Bubble Formation And Elimination Method When Using Polyurethane Prepolymer

1. Raw material pretreatment

In order to reduce the CO₂ bubbles in the process of synthesizing the prepolymer adhesive, the polyester or polyether in the reactor (or reactor) can be melted and vacuum dehydrated first, such as [1, 2] Tetramethylene glycol (PTMG-1000), 1,4-butanediol (1,4-BD) and dibutyltin dilaurate (DBTDL) system are heated and melted, stirred and heated to 90-100°C and vacuumed for 2h, It reacts with isocyanate after cooling to below 60°C. The polyisocyanate is added first when feeding, and then the dehydrated polyester or polyether is dropped into the reaction device, which can reduce the generation of bubbles, facilitate the removal of reaction heat and control the temperature. Note that in the synthesis of transparent polyurethane prepolymer adhesives, the moisture content of all raw materials must reach the polyurethane level (<0, 02%).

2. Vacuum method

In the process of synthesizing the prepolymer adhesive, a vacuum is adopted to make the gas in the bubble escape, so as to achieve the purpose of eliminating the bubble. The difficulty of this method lies in the sealing problem of the reaction device, and the entire reaction system can be placed in a vacuum environment in a mass production line.

3. Add additive method

The CO₂ absorbent or adsorbent is mixed into the adhesive to remove CO2. The available adsorbents are carbon black, PVC paste resin, calcium oxide, calcium hydroxide, etc. The adsorbent is required to contain no moisture and have fine particles, such as 50-500um calcium oxide micro-dispersion as an absorbent.