How Does Heat Cause Paint Degradation?

Here is how high temperature affects the physical and chemical properties of paint:

1. Heat Exposure Begins: The darker paint pigments and binders absorb the heat. The paint undergoes polymer cleavage and expands the film. The upper layers of paint become hollow and allow air to penetrate into them. 
2. Bubble Formation: Moisture below the upper layer of paint does not evaporate. It gets trapped in air and forms bubbles. It pushes the paint layers away from the substrate. 
3. Cracking and Peeling: Paint layers cool down at night due to low temperature and melt at daytime in high temperatures. These frequent freeze-thaw cycles deteriorate the paint and cause orange peels. Paint begins to fall after chemical bond breakages and cracks. 

How Does Heat-Resistant Paint Work?

Heat-resistant paint contains binders like epoxy and resins that prevent freeze-thaw cycles at 1112°F. They contain components that create a thermally stable film to prevent weather changes. Titanium oxide, iron oxide, glass flake, mica, or ceramic compounds are added to increase the paint’s heat tolerance. These additives and pigments do not fade away quickly and preserve the original paint colors. Heat-tolerant paints are formulated to resist heat so they do not cause paint separation and polymer chain breakage. They promote paint adhesion and do not soften or weaken at high temperatures. Heat-resistant paint strengthens the bond between paint particles after drying. This hard layer prevents moisture and air from penetrating and causing oxidation. Some silicone-based paints are formulated to harden when they come in contact with heat. These heat-resistant paints allow the paint to cure and set up to 200 °C.

What are the Types of Heat-Resistant Paint

Here are the seven types of heat-resistant paint:

1. Silicone-Based Paints: Silicon-based paints are composed of silicon resins, pigments, filler, and additives. Silicon-based binders have three types such as DT, MQ, and MTQ resin. Acrylic resin emulsions are added as additives to improve the heat and UV-resistant properties of paint. This paint contains strong siloxane (Si-O-Si) bonds and withstands the high temperature of up to 650°C. 
2. Epoxy-Based Paints: Epoxy-based paints contain epoxy resin (monomeric), fillers, additives, solvents, and hardener. This epoxy-based paint comes in one pack and two packs. One pack is a pre-mixed paint and ready to use. Two-pack epoxy paint contains resin and hardeners in separate cans. These paints utilize water, turpentine, and acetone in their formulations. Hardeners increase the curing process and durability of paint. Epoxy-based paints are used in coating marine, automotive, and interior applications for protection against high temperatures.
3. Ceramic Coatings: Ceramic coatings act as thermal barriers between substrate and exterior heat. They contain silicon dioxide (SiO2) and titanium dioxide, which reflect the heat. There are multiple types of ceramic coating, including ceramic matrix composites (CMC), thermal barrier coatings (TBC), and ceramic solar reflective paints. Ceramic coatings are used on engines, vehicles, and industrial applications to handle temperatures up to 1000°C. Few coatings handle extreme temperatures of up to 2000°C to prevent metal from oxidation.
4. Aluminum or Zinc-Rich Primers: Inorganic zinc-rich primers prevent steel from corrosion and heat. A primer with aluminum flakes creates a protective layer and protects the paint from extreme temperatures. Inorganic zinc-rich primers resist heat up to 400°C. 
5. Polyurethane Heat-Resistant Paints: Polyurethane heat-resistant paints are formulated from polyurethane resins and heat-resistant pigments (talcum, mica powder). Unlike silicon-based paints that withstand up to 650°C, polyurethane paint resists up to 150°C (302°F). It is unfit for regions with extremely high temperatures. Apart from heat resistance, it also improves the durability and thermal insulation.
6. Intumescent Paints: Intumescent Paint is a passive fire protection measure. It contains binder, acid source (ammonium polyphosphate), char former (pentaerythritol), and expanding agent (melamine). Intumescent Paint creates a fifty times thicker layer as compared to the original when exposed to heat. It does not allow the heat to cross even the upper layer of paint. Its formulation makes it a smart and ideal paint for high-temperature regions.
7. Acrylic Heat-Resistant Paints: Acrylic heat-resistant paints are made up of Silicone resins and thermoset pigments. Like Intumescent Paint, they also form an insulating layer to block the heat. Unlike ceramic coating, acrylic heat-resistant paint resists up to 200°C / 392°F.

How to Choose the Right Heat-Resistant Paint

Here is how to choose the right heat-resistant paint:

1. Match the Paint to Temperature Requirements: Understand all the paint types and select the one that resists the maximum surface heat. Compare all heat-resistant paints based on their ability to withstand temperature and shortlist those that meet your environmental temperature. 
2. Select Paint Based on Surface Material: Don’t choose acrylic heat-resistant paints for turbines or engines, as only ceramic coatings withstand their heat. Select the paint that sticks to the substrate well without bubbles. Choose oil-based heat-resistant paints for metal, acrylic masonry paint for masonry, and ceramic coatings for ceramic surfaces. 
3. Differentiate Between Interior and Exterior Use: Heat-resistant paints work best for interiors due to heaters, chimneys, and kitchens. Heat-resistant paint can’t withstand the exterior environmental conditions. Choose the weather-resistant paint with UV and heat-resistant abilities to protect outdoors.
4. Look for Food-Safe or Low-VOC Options: Choose the heat-resistant paints (acrylic) with low VOC content for indoors. This paint reduces the likelihood of VOC fumes in food from painted ovens or grills. Low VOC paint minimizes the risk of allergens, irritation, and respiratory diseases due to oil-based paints.  
5. Determine If a Primer or Base Coat Is Needed: Bare metal, porous wood, or glossy surfaces require primer before heat-resistant paint for proper adhesion. Read the manufacturer’s instructions on paint cans before base coats as some paints contain self priming. 

Where Is Heat-Resistant Paint Commonly Used?

Heat-resistant paint is commonly used in:

1. Industrial Applications: Heat-resistant paint is used to paint furnaces, pressure vessels, kilns, chimneys, pipes, storage tanks, and stacks. It is also applied on boilers, smokestacks, and heat exchangers to resist heat.
2. Automotive Uses: Heat-resistant paint is used to protect the engine parts, tailpipes, rotors, radiators, and turbochargers from extreme heat. It can be used on mufflers, brake calipers, cooling, and exhaust systems.
3. Home & Commercial Settings: Fireplaces, wood stoves, smokers, heaters, ovens, and grills are coated with heat-resistant paints. It is also used to paint chimneys, fire pits, HVAC units, and exhaust ducts. 
4. Marine and Aerospace Industries: Heat-resistant paints are used on components of aircraft engines, jet engines, ship engines, and boilers. It is also applied on exhaust pipes, naval vessels, and turbojets to resist extreme temperatures. 
5. Power Plants and Refineries: Heat-resistant paint is applied on reactor vessels, turbine casings, HRSGs, pipes, and thermal heaters. Flue gas ducts, catalytic converters, and refinery furnaces are also painted with heat-resistant paint to prevent them from corrosion.