JPH02125887A - Discoloration prevention agent for steel plate for cleaning water - Google Patents

Abstract

PURPOSE:To prevent the discoloration of a steel sheet by adding hydrazine to washing water at the time of rinsing a steel sheet to which chemical cleaning, etc., are applied in the above washing water. CONSTITUTION:At the time of rinsing the surface of a steel sheet, after subjected to chemical cleaning and electrolytic cleaning, with washing water, hydrazine or hydrazine and 2-14C hydroxy carboxylic acid or water-soluble salt thereof are added to the above washing water. At this time, N2H4, N2H4.H2O, N2H4.H2SO4, etc., can be used as hydrazine and malic acid, tartaric acid, etc., are cited as hydroxy carboxylic acid and blended by about 1-50wt.% based on N2H4, and further, the amounts of the above hydrazine and hydroxy carboxylic acid to be added to the above washing water are regulated to about 50-1000mg/l. By this method, the occurrence of discoloration to the steel sheet whose surface is activated by means of chemical cleaning, etc., can be prevented.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is a method for discoloring steel sheets for use in cleaning water that is added to cleaning water in order to prevent discoloration of steel sheets whose surfaces have been activated by chemical cleaning or electrolytic cleaning. It relates to inhibitors.

[Conventional technology]

There are many different types of steel sheets, and they are shipped as products after undergoing various processes such as hot rolling, cold rolling, annealing, plating, and painting.

In each of the second steps, chemical cleaning such as acid cleaning and alkaline cleaning, electrolytic cleaning, etc. are performed for the purpose of cleaning the steel plate surface. After these cleanings, in order to remove impurities adhering to the surface, it is washed (rinsed) with industrial water, pure water, etc.

Since the surface of the steel plate that has been cleaned by the above cleaning is activated, corrosion is more likely to occur, and the product becomes discolored due to rusting. Rusted or discolored steel sheets not only reduce product value, but also cause negative effects on the second culm, such as poor plating.

Rusted or discolored steel sheets cause a reduction in product yield due to cutting of defective parts (the defective rate may reach several percent) and increase in process costs due to re-cleaning, resulting in large losses. Defective products mainly occur during low-speed operation or when the line is stopped. As measures against these problems, continuous pickling and cold rolling using a looper, and continuous annealing equipment called CA14 and CAPL have been put into practical use, and the above-mentioned problems have been alleviated.

However, the equipment cannot handle all cases, and for example, discontinuous electrolytic cleaning is used in the production of high-grade steel. In this case, welding is required to clean the next coil, which typically shuts down the line for 3 to 5 minutes. In addition, low-speed operation may be forced due to poor welding or the like, resulting in the production of defective products.

[Problem to be solved by the invention]

The purpose of the present invention is to solve the above-mentioned problems by preventing discoloration of steel plates whose surfaces have been activated by chemical cleaning or electrolytic cleaning, and by improving product quality and product yield. The goal is to provide the following.

[Means for solving problems] The present invention is the following steel sheet discoloration inhibitor for washing water.

(1) Steel sheet discoloration inhibitor for cleaning water consisting of hydrazine.

(2) A discoloration inhibitor for steel sheets for cleaning water comprising hydrazine and an oxycarboxylic acid having 2 to 14 carbon atoms or a water-soluble salt thereof.

The steel sheet discoloration inhibitor for cleaning water of the present invention shows an extremely excellent discoloration prevention effect even when hydrazine is used alone, but it has an even higher effect when used in combination with 1-radine and oxycarboxylic acid or its water-soluble salt. is obtained.

In the present invention, hydrazine is anhydride (N2H4
), as well as hydrates (N211., ・N20) and sulfuric acid 1
Hydrogenium salts such as herazine (N2N4.N2So4) and hydrazine hydrochloride (N2114.II Ci) can be used, but hydrates are preferred.

The oxycarboxylic acid used in the present invention has 2 to 14 carbon atoms and may be monovalent or polyvalent. Examples of monovalent acids include glycolic acid, lactic acid, 2-hydroxybutyric acid, 2-hydroxy-2-methylpropanoic acid, gluconic acid, and mannonic acid. Examples of polyvalent acids include malic acid, tartaric acid, and citric acid.

Examples of these water-soluble salts include sodium salts, potassium 11 salts, and ammonium salts.

When the steel plate discoloration inhibitor for cleaning water of the present invention is composed of hydrazine and oxycarboxylic acid or its water-soluble salt, the blending ratio is determined as appropriate depending on the target to be treated, etc., but in general, it is It is preferable to blend 1 to 50% by weight of oxycarboxylic acid or a water-soluble salt thereof.

When oxycarboxylic acid or its water-soluble salt is added at a high concentration, it exhibits the effect of preventing discoloration of steel sheets even when used alone, but when used in combination with hydrazine, the concentration of oxycarboxylic acid or its water-soluble salt becomes extremely low. Effects are also shown depending on the concentration. Adding oxycarboxylic acid or its water-soluble salt at a high concentration will generate carbon stains during annealing in the subsequent process, causing defects in chemical conversion treatment and plating, so it is necessary to keep the concentration as low as possible, but it is recommended to use it in combination with hydrazine. This solves such problems.

In the present invention, when hydrazine and oxycarboxylic acid or a water-soluble salt thereof are used together, both may be mixed in advance, or each may be added separately to the washing water and blended. Good too.

In addition to hydrazine, oxycarboxylic acid, or a water-soluble salt thereof, the steel plate discoloration inhibitor for cleaning water of the present invention may contain other rust inhibitors, and in addition to these, hydroquinone as a deoxidizing catalyst for hydrazine, Amine, ammonia, sodium hydroxide, potassium hydroxide, etc. may be included as a pi adjuster.

The steel plate discoloration prevention agent for cleaning water of the present invention can be used in cleaning water for each rinsing process after chemical cleaning such as acid cleaning or alkaline cleaning or electrolytic cleaning. As a specific usage method, for example, it is usually 50 to 1000 mg/to washing water.
It is effective to add Q.

The locations where steel plates rust or discolor during low-speed operation or when the line is stopped are generally the water sprinkling area after chemical or electrolytic cleaning, inside the cleaning tank, and from the outlet of the cleaning tank until drying. Therefore, in order to prevent rusting and discoloration that occurs in such places, it is effective to add an anti-discoloration agent to the cleaning water, and it is also recommended to use this cleaning water for spraying chemicals or water after electrolytic cleaning. Effective. The next best method is to apply or spray an anti-discoloration agent on the water spraying area after chemical or electrolytic cleaning. For example, methods such as pumping up and spraying cleaning water containing an anti-tarnishing agent, or directly spraying an anti-tarnishing agent can be adopted. [Example] Examples 1 to 4 Cutting a cold-rolled steel sheet after electrolytic cleaning (SPCG-5B
, 60 mm x 100 mm x 0.8 mm thickness) was used as a test piece. After ultrasonic degreasing using toluene for 30 minutes, this test piece was wiped clean, washed with water, immersed in methanol, dried with cold air using a dryer, and cross-cutted with a cutter. On the other hand, after adding the chemicals shown in Table 1 to tap water heated to 80°C, the test piece was immersed for 5 minutes. The test piece was taken out, immersed in methanol, and dried with cold air using a dryer. The hydrazine used here is a monohydrate, but the amount added in Table 1 is N2
It is displayed as +14.

The treated test pieces were visually observed and the occurrence of rust and discoloration was evaluated using the following criteria.

◎...Excellent (no rusting or discoloration at all) 0.
・Excellent (almost no rust or discoloration) △・Slightly inferior (
There is some rust and discoloration. )×・Poor (Rust and discoloration are noticeable.) The results are shown in Table 1.

Comparative Examples 1 to 4 Comparative Examples 1 to 4 were carried out in the same manner as in "Example" except that the chemicals shown in Table 1 were used.

The results are shown in Table 1.

Table Examples 5 to 6 SS-41 material (10 mm φ
Adding the drug to tap water heated to 0°C (Example 5: Hydrazine 200 mg/Q in terms of anhydride, Example 6: 200 mg/f1 hydrazine in terms of anhydride. Citric acid 10 mg #l)
Polarization resistance (Rp) in the test solution was measured.

The relationship between the immersion time and the reciprocal of Rp is shown in FIG.

Comparative Examples 5 to 6 Instead of the drug used in Example 5, tap water was used as it was (Comparative Example 5), or 200 mg of triethanolamine was used.
The same procedure as in Example 5 was performed except that /+2 was used (Comparative Example 6). The results are shown in Figure 1.

As can be seen from Examples 1 to 4 and Comparative Examples 1 to 4 above, hydrazine or hydrazine mixed with oxycarboxylic acid has a better appearance of the test piece than other amines and has excellent effects. It is clear to show. It is also clear that when used in combination with oxycarboxylic acid, a synergistic effect is exhibited, and excellent effects are exhibited even when the amount of hydrazine added is reduced.

Further, as can be seen from Examples 5 to 6 and Comparative Examples 5 to 6 above, when hydrazine or hydrazine and oxycarboxylic acid are used in combination, the corrosion rate is low.

〔Effect of the invention〕

When a steel plate after chemical cleaning or electrolytic cleaning is brought into contact with rinsing water, rusting is usually observed within 2 to 3 minutes and the steel plate is cut, causing a decrease in yield, but the cleaning method of the present invention By using a steel sheet discoloration inhibitor for water use, excellent rust and discoloration prevention effects can be obtained, and product quality and product yield are improved.

[Brief explanation of drawings]

FIG. 1 shows the results of corrosion rates of Examples 5 and 6 and Comparative Examples 5 and 6. The horizontal axis of the figure is the immersion time of the electrode,
The vertical axis is the reciprocal of polarization resistance. Note that Rp indicates polarization resistance. Agent Patent Attorney Sei Yanagihara

Claims (2)

[Claims] (1) Steel sheet discoloration inhibitor for cleaning water consisting of hydrazine. (2) A discoloration inhibitor for steel sheets for cleaning water comprising hydrazine and an oxycarboxylic acid having 2 to 14 carbon atoms or a water-soluble salt thereof.