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topic 23047

Reduce paint thickness in Cathodic Electrodeposition (CED) system?

adv.    coatec india banner

A discussion started in 2003 but continuing through 2018

2003

Q. I'm working on a cathodic electrodeposition (CED) project. Currently I'm getting paint thickness in the range of 25-32 microns.I want to reduce this thickness up to 18-20 microns.

ACRONYMS:

NVM = non-volatile material

CED bath parameters : pH 5.90-6.10 Conductivity 960 micro Siemens. Temp 28-30 °C NVM(% solids) 9.43 % P/B (pigment binder ratio) 0.10 Voltage 160 V Anolyte conductivity 2500 micro Siemens I have five ways to reduce the thickness:

a. By reducing the bath conductivity
b. By reducing the anolyte conductivity.
c. By reducing the NVM.
d By reducing the voltage/current.
e. By reducing the dipping time in CED bath.

I can't reduce the dipping time in bath as I have some restriction. I can't reduce the anolyte conductivity as on reducing this fungus/bacterial growth is taking place. I can't reduce the NVM as it is already on lower side (standard is 12-14 %). My bath conductivity is already on lower side but still thickness is not coming low. I'm operating at 140 V though my standard is of 250-300 V. Please suggest how I can reduce the thickness.

Manish C [last name deleted for privacy by Editor]
- New Delhi, New Delhi, India


simultaneous 2003

A. Manish,

ACRONYMS:

DI = de-ionized

Please check the pH is per your supplier's standard. Please check that the conductivity conforms to prescribed levels per supplier data sheet. Are you running an Ultrafilter and replacing the discharged permeate with DI water of 5 micro Siemens conductivity? Are the solids as prescribed?

Since we do not have an idea of the proprietary process you are using, some of these suggestions may validate the process. Hope this helps.

Regards,

asif_nurie
Asif Nurie
- New Delhi, India

With deep regret we
sadly advise that
Asif passed away

on Jan 24, 2016



2003

A. I have used electrophoretic paint in the past and found that the thickness of the cathodic electrodeposit could be controlled by either the temperature or the voltage. Changing the bath chemistry is not a wise way to proceed because you are altering an established system and unless you know exactly what you are doing, you will cause a lot of future problems. The deposition thickness is related to the bath temperature, so by reducing this and keeping all other properties constant you will reduce the thickness. The systems I have worked on are quiet sensitive to temperature, so only modest changes will alter the thickness. Alternatively, reduce the voltage; this will also reduce the thickness. I do not know what you mean by operating at 140 V although the "standard is 250-300 V", so perhaps you can elucidate. Finally, if these two changes do not reduce the thickness to your needs, you have to reduce the processing time. Assuming your system is similar to the one I have used, there is no point in reducing the current because this automatically reduces to a very low value as the deposit thickens.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


2003

thumbs up sign Dear Asif,
Thanks for your valuable suggestions. I'm running an ultrafiltration unit and also using DI water of < 5 microsiemens conductivity. pH is in the supplier's range(5.10-6.10), but still I'm not able to reduce the thickness. I'm working with the latest CED technology . Our system is the latest one. We have four ways to reduce the thickness in CED system and which I have described in my previous query and I have tried all except reduction in dipping time. I can't go for this option. I hope that you will further give your valuable suggestions to me.
Thanking you.

Dear Trevor,
Thanks for your valuable suggestions. Yes I am using the same system that you are using there. I am using the latest CED system which is used everywhere in this world. So assume that it's the same as you have. Yes it's true that standard voltage requirement is 230-250 volts but I'm operating at 160 V because I thought it will help me in reducing the thickness. It's also true that my trial can damage our system and can create future problems but I love to do trial because without trial we cannot come to a conclusion.
As far as temperature is concerned our standard is 28-30° C. and I have reduced it to 27 from 30 but still the thickness is coming high and I am surprised that at lower voltage (140 V), low NVM(9.41 %) and low conductivity (960 ms), I am getting high thickness (26-32 microns). Let me reduce the temperature to 25 °C. and then see what happens. Thanks again for your suggestion.

Regards,

Manish C [returning]
- New Delhi, India


2003

A. If you are unable to control the thickness, the problem may lie elsewhere. You need to check if the voltage displayed is the same as the voltage applied on the component.

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


2003

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A. Dear friend,

In my opinion may the conductivity of ED bath is too low. Because I have the opposite problems from you. Since I want to raise the thickness (now is about 20 micron) but the only difference parameter was conductivity of ED Bath whereas too high in mine.

The data parameter from my process are :

1.NV 14.67%
2.Coating voltage is 140 V (range 80 to 160 V)
3.pH is 6.25 (range from 5.9 to 6.3)
4.Conductivity is about 1545 micro Siemens/cm. (standard is 1100 to 1400).
5.Ratio F1 to F2 is 1:10

I also used the latest technology of ED Paint, which is Acrylic CED-Lead Free

Henry S [last name deleted for privacy by Editor]
- Jakarta, Indonesia


2007

A. Dear Mr.Manish,

I understand your problem.

ACRONYMS:

DFT = dry film thickness

You want to control the outer DFT without disturbing any line condition.
In this case you can cover the anode cells simply with the PVC pipe of good quality (Quality in the sense of Good Chemical Resistance).
After doing this definitely you will get reduction of 6 to 8 µ DFT.
Your throw power will not affect after doing this (Kindly check up with the paint supplier).

regards,

Amar Koppa
paints - Pune


May 23, 2008

A. Dear Manish,

One other way of reducing the DFT of your EDP is in choosing mineral fillers with a very fine particle size, good dispersion properties and good flow properties. It often happens that due to cost reasons, producers change the mineral filler included in the original formulation to a cheaper grade locally available. In this case, many properties of the EDP - including the DFT - are getting worse.
Especially the dispersion behavior of the fillers affect the DFT very much. If the filler is not dispersed properly, you will find agglomerates that are actually much larger than the original particle size of the filler. Also the flow properties are affected negatively by a bad dispersion.
There are only very few mineral fillers that are working properly in EDP systems, one I know is called Sillitin.

Best Regards
Christian

Christian Plein
- Neuburg, Germany


June 29, 2008

A. Dear Manish,
I feel sorry to say that the CED you are using have very low rupture limit. Generally rupture limit of CED is more the equal to 350 volt. Nobody can help you; just change the paint supplier.

Alam Farrukh
- Lahore Pakistan


March 9, 2009

A. Dear Manish

Please check the Solvent level of the bath and co relate with the production trend You may be feeding the bath in the higher rate , that means your bath will be fresh and that's why you are getting high DFT.

This is the same problem I observed in my line . I reduced Solvent level.Drained permeate at regular frequency to Keep the DFT and Finish in good condition.

Thanks

Srinivasan

T. Srinivasan
- Chennai, India


December 10, 2008

A. Dear
Please check the applied voltage which is shown by the rectifier & increase the bath conductivity ,reducing the bath temp.

thanks,

Kuldeep Yadav
- Gurgao, India


April 9, 2009

A. You did not write about the number of anode cells and type of anode cells. However, reduce the number of anodes, or cover the membrane from bottom side.

DINESH MAURYA
- jamshedpur, India


December 11, 2009

A. How to reduce Dry Film Thickness?: there are several way to reduce DFT --
1. Decrease applied voltage.
2. Increase of MeQ (milliequivalents) value by adding pH adjuster.
3. Purge of permeate to reduce solvent content.
4. For CED line that have high turn over set MeQ value in maximum specification.
5. Increase conductivity of anolyte tank, it will up MeQ value.

Regards

S Ricardo
- Bekasi, Indonesia


May 20, 2010

A. Dear Manish,

You please reduce your anode no. or Reduce solvent level is only way to reduce DFT. You should must ask your supplier for that. If you will use Sixth generation CED Paint Your problem will resolve.

Ankush shukla
- Ghaziabad, India


August 5, 2010

A. Dear Manish,
Please check calibration of displays & DFT meter etc, then change any variable one by one and note the impact/ results. The change should be economical, not increase the wastage of energy or material. Following steps may help you to overcome this problem:

1: Conductivity of Anolyte seems to be very high as 2500 micro Siemens; decrease gradually as 2400-2300-2200.......
2: Reduce the solvent percentage;
3: Although it may not possible to reduce the dip time in your system but my suggestion is to reduce the dip time any way; will save the cost & energy and also help to reduce the ED thickness.
4: The concentration of electrodes are higher than dipped body area. Reduce the electrode quantity and increase the distance in between the electrodes.
Hope you will post the result of successful measure you have taken so far.
Regards,

Faiz-ur-Rehman
- Karachi, Pakistan


September 25, 2010

A. Dear Manish,
At such parameters still you are getting high DFT, so please check Anode:Cathode it around 1:4 if it's less than this then increase it with isolating/disconnecting some anode.

Sambhaji Godase
- Pune, India


October 31, 2010

A. Dear Manish
You should check these points to reduce the DFT of your component.
1)What is the Anode : cathode ratio
2) You should cover the bottom portion of anode with pvc .
3) You should increase the P/b Ratio of your system.
4) you should check the Actual current and voltage and ramp up time for your system.

Regards
Ravi

Ravi B
- Bareilly, Uttar Pradesh, India


January 19, 2011

A. Dear,

Please note how much time taken to reach maximum DFT, then after cut down the half of the deposition time without changing any bath parameter. you will get lower DFT if not cut it another half. Generally, DFT depends upon deposition time, voltage, micelle size and surface charge ratio.

Raju shukla
- sivassa, india


May 29, 2012

A. Dear all,
To reduce dry film thickness we must concentrate on voltage (280-320), process time (120-130 secs), pH (5.8 to 6.0), conductivity(1200-1600), Meq-24to28, NVM-18 to 22, anolyte conductivity- 500 to 700, voltage rampup time has been separated to 3 stages (10,5,5), hold on (30,25,55), solvent%- 1 to 2

Mohan Ramanujam
- Chennai, India


July 29, 2013

A. Dear Manish,
Increase the P/B ratio and change the permeate water (25% permeate in two days time and do this step in four times).

Basha Mohamed
- Chennai, Kanchipuram, India


July 16, 2014

A. Dear Mr. Manish,

Please check the Bacteria contamination or growth in CED bath, bacteria growth can lead to higher deposition.

ARIJIT DAS
- Jamshedpur, Jharkhand


April 2, 2015

A. Mr.Manish,

I understand your parameters and I suggest you reduce the pH to 5.70 from 5.90~6.10 for reducing thickness ... because pH range is 5.10 to 6.10. So you can maintain pH within 5.50~5.70. It helps to reduce the thickness of the component. I tried many times and got results: low pH can build low DFT.

Kumaravelu Subramanian
- Chennai,Tamilnadu,India


March 17, 2017

A. Please check the solvent level (flow controller) of the tank and circulation rate for smooth CED coating and bubble free.

Ajay Kumar singh
Force motors Ltd - Indore MP India


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