The main causes of bubbles in glue are the following factors:

The viscosity of some glues is too high. Once air is mixed in, it is difficult to discharge smoothly, thus forming bubbles. At the same time, if the surface tension of the glue is small, its ability to wrap bubbles is poor, making it easy for bubbles to form and remain in the glue.

Bubbles are easily introduced into glue during stirring or mixing. When preparing or using glue, if the stirring action is too fast, lasts too long, or the stirring method is unreasonable, a large amount of air will take the opportunity to mix into the glue, creating conditions for the appearance of bubbles.

Environmental factors should not be underestimated. In terms of temperature, too high ambient temperature will cause the viscosity of the glue to decrease, making it easier for air to invade and difficult to discharge; too low temperature will make the fluidity of the glue worse, and it will be difficult for bubbles to break free from the bondage of the glue. In terms of humidity, high ambient humidity may cause water to mix into the glue, interfere with the surface tension and viscosity of the glue, and eventually induce the formation of bubbles.

The packaging and storage conditions of the glue are also related to the formation of bubbles. If the packaging container is not well sealed, air can easily get into the packaging, and bubbles will follow in subsequent use. If the storage conditions are not ideal, such as vibration or abnormal temperature fluctuation during storage, bubbles may also grow inside the glue.

When bubbles appear in the glue, the following degassing methods can be used:

The natural static method is the simplest. Just place the glue containing bubbles steadily and let the bubbles rise to the surface of the glue by their own buoyancy to break and dissipate. This method is suitable for glue with low viscosity, few and small bubbles. The advantage is that the operation is easy and no additional tools are required; the disadvantage is that the degassing process is slow, and the effect is not good when facing high viscosity or glue with dense bubbles.
The heating degassing method is to increase the temperature of the glue moderately, reduce its viscosity, and enable bubbles to rise and discharge more smoothly. The specific operation is to place the glue in a constant temperature water bath, or use a heating device to heat the glue evenly. However, in this process, the heating temperature and duration must be accurately controlled to prevent the quality of the glue from being damaged due to overheating. This method has a relatively fast degassing speed, but it has high requirements for heating uniformity.

The vacuum stirring degassing method has both stirring and degassing functions, which can effectively improve the degassing efficiency. Pour the glue with bubbles into a vacuum container equipped with a stirring device, first turn on the stirring function, so that the internal bubbles can be initially dispersed and broken during the uniform stirring of the glue; then start the vacuuming procedure to reduce the air pressure in the container. At this time, the bubbles remaining in the glue will expand rapidly, float up and escape in a low-pressure environment. When using this method, the stirring speed, vacuum degree and processing time should be reasonably set according to the characteristics of the glue to ensure that it can be fully degassed without affecting the performance of the glue. This degassing method is suitable for glues with medium viscosity and above, especially in industrial production where the quality requirements for degassing glue are high. However, it requires professional vacuum stirring equipment and the initial investment cost is relatively high.

In summary, there are many reasons why PU glue is prone to foaming, involving multiple levels such as operation process, material quality, environmental conditions and chemical changes during curing. Through the comprehensive control and adjustment of the above factors, we can effectively reduce the foaming phenomenon of PU glue and improve its use effect and stability.