy cost in the surface treatment of the aluminum can becomes too high, which is not preferable. By performing the alkali treatment step before the acid treatment step, the temperature of the acid treatment liquid can be lowered by 5 to 20 ° C. compared to the case where the alkali treatment step is not performed.

  In the acid treatment process, it is possible to lower the temperature of the acid treatment, which not only improves the working environment, but also reduces the time required to start up the line stop for processing aluminum cans, improving productivity. it can. In addition, the progress of corrosion of the equipment due to the acid is delayed, and the frequency of equipment renewal can be reduced.

  The acid treatment liquid preferably has a pH of 2 or less. When the pH of the acid treatment solution is larger than 2, etching of the aluminum can surface tends to be insufficient.

The acid treatment liquid preferably contains an inorganic acid.
The inorganic acid has a function as an etching accelerator. Specific examples of the inorganic acid include sulfuric acid, nitric acid, and phosphoric acid, and these inorganic acids are used alone or in combination. In addition, sulfuric acid is more preferably used from the viewpoint of nitrogen-free and phosphorus-free.

  The content of the inorganic acid in the acid treatment liquid is preferably 0.01 to 25 g / L. When the content of the inorganic acid in the acid treatment liquid is less than 0.01 g / L, the etching rate is extremely reduced, and when it exceeds 25 g / L, no further effect on the etching is recognized. It is economically disadvantageous. The content of the inorganic acid in the more preferable acid treatment liquid is 0.5 to 20 g / L.

The acid treatment liquid preferably contains an oxidized metal ion.
Usually, the etching reaction of aluminum in the acid treatment step includes an anode reaction in which aluminum becomes aluminum ions (Al ³⁺ ), and a cathode reaction in which H ⁺ in the acid treatment solution is reduced to 1 / 2H ₂ . For this reason, when an oxidized metal ion such as ferric ion (Fe ³⁺ ) is added to the acid treatment liquid, an anode reaction in which this Fe ³⁺ is reduced to Fe ²⁺ occurs simultaneously with the reduction of H ⁺ , The etching reaction is promoted. Moreover, the adhesiveness of the chemical conversion treatment film formed by the chemical conversion treatment after an acid treatment process and a metal improves because an acid treatment liquid contains an oxidation type metal ion.

As the oxidized metal ions, in addition to ferric ions (Fe ³⁺ ), metavanadate ions (VO ³⁻ ), ceric ions (Ce ⁴⁺ ), cobalt ions (Co ⁵⁺ ), ^stannic ions (Sn) ⁴⁺ ) and the like.

In the present embodiment, trivalent iron ions (ferric ions: Fe ³⁺ ) are preferably used as the oxidized metal ions. Since the oxidized metal ion is preferably supplied as a water-soluble salt such as sulfate or nitrate, the trivalent iron ion is preferably supplied as ferric sulfate or ferric nitrate. As the etching reaction proceeds, the ferrous ion (Fe ²⁺ ) concentration increases, so that the oxidation-reduction potential (hereinafter referred to as ORP: oxidation-reduction potential) decreases (also referred to as aging of the cleaning agent), and the aluminum surface The etching promoting effect disappears. Therefore, an oxidizing agent for controlling ORP may be added as needed or added from the beginning to oxidize ferrous ions to ferric ions. As an oxidizing agent for ORP control at this time, hydrogen peroxide (H ₂ O ₂ ), persulfate (for example, NaS ₂ O ₈ ²⁻ ), ozone (O ₃ ), cerium compound (for example, cerium ammonium sulfate) : (NH ₄ ) ₄ Ce (SO ₄ ) ₄ ), nitrites (for example, NaNO ₂ , KNO ₂ ) and the like. In addition, what is necessary is just to replenish metavanadate as needed when using a metavanadate ion as an oxidation type metal ion.

  The content of oxidized metal ions in the acid treatment liquid is preferably 0.05 to 4 g / L. When the content of oxidized metal ions in the acid treatment liquid is less than 0.05 g / L, the amount of etching is insufficient and the desmutting property is lowered. Is not economically disadvantageous. The content of oxidized metal ions in a more preferable acid treatment liquid is 0.1 to 1 g / L.

The acid treatment liquid preferably contains a surfactant.
The surfactant mainly has a function of removing oil and fat components and lubricant remaining on the surface of the aluminum can. Moreover, it also has a function of preventing the removed oil and fat component and lubricant component from floating in the cleaning agent. That is, when the oil and fat component and the lubricant component are suspended in the cleaning agent, there is a risk of re-adsorption on the surface of the aluminum can, but by adding a surfactant to the acid treatment liquid, This problem can be avoided.

  As the surfactant, nonionic, cationic, anionic or zwitterionic surfactants are used. Among these, nonionic type is particularly preferable, and for example, ethoxylated alkylphenol type, hydrocarbon derivative, abietic acid derivative, primary ethoxylated alcohol, modified polyethoxylated alcohol and the like are preferably used.

  The content of the surfactant in the acid treatment liquid is preferably 0.01 to 10 g / L. When the content of the surfactant in the acid treatment liquid is less than 0.01 g / L, the detergency, particularly degreasing, is reduced. When the content exceeds 10 g / L, the acid treatment agent is foamed and treated. Is difficult, and wastewater treatment is burdened. The content of the surfactant in the more preferable acid treatment liquid is 0.1 to 5 g / L.

  The organic sulfonic acid in the acid treatment liquid is preferably 0.01 to 25 g / L. If the content of the organic sulfone in the acid treatment liquid is less than 0.01 g / L, a sufficient etching amount may not be obtained, and if it exceeds 25 g / L, the liquid stability of the acid treatment liquid is low. It tends to decrease. From the viewpoint of reducing the drainage load, the content of the organic sulfonic acid in the more preferable acid treatment liquid is 0.1 to 5 g / L.

The etching amount on the surface of the aluminum can in the acid treatment step is 60 to 100 mg / m ² . If the etching amount in the acid treatment step is less than 60 mg / m ² , the etching is insufficient, so that it tends to be difficult to form a chemical conversion treatment film or a paint film described later on the surface of the aluminum can. If the etching amount in the acid treatment step is more than 100 mg / m ² , the etching progresses too much, and the surface of the aluminum can may be whitened. The amount of etching on the surface of the aluminum can in the acid treatment step is determined by measuring the mass of the aluminum can with a precision balance before and after the acid treatment step, and dividing the decrease in the mass of the aluminum can before and after the acid treatment step by the surface area of the aluminum can. Can be obtained.

  The processing method of the aluminum can in an acid treatment process is not specifically limited. Examples of the method for treating the aluminum can in the acid treatment step include a spray method and a dipping method.

  The treatment time of the aluminum can in the acid treatment step is preferably 10 to 90 seconds. If the treatment time of the aluminum can in the acid treatment step is shorter than 10 seconds, the treatment time is too short, so the etching of the aluminum can surface tends to be insufficient, and if it is longer than 90 seconds, the surface of the aluminum can is excessive. Etching tends to accelerate the aging of the acid treatment agent. The treatment time of the aluminum can in the acid treatment step is more preferably 30 to 45 seconds.

  The treatment temperature of the aluminum can in the acid treatment step is preferably 30 to 65 ° C. When the treatment temperature of the aluminum can in the acid treatment step is less than 30 ° C, the treatment temperature tends to be difficult to control, and when it is higher than 65 ° C, the energy cost tends to be too high. The treatment temperature of the aluminum can in the acid treatment step is more preferably 40 to 60 ° C.

<Chemical conversion treatment and painting treatment>
The aluminum can after the acid treatment step is washed with water according to a conventionally known method and then subjected to a chemical conversion treatment with a phosphate-based or zircon-based chemical conversion treatment solution.
The aluminum can after the chemical conversion treatment is subjected to a coating treatment after being washed with water as necessary.

  The aluminum can which has been surface-treated by the surface treatment method for an aluminum can according to the present embodiment can form a strong chemical conversion treatment film and a paint film since the surface smut and lubricating oil are sufficiently removed. .

  Next, the present invention will be described in more detail based on examples, but the present invention is not limited thereto. Unless otherwise specified, “part” and “%” are all based on mass.

<Example 1>
As an aluminum can, a lidless container having a lubricating oil and a smut attached, prepared by DI processing of an aluminum plate made of 3004 alloy was prepared. This was spray-treated for 10 seconds at a treatment temperature of 40 ° C. using an alkali treatment liquid whose pH was adjusted to 12.5 with sodium hydroxide as an alkaline substance (alkali treatment). Next, the aluminum can after alkali treatment contained 1 g / L ferric ion and 2 g / L nonionic surfactant, and the pH was adjusted to 1.0 with sulfuric acid as an acidic substance. Spray treatment was performed using an acid treatment solution at a treatment temperature of 50 ° C. for 40 seconds (acid treatment). In addition, the supply source of the ferric ion of an acid treatment liquid is ferric sulfate.

Next, it is washed with tap water for 15 seconds, and further, with a chemical conversion treatment agent (“Alsurf 450” manufactured by Nippon Paint Co., Ltd.), the treatment conditions are adjusted so that the coating Zr amount becomes 11 mg / m ^2, and chemical conversion treatment is performed. (40 ° C., 12 seconds). After the chemical conversion treatment, it was washed with tap water for 15 seconds, then spray-washed with deionized water for 5 seconds, and dried at 195 ° C. for 3 minutes.

<Examples 2 to 26, Comparative Examples 1 to 15 and Reference Examples 1 to 3>
In the alkaline treatment step, the alkaline substances shown in Table 1 and Table 2 were used, and the alkaline treatment liquid adjusted to the pH shown in Tables 1 and 2 was used at the treatment temperature and treatment time shown in Tables 1 and 2. The same aluminum can as in Example 1 was sprayed (alkali treatment). In the acid treatment step, ferric ions, a nonionic surfactant, and an organic sulfonic acid (HSO ₃ —CH ₂ CH (OH) CH ₂ OH), if necessary, at the concentrations shown in Table 1 and Table 2. The aluminum can after the alkali treatment was spray-treated at the treatment temperature and treatment time shown in Table 1 and Table 2 using the acid treatment liquid adjusted to the pH shown in Table 1 and Table 2 (acid treatment). ).
Thus, the aluminum can was processed on the same conditions as Example 1 except changing conditions as shown in Table 1 and Table 2.

  In Example 21 and Comparative Example 11, a mixture of sulfuric acid and nitric acid (mass ratio: 10 to 1) was used. In Example 22 and Comparative Example 12, a mixture of sulfuric acid and phosphoric acid (mass ratio: 10 to 1) was used. In Example 23 and Comparative Example 13, a mixture of sulfuric acid and hydrofluoric acid (mass ratio: 10 to 1) was used as an acidic substance.

  Moreover, in Comparative Examples 5 to 15 and Reference Examples 1 to 3, a solution obtained by diluting an acid treatment solution that uses an aluminum can in an acid treatment step, which is the next step, to a half concentration without performing an alkali treatment step. Then, after washing for 10 seconds at the same temperature as the acid treatment, it was subjected to an acid treatment step. In Example 23 and Comparative Example 13, ferric ions were not included in the acid treatment liquid, and in Comparative Examples 3 and 6, surfactants were not included in the acid treatment liquid, respectively.

<Comparative Example 16>
In Comparative Example 16, the alkali treatment step was not performed, the surfactant and the chelating agent were contained, and the treatment temperature was 60 with an alkaline degreasing solution adjusted to pH 12.5 with sodium hydroxide as an alkaline substance. Spray treatment was performed at 60 ° C. for 60 seconds (alkali degreasing treatment). Next, the aluminum can after the alkali treatment was subjected to an acid treatment step performed under the conditions shown in Table 2.

<Examples 27 to 44 and Comparative Example 17>
In the alkali treatment step, an alkali acid containing an organic acid, a chelating agent, a dispersant, and a surfactant at the concentrations shown in Table 3 and adjusted to the pH shown in Table 3 using the alkaline substance shown in Table 3 was used. Using the treatment liquid, the same aluminum can as in Example 1 was sprayed (alkali treatment) at the treatment temperature and treatment time shown in Table 3. In the acid treatment step, the treatment temperatures shown in Table 3 using an acid treatment solution containing ferric ions and nonionic surfactants at the concentrations shown in Table 3 and adjusted to the pH shown in Table 3 were used. Then, the aluminum can after the alkali treatment was spray-treated for a treatment time (acid treatment).
Thus, the aluminum can was processed on the same conditions as Example 1 except changing conditions as shown in Table 3. When the surfactant was included in the alkali treatment liquid, 2 g / L nonionic surfactant was included. Moreover, the acrylic acid maleic acid copolymer contained in Example 35 is SOKALAN CP5 manufactured by BASF Japan.

  Moreover, in Comparative Example 17, the same aluminum can as in Example 1 was sprayed at the treatment temperature and treatment time shown in Table 3 using an acidic solution containing 0.5 g / L of citric acid without performing the alkali treatment step. Processed. Subsequently, in the acid treatment step, ferric ions and nonionic surfactants are contained at the concentrations shown in Table 3, and the acid treatment liquid adjusted to the pH shown in Table 3 is used and shown in Table 3. Aluminum cans were sprayed at different processing temperatures and times.

[Evaluation]
(A) Amount of etching Before and after the alkali treatment step, the mass of the aluminum can was measured with a precision balance. The numerical value obtained by dividing the decrease in the mass of the aluminum can before and after the alkali treatment step by the surface area of the aluminum can was taken as the etching amount, and the etching amount was evaluated in the following two stages. The results are shown in Table 1, Table 2 and Table 3.
A: Less than 50 mg / m ² B: 50 to 100 mg / m ²

(B) Appearance Whiteness in the container after drying was visually determined. When the degreasing and desmutting had a complete and well-etched white appearance, it was evaluated as good, and was evaluated according to the following five levels depending on the degree of whitening. The results are shown in Table 1, Table 2 and Table 3.
A: Whole white B: Partially light gray C: Whole light gray D: Partially gray E: Whole gray

(C) Water wettability After the chemical conversion treatment, the container immediately after washing with water was shaken three times to drain the water, the container was left to face upward, and the wetted area (%) of the outer surface of the container after 30 seconds was measured. The results are shown in Table 1, Table 2 and Table 3.

(D) Desmutability A transparent adhesive tape is adhered to the surface of the aluminum can after the surface treatment obtained in the examples, comparative examples, and reference examples, and then peeled off and pasted on a white mount, tape The whiteness of the pasting surface was compared with other mount parts. The case where the smut was completely removed and there was no contamination was evaluated as good, and the following five levels were evaluated according to the degree of contamination. The results are shown in Table 1, Table 2 and Table 3.
5: No pollution 4: Trace contamination 3: Slight contamination 2: Moderate contamination 1: Major contamination

(E) Boiling water blackening resistance (corrosion resistance)
Appearance evaluation after the aluminum cans after surface treatment obtained in Examples, Comparative Examples and Reference Examples were immersed in boiling tap water for 30 minutes was performed according to the following criteria. The results are shown in Table 1, Table 2 and Table 3.
5: No change in appearance 4: Partially blackened 3: Overall thinly blackened 2: Partially darkened black 1: Entirely blackened

  As is clear from the comparison between Examples 1 to 11, 13 to 15, 17 and Comparative Example 5 or the like, when acid treatment is performed without alkali treatment, the aluminum can is alkali treated and then acid treated. It was found that good results could not be obtained in the appearance of the aluminum can, water wettability, desmutting property, and boiling water blackening resistance (corrosion resistance). This result is considered to be due to the fact that the surface of the aluminum can is not sufficiently etched in the acid treatment step unless the alkali treatment is performed. As shown in Reference Example 2, even when acid treatment is performed without performing alkali treatment, if the temperature of the acid treatment is increased, the surface of the aluminum can is sufficiently etched, and the appearance and water wettability are increased. Thus, an aluminum can having good desmutability and resistance to boiling water blackening (corrosion resistance) can be obtained.

  When Examples 1-11, 13-15, and 17 were compared with Reference Example 1, Examples 1-11, 13-15, and 17 had good evaluation results similar to Reference Example 1, while The treatment temperature in the acid treatment step is 20 ° C. lower than that in Reference Example 1. Thus, the temperature of the acid treatment step could be lowered by 20 ° C. by performing the alkali treatment step before the acid treatment step.

  Further, from the comparison between Examples 25 and 26 and Comparative Examples 14 and 15, even when an organic sulfonic acid is contained in the acid treatment liquid, the desmutability and boiling water blackening resistance (corrosion resistance) are not particularly required unless alkali treatment is performed. It is clear that sufficiently satisfactory evaluation results cannot be obtained. In addition, when organic sulfonic acid is contained excessively, it exists in the tendency for the process of the waste liquid of an acid treatment liquid to become complicated.

  Moreover, when Example 25 and Reference Example 2 are compared, Example 25 has a good evaluation result as in Reference Example 2, while the treatment temperature in the acid treatment step is higher than that in Reference Example 2. Is also 20 ° C lower. Thus, even if the acid treatment liquid contains an organic sulfonic acid, the temperature of the acid treatment step could be reduced by 20 ° C. by performing the alkali treatment step prior to the acid treatment step. .

  Moreover, when Example 26 and Reference Example 3 are compared, Example 26 has a good evaluation result similar to Reference Example 3, while the treatment temperature in the acid treatment step is higher than that of Reference Example 3. Is also 10 ° C lower. Thus, even if the acid treatment liquid contains a large amount of organic sulfonic acid (25 g / L), the temperature of the acid treatment step is 10 ° C. by performing the alkali treatment step prior to the acid treatment step. It was possible to reduce.

Moreover, even if it is a case where an alkali treatment process is performed before an acid treatment process like Comparative Examples 1-4, when the etching amount in an alkali treatment process is 50 mg / m < ² > or more, the external appearance of an aluminum can It turns out that it gets worse and turns gray all over. This result is considered to be caused by the fact that the etching control becomes difficult when the etching amount increases in the alkali treatment process.

  Further, as in Comparative Example 16, when the etching is sufficiently advanced in the alkaline degreasing step prior to the acid treatment step, as in the case of the aluminum base treatment for the can lid, the appearance of the aluminum can deteriorates, It turns out that it turns gray entirely.

  Further, as apparent from the comparison between Example 27 and Examples 28 to 44, the alkali treatment liquid contains these as compared with the case where no organic acid, chelating agent, dispersant or surfactant is contained. However, it was found that even when the alkali treatment step was performed under mild conditions (for a short time), the desmutability of the surface-treated aluminum can was improved. As a result, when the alkali treatment liquid contains an organic acid, a chelating agent or a dispersant, the formation of a hydroxide film is promoted by efficiently removing the smut on the surface of the aluminum can. Is expected to be due to Further, when the alkali treatment liquid contains a surfactant, it is expected that the formation of a hydroxide film is promoted by efficiently removing the lubricating oil on the surface of the aluminum can.

Claims (7)

An alkali treatment step of treating the aluminum can with an alkali treatment liquid;
An acid treatment step of treating the aluminum can after the alkali treatment step with an acid treatment solution,
The etching amount in the said alkali treatment process is a surface treatment method of the aluminum can which is less than 50 mg / m < ² >.   The surface treatment method for an aluminum can according to claim 1, wherein the alkaline treatment liquid contains at least one selected from the group consisting of sodium ions, potassium ions, and ammonium ions. The alkali treatment liquid is 40 to 70 ° C.,
The aluminum can surface treatment method according to claim 1 or 2, wherein a treatment time of the aluminum can in the alkali treatment step is 1 to 30 seconds.   The surface treatment method for an aluminum can according to any one of claims 1 to 3, wherein the alkali treatment liquid contains at least one selected from the group consisting of an organic acid, a chelating agent, a dispersant, and a surfactant. The acid treatment liquid contains at least one selected from the group consisting of sulfuric acid, nitric acid and phosphoric acid, contains 0.05 to 4 g / L of trivalent iron ions, and has a pH of 2 or less.
5. The surface treatment method for an aluminum can according to claim 1, wherein the treatment temperature of the aluminum can in the acid treatment step is 30 to 65 ° C. 5.   The aluminum can surface treatment method according to any one of claims 1 to 5, wherein a treatment time of the aluminum can in the acid treatment step is 10 to 90 seconds.   An aluminum can that has been surface-treated by the surface treatment method for an aluminum can according to any one of claims 1 to 6.