JPS6136994B2 - - 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. It is. In recent years, in order to improve the corrosion resistance and heat resistance of steel sheets, various types of fused 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 are widely used. . 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 an aluminized steel sheet has only a single color, and therefore is generally finished with various colors of organic paint. Although such coatings improve the weather resistance and anti-corrosion properties of fused aluminized steel sheets, the heat resistance of fused aluminized steel sheets is significantly reduced, and in the related technical field, efforts are still being made to color fused aluminized steel sheets. be. However, the present inventors investigated various methods for treating the molten aluminized steel sheet with inorganic materials, and found that whether it is a phosphate-based binder or a silicate-based binder, it is possible to treat the molten aluminized steel sheet directly on the surface of the steel sheet. When applied, a chemical reaction occurred on the surface and hydrogen gas was generated, causing coating defects such as pinholes and blisters, and the treatment was not satisfactory. Therefore, the present inventors completed the present invention by treating a molten aluminized steel plate at a specific temperature, inactivating the surface of the steel plate, and then coating it with a silicate-based inorganic paint. It has been reached. That is, in the present invention, a molten aluminized steel plate is prepared in advance.
After heating surface treatment at a temperature of 200-700℃, the general formula
M ₂ O・SiO ₂ (where M is an alkali metal, -N
The present invention has completed a method for applying an inorganic paint, which is characterized by applying an inorganic paint using an alkali silicate represented by (ROH) ₄ or -NH ₄ ) as a binder and a phosphorus compound as a hardening agent. The surface of fused aluminized steel sheets is mainly composed of aluminum, which has a particularly low melting point among metals, and is usually
When the temperature exceeds 400°C, a kind of alloy (made of aluminum and metals such as silicon and iron) is formed, and this layer becomes brittle and its anticorrosion properties are significantly reduced. Therefore, the present inventors proposed a method for inactivating the plating layer without alloying it.
They discovered that it can be inactivated by heating at a temperature of 700℃ for a certain period of time. The heating method is hot air,
The plated aluminum layer can be inactivated by any method, such as electric heating, as long as it is in an acidic or neutral atmosphere. The next important thing is the heating time, and as a result of the inventors' study of various heating conditions, it has become clear that the heating time can be approximately within the following range. T3/2×t=2.5 to 15×10 ⁴ (℃〓・min) In the formula, T is temperature (℃), and t is expressed in time (minutes). From this equation, it can be seen that, for example, the heating time at 200°C is 9 to 50 minutes, the heating time at 500°C is 2.5 to 14 minutes, and the heating time at 700°C is 1.5 to 8 minutes. If the temperature is low and the time is short, no result will be obtained from the heat treatment, and if the time is long, signs of alloying will appear and the layer will become brittle. Further, if the temperature is high and the time is short, no results will be obtained from the heat treatment, and if the time is long, the inactivated surface will become activated, resulting in a significant decrease in corrosion protection. In any case, although the form of this treatment is not clear, the surface layer of the molten plating aluminum is inactivated by heating under a specific temperature, forming a so-called "primer layer" and then being plated. It is presumed that the purpose is to stabilize the layer. Next, a silicate-based inorganic paint is applied as soon as possible after the heat treatment, and the paint is of the general formula
Apply an inorganic paint that uses an alkali metal silicate represented by M ₂ O・SiO ₂ or a quaternary ammonium silicate as a binder and a phosphorus compound such as a phosphate or condensed phosphate as a hardening agent. The inorganic coating film is formed on the molten aluminized steel plate by baking and hardening at 150 to 250°C. As mentioned above, the steel plate that is the object to be painted is inert, so it is difficult for chemical reactions to occur when inorganic paint is applied, and even during baking, despite the adverse conditions of relatively high temperatures, chemical reactions do not occur. Since it does not involve
A hard and glossy inorganic coating film that adheres very densely to the steel plate without causing problems such as pinholes, blisters, blisters, or dulling of the coating film is formed. Of course, the inorganic paint can be freely colored by mixing various pigments, and by painting, a colored fused aluminized steel sheet with excellent color and gloss can be obtained. The colored fused aluminized steel sheet obtained by the method of the present invention is essentially made entirely of inorganic materials and is completely non-flammable, and has superior flame resistance and heat resistance compared to conventional steel sheets. Instead, it has various qualities normally required of colored steel sheets, such as physical properties such as adhesion, bending resistance, impact resistance, and bending resistance, as well as chemical resistance, stain resistance, normal water resistance, and weather resistance. It is also excellent. What is noteworthy and unexpected is that the corrosion resistance is much improved compared to the case of fused aluminized steel sheet alone. This probably indicates that the anticorrosion function of the inorganic paint itself and the anticorrosion function of the molten aluminum plating layer are somewhat different, and that a kind of strong inert layer is formed between them by the pretreatment of the present invention. This is presumed to be due to the presence of a corrosion layer, and the effects of these three anti-corrosion factors are mutually enhanced.
Needless to say, these improvements in quality dramatically improve the durability of colored fused aluminized steel sheets. Examples of the present invention will be described below. Example 1 The method of the present invention was carried out according to 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 preheated for 10 minutes in a far-infrared heating furnace adjusted to 300℃, and immediately after thoroughly mixing the inorganic paint base and curing agent below, it was coated at 200g/m ² by spray method. Apply in quantity. (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 far-infrared heating furnace at ℃ and baked to harden for 30 minutes to obtain a colored fused aluminized steel sheet. Observing the surface condition of this colored coating layer,
It was observed that a glossy and firm film was formed without defects such as blisters, blisters, and pinholes. Further, this colored steel plate was tested according to the following test method using a test plate as a test plate, and the results shown in Table 1 were obtained. (1) Chemical resistance test 1 Drop 1 ml of acid-resistant 35% HCl onto the test plate, wash with water after 24 hours, dry, and observe the condition of the coating film. 2 Drop 1 ml of alkali resistance 30% NaOH onto the test plate, wash with water after 24 hours, dry, and observe the condition of the coating film. (2) Cross-cut the Erichsen test test plate, perform the JIS Z2247 test, and observe the state of the paint film. (3) Pencil hardness test According to the test method of JIS G 3312 8.8, the hardness of a pencil is measured just before it scratches the coating on the test plate and causes scratches. (4) Corrosion resistance test 1 Cross-cut the coating film of the salt spray test test plate, and
Conducted the test specified in Z2371 for 500 hours,
Observe the state of rust formation. 2 Salt water immersion test Cross-cut the coating film of the test plate 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 at room temperature for 20 hours in an electric furnace set at 600°C and then leaving it for 4 hours. After 10 cycles, observe the condition of the coating film. (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 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: Heat pretreatment for 5 minutes in a hot air drying oven heated to 500°C. Examples 3 to 7 In the pretreatment in Example 2, the pretreatment was performed as the second
The test was conducted in exactly the same manner as in Example 2, except that the treatment conditions shown in the table were changed, and the results shown in Table 1 were obtained. Comparative Examples 1 to 3 Tests were conducted in exactly the same manner as in Example 2, except that the pretreatment conditions in Example 2 were changed to those shown in Table 3.
The results shown in Table 1 were obtained. Fine blisters were observed on the paint film.

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Claims (1)

[Claims] 1 After preheating and surface treating a molten aluminized steel plate at a temperature of 200 to 700°C, the general formula M ₂ O・SiO ₂
(In the formula, M is an alkali metal, -N(ROH) ₄ or -
A method for applying an inorganic paint, which comprises applying an inorganic paint using an alkali silicate represented by NH ₄ ) as a binder and a phosphorus compound as a hardening agent.