The process of converting monomer polyether waterproof coating raw materials into prepolymers involves multiple key steps and fine control. The following is a detailed analysis of the steps:
1. Raw material selection and preparation
- Polyether polyols: Select polyether polyols (such as polyoxypropylene glycol) with appropriate molecular weight and functionality to affect the flexibility and strength of the final coating.
- Isocyanates: Commonly used diisocyanates (such as MDI, TDI) react with polyether polyols to form prepolymers.
- Catalysts: Organic tin (such as dibutyltin dilaurate) can be used to accelerate the reaction, and the amount needs to be controlled to avoid overreaction.
2. Dehydration treatment
- Purpose: Remove moisture from polyether polyols (usually require moisture content <0.05%) to prevent CO₂ bubbles from reacting with isocyanates.
- Methods: Vacuum dehydration at 100-120℃ for several hours to ensure that the raw materials are dry.
3. Prepolymerization
- Ratio calculation: Determine the molar ratio based on the hydroxyl value and isocyanate content. Usually, the isocyanate is in excess to ensure that the terminal group is -NCO.
- Reaction conditions: Mix the polyether polyol and isocyanate under nitrogen protection, add the catalyst, and control the temperature (usually 60-80°C) to avoid side reactions.
- Reaction monitoring: Determine the -NCO content by titration to confirm the reaction endpoint.
4. Adjustment and post-treatment
- Viscosity adjustment: Add solvents (such as acetone, xylene) or adjust the molecular weight to meet construction requirements.
- Degassing and filtration: Remove bubbles and impurities that may be generated during the reaction to ensure uniform prepolymer.
5. Storage and stability
- Sealed and moisture-proof: Store in a dry and sealed container to prevent contact with moisture that may cause premature curing of the prepolymer.
- Stability detection: Regularly test the -NCO content and viscosity to ensure stable performance during storage.
6. Key control points
- Moisture control: Strictly dehydrate to avoid bubbles.
- Temperature management: Reaction temperature affects the reaction rate and by-product generation.
- Accurate ratio: Ensure that the end group type and prepolymer molecular weight meet the design.
7. Application and curing
- Moisture curing: After construction, the prepolymer end group -NCO reacts with moisture in the environment to form a cross-linked structure to achieve waterproof performance.
Through precise control of raw material processing, reaction conditions and post-processing steps, monomer polyether raw materials can be converted into stable performance prepolymers, providing excellent film-forming and durability for waterproof coatings. This process requires attention to details such as dehydration, ratio and storage conditions to ensure the quality of the final product.