As one of the raw materials of coatings, the amount of coating additives is usually small, but it has a great effect. The addition of it can not only avoid the occurrence of coating defects and film defects, but also make the production and construction process of the coating easy to control, and can also endow the coating with some special functions. Therefore, additives are an important part of coatings.
Commonly used additives for coatings include: anti-settling agent, leveling agent, foam control agent, dispersant, etc.
Most of these products are based on polyolefins, with a solvent as the dispersing medium, sometimes modified with a castor oil derivative.
①. Rheological properties: The main rheological function of anti-settling agents is to control the suspension of pigments—that is, to prevent hard precipitation or avoid settling, which is their typical application.
But in practice, it causes viscosity build-up and also some degree of sag resistance, especially in industrial coatings. Anti-settling agents lose their effectiveness by dissolving at elevated temperature, but their rheology recovers as the system cools.
There are three main types of leveling agents:
① Modified polysiloxane type leveling agent
This type of leveling agent can strongly reduce the surface tension of the coating, improve the wettability of the coating to the substrate, and prevent shrinkage cavities; it can reduce the surface tension difference on the wet film surface due to solvent volatilization, improve the surface flow state, and make The coating quickly leveled; this type of leveling agent can also form a thin and smooth film on the surface of the coating film, thereby improving the surface smoothness and gloss of the coating film.
② long-chain resin type leveling agent with limited compatibility
Such as acrylate homopolymer or copolymer, it can reduce the surface tension between the coating and the substrate to improve wettability and prevent shrinkage; Surface fluidity, inhibit solvent volatilization speed, additive to improve surface gloss, remove defects such as orange peel and brush marks, and make the coating film smooth.
③ Leveling agent with high boiling point solvent as the main component
This type of leveling agent can adjust the volatilization speed of the solvent, so that the coating film has a more balanced volatilization speed and dissolving power during the drying process, preventing the flow of the coating film from being hindered by the solvent volatilizing too fast and the viscosity being too large, resulting in poor leveling. It can prevent the deterioration of the solubility of the base material and the shrinkage caused by the precipitation caused by the rapid volatilization of the solvent.
foam control agent
Foam control agents are also known as antifoams or defoamers.
Antifoam agents prevent or delay the formation of foam;
Defoamers are surfactants that can burst formed bubbles.
The difference is theoretical to some extent, and a successful defoamer can also act like an antifoam to prevent foam from forming.
The primary function of the dispersant is to reduce the time and energy required to complete the dispersion process while stabilizing the pigment dispersion. To sum up, wetting, dispersing, and stabilizing are defined as follows:
Wetting: Under the action of stirring, the dispersion medium is close to the surface of the pigment and filler, and diffuses on the surface, replacing the water and air on the surface of the pigment and filler, usually small molecular wetting agents can promote this process.
Dispersion: Under the action of shearing force, the agglomerates and aggregates of pigments and fillers are dispersed to primary particles.
Stability: In the dispersing medium, the well-dispersed pigment and filler particles are separated, so that they will not re-aggregate together and prevent flocculation and thickening. Usually, the polymer dispersant has an obvious effect on this piece.
Dispersants are generally divided into the following five categories:
2. Cationic type
3. Electrically neutral, amphoteric
4. Bifunctional, non-electrically neutral
5. Non-ionic type
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