• The relationship between defoamer and coating

Paint is an indispensable material in modern industry and daily life, and its performance directly affects the quality of products in the fields of construction, automobiles, furniture, etc. However, during the production and application of paint, a large amount of foam is easily generated due to surfactants in the raw materials and operations such as stirring and pumping.

In addition to being beautiful, paint can also form a strong solid film, which is a protective coating, but it often encounters a problem, that is, foam. Water-based paints and solvent-based paints use various additives in their formulations, such as wetting dispersants that make pigments and fillers easy to wet, disperse and stabilize, additives that improve the storage stability of finished paints, additives that adjust the appearance of the paint film, and some additives that achieve special functions. Most of these additives are surfactants, which can change the surface tension of the paint, which is an internal factor that causes the paint to be prone to foaming. In addition, stirring and high-speed dispersion during the manufacture of paint, and shearing during spraying, rolling and brushing during application construction, will also increase the free energy of the paint system to varying degrees and generate foam, which is an external factor that generates foam.

If the large amount of foam produced by the paint is not eliminated in time, it will cause various defects such as pinholes, shrinkage holes, fish eyes, orange peel, etc. on the surface when it is painted on the object, affecting the finishing and protective properties.

Hazards of foam

1. Foam can easily cause volume expansion, resulting in reduced equipment utilization.

2. Foam limits the stirring speed and prolongs the mixing time of the paint.

3. Foam affects the wetting of pigments and fillers.

4. A large amount of foam affects production line packaging and interferes with packaging operations.

Importance of defoamers

Defoamers are one of the indispensable additives in the coatings industry, as they quickly break and suppress foam, ensure smooth coating production and construction processes, and improve coating quality and efficiency.

Ⅱ·Application of coating defoamer

Production link

During the mixing and grinding process of the paint, foam may cause problems such as uneven stirring and abnormal viscosity. The use of high-efficiency defoaming agents can improve production efficiency and reduce process losses.

Storage link

During storage, the paint may produce foam due to ambient temperature and vibration, leading to sedimentation and stratification. Adding defoaming agents can extend the storage stability of the paint and ensure product quality.

Construction link

During the construction of the paint, spraying, brushing, roller coating and other methods are prone to affect the smoothness and fullness of the coating film due to bubbles. Defoaming agents can quickly solve the construction foam problem and improve the construction effect.

Specific industry

Antifoam for industrial paint; Antifoam for marine paint; defoamer for marine coating; defoamer for automative coating; antifoam for automative paint; aircraft paint; antifoam for Construction machinery coating; Antifoam for wind power coating;  defoamer for neclear coating; defoamer for train coating; defoamer for Concrete anticorrosion; Antifoam for container coating; antifoam for furniture paint; paint antifoam for traffic sign; antifoam for medical coating; antifoam for optical firber paint; antifoam for solar energy;

Ⅲ·Defoaming mechanism of coating defoamer

Reduce surface tension: Defoamers reduce the tension on the foam surface, making the foam film thinner and breaking faster.

Anti-foaming effect: By forming a barrier at the point of foam generation, it prevents further growth and aggregation of bubbles.

Diffusion and wettability: Defoamers can quickly diffuse to the foam surface and wet the foam film, accelerating the dissipation of foam.

The removal of foam requires three processes, namely, the redistribution of bubbles, the thinning of the film thickness, and the rupture of the film. It takes a long time to achieve natural defoaming after these three processes. To solve the problem of paint bubbles, adding a defoamer for paint is the key. Paint defoamer is a chemical additive added to the production and use of paint, which adds a protective shield to the paint, protects the paint from the damage of foam, and quickly eliminates the foam. The defoamer always penetrates into the foam system in the form of particles. After contacting the foam, it captures the hydrophobic chain end on the surface of the foam, and after rapid spreading, it forms a very thin double film layer, which further diffuses and invades. Since liquids with low surface tension always flow to liquids with high surface tension, the low surface tension of the defoamer itself reduces the surface tension of the bubble film locally, and the membrane wall gradually becomes thinner, and is strongly pulled by the surrounding membrane layer with high surface tension, resulting in stress imbalance, which finally causes the bubble to rupture.

• Relationship between Rheology modifier and coating rheology

As a common industrial product, the performance and quality of coatings are greatly affected by rheology (i.e. the flow and deformation characteristics of a substance under external forces). The application of rheology in coatings is especially reflected in the storage, construction and final effect of coatings. Rheology can help us better understand and control the various properties of coatings, thereby improving the stability and construction effect of coatings.

• Four major applications of coatings and rheology

Paint Storage: Sedimentation

Sedimentation is the process by which pigments, fillers and other solid materials sink to the bottom of a container under the influence of gravity. Pigment sedimentation is a low shear rate phenomenon: the shear rates involved are less than 10^-2 s^-1, so the viscosity of the paint at this shear rate is critical to prevent the pigment from settling.

During the storage of paint, rheology plays a vital role. An ideal paint should have good suspension properties to avoid the precipitation of solid substances such as pigments and fillers. Rheology modifiers can reduce these sedimentation phenomena by adjusting the viscosity of the paint and maintain the stability of the paint.

Common methods to overcome sedimentation:

1. Balance the layout of filters/circuits (use small circuit layout instead of partially enlarged circuit layout)
2. Minimize the amount of solvents and surfactants, which will reduce the low shear stress under viscosity
3. Increase the viscosity under low shear by selecting rheology Modifiers
4. Add a small amount (0.5-2 g/L) of HEC to increase the low shear viscosity. However, it will affect the fluidity and leveling and anti-splash performance.

• The coating is very viscous and structures when it is still in the can. It is usually felt that this coating is difficult to apply.
• The coating is very thin in the can, which will cause dripping during brush transfer, severe sagging on vertical surfaces during application, and splashing during roller application.

Controlling the viscosity of the coating in this shear rate range will affect the performance under these medium shear conditions (can appearance, dipping, stirring).

During the coating application process, dipping (brushing or dipping) requires the coating to have the appropriate viscosity in order to control the fluidity of the coating and avoid dripping. By adjusting the viscosity of the coating, the rheology modifier can ensure that the coating flows evenly during application, avoiding too fast flow or the formation of uneven coating.

Paint application: paint film fullness

Brushing, rolling and spraying operations depend on viscosity at high shear rates (>10³sec^-1):

The higher the viscosity at high shear rates, the greater the resistance to the paint distribution during application, so a thicker paint film can be obtained in one application. Conversely, low viscosity at high shear rates means that the paint is less resisted when it is distributed, and the paint is easier to spread on the substrate surface. The corresponding paint film is thinner, resulting in reduced hiding power.

The fullness of the paint film is a key factor affecting the appearance and durability of the coating. During the construction process, the paint needs to have sufficient viscosity to form a thick and uniform paint film on the surface, avoiding a weak or uneven coating caused by too low viscosity.

Paint construction: flow and sagging

Leveling and sagging refers to the fluidity of the paint after coating. Too high fluidity will cause the paint to be unable to be evenly coated and sag, while too low fluidity will cause the coating surface to be rough. The addition of rheology modifier can effectively adjust the leveling of the paint, making the coating surface smooth and uniform.

Factors affecting leveling and sagging:

• paint film thickness,
• drying speed,
• viscosity (under low shear conditions)

The goals of maximum leveling and minimum sag are conflicting.

• Reduced viscosity at low shear rates helps leveling but increases sag.
• Increasing film thickness accelerates leveling but also increases sag.

• Rickman's brand advantage

Rickman not only provides high-quality defoaming solutions, but also has extensive experience in the research and development of rheology modifier. Our rheology modifier products, especially HEUR and HASE thickeners for the coatings industry, undergo strict quality control to ensure long-term stable performance. The rheology modifiers provided by Rickman can not only improve the application performance of the coating, but also optimize the environmental friendliness of the product.

In addition, Rickman's customer service team is always committed to providing customers with technical support and customized solutions. Whether it is product selection, application technical support, or quick response to customer needs, Rickman always stands from the customer's perspective and provides value-added services for your business.