JPH04350181A - Method and device of controlling degreasing solution for aluminum can - Google Patents

Abstract

PURPOSE:To drastically improve the corrosion resistance of the Al can by removing Cu<2+> as copper sulfide and reducing the amt. of Cu to be deposited. CONSTITUTION:A degreasing soln. is sprayed into an airtight vessel 1 from in atomization port 3A, and hydrogen sulfide gas is introduced from an inlet 2. The Cu<2+> contained in the soln. reacts with the hydrogen sulfide gas to form copper sulfide. The soln. discharged from an outlet 1A is pressurized by a pump 5 a passed through a filter 6 to remove the precipitated copper sulfide. The process is conducted continuously or intermittently during the progress of degreasing to keep the Cu<2+> concn. in the acidic degreasing soln. at <=3ppm, and the black spotted corrosion on the surface of the Al can is prevented.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method and apparatus for managing acidic degreasing liquid for degreasing aluminum can bodies used as containers for soft drinks, beer, etc. This invention relates to improvements for increasing the corrosion resistance of chemical conversion coatings.

0002

2. Description of the Related Art Aluminum cans generally consist of a cylindrical can body with a bottom and a circular can lid that fits into the upper opening of the can body. The body and the can lid are each called the can body.

[0003] The can body is formed by deep drawing an aluminum plate, and then removing lubricating oil and dirt that adhered during the forming process in a degreasing process.
They are manufactured by applying chemical conversion treatment to form a chemical conversion film on the surface to improve corrosion resistance and paintability, and then painting the inner and outer surfaces. In addition, can lids are manufactured by applying a chemical conversion coating and painting to an aluminum plate in advance, and then punching and forming the aluminum plate.

[0004] Conventionally, aluminum alloys such as JISA3004 and JISA5182 have been mainly used as the material for these can bodies. These alloys have Al as the main composition, and Mg, Mn, and Cu are also added thereto, and the Cu content is approximately 0.2 to 0.25 wt%.

The main acidic degreasing solutions conventionally used are aqueous solutions containing sulfuric acid and iron ions, sulfuric acid and hydrofluoric acid, or phosphoric acid and sulfuric acid.
Japanese Patent No. 1147 discloses a degreasing liquid containing phosphoric acid and sulfuric acid as main compositions and appropriately adding a surfactant.

On the other hand, chemical conversion treatment is usually carried out using a chromium or zirconium phosphate solution, which produces a chromium phosphate solution (Cr content: 8 to 50 mg/m2) with a thickness of about 10 to 100 angstroms. Alternatively, a zirconium phosphate-based chemical conversion film (Zr content: 5 to 20 mg/m2) is formed on the surface of the can body.

[0007]

[Problems to be Solved by the Invention] However, in conventional aluminum cans, the corrosion resistance of the chemical conversion coating is not as high as expected, and when the filled contents are sterilized with heated water,
Problems such as black spots of corrosion on the outer surface of the bottom of the can were pointed out. For this reason, chemical analyzes of aluminum cans have been carried out using various analytical methods, but the cause has not been determined.

[0008] In order to investigate the cause of this, the present inventors
Using XPS analysis (X-ray photoelectron spectroscopy), which has not previously been used in this type of research, the depth distribution of the constituent elements of the chemical conversion coating on aluminum cans was investigated with high precision.

As a result, a relatively high concentration of Cu of unknown origin is contained in and near the surface layer of the chemical conversion coating.
It was discovered that the corrosion resistance of chemical conversion coatings may be inhibited by u. For example, when the chemical conversion coating of a regular aluminum can is analyzed by XPS, the photoelectron count of Cu on the clean surface of the material is 800 to 2000c.
ps, whereas in the surface layer of the chemical conversion film, it is 3 to 4
A double count of Cu was detected.

[0010] Therefore, the present inventors reexamined the entire process from molding of the can body to chemical conversion treatment, and determined that the Cu in the chemical conversion coating was
We investigated in detail what process this originates from. As a result, a trace amount (8 to 35 ppm
) was detected in the acidic degreasing solution, and this Cu2+
A new fact has been revealed that Cu is precipitated again on the surface of the can body, and a chemical conversion film is formed incorporating this Cu in the chemical conversion treatment process. Such Cu
The contamination of the can impairs the density of the chemical conversion coating, and furthermore, the Al and Cu of the can form an internal battery, causing a decrease in corrosion resistance.

[0011] Therefore, the present inventors further investigated the effect of C in the degreasing solution.
We conducted an experiment to reduce the Cu concentration in the chemical conversion coating by reducing u2+, and found that when the Cu2+ concentration in the acidic degreasing solution was lowered to 3 ppm or less, the amount of Cu precipitation was significantly reduced.

The present invention has been made based on this knowledge, and an object of the present invention is to provide a method and device for managing a degreasing liquid for aluminum can bodies, which can improve the corrosion resistance of a chemical conversion coating.

[0013]

[Means for Solving the Problems] Hereinafter, a method and apparatus for managing a degreasing liquid for aluminum can bodies according to the present invention will be explained in detail. FIG. 1 is a schematic diagram showing an example of a management device of the present invention. Reference numeral 1 in the figure is an airtight container, and a gas inlet 2 is formed in the upper part of the container, which is connected to a hydrogen sulfide gas supply means (not shown) via a valve 2A. Further, a degreasing liquid inlet pipe (degreasing liquid inlet) 3 is horizontally inserted into the upper part of the airtight container 1, and a plurality of spray ports 3A are formed on the lower surface of this degreasing liquid inlet pipe 3. The degreasing liquid inlet pipe 3 is connected to a degreasing liquid circulation path in the degreasing process of aluminum can bodies, and the degreasing liquid used in the degreasing process is sprayed into the airtight container 1 from the spray port 3A. .

On the other hand, the lower part of the airtight container 1 is tapered downward, and an outlet 1A is formed at the lower end. This outlet 1A is again connected to the circulation path via a pump 5 and a filter 6.

A large number of spacers 4 are placed inside the airtight container 1 until a predetermined liquid level is reached. These spacers 4 are for increasing the contact efficiency between the degreasing liquid and the hydrogen sulfide gas, and are made of, for example, a cylindrical body made of resin.

Next, an example of a method for managing degreasing liquid for aluminum can bodies using the above-mentioned apparatus will be explained. In this control method, the degreasing liquid used in the degreasing process is sprayed into the airtight container 1 from the spray port 3A, and at the same time, the valve 2A is opened and hydrogen sulfide gas is introduced into the airtight container 1 from the gas inlet 2 at a constant pressure. do.

Then, the sprayed degreasing liquid becomes fine particles and comes into contact with the hydrogen sulfide gas, and Cu2+ contained in the degreasing liquid reacts with the hydrogen sulfide gas to produce copper sulfide. This reaction continues while the degreasing liquid flows between the spacers 4, and
At the time of flowing out from A, Cu2+ is almost completely converted to copper sulfide.

Next, the degreasing liquid flowing out from the outlet 1A is pressurized by the pump 5, the precipitated copper sulfide is removed through the filter 6, and the degreasing liquid is returned to the degreasing liquid circuit in the degreasing process. By performing the above treatment continuously or intermittently during the degreasing process, Cu eluted from the can body into the acidic degreasing liquid during the degreasing process can be removed.
It is possible to remove Cu2+ by converting it into sparingly soluble copper sulfide, and to always maintain the Cu2+ concentration in the acidic degreasing solution at 3 ppm or less.

[0019] This significantly reduces the precipitation of Cu2+ on the surface of the aluminum can body during degreasing.
Because the amount of Cu incorporated into the chemical conversion coating formed after degreasing is reduced, the corrosion resistance of the chemical conversion coating and, by extension, the corrosion resistance of the aluminum can body is significantly improved compared to aluminum can bodies treated with conventional degreasing solutions. be done. therefore,
After filling degreased aluminum cans with contents, the heated water sterilization process (pastelizer) effectively eliminates the black stain-like corrosion that previously occurred on the unpainted can bottoms. It can be prevented.

[0020] Furthermore, in the above device, hydrogen sulfide gas does not leak outside the device, so the efficiency of using hydrogen sulfide gas is high;
It has the advantage of being low in processing cost and not causing environmental damage.

The management device of the present invention is not limited to the device shown in FIG. 1 described above, and various other modifications are possible. For example, instead of spraying the degreasing liquid in a gas, it is also possible to implement a configuration in which hydrogen sulfide gas is blown into the degreasing liquid.

Furthermore, the management method and apparatus of the present invention can be applied to acidic degreasing liquids of any composition that have been conventionally used. Below are some examples of common compositions of acidic degreasing liquids.

a. Sulfuric acid: 0.5-2wt% phosphoric acid:
0.5-1wt% Surfactant: 0.01-0.2wt%

[0024]b
．． Low temperature type (processing liquid temperature 50℃) SO42-: 600
0ppm F: 100ppm Surfactant: 1200ppm Inhibitor (Cr6+): 100ppm

002
5]c. Medium temperature type (processing liquid temperature 70℃) SO42-:
16000ppm NO3-: 1000ppm Fe: 1200ppm Surfactant: 2000ppm

d. Medium temperature type (processing liquid temperature 70℃) SO4
2-: 6500ppm PO43-: 6500ppm Fe: 200ppm Surfactant: 1500ppm

[0027] e. High temperature type (processing liquid temperature 80℃) SO4
2-: 3700ppm Surfactant: 100ppm Inhibitor (Cr6+): 80ppm

[0028]
Further, the processing conditions of the above-mentioned management method may be the same as the degreasing conditions so that it can be carried out in parallel with the degreasing treatment. For example, the degreasing conditions for the sulfuric acid-phosphoric acid degreasing solution shown in a above are such that the degreasing solution temperature is 40 to 90°C, preferably 65 to 75°C. Furthermore, the degreasing liquids b to e may be treated at the temperatures described.

Further, the material of the can body to be degreased may be any conventionally used material, and for example, the above-mentioned JISA 3004 and JISA 5182 are suitable. For example, JISA3004 has the following composition. Al: 95.5-98.2wt% Mg: 0.8-1.3wt% Mn: 1.0-1.5wt% Cu: 0.25wt% or less

Furthermore, as the chemical conversion coating formed on the can body after degreasing, a chromium phosphate or zirconium phosphate coating is suitable as in the past, and the coating amount is 10% in thickness.
It is preferable that the film has a thickness of 0 to 500 angstroms, and a coating amount of 3 to 20 mg/m2 of Cr or Zr as measured by fluorescent X-rays.

By using the acidic degreasing liquid treated with the degreasing liquid management method and apparatus of the present invention for degreasing, corrosion resistance is improved due to the polar cell action formed between the base material aluminum and the redeposited copper. Deterioration is removed and the chemical conversion film becomes denser and corrosion resistance is improved, so when conventional degreasing liquid is used, at least 250 angstroms (= 12 mg
/m2) It is also possible to reduce the required amount of chemical conversion coating to 8 mg/m2 or less.

[0032] Although such a chemical conversion coating is an extremely thin film of several tens to hundreds of angstroms, its constituent elements and impurity content can be quantified by X-ray photoelectron spectroscopy (XPS). The following shows Cu in the chemical conversion film by XPS.
Explain how to find the quantity.

The photoelectron intensity is a value proportional to the density of atoms. The present inventors investigated the distribution of constituent elements in the depth direction by measuring the photoelectron intensity while etching a sample at a constant rate with Ar ions using MgKα as an X-ray source.

The amount of Cu present in the chemical conversion film is expressed as the ratio of the maximum photoelectron intensity (unit: cps) of Cu to the photoelectron intensity of Al in the bulk (can body material itself) at this time. Expressed in this way, Cu atoms exhibit the maximum photoelectron intensity, that is, the maximum abundance, at a certain depth of the chemical conversion coating, but that depth varies depending on the degreasing conditions, chemical formation conditions, surface analysis method and measurement conditions, sample area, etc. This is because they are different.

According to experiments conducted by the present inventors, the maximum value of the Cu/Al photoelectron intensity ratio at which the chemical conversion coating has good corrosion resistance is 0.
．． It has been found that it is 3 or less, preferably 0.2 or less.

[0036]

[Example] Next, the effects of the present invention will be explained by giving examples. (Comparative Example 1) A can body molded using JISA 3004 material was degreased by immersion at 70° C. for 60 seconds using four kinds of degreasing liquids having the compositions shown in Table 1.

[0037]

[Table 1]

Next, using an XPS analyzer, while etching the outer surface of the bottom part of the can body with Ar ions, Cu, Al
, O, and C were measured under the conditions shown in Table 2.

[0039]

[Table 2]

[0040] No. in Table 1. The results obtained when using the degreasing solution No. 4 are shown in FIG. As is clear from this figure, the photoelectron intensity of Cu reached its maximum value several minutes after the start of etching with Ar ions, and the photoelectron intensity ratio of Cu/Al reached 0.9.

(Comparative Example 2) A can body that had been subjected to the same degreasing treatment as in Comparative Example 1 was soaked in the Zr chemical conversion treatment solution shown in Table 3 at 35°C for 30 minutes.
After dipping for seconds, apply Zr phosphate conversion coating to 15 mg/m of Zr.
It was formed with a thickness of 2.

[0042]

[Table 3]

Next, using an XPS analyzer, while etching the outer surface of the bottom part of the can body with Ar ions, Cu, Al
The photoelectron intensities of L, Zr, F, and P were measured under the conditions shown in Table 2. No. of Table 1 The results obtained using the degreasing solution No. 4 are shown in FIG. As is clear from this figure, the photoelectron intensity of Cu is Ar+
It reaches its maximum value a few minutes after the start of etching with ions,
The photoelectron intensity ratio of Cu/Al reached 0.9.

Next, the bottom portion of the aluminum can body subjected to the above treatment was immersed in heated water at 75° C. for 30 minutes, and the occurrence of corrosion in the form of black stains was examined. Table 4 shows the results.
Shown below. Under conditions where the Cu ion concentration in the degreasing solution exceeded 10 ppm, a significant decrease in corrosion resistance was clearly observed.

[0045]

[Table 4]

(Comparative Example 3) A can body that had been subjected to the same degreasing treatment as in Comparative Example 1 was soaked in a phosphoric acid chromium conversion treatment solution shown in Table 5 at 35°C.
The phosphoric acid Cr-based chemical conversion coating was immersed in
It was formed with a thickness of 5 mg/m2.

[0047]

[Table 5]

Next, using an XPS analyzer, while etching the outer surface of the bottom part of the can body with Ar ions, Cu, Al
The photoelectron intensities of L, Cr, F, and P were measured under the conditions shown in Table 2. The bottom part of the aluminum can body that has undergone the above treatment is
The specimens were immersed in heated water at 5° C. for 30 minutes, and the occurrence of corrosion in the form of black stains was examined. The results are shown in Table 6. Under conditions where the Cu ion concentration in the degreasing solution exceeded 10 ppm, a significant decrease in corrosion resistance was clearly observed.

[0049]

[Table 6]

(Comparative Example 4) A can body formed using JISA3004 material was treated with a degreasing liquid having the composition shown in Table 7.
Degreasing was performed at 0°C for 60 seconds.

[0051]

[Table 7]

Next, 3 was added to the Zr chemical conversion treatment solution shown in Table 3.
Immerse for 30 seconds at 5°C to apply a Zr phosphate chemical conversion film with a Zn content of 1.
It was formed to a thickness of 5 mg/m2. Furthermore, using an XPS analyzer, the photoelectron intensities of Cu, Al, O, Zr, F, and P were measured under the conditions shown in Table 2 while etching the outer surface of the bottom part of the can body with Ar ions.

The bottom portion of the aluminum can body subjected to the above treatment was immersed in heated water at 75° C. for 30 minutes, and the occurrence of corrosion in the form of black stains was examined. The results are shown in Table 8. Under conditions where the Cu ion concentration in the degreasing solution exceeded 10 ppm, a significant decrease in corrosion resistance was clearly observed.

[0054]

[Table 8]

(Example) An acidic degreasing solution having the same composition as Comparative Example 1 was continuously supplied to the above-mentioned apparatus shown in FIG. 1, and the can body was degreased while Cu2+ in the degreasing solution was precipitated and removed as CuS. processed. Next, the degreased can body was immersed in the Zr chemical conversion treatment solution shown in Table 3 at 35° C. for 20 seconds to form a Zr phosphate chemical conversion film with a thickness of 8 mg/m 2 of Zr. Further, using an XPS analyzer, the photoelectron intensities of Cu, Al, Zr, F, and P were measured under the conditions shown in Table 2 while etching the outer surface of the bottom part of the can body with Ar ions. The results are shown in Table 9. Further, the bottom portion of the aluminum can body subjected to the above treatment was immersed in heated water at 75° C. for 30 minutes, and the occurrence of corrosion in the form of black stains was examined.

The results are also shown in Table 9. From this result, even if the degreasing solution contains 10 ppm or more of Cu2+, Cu2+ can be removed as sulfide, and Cu2+ in the degreasing solution can be removed.
It is clear that by reducing the 2+ concentration, redeposition of copper on the surface of the aluminum can can be prevented during degreasing, and the amount of copper in the final chemical conversion coating can be significantly reduced, improving the corrosion resistance of the aluminum can. became.

[0057]

[Table 9]

[0058]

As explained above, according to the method and device for managing degreasing liquid for aluminum can bodies according to the present invention, Al is eluted from the can material as Al is eluted from the can surface during degreasing. Since the Cu2+ is removed as poorly soluble copper sulfide, it is possible to prevent an increase in the Cu2+ concentration in the degreasing solution and reduce the amount of Cu deposited on the can surface during degreasing. This prevents deterioration of the physical properties of the chemical conversion film due to the incorporation of Cu atoms into the chemical conversion film in the chemical conversion treatment step after degreasing, and significantly improves the corrosion resistance of the aluminum can body finally obtained.

Furthermore, since the corrosion resistance of the chemical conversion coating is improved, the chemical conversion coating can be made thinner than conventional products, and there is a possibility that the manufacturing cost of aluminum can bodies can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a degreasing liquid management device for aluminum can bodies according to the present invention.

FIG. 2 is a graph for explaining the effects of the present invention.

FIG. 3 is a graph for explaining the effects of the present invention.

[Explanation of symbols]

1 Airtight container 2 Hydrogen sulfide gas inlet 3　Degreasing liquid introduction pipe (Degreasing liquid inlet) 4 Spacer 5 Pump 6 Filter

Claims (4)

[Claims] 1. A method for managing an acidic degreasing liquid used for degreasing an aluminum can body, the method comprising: intermittently or continuously blowing hydrogen sulfide gas into the acidic degreasing liquid; and acidifying the CuS produced. By separating and removing Cu2+ from the degreasing solution, the concentration of Cu2+ in the acidic degreasing solution can be reduced to 3 ppm.
A method for managing a degreasing liquid for aluminum can bodies, characterized by maintaining the following: 2. The method for managing a degreasing liquid for aluminum cans according to claim 1, wherein the acidic degreasing liquid is a phosphoric acid-based acidic degreasing liquid containing phosphoric acid, sulfuric acid, and Fe3+. 3. The method for managing a degreasing liquid for aluminum can bodies according to claim 1, wherein the acidic degreasing liquid further contains a surfactant. 4. A degreasing liquid management device interposed in an acidic degreasing liquid circulation path for an aluminum can body, comprising: a degreasing liquid inlet into which the acidic degreasing liquid is introduced from the circulation path; an airtight container having an outlet for discharging the acidic degreasing liquid into the airtight container; a gas supply means for supplying hydrogen sulfide gas into the airtight container and bringing the acidic degreasing liquid into contact with the hydrogen sulfide gas; Filter the acidic degreasing solution after
1. A degreasing liquid management device for aluminum can bodies, characterized by comprising a filter for removing precipitates from an acidic degreasing liquid.