Silicon is a compound with unique properties and is widely used in the coatings industry. Its excellent chemical stability, temperature resistance and weather resistance make it an indispensable component in modern coatings formulations. Silicone additives used in coating systems are mainly divided into two categories based on chemical composition: silane and silicone oil. Silanes are mainly small molecular compounds, which are mainly used as adhesion promoters, crosslinkers and dispersants in coatings; the main component of silicone oil additives is modified silicone oil. By adjusting the relative molecular mass of the additive, the type and content of the modified group R and the type of functional group of the end group, additives with various properties can be obtained.

1 Organic silicon additives used as coating leveling agents

The structure of coating leveling agents usually consists of two parts: one is a segment compatible with the system, and the other is a segment incompatible with the system and with a lower surface tension than the system. During the film-forming process, the incompatible segments with low surface tension will spontaneously separate to the surface of the coating system through migration to form a monomolecular film, thereby providing uniform surface tension and eliminating various surface defects of the paint film caused by the surface tension gradient.

When the leveling agent needs to be applied to a high-temperature system (such as baking varnish), due to the low decomposition temperature of polyether, it is easy to decompose during use, resulting in problems on the surface of the paint film, such as poor recoating and shrinkage. Therefore, it is necessary to select modified silicone oils containing high-temperature resistant groups (such as alkyl-modified silicone oils, phenyl-modified silicone oils, and polyester-modified silicone oils). Relatively speaking, in addition to providing a leveling effect, alkyl-modified silicone oils also have good defoaming properties, but their compatibility is poor and they are usually not suitable for varnishes. In contrast, phenyl silicone oil and polyester modified silicone oil have better compatibility and are suitable for high-temperature varnish systems. They also have excellent compatibility and high-temperature resistance.

With the development of technology, some leveling agents that combine silicone with acrylate have appeared in recent years. This type of leveling agent combines the advantages of both and has excellent early and late leveling effects. According to their chemical structures, they can be divided into two types: acrylate-modified silicone leveling agents (with silicone as the main chain and acrylate as the side chain) and silicone-modified acrylate leveling agents. The latter can not only provide good leveling effects, but also have stain resistance.

2 Silicone additives used as paint defoamers

As a defoaming agent for coatings, silicone is widely used in the production of defoaming agents because of its low polarity structure and is incompatible with most coating resin systems. Usually, polydimethylsiloxane with a relative molecular weight of 10,000 to 100,000 is used as a paint defoamer, especially in heavy anti-corrosion systems. In order to improve defoaming efficiency, silica is often added as a synergistic component. Due to the efficient defoaming properties of silicone, it is usually added in the form of a lower concentration solution to meet actual production needs.

In solvent-based coatings, fluorocarbon-modified silicones are often used to enhance defoaming capabilities. This method further reduces the compatibility between the coating and the system by introducing fluorocarbon segments into the silicone main chain, thereby significantly improving the defoaming effect. Generally, the longer the fluorocarbon chain, the better the defoaming effect. This type of defoaming agent is a high-end variety of silicone defoaming agents.

For water-based coating systems, due to the high polarity of water-based resins, conventional polydimethylsiloxane has limited compatibility and is difficult to use directly. Polyether modification of polydimethylsiloxane is often required, especially in high-gloss systems. The higher the degree of polyether modification, the better the compatibility, but the defoaming effect may decrease. Therefore, it is necessary to select an appropriate modification ratio based on the ease of defoaming of the system to satisfy the defoaming capability while minimizing the silicon content.

Water-based silicone defoamer is divided into two categories: concentrated type and emulsion type. Concentrated defoamer has strong foam suppression ability, but is not easy to disperse and requires strong shearing during use; emulsion-type defoamer improves the convenience of use through emulsification and can be introduced into the system with simple stirring.

3 Silicone additives used as wear-resistant additives

In systems that require wear resistance, in addition to increasing the cross-linking density through resin, adding additives is also a common method. Among them, the use of silicone additives is an effective method. Common ones include ultra-high molecular weight silicone microspheres, silicone emulsions, and silicone nano-modifiers.

Ultra-high molecular weight wear-resistant silicone microspheres are composed of high molecular weight polysiloxane with a slightly cross-linked structure and appear in the shape of microspheres. After being added to the system, these microspheres will be oriented and arranged on the surface of the paint film to form a polysiloxane film, thereby significantly improving the slipperiness and surface wear resistance of the system.

In water-based coating systems, ultra-high molecular weight silicone emulsions are also commonly used wear-resistant additives. These emulsions are usually polymerized from silicone and have extremely high internal phase viscosity, with relative molecular weights reaching millions. After adding to the system, a thin layer of ultra-high molecular weight organic silicon will be formed on the surface after film formation, thereby further enhancing the wear resistance of the paint film.

4 Silicone additives used for coating resin modification

Silicone materials often have some unique properties, such as smooth surface, wear resistance, weather resistance and low-temperature flexibility. By using silicone materials with reactive functional groups as modification assistants, silicone segments can be introduced into the resin system, thereby integrating its excellent properties into the coating system.

Silicone materials used for resin modification are usually silicone polymers with reactive groups at both ends and have different functional groups. Silicone materials with carbon hydroxyl groups usually react well with polyurethane materials and are suitable for the modification of polyester or polyurethane resins; while silicone materials with epoxy groups can be used for the modification of epoxy resins. Silicone materials with acrylate double bonds at both ends can not only be used to modify photocurable resins, but can also participate in the synthesis reaction of silicone modified emulsions. Silicone materials with amino groups can be used to synthesize silicone-modified polyimide resin, which is suitable for some high-end applications. In addition, silicone materials with carboxyl groups can be used to modify powder coating resins and participate in related reactions.

5. Other applications of silicone coatings in industry

In addition to the above-mentioned applications, silicone coatings also have a wide range of application potential in industry. The following are some important application areas:

5.1 Improve the weather resistance of coatings

Silicone coatings have excellent weather resistance and can resist UV rays, oxidation and moisture. This property makes silicone coatings particularly suitable for the protection of outdoor buildings, vehicles and equipment. Using silicone coatings can significantly extend the service life of the coating and reduce maintenance costs.

5.2 Improve paint adhesion

Silicones enhance the adhesion between paint and substrate. This is especially important for materials such as metal, plastic and glass. During the painting process, good adhesion can prevent the coating from peeling off and ensure the durability and beauty of the paint.

5.3 Improve the high temperature resistance of coatings

Silicone coatings can maintain their physical and chemical properties stable in high-temperature environments. This makes it suitable for the protection of high temperature equipment such as industrial furnaces, engines and boilers. The high temperature resistance not only improves the safety of the coating, but also reduces the frequency of maintenance due to thermal damage.

5.4 Enhance the waterproofness of coatings

Silicone has excellent hydrophobicity and can effectively prevent moisture penetration. This property makes silicone coatings widely used in waterproof coatings, such as roof coatings and waterproofing of underground structures. By using silicone coatings, structural damage caused by moisture intrusion can be effectively prevented.

The use of silicones in the coatings industry provides coatings with many unique advantages. Its weather resistance, adhesion, high temperature resistance and water resistance make it an indispensable and important ingredient in modern coating formulations. With the advancement of science and technology and changes in market demand, the application prospects of silicone coatings will become broader, injecting new vitality into the development of the coatings industry.