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The role of ESO in coatings is to increase the flexibility of the coating film. For some brittle paint-based materials, plasticizers are essential to obtain a coating film with better flexibility and other mechanical properties.
Plasticizers
in coatings can generally be divided into two categories. One is the main plasticizer (solvent plasticizer), and the other is the auxiliary plasticizer (non-solvent plasticizer). The main plasticizer is like the solvent of the matrix resin, some of their groups can interact with some of the groups in the resin, so the main plasticizer and the resin can be mixed. Because the plasticizer molecule is small, it can enter the molecular structure of the resin polymer and reduce the rigidity of the resin. However, the addition of plasticizers will also cause some loss of mechanical properties of the coating film.
The co-plasticizer has no dissolving effect on the matrix resin, and can be miscible with the matrix resin only when the added amount is not large. The auxiliary plasticizer only has a physical effect on the matrix resin (lubricating effect), so the impact on the mechanical strength of the coating film is not as great as that of the main plasticizer. However, the auxiliary plasticizer is easy to migrate or ooze out of the coating film, which makes the coating film poor in flexibility.
The addition of plasticizers in coatings has certain effects on many coating film properties, such as tensile strength, toughness, elongation, permeability, and adhesion. Depending on the type of base polymer and plasticizer, the impact on these properties is also different. Generally speaking, the addition of plasticizers will increase the extensibility of the coating film and reduce its tensile strength. Within a certain amount of plasticizer added, the permeability of the coating film remains basically unchanged, but when the added amount of plasticizer continues to increase, the permeability of the coating film will increase sharply. The toughness and adhesion of the coating film first increase with the addition of plasticizer, but gradually decrease after reaching a peak. In addition to affecting the mechanical properties of the coating film, plasticizers also affect other properties of the coating film. Therefore, various factors should be considered comprehensively, and the appropriate amount of plasticizer should be determined after a comprehensive balance.
