BriteFlex® Muscovite Mica to Replace Wet Ground Mica in 2-Part Epoxy Corrosion-Resistant Barrier Coatings
Coatings are used for a variety of reasons. In some instances, they are primarily decorative but in other cases, the demands on the coating are far more severe. One example is barrier coatings that are designed to resist chemical attack and to prevent corrosion of the underlying substrate.
In order to achieve those goals, a chemically resistant polymeric matrix is used – a two-part epoxy system is typically chosen. However, that alone is not enough. In order to block the ingress of chemicals and provide mechanical reinforcement, inorganic platy particles must be added to enhance the formulation.
Of the possible plate-shaped minerals available such as talc, kaolin and mica, it has been found that mica performs best of all. In particular, wet-ground mica gives superior performance due to an extremely high aspect ratio (the ratio of the particle breadth to its thickness).
How Does Mica Work in Coatings?
As mentioned, the principal property that determines performance is the aspect ratio of the particles meaning their largest dimension divided by their narrowest dimension but why is that? The easiest way to picture why mica is so effective is to look at scale armor.
Scale armor as used from 1400BC to the present day in various configurations
When mica is added to a coating, the platelets create a pattern similar to fish scales or scale mail armor. The hard mica plates resist not only scratches and abrasion but also inhibit the ingress of chemicals into the coating and the underlying substrate. The wider the scales, the more effective the protection and that explains why very high aspect ratio mica outperforms other products.
How Mica Plates Provide a Barrier Effect Via the Tortuous Path Mechanism
Mica plates are manufactured to be small enough to pass through a spray nozzle but wide enough to give maximum performance. Typically, the platelets are around 40 microns in diameter but less than 1 micron in thickness, so they lay flat within the coating as it hardens.
BriteFlex® Mica – the Cost-effective Alternative
The pre-eminent choice for barrier coatings is wet-ground mica because the wet grinding process preserves the aspect ratio. However, wet-ground mica is inherently more expensive than dry ground mica. BriteFlex® is special because a revolutionary dry-milling process is used to give mica that performs like the industry-standard wet ground product but at a more competitive price point. In order to illustrate that, Arctic Minerals commissioned a study from an independent laboratory specified by one of our clients. The lab conducted a very detailed set of experiments comparing BriteFlex® to wet-ground mica according to standardized test protocols as follows:
5 mil dry thickness 2 part epoxy coatings based on EPON 828 resin mid-coat with a PVC of 33.5% and a VOC of ~ 235 g/l were applied to cold-rolled and sand-blasted steel substrates. Mica was used at 1.96 pounds per gallon and accounted for 35.8% of the total extender pigment by weight, or 39.4% of total extender volume.
No effect was seen when the coatings were exposed to the chemicals, acids or bases. Similarly, there was no blistering or corrosion on any of the coatings after the 14 day condensing humidity test. The only test to show corrosion was, as expected, the infamous salt fog/spray test. The wet-ground mica and BriteFlex® showed no blistering and very little rusting to 500 hours and all showed the same blistering with severe rusting from 1000 hours onward. The image shows that even under severe conditions, the BriteFlex® MR4 product outperformed the more costly wet-ground mica.
Dry-ground BriteFlex® MR4 Performs Better than More Costly Wet-ground Mica
The full report is available upon request, but the conclusion stated the following:
“In review of all test data, it would appear that both the BriteFlex MR-4 and BriteFlex MR-10 exhibit performance that is equal or slightly better than the standard, and should be regarded as being “performance offsets.”
Conclusion
BriteFlex® high aspect ratio specially dry-ground mica is a more cost-effective alternative giving as good or better performance compared to the industry-standard wet ground mica. If you like the idea of top-performance and better margins, then contact Artic Minerals today.
Available in a range of grades and silane surface treatment options, contact Arctic Minerals to get samples from your local sales representative. We keep stock in our 20 warehouses so that our customers get reliable deliveries.