JPS5944912B2 - Fluorine resin coating method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a fluororesin coating method.

Fluororesins have excellent properties such as low friction, non-adhesiveness, chemical resistance, and heat resistance, so they have a wide range of applications such as household use (irons, frying pans, etc.), food industry, electrical industry, mechanical industry, etc. ing.

However, the non-adhesive property also means that it has poor adhesion to all kinds of substrates, making painting operations significantly more difficult than with other common paints. For this reason, when coating with fluororesin, an undercoat (primer) is first applied on a base material that has been roughened by physical or chemical methods, and the adhesion effect depends on the base material. A widely used method is to enable strong adhesion of a fluororesin topcoat layer. Primers used for this purpose must exhibit good adhesion to both the substrate and the fluoropolymer topcoat layer; A primer for coating with a fluororesin usually consists of at least two components: a component with excellent adhesion to the substrate and a fluororesin component. Conventionally, strong acids or strong alkalis have been used as the so-called binder substance for the former component, which tends to contaminate the working environment during the production and use of the primer, and also poses problems such as disposal of losses generated during construction. It was hot. In order to overcome the drawbacks of these strong acid and strong alkali primers, various primers containing effective adhesion aids other than strong acids and strong alkalis have recently been announced and are being put into practical use.These binder materials include titanium, zirconium, etc. Organic chelate compounds of Group 4 transition metals of the Periodic Table of the Elements (JP 50-150735), alkali or amine silicates, alkyl silicates, silica colloids, aromatic polyamide-imide resins, polyimide resins, polyarylene sulfides such as polyphenylene sulfide, etc. Examples include id resin.

Although the adhesion of fluororesin coatings can be considerably improved by primers containing these binder substances, the adhesion may be unsatisfactory depending on the application and purpose because these primers contain a considerable amount of fluororesin. often occurs. In addition, since these primers are mixed with fluororesin and different substances, the density of the coating film is defective no matter what, so the corrosion resistance effect on the base material of the final fluororesin coating is insufficient. It is.

The present invention has been made to solve the problems of the above-mentioned fluorine resin coating.

That is, in the present invention, the first layer is a layer consisting of at least one of polyamideimide resin and polyimide resin, and the second layer is a fluororesin and a binder substance on the surface of the base material to which the fluororesin is applied. A fluororesin coating method is provided in which a fluororesin primer layer containing a fluororesin primer layer and a fluororesin topcoat layer as a third layer are sequentially applied, whereby strong adhesion of each layer between the base material and the fluororesin is achieved. Moreover, a fluororesin coating can be obtained which exhibits corrosion resistance and other excellent properties that a fluororesin coating has, and also exhibits good hardness at high temperatures. The method of the present invention is generally applied to the surfaces of various substrates such as iron, aluminum, stainless steel, various alloys, and ceramics.

The effect of the present invention can be further enhanced by roughening the surface of the base material by subjecting it to a commonly practiced surface treatment in advance.

In the method of the present invention, first, a layer whose main component is a resin consisting of at least one of polyamideimide resin and polyimide resin is applied as a first layer to the surface of the base material. Polyamideimide resin (hereinafter referred to as PA) used in the present invention
Polyamide resin (hereinafter abbreviated as I) and polyimide resin (hereinafter abbreviated as PI) are both known polymers with relatively high heat resistance, and polyamide-imide resin is characterized by having both amide bonds and imide bonds in its molecular structure. For example, the reaction between an aromatic diamine having an amide group in the molecule and an aromatic tetravalent carboxylic acid such as pyromellitic acid, or the reaction between an aromatic trivalent carboxylic acid such as trimellitic anhydride and a diamine such as 4.l-diaminodiphenyl ether. It is produced by reaction between a dibasic acid having an aromatic imide ring in its molecule and a diamine, etc.

On the other hand, polyimide resins are high molecular weight polymers having imide bonds in the molecule, which are obtained, for example, by the reaction of aromatic tetravalent carboxylic acid anhydrides (pyromellitic anhydride, etc.) and aromatic diamines (diaminodiphenyl ether, etc.). The first layer of PAI and PI is applied to the substrate as a solution or dispersion of these resins.

Solvents that dissolve these resins include N-methylpyrrolidone, cresol, phenol, naphtha, dimethylformamide, dimethylacetamide, benzonitrile, methyl glycol acetate, methyl ethyl ketone, 2-nitropropane, ethyl glycol acetate, ethyl succinate, xylene, and toluene. , methyl isobutyl ketone, and mixtures thereof, such as mixtures of N-methylpyrrolidone and toluene, ethyl sulfate, butyl glycol, dioxane, and the like. These resins can also be used as dispersions, in which case it is convenient to use water as the medium.

In order to form a good film with these resins, it is necessary for the dispersion medium to contain at least one of the above-mentioned solvents capable of dissolving PA and/or PI under film-forming conditions. . Depending on the purpose, these coating compositions contain various surfactants such as anionic surfactants, nonionic surfactants, pigments such as oxides of Ti and Fe, viscosity adjusting agents, and binders such as methyl cellulose.
Ethyl cellulose and the like, leveling agents such as fluoroalkyl carboxylic acids and sulfonate salts, film-forming hardening agents such as metal powders and metal compounds, and wetting agents such as organic solvents can be contained.

The coating composition for the first layer is applied to the surface of the substrate by any known means such as spraying, dipping, casting, etc., and if it contains volatile matter, it is heated to volatilize it and then heated to 330-400 ml.
A firing process is performed at a relatively high temperature of about 00°C to tightly adhere the film to the base material.

In the method of the present invention, as a second step, a fluororesin primer layer is applied on the first layer obtained as described above. This primer layer may be of any composition as long as it has adhesion to both the first coating layer consisting of at least one of PAI and P and the third fluororesin layer, but generally A composition in which a binder substance having the above characteristics is added to a fluororesin and dispersed in a liquid medium is used, and various primer compositions that are usually commercially available as primers for fluororesins are suitable for the purpose of the present invention. used for. Examples of the binder substances include chromic acid; organic chelate compounds of Group 4 transition metals in the periodic table such as titanium and zirconium; heat-resistant resins such as aromatic polyamide-imide resins and polyimide resins; lithium polysilicate, amine silicate, alkali silicate,
Examples include silicates such as amine silicate; SiO2 colloid, etc., and it is known that any of these can be blended with a fluororesin and used as a primer for the fluororesin. These primer compositions are also applied by known conventional means such as spraying, dipping, and casting, and are then dried and then subjected to a firing treatment.

Drying is carried out at room temperature to about 100°C, but this is common to all of the first to third layers of the present invention.If direct baking treatment is performed, rapid evaporation of the medium will cause damage to the coating surface. This is just one of the conventional processing means well known to those skilled in the art for the purpose of avoiding cracks, pinholes, etc. The firing of the primer layer is usually carried out at a temperature ranging from room temperature to 400°C, although it depends on its composition. The present invention was completed based on the important discovery that a resin layer made of at least one of PAI and PI and a primer layer for fluororesin have strong adhesive properties. The adhesion between the first layer and the third layer is extremely excellent.

In the present invention, a fluororesin topcoat layer is further applied as a third layer on the primer layer.

Examples of this fluororesin include polytetrafluoroethylene; tetrafluoroethylene and hexafluoropropylene, chlorotrifluoroethylene, and perfluoroalkyl trifluorovinyl ether (RfOCFCF2).
Copolymers with polychlorotrifluoroethylene and mixtures thereof, which are known as fluororesins, can be arbitrarily selected and used. Fluorocarbon resins include not only resin powders, but also aqueous dispersions of fluorocarbon resins obtained by emulsion polymerization, dispersions of fluorocarbon resin powders dispersed in aqueous media, organosols of fluorocarbon resins, and emulsions of organosols in water. It can be used in either form. Various types of these resins are commercially available as fluororesin top coating compositions, and any of them can be suitably used for the purpose of the present invention. The fluororesin composition is also applied by conventional means such as spraying, electrostatic coating, flow coating, etc., followed by drying and baking. In this case, the optimum firing temperature is used depending on the resin used and is well known to those skilled in the art. Usually 340-420°C, preferably 360-400°C, about 230-300°C, preferably 240-400°C in the case of polychlorotrifluoroethylene or a copolymer mainly composed of chlorotrifluoroethylene.
A temperature of 270°C is used. By the method of the present invention described above, it is possible to obtain a coating in which each layer between the base material and the fluororesin layer is extremely tightly adhered. When this adhesion was examined by the peel strength measured by the method shown in Example 1, the peel strength when only the conventional chromic acid primer was used was 2.0k9/? Primer with PPS added to fluororesin (for example,
-12053) or when only PPS is used as a primer (for example, Japanese Patent Publication No. 51-31813), the peel strength is 1.0 to 1.5k9/C! 7L, peel strength of 3-layer coating using the coating method of the present invention is 2.5 to 3.2
It is clear that very good adhesion can be obtained with kg/C7TL. Furthermore, by adding PAI and/or PI to the first layer, the hardness and wear resistance of the coating at high temperatures can be significantly improved. The present invention will be explained below with reference to Examples.

Example 1 was pulverized and mixed in a ball mill for 24 hours to obtain a PI dispersion as a coating composition for the first layer.

Separately, a polytetrafluoroethylene (PTFE) aqueous dispersion with an average particle size of 0.2 μm was blended so that the weight ratio of the PI dispersion PTFE/PI was 3/1, and the mixture was gently stirred. A coating composition for the second layer was made.

An iron plate with dimensions of 200 x 200 x 1 was roughened by blasting and cleaned by blowing compressed air, and then used as a coating base material, and the coating composition for the first layer was applied to the surface of this iron plate. The coating was applied by spraying so that the thickness after firing was about 20 μm, then dried in an infrared dryer for 10 minutes, and then fired in a firing oven at 390° C. for 20 minutes.

After cooling, the second layer coating composition was applied and adhered to the first layer under the same operating conditions as for the first layer. On the thus obtained second layer, a polytetrafluoroethylene topcoat, "Polyflon Enamel EK-4108-GY" manufactured by Daikin Industries, Ltd. (solid content 41%,
Gray) was applied so that the thickness after firing was approximately 25μ, and
Drying and baking were performed in the same manner as in the case of the layer to obtain an adhesive coating film. After cooling, the following properties of this coating film were measured by the following methods.

The results are shown in Table 1. Pencil hardness: JlSK6894
Measured according to. Salt spray test: JIS-Z-2371
Compliant with. In the heat resistance test, the test piece is heated in an electric furnace maintained at 3000°C and 390°C for the specified times, and then the test piece is taken out and cooled, and the pencil hardness is measured according to JIS K6894. Peel strength: Coating compositions for the first and second layers are applied to half the surface of the iron plate, which has been surface-treated and roughened, and after baking treatment, an overcoat layer (
After applying the 3rd layer) and firing, part of the topcoat layer is peeled off from the area where the 1st and 2nd layers have not been applied, and the topcoat layer is coated at a speed of 20m1/min using a self-recording tensile tester. The layer was peeled off in a direction of 180° C. and the strength was measured and expressed in Kg/Cm.

Comparative Example 1 The coating composition for the first layer used in Example 1 as the first layer was
As the second layer, the same fluororesin top coating paint used in Example 1 was applied to an iron plate in the same manner as in Example 1, and the physical properties of the coating film were measured.

The results are shown in Table 1. Example 2 A coating composition for the second layer was prepared by mixing and stirring.

The coating composition for the first layer was applied by spraying onto an iron plate that had been blasted and cleaned in the same manner as in Example 1 so that the film thickness after firing would be about 20 μm, followed by heating, firing, and cooling. The coating composition for the second layer was applied and adhered in the same manner (film thickness after firing: 10 μm), and a PTFE topcoat, “Polyflon Enamel EK-4” manufactured by Daikin Industries, Ltd.
183GB] (solid content 41%, grayish color) was applied and adhered in the same manner to a film thickness of 20 μm after firing. Heating, baking, and cooling were all carried out under the conditions described in Example 1. The various properties of each coating film obtained were measured by the method shown in Example 1, and the results are shown in Table 2. Comparative Example 2 The coating composition for the second layer used in Example 2 was used as the first layer, and the coating composition for the third layer was used as the second layer and similarly applied to an iron plate to obtain a coating film, and the physical properties of the coating film were determined. was measured.

The results are shown in Table 1. Example 3 In addition to using a coating composition for the second layer obtained by mixing and stirring 2% polyvinyl alcohol aqueous solution 1009, and using the above "Neoflon ND-1" as a coating composition for the third layer, A three-layer coating was applied on an iron plate in the same manner as in Example 1.

The measurement results of various properties of these coating films are shown in Table 3. Comparative Example 3 The coating composition for the second layer in Example 3 was applied directly on the iron plate as the first layer, and the composition for the third layer in Example 3 was applied thereon to obtain a coating film. Membrane physical properties were measured.

The results are shown in Table 1. Example 4 According to Example 2, a dispersion of PAI was placed on an iron plate to be roughened and cleaned.
A first layer coating film (film thickness after firing: 15 μm) was prepared by applying the following method.

Next, the following compositions (a) and (b) were each used individually as a composition for the second layer, and applied in the same manner as in Example 2 so that the film thickness after firing was 10 μm. I made it. (b) Mix the following materials uniformly.

Furthermore, on top of the above second layer, a PTFE topcoat paint "Polyflon Enamel EK-4108G" manufactured by Daikin Industries, Ltd.
Y" was used as the third layer (applied by the method of Example 2 so that the film thickness after firing was 20 μm to create a three-layer coating.

The measurement results of the physical properties of the coating film are shown in Table 2. Comparative Example 4 The dispersions (a) and (b) in Example 4 were directly applied as a primer layer on an iron plate, and Polyflon enamel EK-4108GY was applied thereon in the same manner to create a two-layer coating. Ivy.

Claims (1)

[Claims] 1. On the surface of the base material to be coated with fluororesin, a layer consisting of at least one of polyamideimide resin and polyimide resin is applied as a first layer, and a primer layer for fluororesin containing a fluororesin and a binder substance is applied as a second layer. A fluororesin coating method, which further comprises applying a fluororesin topcoat layer as a third layer in the stated order.