What are the properties of water-based paints

Column:Company news Time:2018-11-26

Compared with other coatings, water-based paint has obvious advantages, among which, the biggest advantage is environmental protection. What are the distinctions between waterborne paint and other coatings besides environmental protection, let’s see together next.

(1) Poor dispersibility of pigments.

Water-based paints belong to polymer dispersion system, and the pigment dispersion is not very good, so measures should be taken to improve.

(2) Poor stability of dispersed particles.

Dissolved molecules are very stable to shear force, heat, pH, etc., while dispersed particles are not stable. Therefore, stable measures should be taken for the dispersed system. Dispersed particles will be damaged after being subjected to shear force, so the effect of shear force should be considered in the process of manufacturing and conveying waterborne paint. Dispersed particles are sensitive to pH value, and the mixing of acidic substances into the paint can form acidic particles, resulting in gelatinization and destruction of water-based paint. Dispersed particles of some water-based paints can also be damaged due to freezing during transport.

(3) Large surface tension.

Water is of large surface tension, so the surface tension of water-based paint is also large. The management should be strengthened in the construction process, otherwise the following defects and drawbacks of paint film will easily occur when painting:

a. Easy to sagging;

b. Poor flattening;

c. Easy to generate shrinkage cavity and pinhole;

d. Difficult to stretch into the fine-draw on the painted surface.

(4) Great evaporation heat and heat capacity, greatly influenced by temperature and humidity.

The great evaporation heat and heat capacity of water makes the water vaporize slowly in water-based paint. 50% of the total solvent in solvent-based paint is lost during spray atomization, and that is only 25% for water-based paint. Slow water evaporation in the painting process is easy to produce sagging and lower the painting efficiency. Therefore, an intermediate heating zone is required to force the water to evaporate from the waterborne primer coating. 90% of the water must be removed from the waterborne primer prior to painting (to prevent boiling water from evaporating through the varnish when it is finally baked) to obtain the best appearance of paint film, thus avoiding the waterborne primer being redissolved by the varnish. The evaporation rate of water is closely related to the relative humidity. When the relative humidity is high, the evaporation rate of water is very low. Therefore, the relative humidity and temperature of spray room must be controlled within a certain range to ensure that appropriate amount of water is evaporated in the spray process and that water and organic solvents keep balanced properly in the coating. This proper balance is important to allow the coating to have the proper surface tension to wet the surface.

(5) Good conductivity.

Water is of big dielectric constant, so the conductivity of water-based paint is good, the resistance of water-based paint is less than 0.1 MΩ commonly, and solvent paint has certain resistance: 0.5 ~ 20 MΩ. Water-based paint has good electrical conductivity and special requirements when using electrostatic spraying.

(6) High corrosivity.

Water-based paint contains a large amount of water, so it is corrosive to containers, conveying line, spray rooms and other parts susceptible to moisture. Stainless steel or plastic products are required.

(7) Rheological behavior.

When fluid viscosity 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 is time-dependent, so it is called thixotropic fluid. Based on the characteristics of water-based paint, the viscosity measured by flow cup is not reproducible. Only when the complete rheological curve of data points including low shear rate and high shear rate is measured by rotary viscometer, can the complete characteristics of the rheological behavior of water-based paint be given.

The above is the property of some waterborne paints, which have all sorts of imperfections, but are products that each enterprise takes seriously, "oil changing to water" stirs up a storm in the market gradually.