Overview of waterborne polyurethane coating

2022-01-06

According to the current development trend of waterborne polyurethane coating, green polyurethane coating technology is mainly divided into two categories: waterborne polyurethane coating and solvent-free polyurethane coating.Among them, solvent-free polyurethane coating mainly contains polyurethane hot melt adhesive coating and light curing polyurethane coating.Waterborne polyurethane (WPU) is a polyurethane system with water as the dispersion medium instead of organic solvent.

Compared with the traditional solvent-based polyurethane coating agent, it is environmentally friendly and more safe and reliable in logistics, transportation, production and manufacturing. The actual physical and chemical properties are shown in the figure below.

Comparison of waterborne polyurethane and solvent-based polyurethane

property

Water based polyurethane

Solvent-based polyurethane

viscosity
It is affected by the interparticle force of emulsion particle size
It is affected by relative molecular weight, solid content, solvent, etc
film-processing ability
Film-forming slowly
Easy to film

toxicity

The relative environmental protection
Organic solvents are volatile and have a toxic smell

solvent resistance

Poor water resistance

Poor resistance to toluene butanone
Difference in solvent polyurethane film link of waterborne polyurethane in the film, the emulsion in water at high temperature evaporation concentration gradually, latex particle formation sedimentary gradually, until the interface disappeared and mutual fusion between latex particles, the final latex particle in thread shaped polyurethane chain close to each other mutual diffusion chain end, the last film, as the chart shows.

waterborne polyurethane coating

Difference in solvent polyurethane film link of waterborne polyurethane in the film, the emulsion in water at high temperature evaporation concentration gradually, latex particle formation sedimentary gradually, until the interface disappeared and mutual fusion between latex particles, the final latex particle in thread shaped polyurethane chain close to each other mutual diffusion chain end, the last film, as the chart shows.

The stability of waterborne polyurethane emulsion is an important standard in the production, processing and application of products. In order to obtain better emulsion stability, waterborne polyurethane emulsion is generally prepared by self-emulsification method.According to the introduction of hydrophilic groups in polyurethane molecular chain, stable emulsions can be formed without adding emulsifiers, which can obviously improve the phenomenon of large particle size and multiple dispersion of emulsion and the residue and migration of small molecule emulsifiers commonly existing in external emulsification method.However, the widespread existence of hydrophilic groups in the polyurethane chain segment is easy to reduce the color fastness to water and wet friction of waterborne polyurethane coating products.In order to improve the shortcomings of the self-emulsifying waterborne polyurethane coating products mentioned above, in recent years, research on the modification of waterborne polyurethane has become a hot topic according to the blending modification, crosslinking modification and copolymerization modification, which can significantly improve the water resistance, mechanical properties and wear resistance of waterborne polyurethane coating.

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