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Specific Purpose of UF Membrane [India] 

August 5, 2007

Here in our plant UF Membrane is place which separates the Paint and the Permeate.I Know that the Paint if separated to reduce the Consumption of Paint.
But I have a simple Doubt.The Inlet for the membrane is from the Main Tank which contains Both Paint and Solvent.It is separated by the membrane through Osmosis Process But my Question is The Paint is separated and is delivered to the Main Tank.The Permeate is separated and it is Passed to UF Rinse and again it is cascaded to Main tank when Level Goes Low.
So atlast whatever the paint taken to the Membrane is again taken back to the Tank in Separated condition as Paint and Permeate from Rinses.
What is the Use then since the effect is zero as Paint and Permates comes Back.
Input=Output
This maybe a simple question but I will happy if some one explains me clearly
SLN_TN

Narasimhan
ED-Team leader - India

Dear Mr Narsimhan,
By separating permeate and paint thru UF membrane and using permeate for cascade rinses, you actually form a closed loop which reduces your carry over losses as well as solvent and additive losses.
If you discard the permeate and use fresh water for rinses, then you will loose the solvent and additives in permeate which you will have to add extra in main tank. Also, permeate removes extra paint more effectively than water since it contains these solvents and additives.
Further, cascading brings the paint back to main tank which is carried over to rinses. This saves your paint losses.
Hope the system is clear to you now.

Mangesh Kulkarni
- Pune, INDIA

Dear Mr. Narasimhan:

If you are actually running an Ecoat system, the answer, as given by Mr. Kulkarni will be right in front of you. Allow me to give the same answer using different words.

You seperate permeate from the paint and then mix them togeather. Paint = Permeate + Concentrated Paint = Paint

If you look at your Ecoat system, thep permeate goes into the Permeate rinse 2 tank, cascades into Permeate rinse 1 tank and then finally cascades into the Ecoat tank.

What goes into Permeate 2 tank is clear permeate. What cascades into Ecoat tank is not clear permeate. Instead it is permeate with some solid content. The function of permeate is to recover the paint which goes out of the paint bath along with the compoent and gets accumulated in the rinse tank.

I hope this explains the Ecoat industry first seperates the permeate and then allows it back into the Ecoat paint.

Gurvin Singh Coatec India - Mohali, Punjab, India

Dear Narasimhan,
It is a long time since I was involved with EC (1979) and now I only supply powder coating. However, the basic principles I do not think have change much. The UF Membrane if I am correct is to remove some of the solubilising agent from the tank, which consists of resin, solvent, solubilising and possibly pigment if it is coloured. The ratios of these are finally balanced and if you are to maintain the tank in good working order, these must be kept within certain limits. The solubilising agent if allowed to increase above a certain limit in comparison with the other ingredients would cause the applied wet coating to be removed (washed off) by the demin water rinse. Your lab tests for solids, MEQ's and ph etc should indicate to the person in charge of the plant what is required to keep the tank in balance – more paint, water, less/more solubilising agent.

Terry Hickling Martex Paints Ltd    Birmingham, UK

My question is regarding UF Flow Rate.

1. What are the factors which decide a particular UF Flow rate?
2. What happens to the substrate if the UF flow rate is reduced?

Prasad Bhobe
Paint Shop - Pune