JP7740917B2 - Cleaning solution for aluminum or aluminum alloys - Google Patents

Description

The present invention relates to a cleaning solution for aluminum or aluminum alloys, and a cleaning method and cleaning device using this cleaning solution.

Conventionally, formed products such as rolled sheets, cans, and containers made of aluminum or aluminum alloys (hereinafter, both may be collectively referred to as "aluminum") have been widely used. However, these formed products are contaminated with lubricants, aluminum powder (smut), and the like, and therefore require degreasing and cleaning after forming. Seamless cans made of aluminum or aluminum alloy sheets are obtained by subjecting aluminum sheets to severe processes such as drawing and ironing, and are therefore generally formed using lubricants and coolants. As a result, seamless cans (DI cans) after drawing and ironing contain not only aluminum powder but also oily stains from the lubricants and coolants.
In seamless cans having such a lubricant or the like attached thereto, it is necessary to remove the attached lubricant or the like before the can is subjected to the subsequent painting and printing processes, and the quality of the cleaning ability of the can significantly affects the quality of the subsequent surface treatment and painting.

The cleaning solutions currently used industrially to clean aluminum seamless cans are either aqueous sulfuric acid solutions containing hydrofluoric acid and at least one surfactant, or aqueous solutions containing phosphoric acid, nitric acid, etc. and at least one surfactant. These acidic cleaning solutions have many advantages, such as the ability to chemically inactivate the aluminum surface by forming an oxide layer primarily composed of aluminum oxide or hydroxide, thereby preventing the occurrence of appearance defects known as brown spots (Patent Document 1).

On the other hand, cleaning using acidic cleaning solutions corrodes equipment made of stainless steel and other iron alloys used in cleaning lines for aluminum seamless cans, requiring time-consuming maintenance and sometimes requiring high-temperature cleaning, making it less economical. Furthermore, waste liquid containing hydrofluoric acid and aluminum fluoride poses a significant environmental burden in terms of fluorine waste liquid treatment.

Alkaline cleaning solutions have also been proposed as cleaning solutions for seamless aluminum cans that do not cause such problems.
For example, Patent Document 2 listed below proposes an alkaline cleaning solution for aluminum or aluminum alloys, which comprises a total amount of 0.5 to 40 g/L of one or more alkali builders selected from alkali metal hydroxides, alkali metal carbonates, inorganic alkali metal phosphates, and alkali metal silicates, 0.2 to 10 g/L of one selected from organic phosphonic acids and salts thereof, 0.001 to 2 g/L of one or more metal ions selected from metal ions having a stability constant of 5.0 to 14.0 with organic phosphonic acids and salts thereof, and 0.1 to 10 g/L of a surfactant.

Patent No. 5007482 Patent No. 5051679

The alkaline cleaning solution can improve upon the drawbacks of the acidic cleaning solution, such as the corrosiveness of the cleaning equipment, the ease of treating waste liquid, and the energy cost, and can also degrease and clean seamless aluminum cans in the same way as the acidic cleaning solution.
However, it has been found that aluminum seamless cans cleaned with alkaline cleaning solutions sometimes suffer from metal exposure in the inner coating film formed during the painting process that follows. When the exposed metal areas were examined, inorganic components were detected. These inorganic components are thought to be derived from metallic soaps contained in the cleaning water used in the pre-cleaning process that precedes the cleaning process. Specifically, fatty acids in the coolant used during ironing form metallic soaps during the pre-cleaning process, which then adhere to the surface of the seamless can, inhibiting the formation of a coating film.
This is thought to be because, although conventional alkaline cleaning solutions have excellent cleaning power against oily stains, they tend to preferentially remove only oily stains, which makes it easier for inorganic components adhering to the can surface to remain.
Furthermore, in seamless can washing equipment, washing water is sprayed from above and below the seamless cans while they are being transported on a net-like conveyor belt in an inverted position with the bottom of the can facing up. Therefore, compared to the outer surface of the can where washing water is sprayed directly from above, the inner surface of the can where washing water is sprayed from below over the conveyor belt is somewhat inferior in terms of force and volume in terms of the washing water reaching the dirt to be removed.

The object of the present invention is therefore to provide an alkaline cleaning solution for aluminum or aluminum alloys that can remove metal soap as well as oily stains such as lubricants, without causing the problems described above, and a cleaning method and cleaning device for aluminum seamless cans using this alkaline cleaning solution.

According to the present invention, there is provided a method for cleaning aluminum or aluminum alloys, comprising: a pre-cleaning step of pre-cleaning aluminum seamless cans carried in from a molding device; and cleaning the aluminum or aluminum alloy seamless cans with a cleaning solution for aluminum or aluminum alloys after the pre-cleaning step,
The cleaning liquid for aluminum or aluminum alloys contains an alkaline component and a nonionic surfactant represented by the following formula (1):
The method for cleaning aluminum or an aluminum alloy is provided, in which the alkaline component is contained in an amount of 0.5 to 50.0 g/L, the nonionic surfactant is contained in an amount of 0.1 to 10.0 g/L, and the pH is 10.0 to 12.0 .
RO-(AO) _n -H...(1)
In the formula, R represents a linear or branched alkyl group having 6 to 12 carbon atoms, AO represents an oxyalkylene group having 2 to 5 carbon atoms, and n represents the average number of moles of oxyalkylene groups added (2 to 80).

In the cleaning method of the present invention,
1. The alkaline component is at least one selected from alkali metal hydroxides, alkali metal carbonates, inorganic alkali metal phosphates, and alkali metal silicates ;
is preferred.

In the cleaning solution for aluminum or aluminum alloys of the present invention, the specific nonionic surfactant represented by the above formula (1) is used as the surfactant, which makes it possible to reliably remove smut, lubricants, and other oily stains adhering to the surface of seamless cans, particularly the inner surface of the can, as well as metal soaps that affect coatability, thereby providing seamless aluminum cans that can form inner coatings with excellent coatability.

FIG. 1 is a flow chart showing an example of the process flow for cleaning aluminum seamless cans according to the present invention.

(cleaning solution)
An important feature of the alkaline cleaning solution for aluminum or aluminum alloys of the present invention is that it contains an alkaline component and a nonionic surfactant represented by the above formula (1).
Conventionally, alkaline cleaning solutions have contained an alkaline component (alkali builder) and a surfactant. However, in the present invention, it has been discovered that by using a specific polyoxyalkylene alkyl ether as the surfactant, it is possible to simultaneously remove metal soap along with oily stains such as lubricants and smut powder, thereby effectively preventing poor coating of the internal paint.

[Alkaline component]
The alkaline component (alkali builder) used in the detergent of the present invention may be any of those conventionally used in alkaline detergents, but it is preferable to use at least one selected from alkali metal hydroxides, alkali metal carbonates, inorganic alkali metal phosphates, and alkali metal silicates.
Examples of alkali metal hydroxides include sodium hydroxide and potassium hydroxide, examples of alkali metal carbonates include sodium carbonate and potassium carbonate, examples of inorganic alkali metal phosphates include sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, etc., and examples of alkali metal silicates include sodium metasilicate, etc. One of the above alkali components may be selected as the alkali builder, or two or more compounds may be used in combination.

The alkaline component is preferably contained in the cleaning solution in an amount of 0.5 to 50.0 g/L, particularly 3 to 15 g/L. If the amount of alkaline component is less than the above range, etching of the aluminum surface may not proceed as sufficiently as when the amount is within the above range, resulting in an uneven aluminum surface. On the other hand, if the amount of alkaline component is more than the above range, the aluminum surface may be over-etched, resulting in roughness of the surface, compared to when the amount is within the above range.

[Nonionic surfactants]
As described above, in the nonionic surfactant used in the cleaning solution of the present invention, in the above formula (1), the linear or branched alkyl group represented by R preferably has 6 to 12 carbon atoms, and more preferably 8 to 10 carbon atoms, and the oxyalkylene group represented by AO preferably has 2 to 5 carbon atoms, and more preferably 2 to 3 carbon atoms, and the average number of moles of oxyalkylene groups added is preferably 2 to 80, and more preferably 3 to 20.
The use of the nonionic surfactant makes it possible to exhibit high penetration power against oil stains, and to remove components that should be removed, such as lubricants and metal soaps, together with the surface of the aluminum, thereby making it possible to provide seamless cans that are free from inorganic components and have excellent applicability for the inner coating material.

The nonionic surfactant is preferably contained in the cleaning solution in an amount of 0.1 to 10.0 g/L, especially 0.5 to 3 g/L. If the amount of nonionic surfactant is less than the above range, cleaning performance may be inferior compared to when the amount is within the above range. On the other hand, if the amount of nonionic surfactant is more than the above range, the cleaning solution may foam more than when the amount is within the above range.

[others]
The cleaning solution of the present invention is prepared by using water as a solvent and adjusting the contents of the alkaline component and nonionic surfactant as described above, but may also contain a defoaming agent or a solvent other than water, if necessary, within a range that does not impair the cleaning properties and penetration power into oily stains of the cleaning solution.
The cleaning agent of the present invention preferably has a pH in the range of 10.0 to 12.0. If the pH is lower than this range, etching of the aluminum surface will not proceed sufficiently, and treatment will not be as efficient as when the pH is within the above range. On the other hand, if the pH is higher than this range, etching of the aluminum surface will proceed too quickly, and control of the amount of etching may become more difficult than when the pH is within the above range.

(Method for cleaning aluminum or aluminum alloy)
In the method for cleaning aluminum or aluminum alloys of the present invention, aluminum or aluminum alloys are cleaned using the cleaning solution of the present invention described above. This removes smut, oils, and metal soaps from the aluminum surface, and etches the aluminum surface. Furthermore, when cleaning seamless aluminum cans formed by drawing and ironing, the lubricants and coolants used in the forming process are also removed. The cleaning method can be performed by a conventionally known method, such as immersion in the cleaning solution or spraying with cleaning water.

The etching amount of the aluminum surface can be adjusted by adjusting the concentration of the alkaline component in the cleaning solution, the pH of the cleaning solution, the temperature of the cleaning solution, and the time for which the cleaning solution is in contact with the aluminum surface (cleaning time).
As mentioned above, the pH of the cleaning solution is preferably in the range of 10 to 12, and the progress of etching of the aluminum surface can be controlled by adjusting the pH.
The etching amount can also be controlled by adjusting the cleaning time and the temperature of the cleaning solution. Although not limited to this, it is preferable to adjust the temperature of the cleaning solution having a pH in the above range to 55 to 65°C and bring it into contact with the surface of aluminum or aluminum alloy for 10 to 60 seconds.

(Method for cleaning aluminum or aluminum alloy seamless cans)
The method for cleaning aluminum seamless cans is not particularly limited as long as it includes a degreasing step using the cleaning solution of the present invention, but preferably includes a pre-cleaning step, a degreasing step using the cleaning solution of the present invention, a water-rinsing step, a film-forming treatment step, a water-rinsing step, and a drying step, as shown in FIG. 1 .

[Seamless aluminum cans]
In the cleaning method of the present invention, the aluminum seamless cans to be cleaned are aluminum seamless cans (DI cans) formed using a lubricant and a coolant during molding. Specifically, these seamless cans (DI cans) are formed by rigorous processes such as drawing, drawing/deep drawing, drawing/ironing, and drawing/bending/ironing from aluminum sheets made of known aluminum or aluminum alloys, such as 3004 or 3104, using known lubricants, such as mineral oils or synthetic oils, or known coolants, such as water-soluble lubricants. Furthermore, seamless cans formed by such molding processes contain not only the lubricants but also smut and other substances generated during the processes. Furthermore, an aluminum oxide coating is formed on the aluminum surface.

[Pre-cleaning process, degreasing process, cleaning process]
Aluminum seamless cans with lubricating oil and other contaminants adhering thereto are continuously transported in an inverted state at high speed to the degreasing process of the cleaning equipment. A preliminary cleaning process is provided before the degreasing process, if necessary, to remove smut and other contaminants. As described above, the cleaning agent of the present invention can efficiently remove metal soap adhering to the aluminum surface even when the cleaning water in the preliminary cleaning process contains metal soap.
In the degreasing step, the cleaning solution of the present invention is sprayed onto the aluminum seamless can from above and below, whereby the nonionic surfactant reaches oily stains such as lubricants adhering to the surface of the aluminum seamless can, removing the oily stains and metal soap and also etching the aluminum surface to remove the aluminum oxide film formed on the surface of the aluminum seamless can.
The aluminum seamless cans that have been subjected to the degreasing step are washed with water in a first cleaning step and then transported to a film forming treatment step.

[Film formation process and cleaning process]
In the film-forming treatment step, a layer mainly composed of an oxide or hydroxide of aluminum is formed on the aluminum surface using a conventional film-forming treatment agent containing an inorganic acid such as sulfuric acid, nitric acid, or phosphoric acid, or an inorganic acid salt thereof, thereby chemically inactivating the aluminum surface, thereby making it possible to effectively suppress the occurrence of brown spots on aluminum seamless cans.
In the preferred embodiment shown in FIG. 1, the cleaning step is performed in two steps, a second water washing step and a pure water rinsing step, but the present invention is not limited to this and can be modified as appropriate.

[Drying process]
The aluminum seamless cans that are transported to the drying process are heated and dried in a dryer such as an oven.

(Cleaning device)
The cleaning device for aluminum seamless cans of the present invention is not particularly limited as long as it has a degreasing means using the cleaning solution of the present invention, but it is preferable that the device includes a pre-cleaning means for pre-cleaning aluminum seamless cans having a lubricant or the like attached thereto and supplied from a forming device, a degreasing means for degreasing the aluminum seamless cans supplied from the pre-cleaning means using the cleaning solution of the present invention, a water-washing means for rinsing the aluminum seamless cans supplied from the degreasing means, a coating means for treating the aluminum seamless cans supplied from the water-washing means with a coating-forming treatment agent, a water-washing means for rinsing the aluminum seamless cans supplied from the coating means, a drying means for drying the aluminum seamless cans supplied from the water-washing means, and a conveying means for continuously conveying the aluminum seamless cans from the forming device to the drying means.

The aluminum seamless cans, which have been conveyed from the forming device and have a lubricant or the like attached thereto, are continuously conveyed in an inverted state by a conveying means to a drying means. As the conveying means, a conventionally known conveying means such as a mesh conveyor can be used, and the aluminum seamless cans are placed in an inverted state in a line across the width of the conveying means (a direction perpendicular to the direction of travel) and continuously conveyed.
Each of the pre-cleaning means, degreasing means, cleaning means, and film-forming means is equipped with a spray device having a plurality of nozzles capable of spraying the degreaser comprising the cleaning liquid of the present invention, cleaning water, pure water, and film-forming treatment agent from above and below the aluminum seamless can in each process, and a blower device for blowing off the degreaser, cleaning water, etc. that has accumulated on the bottom of the aluminum seamless can. The installation of the blower device prevents cleaning water, etc. from accumulating even if the can bottom is dome-shaped, with a concave inward recess.

The effects of the present invention will be explained in more detail below using examples and comparative examples.

(Preparation of cleaning solution)
A cleaning solution was prepared using sodium hydroxide and sodium carbonate as alkaline components and a nonionic surfactant having the composition shown in Table 1 as a nonionic surfactant, so as to have the concentration shown in Table 1.

(Test material)
An unwashed DI can (diameter 66 mm x height 124 mm) formed by drawing and ironing a JIS A3004 alloy aluminum plate was used as a test material.

(Test Method)
Test materials (unwashed DI cans) were degreased, washed with water, and dried under the following conditions.
(1) Degreasing step (the cleaning solution of each example and comparative example was sprayed onto the inner and outer surfaces of the test material for 50 seconds)
(2) Water washing process (spray tap water for 20 seconds)
(3) Deionized water washing step (spray with deionized water for 20 seconds)
(4) Drying process (drying with hot air at 200°C for 2 minutes)

(Evaluation method)
(1) ERV (Enamel Rating Value)
The ERV was measured using an enameller. After the drying process, an exposed metal portion was formed on the outer surface of the bottom of the DI can and connected to the anode, while the cathode was immersed in saline solution filled in the can. A DC voltage of 6 V was applied for 4 seconds at room temperature (approximately 23°C), and the ERV was measured as the current value. The evaluation criteria were as follows:
〇: 60mA or less, ×: More than 60mA

(2) Appearance Evaluation After the drying process, the outer surface of the DI can was measured at eight points using a color computer (SM-3 manufactured by Suga Test Instruments) and the average value was calculated. The evaluation criteria were as follows:
◯: Brightness lower than 47 (excellent), ×: Brightness 47 or higher (poor)

(3) Desmutting property After the drying process, cellophane tape (manufactured by Nichiban Co., Ltd.) was attached to the inside surface of the DI can in three places and then peeled off. After peeling, the tape was attached to a blank piece of paper, and the brightness of the five places was measured using a color computer (SM-3 manufactured by Suga Test Instruments) to obtain an average value. The evaluation criteria are as follows:
◯: Brightness lower than 82 (excellent), ×: Brightness 82 or higher (poor)

(4) Water Wettability After the deionized water washing step, the DI can was left for 30 seconds, and the water wettable area at that time was evaluated in %.

(5) Foaming Ability: 50 mL of the cleaning solution heated to 60°C was placed in a 100 mL measuring cylinder with a stopper, and the stopper of the measuring cylinder was held down and vigorously shaken up and down vertically 30 times for 1 minute, and the maximum height of the foam that immediately formed was read. The evaluation criteria were as follows:
◯: Maximum foam height is less than 20 mm (excellent), ×: Maximum foam height is 20 mm or more (poor)

(6) Coating Adhesion An epoxy-acrylic paint was applied to the inner surface of the DI can after the drying process and baked at 215°C for 3 minutes to form a coating film with a thickness of 5 μm. This coating film was scored with a cutter and immersed for 60 minutes in a boiling solution of 5 g/L sodium chloride and 5 g/L citric acid dissolved in deionized water, then rinsed with water and air-dried. Tape was applied to the coating surface and peeled off, and the tape surface was visually evaluated. The evaluation criteria are as follows:
◯: No peeling of coating film (excellent), ×: Peeling of coating film (poor)

Claims (2)

1. A method for cleaning aluminum or aluminum alloys, comprising: a pre-cleaning step of pre-cleaning aluminum seamless cans carried in from a molding device; and a step of cleaning the aluminum or aluminum alloy seamless cans with a cleaning solution for aluminum or aluminum alloys after the pre-cleaning step,
The cleaning liquid for aluminum or aluminum alloys contains an alkaline component and a nonionic surfactant represented by the following formula:
The method for cleaning aluminum or an aluminum alloy, wherein the alkaline component is contained in an amount of 0.5 to 50.0 g/L and the nonionic surfactant is contained in an amount of 0.1 to 10.0 g/L, and the pH is 10.0 to 12.0.
RO-(AO) _n -H
In the formula, R represents a linear or branched alkyl group having 6 to 12 carbon atoms, AO represents an oxyalkylene group having 2 to 5 carbon atoms, and n represents the average number of moles of oxyalkylene groups added (2 to 80). 2. The method for cleaning aluminum or an aluminum alloy according to claim 1, wherein the alkaline component is at least one selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, inorganic alkali metal phosphates, and alkali metal silicates.