Function and market prospect of powder coatings (3 of 4)

High temperature resistant powder coating

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

At present, the long-term temperature resistance of general powder coatings on the market is low. At the high temperature of 200 ℃ and above, the coating will fade, yellowing and pulverization. Therefore, the powder coating that can withstand the temperature above 200 ℃ is generally called high temperature resistant powder coating. It is understood that the selection of film-forming substances is the key factor to determine the temperature resistance of powder coatings. At present, high temperature resistant powder coatings are mainly obtained through physical and chemical modification:

Physical modification refers to the high temperature resistant powder coating obtained by mixing silicone resin, fluororesin and polyester / epoxy resin, or by adding appropriate curing agent and pigment and filler;

Chemical modification is to modify the resin through chemical methods, change the structure of polymer and increase the relative molecular weight of polymer, so that the resin can withstand high temperature.

Polyester resin is the most common film-forming resin. However, due to the existence of a large number of C-O bonds in the main chain of polyester resin, ordinary polyester resin will pulverize and fall off under high temperature conditions. Therefore, it is necessary to improve the heat resistance of polyester powder coating through modification. Moreover, the miscibility of polyester resin with pigments, fillers and silicone resin is poor, and the leveling property is not good; Epoxy resin is also a common film-forming resin. In order to enhance the heat resistance of epoxy resin powder coating, epoxy resin powder can be modified or appropriate curing agent, pigment and filler can be added.

Superhydrophobic powder coating

Hydrophobic coating usually refers to a low surface energy coating, and the static water contact angle of the coating surface θ More than 90 °, and superhydrophobic coating is a new type of coating with special surface properties. The contact angle of water droplets on its surface exceeds 150 °, and the sliding angle is less than 10 °, which is almost spherical. It is easy to take away the dust on the coating surface by rolling, so it has good self-cleaning ability.

There are two main methods to construct superhydrophobic coatings:

(1) The rough substrate surface is modified by low surface energy substances such as organic fluorine, silicone resin and long-chain fatty alkanes containing active groups to reduce the surface free energy.

(2) Constructing rough micro nano structures and improving the roughness of hydrophobic surfaces mainly include etching method, template method, self-assembly method, lithography method and vapor deposition method.

In addition to modifying the resin, adding hydrophobic additives to commonly used powder coatings is the simplest and fastest way to achieve superhydrophobic, but the amount of addition is often large, usually more than 10%, or even 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 the action of force, the exposed inner layer is still a superhydrophobic layer.

It is worth noting that the durability of hydrophobic coating is inversely proportional to the hydrophobic performance, which is difficult to meet the needs of hydrophobicity and durability at the same time, which limits its application in real life. Products with hydrophobic coatings are very rare on the market, especially products with superhydrophobic surfaces. This is mainly due to the limited compatibility and low bonding strength between low surface energy materials and the matrix, resulting in insufficient firmness and poor durability of the coating.

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

(1) Prepare superhydrophobic coatings with general durability but strong hydrophobicity for specific fields requiring self-cleaning;

(2) Preparation of hydrophobic coatings with high durability but general hydrophobicity, which can be used in fields requiring hydrophobicity for a long time;

(3) The preparation of multifunctional powder coatings can not only be hydrophobic, but also have other properties such as weather resistance, high temperature resistance and anti-corrosion, so as to meet people's requirements for high-performance coatings.

Nanjing Powder New Material Co., Ltd. is specialized in producing various epoxy powder coating, epoxy polyester powder coating, polyester powder coating, flat powder coating, texture powder coating, functional powder coating, polyurethane powder coating, acrylic powder coating and other powder coating products.

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