JP7656419B2 - Acid cleaning agent for aluminum-based metal materials and cleaning method for aluminum-based metal materials - Google Patents

Description

The present invention relates to an acidic cleaner for aluminum-based metal materials and a method for cleaning aluminum-based metal materials. More specifically, the present invention relates to an acidic cleaner for aluminum-based metal materials that has good desmutting properties even when cleaning at low temperatures and can suppress the occurrence of brown spots even when chemical conversion treatment is omitted, and a method for cleaning aluminum-based metal materials using the cleaner.

Aluminum-based metal materials made from aluminum or aluminum alloys generally have aluminum oxides and oils on their surfaces. Furthermore, aluminum cans such as beverage cans made by a drawing process called drawing and ironing (hereinafter referred to as DI processing) have aluminum powder (hereinafter referred to as smut) and lubricating oil that are generated by shaving during drawing on their surfaces.

Normally, aluminum cans such as beverage cans are first treated with a chemical conversion coating, and then painted with a coating film. In order to form a strong chemical conversion coating and a coating film, it is necessary to thoroughly remove aluminum oxide, oil, smut, etc. present on the surface and clean the surface.

A typical method for cleaning the surface of aluminum-based metal materials is to use an acidic cleaner that moderately etches and cleans the surface. Traditionally, hydrofluoric acid-based cleaners have been used as acidic cleaners, but in recent years, fluorine-free cleaners have been used in light of environmental protection.

As such a fluorine-free cleaning agent, an acidic aqueous cleaning solution for aluminum-based metal materials has been proposed that contains at least one inorganic acid, bromide ions, and oxidized metal ions in predetermined amounts (see Patent Document 1).

Japanese Unexamined Patent Publication No. 7-113189

However, acidic cleaning agents containing oxidized metal ions such as ferric ions (Fe ³⁺ ) and metavanadate ions (VO ³⁻ ) require the treatment temperature to be set at a high temperature of 70 to 80° C. in order to ensure etching ability, which makes them less economical.

As mentioned above, aluminum cans such as beverage cans undergo a process of cleaning the surface with an acidic cleaning agent, followed by a chemical conversion treatment to form a chemical conversion coating. If a chemical conversion coating has not yet been formed, the washing water reacts with aluminum to form aluminum hydroxide when the washing water dries, causing the affected area to appear brown, resulting in so-called brown spots.

If a film could be formed on the aluminum-based metal material at the same time as cleaning the surface with an acidic cleaner, it would be possible to omit the chemical conversion treatment process for forming the chemical conversion coating. If the chemical conversion treatment process could be omitted, it would be possible to move directly to the painting process after cleaning, and the economic effect of omitting the process would be very large. However, to date, such a cleaner has not been proposed.

The present invention has been made to solve the above problems, and its purpose is to provide an acidic cleaning agent for aluminum-based metal materials and a cleaning method for aluminum-based metal materials that have good desmutting properties even when cleaning at low temperatures and can suppress the occurrence of brown spots even if chemical conversion treatment is omitted.

The present inventors conducted extensive research to solve the above problems. They discovered that, in an acidic cleaning agent containing phosphate ions, sulfate ions, and ferric ions, if phosphate ions are the main component and the concentration ratio of phosphate ions to ferric ions is within a specific range, the surface of an aluminum-based metal material can be sufficiently cleaned even at a low treatment temperature, and a phosphorus-based film can be formed, thereby solving the above problems and completing the present invention.

That is, the present invention is an acidic cleaning agent for aluminum-based metal materials that contains phosphate ions, sulfate ions, and ferric ions, in which the concentration of the phosphate ions is 13 to 26 g/L, the concentration of the phosphate ions is greater than the concentration of the sulfate ions, and the concentration ratio of the phosphate ions to the ferric ions is 35:1 to 180:1.

The concentration of the sulfate ions may be 0.25 to 1.25 g/L.

The concentration of the ferric ions may be 0.1 to 0.5 g/L.

The concentration ratio of the phosphate ions to the sulfate ions may be 10:1 to 75:1.

It may also contain a surfactant.

The concentration of the surfactant may be 0.5 to 3.0 g/L.

It may also contain organic sulfonic acid.

Another aspect of the present invention is a method for cleaning aluminum-based metal materials, which includes a cleaning step in which the above-mentioned acidic cleaning agent for aluminum-based metal materials is brought to a liquid temperature of 40 to 70°C and brought into contact with the surface of the aluminum-based metal material to clean it.

The contact time may be from 15 to 60 seconds.

The acidic cleaning agent for aluminum-based metal materials of the present invention has good desmutting properties even when cleaning aluminum-based metal materials at low temperatures, and can suppress the occurrence of brown spots even if chemical conversion treatment is omitted after cleaning. Therefore, it has great economic value.

The following describes an embodiment of the present invention. Note that the present invention is not limited to the following embodiment.

<Acidic cleaner for aluminum-based metal materials>
The pickling agent for aluminum-based metallic materials of the present invention contains phosphate ions, sulfate ions, and ferric ions as essential components, and has phosphate ions as a main component, with the concentration ratio of the phosphate ions to the ferric ions being within a specific range.

[Phosphate ion]
The phosphate ion (PO ₄ ³⁻ ) contained in the pickling agent for aluminum-based metallic materials of the present invention is the main component among the components constituting the pickling agent for aluminum-based metallic materials.

The acid cleaner for aluminum-based metal materials of the present invention contains phosphate ions, sulfate ions, and ferric ions as essential components, but the concentration of phosphate ions is greater than the concentration of sulfate ions.

Because phosphate ions are the main component, it is possible to form a phosphorus-based film on the surface of an aluminum-based metal material cleaned with the acidic cleaning agent of the present invention. By covering the surface of the aluminum-based metal material with a phosphorus-based film, it is possible to prevent exposure of aluminum and to prevent brown spots that occur as a result of reaction with the washing water.

Therefore, with the acid cleaner for aluminum-based metal materials of the present invention, it is possible to omit the process of forming a chemical conversion coating by chemical conversion treatment, which has been conventionally performed, and after cleaning, the process can be directly transferred to a painting process to form a paint coating. Therefore, in the field of beverage cans, etc., this can greatly contribute to the economic effect of omitting processes.

The concentration of phosphate ions is 13 to 26 g/L, preferably 18 to 23 g/L, and particularly preferably 18 to 20 g/L.

If the phosphate ion concentration is less than 15 g/L, the effects of removing smut and suppressing brown spots will be insufficient. On the other hand, if the phosphate ion concentration exceeds 26 g/L, excessive matte will be removed, inhibiting the formation of a phosphorus-based film that has the effect of suppressing brown spots.

The concentration ratio of phosphate ions to ferric ions is 35:1 to 180:1, preferably 90:1 to 115:1, and particularly preferably 90:1 to 100:1.

If the concentration ratio of phosphate ions to ferric ions is outside the range of 35:1 to 180:1, the effects of removing smut and suppressing brown spots will be insufficient.

The concentration ratio of phosphate ions to sulfate ions is preferably 10:1 to 75:1, more preferably 30:1 to 52:1, and particularly preferably 36:1 to 40:1.

If the concentration ratio of phosphate ions to sulfate ions is outside the range of 10:1 to 75:1, the effects of removing smut and suppressing brown spots will be insufficient.

The source of phosphate ions contained in the acidic cleaner for aluminum-based metal materials of the present invention is not particularly limited as long as it can be ionized in the cleaner to generate phosphate ions. Examples include phosphoric acid, phosphonic acid, pyrophosphoric acid, metaphosphoric acid, etc. In the present invention, the substance that serves as the source of phosphate ions may be used alone or in combination of two or more types.

Among these, phosphoric acid is preferred because it is widely used industrially and is also used as a food additive. Phosphoric acid also functions as an etching accelerator.

[Sulfate ion]
The sulfate ion contained as an essential component in the pickling agent for aluminum-based metallic materials of the present invention functions as an etching accelerator.

The concentration of sulfate ions is preferably 0.25 to 1.25 g/L, and more preferably 0.5 to 1.25 g/L.

If the sulfate ion concentration is less than 0.25 g/L, the etching rate decreases and the effect of removing smut becomes insufficient. On the other hand, if the sulfate ion concentration exceeds 1.25 g/L, no further effect on etching is observed, which is economically disadvantageous.

The source of sulfate ions contained in the acidic cleaning agent for aluminum-based metal materials of the present invention is not particularly limited as long as it can be ionized in the cleaning agent to generate sulfate ions. Examples include sulfuric acid or its salts (iron sulfate, aluminum sulfate, calcium sulfate, sodium sulfate, etc.). In the present invention, the substance that serves as the source of sulfate ions may be used not only as a single type, but also as a combination of two or more types.

For example, when ferric sulfate is supplied as a source of ferric ions, which are an essential component of the pickling agent for aluminum-based metal materials of the present invention, sulfate ions will be ionized along with the ferric ions. In the present invention, the concentration of sulfate ions contained in the pickling agent can be adjusted by combining ferric sulfate with another sulfate ion source.

As a source of sulfate ions, sulfuric acid is particularly preferred because it is widely used industrially and is economically viable.

[Ferric ion]
The ferric ion contained as an essential component in the pickling agent for aluminum-based metallic materials of the present invention functions as an etching accelerator.

Usually, the etching reaction of aluminum-based metals in an acidic cleaning agent consists of an anodic reaction in which aluminum becomes aluminum ions (Al ³⁺ ) and a cathodic reaction in which H ⁺ in the acidic cleaning agent is reduced to 1/2H _2. Therefore, if ferric ions (Fe ³⁺ ), which are oxidized metal ions, are present in the acidic cleaning agent, the anodic reaction in which this Fe ³⁺ is reduced to Fe ²⁺ occurs simultaneously with the reduction of the H ⁺ , accelerating the etching reaction of aluminum.

The concentration of ferric ions is preferably 0.1 to 0.5 g/L, and more preferably 0.2 to 0.5 g/L.

If the concentration of ferric ions is less than 0.1 g/L, the etching rate decreases and the effect of removing smut becomes insufficient. On the other hand, if the concentration of ferric ions exceeds 0.5 g/L, no further effect on etching is observed, which is economically disadvantageous.

The source of the ferric ions contained in the acidic cleaning agent for aluminum-based metal materials of the present invention is not particularly limited, as long as it can be ionized in the cleaning agent to generate ferric ions.

In particular, it is preferable to supply the ferric ions as water-soluble salts such as sulfates or nitrates, and therefore the ferric ions are preferably supplied as ferric sulfate or ferric nitrate. When supplied as ferric sulfate, sulfate ions ionize along with the ferric ions, and when supplied as ferric nitrate, nitrate ions ionize along with the ferric ions.

As the etching reaction progresses, the concentration of ferrous ions (Fe ²⁺ ) increases, causing a decrease in the oxidation-reduction potential (hereinafter referred to as ORP) (also known as aging of the cleaning agent), and the etching promotion effect on the aluminum surface disappears. Therefore, an oxidizing agent that controls the ORP may be added as needed or from the beginning to oxidize the ferrous ions to ferric ions.

[Other ingredients]
The pickling agent for aluminum-based metallic materials of the present invention may contain other components, such as surfactants and organic sulfonic acids, in addition to the essential components of phosphate ions, sulfate ions, and ferric ions.

(Surfactant)
Surfactants are primarily used to remove oily and grease components adhering to the surface of aluminum-based metal materials, and in particular, to remove lubricants from aluminum cans after DI processing.

Additionally, surfactants prevent the removed oil and lubricant components from floating in the cleaning agent. If oil and lubricant components are floating in the cleaning agent, there is a risk that they will be re-adsorbed onto the surface of the aluminum-based metal material, but this can be avoided by adding a surfactant.

The type of surfactant is not particularly limited, and any of nonionic, cationic, anionic, and amphoteric surfactants can be used. Of these, nonionic surfactants are preferred, and examples of surfactants that are preferably used include ethoxylated alkylphenols, hydrogen carbonate derivatives, abietic acid derivatives, primary ethoxylated alcohols, and modified polyethoxylated alcohols.

The concentration of the surfactant is preferably 0.5 to 3.0 g/L, more preferably 1.0 to 2.5 g/L, and particularly preferably 1.5 to 2.0 g/L.

If the surfactant concentration is less than 0.5 g/L, cleaning performance, especially degreasing performance, will decrease. On the other hand, if the surfactant concentration exceeds 3.0 g/L, foaming will occur in the detergent, making cleaning difficult and placing a strain on wastewater treatment.

(Organic sulfonic acid)
The organic sulfonic acid is added mainly to provide a sufficient etching effect even under low temperature conditions.

The organic sulfonic acid has a structure represented by the following formula (1):
[Chemical formula 1]
R- _SO3H ...(1)
(In the formula, R represents a methyl group or a substituted alkyl group having 1 to 9 carbon atoms and at least one hydroxyl group.)

The substituted alkyl group in the above formula (1) is not limited to a straight chain, and may be a branched chain. Specific examples of the organic sulfonic acid include HSO ₃ -CH ₃ , HSO ₃ -CH ₂ OH, HSO ₃ -CH ₂ CH ₂ OH, HSO ₃ -CH ₂ CH ₂ CH ₂ OH, HSO ₃ -CH ₂ CH (OH) CH ₂ OH, etc. The organic sulfonic acid may be used alone or in combination of two or more kinds.

The content of organic sulfonic acid is preferably 0.01 g/L to 0.2 g/L. If the content is less than 0.01 g/L, the effect will be insufficient, and if the content exceeds 0.2 g/L, no further effect will be observed, which will be economically disadvantageous.

<Method for cleaning aluminum-based metal materials>
The method for cleaning aluminum-based metallic materials of the present invention includes a cleaning step in which the above-mentioned acidic cleaning agent for aluminum-based metallic materials of the present invention is brought into contact with the surface of an aluminum-based metallic material at a liquid temperature of 50 to 60° C. As long as the method includes the cleaning step, it may include any other steps.

The method for contacting the aluminum-based metal material with the acidic cleaner is not particularly limited, and any method known in the art can be appropriately selected. Examples include the spray method and the immersion method.

In the method for cleaning aluminum-based metal materials of the present invention, the acidic cleaning agent is used at a liquid temperature of 40 to 70°C. In other words, compared to conventional cleaning methods, cleaning can be performed at a lower temperature. A more preferred treatment temperature is 40 to 60°C, and 40 to 50°C is most preferred.

The time for which the acidic cleaning agent is in contact with the aluminum-based metal material is not particularly limited, so long as it is a time that allows sufficient etching and allows a uniform phosphorus-based coating to be formed on the surface of the aluminum-based metal material. It can be set appropriately depending on the treatment temperature.

For example, when the acidic cleaning agent is used at a liquid temperature of 50 to 60°C, the contact time is preferably 15 to 60 seconds. More preferably, it is 25 to 45 seconds, and most preferably, it is 25 to 45 seconds.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. However, Examples 3 to 6 are reference examples.

<Ingredients>
The materials used in the examples and comparative examples are shown below.
[Phosphate ion source]
Phosphoric acid (manufactured by Co-op Chemical Co., Ltd., product name: 75% phosphoric acid)
[Sulfate ion source]
Sulfuric acid (Mitsubishi Materials Corporation, product name: dilute sulfuric acid)
[Ferric ion generation source]
Ferric sulfate (manufactured by Jujo Synthetic Chemical Laboratory, product name: Ferric sulfate liquid)
[Organic sulfonic acid]
Methanesulfonic acid (manufactured by BASF Japan, trade name: Lutropur MSA)
[Surfactant]
Polyoxyalkylene ether (ADEKA Corporation, product name: ADEKA NOL LG294)

<Examples 1 to 16 and Comparative Examples 1 to 20>
[Preparation of coating composition]
The materials were mixed to the concentrations shown in Tables 1 and 2 to prepare pickling agents for aluminum-based metallic materials of Examples and Comparative Examples.

Specifically, the materials were mixed and stirred in industrial water to the concentrations shown in Tables 1 and 2. In this case, the activator was added last after the materials were mixed. After the acidic cleaning agent for aluminum-based metal materials was prepared, it was heated until the specified processing conditions were met.

[Treatment of aluminum-based metal materials]
A lidless container with lubricating oil and smut attached thereto was prepared by DI processing an aluminum plate of alloy 3104. The lidless container was sprayed with the acidic cleaner for aluminum-based metal materials obtained in the examples and comparative examples under the treatment conditions shown in Tables 1 and 2.

Then, it was washed with tap water for 15 seconds, followed by a spray rinse with deionized water for 5 seconds, and dried at 195°C for 3 minutes.

<Evaluation>
After drying, the following evaluations were carried out for each of the resulting containers.

[De-smutting]
A transparent adhesive tape was attached to the inner surface of the container after drying, and the tape was peeled off and attached to a white mount. Similarly, a tape that had not been peeled off was attached to the white mount. Thereafter, the whiteness of the tape-attached surface was compared between the tape that had been peeled off and the tape that had not been peeled off. Specifically, the degree of contamination (presence or absence of adhesion, or blackening) of the tape-attached surface was evaluated on the following 10-point scale.
5 No contamination 4.5 Contamination that is difficult to detect with the naked eye 4 Contamination with traces 3.5 Slight contamination 3 Slight contamination 2.5 Contamination less than 2 points 2 Moderate contamination 1.5 Contamination less than 1 point 1 Heavy contamination 0 Attachment or contamination over the entire surface

[Whether or not brown spots occur]
5.0 mL of industrial water was dropped onto the center of the bottom (dome portion) of the treated can with a dropper, and the can was dried in a hot air drying oven at 195° C. for 3 minutes, after which the percentage of discoloration occurring in the dome portion was visually confirmed. The evaluation criteria are shown below. The number of evaluations was 100 cans, and the percentage of discoloration occurring was confirmed.
4 No occurrence 3 Occurred in less than 1.0% of the number of processed items 2 Occurred in less than 5.0% of the number of processed items 1 Occurred in 5.0% or more of the number of processed items

Claims (9)

An acidic cleaning agent for aluminum-based metallic materials, comprising phosphate ions, sulfate ions, and ferric ions,
The concentration of the phosphate ions is 18 to 20 g/L;
the concentration of the phosphate ions is greater than the concentration of the sulfate ions;
The concentration ratio of the phosphate ions to the ferric ions is 35:1 to 180:1.
Acidic cleaning agent for aluminum-based metal materials. The acidic cleaning agent for aluminum-based metallic materials according to claim 1, wherein the concentration of the sulfate ions is 0.25 to 1.25 g/L. The acidic cleaning agent for aluminum-based metallic materials according to claim 1 or 2, wherein the concentration of the ferric ions is 0.1 to 0.5 g/L. The acidic cleaning agent for aluminum-based metal materials according to any one of claims 1 to 3, wherein the concentration ratio of the phosphate ions to the sulfate ions is 10:1 to 75:1. The acidic cleaning agent for aluminum-based metal materials according to any one of claims 1 to 4, further comprising a surfactant. The acidic cleaning agent for aluminum-based metal materials according to claim 5, wherein the concentration of the surfactant is 0.5 to 3.0 g/L. The acidic cleaning agent for aluminum-based metal materials according to any one of claims 1 to 6, further comprising an organic sulfonic acid. A method for cleaning aluminum-based metal materials, comprising a cleaning step in which the acidic cleaning agent for aluminum-based metal materials according to any one of claims 1 to 7 is brought to a liquid temperature of 40 to 70°C and brought into contact with the surface of the aluminum-based metal material to clean it. The method for cleaning aluminum-based metal materials according to claim 8, wherein the contact time is 15 to 60 seconds.