JPH07252676A - Rust preventive composition and cleaning method using the same - Google Patents

Abstract

PURPOSE:To produce a rust preventive composition effective for cleaning a iron based material or the like by preparing the rust preventive composition comprised of an amine compound, an inorganic salt of H3BO3 or the like and a hydroxide of alkali metal or the like. CONSTITUTION:The rust preventive composition comprised of the amine compound (triethanol amine or the like), the inorganic salt selected from a group composed of H3BO3, Na2B4O7, Na2B4O7.10H2O, Na2HPO4, Na2HPO4.2H2O, Na4P2O7 and Na2SiO3 and the hydroxide of alkali metal or alkaline earth metal (NaOH, Ca(OH)2 or the like) is prepared. As a result, the rust preventive composition exhibiting rust preventive effect continuing particularly to the Fe based material for a long period at the time of using for a water soluble rinse solution is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a rust preventive composition, and more particularly to a rust preventive composition and a rust preventive treatment method effective for cleaning iron-based materials.

[0002]

2. Description of the Related Art Machining a metal material includes a step of washing a work after the machining to remove the adhering machining oil. The cleaning process has been conventionally performed using an organic solvent, but the organic solvent is harmful to the environment and human body, and its use is about to be subject to regulation in the future. Therefore, there is a need for a detergent that replaces the organic solvent and a cleaning treatment method using the detergent.

In place of the conventional organic solvent, use of a water-soluble detergent which has little influence on the environment or the human body, is inexpensive, has no flammability, and has high work safety has been studied. However, when using such a water-soluble detergent, a rinsing step of removing the detergent from the work after the degreasing and cleaning work with the detergent is indispensable. In such a rinsing step, the work is immersed in a water bath and ultrasonically cleaned at a temperature of 50 to 60 ° C. to remove the detergent remaining on the work surface.

[0004]

When the cleaning and rinsing steps are applied to an iron-based metal material, particularly a cast iron work, large-scale rust is generated on the work surface due to the rinsing. Was found. It is believed that such rust is formed as a result of the temperature of the water during rinsing and the applied ultrasonic excitation. More specifically, it is considered that the following reactions occur between iron and water in an aqueous solution.

Fe + H ₂ O + 1/2 O ₂ → Fe ^{2 +} +
2e ⁻ + H ₂ O + 1/2 O ₂ → Fe ^{2 +} + 2OH ⁻
+1/2 O ₂ → Fe (OH) ₂ +1/2 O ₂ 2Fe (OH) ₂ + H ₂ O + 1/2 O ₂ → 2Fe (O
H) ₃ (red rust) 3Fe (OH) ₂ + 1/2 O ₂ → Fe ₃ O ₄ (black rust)
+ 3H ₂ O If rust occurs on the surface of the work, the work cannot be used in the product. Therefore, a rust preventive composition that suppresses rust by adding it to water in the rinsing process is commercially available. There is. However, such commercially available anticorrosion compositions are generally effective only for a short time of the day, even if long.
For this reason, it is necessary to replace the water in the rinsing tank with fresh water and to add the rust preventive composition again every day or many times a day, but such a step is disadvantageous in terms of working cost.

Therefore, it is a general object of the present invention to provide a novel and useful rust preventive composition which solves the above problems and a rust preventive treatment method using the rust preventive composition. A more specific object of the present invention is to provide a rust preventive composition whose ability is maintained for a long period of time when applied in an aqueous solution, and a rust preventive treatment method using such a rust preventive composition. .

[0007]

The present invention solves the above-mentioned problems.
With an amine compound; H₃BO₃And Na₂B_FourO₇When,
Na₂B_FourO₇・ 10H₂O and Na₂HPO_FourAnd N
a₂HPO_Four・ 2H₂O and Na_FourP₂O₇And Na₂
SiO₃An inorganic salt selected from the group consisting of
Protection consisting of hydroxides of metal or alkaline earth metals
Washing with rust composition or cleaning the workpiece with detergent
A cleaning step; the work cleaned in the cleaning step is treated with an amine
System compounds; H₃BO₃And Na ₂B_FourO₇And Na₂
B_FourO₇・ 10H₂O and Na₂HPO_FourAnd Na₂H
PO_Four・ 2H₂O and Na_FourP₂O₇And Na₂SiO
₃An inorganic salt selected from the group consisting of; and an alkali metal
Or rust preventive composition consisting of alkaline earth metal hydroxide
Dip it in an aqueous solution containing
Cleaning method characterized by comprising a rinsing step for removing
Solve by law.

[0008]

[Action] It is considered that the following reaction occurs by adding the amine compound to the aqueous solution in the rinse step. (HOCH ₂ CH ₂ ) ₃ N: + Fe + H ₂ O + 1/2 O ₂
→ (HOCH ₂ CH ₂ ) ₃ N: + Fe ²⁺ + 2e ⁻ + H ₂
O + 1/2 O ₂ → (HOCH ₂ CH ₂ ) ₃ N: + Fe ²⁺ +
_{^{2OH - +1/2 O 2 → (HOCH}} 2 CH 2)
₃ N: Fe ²⁺ + 2OH ⁻ +1/2 O _{2 The} above reaction corresponds to the case where triethanolamine is used as a rust preventive compound. In such reaction, the unshared electron pair of triethanolamine coordinates with the iron ion. It is believed that they bind and form a monomolecular film of the coordination compound on the iron surface. By such a coating, the reaction between water and iron is suppressed and rust prevention is performed.

In the rinse step, the following reaction is also considered. (HOCH ₂ CH ₂ ) ₃ N: + Fe + H ₂ O + 1/2 O _{2
→ (HOCH 2 CH 2) 3} N: + 4Fe 2+ + 8e - →
(Fe ^{2 +} ) ₃ O ₃ (CH ₂ CH ₂ ) ₃ N: Fe ²⁺ +3
H ⁺ + 8e ⁻ By the way, since the aqueous solution charged with such a rust preventive compound is open to the air, carbon dioxide in the air is constantly dissolved in the aqueous solution, and as a result, the pH of the aqueous solution is changed by the reaction shown below. Will decrease. When such a decrease in pH occurs, it is considered that the coordination bond between the amine compound and the iron ion described above does not proceed. (HOCH ₂ CH ₂ ) ₃ N: + H ₂ O + CO ₂ → (HO
CH ₂ CH ₂ ) ₃ N: + HCO ₃ ⁻ + H ⁺ The following reaction is also possible (HOCH ₂ CH ₂ ) ₃ N: + H ₂ O + CO ₂ → (HO
CH ₂ CH ₂ ) ₃ N: (HCO ₃ ⁻ ) ₂ + H ^{+ In the} present invention, in order to stabilize the pH of the rinse aqueous solution and to capture the carbonate ion generated as a result of the above reaction, a boric acid-based pH buffering agent is used. It was added to the rust solution. As a result, it is presumed that in the aqueous solution, the chemical reactions shown in the following reaction processes (1) and (2) proceed in a complicated manner to prolong the rust preventive life of the rinse aqueous solution. (HOCH ₂ CH ₂ ) ₃ N: + H ₂ O + CO ₂ + NaO
H + Na ₂ B ₄ O ₇ · 10H ₂ O reaction process (1) → (HOCH ₂ CH ₂ ) ₃ N: + HC
^{_{O 3 - + H + + NaOH}} + Na 2 B 4 O 7 · 10H 2
O → (HOCH ₂ CH2) ₃ N: + HCO ₃ ⁻ + H ⁺ +
_{^{Na + + OH - + Na 2}} B 4 O 7 · 10H 2 O → (H
_{OCH 2 CH2) 3 N: +} NaHCO 3 + H 2 O + N
a ₂ B ₄ O ₇ · 10H ₂ O reaction process (2) → (HOCH ₂ CH ₂ ) ₃ N: + HC
^{_{O 3 - + H + + 2Na}} + + B 4 O 7 2- · 10H 2 O +
NaOH → (HOCH ₂ CH ₂ ) ₃ N: + Na ₂ CO ₃
+ 2H ⁺ + B ₄ O ₇ ^2- · 10H ₂ O + NaOH → (H
_{OCH 2 CH2) 3 N: +} NaCO 3 + H 2 B 4 O 7
10H ₂ O + NaOH According to the present invention, even when a work made of an iron-based material is washed with a water-soluble detergent and then rinsed while applying ultrasonic waves, the surface of the work does not rust. Particularly, in the rust preventive composition according to the present invention, the effect of the rust preventive composition in the aqueous solution is 25 even when the rinse liquid is left in the air.
It is maintained for longer than a day, thus eliminating the need for frequent rinse solution changes. Along with this, it becomes possible to substantially reduce the machining cost of the work. In addition,
In the above reaction, NaOH alone or Na ₂ B ₄ O7.
Addition of 10H ₂ O alone has little effect.

Other features and advantages of the present invention will be apparent from the following detailed description of the embodiments with reference to the drawings.

[0011]

【Example】

Experimental Example 1 The surface of an iron-based casting (FC-20) was polished with # 500 sandpaper, and then immersed in an aqueous solution containing a rust preventive composition according to the present invention at room temperature. After ultrasonic excitation was applied for 10 minutes in the aqueous solution, the work was pulled up, and the generation of rust on the work surface was visually inspected. The rust preventive composition was composed of an amine compound, NaOH, and an inorganic salt. The composition of the composition used in this experiment and the concentration in the aqueous solution were as follows. Amine compound Triethanolamine 2000 wtppm NaOH 400 wtppm Inorganic salt Na ₂ B ₄ O ₇ 6000 wtppm The aqueous solution containing such a composition was effective for rust prevention even after 35 days from the preparation. That is, no rust was found on the surface of the work even when the work was treated with ultrasonic wave excitation for more than 35 days from the preparation of the aqueous solution. Experimental Example 2 The surface of an iron-based casting (FC-20) was polished with # 500 sandpaper, and then immersed in an aqueous solution containing a rust preventive composition according to the present invention at room temperature. After ultrasonic excitation was applied for 10 minutes in the aqueous solution, the work was pulled up, and the generation of rust on the work surface was visually inspected. The rust preventive composition was composed of an amine compound, NaOH, and an inorganic salt. The composition of the composition used in this experiment and the concentration in the aqueous solution were as follows. Amine-based compound Triethanolamine 2000 wtppm NaOH 400 wtppm Inorganic salt H ₃ BO ₃ 6000 wtppm The aqueous solution containing such a composition was effective for rust prevention even after 35 days from the preparation. That is, no rust was found on the surface of the work even when the work was treated with ultrasonic wave excitation for more than 35 days from the preparation of the aqueous solution. Experimental Example 3 The surface of an iron-based casting (FC-20) was polished with # 500 sandpaper, and then immersed in an aqueous solution containing a rust preventive composition according to the present invention at room temperature. After ultrasonic excitation was applied for 10 minutes in the aqueous solution, the work was pulled up, and the generation of rust on the work surface was visually inspected. The rust preventive composition was composed of an amine compound, NaOH, and an inorganic salt. The composition of the composition used in this experiment and the concentration in the aqueous solution were as follows. Amine compound Triethanolamine 2000 wtppm NaOH 400 wtppm Inorganic salt Na ₂ HPO ₄ 6000 wtppm An aqueous solution containing such a composition was effective for rust prevention even after 19 days from the preparation. When the work with the ultrasonic excitation was processed 20 days after the preparation of the aqueous solution, rust was observed on the work surface. Experimental Example 4 The surface of an iron-based casting (FC-20) was polished with # 500 sandpaper, and then immersed in an aqueous solution containing a rust preventive composition according to the present invention at room temperature. After ultrasonic excitation was applied for 10 minutes in the aqueous solution, the work was pulled up, and the generation of rust on the work surface was visually inspected. The rust preventive composition was composed of an amine compound, NaOH, and an inorganic salt. The composition of the composition used in this experiment and the concentration in the aqueous solution were as follows. Amine compound Triethanolamine 2000 wtppm NaOH 400 wtppm Inorganic salt Na ₂ B ₄ O ₇ 3000 wtppm Na ₂ HPO ₄ 3000 wtppm Aqueous solution containing such composition is effective for rust prevention even after 35 days from preparation. It was That is, no rust was found on the surface of the work even when the work was treated with ultrasonic wave excitation for more than 35 days from the preparation of the aqueous solution. Experimental Example 5 The surface of an iron-based casting (FC-20) was polished with # 500 sandpaper, and then immersed in an aqueous solution containing a rust preventive composition according to the present invention at room temperature. After ultrasonic excitation was applied for 10 minutes in the aqueous solution, the work was pulled up, and the generation of rust on the work surface was visually inspected. The rust preventive composition was composed of an amine compound, NaOH, and an inorganic salt. The composition of the composition used in this experiment and the concentration in the aqueous solution were as follows. Amine compound Triethanolamine 2000 wtppm NaOH 400 wtppm Inorganic salt Na ₂ B ₄ O ₇ 3000 wtppm Na ₂ P ₄ O ₇ 3000 wtppm Aqueous solution containing such composition is effective for rust prevention even after 35 days from preparation. Met. That is, no rust was found on the surface of the work even when the work was treated with ultrasonic wave excitation for more than 35 days from the preparation of the aqueous solution. Experimental Example 6 The surface of an iron-based casting (FC-20) was polished with # 500 sandpaper, and then immersed in an aqueous solution containing a rust preventive composition according to the present invention at room temperature. After ultrasonic excitation was applied for 10 minutes in the aqueous solution, the work was pulled up, and the generation of rust on the work surface was visually inspected. The rust preventive composition was composed of an amine compound, NaOH, and an inorganic salt. The composition of the composition used in this experiment and the concentration in the aqueous solution were as follows. Amine-based compound Triethanolamine 2000 wtppm NaOH 400 wtppm Inorganic salt H ₃ BO ₃ 3000 wtppm Na ₂ HPO ₄ 3000 wtppm An aqueous solution containing such a composition was effective for rust prevention even after 35 days from preparation. That is, no rust was found on the surface of the work even when the work was treated with ultrasonic wave excitation for more than 35 days from the preparation of the aqueous solution. Experimental Example 7 The surface of an iron-based casting (FC-20) was polished with # 500 sandpaper, and then immersed in an aqueous solution containing a rust preventive composition according to the present invention at room temperature. After ultrasonic excitation was applied for 10 minutes in the aqueous solution, the work was pulled up, and the generation of rust on the work surface was visually inspected. The rust preventive composition was composed of an amine compound, KOH, and an inorganic salt. The composition of the composition used in this experiment and the concentration in the aqueous solution were as follows. Amine-based compound Triethanolamine 2000 wtppm KOH 400 wtppm Inorganic salt Na ₂ B ₄ O ₇ 6000 wtppm The aqueous solution containing such a composition was effective for rust prevention even after 25 days from the preparation. That is, even when 25 days had passed since the preparation of the aqueous solution and the workpiece was treated with ultrasonic excitation, no rust was found on the surface of the workpiece. Experimental Example 8 The surface of an iron-based casting (FC-20) was polished with # 500 sandpaper, and then immersed in an aqueous solution containing a rust preventive composition according to the present invention at room temperature. After ultrasonic excitation was applied for 10 minutes in the aqueous solution, the work was pulled up, and the generation of rust on the work surface was visually inspected. The rust preventive composition was composed of an amine compound, KOH, and an inorganic salt. The composition of the composition used in this experiment and the concentration in the aqueous solution were as follows. Amine-based compound Triethanolamine 2000 wtppm KOH 400 wtppm Inorganic salt H ₃ BO ₃ 6000 wtppm The aqueous solution containing such a composition was effective for rust prevention even after 25 days from the preparation. That is, even when 25 days had passed since the preparation of the aqueous solution and the workpiece was treated with ultrasonic excitation, no rust was found on the surface of the workpiece. Experimental Example 9 The surface of an iron-based casting (FC-20) was polished with # 500 sandpaper, and then immersed in an aqueous solution containing a rust preventive composition according to the present invention at room temperature. After ultrasonic excitation was applied for 10 minutes in the aqueous solution, the work was pulled up, and the generation of rust on the work surface was visually inspected. The rust preventive composition was composed of an amine compound, Ba (OH) ₂ and an inorganic salt. The composition of the composition used in this experiment and the concentration in the aqueous solution were as follows. Amine compound Triethanolamine 2000 wtppm Ba (OH) ₂ 400 wtppm Inorganic salt H ₃ BO ₃ 6000 wtppm An aqueous solution containing such a composition was effective for rust prevention even after 25 days from preparation. That is, no rust was found on the surface of the work even when the work was treated with the ultrasonic wave excitation 25 days after the preparation of the aqueous solution. Experimental Example 10 The surface of an iron-based casting (FC-20) was polished with # 500 sandpaper, and then immersed in an aqueous solution containing a rust preventive composition according to the present invention at room temperature. After ultrasonic excitation was applied for 10 minutes in the aqueous solution, the work was pulled up, and the generation of rust on the work surface was visually inspected. The rust preventive composition was composed of an amine compound, LiOH, and an inorganic salt. The composition of the composition used in this experiment and the concentration in the aqueous solution were as follows. Amine compound Triethanolamine 2000 wtppm LiOH 400 wtppm Inorganic salt H ₃ BO ₃ 6000 wtppm The aqueous solution containing such a composition was effective for rust prevention even after 25 days from the preparation. That is, even when 25 days had passed since the preparation of the aqueous solution and the workpiece was treated with ultrasonic excitation, no rust was found on the surface of the workpiece. Experimental Example 11 The surface of an iron-based casting (FC-20) was polished with # 500 sandpaper, and then immersed in an aqueous solution containing a rust preventive composition according to the present invention at room temperature. After ultrasonic excitation was applied for 10 minutes in the aqueous solution, the work was pulled up, and the generation of rust on the work surface was visually inspected. The rust preventive composition was composed of an amine compound, Ca (OH) ₂ and an inorganic salt. The composition of the composition used in this experiment and the concentration in the aqueous solution were as follows. Amine compound Triethanolamine 2000 wtppm Ca (OH) ₂ 400 wtppm Inorganic salt H ₃ BO ₃ 6000 wtppm The aqueous solution containing such a composition was effective for rust prevention even after 25 days from the preparation. That is, even when 25 days had passed since the preparation of the aqueous solution and the workpiece was treated with ultrasonic excitation, no rust was found on the surface of the workpiece. Comparative Example 1 The surface of an iron-based casting (FC-20) was polished with # 500 sandpaper, and immersed in an aqueous solution at room temperature containing only triethanolamine as a rust preventive composition at a ratio of 2000 wtppm. After ultrasonic excitation was applied for 10 minutes in the aqueous solution, the work was pulled up, and the generation of rust on the work surface was visually inspected. It was found that an aqueous solution containing such a composition loses its rust preventive effect after 2 days from the preparation. That is, generation of rust was observed on the surface of the work when the work was processed with ultrasonic excitation for more than 2 days from the preparation of the aqueous solution. Comparative Example 2 The surface of an iron-based casting (FC-20) was polished with # 500 sandpaper and immersed in a room temperature aqueous solution containing a commercially available rust preventive composition at a ratio of 2000 wtppm. 1 in aqueous solution
After applying ultrasonic excitation for 0 minutes, the work was pulled up, and the generation of rust on the work surface was visually inspected. It was found that the aqueous solution containing such a composition already lost its rust preventive effect on the day of preparation. Comparative Example 3 The surface of an iron-based casting (FC-20) was polished with # 500 sandpaper, and a commercially available rust preventive composition different from that of Comparative Example 2 was used.
It was immersed in an aqueous solution at a room temperature containing 000 wtppm. After ultrasonic excitation was applied for 10 minutes in the aqueous solution, the work was pulled up, and the generation of rust on the work surface was visually inspected. It was found that an aqueous solution containing such a composition loses its rust preventive effect two days after the preparation of the aqueous solution. From the above results, it can be seen that the rust preventive composition according to the present invention, after being dissolved in an aqueous solution, retains its effect for a very long time as compared with the conventional one. Table 1 below shows a summary of the above experimental results.

[0012]

[Table 1]

Next, a method of cleaning a work using the rust preventive composition according to the present invention will be described. First, a work such as an iron-based casting is cleaned in a container holding a water-soluble detergent while applying ultrasonic excitation to remove dirt and oils and fats adhering to the work surface and recesses. At this stage, the surface of the work is covered with the detergent film and rust does not occur.

Next, the work thus washed is immersed in a container holding an aqueous solution in which the rust preventive composition of the present invention is dissolved, and in the aqueous solution, 50 to 6 is added.
Rinsing is performed while applying ultrasonic excitation at a temperature of 0 ° C. or less, and the detergent remaining on the work surface is removed. The rust preventive composition may be any of the aforementioned Experimental Examples 1 to 11. As a result, the detergent is effectively removed from the work without rusting the work surface.

The rust preventive composition of the present invention is not limited to the one using triethanolamine as the amine compound, and similar effects can be obtained by using diethanolamine and monoethanolamine. In general, the amine compounds contained in the rust preventive composition of the present invention include ammonia, ethylamine, isopropylamine, isobutylamine, amylamine, isoamylamine, hexylamine, octylamine, decylamine, dodecylamine, diethylamine, diisopropylamine, dibutylamine. , Diamylamine, tripropylamine, triisobutylamine, monoethanolamine, diethanolamine, triethanolamine, morpholine, cyclohexylamine, dicyclohexylamine, phenylamine, benzylamine, 2-naphthylamine, diphenylamine, triphenylamine, phenylene Includes diamines and phenylhithrazine.

The present invention also relates to the iron-based casting F described above.
It is effective not only for C-20 but also for other iron-based materials. These iron-based materials include S45C, SKS2, SUM3
2, SPC, SKD11, SS41, SK3, SUY
(Pure iron) and the like, but not limited thereto.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to such embodiments, and various modifications and changes can be made within the scope of the present invention.

[0018]

According to the present invention, an amine compound; an alkali metal or alkaline earth metal hydroxide; H ₃
BO ₃ , Na ₂ B ₄ O ₇ , and Na ₂ B ₄ O ₇ · 10H
₂ O, Na ₂ HPO ₄ , Na ₂ HPO ₄ · 2H ₂ O
By using a rust preventive composition consisting of an inorganic salt selected from the group consisting of Na ₄ P ₂ O ₇ and Na ₂ SiO ₃ , a work made of a material that easily rusts, such as an iron-based casting, Even when rinsing in warm water while applying ultrasonic excitation, generation of rust on the work surface is effectively suppressed. Further, the rust preventive effect of the aqueous solution containing such a rust preventive composition lasts for a long period of time, so that it is not necessary to frequently replace the aqueous solution used for rinsing with a fresh one. As a result, the processing cost of the work including cleaning is greatly reduced.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C23G 1/18

Claims (7)

[Claims] 1. An amine compound; H ₃ BO ₃ and Na
₂ B ₄ O ₇ , Na ₂ B ₄ O ₇ · 10H ₂ O, Na ₂
HPO ₄ , Na ₂ HPO ₄ · 2H ₂ O, and Na ₄ P ₂
A rust preventive composition comprising O ₇ and an inorganic salt selected from the group consisting of Na ₂ SiO ₃ ; and a hydroxide of an alkali metal or an alkaline earth metal. 2. The rust preventive composition according to claim 1, comprising at least two kinds of inorganic salts selected from the group. 3. The amine compound is ammonia, ethylamine, isopropylamine, isobutylamine, amylamine, isoamylamine, hexylamine, octylamine, decylamine, dodecylamine, diethylamine, diisopropylamine, dibutylamine, diamylamine, tripropylamine, Group consisting of triisobutylamine, monoethanolamine, diethanolamine, triethanolamine, morpholine, cyclohexylamine, dicyclohexylamine, phenylamine, benzylamine, 2-naphthylamine, diphenylamine, triphenylamine, phenylenediamine, phenylhitrazine The rust preventive composition according to claim 1, which is selected from the following. 4. The rust preventive composition according to claim 1, wherein the amine compound is triethanolamine. 5. A cleaning process for cleaning a work with a detergent.
And; the work washed in the washing step is treated with an amine compound.
Things and; H₃BO₃And Na ₂B_FourO₇And Na₂B_FourO
₇・ 10H₂O and Na₂HPO_FourAnd Na₂HPO_Four
・ 2H₂O and Na_FourP₂O₇And Na₂SiO₃Toyo
An inorganic salt selected from the group consisting of; alkali metal or
It contains a rust preventive composition consisting of an alkaline earth metal hydroxide.
To remove the detergent from the work.
And a rinsing step. 6. The cleaning method according to claim 5, wherein the rinsing step is performed while applying ultrasonic waves to the work. 7. The temperature of the aqueous solution in the rinsing step is 50.
The cleaning method according to claim 5, wherein the cleaning method is performed at a temperature of -60 ° C or lower.