01 Conditions for film formation

Stowing operation

The water evaporates, and the particles are close to each other to achieve a dense charging state

Fusion process

The surface layer of the particles is destroyed, and the particles are in contact with each other.

Diffusion process

The molecular chains between the dispersion particles are diffused with each other to form a homogeneous film with certain mechanical properties

02 Film forming properties

The film forming property of the emulsion refers to the ability of the emulsion to form a uniform film on the surface of the substrate after it is applied to the bottom. The film forming performance of polyurethane emulsion is closely related not only to the molecular weight of polyurethane vinegar, the type and number of residual solvents in the emulsion, the average diameter of particles and the viscosity of the emulsion, but also to the curing rate of the emulsion. If the residual stock of volatile solvent is large, the curing rate of emulsion is fast, and the cured film is easy to produce bubbles, shrink and wrinkle. If a small amount of high boiling point solvent is added to the emulsion, the curing rate will not be affected, and a flat film without bubbles can be obtained. The particle diameter also affects the curing rate. The smaller the diameter, the slower the curing rate, but the better the film formation, the better the physical and mechanical properties of the cured film. The requirements for emulsion viscosity depend on the specific application.

03 The development direction of waterborne polyurethane

The future development trend of polyurethane is to develop water-based polyurethane with high performance, low energy consumption and no pollution. In the next few years, the development direction of water-based polyurethane will mainly focus on the following aspects.

1.Improve the water resistance of waterborne polyurethane.

2.improve the stability of waterborne polyurethane, while maintaining water resistance of waterborne polyurethane, improve the storage stability of waterborne polyurethane is an important direction of foreign waterborne polyurethane research.

3. improve the solid content of water-based polyurethane, the current production of water-based polyurethane solid content is more than 20% to 40%, drying and transportation costs are high, should try to improve it; If the solid content is increased to more than 45%, the drying rate at the drying temperature of 40 to 60°C can be similar to the drying rate of ordinary solvent-based polyurethane resin at room temperature.

4.Strengthen the research of composite modified water-dispersed polyurethane, and use the designability of polyurethane molecules to introduce molecular structures with special functions on the polyurethane chain, such as fluorine-containing and silicon-containing polymer chains, so that the coating film has more functionality.

5.Develop antistatic and antibacterial water-based polyurethane.

6.The research on high solid content and powdered water dispersible polyurethane should be strengthened.

7.Using renewable resources such as vegetable oil, rosin and waste plastics to prepare polyols, and then using the polyols to synthesize waterborne polyurethane to prepare modified waterborne polyurethane.

8.Active research on two-component waterborne polyurethanes was carried out to develop high-performance, low-VOC two-group water-splitting polyurethanes.

9.Further develop the application field of waterborne polyurethane.