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Interesting facts
...........about water-soluble coating systems


Our water-based coating technology is more than "just" a solution for VOC demands.
It offers benefits today which pay off both in technical and economic terms, with regard to (among other things):

   

Protection of the environment:

Considerable decrease in environmental pollution due to a reduction in organic solvents

 

Health:

Water-based coatings are less harmful than solvent-based ones as far as occupational health is concerned.

 

Economic efficiency:

Reduction in spray diluents since suitable water can be used as a thinner. Additional cost savings because of the elimination of exhaust air treatment and lower insurance/fire protection premiums.

 

Quality:

For many applications, modern water-based coating systems cannot only be used without any loss of quality when compared with conventional systems, they even provide considerable quality benefits for numerous tasks.

 

Specific features worth knowing when using water-based coatings:

Water acts as both solvent and dispersing agent in water-soluble coatings.
Compared with customary lacquer thinners, water has properties that differ considerably:


>> Water freezes to ice at 0°C. Water-based coatings should, therefore, be stored at temperatures above freezing point.

>> Water boils at +100°C and evaporates as a uniform substance with a relatively high evaporation rate, compared with solvents. To avoid problems with the visual surface quality of coatings, water-based coatings contain co-solvents and film former additives.

>> Water has a considerably higher surface tension than organic solvents. This results in poor wetting of the uncoated surface. A thorough cleansing of the substrate is, therefore, mandatory when working with water-based coatings.

>> Water has a higher evaporation enthalpy than solvents. Therefore, drying water-based coatings requires the supply of higher quantities of energy and, as a rule, takes more time.

>> Both the electric and thermal conductivity of water have different dimensions from that of organic solvents. In contrast to solvents, the water used in lacquers does not act as an isolator. For that reason, special criteria have to be met and special factors to be taken into account when developing water-based coatings that are electrostatically sprayable.


An anomaly in viscosity has been found in a number of water-based lacquers inasmuch as viscosity initially only declines slowly after the addition of thinner, then shows a slight rise, before dropping abruptly after further additions of water.

This peculiarity has to be taken into account when diluting the paints so that the viscosity for processing is adjusted correctly. The water used for dilution has to be worked in intensively, too (explosion-protected agitator) in order to achieve an homogeneous mixture. Many of the neutralising agents used possess a certain volatility. When this neutralising agent evaporates, viscosity increases accordingly, i.e. the lacquer gets "thicker". Containers should, therefore, always be well sealed. The pH-value of larger trading units (barrels or containers) should be checked regularly if possible.

 

Facts worth knowing about preparation

Due to their peculiarities in terms of surface tension and wetting of the substrate, it is imperative to ensure a thorough cleansing and degreasing of the object to be coated when using water-based paints. The quality of a coating system depends to a great extent on the surface characteristics at the time of coating. If blasting is not feasible, a chemical pre-treatment should be carried out where possible (e.g . iron phosphating). If such detergent additives are used, it is recommended to follow this with rinsing the surface with fully desalted water  to ensure that no irritating residues remain on the object to be coated.

 

Facts worth knowing about drying behaviour

Water-based paints show a drying behaviour which deviates from the one displayed by conventional systems. It is, therefore, necessary to allow for the physical factors with appropriate drying conditions (time, temperature, speed of air flow, etc.). Great attention should also be paid to the relevant lower and upper working temperatures. As a rough guide, and depending on product properties, a range between +10°C and +30°C can be specified. Higher or lower temperatures may cause problems with overspray absorption, running or film formation.  Humidity has a great influence on drying speed and film formation of water-soluble systems. If humidity is high, drying slows down since the ambient air is already saturated with water vapour. For the reasons named above, forced oven drying at approx. 60 to 100° C. is often recommended to expel the water included in the paint film. If the air is extremely dry, the water is extracted spontaneously which may result in spray particles that are already very dry which then leads to visually "rough" surface. Other effects that may be caused by such fluctuations in humidity include flash rust, loss of gloss, and a reduced resistance against corrosion.

 

Miscellaneous

Attention: Do not place any packaging film between coated parts as this prevents the hard-drying of the paint film. Since water-based paints normally surface-dry very quickly, any delivered drums or storage containers must be kept sealed tightly.  Surface-dried "skin” cannot be dissolved again and will lead to spots on the coated object or to blocked spraying nozzles. Spraying machines, equipment, containers, etc. should be made from rustproof materials such as stainless steel and plastics to prevent corrosion from water-based paints.