JPH0225980B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention belongs to the field of manufacturing single-sided hot-dip galvanized steel sheets by applying a plating inhibitor, and provides an effective method for easily and completely removing the plating inhibitor after hot-dipping. The present invention relates to a method for preventing sticking. Mainly, the present invention aims at improving the removability of the plating inhibitor by treating the steel surface before applying the plating inhibitor with an aqueous solution containing thiosulfuric acid or its salt. (Prior Art) Various methods have been proposed for manufacturing single-sided hot-dip galvanized steel sheets. One of them is to apply a plating inhibitor on one side of the steel sheet in advance, apply plating on multiple sides, and then apply the above-mentioned method. There is a method to achieve single-sided plating by removing the plating inhibitor. Many proposals have been made in the past for methods of applying a plating inhibitor to one surface. For example, the method proposed in Japanese Patent Publication No. 39-7112 uses water glass as a plating inhibitor, and
53-3928, SiO ₂ ,
Using a composite compound such as Al ₂ O ₃ , BeO, MgO, K ₂ O, Na ₂ O, etc. as the main component, JP-A-53-48029
In this issue, a water slurry containing alkali metal silicate and ammonium silicate as the main components was used.
No. 55-40659 uses an aqueous slurry of MgO, alkali silicate, boric acid and alkali, and
No. 54-64026 discloses a method using an aqueous slurry of a synthetic scale-like silicic acid compound, and JP-A-57-174439 discloses a method using an aqueous slurry of a compound of caustic soda, MgO, water glass, boric acid, titania, and alumina. Disclosed. When producing a single-sided hot-dip galvanized steel sheet using such a plating inhibitor, it is necessary to remove the plating inhibitor after hot-dipping, and the removal methods include (1) polishing, grinding, ( 2) high-pressure water spray, (3) chemical or electrical dissolution using a delamination liquid, and (4) delamination using a bending roll have been proposed. In addition, in the production of single-sided hot-dip plating using the plating prevention method, the plating inhibitor is used to prevent the oxidation of the steel plate, to prevent the molten metal to be plated from adhering to the stopper film, and to It is a necessary condition that the peeling can be easily and completely removed after plating, and the selection of a plating inhibitor that satisfies these requirements is an important issue. The method shown above has been proposed as a method for removing the plating inhibitor, but the difficulty of removing the flaking depends on the type of the plating inhibitor used and the manufacturing conditions (materials used,
It depends on the sintering conditions, furnace dew point, line speed, plating conditions), etc. Therefore, when manufacturing on an industrial scale, it is difficult to peel off easily and completely in-line in any method. is often difficult. For example, in the polishing/grinding method, a large number of polishing/grinding devices are required to obtain a completely non-plated surface, and it is difficult to easily perform in-line polishing/grinding. Alternatively, when using a deburring liquid or a bending peeling method, the former requires a long time to completely remove the peeling, while the latter requires multiple bending rolls, so it is still possible to completely peel off in-line in a short time. It's difficult. In addition, even if a clean non-plating surface is obtained by visual observation by these known methods, the remaining plating inhibitor component on the non-plating surface can be detected, for example, by In the case of agent slurry, Mg
may show a high value of 10 mg/m2 or ^more ,
In this case, the chemical conversion treatment properties in the next process are significantly inferior.
Not suitable as surface-treated steel sheets for automobiles and home appliances. (Problems to be Solved by the Invention) As mentioned above, various methods for removing the conventional plating inhibitor have already been proposed. The anti-glare agent must be able to reliably prevent the metal to be plated from adhering, while being able to be easily and completely peeled off after plating. From this point of view, in the peeling treatment methods that have been proposed in the past, the physical properties of the film of the inhibitor change slightly depending on the type of plating inhibitor used and the manufacturing conditions for single-sided melt plating. Specifically, there were problems in that the cutting properties deteriorated and the inhibitor remained in the form of dots or bands. In addition, visual observation shows that even if a clean non-plated surface is obtained, there is a significant amount of inhibitor components remaining on the non-plated surface, and even with chemical conversion treatment, the crystals become coarse and scale occurs. This problem also remained. (Means for Solving the Problems) The present invention makes it possible to easily and completely remove the peeling of the plating inhibitor after hot-melting when producing a single-sided hot-dip galvanized steel plate by the galvanizing agent method. To do this, a steel plate coated with a galvanizing agent on one side is introduced into a hot melting bath and shaken, and after the hot melting process, the galvanizing agent is peeled off to produce a single side galvanized steel plate. When performing single-sided plating prevention treatment, the steel surface to be coated with a plating inhibitor is coated with at least one of thiosulfuric acid or its salts in advance.
The purpose is to improve the peeling and removability of the plating inhibitor by treating with an aqueous solution or suspension containing 0.01 to 1 mol/ml and then applying the plating inhibitor. (Function) The present invention is characterized in that the surface of the steel plate to be coated with the inhibitor is treated in advance with a solution in which at least one kind of thiosulfuric acid or its salt is dissolved or suspended in water. Examples of thiosulfate or its salts include Na ₂ S ₂ O ₃ , K ₂ S ₂ O ₃ , FeS ₂ O ₃ , MgS ₂ O ₃ , Bi ₂
(S ₂ O ₃ ) ₃ , BaS ₂ O ₃ and other anhydrides or hydrates are used. By pre-coating these aqueous solutions or suspensions on the surface of the steel plate to which the inhibitor is to be applied, the inhibitor can be removed and removed significantly more easily after melt-melting. The reason may be as follows. In other words, in general, when adhering "metal" and "inorganic compound forming a glassy substance such as a plating inhibitor," the quality of adhesion is influenced by the concentration of metal oxide formed at the interface between metal and glass. It is said that the closer the oxide concentration (activity) is to the equilibrium concentration, the better the adhesion. Conversely, it can be said that the smaller the metal oxide concentration is than the equilibrium concentration, the worse the adhesion between the metal and the vitreous material, and the more likely the vitreous material is to peel off. Based on this idea, the present inventors
Although various inorganic metal compounds were selected, it was found that an aqueous solution or suspension of thiosulfuric acid or its salt facilitates peeling off the plating inhibitor after melt plating. The reason is that when these thiosulfuric acid or its salt compounds are applied to the steel sheet surface, iron oxide on the steel surface becomes difficult to diffuse into the inhibitor, and the oxide concentration at the metal-glass interface, that is, the oxidation of the steel surface is suppressed. However, it is thought that peelability is improved as a result. In short, it can be seen that it is sufficient if the reducing agent is present at the interface. Appropriate treatment solution concentrations include thiosulfate or K, Na,
As thiosulfates of Mg, Ba, Fe, Ca, Bi, etc.
It is in the range of 0.01 mol/~1 mol/. The degree of difficulty in peeling off and removing the plating inhibitor varies depending on the type of plating inhibitor used, but in the present invention, as an example, caustic soda, MgO, water glass,
Its effectiveness was confirmed using an aqueous slurry anti-plating agent of boric acid, titania and alumina compounds. As a result, at a concentration of 0.01 mole or less, the oxidation inhibiting effect on the surface of the steel plate coated with the plating inhibitor is insufficient, and the peeling and removability of the plating inhibitor is not improved. On the other hand, at a high concentration of 1 mole/or more, the steel surface is etched, rust is likely to occur, the peelability deteriorates, and the amount of residue of the inhibitor component increases significantly. The coating method on the surface of the steel plate may be any method such as spraying, dipping, or roll coater. Also, regarding application to the steel surface side to be hot-dipped,
Although it does not have any adverse effect on the plating property, it is desirable to treat only the surface of the steel plate coated with the plating inhibitor from the economic point of view. The temperature and treatment time of the treatment solution are thiosulfuric acid, K, Na, Mg, Ba, Fe, Ca,
There are no particular restrictions as long as the aqueous solution or suspension of thiosulfate such as Bi is uniformly applied to the surface of the steel plate coated with the anti-glare agent. As explained above, thiosulfuric acid or a thiosulfate of K, Na, Mg, Ba, Fe, Ca, Bi, etc. is melted in an aqueous solution or suspension containing 0.01 to 1 mol/mol of thiosulfate, which is controlled at an appropriate concentration. If the surface of the steel sheet to be single-sided plated introduced into the bath is treated in advance, the peeling off of the plating inhibitor after melt plating can be easily and completely removed. (Example) The effects of the present invention will be specifically explained below with reference to Examples. Example 1 A mixed aqueous solution of 0.1 mol/FeS ₂ O ₃ was prepared, and the above solution was sprayed onto the inhibitor-coated steel plate surface prior to plating, and after drying, the above mixed aqueous solution was subsequently applied to the steel plate surface. Inhibitor slurry on the side (10 g of water glass, 6 g of boric acid, 4 g of caustic soda)
g, MgO12g, titania 4g, alumina 4g,
A slurry of 17g of water) was applied and fired, and then the steel plate was hot-dip galvanized (470±5℃, Al0.15% in the bath,
5 seconds immersion). After that, when the inhibitor film was bent off toward the compression side using a bending roll (80 mmφ, bending angle 30°), the inhibitor film was completely peeled off and remained on the non-plated surface that had been washed with water. The plating inhibitor component was about 2 mg/m ² or less and was as clean as a normal cold rolled steel sheet. Example 2 An aqueous solution of 0.2 mol/K ₂ S ₂ O ₃ and _0.1 mol/MgS ₂ O 3 was prepared, and this solution was sprayed in advance on the surface of the inhibitor-coated steel plate, and after drying, the above mixed aqueous solution was subsequently applied. Inhibitor slurry (12 g of water glass, 5 g of boric acid, 3 g of caustic soda,
MgO 10g, titania 4g, alumina 3g, water 16
g slurry) was applied and fired, and hot-dip galvanizing as shown in Example 1 was performed. Thereafter, the inhibitor film was bent off toward the compression side using a bending roll (60 mmφ, bending angle 20°) to obtain a completely non-plated surface. The anti-plating agent content on the non-plated surface was about 3 mg/m ² or less, and it was as clean as a normal cold-rolled steel sheet. Example 3 Inhibitor obtained when a cold rolled steel sheet is treated with an aqueous solution or suspension containing the thiosulfuric acid or its salt of the present invention, then coated with an inhibitor slurry, fired, and hot-dip galvanized. The peelability of the film is shown in Table 1 along with comparative examples. From the above results, 0.01% of thiosulfate or thiosulfate
By pre-treating the surface of the steel plate coated with the plating inhibitor with an aqueous solution or suspension containing ~1 mol/ml, the plating inhibitor can be removed after melt plating.
It turns out that this can be accomplished easily and completely.

[Table] (Effects of the Invention) As explained above, according to the present invention, peeling off of the inhibitor can be easily and completely removed in the production of single-sided hot-dip galvanized steel sheets using the galvanizing inhibitor method. .

Claims (1)

[Claims] 1. When producing a single-sided plated steel plate by introducing a steel plate coated with a plating inhibitor on one side into a hot-dip galvanizing bath and peeling off the galvanizing agent after hot-dipping treatment. For single-sided plating prevention treatment, the steel surface to be coated with a plating inhibitor is coated with at least one of thiosulfuric acid or its salts in advance.
A method for preventing plating during the production of a single-sided hot-dip galvanized steel sheet, which comprises treating with an aqueous solution or suspension containing 0.01 to 1 mol/ml, and then applying a plating inhibitor.