Jul 14, 2021
Polyurethane wood paint occupies a very important position in the Chinese market. With the increase in user requirements and the intensification of competition, higher and newer requirements have been put forward for PU wood paint. As a result, there are some issues worthy of discussion, such as: drying in winter , PU matt finish paint, anti-scratch, PU paint defoaming, hand brush leveling of PU decoration paint, yellowing resistance, PU primer collapse, PU paint thick coating, PU paint dark foam, biting and other series of problems , This article focuses on the preliminary discussion on the defoaming problem of PU paint.

The stirring of PU wood paint during the production process, filling and construction process can easily introduce air to produce bubbles. In addition, the wood is a porous material, and the holes are filled with air and water vapor, which is also very easy in the coating process. Air bubbles are generated. If these bubbles are not eliminated in time, they will eventually cause unacceptable board surface defects such as pinholes, bubbles, shrinkage, etc. after the paint film dries, which will affect the decorative effect. Therefore, the defoamer has its meaning.

The defoamer penetrates into the thin layer of bubbles formed by the surfactant, causing the surface tension of the foam to be unbalanced and breaking the foam. The defoamer must be incompatible with the product formulation system. Generally speaking, the worse the compatibility, the stronger the defoaming ability, but it may cause product turbidity or other board surface defects (such as Shrinkage phenomenon). On the contrary, if the defoamer has good compatibility with the formulation system, the defoamer cannot penetrate into the thin foam layer well, resulting in unsatisfactory defoaming effect.

Many other surfactants are added to the coating product formulation system, such as leveling agents, silicone hand-feeling agents, wax liquids, metal soaps, etc. The use of these surfactants often reduces the surface tension of the foam thin layer, so this Engineers have increased the difficulty in choosing a good defoamer. For example, leveling agents, generally better leveling agents are more likely to produce foam, and stronger defoamers are more likely to produce shrinkage. The two are inherently contradictory, so if you want to use the defoamer and the other system To find the balance point in the foam stabilizer active agent, it is necessary for engineers to find a suitable ratio through a lot of experimental work. This is the best formula system.

In the test and practice, it is found that the type and amount of defoaming agent used in the formula system of different types of PU coatings and construction methods will also be different. In many cases, two defoaming agents will be used to achieve the desired defoaming effect (such as hand Paint), another example is PU primer. To improve the polishing effect, materials such as zinc stearate are often used. Because zinc stearate itself is a saponified product, it has high activity and is easy to produce and stabilize foam. Therefore, the type and amount of defoamer used will vary. At present, the main types of defoamers used in PU wood paint are: silicone, acrylic, solvent, etc.

In summary, when choosing a defoamer in PU wood paint, it is necessary to fully consider the compatibility with the resin, defoaming ability and durability, based on the principle of basically eliminating foam, and not excessively pursuing the defoaming effect to avoid other side effect.

Top Win is one of the leading & professional manufacturers with  more than 20 years' experience, have domestic top-level engineers in silicone surfactant industry. We specialized in producing all kinds of SILICONE BASED new materials and specialized in research, production, sales and marketing in silicone-based performance materials. Provide good OEM&ODM service.Our products are mainly used in polyurethane foam, Agriculture,Coatings and Inks, Leather & Textiles, Pulp and Paper, Cosmetic industry, etc.