JPH0442072B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for forming a fluororesin coating layer for use in cooking utensils, particularly frying pans, hot plates, pots, rice cookers, and the like. Conventional structure and its problems Conventionally, when base metals such as iron and aluminum are used and fluororesin is coated on the surface,
Broadly speaking, there are methods in which a fluororesin is directly coated on the surface of the base metal, methods in which the surface of the base metal is roughened by sandblasting etc., and then a fluororesin is coated on the surface of the base metal, and a method in which the surface of the base metal is enameled. There is a method of coating the surface of the enamel with a fluororesin, a method of roughening the surface of the base metal or the enamel by sandblasting, etc., then spraying an inorganic powder, and coating the surface with a fluororesin. However, each of the above-mentioned methods has drawbacks and problems. In other words, when a fluororesin is directly coated on the surface of the base metal, the adhesion between the fluororesin and the metal is poor, and the base metal is corroded due to peeling, flaking of the fluororesin, and wear, resulting in poor durability. . Compared to when a fluororesin is coated on the roughened surface of a material, adhesion is considerably improved, but corrosion occurs due to peeling and abrasion, and durability is inferior. In particular, it is generally used in the inner pot of the rice cooker,
Suitable for use with low wear resistance. On the other hand, in the case of grilled cooking utensils such as frying pans and hot plates, they are easily scratched and abraded by metal spatulas, knives, etc., so the metal surface is treated with abrasion-resistant processing and a base treatment with excellent corrosion resistance. It is. However, in the case of enameling, even if a smooth enamel is simply formed, the adhesion to the fluororesin is poor. To achieve this, the enamel treatment is performed to improve adhesion, by adding an appropriate amount of matte-forming materials (wear-resistant materials) such as alumina and silica to the glaze, making the enamel surface matte, and coating the surface with fluororesin. A fluororesin coating with excellent corrosion resistance and abrasion resistance can be obtained (Japanese Patent Publication No. 57-49266, JP-A No. 56-150467)
(disclosed in the Publication No. When a fluororesin is coated on a surface sprayed with inorganic powder, the plasma spraying method must be used as the thermal spraying method because inorganic powders such as alumina and silica generally have a high melting point, which increases costs. During thermal spraying, the surface of the base metal becomes high temperature, which has disadvantages such as adverse effects on the base metal (formation of oxides, corrosion resistance, etc.). Regarding the above-mentioned enamel processing, please contact Tokuko Sho.
It is disclosed in Japanese Patent Laid-open No. 57-49266 and Japanese Patent Application Laid-open No. 150467/1983. First, the above-mentioned Japanese Patent Publication No. 57-49266 describes an enameling method in which a matte-forming material such as alumina powder or silica powder is added to the glaze or sprinkled on the surface after glazing to form a composite film having an uneven shape. ing. However, the specification states that the particle size and content of alumina and silica powder have a significant effect on the adhesion to the base metal and also to the fluororesin. That is, the particle size of the alumina powder is 200 to 400 mesh, preferably 280 to 360 mesh, but as is clear from Examples 1 and 2 in this prior document, the alumina powder is added just before the end of milling, and then It is said that it will be milled again for 10 to 15 minutes. In this method, the particle size of alumina in the glaze is no longer finer than when it was added.
Discrimination is made only by the particle size before addition. Although this document states that the particle size of alumina is important, it does not mention anything about the particle size in the glaze. Generally, it is possible to mainly form the uneven shape using alumina alone, but it is determined by the particle size of the frit and alumina (matte forming product) contained in the glaze. In addition, in Example 4, after applying the glaze, alumina is sprinkled on the surface and fired, but it is difficult to uniformly distribute the alumina (difficult to form a uniform uneven shape). Since the bonding is performed only at the interface with the enamel, that is, at the contact area with the enamel, there are many problems such as not completely adhering to all the alumina powder. Next, Japanese Unexamined Patent Application Publication No. 150467/1986 is a partial improvement of the above-mentioned prior document. That is, a two-coat, two-bake method is used in which a lower glaze is applied, then fired, an upper glaze is applied again, and then fired. In this case, the bottom glaze is for corrosion resistance, and the top glaze is made of matte (alumina powder) to improve adhesion to the fluororesin.
It contains. In this document, it is true that the corrosion resistance of the base metal is achieved by an undercoat, and the adhesion with the fluororesin is achieved by an overcoat.
However, in the case of the two-coat, two-bake method, when the undercoat and overcoat have different compositions, the adhesion at the interface between the undercoat and overcoat is poor. This is because there is almost no enamel diffusion layer at the interface between the undercoat and overcoat, which is particularly bad for impacts such as falling steel balls, and the overcoat (top glaze) contains a large amount of alumina etc. However, since the firing conditions were the same in the examples, the adhesion was poor, and more importantly, the glaze particle size of the overcoat was higher than the glaze particle size of the undercoat. Since it is finer, it is not possible to obtain the uneven shape needed to improve the adhesion with the fluororesin. Figure 2 shows 2 coats 2 of JP-A No. 57-49266.
A schematic cross section of the enamel layer formed by baking is shown. Reference numeral 1 indicates a base metal, and on both sides of the base metal there is a bottom enamel 2 having excellent corrosion resistance, and on one side of the bottom enamel 2, a pine-like top enamel 3 containing a pine molded product 4 is formed. A fluororesin layer 6 is formed on the surface of the top enameled enamel 3 by a known method. As is clear from the figure, in the case of two coats and two bakes, there is no mutually diffused enamel layer 5 at the interface between the undercoating enamel 2 and the top coating enamel 3. In the specifications of the two publications mentioned above, it is stated that the adhesion with the fluororesin forms an uneven shape, but there is no mention of quantitative roughness.
That is, in the case of a mat-like (uneven) enamel surface, even if it simply contains a mat-forming material such as alumina, the adhesion to the fluororesin is not necessarily excellent. This is because it is not clear what kind of uneven shape should be used. For example, when using an aluminum substrate, good adhesion between the base metal and fluororesin can be obtained if the Ra (center line roughness) is 2.5 μm or more, but in the case of an enamel substrate, good adhesion cannot be achieved unless it is 4.0 μm or more. I can't get it. Because, in the case of enamel substrate, about 60
~80% is glass frit, so the parts other than the alumina powder must be smooth or in close contact, and the edges of the alumina powder will disappear due to milling, and the physical bond with the fluororesin will be poor, so the Ra will be large. There is a need to. Furthermore, Rtm (average maximum roughness) is 10μm for aluminum substrates.
If the thickness is more than 25 μm, the adhesion and abrasion resistance are excellent, but in the case of enamel substrates, it has been found in the present invention that the adhesion and abrasion resistance are poor unless the thickness is 25 μm or more. As mentioned above, there are no quantitative descriptions in these prior documents. OBJECTS OF THE INVENTION It is an object of the present invention to provide a method for forming a fluororesin coating layer that eliminates the above-mentioned disadvantages and has excellent corrosion resistance, adhesion, abrasion resistance, mechanical strength, etc. Structure of the Invention The present invention consists of a first step of applying a glaze with excellent corrosion resistance to the surface of a base metal and forming a dry undercoating glaze layer as needed, and then applying fluorine to the surface of the undercoating glaze layer. A glaze with excellent adhesion to resin and abrasion resistance is applied, a dried top glaze layer is formed as needed, and the bottom glaze layer and top glaze layer are simultaneously fired to create a base with a multilayer structure. A fluororesin coating formation method consisting of a second step of forming an enamel layer and a third step of coating the surface of the base enamel layer with a fluororesin, improving the corrosion resistance of the base metal by the undercoat glaze layer. However, since the bottom glaze layer and top glaze layer are fired simultaneously, a mutually diffused diffusion layer is formed at the interface between the bottom glaze layer and top glaze layer, which reduces mechanical strength such as steel ball falling. will improve. FIG. 1 shows a schematic cross section of an enamel layer formed by two coats and two bakes according to the present invention. 1 indicates the base metal;
A base metal enamel 2 has an excellent corrosion resistance on both sides, and a mat-shaped top enamel 3 including a mat formation 4 is formed on one side of the bottom enamel 2. A fluororesin layer 6 is formed on the surface of the top enameled enamel 3 by a known method. As is clear from a comparison with FIG. 2, there is a mutually diffused diffusion layer 5 at the interface between the lower coating enamel and the upper coating enamel 3, and the diffusion layer 5 has a mutually uneven shape. . On the other hand, because of simultaneous firing, it is possible to save energy. In addition, the top glaze contains alumina, silica, mullite,
It is preferable to use siyamoto, sillimanite, corundum, or the like, and to have the role of an abrasion-resistant material that improves the abrasion resistance of the fluororesin coating layer. Here, preferred combination examples of the undercoat glaze and topcoat glaze are shown below. Bottom glaze Top glaze Fritz 100 parts by weight 100 parts by weight Mill additives 5-10 〃 5-10 〃 Mattu formation 3-30 〃 25-50 〃 Water 40-55 〃 50-65 〃 Bottom glaze Bottom glaze The purpose of the frit used is to provide corrosion resistance to the base metal, so a frit with excellent adhesion to the base metal is used. That is, it is preferable that the frit contains an adhesion improver and a heavy metal oxide such as Co, Ni, or Cr. Commonly used mill additives include clay, sodium nitrite, hydrated borax potassium chloride, and bentonite. For matte formations, especially for undercoat glazes, commonly used silica powder and alumina powder are used. Typical examples of undercoating glaze compositions and glaze particle sizes are shown below (referred to as undercoating glaze A). Fritt #2246 5.0 parts by weight Fritt #0-17 50 〃 Clay No. 9 7 parts by weight Sodium nitrite 0.2 〃 Hydrated borax 0.5 〃 Silica powder (200 mesh pass) 5.0 〃 Black pigment 3.0 〃 Water 50 〃 Particle size 5-35g/300 Metsushiyu / Glaze 100c.c. Top glaze The frit used for the top glaze is one that has a firing temperature that is the same or slightly higher than the frits mentioned above, and that does not contain adhesion promoters such as Co, Ni, and Cr. It is also possible to use The mill additives used are the same as those used for the base glaze. Unlike the undercoat glaze, the mat forming material is preferably a substance that does not readily react with (dissolve) the frit during glaze firing, such as alumina, mullite, sillimanite, or the like. This is because ceramic powder with a high melting point is indispensable for mat formation and as a wear-resistant material. Typical undercoating glaze composition examples and glaze particle sizes are shown below (top glaze A) Fritz #2001 40 parts by weight #20250 30 〃 #1470-B 30 〃 Clay No. 9 7 〃 Sodium nitrite 0.2 〃 Water content Borax 0.5 Alumina powder (20 mesh pass product) 35 Black pigment 5 Water 60 Particle size 20-50 g/300 mesh/100 c.c. glaze 25-65 g/500 mesh/100 c.c. glaze is preferred. Description of Examples Next, the method for forming the fluororesin coating layer of the present invention will be described with reference to Examples. (1) Formation method First, the above-mentioned undercoating glaze A (particle size 15 g/300 mesh) was sprayed on both sides of a steel plate for enameling (SPP) 300 mm x 200 mm x 1.6 mm that had undergone the usual pretreatment (after firing). Film thickness: 60-80μm). next
Preliminary drying was performed at 100°C for 10 minutes to form a base glaze.
The above-mentioned top glaze A is applied on one side of the bottom glaze layer.
(Particle size: 30g/300 mesh, 45g/500 mesh)
was applied by spraying (total film thickness 100 mm after firing)
~120μm). Next, after preliminary drying at 100°C for 10 minutes, firing was performed at a firing temperature in the range of 780 to 840°C for 2 minutes each to form a base enamel layer. A fluororesin primer is spray applied to the surface of the base enamel layer (baked film thickness 10-15 μm), and after drying at 80°C for 10 minutes, a fluororesin top is spray applied (baked total film thickness 40-45 μm). , and baked at 380°C for 15 minutes to form a fluororesin coating layer. The base enamel layer and the fluororesin coating layer were evaluated based on adhesion, adhesion, corrosion resistance, and abrasion resistance. (a) Adhesion was determined by an adhesion test for the base enamel layer and a steel ball drop test in accordance with JIS R 4301-1978. The impact height was 100cm. ○...No peeling between the base metal and the base enamel layer △...Peeling from the interface between the base enamel and the top enamel ×...Peeling from the base metal and the base enamel layer (B) Adhesion between the base enamel and the fluororesin Judgment was made using a close contact test. () Use a cutter to make a ^1mm2 square that reaches the base enamel layer.
Make 100 pieces, () Sellotape 12mm width (JIS Z
1522 compliant product) was brought into close contact with the tip of the toe and then instantly pulled apart. The above () was used as a cycle, and the number of particles remaining after 10 cycles was shown. ○...100/100 to 90/100 △...89/100 to 80/100 ×...79/100 or less (c) Corrosion resistance was tested according to the salt spray test JIS Z 2371 for 100 hours. The number of spots due to corrosion on the surface of the coating layer (per ^100cm2 ) is: ○...0 spots △...5 spots or less ×...6 spots or more
mm, board thickness 0.6mm) tilted at 45 degrees, the entire spatula weighs 0.5Kg
By applying a load of Two-coat one-bake method has better adhesion and corrosion resistance between the base enamel layer and the base metal, as well as better adhesion and wear resistance between the fluororesin and the base enamel layer. That is, in the case of two coats and two bakes, when the firing temperature is low, there is almost no diffusion layer between the bottom enamel layer and the top enamel layer, resulting in poor adhesion due to falling steel balls. On the other hand, if it is high, the adhesion is excellent, but the base enamel is baked twice, some bubbles are generated, and the corrosion resistance is deteriorated. Furthermore, since some bubbles were generated, the uneven shape became non-uniform and the adhesion to the fluororesin was also poor.

[Table] (2) Surface roughness Ra (center line roughness), Rtm (average maximum height) It was found that the wear resistance is determined by Rtm (average maximum roughness). The surface roughness was measured using a Talysurf surface roughness meter.
Ra and Rtm were measured. Table 2 shows the results of the same tests as above while changing Ra and Rtm. However, the glaze is lower glaze glaze A (particle size 15g/300 mesh/glaze
100c.c.) and top glaze glaze A (particle size 30g/300mesh/glaze 100c.c., 45g/500mesh/glaze 100c.c.)
was used. The fluororesin coating was formed in the same manner as described above.

[Table] Table 3 also shows the results of the same tests as above while changing the particle size of the top glaze. The formation of the fluororesin coating is the same as described above.

[Table] As is clear from Tables 2 and 3, Ra is
Adhesion with fluororesin () below 4.0μm
is poor, and when Rtm is less than 25 μm, the wear resistance of the fluororesin is also poor. Although the appearance is not described in the Examples, in particular, when Rtm is 70 μm or more, the uneven shape becomes large, which is not desirable in terms of appearance. (3) Amount of pine-forming material added The amount of pine-forming material added is important because it has a large effect on Ra and Rtm together with the glaze particle size. Fourth
The table shows the results of tests similar to those described above, with the amount of matte forming material added to the top glaze being varied. As the undercoating glaze, the aforementioned undercoating glaze A was used. In the table, the amount of alumina added is 100g of frit.
It shows the amount added to. The fluororesin coating was formed in the same manner as described above.

[Table] As is clear from Table 4, the preferred amount of matte forming material added is 25 to 50 parts by weight per 100 parts by weight of frit.
In terms of parts by weight, especially if the matte formed product is less than 25 parts by weight, a favorable uneven shape in both Ra and Rtm cannot be obtained, and therefore adhesion b with the fluororesin and abrasion resistance are also unfavorable. Effects of the Invention As described above, by forming the base enamel layer using the 2-coat 2-bake method as the firing condition, the enamel characteristics of the base enamel layer can be improved, especially the mutual diffusion of the enamel at the interface between the undercoating enamel and the top enamel. By forming the layer, it is possible to form a base enamel layer that has not only excellent corrosion resistance but also excellent adhesion. Furthermore, adhesion and abrasion resistance with fluororesin are correlated to the surface roughness of the underlying enamel layer, and adhesion is determined by Ra.
4.0μm or more, wear resistance is determined by Rtm
It was found that when using an enameled substrate with a thickness of 25 μm or more, it was not possible to obtain good adhesion and abrasion resistance with the fluororesin. This is a method for forming a fluororesin coating layer. In the examples, only two coats and one bake were described, but the same effect can be obtained with three coats and one bake. In addition, although the method of drying the undercoat glaze and forming the undercoat glaze layer has been described in detail, the two-coat one-bake method using the wet method, in which the top coat glaze is immediately applied after applying the undercoat glaze, also has corrosion resistance, A fluororesin coating layer with excellent adhesion and abrasion resistance can be formed.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a base enamel layer formed by two coats and one bake according to the present invention, and FIG. 2 is a schematic cross-sectional view of a base enamel layer formed by two coats and two bakes according to the prior art. 1... Base metal, 2... Bottom enamel, 3...
...Top enamel, 4...Matsuto molding, 5...
Diffused enamel layer, 6...fluororesin layer.

Claims (1)

[Scope of Claims] 1. A first step of applying a glaze with excellent corrosion resistance to the surface of the base metal and forming a dry undercoating glaze layer if necessary, and then applying fluorine to the surface of the undercoating glaze layer. A glaze with excellent adhesion to resin and wear resistance is applied, a dried top glaze layer is formed as needed, and the bottom glaze layer and top glaze layer are fired simultaneously to create a base with a multilayer structure. A method for forming a fluororesin coating layer, comprising a second step of forming an enamel layer, and a third step of coating the surface of the base enamel layer with a fluororesin. 2. The method for forming a fluororesin coating layer according to claim 1, wherein the lower glaze layer and the upper glaze layer diffuse into each other, and after firing, a diffusion layer is provided in the base enamel layer. 3 The surface roughness of the base enamel layer is Ra,
The method for forming a fluororesin coating layer according to claim 1, which has a thickness of 4.0 μm or more and an Rtm of 25 μm or more.