What Is Defoamer Silicon Spot?

Silicone defoamers have a wide range of applications, including metalworking, papermaking, wastewater treatment, pesticides, and petroleum refining. Defoamers are used in the printing and dyeing industry in two ways: 

1. Direct addition during the wet finishing process;

2. Pre-addition to surfactant-based additives to achieve low or no foaming. Examples include anionic and nonionic systems such as scouring agents and degreasers, and cationic systems such as water repellents and softeners.

Products that require direct addition typically require rapid foam breakage and, ideally, a certain degree of sustained foam suppression. Furthermore, they must avoid demulsification and the formation of oily stains, a phenomenon known in the industry as "silicon spots."

We collected dozens of defoamers from the market for testing, and found that most exhibited oily stains:

1. Laboratory beaker tests show only a small amount of oily stains per 500ml due to the low volume. 

2. Because defoamer addition levels are typically in the tens of ppm range, even if oily stains are present, they can accumulate over time before being detected, and by then, people may not necessarily identify them as the cause (people in the workshop might think, "I've always used it just fine"). 

3. The market is still short of products with minimal oily stains, leading many users to assume this is the norm.

Appearance of defoamer

What's the simplest and quickest way to evaluate a defoamer product? Besides diluting it and observing, there's actually an even simpler way: just observe the defoamer itself. A good defoamer has a uniform, milky white texture, like yogurt. It appears smooth and even when poured, with no large or small particles. This indicates meticulous attention to detail from the formulation to the emulsification process. If you see flocculent, granular, or even lumpy particles (like rice porridge), it's usually not stable and is more suitable for rapid defoaming and for applications where oil pollution is less of a concern (such as sewage treatment).

Redispersible after Settling

Due to differences in silicone paste raw materials and formulations, many defoamers can exhibit oily dispersion. This is typically characterized by rapid dissolution and instability, with the floating oil remaining even after stirring. We have observed that some of Maisong's products tend to sink slightly after a period of time, but can be evenly dispersed in the system upon stirring. This is considered excellent redispersibility, and naturally, their stability provides greater user confidence than products that exhibit excessive oil dispersion. The difference between these two properties can also be used as a basis for evaluating internally added defoamers.