JPH03224666A - Coating method with fluororesin - Google Patents

Abstract

PURPOSE:To economically produce a fluororesin coated body having fine appearance by finely roughening the surface of a base material such as Al by chemical etching, chemically treating the roughened surface with an alkali or a halogen free acid and coating the treated surface with fluororesin. CONSTITUTION:The surface of Al or Al alloy is finely roughened by chemical or electrochemical etching. The roughened surface is chemically treated with an alkali such as NaOH or a halogen free acid such as sulfuric acid so that the weight of the surface is reduced by <=50g/m<2> and then the treated surface is coated with fluororesin. A fluororesin coated body having high adhesive strength of the fluororesin coating layer to the base material and fine appearance can be economically produced.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention relates to a fluororesin coating method, and more particularly to a method for coating the surface of a substrate such as aluminum with a fluororesin.

``Prior art'' Fluorine-based resins, such as tetrafluoroethylene resins (hereinafter abbreviated as PTFE), are plastics with excellent non-stick properties, heat resistance, chemical resistance, and electrical insulation properties. Metal molded products coated with PTFE have become widely used in household kitchen appliances and industrial parts such as fixing rollers for copying machines.

By the way, such fluorine-based resins, such as PTFE and tetrafluoroethylene-hexafluoropropylene copolymer resins, are known to have very poor adhesion to metals, and a unique method is required for adhesion to metals. However, methods for adhering to base metals can be roughly divided into two types, chemical adhesion methods and mechanical adhesion methods, depending on the adhesion mechanism. For example, the former method is the Braimer method, and the latter method is the etching method. That is, ■ After roughening the metal surface by sandblasting etc., an adhesive layer called a brimer is provided on the metal surface, and then a fluororesin is coated on top of this and the metal and resin are bonded via the brimer.
Brymer method).

■ When aluminum is used as a metal, the surface is electrochemically or chemically etched to create moldy irregularities on the aluminum surface, and this surface is coated with resin to bond the aluminum and resin using the so-called anchor effect.
etching method).

Comparing these two methods, the etching method has a stronger adhesive force (and can be molded after processing on a flat plate.The inner pot of a rice cooker, etc., is coated with this etching method. It was almost.

The present invention relates to the field of coating using this etching method.

``Problems to be Solved by the Invention'' Conventional etching methods can be roughly divided into two types: electrochemical methods and chemical methods.

The electrochemical method is carried out in an aqueous solution of an alkali halide or the like, with the aluminum plate to be etched being etched as a positive electrode, and at a current density of about 0.1 = I A 7 cm2.
This is a method of processing with an amount of electricity of 50Q 7cm" to create fine irregularities on the surface.

The chemical method is a method in which fine irregularities are formed by immersing aluminum in a strong acid containing halogen, such as HC3.

The problem with these methods is that after etching, streaks tend to appear along the rolling direction of the aluminum plate. In other words, these lines appear like lines because the uneven shapes of the etched surface of the aluminum differ along the rolling direction.

After etching, it is often coated with a resin that does not contain fillers such as pigments (in this case, the streaks after etching along the rolling direction are visible as they are, resulting in poor appearance). Ta.

Therefore, when producing aluminum plates to be etched in this way, countermeasures such as modifying the temperature during hot rolling have been proposed in order to eliminate the above-mentioned blanking point (for example, see Japanese Patent Publication No. 59-48860). ).

However, there is a problem in that there is a limit to taking only such measures during the production of the aluminum plate, and the cost is also quite high.

As described above, the present invention aims to economically obtain a fluororesin coating with a good appearance without streaks.

``Means for Solving the Problems'' That is, the present invention provides a method of forming fine irregularities on the surface of aluminum or an aluminum alloy by a chemical or electrochemical etching method as a first step, and then as a second step. A fluororesin characterized in that the surface is chemically treated with an alkali or a halogen-free acid so that the amount of weight loss on the surface is reduced to 50 g/@" or less, and then a fluororesin is coated on the surface. This is a coating method.

Note that the embodiments of the present invention include the following.

(b) As a chemical treatment after etching, NaOH
Alternatively, the fluororesin coating method of the present invention is characterized in that KOH is used.

The present invention will be explained in detail below.

The present inventors have carried out extensive studies to solve the problems of the prior art from the etching method side, and as a result have completed the present invention.

"Operation" The feature of the present invention is that the aluminum surface is first electrochemically or chemically engineered using a conventional method to form fine irregularities on the surface, and then alkali or halogen is added to the surface. A chemical etching treatment is performed using an acid that is not
It must be less than m2.

In other words, even if a streak pattern occurs along the rolling direction after the conventional machining/nching process as the first step, it can be made relatively uniform by the next chemical etching method, and the appearance will be improved even if the stripe pattern appears along the rolling direction. It is also possible to make the entire surface uniform and good.

Furthermore, this also improves the adhesive strength between aluminum and resin. Another characteristic of this process is that the entire image becomes slightly whitish.

Unlike the etching process in the first step, this etching process does not have the effect of creating fine anchors, and instead elutes from the aluminum surface sequentially. The fine unevenness created by the etching process collapses, and after coating with fluororesin, the adhesive strength of the resin rapidly decreases.

This limit throughput can be determined by the weight reduction due to the chemical treatment as the second step, which is 50 g/m''.If the treatment is applied beyond this, the adhesive strength will decrease rapidly.

For the chemical treatment as the second step, a strong alkaline aqueous solution such as NaOH or KOH or an aqueous solution of a halogen-free acid such as sulfuric acid or nitric acid is effective. If an acid containing halogen such as hydrochloric acid is used, the process is the same as the first step and the present invention has no effect.

Among these, it is more preferable to use strong alkalis such as NaOH and KOH.

This method has the advantage that the etching speed is about 10 times faster than when using sulfuric acid, and the process can be completed in a short time.

Further, the concentration, temperature, and time for treatment may be appropriately set within a range that does not exceed the above-mentioned limit treatment amount.

In addition, the minimum processing amount varies depending on the degree of occurrence of streaks after etching in the first step, but it is approximately 1 ge
A throughput of more than m'' is preferred.

By performing such processing, there is a great effect in eliminating the striped pattern that has been a problem in the past.

More preferably, after chemical treatment, providing an oxide film on the surface by anodic oxidation or the like leads to improved corrosion resistance.

"Example" Examples of the present invention will be described below.

Example 1 JIS-3004 material (manufacturer: Sidard, Belgium) as an aluminum material (size 2.0 mm)
After the surface was degreased and cleaned using a 5% aqueous sodium chloride solution, electrochemical etching was performed using the aluminum material as an anode and an amount of electricity of 20 quarons 7 cm''.

This etching plate was etched with NaOH water under the conditions shown in Table 1. 8
After immersing in a liquid and washing with water, a tetrafluoroethylene resin dispersion (product name D-IF manufactured by Daikin Industries, Ltd.) was applied by roll coating, and after drying the moisture, it was baked at 400°C for 10 minutes. The coating method of the invention was carried out.

The appearance of these coated plates was evaluated visually and with a color difference meter (brightness), and the adhesive force between the aluminum surface and the tetrafluoroethylene resin was measured by a beer ring test.

The results are shown in Table 1.

In Table 1, the appearance was determined by visually observing the degree of streak pattern formation after etching.

Further, the measurement was carried out using a color difference meter manufactured by Tokyo Denshoku ■ (TC-3[)On), and the measurement was quantified by the L value.

In addition, the adhesive strength is determined by using 200μ thick FEP on the coating surface.
The resin was reinforced by heat welding the film, and the peel force in the 180° direction was measured using a tensile tester.

Looking at the results in Table 1, by applying NaOH treatment after etching, the striped pattern caused by the aluminum material in conventional etching is eliminated, and the appearance is also good.

Furthermore, the adhesive strength between aluminum and resin is also improved. This is thought to be because the unevenness of the etching becomes more uniform.

However, when the NaOH treatment increases the Flit, the fine uneven shape formed in the first step collapses, so when the processing amount exceeds 30g/+", it decreases to 50g/m".
If it exceeds , practical problems will occur. In other words, when used in the inner pot of a rice cooker, the resin peels off after cooking rice several dozen times.

"Effects of the Invention" As described above, according to the coating method of the present invention, a fluororesin coating with strong adhesive strength between the two base materials and the fluororesin coating layer and a good appearance can be obtained economically.

Claims (2)

[Claims] (1) As a first step, fine irregularities are created on the surface of aluminum or aluminum alloy using a chemical or electrochemical etching method, and then as a second step, this surface is etched with an alkali or halogen-free acid. A fluororesin coating method, characterized in that a chemical treatment is performed to reduce the weight loss of the surface by 50 g/m^2 or less, and then a fluororesin is coated thereon. (2) NaOH or K as a chemical treatment after etching
Claim No. (1) characterized in that OH is used.
Fluororesin coating method described in section.