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Only when the surface tension of the coating is lower than that of the substrate, can the coating complete the spreading and wetting process. In water-based coatings, the surface tension of water is relatively high, far exceeding that of various common substrates. So water-based coatings, especially water-based industrial paints, water-based wood paints, etc., which wet the substrate, often become the first problem to be solved.

When the contact angle between the coating and the substrate is less than 90 °, the substrate can be wetted. Substances that can usually reduce the surface tension of aqueous systems can be used as substrate wetting agents. There are many common types of substrate wetting agents. The most commonly used substrate wetting agents are organosilicon based, such as trisilane structured wetting agents. These wetting agents can reduce surface tension to 20.5~23.5, and by adjusting their structure, unstable foam can be achieved, while in most cases, stable foam can be achieved. Its ability to reduce surface tension is very strong, about 20.5 dynes, and its versatility is very strong.

This substrate wetting agent with a binary star structure of siloxane may have better performance, as it can simultaneously reduce static and dynamic surface tension, but also has unstable foam and strong anti shrinkage ability, and has a relatively small impact on recoating.

The second type is fluorine-containing substrate wetting agents. This type of substrate wetting agent can minimize the surface tension of water, even up to about 15 dynes, so it has strong wetting, anti shrinkage, and pore entry properties. It is most commonly used in water-based wood coatings. However, these fluorine-containing surfactants also have drawbacks, mainly due to their relatively stable foaming, which can have adverse effects on defoaming. We have developed a fluorine-containing wetting agent with a completely new structure, and its surface tension in aqueous solution can even be lower than 10 dynes in our laboratory tests. It is about 1 ‰, which can be lower than 10 dynes and has the strongest ability to reduce surface tension, while also having the advantage of unstable bubbles.

The third type, the most commonly used substrate wetting agent, is alkynediol type, which does not contain silicon, so it cannot strongly reduce its static surface tension. But its molecular weight is relatively small. It has two active groups at each end, and throughout its entire movement, regardless of which end, it has a surface tension reducing effect on it. So this product can effectively reduce the dynamic surface tension of the system.

At the same time, this wetting agent is also a panacea. It is unstable and has good acid-base stability, low water sensitivity, and can assist in pigment wetting, defoaming, substrate wetting, leveling, and does not affect recoating. Its safety is also high. However, it basically has all kinds of functions, but none of them are strong, and it cannot be fully relied on.

So, if the cost allows, it can be added completely. However, without the addition of other additives, this requirement can still be achieved. This type of substrate wetting machine is most commonly used in situations that require rapid wetting, such as printing ink, wallpaper, etc. It is only used as an auxiliary in conventional coatings.