Application and selection of leveling agent

For a certain formula system, the appropriate leveling agent should be selected according to the properties of the formula and the performance that the leveling agent is expected to achieve.

1. When determining the water-based formula, wetting agent is often selected first, and then leveling agent. Some additives can act as both wetting agent and leveling agent.

2. Do not use a large amount of wetting agent that strongly reduces surface tension, just enough is enough, because it will prolong the leveling time.

● In the formulation of primer and mid-coat paint, solvent-based coating systems usually use acrylic leveling agent. If degassing and substrate wetting are required, it is advisable to choose medium molecular weight or high molecular weight acrylic leveling agent.

In primers, if stronger substrate wettability is required, silicone leveling agents and modified acrylic leveling agents (such as fluorine-modified acrylic leveling agents and phosphate-modified acrylic leveling agents) that can significantly reduce surface tension can be considered. If silicone leveling agents and fluorine-modified acrylic leveling agents have side effects such as stabilizing foam and affecting interlayer adhesion, phosphate-modified acrylic leveling agents should be used. In the formulation of topcoats and clearcoats, the requirements for the appearance of the paint film are relatively high. Generally, low molecular weight acrylic leveling agents can be used, which will obtain good leveling and will not easily produce haze in the paint film.

In cross-linked curing systems, acrylic leveling agents containing reactive functional groups are often used to obtain better leveling and improve the physical and chemical properties of the paint film. If the paint film needs to have better fluidity or needs smoothness and scratch resistance, silicone leveling agents are necessary. In this case, it is best to use silicone leveling agents and acrylic leveling agents in combination. It should be pointed out that when applying on vertical surfaces, silicone leveling agents can effectively reduce the tendency of coatings to sag while providing leveling properties.

In addition, in the formula of metallic glitter paint, silicone leveling agents should be used with caution, because it may cause uneven arrangement of flaky aluminum pigments and uneven color of the paint film.
 

● Powder coating system The leveling process of powder coating is divided into two stages. The first stage is the melting of powder particles, and the second stage is the melting of powder particles and the flow of powder particles into a smooth paint film.

Powder coating does not contain solvents, and no surface tension gradient will be generated during the film formation process. Leveling is more related to the wetting of the substrate. Powder coatings often use acrylic leveling agents. If the leveling agent is in liquid form, it is generally necessary to make a masterbatch in advance before use. There are also acrylic leveling agents made into powders, which are specially used for powder coatings. This type of product is to adsorb liquid acrylic leveling agents on silica powder, and some low-grade leveling agents are adsorbed with calcium carbonate.

If the powder coating needs smoothness and scratch resistance, a silicone leveling agent must be used. There are already silicone leveling agents made into powders specifically for powder coatings. When using silicone leveling agents, be careful to avoid the formation of shrinkage holes.
 

● Waterborne coating system Waterborne coating systems are divided into water-soluble systems and latex systems.

In water-soluble systems, the surface tension of the system needs to be strongly reduced. The most commonly used are silicone leveling agents and fluorocarbon leveling agents, which play the same role as they are used in solvent-based coating systems. Of course, if a truly flat surface is required, acrylic leveling agents for waterborne systems are necessary.

For latex systems, the film-forming mechanism is completely different, and the viscosity does not change with the volatilization of the solvent. The use of leveling agents in the formula may improve the wettability of the substrate of the coating, and acrylic leveling agents can improve the flatness of the paint film, but the main flow properties of the coating are more controlled and adjusted by adding rheology control agents.