Waterborne paint belongs to polymer dispersion system, and the pigment dispersion is not very good, so measures should be taken to improve it.
(2) The stability of dispersed particles is poor.
Dissolved molecules are stable to shear force, heat, pH, etc. However, the dispersed particles are unstable, so measures should be taken to stabilize the dispersion system.
The dispersed particles will be destroyed by shear force, so it is necessary to avoid the effect of shear force in the transportation of water-based paint.
Dispersed particles are very sensitive to pH value, and acid particles will be formed when mixed with acid substances in coatings, which will lead to gelation and damage to water-based paints.
In addition, the dispersed particles of water-based paint will be destroyed after being frozen during transportation.
(3) High surface tension.
The surface tension of water is large, so the surface tension of water-based paint is also large, so management should be strengthened in the construction process, otherwise the following defects and paint film defects are easy to appear when painting: a. It is easy to sag; B. poor flattening; C. Shrinkage holes and pinholes are easy to occur; D. it is not easy to extend into the small cracks on the surface of the coated object.
(4) heat of vaporization, with large heat capacity, is greatly influenced by temperature and humidity.
The evaporation heat and heat capacity of water are high, which makes the evaporation of water in water-based paint slow.
50% of the total solvent in solvent-based coatings volatilizes during spraying and atomization, while only 25% in water-based coatings.
Slow evaporation of water easily leads to sagging during painting, which makes the painting efficiency worse.
Therefore, it is necessary to set an intermediate heating zone to forcibly volatilize the water in the water-based primer coating.
Before spraying the varnish, 90% of the water in the water-based primer coating must be removed (to prevent the boiling water from volatilizing through the varnish during the final baking) to obtain the best paint film appearance, so as to avoid the water-based primer from being re-dissolved by the varnish.
(5) Good electrical conductivity.
The dielectric constant of water is large, so the water-based paint has good conductivity. Generally, the resistance of water-based paint is less than 0.1mΩ), while solvent-based paint has a certain resistance: 0.5 ~ 20MΩ.
Waterborne paint has good conductivity, so there are special requirements when using electrostatic spraying.
(6) corrosiveness.
Water-based paint contains a lot of water, which is corrosive to containers, transportation pipelines, spray booth bodies and other parts that are prone to moisture, so stainless steel or plastic products are needed.
(7) Rheological behavior.
When the viscosity of fluid decreases with the increase of shear rate, it is called pseudoplastic fluid.
The rheological behavior of pseudoplastic fluid is related to its rheological path, that is, it depends on time, so it is called thixotropic fluid.
Based on the characteristics of water-based paint, it is unrepeatable to measure viscosity with a flow cup. Only by measuring the complete rheological curve of data points including low shear rate and high shear rate with rotary viscometer can the complete rheological behavior of waterborne coatings be given.
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