JPS581982B2 - Tetrafluoroethylene - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention eliminates the step of baking or drying a single layer of primer, which was previously considered essential, and eliminates the risk of uneven coating. The present invention relates to a method for forming a coating film of a TFE copolymer (hereinafter sometimes abbreviated as TFE) which can be formed with easy operation and reduced cost.

Conventionally, when forming a coating film of TFE copolymer, the adhesion of the TFE copolymer film to metal and non-metallic surfaces is weak, so primer treatment, etching treatment, hard anodizing treatment, etc. are performed on the surface of the object to be coated. It is common to apply the copolymer after improving the adhesion of the surface of the object to be coated.

Among these treatments, primer treatment is most often used because of its wide applicability and operational advantages.

In this conventional method, after a primer is applied to the surface of the object to be coated, one layer of the brimer is baked or dried to form a non-wet brimer layer, and on this baked or dried primer layer, for example, TFE is coated. Applications of water or organic liquid dispersions of polymers have been used.

When carrying out such a method, the above TF
If the E copolymer dispersion is applied, the primer and the dispersion will mix, which defeats the purpose of priming.
The baking or drying treatment of the above-mentioned primer layer has been carried out as an essential step.

Furthermore, when applying TFE copolymer powder by, for example, powder coating means, baking or drying of a single layer of primer has been similarly employed.

The baking or drying treatment of the primer treatment in such conventional methods has operational and cost disadvantages in terms of processing operations, processing time, heat consumption, and the like.

Furthermore, when applying TFE copolymer powder to a single layer of primer, for example, by electrostatic powder coating, the TFE copolymer powder may vary depending on the shape of the object to be coated, as in the case where such a single layer of primer is not formed.
Since there are dead spots such as corners where the FE copolymer is difficult to adhere due to electrostatic repulsion, there is a problem in that coating unevenness tends to occur.

As a result of research to overcome the disadvantages or defects of the conventional method of forming a TFE copolymer coating film after primer treatment as described above, the inventors of the present invention discovered that a single layer of primer in a wet state that omitted the baking or drying step of the primer layer was used. Above is a T charged with static electricity.
By applying the FB copolymer powder and melting the powder according to a conventional method to form a coating film, the disadvantages of the above-mentioned baking or drying process and the defects of uneven coating can be overcome at once, and thick-walled It has been discovered that a coating film of a TFE copolymer with high adhesive strength and high adhesive strength can be formed easily and at low cost.

Therefore, an object of the present invention is to provide a method for forming a TFE copolymer coating film that can overcome all the disadvantages and defects of the conventional method of forming a TFE copolymer coating film after primer treatment.

The above objects and many other objects and advantages of the present invention include:
This will become clearer from the description below.

In the method of the present invention, a primer is applied to the surface of the object to be coated,
Electrostatically charged tetrafluoroethylene copolymer powder is applied onto the wet layer of the brimer.

The material to be coated may be any material as long as it can withstand a temperature equal to or higher than the melting point of the TFE coweight used, and usually one that can withstand a temperature of at least about 250°C or higher, preferably about 270°C or higher. Can be used.

Examples of such materials include iron, steel, stainless steel,
Examples include aluminum, titanium, alloys thereof, and metal and non-metallic inorganic materials such as ceramics and glass.

In addition, as a primer applied to the surface of the object to be coated, for example, an aqueous solution containing phosphoric acid, phosphate, chromic acid or dichromate, or polyimide, polyamideimide,
Organic liquid solutions containing heat-resistant resins such as polyimidazole or silicone resins, and particles having a particle size of about 0.5 mm in these solutions.
Examples include those in which fluororesin of 0.05 to about 0.5 μm is dispersed.

These primers may be the already known sintered primers used for water or organic liquid dispersion coatings of fluoropolymers.

For example, the primers described in US Pat. No. 2,562,117, US Pat.

There are no particular restrictions on the means for applying the primer as described above to the surface of the object to be coated, and any means such as spraying, dipping, brushing, roller coating, etc. can be employed.

In the method of the present invention, the baking or drying of the primer layer in the conventional method is omitted, and the electrostatically charged TFE copolymer powder is applied onto the wet primer layer.

Preferred examples of the TFE copolymer include copolymer powders of tetrafluoroethylene and perfluoroalkyltrifluoroethylene or perfluoroalkoxytrifluoroethylene having 3 to 10 carbon atoms.

The average particle size is about 2 to about 150μ and the porosity is about 0.
．． A TFE copolymer powder having a particle size of 74 or less can be used as a powder suitable for carrying out the method of the present invention in terms of forming a smooth and pinhole-free coating film.

In the present invention, the average particle size and porosity are determined as follows.

(1) Average particle size: Powders with an average particle size of 10 μm or less were measured as follows.

In other words, scoop a small amount of the sample onto a glass slide, shake it gently to spread the powder into a single layer, take a micrograph, and randomly plot more than 300 n particles on photographic paper and measure the longest diameter of the image of each particle. After accurately measuring a and the shortest diameter b, calculate according to the following formula.

In addition, for powders with an average particle size exceeding 10μ, the average particle size is determined by the d50 of the powder distribution curve measured using the air powder sedimentation method (trade name: Micromerograph, manufactured by Valdel, USA). be done.

(11) Porosity 21 The porosity is expressed by the following formula.

The above apparent specific gravity is measured by the method described in American Standard D-1457-62T.

Further, the specific gravity of the resin is measured at a temperature of 23° C. by a pycnometer method using trichlorethylene as a liquid.

In the method of the present invention, the electrostatically charged TFE copolymer powder can be applied onto the wet primer layer by spraying, fluid dipping, spreading, or other arbitrary means.

As a means of imparting static electricity to the TFE copolymer powder,
In addition to applying a voltage to the powder using an electrostatic powder coating method to charge the powder, collision between the powders or between the powder and a wall made of an electrically insulating material can be applied. There are several ways to generate friction.

As described above, an article in which an electrostatically charged TFE copolymer powder is applied onto a wet primer layer on the surface of an object to be coated is prepared by applying the copolymer powder to a temperature higher than the melting point of the copolymer. A coating film is formed by heating and melting at a temperature of .

Usually, a temperature of about 250°C or higher, preferably about 270°C or higher is employed.

In this way, the baking of a single layer of primer and the formation of a coating film are performed at once, and the coating film thus obtained becomes a smooth coating film that firmly adheres to the object to be coated.

Thus, according to the method of the present invention, after primer treatment, TF
It eliminates the baking or drying of a single layer of primer in the conventional method of forming E copolymer coatings, eliminates the risk of uneven coating, and allows easy operation of thick TFE copolymer coatings with high adhesive strength. It can be formed at low cost.

Several embodiments of the implementation of the method of the invention will now be explained in more detail by way of examples.

Example 1 A 10 mm thick iron plate was plastered with alumina abrasive grains, and a chromic acid monophosphate primer was sprayed on top of it.
The coating was applied so that the dry thickness was approximately 7 μm.

Next, on a steel plate having one layer of primer in a wet state that had been subjected to primer treatment, an average particle size of 35μ and a porosity of 0.4 were applied.
The tetrafluoroethylene-perfluoroalkoxytrifluoroethylene copolymer powder No. 9 was applied by electrostatic spray coating.

The powder was then melted in an electric furnace at 300°C for 30 minutes, then at 310°C for 30 minutes, and then at 330°C for 1 hour to obtain a coating film of the copolymer.

The resulting coating film had a thickness of 60 μm and was smooth and had excellent adhesion.

(The adhesion of the coating film was tested by the drawing test described in JIS-K-6894.

) Example 2 An aluminum plate with a thickness of 3 mm was blasted with alumina abrasive grains, and a chromic acid-phosphoric acid based brimer was applied on it in Example 1.
Sprayed in the same way.

Next, an average particle size of 20 μm was placed on an aluminum plate having one layer of primer in a wet state that had been subjected to primer treatment.
Tetrafluoroethylene-hexafluoropropylene copolymer powder with a porosity of 0.47 was applied by electrostatic spray coating.

The powder was then melted in an electric furnace at 300°C for 30 minutes, followed by 330°C for 30 minutes, and further at 3600°C for 20 minutes.
A coating film of the copolymer was obtained.

The resulting coating film had a thickness of 40 μm and was smooth and had excellent adhesion.

Example 3 A polyimide resin solvent solution was applied by spraying onto the same blasted aluminum plate as in Example 2, and then immediately the tetrafluoroethylene-perfluoroalkoxytrifluoroethylene copolymer powder of Example 1 was electrostatically sprayed. It was attached by applying paint.

The powder was then heated in an electric furnace at 150°C for 15 minutes at 310°C.
The mixture was melted at 350° C. for 30 minutes and then for 1 hour to obtain a smooth coating film with a thickness of 100 μm and excellent adhesion.

Claims (1)

[Claims] 1 Apply a primer to the surface of the object to be coated, apply electrostatically charged tetrafluoroethylene copolymer powder on one layer of the primer in a wet state, and then heat the copolymer at a temperature equal to or higher than the melting point of the copolymer. A method for forming a coating film of a tetrafluoroethylene copolymer, the method comprising forming a coating film by melting powder.