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Column 技術屋の解説

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  • Nature of the corrosion inhibiting ability in the case of Anticorrosive polymer film

Column 技術屋の解説

2021.04.14

Nature of the corrosion inhibiting ability in the case of Anticorrosive polymer film

In my last column, I have explained that the volatile corrosion inhibiting ability power of the most anticorrosive polymer films in the market is almost nothing or very small and rather much weaker if any. So can you guess by what mechanism the corrosion inhibiting ability has been generated in those anticorrosive polymer films?

If saying before the answer, it may be said that the moisture-prof property, which the film itself has, is the most greatly contributing.

On top of the above reason, I also think the rust occurrence is controlled by the corrosion inhibitor (rust preventive agent), which have been solved into the adsorbed water on the steel surface, contained in anticorrosive polymer film. In this action, it is not required for corrosion inhibitor to be volatile, as far as they have the soluble property in water. 

However, we should never have confidence too much on the effect of the corrosion inhibitor solved into the adsorbed water.  As the polymer film, as a base of anticorrosive polymer film, has the hydrophobic property, the employed corrosion inhibitor must have the hydrophobic property so as to be familiar to the polymer film. It does not mean any types of corrosion inhibitor are acceptable, as the water solubility is given to the polymer film on it.

It is not reasonable to use as a matter of course the corrosion inhibitor used for VCI paper which have powerful water-soluble property.

In addition, the volume of corrosion inhibitor contained in anticorrosive polymer film is very small as explained last time. Furthermore, the volume is very, very few even if solved into the adsorbed water on the steel surface, as the corrosion inhibitor inside the film are not easily coming out the surface of film.

In other words, it means that the corrosion inhibitor, not so strong and also to be extremely small amounts only, cannot be solved into the adsorbed water.

Let me disclose my experience on the test a long time ago.

I had tried to make rust by forcible condensation after tightly sealed packaging steel, which was polished neatly in the laboratory with anticorrosive polymer film. It was a long testing period, enough to rust on them because of the chemicals flowing out in the case of the same type of test using VCI paper without moisture-proof.

The rust could not be seen on the steel packed with anticorrosive polymer film, and also with the same thickness blank film (usual film without any corrosion inhibitor). It can be explained that the high moisture-proof of the film has resulted to prevent rusting on the steel. The effectiveness of anticorrosive polymer film cannot be confirmed by this test.

Then, I tried to make a situation in which the condensed water was likely to enter inside the incomplete packaging. When I tested by forcible condensation to rust steel just like tightly sealed case, the difference could be seen between anticorrosive polymer film and blank film in the case of small volume of water entered. But, I remember the steel was rusted even with anticorrosive polymer film in the case of much volume of water entered. I understood as the reason that the solved volume of corrosion inhibitor was not enough in the water even with anticorrosive polymer film.

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