Heat Resistant and Flame Retardant Coatings

TAGS:  Flame/Fire Retardants      Epoxy Coatings      Powder Coatings    

As I write this article, I can hear an aircraft flying overhead fighting an 11,000-hectare wildfire near my Southern California home. These converted civilian and military airplanes and helicopters, drop water and fire-retardant solutions on wildfires in canyons and atop mountains which are otherwise inaccessible.

Fire retardants moderate the spread of wildfires by acting as a temporary coating for nearby fuels. Often brightly colored to show the pilots where the flame retardants have been applied, they are a valuable tool in the fight to save lives, homes and forestlands.

Heat resistant and flame-retardant coatings can protect materials from damage due to high temperatures and fire. The two types function very differently, even though they might seem to be the same.

• Heat resistant coatings protect a surface for prolonged periods at elevated temperatures. This protection might be from corrosion or chemical attack, such as an interior pipeline coating.
• Flame retardant coatings, on the other hand, prevent the fire from spreading and/or prevent catastrophic damage to the coated object.

While heat resistant coatings are designed for use under the normal service conditions of the intended application, flame retardant coatings are designed to protect under extreme conditions.


Let’s review the types of heat resistant and flame retardant coatings along with their recent developments in detail.

Heat Resistant Coatings

If a coating remains unaffected by elevated temperatures, it can be called a heat resistant. Heat resistant coatings protect components exposed to extreme temperatures or temperature fluctuations. Formulating coatings which continue to fulfill their intended protective function when exposed to prolonged heat or extreme temperature changes is challenging.

Types of Heat Resistant Coatings

The different types of heat resistance coatings include epoxy and silicone, ceramic, powder coatings, etc.

Epoxy and Silicone Coatings

Epoxy and silicone-based coatings offer a medium to high-temperature protection in combination with the corrosion and chemical resistance expected of this family of protective coatings.

Silicone and organo-silicone coatings are widely used for their broad utility as heat resistant coatings and for their ability to be formulated to achieve a price/performance balance. While pure silicone coatings are expensive silicone resins can be blended with other binders, such as epoxies, alkyds and polyesters to improve the heat resistance of the lower cost base polymer.

Metal Additive Coatings

When corrosion resistance and the ability to withstand service temperatures above 400°C are required, metal pigments are often utilized in the coating. Leafing aluminum pigments are widely used in these applications, often combined with silicone or epoxy resins.

Ceramic Coatings

Ceramic coatings provide a hard finish with corrosion and chemical resistance at temperatures exceeding 590°C. These are often applied as so-called burn off coatings.

A coating containing an organic binder and ceramic components is applied to the surface and cured at a temperature below the ultimate service temperature. While the coated object is reaching the surface temperature, the organic binder burns off, leaving a ceramic coating on the surface.

Powder Coatings

Depending on the powder coating type, they can resist temperatures between 200 and 550°C. Heat resistant powder coatings are often used on consumer products which reach high temperatures during use, such as:

• Stoves
• Ovens, and
• Barbecue grills

Key Factors for Selecting Heat Resistant Coatings

The key factors when choosing a heat resistant coating are:

• The substrate
• The application method
• The expected service temperature, and
• The end-use of the coated component

The binder system, pigment composition and loading are primary factors affecting the properties of a heat resistant coating.

Flame Retardant Coatings

The market for intumescent coatings used in fire protection is expected to reach 1.3 billion USD by 2026. Flame retardant coatings are most commonly used in three areas, such as:

• Industrial infrastructure
• Built environment, and
• Transportation

These application areas include places where people spend most of their time. This also includes the most dangerous fire locations meaning industrial plants, buildings and modes of transportation.

Important uses of flame-retardant coatings are in:

• Chemical plants
• Building products
• Aircraft, and
• Public transport

Governmental agencies, NGO’s, corporations and trade associations set requirements, guidelines and test methods for flame retardant coatings.

The Fire Triangle

The intersection of fuel, heat energy and oxygen needed to sustain combustion is called the “fire triangle”. If one side of the triangle is missing, the uncontrolled oxidation-reduction reaction cannot take place, and the fire is extinguished.

Flame Retardant Materials

The market for flame retardant coatings materials is expected to exceed 200 million USD in 2020, with new, safer materials steadily gaining a greater share of the total spend. Europe is the largest market for flame retardant materials accounting for 20,000 tons of global consumption. The four largest suppliers produce the majority of the flame-retardant materials in a highly consolidated market. These suppliers include:

• BASF
• Lanxess
• DuPont, and
• Clariant

The selection of flame-retardant materials depends on the intended end use of the coating. Performance is a primary factor to consider while selecting flame-retardant materials. Other key factors include:

• Cost
• Application method
• Substrate type
• Environmental and health guidelines

Flame retardants act through many modes, but all interfere with one side of the “fire triangle” to prevent flame propagation. The three common modes of action for flame retardants are:

• Generation of free radicals driving combustion and reducing the burn rate until the fire is unsustainable. Since fire is an oxidation-reduction (REDOX) reaction, the free radicals absorb excess electrons to interrupt the reaction pathway.
• Rapidly increasing in volume, creating a non-flammable char layer which insulates the substrate while preventing oxygen from reaching the surface. These are commonly referred to as intumescent coatings.
• Absorbing the heat of combustion by undergoing dehydration or endothermic decomposition. This action cools the flames below the ignition temperature and suppresses the fire.

Types of Flame Retardant Materials

Flame retardant additives are often classified into two broad categories of halogenated and non-halogenated compounds. Each of these categories have advantages and disadvantages, some of which are discussed below.

#1 Halogenated Compounds

Halogenated flame retardants based largely on Bromine and Chlorine are the most commonly used materials on a global basis.

• They are the most established and lowest cost flame retardant additive category. 
• Their ease of incorporation makes it easy to formulate and manufacture fire-resistant coatings based on halogenated compounds.
• The chief drawbacks of this category of materials are the fact that they produce toxic, corrosive smoke and the move in many regions to ban Chlorine and Bromine from all consumer products.

#2 Halogen-Free Compounds

Non-halogenated compounds are steadily growing their market share. They are the focus of new product development in flame retardants.

• This category does not contain Chlorine and/or Bromine, which are under increasing regulatory scrutiny.
• Production of toxic and/or corrosive smoke is reduced or eliminated with halogen-free flame retardants.
• Halogen-free flame retardants include:
  • Metal hydroxides such as Magnesium hydroxide
  • Phosphorous compounds, and 
  • Melamines which show synergistic effects with phosphorus compounds.
• Two disadvantages of non-halogenated fire retardants are higher cost and difficulty of incorporation into coating.

Much of the innovation in the commercial development of these materials is focused on reducing costs and facilitating ease of incorporation.

Recent Developments in Flame Retardant Materials

Clariant recently introduced Exolit® 855, a non-halogenated flame retardant for transparent intumescent wood coatings. Meeting strict requirements for built environments such as public buildings, coatings utilizing Exolit® 855 can facilitate longer evacuation times for occupants.


Source: Clariant

Clariant also launched two other non-halogenated flame retardants for coatings recently.

• Exolit® AP 435 was developed for waterborne intumescent coatings for steel. This additive overcomes well-known storage stability and cold weather application problems associated with waterborne intumescent coatings.

Source: Clariant

• In solvent-borne flame-retardant coatings, Exolit® AP 468 (TP) reduces the possibility of water blister formation which can reduce the fire resistance performance.

Source: Clariant
Evonik markets 2-hydroxyethyl methacrylate phosphate as a flame-retardant monomer for use in acrylic co-polymerizations or UV curing coatings to increase fire resistance. VISIOMER® HEMA-P 70M does not migrate as some flame-retardant additives can, and it also improves corrosion resistance. This highly versatile and easy to process monomer contains 30% methyl methacrylate and has a low color index making it ideal for surface coatings.

Recent Developments in Flame Retardant Coatings

Hempel has recently launched Hempafire Optima 500 waterborne flame-retardant coatings for the protection of structural steel from losing load-bearing strength during a fire.

• This allows additional time for building evacuation and emergency response. 
•  This low VOC coating can provide up to two hours of protection to structural steel in ISO 12944 C3 interior environments. 
•  Up to 750 microns of dry film thickness can be applied in one coat, and the redcoat time is just three hours.

FIRETEX® M90/03 by Sherwin Williams

Heat resistant and flame-retardant coatings encompass thousands of commercial formulations and hundreds of unique raw materials. It would take volumes to thoroughly explore this topic. If you would like to know more, here are some references which might be helpful.

Find Out the Suitable Flame Retardant Materials for Coatings Application