Firebrake ZB in Coatings for Fire Retardant Paint

:: Wednesday, January 20, 2021 :: Posted By Emmanuel Laval
Across industries, coatings—including paints, stains, powder coatings, and resin coatings—are used to protect, beautify, and strengthen materials of all kinds. Protecting everything from the wood on decks to steel structures to industrial machinery, these coatings are the finishing touch that ensures a long life for many of the products that support our modern lives. In addition to protecting the materials they cover, modern paints and coatings can have an added benefit: Fire retardancy.
When zinc borate additive is included in the formulation of paints and coatings, it acts as a flame retardant, char promoter, and smoke suppressant. In addition, borates enhance many of the desirable properties of the coatings themselves—making a good product even better.

Firebrake ZB: An ideal solution for intumescent coatings

U.S. Borax is a trusted supplier of zinc borate to manufacturers in the coatings industry, who rely on 20 Mule Team® Borax Firebrake® ZB as an ideal fire-retardant paint additive. This product has innate properties that make it effective in a diverse range of coating types:
  • Low solubility and reactivity: Firebrake ZB’s stability prevents cross-linking and interference with the paint’s rheological properties
  • High dehydration temperature (>290° C): Some other forms of zinc borate have dehydration temperatures in the range of 100°-200° C, making them potentially unsuitable for use in hot pigment grinds, bake finishes, and powder coatings
  • Nearly neutral pH (7.1-7.8) in aqueous slurry: Neutral pH makes Firebrake ZB compatible with a wide variety of aqueous and non-aqueous resin systems
  • Low reflective index: Allows for the formulation of a wide range of bright colors and clear coatings

More than just a fire-retardant paint additive

For paint and coating manufacturers, fire retardancy can be an important differentiator—or a compliance requirement. But what if the flame retardant goes further and improves the performance of the coating? Such a multi-functional additive is a cost-effective choice. Firebrake ZB is a unique zinc borate that combines the best benefits of zinc and boron oxides.

Fire retardancy for coatings

Flame-retardant coatings are widely used to improve the safety of both flammable materials (eg, polymers and wood) and nonflammable materials (eg, steel). Flame-retardant coatings are categorized into two groups: Intumescent coatings and non-intumescent coatings.
Intumescent flame retardant (IFR) coatings work by producing gases when heated. In a fire, they swell to form a porous char, which expands into foam as the gases release. This insulating layer of carbon protects the underlaying substrate.
IFR coatings are commonly used in the construction industry to improve the fire resistance of building materials. The protective char reduces the rate of heating, extending the time it takes for the building materials to reach critical failure temperature.
Zinc borate is an important component in many fire-retardant and intumescent coating formulations. It is frequently combined with other fire-retardant additives—such as antimony trioxide or alumina trihydrate—to provide a synergistic effect that results in a highly effective fire retardant. In addition to promoting char formation, Firebrake ZB acts as a smoke suppressant and afterglow inhibitor. It also has anti-arcing properties that are beneficial for insulation used in electrical applications.

Anti-corrosion protection for metals

Soluble borate compounds have been widely used as corrosion inhibitors in a range of applications, from recirculating cooling water towers to automotive antifreeze/coolant solutions, cutting fluids, and lubricants.
Borates provide corrosion protection because they are anodic passivators—they promote the formation of a passivating oxide layer of unusual integrity on metal surfaces. Zinc borate also provides a buffering capacity that may neutralize the extreme pH environment associated with the establishment of functional anodic and cathodic sites. Those sites on a surface enable an electrochemical process that leads to corrosion and loss of adhesion.
Firebrake ZB is a unique form of zinc borate that can be used as a corrosion inhibitor in both organic solvent-based and water-based coatings. When combined with common corrosion inhibitive pigments such as zinc phosphate and barium metaborate, zinc borate produces synergistic performance enhancements, making it an efficient and cost-effective corrosion inhibitor in high-performance coatings.

Adhesion promotion

Adhesion is the most critical property of a coating’s durability. Studies have shown that the addition of zinc borate can promote wetting and adhesion between coating films and metal substrates including steel, aluminum, and copper.

UV protection

Zinc borate is synthesized with zinc oxide and boric acid. The zinc oxide, which is present chemically and physically in the zinc borate, is used as an antioxidant in many cosmetic formulations and as a light stabilizer for polymer formulations.
In zinc borate, the zinc oxide is the main ultraviolet absorber in the polymer material. This inorganic additive absorbs ultraviolet rays and light, reducing the polymer’s UV exposure, making it much more stable and extending its wear life with no significant change in mechanical or other properties.

Tannin stain blocker

When wood is exposed in moist environments, it often develops tannin stain, a discoloration of the wood coating. The problem happens when water extractable components bleed out of the wood. Colored extractable rich woods such as redwood or cedar are especially vulnerable to tannin staining. Incorporating zinc borate into wood primers and topcoats can significantly reduce or eliminate tannin staining.

Stable formulations

In water-borne systems, pH often has a profound effect on viscosity and general stability. Aqueous paint compositions are often basic in nature and can become unstable below the minimum pH level specified by the resin supplier. Below this critical level, the paints have a propensity to gel or coagulate.
Paint manufacturers count on Firebrake ZB to eliminate this issue. In some cases, adding Firebrake ZB in aqueous paint may result in a slight drop of pH (usually no more than a few tenths of one pH unit) but in most cases, the pH will remain stable.

A trusted supplier and partner for the coatings industry

Because of its multi-functional benefits, Firebrake ZB has been employed in a wide variety of solvent-based and aqueous fire-retardant coatings, including solvent epoxies, vinyl chlorides, and acrylics.
U.S. Borax is a trusted partner for coatings manufacturers, offering consultative technical support to ensure you are getting the right fire retardancy additive for your specific coating product. Our tech support team includes fire retardancy experts who can provide insights about how Firebrake ZB will work in your formulation and recommendations for optimizing your use of the product in your process. Our experts thoroughly understand our products—and the business of manufacturing.
Request a sample of Firebrake ZB to test in your formulations. Or contact us with your questions.



U.S. Borax, part of Rio Tinto, is a global leader in the supply and science of borates—naturally-occurring minerals containing boron and other elements. We are 1,000 people serving 650 customers with more than 1,800 delivery locations globally. We supply around 30% of the world’s need for refined borates from our world-class mine in Boron, California, about 100 miles northeast of Los Angeles.  Learn more about Rio Tinto.

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