During the preparation process of polyurethane prepolymer, the causes of bubbles include the following aspects:
1. The increase in material viscosity leads to an increase in bubbles.
2. The moisture content in the raw materials (oligomeric polyol and polyisocyanate) exceeds 0.05%, which causes it to react with the polyisocyanate and produce CO2 bubbles.
3. There is moisture in the reaction device.
4. If the negative pressure in the reactor is too large, the boiling point of the material will be lowered and the material will vaporize, resulting in a large number of bubbles.
5. Adding too much filler will easily produce more bubbles under stirring.
The above five sources of bubbles can be solved one by one. For example, extend the dehydration time of raw materials and control the moisture content below 0.05%; thoroughly dry the reaction vessel; while ensuring that the materials are not vaporized, try to increase the negative pressure value and find a suitable vacuum to stabilize the production process and reduce or Avoid material vaporization and other phenomena. When synthesizing prepolymers, the generation of bubbles is extremely unfavorable. A large number of bubbles in the liquid will cause the temperature of the reaction system to fluctuate greatly, making the reaction difficult to control. The generation of bubbles should be minimized to facilitate the smooth completion of degassing of the prepolymer.