The Application and Development of Fireproof Coatings

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In recent years, significant progress has been made in the research of fire-retardant coatings in our country; the performance of these products has improved markedly, and a distinct system of our own is being established. Prospects for flame-retardant technology: Looking at the overall international development trends, the requirements for the performance of flame-retardant products are becoming increasingly stringent and comprehensive. Below are some brief highlights of the new trends in these performance requirements: 1. Flame retardants themselves are required to be non-toxic, and they must not cause environmental pollution during the manufacturing process. It is required that the decomposition products at high temperatures during the flame-retardant process be non-toxic and non-irritating, with as little smoke as possible. In short, there is a need to develop flame-retardant products that are environmentally and safely usable. 2. Flame-retardant products with composite functions are required. The most basic requirement is not to impair the original properties of the material being flame-retarded; for example, this means not reducing the mechanical or electrical properties of polymers, and not affecting the durability, feel, color, or color stability of fiber products. Now, the requirements for development are such that, in addition to these basic requirements, certain specific functions are also needed; there is a trend toward flame-retardant materials with multiple, composite functions. 3. To obtain flame-retardant products that meet certain practical requirements, it is necessary to comprehensively balance the physical and chemical properties of various components, their flame-retardant effects, as well as their various functions under actual usage conditions; this has given rise to new concepts in flame-retardant design. However, the accuracy of the testing methods used to characterize flame retardant properties is still far from sufficient; it is necessary to continuously improve these analytical testing methods for assessing flame retardancy. New developments in flame retardants: Non-halogenated flame retardants. In order to reduce the harmful effects of flame retardants and develop ones that are safe for use, various countries are focusing on creating high-performance inorganic flame retardants. Since these flame retardants consist of compounds that do not contain halogen elements, they are also known as non-halogenated flame retardants. Today, for flammable polyolefins, products that are flame-retarded using non-halogenated flame retardants have been developed; these products possess good processability and physical properties, with an oxygen index of 34–36. The amount of smoke produced is reduced, and they are also non-toxic. Such non-halogenated flame retardants are already being used in the insulating materials of wires and cables, as well as in enclosed control rooms in subways and underground passages and in electronic equipment. We should proceed promptly with the development of such non-halogenated flame retardants. For the more effective use of inorganic flame retardants such as aluminum hydroxide, magnesium hydroxide, and antimony oxide, new powder engineering techniques are required to reduce their particle size. Aluminum hydroxide requires an average particle size of around 1 μm, while antimony oxide demands even finer particles. Research results show that particle size is related to the flame retardant effect; therefore, new grinding techniques must be developed. On the basis of physical parameters such as the required particle size, particle size distribution, and particle shape of flame retardants, it is also necessary to use surface chemistry methods to treat the surfaces of substances like aluminum hydroxide, in order to increase their affinity for the resin being flame-retarded. A flame retardant system treated in this way can achieve good physical and chemical properties while still providing the same level of flame retardancy. Discussion on intumescent fire-resistant coatings for steel structures: Currently, the most common method for protecting steel structures is to apply fire-resistant coatings to their surfaces. In the event of a fire, these coatings act as a fire-resistant and insulating layer, effectively increasing the fire resistance of the steel components and meeting the requirements of current **standards. Applying fire-resistant coatings to steel structures as a means of fire protection not only provides high levels of fire resistance but is also very convenient to use. The application process is not restricted by the geometric shape of the steel structure, and no additional facilities are generally required, making it highly versatile. Based on the fire protection mechanism, they can be divided into two main categories: thermal insulation fireproof coatings and intumescent fireproof coatings for steel structures. The main mechanism of action of intumescent fireproof coatings for steel structures is that the coating rapidly foams and expands when heated, thereby forming a honeycomb-like carbonized foam layer that acts as an oxygen-barrier and insulating layer. This foam layer has a very low thermal conductivity, which helps to significantly reduce heat transfer to the steel, thus providing effective protection for the steel structure and increasing its fire resistance. Generally, intumescent fireproof coatings for steel structures are based on natural or synthetic polymer matrices, with additives such as foaming agents, co-foaming agents, and carbon sources used to create the intumescent effect; these components are then combined with various pigments, fillers, and additives to form a composite material. It forms a regular coating at normal temperatures, and expands and carbonizes during a fire to provide fire protection. Selection and application of fire-resistant coatings for steel structures: The practical use of fire-resistant coatings in steel structure projects involves various aspects, requiring attention to the selection of coating types, product quality, as well as construction quality. 1. Selection principles: Given that steel structures are used in different parts of buildings, with varying load-bearing mechanisms and strengths, the requirements regarding their fire resistance also differ. Additionally, depending on the characteristics of the building as well as the risks and hazards associated with fires, the fire resistance requirements for various components vary as well. Therefore, it is crucial to select fireproof coatings in a scientific and rational manner to ensure the fire safety of steel structures. It is essential to prioritize product quality and construction quality; overemphasis on reducing costs can lead to issues with the quality of the coating and its thickness, ultimately affecting the fire protection capabilities of the steel structure. The following principles are generally followed: First of all, the fire-resistant coating used for steel structures must come with a qualified inspection report issued by a **certified testing laboratory, and it must also have type approval. Decorative fire-resistant coatings should not be used on steel structures, as they are unable to meet the fire resistance requirements of such structures ； Secondly, fire-resistant coatings that meet the required performance standards should be selected based on the type and characteristics of the steel structure, its fire resistance rating, and the operating environment. For exposed steel structures indoors, lightweight roof structures, and areas with decorative requirements, where the required fire resistance duration is less than 1.5 hours, intumescent fire-resistant coatings for indoor steel structures can be used ； It should be used when the fire resistance rating is 2.0 hours or more. For special coatings that can indeed ensure fire resistance even when the coating layer is thin, they may be used under certified conditions and with guaranteed reliability, depending on the actual circumstances of the project. Expansion-type fireproof coatings for steel structures are not recommended for concealed areas indoors, as well as for high-rise fully steel-framed buildings and multi-story factory buildings with steel frameworks. Outdoor fireproof coatings should be used for steel structures in outdoor environments; fireproof coatings designed solely for indoor use should not be applied to outdoor settings ； Finally, it is not advisable to overpromote fire-resistant coatings for steel structures of the type that offer extreme protection against fire. It cannot be assumed that the thinner the coating layer, the better; from a fire prevention perspective, such coatings work by expanding and forming bubbles to provide fire resistance. However, stricter controls are required regarding the raw materials and a more optimized formulation is needed, which also increases the difficulty of processing. Since these coatings rely primarily on the physical and chemical reactions of organic components, any factor that affects expansion will ultimately impact their fire-resistant properties. Some of these components are sensitive to temperature; exposure to air over time will inevitably lead to precipitation and decomposition, causing the coating to crack, peel off, and become degraded, thereby losing its ability to expand and thus its fire-resistant capabilities. 2. Construction techniques: As an important fire protection measure, the performance of fire-resistant coatings for steel structures depends not only on the quality of the coating products themselves but also on the techniques used during their application. Even with high-quality coating products, without proper application techniques, the coatings may end up becoming dusty, cracked, or peeling off. Therefore, it is essential to follow strict construction techniques to ensure the optimal performance of the coatings. There are several factors involved in the construction process: first is the personnel; those responsible for applying the paint must be properly trained before they can carry out the work, in order to ensure the quality of the project. Secondly, before applying fire-resistant coating to a steel structure, its surface must be thoroughly cleaned to ensure there are no oils, water, or other contaminants present; moreover, an anti-rust paint should be applied, ensuring that this anti-rust paint does not react chemically with the fire-resistant coating. Furthermore, the ambient temperature during application has a significant impact on fire-retardant coatings. For most such coatings, the ambient temperature should be maintained between 5 and 40 degrees Celsius during application and before the coating dries, with relative humidity not exceeding 90%, and good ventilation at the site is required. Work should not be carried out when the wind speed is high, it is raining, or there is dew on the surface of the components. The freshly applied coating must be protected from rain, exposure to sunlight, contamination, and mechanical damage. If any damage occurs, it must be repaired. To ensure the required fire resistance, every type of fireproof coating has a specified thickness; it is not advisable to strive for a thinner coating or to use less of it. Fireproof coating should be applied to all parts of the load-bearing steel components, and the protective layer on each surface should have the same thickness. Therefore, the construction process must be followed strictly to avoid creating any safety hazards in the building. After completion, the coating also requires maintenance and management to eliminate weak points and repair any defective areas as appropriate, in order to ensure its effectiveness. It cannot be considered a one-time solution; the use of fire-resistant coatings on steel structures does not guarantee the structural stability of the building. At present, intumescent fireproof coatings for steel structures have been successfully used for the fire protection of steel structures in various industrial and civil buildings. Although their research and application in China started relatively late, they are developing rapidly and actively, moving toward more functional versions that are ultra-thin, produce less pollution, offer high performance, and have good decorative qualities. (Author: Wang Ruisheng, Li Xin, Deng Jidong)