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With the changes in national environmental protection policies, traditional organic solvent-based paints are gradually being replaced by water-based solvent paints.
The biggest feature of water-based paint is that it replaces the original organic solvent with water as the paint dispersant and thinner.
However, the volatility of water is much worse than that of organic solvents.
The natural volatilization (evaporation) of water at room temperature and pressure is minimal compared with organic solvents.
Therefore, the film forming process of water-based coatings in industrial production is Using heating type drying, only a few large-scale equipment can not be heated and dried or manufacturers that do not have high requirements for production efficiency will use natural drying com" href="http://">paint online coatingol.
com .
So what are the internal factors that affect the drying efficiency of water-based coatings?
Aqueous polyurethane is a new type of polyurethane system in which water replaces organic solvents as the dispersion medium.
It is also called water-dispersed polyurethane, water-based polyurethane or water-based polyurethane.
Waterborne polyurethane uses water as the solvent, and has the advantages of no pollution, safety and reliability, excellent mechanical properties, good compatibility, and easy modification.
Polyurethane (PU) is a type of polymer compound containing repeating structural units of urethane bonds on the main chain.
Water-based polyurethane (WPU) refers to an emulsion formed by dissolving or dispersing PU in water.
Because WPU uses water as the dispersion medium, it has the advantages of non-toxic, non-flammable, and environmental protection.
It can be used on the surface of textiles, leather, paper, rubber, automobiles or furniture for decoration and protection.
It has gradually replaced it.
Solvent-based PU paint.
There are three main forms of water molecules in waterborne polyurethane coatings: free water, bound water and gel water.
Compared with solvent-based PU paint, the WPU drying process is characterized by a high temperature at which water starts to evaporate, and there is a certain amount of humidity in the external environment (the water vapor pressure of the paint film itself must be greater than the ambient water vapor pressure to evaporate).
These two characteristics make the drying rate of water-based polyurethane paints slower than that of solvent-based paints, which affects the promotion of WPU to a certain extent, so improving the drying rate of water-based paints is a research that must be done to expand the market.
What are the internal factors that affect the drying rate of waterborne polyurethane coatings?
First, the influence of solid content.
The content of free water is closely related to the solid content.
Second, the influence of the content of hydrophilic groups.
In order to improve the dispersibility of WPU, hydrophilic ionic groups are usually introduced into the molecular chain of PU.
Bound water is the water in a PU colloidal particle formed by hydrogen bonding and intermolecular force equal to PU hydrophilic group.
Its volatilization rate is much lower than free water.
Third, the impact of hard segment content.
The increase of hard segment content can speed up the drying rate.
Fourth, the influence of neutralization degree.
The polite carboxylic acid group has weak hydrophilicity, while the carboxy anion that is neutralized to form a salt has good hydrophilicity.
Fifth, the influence of the film-forming substrate.
The surface properties of the film-forming substrate determine the force between its water molecules, so it has a great influence on the drying rate of the paint.
