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Corrosion inhibiting paper and corrision inhibiting film

What is corrosion inhibiting paper?

It is a kind of paper that has been impregnated with chemicals capable of preventing metal rust, such as kraft paper.
Anticorrosion oil is widely used to protect metal products, especially steel products, from rust. However, if you use corrosion inhibiting paper, you do not need to use corrosion inhibiting  oil, which will save your time and efforts in removing anti-corrosion oil after unpacking the product. In other words, you can reduce the amount of labor for those receiving products packaged with corrosion inhibiting paper.

Corrosion inhibiting papers defined by Japanese Industrial Standard (JIS)

According to JIS, the packaging methods for preventing iron rust are classified into five categories. This classifying standard can be regarded as generally applicable to metals other than iron.
① Moisture-proof packaging
② Waterproof packaging
③ General packaging
④ Dehumidifying packaging
⑤ Deoxygenated packaging
For each of the five categories, it describes what corrision inhibitinging packaging material should be used.
Out of the five categories, moisture-proof packaging, waterproof packaging, and general packaging are classified according to the degree to which moisture infiltration can be prevented. The moisture-proof packaging allows the least infiltration of water, and the waterproof packaging can prevent the infiltration of water but not water vapor, while general packaging has no water permeation prevention measures at all. 
corrision inhibiting paper is used in all three categories. By using this packaging method, corrision inhibiting oil does not need to be applied.
As for how to use the corrision inhibiting paper, it is divided into two methods: wrapping or inserting in a sealed space. Wrapping refers to wrapping the products directly with corrision inhibiting paper. The second method is to put the corrision inhibiting paper together with the product into a polyethylene film bag or a moisture-proof cardboard box. 

Two classification methods of corrosion inhibiting papers

There are two ways to classify corrosion inhibiting papers: one is the kinds of metals it can prevent from rusting and the other is the usages of the corrosion inhibiting papers.

➀The kinds of metals it can prevent from rusting
Each targeted metal has a different type of corrosion inhibiting paper. It is impossible to handle all metals with only one type of corrosion inhibiting paper because the effect of corrosion inhibitors differs for different metal.  For example, corrosion Inhibiting paper dedicated to steel does not work for copper. In contrast, corrosion inhibiting paper for copper is ineffective on steel.
Therefore, neither of the corrosion inhibiting papers can be used when steel and copper are bundled together. Recently, efforts have been exerted on the development of the kind of corrosion inhibiting paper that can be effective for ferrous and nonferrous metals, but its effect is not comparable to designated corrosion inhibiting papers for steels.

When corrosion inhibiting paper is used as a material for metal wrapping, it is necessary that it withstand the packaging operation and be strong enough to not hinder the transportation of the packaged product.
If sealed packaging is possible, it is desirable to carry out an additional polyethylene laminating process on one side of the package already wrapped with the corrosion inhibiting paper to provide a moisture barrier function. In this case, the infiltration of moisture from the outside of the package can be prevented and the evaporation of the corrosion inhibitor suppressed, thus prolonging the anticorrosive effect.
On the other hand, when corrosion inhibiting paper is used by inserting it into a sealed space, it has no strength requirements. Since it is based on a thin paper, it will be sufficient if the corrosion inhibitor works well.

Is the anti-rust agent easy to vaporize?

The most well-known anti-rust agent for steel is a substance called DICHAN (dicyclohexyl ammonium nitrite), while for cooper it is benzotriazole (BTA: 1.2.3-benzotriazole). Many of these anti-rust agents used in corrision inhibiting paper are slightly volatile.
The antirust agent used in the corrision inhibiting paper is generally called Volatile Corrosion Inhibitor, so it gives people the impression of being a substance that is very easy to vaporize, but the vaporization speed of these agents is actually so slow that it is totally non-comparable to the evaporation of water. 

Points to be noted when using corrision inhibiting paper

➀The corrision inhibiting paper should match with the metal
The most important thing is to use the kind of paper that matches the type of metal to be packaged. If the paper is inappropriate, it may promote rusting rather than prevent it.

②Pay attention to plating products
Depending on the purposes of preventing corrosion on the surface of the plating or the underlying metal, or both, different kinds of corrosion inhibiting paper are used. 
For example, in the case of a galvanized steel plate, since a conversion treatment is applied to the plating surface, corrosion inhibiting paper using pyrazolone, an anticorrosion agent for zinc, cannot directly act on the zinc to achieve its effect.

③Wash before using
Corrosion inhibiting paper cannot remove dirt and other corrosive substances from metal products. If any corrosive substance remains on the surface of the metal, the corrosion inhibitor cannot reach the metal. The anti-corrosion effect for parts of the metal covered in fingerprints, sweat, and dirt will be influenced.

④Quickly stick the corrosion inhibiting paper to metal products
As previously mentioned, corrosion inhibitors in which the corrosion inhibiting paper is soaked or coated are substances that are less likely to vaporize than water. Therefore, if the paper and the metal surface are separated, it will take a long time for the necessary amount of corrosion inhibitor to reach the metal surface. What is worse is that water may be well adsorbed on the surface of the metal product before the corrosion inhibitor can act on the metal surface. Under this circumstance, condensation may occur and may result in a progression of corrosion.

⑤Do not wet corrosion inhibiting paper
Water-soluble chemicals are used as corrosion inhibitors, and no adhesives are used here. Therefore, if corrosion inhibiting paper gets wet, corrosion inhibitors will flow out easily. Do not store corrosion inhibitors in places where rainwater may enter, where condensation may cause water droplets to fall from the ceiling, or where the floor may become wet.
It is also not preferred to store corrosion inhibiting paper in places exposed to direct sunlight or high temperatures.

About corrosion inhibiting films

There are two types of corrosion inhibiting films, one is made by kneading resins such as polyethylene into corrosion inhibitors, heating the resin to turn it into a liquid state, then extruding it into a film; the other is made by coating the corrosion inhibitor together with an adhesive onto the surface of a plastic film. Most corrosion inhibiting  films currently sold on the market are of the former type.
The latter type is basically the same as corrosion inhibiting paper. Therefore, it is possible to manufacture films with high corrosion resistance. However, since the kneading-in type is exposed to high temperatures during the manufacturing process, only corrosion inhibitors that can withstand that temperature and do not easily evaporate can be used.
The reason why the kneading-in type is more popular is that the manufacturing cost of the coating type is higher. The coating type of corrosion inhibiting films requires a solvent that can dissolve the corrosion inhibitor and an adhesive for sticking the inhibitor to the film.

Comparison between corrosion inhibiting paper and corrosion inhibiting films

➀Corrosion inhibiting paper has a superior anti-corrosion effect
The anti-corrosion effect of corrosion inhibiting paper is generally better than that of corrosion inhibiting  film. As previously mentioned, most corrosion inhibiting  films are made by kneading the corrosion inhibitor into the resin, so the amount of corrosion inhibitor contained in the films is much less than that in the paper. However, when used in direct contact, there is little difference in corrosion inhibiting effect since the corrosion inhibitor can directly contact the product.

②Films have better moisture-proof effect
With regard to the moisture-proof effect, Corrosion Inhibiting  film is clearly better. However, if condensation occurs inside the package, the corrosion inhibiting film cannot absorb the water. Therefore, when packaging with moisture-proof film, pay careful attention to the humidity of the working environment.

③Films have plastic-like properties 
Corrision inhibiting films are flexible and not as stiff as paper, but they are transparent and can be heat-sealed (melted and bonded by heat). Furthermore, dust is less likely to get in. Corrision inhibiting paper does not have these properties.

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