JPS6159791B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for preparing a molten aluminized steel sheet that is colorful and has excellent heat resistance and corrosion resistance, and is characterized in that the molten aluminized steel sheet is painted after a specific pretreatment using an inorganic paint. In recent years, various types of molten aluminized steel sheets, that is, steel sheets plated with aluminum alone or with aluminum containing silicon or iron as an auxiliary component, have been developed and widely used to improve the corrosion resistance and heat resistance of steel sheets. . For example, it is applied to automobile parts such as mufflers, converters, and shear heating plates, combustion equipment such as stoves, bathtubs, chimneys, and gas ranges, and various household appliances, and the range of applications is gradually expanding. However, the surface of such aluminized steel sheets only has a single color;
For this reason, it is generally finished with various colors of organic paint. Although such coating improves the weather resistance and corrosion resistance of molten aluminized steel sheets to a considerable extent, the heat resistance of molten aluminized steel sheets significantly decreases, and in this technical field, efforts are still being made to color molten aluminized steel sheets. . However, the present inventors investigated various methods of treating the molten aluminized steel sheet with inorganic materials, and found that whether a phosphate-based binder or a silicate-based binder is used, a chemical reaction occurs on the surface of the steel sheet. This produced hydrogen gas, which caused coating defects such as pinholes and blisters, and the treatment was not satisfactory. Therefore, the present inventors happened to treat a molten aluminized steel plate using a specific treatment liquid, inactivate the surface of the steel plate, and then apply a silicate-based inorganic paint to complete the present invention. It has been reached. That is, in the present invention, a molten aluminized steel plate is prepared in advance.
SiO ₂ /R ₂ O (where R is an alkali metal) molar ratio is 1
After surface treatment with a mixed aqueous solution of the above aqueous alkali metal silicate solution and an aqueous solution of a chloric acid compound and/or perchloric acid compound, the general formula R′ ₂ O・SiO ₂ (wherein R′ is an alkali metal or ammonium ) to display 〓〓〓〓〓
The present invention has completed a coating method for an aqueous inorganic paint, which is characterized by applying an aqueous inorganic paint using an alkali silicate as a binder and a phosphorus compound as a hardening agent. What is the alkali metal silicate used in the present invention?
The molar ratio of SiO ₂ /R ₂ O is 1 or more, specifically lithium silicate, sodium silicate, potassium silicate,
Rubidium silicate is used, and alkali metal metasilicate, alkali metal sesquisilicate, and various ordinary water glasses can be used. This aqueous alkali metal silicate solution is preferably used at a concentration of 2 to 40% by weight. Next, as the chloric acid compound, in addition to chloric acid, chlorates that are soluble or easily soluble in water can be used, such as Zn(ClO ₃ ) ₂ , Al(ClO ₃ ) ₃ , Cd(ClO ₃ ) ₂ KClO ₃ , Ca(ClO ₃ ) ₂ , AgClO ₃ Co(ClO ₃ ) ₂ , Hg ₂ (ClO ₃ ) ₂ , Hg(ClO ₃ ) ₂ , Sr(ClO ₃ ) ₂ , Fe(ClO ₃ ) ₂ , Fe(ClO ₃ ) ₃ , Cu(ClO ₃ ) ₂ NaClO ₃ , Pb(ClO ₃ ) ₂ , Ni(ClO ₃ ) ₂ , Ba(ClO ₃ ) ₂ , Mg(ClO ₃ ) ₂ , LiClO ₃ , RbClO ₃ , TlClO ₃ as examples. can do. The chlorate may be an anhydrous salt or a salt containing water of crystallization, which forms an aqueous solution and can be used as long as it does not undergo severe hydrolysis. Furthermore, as perchloric acid compounds, in addition to perchloric acid, perchlorates which are soluble or easily soluble in water are used, such as Zn(ClO ₄ ) ₂ , Al(ClO ₄ ) ₃ , Cd(ClO ₄ ) ₂ , Gd(ClO ₄ ) ₃ , KClO ₄ , Ga(ClO ₄ ) ₃ , Ca(ClO ₄ ) ₂ , AgClO ₄ , Cr(ClO ₄ ) ₃ , Co(ClO ₄ ) ₂ , Hg ₂ (ClO ₄ ) ₂ , Hg(ClO ₄ ) ₂ , Sr(ClO ₄ ) ₂ , CsClO ₄ , Ce(ClO ₄ ) ₃ , Fe(ClO ₄ ) ₂ , Fe(ClO ₄ ) ₃ , Cu(ClO ₄ ) ₂ , NaClO ₄ , Pb( _ClO4 ) ₂ , Ni( _ClO4 ) ₃ , Ba( _ClO4 ) ₂ , Bi( _ClO4 ) ₃ , Mg( _ClO4 ) ₂ , Mn( _ClO4 ) ₂ , LiClO4, _{RbClO4 ,} Nd( _ClO4) ) ₃ can be exemplified, and can be used as long as it is an anhydrous salt or a salt containing water of crystallization and does not form an aqueous solution and undergo severe hydrolysis. These aqueous solutions of chloric acid compounds and perchloric acid compounds may be used alone or in combination, and are adjusted to a concentration of 0.1 to 10% by weight, preferably 0.3 to 8% by weight. next,
Alkali metal silicate aqueous solution and chloric acid compound and/or
Or the mixing ratio with the perchloric acid compound aqueous solution is about 1:
The ratio is 0.05 to 5 (solid content weight ratio), preferably 1:0.08 to 2. Immerse a molten aluminized steel plate in the above pretreatment aqueous solution or apply the aqueous solution and leave it for 10 minutes at room temperature.
Process for ~30 minutes. Desirably, the higher the concentration of the aqueous solution and the lower the SiO ₂ /R ₂ O molar ratio, the more remarkable the effect becomes. On the other hand, if the aqueous solution is heated in advance to accelerate the treatment, the treatment time can be shortened to about 1 to 5 minutes by adjusting the temperature to, for example, 80°C.
Processing operations become very advantageous. After this pretreatment is completed, it is preferable to wash with water, although this may be done as needed. In any case, although the form is not clear through such treatment, the alkali metal silicate advances the inactivation of the molten plating aluminum surface layer,
While playing an auxiliary role in promoting the uniformity and density of the chloric acid compound and/or perchloric acid compound, a so-called "primer layer" is formed to stabilize the plating layer. It is estimated that In this case, if the molar ratio of SiO ₂ /R ₂ O is less than 1, blistering is particularly likely to occur during subsequent application of the inorganic paint, resulting in poor results.
Further, if the concentration of the aqueous solution is too dilute, the treatment effect will not be apparent, and if the concentration is too high, the treatment form will be inhibited by the viscosity of the treatment solution, and no effect will be exhibited as in the case where the aqueous solution is too dilute. Furthermore, if the treatment time is short, there is no treatment effect, and on the other hand, if the treatment time is too long, the inert layer that has been painstakingly formed will be re-dissolved, and the treatment will eventually become meaningless. Furthermore, when the mixing ratio of the chloric acid compound and/or perchloric acid compound to the alkali metal silicate is small, the degree of inactivation becomes slightly weaker and the adhesion slightly decreases, and conversely, when the mixing ratio becomes large, The oxidation of the plating aluminum layer becomes intense and has the opposite effect. Next, a silicate-based inorganic paint is applied, which uses an alkali metal silicate or ammonium silicate represented by the general formula R ₂ O.SiO ₂ as a binder, and uses phosphates, condensed phosphorus, An inorganic paint made of a phosphorus compound such as an acid salt as a hardening agent is applied and cured by baking at 150 to 250°C to form an inorganic paint film on the molten aluminized steel plate. As mentioned above, the steel plate that is the object to be painted becomes inert.
Therefore, it is difficult for chemical reactions to occur when applying inorganic paints, and even during baking, there are no chemical reactions despite the adverse conditions of relatively high temperatures, so there are no pinholes, blisters, blisters, or gloss in the paint film. A hard and glossy inorganic coating film with high adhesion is formed on the steel plate very densely without causing problems such as blurring. Of course, the inorganic paint can be colored freely by mixing various pigments, and by painting, a colored fused aluminized plate with excellent color and gloss can be obtained. The colored hot-dipped aluminized steel sheet obtained by the method of the present invention is essentially made entirely of inorganic materials, and is completely non-combustible and has superior flame resistance and heat resistance compared to conventional steel sheets. In addition to the physical properties normally required for colored steel sheets, such as adhesion, bending resistance, impact resistance, and bending resistance, it also has excellent chemical resistance, normal water resistance, and weather resistance. There is. What is noteworthy and unexpected is that the corrosion resistance is much improved compared to the case of molten aluminized steel sheet alone. This is probably due to the fact that the anticorrosion function of the inorganic paint itself is somewhat different from that of the molten aluminized layer, and that a kind of strong inert layer is formed between them by the pretreatment of the present invention. is intervening,
It is presumed that these three anti-corrosion factors mutually enhance hardening. Examples of the present invention will be described in detail below. Example 1 The method of the present invention was carried out in accordance with the following procedure using a molten aluminized steel plate in which the plating layer was formed of 81% aluminum, 5% silicon, and 14% iron. First, the above steel plate was mixed with 4% by weight in a 15% aqueous solution of No. 1 water glass with a SiO ₂ /Na ₂ O molar ratio of 2.1.
After pre-treatment by immersing in a mixture of potassium chlorate for 20 minutes, immediately washing with water and drying the surface to be coated, thoroughly mix the inorganic pigment base and curing agent below and spray 200g/ Apply with a coating amount of m ² . (Inorganic paint formulation) = Base = Sodium silicate No. 2 aqueous solution 1000 parts by weight Titanium oxide (rutile type) 100 parts by weight Inorganic pigment 100 parts by weight = Hardening agent = Aluminum phosphate 200 parts by weight Water 300 parts by weight 200 parts by weight after application It was placed in a hot air drying oven at ℃ and dried for 30 minutes to obtain a colored fused aluminized steel plate. When the surface condition of this colored coating layer was observed, it was observed that there were no defects such as blisters, blisters, pinholes, etc., and a glossy and firm film was formed. Further, this colored steel plate was used as a test plate and tested according to the following test method, and the results shown in Table 1 were obtained. 1 Chemical Resistance Test 1 Acid Resistance 1 ml of 35% HCl is dropped onto the test plate, washed with water after 24 hours, dried, and the condition of the coating film is observed. 2 Alkali resistance Drop 1 ml of 30% NaOH onto the test plate, wash with water after 24 hours, dry, and observe the condition of the coating film. 2 Erichsen test Cross-cut the test plate, perform the JIS Z 2247 test, and observe the state of the coating film. 3 Pencil hardness test According to the test method of JIS G 3212 8.8, the hardness of a pencil is measured just before scratches are observed on the coating on the test plate. 4. Corrosion resistance test 1. Salt spray test Cross-cut the coating film on the test plate, perform the test specified in JIS Z 2371 for 1000 hours, and observe the state of rust formation. 2 Salt water immersion test Cross-cut the coating film of the test liquid and immerse it in salt water.
Soak for 30 days and observe the state of rust formation. 5. Heat resistance test One cycle consists of leaving the test plate in an electric furnace set at 600°C for 20 hours and at room temperature for 4 hours. After 10 cycles, the condition of the coating film is observed. 6 Flame resistance test The tip of the gas burner flame (approx.
1100℃) for 5 minutes, then observe the condition of the coating film. Example 2 The following pretreatment method was used in Example 1.
Tests were conducted in exactly the same manner as in Example 1, and the results shown in Table 1 were obtained. Pretreatment method: A mixture of No. 2 water glass with a SiO ₂ /Na ₂ O molar ratio of 2.5 and 8% by weight of sodium perchlorate was heated to 80°C for 3 minutes. Soaked and pretreated. Example 3 The procedure was exactly the same as in Example 1, except that in the pretreatment in Example 1, the 15% aqueous solution of No. 1 water glass was changed to a 15% aqueous solution of lithium water glass with a SiO ₂ /Li ₂ O molar ratio of 2.0. A test was conducted and the results shown in Table 1 were obtained. Example 4 A test was conducted in exactly the same manner as in Example 1, except that the pretreatment was performed in the following manner, and the results shown in Table 1 were obtained. Pretreatment method: A mixture of 1% by weight of magnesium chlorate and 1% by weight of calcium perchlorate was added to a 15% aqueous solution of No. 1 water glass with a SiO ₂ /Na ₂ O molar ratio of 2.1 at 50% by weight. Pretreatment was carried out by immersing the sample in a heated state at ℃ for 5 minutes. Example 5 A test was conducted in exactly the same manner as in Example 4, except that the pretreatment was performed in the following manner, and the results shown in Table 1 were obtained. Pretreatment method: Pretreatment was carried out by applying the same solution for about 10 minutes by spraying at room temperature. Comparative Example 1 A test was conducted in exactly the same manner as in Example 1, except that the pretreatment was performed in the following manner, and the results shown in Table 1 were obtained. Fine blisters were observed on the paint film. Pretreatment method: Pretreatment was performed by immersing in a 20% aqueous solution of sodium orthosilicate for 25 minutes. Comparative Example 2 A test was carried out in exactly the same manner as in Example 1, except that a treatment liquid without monopotassium chlorate was used, and the results shown in Table 1 were obtained.

[Table] 〓〓〓〓〓

Claims (1)

[Claims] 1. A molten aluminized steel sheet is pretreated with an aqueous alkali metal silicate solution having a molar ratio of SiO ₂ /R ₂ O (where R is an alkali metal) of 1 or more and an aqueous solution of a chloric acid compound and/or a perchloric acid compound. After surface treatment with a _mixed aqueous solution of A method for applying water-based inorganic paint, which is characterized by applying paint. 2. The method for applying an aqueous inorganic paint according to claim 1, wherein the surface treatment of the molten aluminized steel sheet is carried out under heating.