Classification and usage points of coating leveling agents

Leveling agents used in coatings are generally categorized as mixed solvent, acrylic, silicone, fluorocarbon polymer, and cellulose acetate butyrate.

Due to their low surface tension, leveling agents not only help the coating level, but they can also cause side effects. During use, the primary consideration is the potential adverse effects of leveling agents on the coating’s recoatability and crater resistance. Compatibility testing of the selected leveling agent is also necessary.

The following describes the respective characteristics of mixed solvent, acrylic, and silicone leveling agents, and briefly discusses the key points of their use.

1.Mixed solvent leveling agent

It is primarily composed of high-boiling-point aromatic hydrocarbon solvents, ketones, esters, or other high-performance solvents with various functional groups, or mixtures of high-boiling-point solvents.

When formulating and using solvents, attention should be paid to their evaporation rate, evaporation balance, and solvency, ensuring that the paint exhibits a uniform evaporation rate and solvency during the drying process. If the evaporation rate is too low, the solvent will remain in the paint film for an extended period without being released, affecting the film’s hardness.

This type of leveling agent is only suitable for correcting leveling defects (such as craters, blushing, and poor gloss) caused by rapid solvent drying and poor binder solubility in the coating. The typical usage level is 2% to 7% of the total paint volume. It prolongs the drying time of the coating. For room-temperature drying coatings prone to sagging (such as nitrocellulose lacquer) applied to facades, it not only helps with leveling but also improves gloss. It also prevents blistering and pinholes caused by rapid solvent evaporation during the drying process. Especially useful in high-temperature and high-humidity climates, it prevents premature drying of the paint film surface, provides a uniform solvent evaporation profile, and prevents the white haze phenomenon associated with nitrocellulose lacquer. This type of leveling agent is generally used in conjunction with other leveling agents.

2.Acrylic leveling agent

This type of leveling agent is mostly a copolymer of acrylic esters. Its characteristics are:

(1) Alkyl esters of acrylic acid provide basic surface activity;
(2) Its −COOH, −OH, and −NR can help adjust the compatibility of the alkyl ester structure;
(3) The relative molecular weight is directly related to the final spreading performance. Critical compatibility and the chain configuration of polyacrylate are necessary conditions for becoming a suitable leveling agent. Its possible leveling mechanism is mainly manifested in the later stage;
(4) It exhibits anti-foaming and defoaming properties in many systems;
(5) As long as there are a small number of active groups (such as −OH, −COOH) in the leveling agent, the impact on recoating is almost imperceptible, but there is still the possibility of affecting recoating;
(6) There is also the problem of matching polarity and compatibility, which also requires experimental selection.

3.Silicone leveling agent

Silicones are a class of polymers with a silicon-oxygen bond (Si-O-Si) as their backbone, with organic groups attached to the silicon atoms. Most organosilicon compounds have low-surface-energy side chains, resulting in very low surface energy and surface tension.

The most commonly used polyorganosiloxane additive is polydimethylsiloxane, also known as methyl silicone oil. Its primary use is as a defoaming agent. Low-molecular-weight versions are more effective in promoting leveling, but due to severe compatibility issues, they can easily cause cratering or prevent recoating. Therefore, polydimethylsiloxane must be modified for safe and effective use in coatings.

Modification methods primarily include: polyether-modified silicones, alkyl- and other pendant-modified silicones, polyester-modified silicones, polyacrylate-modified silicones, and fluorine-modified silicones. Polydimethylsiloxane can be modified in numerous ways, all with the goal of improving its compatibility with coatings.

This type of leveling agent typically provides both leveling and defoaming properties. Compatibility with coatings should be verified through testing before use.

4.Key points for use

Choose the right type: Select the appropriate leveling agent based on the type and functional requirements of the paint. When selecting a leveling agent, consider its composition and properties, as well as its compatibility with the paint itself. It’s often necessary to combine various leveling agents or other additives to achieve a balanced balance.

Pay attention to the dosage: Excessive addition can cause problems such as cratering and sagging on the painted surface, while too little can result in ineffective leveling. The dosage should generally be determined based on the paint’s viscosity and leveling requirements, following the agent’s instructions, and combining actual test results.

Application method: The leveling performance of a paint is affected by the application method. When applying a leveling agent, brush, roller, or spray can be used to maximize its effectiveness.

Stirring: When applying a leveling agent, stir the paint thoroughly to ensure that the agent is evenly dispersed throughout the paint. The stirring time should depend on the properties of the leveling agent and generally should not exceed 10 minutes.