More and more coating users appreciate the advantages of powder coatings, such as pollution-free, stable storage, easy transportation, resource saving, and high efficiency. With the support of demand, the types of powder coatings are gradually increasing, and their application scope is wide. Powder coatings can be seen in the coating of small components to various large equipment. The market expects the global powder coating market size to reach $15 billion by 2026, with a compound annual growth rate of 6.8%.

It is worth noting that powder coatings in China mainly include epoxy, polyester, and epoxy/polyester powder coatings. The proportion of high-end acrylic, polyurethane, and fluorocarbon powders is very small, less than 1%. Foreign production enterprises occupy 80% of China's high-end powder coating market. Most domestic powder coating enterprises lack innovation and have relatively backward technological levels. The powder coatings produced are mainly ordinary powder coatings.

At present, the ordinary powder coating market has experienced a situation of oversupply, intensified market competition, and enterprises with insufficient core competitiveness have been eliminated by the market. This has prompted companies to transform and upgrade, focusing on the high-end powder market and developing functional powder coatings with special functions to meet specific surface coating needs.

Functional powder coatings refer to powder coatings that are suitable for specific occasions and have special functions. It endows coatings with various special properties, including insulation, corrosion resistance, waterproofing, high temperature resistance, and radiation resistance, on the basis of traditional protective and decorative functions. According to their functions, they can be divided into various types such as anti-corrosion, weather resistant, heat-resistant, hydrophobic, and antibacterial powder coatings. At the same time, with the development of powder coatings, new types of powder coatings such as mosquito repellent and anti graffiti are also emerging.

Functional powder coatings cover all aspects of human life, such as anti-corrosion powder coatings covering pipeline facilities, energy facilities, highway transportation, marine facilities, and military equipment. However, the development of functional powder coatings in China is relatively slow. Except for decorative, anti-corrosion, and weather resistant powder coatings, other functional powder coatings have not developed much.

Based on this background, this article focuses on introducing six functional powder coatings: heavy-duty anti-corrosion powder coatings, weather resistant powder coatings, antibacterial powder coatings, high-temperature resistant powder coatings, hydrophobic powder coatings, and self-healing powder coatings.

Heavy duty anti-corrosion powder coating

The direct losses caused by corrosion in countries around the world each year account for about 2% to 4% of their GDP, and the harm exceeds the total losses caused by natural disasters and various accidents. To prevent corrosion of components, people choose to apply anti-corrosion coatings on the surface to isolate the material from contact with the external environment, protect the metal materials inside the coating, and ensure the long-term use of the components.

According to the data, anti-corrosion coatings are divided into general anti-corrosion coatings and heavy-duty anti-corrosion coatings: general anti-corrosion coatings have a service life of 5-10 years; Compared with general anti-corrosion coatings, heavy-duty anti-corrosion coatings have good adhesion, resistance to the penetration of corrosive media, or chemical resistance to corrosive media. In addition, the coating itself has strong durability, providing corrosion resistance for the coated material. The service life can reach more than 30 years, and the anti-corrosion effect can be improved by 4-5 times.

Common anti-corrosion powder coatings are divided into ordinary modified anti-corrosion coatings, fusion bonded epoxy powder coatings, and epoxy zinc rich powder coatings.

At present, heavy-duty anti-corrosion powder coatings mainly achieve material protection through physical shielding, including base resin, pigment, and filler modification; Simultaneously using thick coating, multi coating, or composite coating methods to generate one or even multiple layers of dense protective film, enhancing the heavy-duty anti-corrosion performance of the coating. The use of nano iron titanium powder, graphene, diamond sand, and chemically modified resins can further improve the anti-corrosion ability of the resin

Due to construction conditions and other limitations, heavy anti-corrosion coatings are still mainly liquid coatings today. Environmental protection, high performance, multifunctionality, and low energy consumption are the development directions for heavy-duty anti-corrosion coatings in the future.

Weather resistant powder coating

Weather resistant powder coating refers to a powder coating that can withstand outdoor environmental tests and maintain its decorative and protective functions for a long time. Powder coatings exposed outdoors can undergo aging and degradation due to various factors such as sunlight exposure, humidity, temperature, and pollutants (such as acid rain). Exposure to sunlight can cause yellowing, fading, and even powdering of coatings; Dripping and condensation can cause discoloration, loss of gloss, and rusting of the coating. At present, the application of powder coatings in outdoor areas is becoming increasingly widespread, such as transportation, outdoor decoration, engineering machinery, etc., which puts higher demands on the weather resistance of powder coatings.

The improvement of weather resistance of powder coatings depends on the selection and matching use of resin types, pigments and fillers, and additives. On the one hand, it is possible to choose a suitable base resin or modify the base resin and select a suitable curing agent. Such as polyester/TGIC system, polyester/HAA system, acrylic ester, polyurethane, polyvinylidene fluoride (PVDF), fluorocarbon and organosilicon modified polyester system, etc. On the other hand, a certain amount of antioxidants, UV absorbers, and free radical scavengers can be added to slow down the aging of coatings. China has begun to systematically use additives to improve the weather resistance of powder coatings.

There are various types of resins used for weather resistant powder coatings, but their durability is generally poor. Fluorocarbon powder coatings (a general term for powder coatings containing fluororesins) exhibit excellent weather resistance due to their inherent characteristics, and are widely used in high-end building aluminum profiles, electrical electronics, aerospace and other fields. With mature production and construction processes, they are widely recognized as a super weather resistant coating variety in the world. The performance of thermosetting fluorocarbon powder coatings (such as weather resistance, corrosion resistance, etc.) is much higher than that of polyester and epoxy powder coatings.

However, fluorocarbon powder coatings have excellent weather resistance, but their market share is very small, and a series of fluorocarbon powder coating products have not yet been formed in China. There are still many problems to be solved, including optimizing the production process of fluorocarbon powder coatings and reducing production costs; Improve the appearance, glossiness, and impact resistance of fluorocarbon powder coatings. Developing high-performance super weather resistant powder coatings remains a challenging task.

Antibacterial powder coating

Antibacterial powder coating refers to powder coating that can kill microorganisms or hinder their growth and reproduction. In daily life, ordinary disinfectants and other sterilization products can only have a short-term bactericidal effect, but if the antibacterial performance of the surface coating itself is improved, the coating can inhibit the growth of microorganisms on the surface on its own, and maintain long-term cleanliness of the surface.

The main component in antibacterial coatings is antibacterial additives. Most organic antibacterial materials are liquid and their application is limited; Inorganic antibacterial agents, including silver ions and copper ions. Although this type of antibacterial agent takes effect slowly, it has the advantages of low toxicity, heat resistance, persistence, broad-spectrum antibacterial activity, and no development of drug resistance. PPG、 BASF and other companies have added silver ions to powder coatings.

Unfortunately, inorganic antibacterial agents have disadvantages such as poor compatibility with high molecular weight polymers, poor solubility, slow sterilization, and discoloration, making it difficult to meet the needs of human life. Therefore, antibacterial powder coatings have gradually evolved from single type to composite antibacterial powder coatings. In addition, there are still many problems to be solved in the preparation methods of antibacterial agents. For example, the loss of widely used silver based antibacterial agents has weakened the durability of antibacterial coatings; Therefore, developing universal antibacterial coatings with excellent properties such as durability and low toxicity remains a challenging task.

High temperature resistant powder coating

With the increasing application range of powder coatings, some extreme environments have put forward higher requirements for powder coatings, thereby promoting the development of high-temperature resistant powder coatings. This type of powder coating not only has strong heat resistance, but also excellent properties such as corrosion resistance and weather resistance. It is widely used in various high-temperature resistant equipment such as cooking components, high-power lighting fixtures, boilers, ovens, high-temperature furnaces, and automotive parts.

At present, the long-term temperature resistance of general powder coatings on the market is relatively low. At high temperatures of 200 ℃ and above, the coating may experience fading, yellowing, and powdering. Therefore, powder coatings that can withstand temperatures above 200 ℃ are generally referred to as high-temperature resistant powder coatings. Qutu Coatings (Qutu Network) has learned that the selection of film-forming substances is a key factor in determining the temperature resistance of powder coatings. Currently, the main technology for obtaining high-temperature resistant powder coatings is through physical and chemical modifications

Physical modification refers to the production of high-temperature resistant powder coatings by mixing organic silicon resin, fluororesin, and polyester/epoxy resin, or by adding appropriate curing agents and fillers;

Chemical modification is the process of modifying resins through chemical methods, altering the structure of high molecular weight polymers and increasing their relative molecular weight to enable the resin to withstand high temperatures.

Polyester resin is the most common film-forming resin, but due to the presence of a large number of C-O bonds in the main chain of polyester resin, ordinary polyester resin will pulverize and peel off under high temperature conditions. Therefore, modification is needed to improve the heat resistance of polyester powder coatings. Moreover, the miscibility and leveling properties of polyester resin with pigments, fillers, and silicone resin are poor; Epoxy resin is also a common film-forming resin. In order to enhance the heat resistance of epoxy resin powder coatings, the epoxy resin powder can be modified or appropriate curing agents and fillers can be added.

Superhydrophobic powder coating

Hydrophobic coatings typically refer to a type of low surface energy coating with a static water contact angle on the coating surface; Greater than 90 degrees;, And superhydrophobic coating is a new type of coating with special surface properties, where the contact angle of water droplets on its surface exceeds 150 degrees;, The sliding angle is less than 10 degrees;, Almost spherical in shape, it is easy to remove dust from the coating surface by rolling, thus having good self-cleaning ability.

There are two main methods for constructing superhydrophobic coatings:

(1) Using low surface energy substances such as organic fluorine, silicone resin, and long-chain fatty alkanes containing active groups to modify rough substrate surfaces and reduce surface free energy.

(2) Constructing rough micro nano structures to improve the roughness of hydrophobic surfaces mainly includes various methods such as etching, templating, self-assembly, photolithography, and vapor deposition.

In addition to modifying the resin, adding hydrophobic additives to commonly used powder coatings is the simplest and quickest way to achieve superhydrophobicity. However, the amount added in this way is often large, usually above 10%, and can even reach 50%. On the other hand, it can also make the internal and external structures of the coating the same, even if the outer layer is damaged under force, the exposed inner layer is still a superhydrophobic layer.

It is worth noting that the durability of hydrophobic coatings is inversely proportional to their hydrophobicity, making it difficult to meet both hydrophobicity and durability requirements, which limits their practical applications in daily life. Products with hydrophobic coatings are very rare in the market, especially those with superhydrophobic surfaces that are almost non-existent. This is mainly due to the limited compatibility between low surface energy substances and the substrate, low bonding strength, resulting in insufficient coating firmness and poor durability.

Due to the contradiction between the durability and hydrophobicity of hydrophobic coatings. There are three development directions for future hydrophobic coatings:

(1) Prepare superhydrophobic coatings with average durability but strong hydrophobicity for specific fields that require self-cleaning;

(2) Prepare hydrophobic coatings with extremely high durability but average hydrophobicity, which can be used in fields that require hydrophobicity for a long time;

(3) Prepare multifunctional powder coatings that not only have hydrophobic properties, but also other properties such as weather resistance, high temperature resistance, and corrosion resistance to meet people's requirements for high-performance coatings.

Self-healing powder coating

At present, coating performance is mainly protected by improving resin, pigment, additive, and formulation technology. However, once the coating is damaged, the substrate will be corroded at the exposed area, which will continuously corrode the substrate protected by the coating. In 2001, polymer self-healing technology was first proposed in a natural science journal.

The common self-healing composite materials are divided into two self-healing mechanisms: autonomous and non autonomous.

The self-healing mechanism usually involves embedding polymerizable healing agents or corrosion inhibitors in the coating to achieve self-healing function;

For non autonomous healing mechanisms, they are usually triggered by external heat or light stimulation to induce chemical reactions or physical transformations, thereby achieving self-healing function. It is mainly based on the self-healing material uniformly dispersed in the matrix material, which releases its internal repair agent when it fractures under external stress, allowing the catalyst and self repair agent to undergo cross-linking and curing reaction to fill the wall cracks.

As a newly emerging functional coating variety in the coating market, self-healing powder coating has the advantages of self repair when damaged, convenience, durability, etc. It can protect the substrate for a long time and will become an important direction for the development of coatings in the future. However, the production process of self-healing powder coatings is relatively complex, so it is particularly important to develop self-healing powder coatings that are convenient and conducive to industrial production.

summary

Heavy duty anti-corrosion coatings and weather resistant coatings are still the mainstream trend of future development due to their wide application. Hydrophobic coatings and high-temperature resistant coatings will also develop more adaptable varieties according to their corresponding application environments, and other new powder coatings for specific purposes will continue to emerge.

At present, the market share of powder coatings is low, and the development of functional powder coatings is still at a relatively low level. However, due to the performance and environmental advantages of functional powder coatings, they have huge application prospects in fields such as automobiles, ships, pipelines, and construction, and have significant development space. Therefore, continuous exploration and research are still needed.