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topic 46042

Specific Purpose of UF Membrane in Rinse Tank

A discussion started in 2007 & continuing through 2017 . . .


Q. Here in our plant UF Membrane is in place which separates the Paint and the Permeate. I Know that the Paint is 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 at last 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.
This maybe a simple question but I will happy if some one explains me clearly.

ED-Team leader - SLN_TN, India


A. 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


A. Dear Mr. Narasimhan:

If you are actually running an E-coat 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 separate permeate from the paint and then mix them together. Paint = Permeate + Concentrated Paint = Paint

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

What goes into Permeate 2 tank is clear permeate. What cascades into E-coat 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 component and gets accumulated in the rinse tank.

I hope this explains the E-coat industry first separates the permeate and then allows it back into the E-coat paint.

Gurvin Singh
Coatec India
supporting advertiser
Mohali, Punjab, India
coatec india


A. 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
Birmingham, United Kingdom

March 20, 2008

Q. 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

A. Hi Prasad. I'm neither an e-coat nor a UF expert, but from experience in somewhat analogous cases, it certainly seems that the higher the flow rate the lower the loss of wasted non-deposited paint from the final rinse ... but the more expensive the recovery process. I would also assume that the unrinsed non-deposited paint could cause various problems like rubbing off, staining, etc., if it's really excessive.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

May 21, 2012

Q. Dear Sir,

We are having 85KL capacity CED bath having closed loop with 3 UF rinses - 2 spray and one dip rinse. The UF system is having capacity of 1200 LPM which consumes relatively high electricity (UF system feed pump and chiller load).

For next few months from now, we have very low volume to process for CED coating (10% capacity utilisation) - in the range of 2500 sq.m only. Considering the low volume and high fixed cost for running the UF system, we want to isolate the UF module.

My question to this forum is what are the implications, if we process low volume for CED coating without running the US system? Will it have any issue other that high consumption of CED paint (due to high carry-over)? What will be the effect on bath balancing and if any how to tackle it ?

I kindly request your prompt response, please.

Warm regards,

Daxesh Shah
- Baroda, Gujarat, India

June 2, 2017 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Good day. I am from Mexico. is it possible to use ultrafiltration for paint recovery from rinse bath located after the autophoretic paint?

Gerardo Ruiz
- Mexico city, Mexico

June 2017

A. Hi Gerardo. We appended your question to a thread on a related subject which indicates that the answer is clearly "Yes!" for electrocoated paint. We'll see what people say about autophoretic.


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Ted Mooney, P.E. RET
Pine Beach, New Jersey
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