Normal Water:-
Normal water is the water which is easily available to us. It can be water which is provided by government/corporation or procured from wells, rivers, canals etc. This water contains many free salts & minerals like Ca(HCO3), CaSO4, MgSO4, CaC12, NaCl, SiO2, this can vary from source to source & place to place. This water may also contain many organic contents like bacteria, Fungi, algae etc. which again can vary.
Distilled Water:-
Distilled water is water that has been boiled in an apparatus & then recondensed in a cooling unit called condenser. Distilling is used to purify water. It might not work if the contaminants are volatile.
Since there is no protection from CO2 dissolving into the distilled water during condensation, the ph is generally acidic (4.5 to 5.0). Additionally you have to be careful not to recontaminate the water after distilling it.
Demineralised or deionized water:-
It’s a process utilizing specially manufactured ion exchange resins which remove ionized salts from water and can theoretically remove 100% of salts. It typically doesn’t remove organic contents, viruses or bacteria except through accidental trapping in resin or strong base anion resins which will remove gram-negative bacteria.
RECOMMENDATION
For water based paints:-
The water which is ideal to be used in water based paints should be free from bacteria or fungi and should have minimal salts (less than 50ppm).
Basics:-
Water based paints tend to degrade, causing foul odour. This is primarily caused by enzymes secreted by bacteria for predigesting the food for them to feed on. Enzymes are polypeptides that are biocatalysts. They do not consume themselves and continue to degrade the material thousands of times. Thus even a very small concentration of enzyme can over a period of time degrade a large volume of material.
Testing:-
It is very difficult to test the water for bacteria or fungi in small scale industry.
So, we recommend that everyone should heat their water to 70⁰C by using solar heaters to deactivate the enzyme and use a suitable biocide, to be on safer side.
Testing for salts:-
Make a 0.1 to 0.3% soap solution in a sample of water which is to be used. If precipitation is noted then the water is not fit to be used and if no precipitation is noted then it is safe to use the water. This is a very crude method of testing and can give false result if the soap contains softeners. Ideally use demineralised water. Water will cost about 4 to 5 paise /litre by using a DM plant with an output of 75 lts. of water/hour, which is not much.
For solvent based paints:-
Solvent based paints are not easily prone for bacterial or fungal attack, so there is no need to boil/heat water.
As far as salts are concerned the recommendation is same as that for water based paints.
PROBLEMS CAUSED BY USE OF IMPROPER WATER.
Gellation:- This problem starts with thickening of water based paints which then worsens into gellation. It is caused due to breaking of emulsion because of excessive salts in water.
Failure of dispersants:- Because of precipitation of the dispersing agent, it fails to disperse the pigment. So more pigment is required to get the desired result.
Unstable Rheology:-
Because thickeners do not perform as expected in presence of salts in water, the rheology of paint becomes unstable.
Problem caused by fungus and bacteria:-
- I)Foul smell
- II)Blackening of paint
III) Paint film deterioration
- IV)Separation of water because of biodegradation of binder
Problem caused by water in solvent based paint
- I)Water separation caused by salts in water which render the additives ineffective
- II)Precipitation of driers by salt in water.
III) Pin holing in the applied film during summers.
- IV)Any regular variation in pH of paint on standing is amplified in presence of water, causing noticeable and sometimes catastrophic problems.
Please note: We have mentioned only problems caused by water, and not those caused because of use of wrong additives for water addition in solvent based paint.
FREQUENTLY ASKED QUESTIONS:-
- We are using water softners like SHMP then why is it necessary to demineralise the water?
Ans: We believe that all water softners have a limited action. They will take care of the problems arising from the water added at user’s end where paint will be consumed early. But they will fail if the paint is stored for a longer duration. So it is wise not to depend on water softners.
- We are using antifungal & biocide preservatives then why is it necessary to heat water?
Ans: Again we believe that all antifungal agents & biocides have a limitation, further they tend to destabilize with temperature and become ineffective. Further the antifungal preservatives/biocides work on the organism but not on enzymes secreted and thus fail to prevent the problems.
- Which additives are ideal for water addition in solvent based paint?
Ans: An ideal additive should have following points
- I)Firstly the additives should not be very costly. But while seeing the cost care should be taken to calculate cost per batch because some additives are cheap but their dosage is high, so eventually they turn out costly batch wise.
- II)Emulsions tend to destabilize. So any additive which is not in emulsion form is recommended.
III) Quality of paint should not be affected. Following points are to be considered
- a)Viscosity of the paints:- some water additives lead to increase in viscosity of the paint on addition of water. This is not ideal as such paints invariably sooner or later tend to have problems associated with water separation which are disastrous.
- b)Shade of paint:- the shade of paint should not change on addition of water. But please note that the comparison should be done after the paint film has dried as a wet film study can be misleading.
- c)Gloss:- the gloss of paint should not be reduced.
- d)Hiding powder: – the hiding powder of paint should not be affected.
- e)Brushablity should be maintained.
- f)Drying time should not increase.
- g)Stability of paint should not be affected.
4) What are the advantages of water addition in solvent based paint?
Ans:- First and the most obvious advantage is reduction in the RMC of paint. Second advantage is that by addition of water we are making the paint more ecofriendly by reducing the % of volatile solvents.
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