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Adhesive Properties of Organic Silicone Resin

Jun 21, 2024

Adhesion is another important indicator for measuring the mechanical properties of silicone resins. Silicone resin has good adhesion to metals such as iron, aluminum, silver, and tin, and is also easy to bond to glass and ceramics. Generally speaking, pre-treatment of these materials is not necessary, but if mechanical cleaning methods such as sandblasting are used on the surface of the substrate, it can improve the adhesion of silicone resin to metals, especially iron. The adhesion of silicone resin to copper is unsatisfactory, especially during high temperature and long-term thermal aging, where the oxide film on the surface of copper has a significant catalytic degradation effect on silicone resin.

The adhesion of silicone resin to organic materials such as plastic and rubber mainly depends on the surface energy of the latter and its compatibility with silicone resin. Materials with lower surface energy and poorer compatibility are more difficult to bond. By treating the surface of the substrate, especially introducing viscosity enhancing components into silicone resin, the adhesion of silicone resin to difficult to adhere substrates can be improved to a certain extent.

Silicone resin itself has a very low solubility in water and is difficult to absorb water. When it comes into contact with water droplets, the droplets can only roll off their surface and cannot be wetted, so it has excellent hydrophobicity. Its contact angle with water is similar to that of paraffin (>90 °), making it a good waterproof material.
When silicone oil or silicone resin is coated on the surface of other materials (metal, glass, ceramics, fabrics), due to the significant difference in the negative charge between silicon and oxygen atoms, the silicon oxygen bond becomes polar. Therefore, the oxygen atoms on the main chain of polyorganosiloxane molecules are oriented towards the surface of the coated material, forming valence bonds or dipole attraction with certain atoms on the surface of the coated material, and firmly connecting to the contact surface. Non polar organic groups are arranged outward, forming a surface layer of hydrocarbon groups, which hinders water molecules from interacting with S! - The O polar bond contact has strong hydrophobicity.

When heated, the elongation of the molecular chain increases its contact point with the surface of the object, forming a more solid and uniform surface layer of hydrocarbon groups. The latter hinders the interaction between water molecules and S! - O-polar bond contact, with strong hydrophobicity. Therefore, glass fiber laminates made of organic silicone resin have very low water absorption, and their performance can still be maintained under humid environmental conditions.
However, the intermolecular forces of siloxanes are weak and the spacing is large, resulting in higher moisture permeability and higher moisture permeability than organic resins. Although there are disadvantages to this, it is necessary to cooperate with materials with lower moisture absorption to improve their moisture resistance. However, in turn, it is easier to expel the inhaled moisture, making it easier to restore electrical performance and other properties. However, ordinary organic resins have significantly reduced electrical properties after immersion, and the absorbed moisture is also difficult to remove, resulting in a slower recovery of electrical properties.

Based on the above reasons, the hydrophobicity of silicone resin paint films should depend on specific conditions. Generally, silicone resin has a strong resistance to cold water. For example, the cured silicone resin paint film can remain unchanged for several years after being immersed in distilled water; The resistance to boiling water is weak and related to its composition and structure. For example, hard, low thermoplastic, and pigment added silicone resin paint films have strong resistance to boiling water. Conversely, soft, thermoplastic, and non pigment added paint films form bubbles after soaking in boiling water for 10-20 hours; The resistance to water vapor, especially high-pressure steam, is poor. High pressure steam can not only greatly reduce the adhesion of the paint film to the substrate, but also lead to the cracking of the main chain of the silicone resin.

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