In order to avoid the shrinkage phenomenon of the coating due to excessive addition of defoamer, the following key aspects can be taken into consideration:

1. Accurately measure and control the dosage

Experimentally determine the optimal dosage: 

Before formal production, it is imperative to determine the precise dosage of the defoamer through laboratory testing. The specific operation is to prepare multiple identical paint samples and add different proportions of defoamer to each sample. For example, test with different gradient addition amounts such as 0.1%, 0.3%, and 0.5%. Carefully observe the defoaming effect of each sample, including the speed of bubble elimination and whether there are residual bubbles. At the same time, pay close attention to the surface condition of the paint after drying to see if shrinkage cavities appear. After a comprehensive evaluation, determine the optimal defoamer dosage that can achieve good defoaming effects without shrinkage cavities.

Strictly implement dosage standards in production:

During large-scale production, the addition must be strictly carried out in accordance with the optimal dosage determined by the experiment. This requires the use of high-precision metering equipment, such as electronic scales, metering pumps, etc., to ensure that the amount of defoamer added is accurate. At the same time, establish a complete production operation specification, requiring operators to strictly abide by the dosage standards, and prevent the occurrence of arbitrary increases or decreases in the amount of defoamer.

2. Choose defoamers reasonably

Choose according to the type of coating: 

Different types of coatings, such as water-based coatings, solvent-based coatings, powder coatings, etc., have different chemical properties and surface tension characteristics, and need to be matched with different types of defoamers. For example, since water-based coatings use water as a solvent, polyether or silicone polyether composite defoamers with good hydrophilicity should be selected. These defoamers can quickly disperse in the water-based system and play a defoaming role. Solvent-based coatings need to use defoamers with good compatibility with organic solvents, such as some modified silicone defoamers.

Consider the ingredients of the coating formula:

Ingredients such as resins, pigments, fillers and other additives in the coating formula will affect the effect of the defoamer. If the coating contains a large amount of surfactants, it may be necessary to select a defoamer with stronger defoaming ability and good compatibility with these surfactants. For example, when anionic surfactants are used in the coating, cationic defoamers should be avoided to avoid chemical reactions that cause the defoamer to fail or produce shrinkage holes.

Meet the requirements of construction process: 

Different construction processes, such as brushing, spraying, roller coating, etc., have different requirements for the fluidity and defoaming performance of the coating. For example, spraying construction requires the coating to have good atomization and low foaming properties. At this time, a defoamer that can quickly defoam and will not affect the atomization effect of the coating should be selected. If the roller coating process is used, the effect of the defoamer on the leveling of the coating needs to be considered to ensure that the defoaming can be effectively performed during the roller coating process without generating shrinkage holes, so as to ensure the flatness of the coating.

3. Optimize the adding process

Use the appropriate adding method: 

the defoamer can be diluted first and then slowly added to the coating. For example, the defoamer can be diluted with an appropriate amount of solvent or the coating itself to prepare a solution of a certain concentration, and then slowly added to the coating in a thin stream under stirring. This can make the defoamer more evenly dispersed in the coating system to avoid excessive local defoamer concentration. For some defoamers that are easy to agglomerate, a step-by-step addition method can also be adopted. First, add a part of the defoamer for preliminary defoaming, and then add the remaining part after stirring evenly to further optimize the defoaming effect.

Control the stirring conditions: 

In the process of adding the defoamer, the stirring speed and time are crucial. The stirring speed should not be too fast to avoid introducing a large amount of air again to form new bubbles; but it should not be too slow, otherwise the defoamer cannot be fully dispersed. Generally speaking, the stirring speed can be controlled at 300-600 rpm. The stirring time should also be appropriate, usually around 15-30 minutes, and the specific time needs to be adjusted according to the amount of coating and the performance of the stirring equipment. At the same time, to ensure the uniformity of stirring, multi-directional stirring can be adopted or equipment with good stirring effect, such as high-speed disperser, can be used to make the defoamer evenly distributed in the coating to avoid shrinkage holes caused by uneven dispersion.

4. Strengthen production process monitoring

Real-time monitoring of defoaming effect: During the coating production process, multiple monitoring points are set up to observe the effect of the defoamer in real time. For example, after the defoamer is added, during the stirring process, and before the coating is canned, the number, size, and distribution of bubbles in the coating can be checked by visual observation, microscopic detection, or the use of bubble detection instruments. Once the defoaming effect is poor or there are signs of excessive defoaming, adjust the amount of defoamer or take other remedial measures in time.

Regularly check product quality: Establish a strict quality inspection system and conduct regular quality inspections on the coating products produced. In addition to checking the conventional performance indicators of the coating, focus on the surface condition of the coating after drying to check for defects such as shrinkage cavities and orange peel. For products with shrinkage cavities, trace the production process in a timely manner, analyze the causes, summarize lessons learned, and continuously optimize the production process to prevent similar problems from occurring again.