JPS648712B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to enameled stainless steel products such as building materials, kitchen utensils, bathtubs, and pipes for chemical plants, etc., and does not require any special pretreatment and can be applied to stainless steel surfaces. This invention relates to a method for producing stainless steel enamel having excellent adhesion. (Prior art and its problems) Stainless steel is rust resistant, highly corrosion resistant, and retains its shine for a long time, so it is used for architectural interior and exterior walls, kitchen products,
It is used in many areas such as bathtubs, wash basins, and vehicles. However, while stainless steel has its advantages, it is also susceptible to scratch rust, crevice corrosion caused by contact between dissimilar metals, dirt, and dirt.
It has disadvantages such as being easily attacked by Cl ^- ions and not being able to be colored freely. Therefore, various methods of enameling stainless steel have been studied in the past as a way to further enhance the properties of stainless steel and at the same time eliminate these drawbacks, but the current situation is that nothing that is fully satisfactory has yet been achieved. . Generally, in the case of enamel, in order for the glaze and base metal to adhere firmly, it is essential that the base metal be sufficiently oxidized at the firing temperature of the glaze. Stainless steel is quite stable at the firing temperature of normal iron enamel glazes, and the oxidation does not progress sufficiently for the glaze to react with the base material, so conventional stainless steel enamels do not provide good adhesion. It was thought that Therefore, in order to obtain good adhesion between stainless steel and glaze, the stainless steel surface is roughened mechanically or chemically. Studies have been conducted on methods of introducing special metal oxides into the frits that make up the glaze, which promote oxidation or attack the stainless steel. As a method, for example, the depth of the recess is 80 to 400 μm on the stainless steel surface, and the roughness of the concave surface is 2
It has been disclosed that the adhesion between stainless steel and glaze can be ensured by providing an uneven pattern of ~30 μm by mechanical or chemical means (Special Publication No. 52-1729). It is extremely difficult to find a way to form a concave roughness of 2 to 30 μm and to confirm it. Also, stainless steel is heated in advance in an oxidizing atmosphere to form an oxide film on the surface, and then immersed in an aqueous solution containing divalent nickel ions to evenly adhere the nickel ions to the oxide film. A method for strengthening the adhesion of the glaze has been disclosed (Special Publication 1973-
No. 30588), this method has a problem in that it requires two steps for pretreatment of stainless steel. (It goes without saying that sufficient adhesion cannot be obtained by mere surface roughening methods such as sandblasting, shotblasting, and chemical etching methods commonly used in the enamel industry.) There is a method of introducing 1 to 3 wt% of M ₀ O ₃ into the frit component that can be fired at a relatively low temperature (Japanese Patent Publication No. 14819/1983), but this method can be applied directly to stainless steel only once. The frit composition is very specific, and the frit composition is very specific. Furthermore, an enamel frit with improved adhesion to stainless steel has been disclosed by introducing 5 to 30 wt% Fe ₂ O ₃ into a glass mainly composed of borosilicate that does not contain a fluorine component. (Unexamined Japanese Patent Publication No. 1973-
810), this method requires a large amount of
Introducing Fe ₂ O ₃ causes significant contamination of the glass melting furnace and kiln, which is very uneconomical in frit manufacturing.In addition, due to the large amount of Fe ₂ O ₃ contained in the frit, it is necessary to Repeated firing causes Fe ₂ O ₃ to precipitate into the glass matrix, which causes the glaze to easily devitrify, resulting in unstable adhesion. As mentioned above, stainless steel enamel is not yet a completed technology, and is a technical field in which further improvement is desired. (Objective of the Invention) The present invention improves the problems of the conventional methods as described above, and provides a method for producing stainless steel enamel with extremely good adhesion using relatively simple means. (Structure of the Invention) The present invention is aimed at maintaining the vicinity of the interface between the stainless steel and the glaze in a reducing atmosphere during firing in the production of stainless steel enamel in which a stainless steel plate coated with glaze is fired in a furnace. (a) The temperature inside the furnace was maintained at 700 to 900°C, the air inside the furnace was replaced with nitrogen gas, and then the nitrogen gas was replaced with hydrogen gas, and then the hydrogen gas was continuously introduced while applying the drug. Stainless steel sheets are fired, or (b) as reducing agents, (a) metal powders such as aluminum powder, copper powder, iron powder, etc., (b) formic acid, oxalic acid, and their salts are decomposed during firing. A method for producing stainless steel enamel characterized by using a glaze to which either an organic compound that generates a reducing gas or (c) a reducing inorganic compound such as carbon powder or silicon carbide is added in a mill. . (Embodiments and effects) In the method for producing stainless steel enamel of the present invention,
Using a standard milling formula, the milled glaze is applied to a degreased stainless steel surface.
When firing at 700 to 900℃ after drying, good adhesion can be obtained by making the firing atmosphere a reducing atmosphere, so it is sufficient to simply degrease the stainless steel surface as a pretreatment, which is different from conventional methods. There is no need to roughen the surface by mechanical or chemical means. For the adhesion between stainless steel and glaze, elements such as Fe, Cr, and Ni that make up stainless steel are oxidized during firing, and as the viscosity of the glaze decreases,
When these oxides dissolve into the glaze,
It was conventionally believed that the adhesion reaction progressed, but the inventors of the present application conducted various studies on stainless steel enamel and found that in order to achieve good adhesion between stainless steel and glaze, it is of course necessary that the stainless steel It is essential that the constituent elements are oxidized, but under normal firing conditions, the stainless steel surface
Since the Cr ₂ O ₃ oxide layer becomes passivated, further oxidation of stainless steel is significantly suppressed, and the rate of infiltration of oxides such as Cr ₂ O ₃ , FeO, and NiO into the glaze is significantly reduced. I came to the idea that it was decreasing. Therefore, it is believed that the adhesion between the glaze and stainless steel can be promoted by controlling the firing atmosphere to a reducing atmosphere to the extent that the growth of a stable and passivated Cr ₂ O ₃ layer can be suppressed. I gained knowledge. The concept of controlling the firing atmosphere to a reducing atmosphere is completely unthinkable in the conventional enamel industry. In the conventional method, in order to obtain relatively good adhesion with stainless steel enamel, the firing temperature is raised to around 1000℃ in an oxidizing atmosphere, and the passivated Cr ₂ O ₃ oxide layer is removed during glazing. A method of infiltration was used. Therefore, the present invention is the first to provide a method for producing stainless steel enamel that can obtain good adhesion at a firing temperature of 700 to 900°C and without roughening the stainless steel surface either mechanically or chemically. It is no exaggeration to say that it has become possible. Next, in the present invention, specific methods and methods for maintaining the firing atmosphere in a reducing atmosphere will be described. Use of atmosphere furnace. A method of mill-adding reducing agent to glaze. When firing in an atmospheric furnace, the temperature is maintained at 700 to 900°C, the air in the furnace is replaced with nitrogen gas, hydrogen gas is then introduced into the furnace, and the sample is heated after replacing the nitrogen gas with hydrogen gas. Charge it into the furnace and fire it. During firing, hydrogen gas is continuously introduced. If it is difficult to use an atmospheric furnace due to the shape, size, productivity, production cost, etc. of the product, it is preferable to add a reducing agent to the glaze in a mill. The object of the present invention can also be sufficiently achieved by adding a reducing agent in a mill to maintain a reducing atmosphere near the interface between the glaze and stainless steel during firing. Mill additives that are effective in maintaining a reducing atmosphere to inhibit passivation of the Cr ₂ O ₃ oxide layer in stainless steel during firing include (a) metal powders, such as metal aluminum powder, copper powder, iron powder; Although it can be mentioned,
During slip manufacturing, water-soluble components (monovalent alkali metal oxides, B ₂ O ₃ , etc.) in the frit components are eluted, so metals that have significant reactivity with these eluted components and metal powders that react with water are Should be avoided. Therefore, in general, the objects of the present invention can be achieved using metal powders that do not have significant reactivity with water, are stable in air, and can be combined with oxygen. (b) Organic compounds that decompose during firing to produce reducing gases, such as formic acid, oxalic acid, and their salts; If there is a large amount of glaze, the glazed surface after firing will deteriorate significantly and should be avoided. Furthermore, (c) a reducing inorganic compound such as carbon powder,
Silicon carbide and the like may also be mentioned. As detailed above, the present invention applies to mill additives that have a reducing effect, do not react violently with water, are stable in the air, and do not cause defects on the glazed surface after firing. Can be used for Furthermore, tartrate salts can be dissolved in the frit component together with other metal oxides as a form of reducing agent that meets the objectives of the present invention. Next, the present invention will be explained in detail using examples. Example 1 Raw materials were prepared according to the oxide composition shown in Table-1,
A frit was obtained by melting at 1300°C and rapidly cooling. The obtained frit was milled according to the milling composition shown in Table 2 to obtain a glaze.

【table】

[Table] The thickness of the obtained glaze is SUS-304.
Approximately 2g per side on 0.4mm, 50 x 75mm stainless steel
(Wet) (equivalent to a glaze thickness of approximately 70 to 90 μm after firing), dried, and fired in an atmospheric furnace with a total internal volume of approximately 5.7 μm. For firing, nitrogen gas was flowed into the furnace at a rate of 3/min while the temperature was kept at 800°C, and after completely expelling the air inside, the sample was placed near the entrance of the furnace with the lid open, and heated for another 8 minutes. 3/
After nitrogen was flowed at a rate of min, hydrogen gas was flowed into the furnace at a rate of 25 min for 10 minutes to completely replace the nitrogen gas with hydrogen gas, the sample was held at 800 °C with a Kanthal push rod. The sample was then pressed into a firing zone and fired for 2 minutes, and then taken out from the atmosphere furnace. The surface of the glaze was very smooth, and in the following adhesion evaluation test, there was little peeling of the glaze, and the adhesion was sufficient. [Adhesion evaluation test: Bend one end of the sample piece to 180 degrees and return the bent part to its original position to evaluate the degree of peeling of the glaze. ] Example 2 Raw materials were prepared according to the oxide composition shown in Table 3,
It was melted at 1330°C and rapidly cooled to obtain a frit. The obtained frit was milled according to the milling composition shown in Table 4 to obtain a glaze.

【table】

【table】

[Table] Apply the obtained glaze on both sides of a 30cm square test piece at a rate of 40g on each side, and after drying
After baking at ℃ for 4 minutes, many irregularities were observed on the surface, but it was evaluated by PEI adhesion tester as 95%.
showed close contact. When a commercially available titanium-based polish was applied on top of this and fired again at 800°C, the surface was extremely smooth and beautifully finished. Adhesion evaluation using PEI showed 85% adhesion. Example 3 The frit obtained in Example 2 was milled according to the milling composition shown in Table 5 to obtain a glaze. This glaze is SUS-304 thickness 1.0mm, size
Apply medicine to both sides of a 900 mm square stainless steel plate at a rate of 250 g per side, and after drying, set the temperature to 830.
When fired in a continuous firing furnace at ℃, a very smooth enamel surface was obtained. The adhesion of the enamel on this panel was evaluated in accordance with JIS R4301, but no peeling of the enamel was observed. Furthermore, a commercially available titanium opalescent glaze was applied over this and fired in a continuous furnace set at 800°C to obtain a good enamel surface with no imperfections, and no peeling of the glaze occurred in an adhesion test according to JIS R4301. Nakatsuta.

【table】

[Table] Example 4 The frit obtained in Example 2 was milled using the milling composition shown in Table 6 to obtain a glaze. This glaze is SUS-304 thickness 0.4mm, size
Rub both sides of a 900 mm square stainless steel plate at a rate of 220 g on each side, bake in a continuous furnace set at 810°C, and then apply 200 g of commercially available titanium milky paste.
When the material was coated with g-chemicals and fired in a continuous furnace set at 790°C, a fairly smooth and defect-free enamel surface was obtained. A portion of this board was cut out and adhesion was evaluated using a PEI adhesion tester, and the adhesion was 82.5%.

【table】

[Table] (Effects of the invention) By maintaining the firing atmosphere in a reducing atmosphere during firing, this method provides good adhesion regardless of the type of glaze or frit. Sufficient effects can be obtained by introducing hydrogen gas or adding organic substances that decompose during firing to produce reducing gases, and it is possible to maintain a reducing atmosphere at low cost industrially.
This invention has excellent effects such as no need to perform special pretreatment on stainless steel.

Claims (1)

[Claims] 1. In the production of stainless steel enamel, in which a stainless steel plate coated with glaze is fired in a furnace, in order to maintain a reducing atmosphere near the interface between the stainless steel and the glaze during firing, (a) the temperature inside the furnace is The temperature in the furnace is maintained at 700 to 900°C, the air in the furnace is replaced with nitrogen gas, the nitrogen gas is replaced with hydrogen gas, and then the coated stainless steel sheet is fired while hydrogen gas is continuously introduced, or (B)
As reducing agents, (a) metal powders such as metal aluminum powder, copper powder, and iron powder; (b) organic compounds that decompose during firing to produce reducing gases such as formic acid, oxalic acid, and their salts; (c) ) A method for producing stainless steel enamel, characterized by using a glaze to which either carbon powder or a reducing inorganic compound such as silicon carbide is added in a mill.