JPS5912461B2 - Articles with fluororesin coating layer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a product J in which the surface of a base material made of aluminum or an aluminum alloy is coated with a fluororesin.

In recent years, coating with fluororesin has been widely used as a surface treatment method for household products.

In particular, fluororesin coatings are widely used for household cooking utensils such as frying pans, hot plates, and rice cookers. This type of cookware is usually made of aluminum.
When coating these surfaces with fluororesin, there are two methods: (1) direct coating with fluororesin, (2) method of coating the bale surface with sandplast to make the surface rough and coating with fluororesin, (3)
There were methods such as applying borosilicate enamel treatment and then coating with fluororesin, and (4) spraying ceramic powder such as stainless steel or alumina and then coating with fluororesin.

However, when cooking utensils are coated with fluororesin using these methods, there are problems such as peeling of the fluororesin and corrosion of aluminum.

That is, since the cooking utensils are subjected to large thermal and mechanical shocks, the coating layer formed by the methods (1) and (2) has an extremely short lifespan and is hardly used these days. (3)
Although the method according to the above is the most excellent method from the viewpoint of corrosion resistance of the coating layer, it has the following drawbacks from an industrial viewpoint. First, borosilicate frit is the most expensive of conventional enamel frits and is disadvantageous in terms of price.

Furthermore, the process of synthesizing the slip for spraying onto aluminum is complicated and requires a firing process. In addition, since this firing temperature is close to the melting point of aluminum, the aluminum molded product may be deformed, so the design of the cookware may be affected.
There are disadvantages such as restrictions on the processing process. Also (4)
Since the melting point of alumina is high, the method of thermal spraying alumina powder is relatively expensive as it has to use plasma spraying, and the coverage rate with alumina powder is extremely low at 20 to 30%. .

Therefore, it cannot be said that it is sufficient from the viewpoint of corrosion resistance. There is also a method of thermally spraying stainless steel or nickel-chromium alloy powder, but this creates a potential difference with the base metal and has the disadvantage of causing significant corrosion when used as a cooker.

The present invention particularly improves the method (4) to improve corrosion resistance.

This method (4) involves roughening the surface of the aluminum base material using a method such as plasting, then creating a porous sprayed layer by spraying wear-resistant particles, and coating this with fluororesin. Therefore, this is a method for improving the wear resistance of fluororesin. Note that the wear-resistant particles mentioned here are ceramic particles. The fluororesin coating obtained by this method is non-adhesive to the food to be cooked, etc. even if the fluororesin layer on the surface is worn out because the fluororesin fills the pores in the porous layer attached by thermal spraying. However, from the viewpoint of corrosion resistance, these methods are still unsatisfactory. The causes that affect corrosion resistance are (1) the influence of aluminum and aluminum alloy base materials;

(2) Effect of surface roughening due to plasting for thermal spraying. (3) Adhesion state of sprayed material and influence of sprayed material. (4)
There are processing conditions for fluororesin, and these settings can significantly affect corrosion resistance. The effects of aluminum and aluminum alloy substrates are issues of aluminum purity and corrosion.

In other words, the more impurities a base material has, the worse its corrosion resistance is. Furthermore, there are differences between plate materials and cast products. Compared to plate materials, cast products, especially die-cast base materials, contain more impurities and more cavities in order to improve flowability. Therefore, from the viewpoint of corrosion resistance, it becomes extremely poor.
In the processing technology of fluororesin, the fluororesin coating layer generally coated for cooking utensils has a thickness of approximately 40 to 50%.
Since it is relatively thin (less than 1 tm) and has some pinholes, the aluminum base material is not completely effective as a corrosion protection layer.

Therefore, when fluororesin is used for cooking utensils, pitting corrosion occurs through the thin fluororesin coating or pinholes. The present invention solves the above-mentioned corrosion problem by forming an aluminum oxide film layer by anodic oxidation or the like on the exposed parts of the base material surface where the wear-resistant particles are not welded.

FIG. 1 shows an enlarged cross-sectional view of a part of an article having a fluororesin coating layer according to the present invention, in which 1 is a base material made of aluminum or an aluminum alloy; 2 is a base material made of aluminum or an aluminum alloy; 3 is an oxide film layer of aluminum formed by anodizing treatment on the exposed surface of the base material after the thermal spraying, and 4 is a fluororesin coating layer. Hereinafter, the present invention will be explained with reference to examples thereof.

Example 1 Aluminum plate material JISAAllOO [Al99. 0% by weight or more] and die-cast product ADC-10 [Al85.
2% by weight] were used.

After degreasing this base material by firing, the surface was roughened using a plasting method using alumina-based abrasive material #80, and then ceramic powder with an alumina content of 96% by weight was sprayed by plasma spraying. Sample A was then coated with fluororesin.
Table 1 shows the results of the corrosion test for samples B-D in which an aluminum oxide film was formed after ceramic spraying, and a fluororesin coating was applied after washing and drying. Sample B was prepared by boiling for 1 hour in an aqueous solution containing 5% by weight of soda carbonate and 0.1% by weight of sodium chromate to form an aluminum oxide film by chemical oxidation. Anodic current density 5 in sulfuric acid solution.

Sample D was anodized for 1 hour at 0A/Dm3 to form an oxide film, and sample D was anodized for 1 hour at an anode current density of 0.5A/Dml in a 1% by weight oxalic acid solution to form an oxide film. It is.

After 100 hours of immersion in a saline solution with a concentration of 75°C by weight, no corrosion was observed with an ○ mark, slight corrosion was observed with a Δ mark, and severe corrosion was observed with an × mark. .

As is clear from the above results, after ceramic spraying,
For those with an oxide film formed, the base material is aluminum plate material A
As for llOO, remarkable corrosion resistance effects are observed in both chemical oxidation treatment and anodic oxidation treatment.

Furthermore, when a die-cast product ADC-10 containing many impurities is used as a base material, chemical oxidation treatment is ineffective, and anodization treatment may also be ineffective depending on the conditions. Example 2 Next, the results of examining the thickness of the oxide film, which is a corrosion-resistant treatment, will be explained.

An aluminum plate AllOO was used as the base material, the surface was roughened in the same manner as in Example 1, and ceramic was sprayed.
An oxide film was formed by anodizing in a 3% by weight oxalic acid solution, and then a fluororesin coating was applied.

Table 2 shows the results of comparing the corrosion resistance of various oxide film thicknesses by adjusting the current density and electrolysis time. The corrosion resistance evaluation criteria and the corrosive liquid were the same as in Example 1.
The immersion time was 200 hours. In addition, the thickness of the oxide film was determined from the micrograph. The drawing test in the table is JISK-
This table shows the results of measuring the adhesive strength of fluororesin based on the method of No. 6894, where 1 represents the lowest adhesive strength and 5 represents the highest adhesive strength.

As is clear from the results in Table 2, when the thickness of the oxide film increased to 1001 tm, the adhesion strength of the fluororesin deteriorated, and some peeling was observed during the rapid thermal cycle test. Therefore, when an aluminum plate material is used as the base material and an anodic oxide film is formed after welding the wear-resistant particles, the thickness of the oxide film is suitably 10 ttm or less. In addition,
Usually, the thickness of the fluororesin coating layer is often about 40 to 50 μm, and the particle size of the wear-resistant particles used as the thermal spraying material is often in the range of several microns to several tens of microns.

If the thickness of the thermally sprayed wear-resistant particles becomes smaller than the thickness of the oxide film layer, the adhesion effect of the wear-resistant particles to the fluororesin will be lost. Also from this point of view, the thickness of the oxide film is preferably 10 μm or less. Example 3 Next, in order to confirm the corrosion resistance effect of the oxide film, after thermally spraying ceramic with an alumina content of 96.0% by weight, 1% by weight was applied to the ceramic with and without the oxide film.
The changes in weight after boiling in saline solution for a predetermined period of time were compared.

The base material used is aluminum plate material AllOO and die cast product ADC-10, and its surface area is 50 x 50 m71.
It was set as L. The oxide film was formed by anodic oxidation in a 10% by weight sulfuric acid solution at an anodic current density of 5.0 VdTI for 1 hour. The relationship between the boiling time in saline water and the amount of weight change is the second
It was like the picture. In the figure, curve a is the base material of AllOO with an oxide film, a' is the same base material but without the oxide film, b is the base material of ADC-10 with an oxide film, and b' is the same. Indicates a base material that does not have an oxide film. As is clear from the figure, the substrate in which an oxide film is formed using AllOO is stable with little change in weight due to corrosion.

Further, when the base material is ADC-10, there are many impurities, so when sulfuric acid is used as the chemical conversion liquid, the dissolution of the film is more pronounced than the formation of the anodic oxide film, and no corrosion resistance effect is observed. As is clear from the above examples, when high-purity aluminum is used as the base material, chemical oxidation and anodic oxidation do not affect the exposed parts of the base material, which are the non-welded parts of the wear-resistant particles. By forming an oxide film, corrosion resistance can be significantly improved.

Furthermore, even when a low-purity die-cast product is used as a base material, corrosion resistance can be improved compared to conventional products by forming an oxide film by anodic oxidation under appropriate conditions. In the above example, the thermal spraying material, which is wear-resistant particles welded to the base material, was made of Al2O3 as the main component (96.0% by weight) and mixed with a small amount of TlO2 and SiO2. In the present invention, the exposed parts of the base material are protected with an oxide film, so it is also possible to use metal powders such as stainless steel and Nickel-chromium alloy powders that would cause electrolytic corrosion and have an adverse effect in the absence of this oxide film. can.

Other ceramic powders such as alumina, silica, zirconia, tungsten carbide, and mullite; glass powders such as quartz glass, alumina borosilicate glass, Vycor glass, soda lime glass, and borosilicate glass; borosilicate frits; Frit powders such as lead-based frits, various cermet powders that are composite materials, etc.
It has appropriate hardness and melts when heated to high temperature,
Any inorganic material that can be applied to various thermal spraying methods including plasma spraying can be similarly used. In addition, in order to manufacture an article having a fluororesin coating of the present invention, as shown in the above example, roughening of the surface of the base material, thermal spraying of wear-resistant particles, formation of an oxide film, and removal of the fluororesin coating are necessary. It is preferable to carry out each step in the above order. For example, if thermal spraying is performed after the formation of an oxide film, the adhesion strength of the thermal spray material will deteriorate, and the oxide film will also deteriorate, impairing corrosion resistance.

As described above, according to the present invention, an article having a fluororesin coating layer that has excellent corrosion resistance and is particularly suitable for cooking utensils can be obtained.

[Brief explanation of the drawing]

Fig. 1 is an enlarged cross-sectional view of an article having a fluororesin coating layer in an example of the present invention, and Fig. 2 shows a base material to which wear-resistant particles are welded and a base material on which an oxide film is further formed, boiled in saline solution. FIG. 3 is a diagram comparing weight changes between cases. 1... Base material, 2... Wear-resistant particles, 3
... Oxide film, 4 ... Fluororesin coating layer.

Claims (1)

[Claims] 1 Ceramic particles are welded in an island shape to the surface of a base material made of aluminum or aluminum alloy, an aluminum oxide film layer with a thickness of 10 μm or less is provided on the exposed surface of the base material, and fluorine is applied to the aluminum oxide film layer and the ceramic particles. An article having a fluororesin coating layer formed by forming a resin coating layer.