Asconium® Liquid Corrosion Inhibtors for Anti-Corrosion Coatings

Is Your Protective Coating Losing its (corrosion) Inhibition?

Aside from the aesthetic reasons for applying a coating to an asset, the primary objective is likely to be protection of that asset from the effects of the environment in which it is situated, particularly against the effects of corrosion caused by rain, humidity and water immersion etc. However, the process of corrosion takes place over a long period of time. Therefore, the technology employed to prevent or minimize corrosion also needs to have significant longevity and not lose its efficacy. This can be achieved to some degree by the use of platy fillers such as mica or micaceous iron oxide or glass bubbles which hinder the ingress of water from the outside to the substrate. More often though some form of corrosion inhibitor is required to impart the necessary protection.

Figure 1: Utilising a good anti-corrosion coating can increase the life of both the coating and the asset.

What is the Conventional Approach to Corrosion Inhibition in Coatings?

Historically, inorganic inhibitors such as zinc phosphate, modified zinc phosphates and other mixed metal phosphates have been the conventional choice of inhibitors.  For extremely demanding markets such as aerospace and defence, chromate-based inhibitors have been the “go-to” first choice but regulatory forces and safety concerns now require coatings formulators to find other solutions.

These chemistries have served the coatings industry well but with some compromises, for example,

• The need for milling, high-speed dispersion.
• Reduction of gloss in primer/topcoat formulations.
• Typically high dosage rates.
• Labelling requirements.
• Vulnerability to blistering.

What are the Alternatives to Inorganic Inhibitors?

The Asconium® range of corrosion inhibitors from ASCOTEC have been designed to overcome or at least to reduce some of the above-mentioned compromises.  These liquid additives are multi-component blends that function through a combination of mechanisms but mainly,

• By creating a hydrophobic barrier to water ingress through the film of the coating.
• Enhancing the adhesion of the coating to the substrate.
• Creating resin-filler interactions to improve film cohesion.

With these mechanisms working simultaneously and synergistically, excellent corrosion protection properties can be imparted to the coating.

The hydrophobic nature of the Asconium® inhibitors is particularly important as this contrasts greatly with inorganic inhibitors which depend on a controlled level of water solubility in order to function which can also be their Achilles heel in terms of increasing the water sensitivity of the film and vulnerability to blistering etc.

Therefore, to summarise, Asconium® inhibitors offer the coatings chemist the following benefits,

• Ease of incorporation (no milling required)
• Excellent, long-term corrosion protection at low dosage rates.
• Reduced blistering tendency.
• Gloss preservation.
• Multi-substrate protection.
• Potential for reduced labelling requirements.

Figure 2: A good corrosion inhibitor should provide long-term corrosion protection at low dosage and be easy to incorporate. Asconium® offers this plus more to coatings formulators.

Do Asconium® Inhibitors Limit Resin Selection in a Coatings Formulation?

The Asconium® allows for the formulation of both solvent-borne and water-borne direct-to-metal coatings so do not limit resin selection. In addition, two-pack polyurethane and epoxy coatings are easily achievable. 

Formulation Considerations with Asconium®

While Asconium® can overcome many of the compromises that were required when formulating with conventional inorganic inhibitors, there are still formulation considerations.  For example, if you are removing an inorganic inhibitor from a formulation and replacing it with an Asconium® liquid inhibitor, it is important you balance the pigment volume concentration with more filler.

In water-based systems, there are essentially two recommended ways of introducing Asconium® inhibitors in terms of the order of addition and this advice is available upon request.   Also, the performance of a waterborne direct-to-metal coating may be further enhanced by the use of a non-ionic pigment dispersant (such as Edaplan 490 from Munzing Chemie) along with an inherently hydrophobic flash rust inhibitor from the ASCOTEC Ascotran® range.

If you are developing a coating to be applied at a dry film thickness of less than 15 microns then depending on the performance requirements, you may need to consider a synergistic blend of Asconium® inhibitor with a conventional inhibitor for the best results.

What Next to Develop an Anti-Corrosion Coating Project?

This article is really an introduction to the Asconium® concept and the potential benefits for you as a formulator and deliberately does not drill down into specific Asconium® products and their suitability.  Since every project has its own requirements, it is recommended you contact us to discuss the specifics of your formulation and requirements to get the right match.