Polyurea coatings have some unique advantages that set them apart from other types of protective coatings. They also have some limitations and special requirements in order to properly apply them. This article examines eight questions that must be answered when considering these coatings.
1. What is Polyurea?
Polyurea is an elastomer substance derived from step-growth polymerization, which involves combining a synthetic resin and isocyanate reactive materials. Thus, the reaction of an isocyanate part with a resin blend component part through the step growth process of polymerization produces polyurea.
Various formulations of resins and isocyanates can provide the desired setting time, moisture resistance, pigmentation, flame retarding properties and other unique features.
A hybrid coating is polyurea blended in polyurethane in predetermined proportions. The hybrid coating provides certain physical properties of the pure polyurea at a lower cost.
2. How do Aliphatic Polyurea Differ from Aromatic Polyurea?
Polyureas derived from aromatic diisocyanates are distinguished by ultraviolet (UV) light sensitivity.
Sunlight exposure or artificial UV light can cause deterioration of the polyurea's physical properties and color changes such as darkening and chalking. Aromatic polyurea is a low cost alternative but is not appropriate as a top coat; it can be adequate for a base coat application.
Polyureas derived from aliphatic diisocyanates can resist color change due to sunlight exposure and maintain their physical properties even under UV exposure conditions. They are preferred for outdoor applications because they can improve aesthetics with a glossy appearance and can be used at lower film thicknesses of around 30 mills. However, they are expensive when compared to aromatic polyureas, due to the complicated processing involved.
3. What are the Unique Features of Polyurea?
There is no coating system that can successfully replace polyurea in all respects, due to its unique physical properties and durability. However, it's surface preparation requirements are very stringent.
Polyurea protects wooden, concrete and steel surfaces and structures from abrasion and corrosion damage. It can help preserve a deteriorating concrete structure and help repair and keep canals intact. It resists scratches, chemicals, oils and salts in commercial and industrial floor applications. It can also preserve boats and other vessels by providing protection from cracking and deterioration.
Advantages of polyurea coatings include:
- Very fast setting (curing time typically 2 to 5 minutes) depending upon the formulation
- Excellent abrasion and scratch resistance
- Very stable resistance to weather and environmental conditions
- Very beneficial elongation characteristics
- Can be applied in variable temperature conditions, even in high humidity
- Stable heat resistance up to 130°C (266°F) and short term rating of 220°C (430°F)
- Coating thickness can be finely controlled
- Very effective bonding on correctly prepared surfaces of wood, cement, concrete and metals
- Excellent chemical resistance
- Feasibility of low viscosity, thus enabling mixing and spraying at desired temperatures
- Can be formulated for a very high tensile strength up to 4350 psi
4. What is the Polyurea Market Outlook?
The global market size in 2015 for all coatings and paints was USD $141.58 billion. Of that, polyurea coatings were greater than USD $500 million, with the construction sector making up 40% of the market share. The global polyurea coating consumption in 2014 was 114.3 kilotons. The global market size in 2017 for polyurea coatings rose to USD $684 million.
Polyurea's market size is growing rapidly, partly due to it being approved as an eco-friendly low volatile organic compound coating (low VOC). Substitution of cheaper epoxies and other coatings by eco-friendly polyuria coatings is expected to cause a spurt in demand for polyurea. The global market share is expected to reach USD $1.59 billion by 2022.
Hybrid polyuria products are expected to be a major contributor to the polyuria market size because they are less expensive and have good abrasion resistance and adhesion to concrete and metallic surfaces. However, hybrid polyurea products may be lacking in moisture resistance as well as high temperature resistance as compared to pure polyuria coatings. (Learn more about the polyurea market in the article The History and Industry Adoption of Polyurea Coating Systems.)
Faster growth in developing countries with their increasing need to protect infrastructure investment, machinery parts, equipment and machine tools could contribute to growth in demand. Higher moisture resistance and the quick setting properties of polyuria could generate demand for its use in containment liners, roof top coatings, bridges, offshore structures and car parking lot applications.
By region, North America has had a dominant market share, whereas Asia-Pacific is expected to grow faster than other regions due to government-funded infrastructure projects in China and India as well as foreign investment in various sectors of the economy.
5. How does Polyurea Compare to Epoxy and Polyurethane?
Compared to epoxy coatings, polyurea is greatly superior in moisture resistance, UV resistance (for aliphatic coatings), abrasion resistance, chemical resistance, temperature resistance and durability. It also has a quicker cure time.
Compared to polyurethane, polyurea has superior durability, chemical resistance and moisture resistance.
6. What are the Significant Applications for Polyurea Coatings?
There are numerous application that benefit from polyurea coatings, including the following:
Automotive industry and material handling
The auto industry has used polyurea coatings for more than three decades. The coating is popular because of its impact resistance and other mechanical properties.
Polyurea provides abrasion protection in mining and construction equipment, and for lining dumpers that are used for abrasive materials such as coal and metallic ores. It protects conveyors and rollers of conveyor systems that transport abrasive coal, stones and metallic ores.
It is also used for bed liners for large commercial vehicles and material handling trucks.
Pipelines, pumps and irrigation systems
Polyurea provides corrosion and abrasion protection of pipelines that carrying abrasive and corrosive materials. It is applied as base coating to prevent cathodic disbonding.
It is used as a pump coating to reduce cavitation and erosion, and to improve pump output. (For more on this topic, see Erosion Corrosion: Coatings and Other Preventive Measures.) It is also used to line aquaculture tanks and ponds, and for canal repairs and leakage proofing.
Defense and security sectors
Due to their proven impact resistance, ability to absorb explosive energy, durability and quick setting features, polyurea coatings and linings easily find use in the defense and security sectors.
Polyurea's application in ballistic missile system is well documented. As a military equipment coating, polyurea can contract and expand with changes in ambient temperature and form a moisture tight seal. Coatings will be free of scratches, dents and abrasion damage, all while ensuring an attractive glossy appearance. A spray coating of polyurea on truck bed liners can reduce vibration and contribute to safety. Coating military buildings with polyurea can minimize damage due to bomb blasts.
In a hospital environment, ideally the floor and wall coverings will be resistant to viruses and bacteria because there is a constant risk of patients acquiring a secondary infection. Cracks, crevices and scratches on the floor can cause moisture seepage and spread dangerous diseases.
Polyurea coatings seal cracks and prevent scratches that might otherwise occur due to frequent scrubbing, thus minimize the risk of bacterial propagation. These coatings can help maintain sterile conditions in surgical areas, intensive care units and neonatal care units.
Surfaces of steel and concrete bridges
Polyurea is used for the initial coating and as a repair/maintenance coating because of its fast curing ability, impact resistance, and elongation and tensile strength. Polyurea’s structure (molecular chain) makes it an elastomer of high durability. This is the secret of its suitability in construction and other fields.
Polyurea coatings can prevent the collapse of concrete structures by effectively repairing a deteriorating portion of the concrete structure and by providing a protective seal around cracking and deteriorating concrete.
7. What Application Methods are Best for Polyurea?
Four application methods are currently used:
1. High pressure hot spray
This method consists of:
- Preparing the surface
- Mixing the component parts
- Performing the coating application
The high pressure method is chosen for very high volume coating jobs. Formulators must prepare a lower viscosity coating at operating temperature to ensure a favorable flow of the fluid within the machine and a uniform thickness on the surface.
During initial surface preparation, oily contaminants and dirt must be removed by means such as abrasive sand blasting. Surface should be checked for cleanliness to ensure strong adhesion of the polyurea coating. This is a critical step to ensure the coating's durability.
In the mixing stage the prescribed pressure and temperature range must be maintained. Component dosing and mixing must be done with precision. The spray system must be designed to maintain pressure as well as temperature.
The formulated mixture is sprayed on the clean de-dusted surface. The first coat is produced directly on the surface. A second coat is applied to ensure a leak-proof barrier.
Machines used for polyurea spray coatings must be able to maintain temperatures up to 80°C (176°F) and pressure up to 210 bars.
2. Warm spray coating
This method is chosen when the volume of the spray coating job is medium and formulators are able to ensure a low viscosity of fluid mix below 60°C (140°F).
3. Low pressure cold spray
In the case of cold spray, formulators must ensure low viscosity at ambient temperatures to enable spray coating. This is a convenient method for small surface area jobs and repairs.
4. Other methods
Roller or brush on methods are used when spraying is not feasible, such as a small pipe interior coating.
8. What are the Limitations and Critical Issues for Polyurea Coatings?
Polyurea coatings do have some limitations and special considerations.
Because the coating is highly reactive and quick-curing, setting of the coating without adequate wetting out time can cause poor adhesion to the substrate. Formulators must ensure complete wetting out of the surface before the coating sets. It is a tricky situation.
Aromatic polyurea coatings may react to UV radiation, resulting in color changes and chalking. The aesthetics are negatively affected by UV radiation. For those applications that require visual appeal, aliphatic polyurea must be used.
Hot spray applications require specialized and sophisticated spray equipment that are able to generate high pressures and high temperatures. Technicians must be specifically trained for this task.
Formulation, primer selection and stringent surface preparation are all critical steps for success.