JPS586543B2 - Method of forming a fluororesin film on the surface of iron enamel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for forming a fluororesin film with excellent corrosion resistance and wear resistance on the surface of iron enamel.

Conventionally, the method of forming a fluororesin film on the surface of iron enamel (hereinafter referred to as enamel) involves applying so-called blasting (surface treatment) to form countless irregularities on the enamel surface, then applying fluororesin to the surface and firing. is well known, and the following methods of surface treatment are also known.

In other words, (1) mild blasting is applied to the enamel surface (
2) Etching the enamel surface with a chemical (e.g. fluoric acid) (3) Applying and firing an enamel glaze containing alumina or silica powder alone or a mixture to the enamel surface (4) Mixture of enamel glaze and recrystallized glaze For example, when alumina or silica powder alone or a mixture is added to the enameled steel plate, and when this is applied to a steel plate for enameling and fired, the ability of the added substance to form irregularities is effectively utilized.

It is common practice to undercoat a fluororesin primer on the enamel surface that has undergone such surface treatment, then apply a fluororesin to the surface and bake it.The film obtained in this way is generally wear-resistant, but Due to its chemical properties, it has poor alkali resistance, acid resistance, especially acetic acid resistance,
Moreover, depending on whether the enamel glaze (see (3) and (4) above) is adopted, the actual situation is that water resistance and water vapor resistance are not necessarily good.

The reason for the above is that it is difficult to obtain the desired constant roughness under the surface treatment conditions, for example, in (1), the target surface (
When blasting is applied to enamel (enamel), if the blast exceeds a certain range, the metal surface will be exposed, and in the case of (2), it is not only difficult to obtain the desired uniform rough surface mainly due to the non-uniformity of the enamel components, but also the processing Due to the difficulty of complete rinsing with water afterwards, and in the case of (3) and (4), the treated surface does not have the high precision and uniform roughness necessary for the most effective adhesion of the fluororesin. When you can't do it,
Usually, the fluororesin film applied to the surface and fired does not always have the desired uniform roughness.

Therefore, in order to obtain the desired film, the ingredients of the glaze applied in (3) and (4) above, its composition, the weight and thickness of the steel material, the heating temperature, speed, and time after application of the glaze, as well as cooling. This requires advanced technical management that takes into account the effects of speed, humidity changes, etc.

In order to improve the above-mentioned points, the present invention and others have conducted various researches, and as a result, a metal oxide powder mainly composed of Al2O3 is thermally sprayed onto the enamel surface, and a fluororesin is applied to the surface. This solution solves the following points all at once.

In other words, the present invention provides a method that is minimally influenced by the above-mentioned conditions (components, composition, and other related conditions of the applied glaze) in order to obtain the uniform roughness necessary for adhering the fluororesin most effectively and rationally. The feature and significance of the present invention is that a metal oxide powder mainly consisting of Al2O3, which is a much more chemically stable substance than enamel itself, is plasma sprayed onto the target enamel surface.

However, lever plasma spraying depends on the particle size of the powder used in the plasma gun, the amount of injection, the distance to the target object (enamel), the spraying angle, the spraying speed, the gas pressure necessary for plasma generation, the amount of gas, and the powder transport. (3) and (4) are satisfied by keeping the gas pressure etc. constant.
), the desired work can be carried out smoothly without being affected by the environmental conditions at the time of application, that is, changes in temperature and humidity.

What is particularly effective in the above is that when the particle size of the Al2O3 powder used is, for example, 240 mesh, the width of the roughness that appears on the enamel surface during thermal spraying is moderately uniform, and the width of the roughness that appears on the enamel surface during thermal spraying is moderately uniform. By simultaneously obtaining a mountain shape, it is possible to ensure perfect adhesion of the fluororesin applied to the surface, and to ensure an appropriate roughness on the surface of the film.

The above is for the case where the Al2O3 powder particle size is 240 mesh, but even if the powder particle size is less than the above, it has almost no effect on the roughness unless it is extremely rough, for example, 120 mesh or less. You can always expect the desired and appropriate roughness on the film surface after resin baking.

In general, the adhesion of fluororesin directly to the enamel surface is determined by:
Although it depends on the roughness of the unevenness (number of peaks/mm) formed on the enamel surface and the shape of the peaks, according to the present invention, it is possible to obtain a material with a large number of peaks and a uniform shape. This will strengthen the adhesion of the fluororesin.

Moreover, since the roughness of the sprayed surface is obtained regardless of the roughness of the enamel surface, the fluororesin coating surface forms a uniform roughness.

The surface condition when Al2O3 powder (240 mesh) was thermally sprayed onto enamel and the condition of the enamel surface before thermal spraying are shown below.

Next, the following tests were conducted based on the above experimental examples, and satisfactory results were confirmed in all cases.

(1) Regarding the adhesion of the alumina powder to the enamel surface, there was no abnormality at all even when an adhesion test was performed using duct tape or the like.

(2) A fluororesin was applied on top of this, cross-cuts were made after firing, and a peel test was performed using cellophane tape, but no abnormalities were found.

This means that the adhesion of alumina powder on enamel is caused by the alumina powder flying through high-temperature plasma being well melted and colliding with the enamel surface, giving its retained heat to the enamel at the collision point and melting the enamel. phenomenon occurs.

This is due to the poor thermal conductivity of enamel and molten alumina (
It is understood that when the two materials collide at a temperature of approximately 2000° C., the collision area is locally heated, the enamel melts (approximately 850° C.), and the two are fused together.

At this time, the adhesion rate of thermal spraying is better if the enamel surface is slightly rougher than if it is smooth, but this is because even alumina melt (fine powder), which has little ability to melt enamel, can be machined onto rough enamel surfaces. It is thought that this is to create a sense of attachment.

Examples are shown below.

Example 1 Enamel containing XG-147 frit (manufactured by Nippon Ferro Ichi Co., Ltd.) as a main ingredient was formed on a 100 mm x 100 mm x 1.2 mm enameling steel plate by a conventional method and fired at 850°C.

This product has a glossy surface.

The surface roughness of this product was 3μ in RMS.

A mixed powder of 95 parts alumina and 5 parts titania (
240 mesh) was thermally sprayed using an 80kW plasma machine to obtain 50
A sprayed coating of μ was obtained.

Next, a peel test was performed by pressing adhesive tape onto the membrane surface using a conventional method, but no abnormality was observed.

Further, a fluororesin was applied to this surface by a conventional method, and after baking, a cross cut was made on the film surface and a peel test was performed using cellophane tape, but no abnormality was found.

In addition, the same test as above was conducted by boiling in hot water at 100° C. for 30 minutes, but no abnormality was found.

Furthermore, after being immersed in a 4% acetic acid aqueous solution at room temperature for 25 hours, the sample was washed with water, cross-cut, and the degree of adhesion was examined using cellophane tape, but as above, no abnormalities were observed.

Example 2 50 parts of XG-147 frit, #1091, was applied to a 100 mm x 100 mm x 1.2 mm enameling steel plate by a conventional method.
Enamel was formed using 50 parts of frit (manufactured by Nippon Fellow Co., Ltd.) and 10 parts of alumina powder (260 mesh) as main ingredients, and was fired at 850°C.

The surface of this product has no gloss.

The surface roughness was 8 to 10 microns in RMS.

A mixed powder of 95 parts alumina and 5 parts titania (
400 mesh) was thermally sprayed using an 80kW plasma machine.
A sprayed film of 0μ was obtained.

The same test as in Example 1 was conducted to determine the degree of adhesion, but no abnormality was observed.

Next, a fluororesin film was formed on this surface in the same manner as in Example 1, and an adhesion test and a hot water test were conducted in the same manner as in Example 1, but as in Example 1, no abnormalities were found.

Further, as in Example 1, an adhesion test was conducted by immersing the sample in a 4% acetic acid aqueous solution (25 hours), but as in Example 1, no abnormalities were observed.

Example 3 A steel plate for enameling measuring 100 mm x 100 mm x 1.2 mm was coated with an undercoat of enamel by a conventional method, and a topcoat of enamel containing Frit T-3891 (manufactured by Nippon Fellow Co., Ltd.) as the main ingredient was applied to the top surface.

A powder (230 mesh) of 95 parts of alumina and 5 parts of titania was sprayed on this surface under the same conditions as in Example 1 to obtain a sprayed film with a thickness of 40 μm.

The roughness of this product was 5 to 7μ in RMS.

A fluororesin was applied to this surface in the same manner as in Example 1, and the adhesion strength after firing, hot water test, and acetic acid immersion test were conducted in the same manner as in Example 1, and all of the results were satisfactory.

Claims (1)

[Claims] 1. A method for forming a fluororesin film on the surface of iron enamel, which comprises spraying metal oxide powder mainly composed of Al2O3 onto the surface of iron enamel and applying fluororesin to the surface.