JPS625465B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a fluororesin coating composition for top coat or intermediate coat, and more particularly to a fluororesin coating composition for top coat or intermediate coat that contains mica-like iron oxide and provides a coating with excellent scratch resistance. . Fluorine resin is coated on cooking utensils to take advantage of its unique non-stick properties, but since this resin is a relatively soft synthetic resin, it is said to be susceptible to scratches from metal spatula etc. during use. It has its drawbacks. This drawback becomes a problem because it becomes noticeable when used at high temperatures such as around 200°C. Therefore, various methods have been developed to improve the scratch resistance of fluororesin coatings. One of them is the method described in Japanese Patent Application Laid-Open No. 10386/1986. This method involves coating a fluororesin-coated article consisting of a base coat and a top coat derived from a transparent fluororesin dispersion with a fluororesin and mica particles, pigment-coated mica particles, or metal flakes. It is composed of a membrane. However, according to the inventors' study,
This coating still does not have abrasion resistance that is satisfactory for practical use. As a method to improve the abrasion resistance of fluororesin coatings,
The method that has been put into practical use is to thermally spray ceramic or hard metal onto the metal base material before coating it with fluororesin.
This is a method in which irregularities are formed on the surface of the base material, and then a fluororesin is coated on top of the irregularities. According to this method, the adhesion of the paint film to the base material is ensured due to the anchor effect, and at the same time, even if the surface portion of the paint film is scratched off, the resin that has entered the recesses will not be scraped off. The properties of the resin, such as non-stick properties, are maintained indefinitely. Several thermal spraying materials and implementation methods have been developed for this method, but all of them use expensive metal materials or require large equipment and power (energy costs) such as plasma spraying when using ceramics. Since this method requires a method that requires The object of the present invention is to improve the drawbacks associated with the prior art as described above, and to obtain a fluororesin coating film with excellent abrasion resistance without using any special method. This object is achieved by the fluororesin coating composition for top coating or intermediate coating of the present invention, which contains a fluororesin selected from tetrafluoroethylene homopolymers and copolymers and mica-like iron oxide. The mica-like iron oxide (hereinafter abbreviated as MIO) contained in the composition of the present invention is a thin scale-like crystal whose main component is ferric oxide (α-Fe ₂ O ₃ ). In this case, synthetic α-oxidized pigments with smooth crystal faces, such as those conventionally used as anti-corrosive pigments (see Color Materials Vol. 52, p. 258 (1979)) and those described in Japanese Patent Publication No. 12435-1973 Iron powder can be used. Since MIO is non-toxic and non-polluting, it can be used as a coating for cooking utensils, etc. without any problems. The size of the MIO crystal flakes incorporated into the composition of the present invention is 5 to 100 microns, preferably 10 to 60 microns. The blending ratio of MIO is 5% based on the weight of fluororesin.
-100% by weight, preferably 20-70% by weight.
If the blending ratio of MIO is lower than 5% by weight, the abrasion resistance of the coating film cannot be obtained, while if it is higher than 100% by weight, the non-adhesiveness of the coating film becomes low. Homopolymers or copolymers of tetrafluoroethylene also include copolymers of tetrafluoroethylene with olefins such as ethylene and propylene (containing at least 75 percent by weight of fluoroolefins), among others, Preferred are tetrafluoroethylene, tetrafluoroethylene/hexafluoropropene copolymers, tetrafluoroethylene/ethylene copolymers, etc., the particle size of which does not exceed about 50 microns;
Usually, those in the range of 0.1 to 50μ are used.
A so-called dispersion produced by a conventional emulsion polymerization method has a particle size generally in the range of 0.1 to 3.0 μm, and can be suitably used in the composition of the present invention. Moreover, this dispersion is very advantageous because it can be used as is when producing the composition of the invention. The content of fluororesin in the composition of the present invention may generally be from 10 to 40 percent by weight. The vehicle for the composition may be water or an organic solvent (for example, N,N-dimethylformamide, N,N
-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, methyl ethyl ketone, methyl glycol acetate, 2-nitropropane, ethylene glycol acetate, toluene, etc.), and the composition is usually prepared as an aqueous dispersion. In addition to the fluororesin selected from mono and copolymers of tetrafluoroethylene and MIO, the composition of the present invention contains other additives, such as various surfactants (anionic surfactants, nonionic surfactants, etc.). ), pigments (titanium and iron oxides, etc.), viscosity adjusting and binding agents (methyl cellulose, ethyl cellulose, etc.), leveling agents (fluoroalkyl carboxylic acids, etc.), film-forming hardening agents (metal powders, metal compounds, alkali or amine silicate, alkyl silicate, lithium polysilicate, or silicon compounds such as colloidal silica), wetting agents (organic solvents, etc.). The composition of the present invention is prepared by uniformly dispersing a fluororesin selected from tetrafluoroethylene homopolymers and copolymers and MIO in a liquid medium at the above blending ratio. Actually, fluororesin and
It is convenient to prepare both MIOs as liquid dispersions or solutions and to mix them together.
Also, when the raw material fluororesin is powder,
The former may be added to the aqueous dispersion of MIO and mixed uniformly. In order to achieve uniform mixing, it is desirable to use a colloid mill, a ball mill, or the like. To form the composition of the present invention into an intermediate or topcoat coating, a basecoat layer applied to a substrate is coated with
As is conventional, the composition may be applied by various methods such as spray coating, brush coating, etc. Furthermore, the fluororesin coating can also be formed on the base material by thermocompression bonding a previously prepared fluororesin thin film onto the undercoat layer. The type of fluororesin used for this intermediate coat or top coat does not have to be the same as that used for the undercoat, and the type of fluororesin for the top layer can be selected depending on the purpose. The fluororesin coating obtained in this manner has improved abrasion resistance and does not exhibit much deterioration in non-adhesiveness. Next, the present invention will be specifically explained with reference to Examples and Comparative Examples. Examples 1 (1) to (12) and Comparative Examples 2 to 3 Polytetrafluoroethylene (Polyflon Dispersion D-1 (aqueous, solid content 60%) manufactured by Daikin Industries, Ltd.), the average major axis of the flakes was Mix 100μ, 50μ, or 5μ MIO (KS manufactured by Kikuchi Shiki Kogyo Co., Ltd.) and quaternary amine silicate (manufactured by Nissan Chemical Co., Ltd., solid content 30%) at the blending ratio shown in Table 1 below. Then, a methylcellulose aqueous solution (solid content: 5%) is added to adjust the viscosity, thereby obtaining a fluororesin composition suitable for spray coating. Spray a fluororesin primer (Polyflon EK-1783GB, manufactured by Daikin Industries, Ltd.) onto an aluminum plate and an aluminum frying pan whose surfaces have been roughened by sandblasting, and apply the film to a thickness of 7 to 12μ after firing. . Next, this is heated with an infrared dryer to sufficiently remove volatile substances, and then fired and fused for 20 minutes in an electric heating furnace maintained at 380°C. After treatment, remove from the oven and allow to cool at room temperature. The previously prepared fluororesin coating composition is sprayed onto the obtained primer coating to give a coating thickness of 20 to 25 μm after baking.
Apply it so that it looks like this. Thereafter, drying and firing and fusing treatments are performed in the same manner as in the case of the primer. Regarding the obtained coating film, non-adhesion and abrasion resistance were measured as coating film physical properties. The results are shown in Table 1. The physical properties of the coating film were measured by the following method. Non-stickiness: Using the sample frying pan, after actual cooking was carried out corresponding to one year of use under normal household cooking conditions, the ease with which the cooked food would stick was determined and evaluated using the following criteria. 〇 Cooked food does not stick. △ Cooked food becomes slightly sticky. × Cooked food becomes very sticky. Abrasion resistance: After placing the sample on an electrically heated hot plate and fixing it, the aluminum plate was heated to 200°C ± 10°C, and the surface was rubbed with a metal spatula under a constant load. The test shall be carried out using a moving type test device. The gold spatula is 15mm wide and 0.5mm thick.
It is made of stainless steel and is placed in contact with the sample surface at an angle of 45 degrees, and is moved back and forth linearly back and forth (in a direction perpendicular to the width of the metal spatula) with a load of 300 g applied. Note that the tip of the metal spatula that comes into contact with the sample is polished so that it is perpendicular to each measurement. Using this test method, the degree of wear due to sliding and scratching of a metal spatula, which corresponds to about two years of use under normal household cooking conditions, is measured. The evaluation criteria in Table 1 are as follows. ◎ No base metal is exposed. 〇 Only a small amount of base metal is exposed. △ Base metal is slightly exposed. × Base metal completely exposed. In addition, nickel aluminide (Meteco 404 manufactured by Metco, USA) was thermally sprayed on the same aluminum plate to a thickness of 25 μm, and polytetrafluoroethylene primer (Polyflon manufactured by Daikin Industries, Ltd.) was applied on top of this.
EK-1783GB) and top coat (ES-5109BK manufactured by Daikin Industries, Ltd.) at 10μ and
The abrasion resistance of the coating coated to a thickness of 20 to 30μ is approximately 0 to △ based on the above criteria. Comparative Examples 1 and 4 Instead of MIO, red red paste (30 parts by weight of red red pigment, 65 parts by weight of deionized water and 5 parts by weight of sodium lauryl sulfate was added by paint mill to 5 parts by weight).
Example 1
The test was conducted in the same manner. The results are shown in Table 1.

[Table] Example 2 A fluororesin primer (Polyflon EK-1783GB manufactured by Daikin Industries, Ltd.) was applied to an aluminum plate and an aluminum frying pan whose surfaces had been roughened by sandblasting in the same manner as in Example 1, dried, and baked. , fusion treatment. On top of that, the coating composition of Example 1 (8) was sprayed in the same manner as the primer of Example 1, and the film thickness after baking was 20 to 25 μm.
Apply it in the same manner as the primer, dry, bake, and fuse. Further, the coating composition of Comparative Example 1 was sprayed onto the obtained coating film so that the film thickness after firing was 20 to 25 μm, and the coating composition was dried, fired, and fused in the same manner as the primer. The non-adhesiveness and abrasion resistance of the resulting three-layered coating film were measured using the method described in Example 1. As for the non-adhesive property, even after one year's worth of cooking, cooked food remained sticky. Regarding wear resistance, the base metal was not exposed at all even after three years of wear. Separately, a three-layer coating was prepared under the same conditions except that the coating composition of Comparative Example 1 was used for the second layer of the coating. When we measured the non-stick properties and abrasion resistance of this coating, we found that the non-stick property did not stick to cooked food even after one year's worth of cooking, but the abrasion resistance was equivalent to two years' worth of cooking. The base metal was completely exposed after a wear cycle of . Example 3 First, coating compositions A and B having the following compositions
Prepare. Coating composition A Polytetrafluoroethylene (Polyflon dispersion D-1 manufactured by Daikin Industries, Ltd.,
Aqueous, solid content 60%) 100 parts by weight MIO (Kikuchi Shiki Kogyo Co., Ltd. KS) 18 parts by weight colloidal silica (Snowtex S manufactured by Nissan Chemical Industries, Ltd., solid content 30%) 6 parts by weight Triton X-100 (Nonionic surfactant manufactured by Rohm & Hass, 20% aqueous solution)
18 parts by weight Deionized water 15 parts by weight Coating composition B Polytetrafluoroethylene (same as coating composition A) 80 parts by weight Deionized water 13 parts by weight Xylene 3 parts by weight Aluminum plate with roughened surface by sandblasting Then, a fluororesin primer was baked and fused to an aluminum frying pan in the same manner as in Example 1. Thereafter, the above-mentioned coating composition A is sprayed as an intermediate coat, and applied so that the film thickness after firing is 20 to 25μ, and then dried, fired, and fused in the same manner as the primer in Example 1. . Furthermore, the coating composition B described above is sprayed as a top coat so that the film thickness after firing is 10 to 15 μm. below,
Drying, baking, and fusing treatments are performed in the same manner as the intermediate coating. The non-adhesion and abrasion resistance of the obtained coating film were measured in the same manner as in Example 1. As for non-stick properties, no phenomenon of sticky food was observed even after one year's worth of cooking. Regarding abrasion resistance, no exposure of the underlying base material was observed after one year's worth of wear. On the other hand, a coating film was prepared in the same manner as in the above-mentioned coating film preparation method, except that coating composition C having the following composition was used as the coating composition for intermediate coating of the above-mentioned coating film. The non-adhesion and abrasion resistance of the obtained coating film were measured in the same manner as in Example 1. As for non-stick properties, no phenomenon of sticky food was observed even after one year's worth of cooking. Regarding abrasion resistance, the base material was completely exposed after one year's worth of wear. Coating composition C Polytetrafluoroethylene (same as that of coating composition A) 100 parts by weight Mica coated with TiO ₂ (manufactured by A-Melarc)
10 parts by weight Triton X-100 20 parts by weight Deionized water 15 parts by weight

Claims (1)

[Scope of Claims] 1. A coating composition for a fluororesin top coat or intermediate coat, characterized in that a fluororesin selected from tetrafluoroethylene homopolymers and copolymers is blended with mica-like iron oxide. 2. The composition according to claim 1, wherein the proportion of mica-like iron oxide is 5 to 100% by weight based on the weight of the fluororesin. 3. Claim 2, in which the blending ratio of mica-like iron oxide is 20 to 70% by weight based on the weight of the fluororesin.
Compositions as described in Section.