Canadian Finishing & Coatings Manufacturing Magazine September/October 2021 - 37

PAINT AND COATINGS MANUFACTURING: FIRE RETARDANTS
Alumina Trihydrate (ATH), an Effective and
Environmentally Friendly Coatings Additive
HUBER ENGINEERED MATERIALS
W
hen seeking effective additives for a coatings
formulation, you might not immediately think
of Alumina Trihydrate (ATH) as the number
one option. Also known as Hydrated Alumina,
Aluminum Hydroxide and Aluminum Trihydroxide, ATH is often
associated with its role first and foremost as a halogen-free flame
retardant and smoke suppressant. This is for good reason. ATH is
the largest-selling fire retardant additive worldwide.
ATH is also an extremely functional and versatile pigment
and use useful in coatings, inks, adhesives, caulks, and sealants
applications. There are many key reasons why. Here are the key
characteristics for consideration:
* Inert
* Acid Resistant
* Chemical Resistant
* Water Insoluble
* Low Density (2.42)
* High Brightness
* Transmits UV Radiation (Does not retard the cure)
* Index or Refraction Similar to Coatings Resin (1.57)
* Available in a Variety of Particle Size Distributions
* Imparts Fire Retardance
* Reduces Smoke Generation
How Does ATH Function as a Fire Retardant?
When the ATH in a coatings application reaches approximately
200 deg. C, it begins to decompose in an endothermic reaction.
This reaction takes heat away from the flame, reducing the flame
propagation, and happens regardless of what other ingredients
are in the formulation.
Thermal Decomposition Reaction (Endothermic):
2 AL(OH)3
+ Heat → AL2O3
Consuming 280 cal/g
Which ATH Grade is Recommended to Impart Fire
Retardance to Coatings?
In order to answer, it is important to understand the details of the
application. The choice of an appropriate ATH grade depends on
many variables:
* Fire Retardant Properties Required, Test Method
* Smoke Suppressant Properties Required, Test Method
* Substrate
* Film Thickness
* Hegman Grind Requirements
* Coating Carrier (Water; Solvent; 100 Percent Reactive)
* Resin Type
* Coating Texture (Smooth, Textured)
* Coating Gloss
* Pigmented or Clear
In general, to maximize fire retardance in coatings-related
applications, Huber Engineered Materials, based in Atlanta, GA,
recommends the following:
1. Use the highest ATH loading possible while balancing the
need to give paint properties, which include gloss, abrasion
resistance, durability, contrast ratio, flow, and leveling.
2. Remove or minimize ingredients that are flammable, such as
plasticizers or coalescing additives which do not evaporate.
(Phosphate ester plasticizers are suitable alternatives since
they are not flammable).
3. Replace other fillers (including talc and calcium carbonate)
which do not impart fire retardance with ATH.
4. Add a phosphate type fire retardant if the fire retardance
with ATH alone is not acceptable. Phosphates and ATH are
commonly used in coatings formulations.
5. Choose an ATH grade which has the particle size distribution
that will enable the coating to meet Hegman grind requirements
and other physical properties.
www.cfcm.ca
37
+ 3H2
O Starting @200 deg. C
http://www.cfcm.ca
Canadian Finishing & Coatings Manufacturing Magazine September/October 2021

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