JPS6156311B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a single-sided plated steel sheet using a plating inhibitor. Recently, there has been a strong demand for single-sided plated steel plates that are used for automobiles, home appliances, construction materials, etc., and have been plated on one side to achieve the necessary corrosion resistance and to improve weldability. . Single-sided plated steel sheets can also be produced by electroplating, but
Since the plating speed is slow and the cost is high, the melt plating method is more advantageous especially when the amount of plating is large. Conventionally, methods for manufacturing single-sided galvanized steel sheets using the hot-dip galvanizing method include, for example, in the case of galvanizing, a method in which two steel plates are stacked, both ends are welded and plated, and then both ends are cut off. There are methods in which molten zinc is applied only to one side of the steel plate by roll or curtain flow coating, methods in which both sides are plated and then the zinc on one side is removed by grinding or electrolysis, and there are methods in which molten zinc is applied to one side of the steel plate in advance. There is a method of applying an anti-glazing agent, plating, and then removing the film of the anti-glazing agent, and a method of raising the surface of the plating bath using an ultrasonic wave or an electromagnetic pump to glaze only one side. Many proposals have been made for methods. However, these methods have drawbacks such as being technically difficult to implement and having high manufacturing costs, and there are almost no examples of successful production on a commercial scale. Since the present invention relates to a method using a galvanizing agent, in particular, a single-sided galvanizing method that has been proposed in the past with regard to a method using a galvanizing agent will be discussed. Publication No. 39-4204), alkali metal silicates,
Water slurry containing ammonium silicate as the main component (Japanese Patent Application Laid-open No. 53-48029), non-staining agent containing silicone resin as the main component (Japanese Patent Publication No. 51-8101), synthetic flaky silicic acid compound Water slurry (Unexamined Japanese Patent Publication No. 1987-
64026) or alkaline earth metal oxides (US Pat. No. 3,121,019). However, these conventional techniques have the following drawbacks. In other words, annealing in a cyclic atmosphere (approximately 700
In the continuous hot-dip galvanizing method, in which the galvanizing agent is applied to one side of the steel plate, it is difficult to completely prevent the galvanizing from adhering to one side of the steel plate, as the galvanizing agent coating decomposes during annealing or peels off from the surface of the steel plate in some areas. It is difficult to prevent
Furthermore, since the steel sheet may be oxidized in the atmosphere after plating, it is necessary to remove this oxide either by ring removal or mechanically. In addition, the coating film formed on one side of a steel plate using a plating inhibitor generally has poor removability, so it is almost impossible to completely remove the coating film without damaging the appearance of the steel plate surface. Removal of the top coat required high costs. The present inventors previously discovered magnesia,
An aqueous slurry containing four components: boric acid, an alkali, and an alkali silicate salt (Japanese Patent Application Laid-Open No. 146730/1983), followed by a five-component slurry in which one of titania and titanium hydroxide was added to these four components. (Japanese Unexamined Patent Publication No. 119157/1982), but even in these cases the following drawbacks still remain. When producing single-sided galvanized steel sheets using a galvanizing agent in a continuous hot-dip galvanizing line that performs pre-plating reducing atmosphere annealing, the galvanizing agent properties are as follows: It is necessary that molten Zn does not adhere to the blocking film (molten metal adhesion prevention property on the coating film), and that the blocking film can be easily removed after dazzling. This molten metal adhesion prevention property is also significantly influenced by the pre-plating annealing temperature and the upward pulling rate from the molten Zn. When using the above inhibitors (JP-A-52-146730, JP-A-55-119157) in an actual line, when the pulling speed of the steel plate from the molten zinc bath is high, or when zinc with excellent workability is used, When annealing at a temperature above the _A1 transformation point to obtain a galvanized steel sheet, zinc adheres to the galvanizing inhibitor coating, which is not only economically disadvantageous, but also prevents the production line of the steel sheet from being exposed to this deposited zinc. In some cases, it peeled off and stained the line. Therefore, the present invention focuses on the annealing temperature and pulling rate, and develops an anti-sticking agent that has excellent properties in preventing molten metal from adhering to the coating film and in peeling off the fired film even when the annealing temperature is high and the pulling rate is fast. This is what we did. One side of a steel plate was coated with a water slurry in which at least one compound selected from the group consisting of alumina, aluminum hydroxide, and alumina sol was added to one of the previously invented magnesia-boric acid-alkali-silicate salt-titania and titanium hydroxide. In this method, the steel sheet is coated and fired, then immersed in a molten metal plating bath and pulled upward to apply a single side of the steel plate. Even if the pre-plating annealing temperature is higher than the _A1 transformation point,
The present invention also aims to produce a single-sided plated steel sheet that has excellent plating prevention properties, molten metal adhesion prevention properties on coating films, and annealing film release properties even when the pulling speed is high. The present invention improves the physical properties of magnesia, which is one of the inhibitor components, and uses magnesia hydrated at least 1% when performing single-sided plating using an anti-glare agent. The present invention aims to provide a method for producing a single-sided plated steel sheet having ductility. Magnesia as used in the present invention is mainly composed of magnesium oxide, which is produced by converting bittern recovered from seawater into magnesium hydroxide with slaked lime, filtering it, and firing it in a rotary kiln or Matsufuru furnace, followed by a crushing and classification process. It is a general term for powders that are Hydration means that this magnesium oxide reacts with moisture in the atmosphere and changes from MgO + H ₂ O to Mg(OH) ₂ . This hydration proceeds from the surface of each particle, so if the surface is covered with magnesium hydroxide, the rate of hydration to the center is considerably suppressed. The method for quantitatively understanding hydration is as follows. In other words, the surface of MgO particles is Mg
A predetermined amount of the powder converted to (OH) ₂ is weighed in a well-baked alumina boat, and then fired in an electric furnace at 1000°C to convert Mg(OH) ₂ →MgO.
＋H ₂ O ↑ dehydration reaction, 100~ to avoid moisture absorption
After cooling to 200℃, cool it to room temperature in a desiccator, weigh it again, and calculate the Mg in magnesia from the difference.
(OH) ₂ is calculated. The plating inhibitor of the present invention includes at least one of magnesia and magnesium hydroxide, an alkali silicate salt (M ₂ O·nSiO ₂ ·mH ₂ O, in which M represents an alkali metal), boric acid, and an alkali metal. hydroxide, titania, and titanium hydroxide, and further contains at least one compound among alumina, aluminum hydroxide, and alumina sol. In the process of applying the inhibitor slurry consisting of the above six components to a steel plate, drying it, and annealing it, the present inventors do not use magnesia with a hydration amount of at least 1% prior to use in the inhibitor slurry. After annealing, it was discovered that cracks and peeling occur on the surface of the coating film, and fine zinc adheres to those areas, leading to the present invention. It is not clear why the surface of the paint film does not crack or peel when magnesia with a hydration level of 1% or more is used, but the MgO surface is stabilized by being covered with Mg(OH) ₂ and the inhibitor slurry is stabilized. When the hydration reaction is suppressed compared to MgO with an unhydrated active surface, Mg(OH) ₂ →
This is probably because the amount of dehydration in the MgO+H ₂ O↑ reaction is small and the shrinkage of the coating film is small. The most important components in the plating inhibitor of the present invention are at least one of titania and titanium hydroxide, alumina,
At least one compound selected from the group consisting of aluminum hydroxide and alumina sol. These components include at least one of magnesia and magnesium hydroxide in the plating inhibitor;
It acts to suppress the degree of vitrification of substances formed by alkali silicates, boric acid and alkali metal hydroxides. As the degree of vitrification of the above-mentioned substance progresses, the adhesion of molten metal onto the plating inhibitor coating becomes intense, and it no longer exhibits properties as a plating inhibitor. Titania or titanium hydroxide is mainly used to prevent molten metal from adhering to the plating inhibitor coating, and at least one of titania and titanium hydroxide is used for 10 g of at least one of magnesia and magnesium hydroxide. It is necessary to add 1.4 to 10g of. This is because if it is less than 1.4 g, it will not have the effect of preventing the adhesion of molten metal, and if it exceeds 10 g, cracks will occur in the plating inhibitor coating and it will not function as a plating inhibitor. The main purpose of alumina, aluminum hydroxide, or alumina sol is to suppress the degree of vitrification of the plating inhibitor substance, and a group consisting of alumina, aluminum hydroxide, and alumina sol is added to 10 g of at least one of magnesia and magnesium hydroxide. It is necessary to add 3 to 10 g of at least one of the more selected compounds. If it is less than 3g, there will be no effect of suppressing the progress of vitrification, and if it exceeds 10g, the peelability when removing the plating inhibitor coating after molten metal plating will deteriorate, and the plating inhibitor coating will not form on the steel plate. This is because it remains attached. In the present invention, first,
The six-component water slurry described above is applied to one side of a well-degreased steel plate, and dried preferably at a temperature of 200° C. or lower. The coating method may be any method such as roll coating, spray coating, or brush coating, and the appropriate coating amount is 5 to 300 g/m ² after drying. If the coating amount is too small and the coating is incomplete, or too large and the coating film cracks when drying, it will not be possible to completely prevent plating on the coated surface. In addition, it is desirable to evaporate the moisture in the coating film by drying at a low temperature of 200°C or less, but this is done to keep the subsequent annealing atmosphere cyclic and to prevent cracking or peeling of the coating film due to rapid high-temperature heating. This is to do so. After forming a uniform dry coating on one side, the steel plate is annealed (approximately 700 to 900°C) in the same way as in the normal continuous hot-dip metal plating method, and the steel plate temperature is adjusted to the plating bath temperature (zinc plating). If using a plating bath, cool to around 460℃) and then immerse in a plating bath. During this time,
During annealing, the coating partially flows and becomes glassy, and then becomes a solid coating during cooling or in a plating bath, preventing contact between the steel plate surface and the molten metal in the bath. The steel plate taken out of the plating bath is plated on only one side, and the other side is not plated and is covered with a coating film. This coating film has extremely poor wettability with molten metal even if the annealing temperature is high or the steel plate is pulled up at a high speed, so molten metal rarely adheres to the coating film, but in rare cases Dross may adhere to the surface, so gas wiping is recommended after plating. This gas wiping is also more ideal if a combustion gas such as butane or propane is used. Also,
Since this coating film is extremely dense, it was found that it also plays an important role in completely preventing air oxidation of the steel plate after it is removed from the plating bath. After plating, the coating film must be removed from the steel sheet, but when the plating inhibitor of the present invention is used, the steel sheet removed from the plating bath is heated to approximately 100°C.
It has been found that the coating film can be easily peeled off by rapidly cooling from the above temperature. The spangle size may be adjusted before the quenching is solidified, or after the quenching is solidified, or even after being slowly cooled and then reheated at a convenient time. . As a rapid cooling method, immersion in water is easy and effective. It has been found through experiments that by quenching in water, the coating film is completely peeled off from the steel sheet surface, and is not oxidized at all, resulting in a steel sheet surface that is exactly as it was rolled. In addition to the water cooling method described above, slight repeated bending, grinding,
The coating film can also be easily peeled off and removed by polishing. After removing the coating film using this method, a final finishing cleaning process including washing with water and light brushing can yield a completely plated steel plate on one side. According to the present invention, the adhesion of weld metal to the surface coated with a plating inhibitor when the pulling speed is high or when annealing is performed at a high temperature, which was a problem in the past, has been significantly improved, and a completely single-sided plated steel sheet can be obtained. can be easily obtained. The above-mentioned effects of the present invention were obtained for the first time through the development of a new licking inhibitor coating agent, but the most effective licking inhibitor was obtained by applying 10g of MgO (some or all of the MgO was may be replaced with the number of molecules of Mg(OH) ₂ ),
1 to 30 g of aqueous alkali silicate salt as the heat-dehydrated residue (M ₂ O・nSiO ₂ , n=0.5 to 4), 1 to 30 g of boric acid as H ₃ BO ₃ , 0.1 to 20 g of alkali as MOH, TiO ₂ 1.4g to 10g of titania (part or all of TiO ₂ may be replaced with titanium hydroxide of the same number of molecules), 3 as Al ₂ O ₃
It was a water slurry in which ~10 g of alumina (part or all of Al ₂ O ₃ may be replaced with aluminum hydroxide or alumina sol having the same number of molecules) was dissolved or dispersed in water. Hereinafter, the present invention will be explained in detail with reference to Examples. Example 1 10 g of MgO, 10 g of water glass (4.5 g as ₂ minutes of Na ₂ O.2SiO), 4 g of NaOH, 6 g of H ₃ BO ₃ , TiO ₂
A water slurry was prepared by dissolving or dispersing 2 g of Al ₂ O 3 and 3 g of Al 2 O ₃ in an appropriate amount of water. This water slurry was applied by roll coating onto one side of a cold-rolled steel sheet that had been cleaned by ordinary alkaline degreasing and water washing in an amount of about 50 g/m ² after drying. After application, dry at a low temperature of 150°C for 1 minute in the atmosphere, 10% H ₂ +
Annealing for 2 minutes at a temperature of 700 °C in a 90% _N2 atmosphere,
Cooling to about 530° C. was performed continuously in the same atmosphere in this order, and then the steel plate was immersed in a hot-dip galvanizing bath. The plating conditions were as follows: bath composition: 0.18% Al-Zn, bath temperature:
The temperature was 465±5°C, and the immersion time was 3 seconds. After plating, the steel plate is removed from the plating bath, the amount of plating is adjusted using a nitrogen gas wiper directly above the plating bath, and then, when the steel plate temperature reaches approximately 300℃, the steel plate is immersed in water at approximately 20℃. It was rapidly cooled. The steel plate after plating is
One side was galvanized and the other side was completely coated with a coating film, but the coating peeled off from the steel plate surface when quenched with water. Next, the steel plate was washed with water, brushed, and then dried with a blower.
A single-sided galvanized steel sheet was obtained, which had a uniform galvanization of 150 g/m ² and maintained a clean cold-rolled surface on the other side. Example 2 Mg(OH) ₂ 14.5g, potassium silicate aqueous solution 10
g (K ₂ O・SiO 6 g for ₂ minutes), KOH 6 g,
A water slurry was prepared by dissolving or dispersing 5 g of H ₃ BO ₃ , 3 g of TiO ₂ and 4 g of Al(OH) ₃ in an appropriate amount of water. Example 1 Using this as a coating agent for preventing plating
By performing the same treatment as in Example 1, a complete single-sided galvanized steel sheet was obtained. Example 3 Using a plating inhibitor having the composition shown in Table 1, the annealing temperature was set to three levels, 700°C, 750°C, and 850°C, and the rate of withdrawal from the hot-dip galvanizing bath was adjusted.
When single-sided galvanized steel sheets were manufactured at two levels of 40mpm and 60mpm, the adhesion of molten zinc and the peeling and removability of the plating inhibitor were investigated depending on the annealing temperature and steel sheet pulling speed.
The results are also shown in Table 1. In Table 1, the evaluation of the zinc adhesion status and the peeling removability of the plating inhibitor is as follows. (1) Evaluation of zinc adhesion status 〇: Hardly any molten zinc adhered to the surface coated with the plating inhibitor △: Molten zinc adhered to a part of the surface coated with the plating inhibitor ×: The entire surface coated with the plating inhibitor Molten zinc attached to (2) Evaluation of peeling and removal method of plating inhibitor 〇: Fully peeled △: Partially not peeled ×: Fully not peeled As is clear from Table 1, the plating inhibitor in the present invention By using this method, even if the annealing temperature of the steel sheet becomes high, the pulling speed from the molten zinc bath can be increased.
Even at speeds as high as 60mpm, there is almost no adhesion of molten zinc to the surface coated with the anti-glaze agent, and the anti-glaze agent can be easily peeled off by water cooling or by light repeated bending. It is. Further, magnesia, which is one of the components in the above-mentioned anti-glare agent, should preferably have a hydration amount of 1% or more, preferably 1 to 10%. This is because if the magnesia content is less than 1%, fine cracks will occur in the plating inhibitor coating and a trace amount of zinc will remain on the non-plated surface, as will be clear from the Examples and Comparative Examples that follow. Hereinafter, the influence of the hydration amount of magnesia in the plating inhibitor of the present invention will be specifically explained with reference to Examples and Comparative Examples. Comparative example 1 10 g of MgO with a hydration amount of 0.3%, 10 g of water glass,
(Na ₂ O・2SiO 4.5g for ₂ minutes), NaOH 4g,
A water slurry was prepared by dissolving or dispersing 6 g of H ₃ BO ₃ , 2 g of TiO ₂ , and 3 g of Al ₂ O ₃ in an appropriate amount of water. This water slurry was applied by roll coating onto one side of a cold-rolled steel sheet that had been cleaned by ordinary alkaline degreasing and water washing in an amount of about 50 g/m ² after drying. After coating, dry at a low temperature of 150°C for 1 minute in an open air oven, then dry at 700°C in a 10% H ₂ + 90% N ₂ atmosphere.
Annealing at a temperature of 2 minutes and cooling to about 530°C in the same atmosphere were successively performed in this order, and then the steel plate was immersed in a hot-dip galvanizing bath. The plating conditions were as follows: bath composition: 0.18% Al-Zn, bath temperature:
The temperature was 465±5°C, and the immersion time was 3 seconds. After plating, the steel plate is removed from the plating bath, the amount of plating is adjusted using a nitrogen gas wiper directly above the plating bath, and then, when the steel plate temperature reaches approximately 300℃, the steel plate is immersed in water at approximately 20℃. It was rapidly cooled. The steel plate after plating is
One side was galvanized, but the coating on the other side had minute cracks, and a small amount of Zn remained on the steel plate surface. Comparative Example 2 10 g of MgO with a hydration amount of 0.7%, 10 g of potassium silicate aqueous solution (6 g as K ₂ O・SiO ₂ minutes), KOH
6g, H ₃ BO ₃ 5g, TiO ₂ 3g, Al(OH) ₃ 4
A water slurry was prepared by dissolving or dispersing g in an appropriate amount of water. When the same treatment as in Comparative Example 1 was carried out using this coating as a coating agent for preventing plating, fine cracks appeared in the coating film and a small amount of Zn remained on the surface of the steel plate, as in Comparative Example 1. Example 1 When the same treatment as in Comparative Example 1 was carried out using the water slurry of Comparative Example 1 except for 10 g of MgO with a hydration amount of 1.5%, the coating film had no cracks and was galvanized on one side with a perfect cold-rolled surface. A steel plate was obtained. Example 2 When the same treatment as in Comparative Example 2 was performed using the water slurry of Comparative Example 2 except for 10 g of MgO with a hydration amount of 5%, the coating film had no cracks and was galvanized on one side with a perfect cold-rolled surface. A steel plate was obtained. In addition, in the above-mentioned embodiment, the case where hot-dip galvanizing is applied to one side of a steel plate was explained, but the present invention can also be applied to hot-dip galvanizing of Al, Zn-Al, Sn, Pb, Pb-Sn, etc. Of course. As explained above, according to the present invention, the plating prevention coating does not decompose or peel off during annealing unlike in the past, and it is possible to completely prevent melt plating on one side of the steel sheet. Furthermore, the surface of the steel sheet from which the coating has been peeled off can be maintained in the same condition as before plating without being oxidized or changing the surface condition as in the case of conventional methods. 【table】

Claims (1)

[Claims] 1. (a) At least one of magnesia and magnesium hydroxide, (b) Alkaline silicate (M ₂ O・nSiO ₂・mH ₂ O,
(in the formula, M represents an alkali metal), (c) boric acid, (d) an alkali metal hydroxide, (e) at least one of titania and titanium hydroxide, (f) alumina, aluminum hydroxide, and alumina sol. containing at least one compound selected from the group, and (a) 10 g of at least one of magnesia and magnesium hydroxide, (e) 1.4 to 10 g of at least one of titania and titanium hydroxide, (f) alumina, A water slurry containing 3 to 10 g of at least one compound selected from the group consisting of aluminum hydroxide and alumina sol is applied to one side of a steel plate, the steel plate is heated and dried, annealed, and then immersed in a molten metal plating bath. A method for producing a single-sided plated steel plate, comprising plating only one side of the steel plate by lifting the steel plate from the bath. 2. The method for producing a single-sided plated steel sheet according to claim 1, wherein magnesia having a hydration amount of at least 1% is used as the magnesia.