JPS5870867A - Undercoating method for fluororesin coating - Google Patents

Abstract

PURPOSE:To improve the adhesiveness of a fluororesin coating, by treating the enameled surface of a metal base with an undercoating agent prepared by mixing glass or the like with the substance which is decomposed to form gas at a temperature lower than the melting point of the frit of the glass or the like. CONSTITUTION:Glass or the like (frit as a main component is SiO2-Al2O3, SiO2- Al2O3-B2O3, etc.) is mixed with the substance which is decomposed to form gas at a temperature lower than the melting point of the frit of the glass or the like (Al2(SO4)3 as a sulfate, ZnCO3 as a carbonate, AgNO3 as a nitrate, KClO3 as a chloride, BaH2 as a hydride, phenol resin as an organic compound, etc.) to prepare the composition. Said composition is applied onto an enameled steel sheet or the like and then dried. Thereafter, the composition is baked to decompose the gas-forming substance in it and to form a porous undercoat layer. Fluororesin is then applied thereon as a topcoat.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for preparing a surface for coating with a fluororesin, and more specifically, a method for coating a fluororesin on the surface of a metal base material with good adhesion while avoiding the risk of corrosion of the base material. Concerning a new and improved method of preparing a surface for painting.

When applying fluororesin coating to the surface of metal substrates such as iron, aluminum, and stainless steel, the surface of the metal substrate is enameled in advance, and then the fluororesin coating is applied to improve overall adhesion and corrosion resistance of the coating film. It is known that lifespan can be improved (Special Publication No. 47-17635, Special Publication No. 17635,
-"17635, Special Publication No. 55-46, J). When applying a fluororesin coating to such an enameled surface,
Usually, a so-called primer method is used in which a fluororesin primer is applied and then a fluororesin topcoat is applied. However, since the above-mentioned primer was originally developed as an adhesive reinforcing agent for coating metal substrates with fluororesin, its adhesion to inorganic substrates such as enamel is not necessarily good, and Fluororesin coatings have a problem in that they tend to peel off when immersed in hot water or exposed to water vapor.

The present invention provides a new surface treatment method that eliminates all the drawbacks and problems found in the conventionally known surface treatment methods, and its gist is to provide a new surface treatment method that eliminates all of the drawbacks and problems found in the conventionally known surface treatment methods. A mixture of at least one kind of frit and a blowing agent that decomposes at a temperature lower than the melting point of the frit to generate gas is applied to the surface of the substrate, dried, and then baked, whereby the blowing agent decomposes. A method for treating a base for coating with a fluororesin, comprising forming a porous base layer having an uneven surface on the surface of the base material.

According to the present invention, by simply impregnating and baking a fluororesin dispersion, it is possible to easily form a base treatment layer having a unique performance characterized by a desired fluororesin coating with significantly superior adhesion. In addition, the fluororesin-coated product thus obtained has guaranteed water resistance and water vapor resistance.

, the present invention requires the use of a specific frit and blowing agent mixture. The frit, which is the main component of the mixture, is appropriately selected from ordinary glass, enamel glaze, and ceramic glaze, which have been known to be used as so-called acid-resistant top glazes in this type of surface treatment. Ru. Preferred frit (!: Shiteu For example, SiO2-
At203 also has h s”2- ”203- B2O3 as the main component, and M”-0 (M”= Nα, K, Li
), M”0 (M” = Ea, Ca, ZrL%Co
, Ni), M"02Ct"=ri, Kn) e
You can use 40% of the mixture as appropriate. Specific examples thereof include those having the following compositions.

St O246~55 66.9 60.0 5l-I
At2035~10 3-0 2.0 2.6B
20312～15-7.0 9.4Z *
20-3, □-17”t ()2
- 5.0 -BaO-2,0- CaOO~2 7.3 2-5 6.5ZnO
-1,111,8 0αF2 2~7 - - -Coo
0=0-5-2.0-M
nO20~O-751,5- Ni0 0~0.75 - -
- Furthermore, the blowing agent mixed in the frit must be selected from a substance that decomposes to generate gas at a temperature lower than the melting point of the frit. This is appropriately selected from various inorganic compounds such as sulfates, carbonates, nitrates, chlorides, hydrides, etc. of various metals, and organic compounds such as phenol resins, silicone resins, acrylic resins, polystyrene, boriatrido, polyesters, etc. . The following are typical examples of inorganic compounds and their decomposition temperatures:

<Sulfate> Decomposition start temperature (℃) At2 (SO4) 3770 Pa (SOa) 3485 Cd 50. 700Z
Le 504740 CO5O4700 Cu S□ a 65
0B, (SO,)3>400 MrLSO4850 <Carbonate> ZnCd 300, 3 CdCO357 CcLCO3825 Cd2 (:'03 600pbc
O, 315 ('aMg (C03)2 730~
760〈Sulfate〉 AgN0. 444pbNo3>
470 L L NO3600 <Perchlorate> KClO3400 AgCIo, 270Na('Z
()3300 pd C12600 <Hydride> BaH2675 KBH4>30O NaBHu) 400L
z BN2> 275 The mixing ratio of the blowing agent to the frit is not limited depending on the type of each component used, the construction conditions of the subsequently obtained mixture, the type of base material, etc., but the mixing ratio of the blowing agent to the frit is usually about 2-100% by weight, preferably about 5-50%
It is appropriate to express the proportion in % by weight.

In the present invention, first, a mixture of the above-mentioned frit and a foaming agent is applied to the surface of a substrate and dried. Here, as the base material, for example, an enameled steel plate, an aluminum enameled steel plate, a glass-lined steel plate, etc. can be advantageously used. The above-mentioned mixture is applied in a liquid form by diluting the above-mentioned mixture with water or the like according to a conventional coating method such as a spray coating method, a casting method, or a dipping method. The amount of coating is not particularly limited, but it is usually appropriate to set the coating amount to an extent such that the thickness of the coating after subsequent drying and baking is about 5 to 50 μm. The subsequent drying is carried out according to a conventional method under conditions that allow water and the like to evaporate. This may be done by natural air drying, but it is usually preferable to use a suitable dryer.

In the present invention, the mixture coating film coated and dried as described above is then baked to form a porous base layer with irregularities on the surface due to the decomposition of the blowing agent in the mixture on the surface of the substrate. This firing is generally carried out in a furnace at about 520 to 800°C for several minutes to several tens of minutes. In this way, the base treatment of the present invention is completed.

In addition, in the present invention, the uneven surface of the porous base layer formed as described above is further lightly ground using, for example, sand blasting to remove the surface layer and partially destroy the partition walls of the air bubbles contained inside. It is also possible to form more complex surface irregularities. According to the method of the present invention, which also includes such grinding treatment, there is an advantage that fluororesin coating can be performed with even better adhesion.

The fluororesin coating on the base material treated by the method of the present invention can be carried out by various known methods.

A typical example is double coating with an undercoat and a topcoat. Topcoat paints are usually composed of almost only fluororesin except for pigments, and undercoat paints are made of paints that have good adhesion to both the base material and the topcoat film. A paint consisting of a component that has good adhesion between the auxiliary agent and the top coat fluororesin, that is, the fluororesin itself, is used.

When a substrate treated by the method of the present invention is coated with a fluororesin according to a conventional method, its adhesive strength is extremely strong as shown in the examples below, and the water resistance and water vapor resistance are also excellent.

The method of the present invention will be specifically explained below with reference to Examples.

Example 1 An enameled steel plate is prepared by baking an acid-resistant top glaze on a Kuroko gusushi having the following composition according to the enamel processing method.

Composition Kurokogusushi Acid-resistant Jogusushi 5
io2+ At20349.0 54.6B20
．． +7.5 12.
OL z 2() + 20 to Nα20+ 18
．． 1 13.8CaO+ZnO+Ba0
2.2 9.5Ca F2
5,4-Ha3A
tF6+Na2SiF62.5Coo+NiO+Mr
LO27,8-rio27.6 Next, prepare a mill by mixing a mixture of the acid-resistant top sieve with predetermined amounts of various blowing agents shown in Table 1 below with water,
This is spray-coated onto the surface of the above-mentioned enameled steel plate to a thickness of about 40 μm (thickness after firing), and then water is sufficiently evaporated using a dryer.

This coated product was placed in an electric furnace maintained at 750°C, and
Bake for 0 minutes. The surface of the enamel removed from the electric furnace was extremely uneven due to the decomposition of the blowing agent.

A fluororesin undercoating paint [BORIFUON ZX-1809BxJ (manufactured by Tai + Shi Kogyo ■) was applied to the surface of the treated base material after the above-mentioned surface treatment so that the film thickness after firing was 8 to 12 μm. Next, it was heated in an infrared dryer to sufficiently remove volatile substances, and then fired and fused in an electric heating furnace maintained at 380° C. for 15 minutes, and then taken out from the furnace and allowed to cool at room temperature.

A fluororesin top coat "Polyflon Enamel ES-5109BK" (manufactured by Tai + Shi Kogyo ■) was applied onto the thus obtained undercoat film so that the film thickness after firing was 25 to 30 μm. Next, drying and baking were performed in the same manner as the undercoating described above. The durability of the obtained coating film after being immersed in hot water at 90 to 95° C. for 3 hours was measured. The results are shown in Table 1. The methods for measuring each physical property in Table 1 are as follows.

Pencil hardness: JIS-6894 Drawing characteristics 2 Same as above Table 1 Example 2 Test number of Example 1 An enameled steel plate having an uneven surface which has been subjected to surface treatment is obtained in the same manner as in Inventions 1 and 2.

This treated surface is then sand blasted using alumina as an abrasive. As a result, the surface of the foamed top layer (base treatment layer) is scraped, and the bubbles existing in the top layer are destroyed, resulting in an even more uneven surface.

After the above-mentioned sand blast treatment, the treated surface is coated with fluororesin paint “Polyflon Enamel ES-5109B”.
K" was applied so that the film thickness after firing was 25 to 30 μm. Next, this was heated with an infrared dryer to remove volatile substances, and further baked and fused in an electric heating furnace maintained at 380° C. for 15 minutes, taken out from the furnace, and allowed to cool at room temperature.

Also, for comparison, an example! The enameled steel plate prepared in
A substrate (not subjected to surface treatment with the mixture of the present invention) is subjected to sand blast treatment in the same manner as described above to roughen the surface, and then coated with a fluororesin.

The obtained coating film was subjected to the same hot water immersion test as in Example I, and the results are shown in Table 2 below.

Claims (1)

[Claims] ■ A mixture of at least one kind of frit selected from the group consisting of glass, enamel shaft, and ceramic shaft, mixed with a blowing agent that decomposes at a temperature lower than the melting point of the frit to generate gas. is coated onto the surface of the substrate, dried, and then baked to form a porous base layer with irregularities on the surface due to the decomposition of the foaming agent, on the surface of the substrate. Ground treatment method. (2) The method according to claim 1, wherein the blowing agent is used in an amount of about 2 to 100% by weight based on the frit. (2) The method according to claim 1, wherein the surface of the base layer is further sand-struck treated.