Dear All,
We have a number of threads related to (various) coatings applications but I decided to start a new thread as it is related to preparation for coating application only.
Recent coatings are more environmentally friendly and based on (I think) water-soluble acrylics or polyurethanes which is great.
However, regardless of the type of coating, there is always a question of how easy/difficult coating application is and the wettability of the used diaphragm film.
A long, long time ago (could be a decade ago
) SY mentioned that corona treatment prior to application of coatings should be beneficial.
SY also said that a corona or plasma treatment could be done using a small Tesla coil.
There are small commercial corona treaters like BD-20AC Lab Corona Treater, however, I'm not prepared to pay $US 1,000 (my wife would kill me).
So before I refurbish my old ESLs, the challenge was to corona treat a sample film.
TAKE 1 - Build and use Tela coil - FAILURE
The idea was to build a small Tesla coil and replace the HV coil load (sphere or doughnut) with something suitable for film treatment - something like a coat-hanger.
So I built this "small" Tesla coil and it was great fun (for my kids) as it produced copious sparks - to be honest, I was a little bit scared, it was also very noisy.
TAKE 2 - Use AC flyback to make a treater - SUCCESS
Build a driver for AC flyback and use a 300mm long 19mm Dia (3/4in) copper pipe as an electrode.
This is a small treater that does 100W at approximately 30kHz and the photos of the unit in action are below.
To my surprise, this treatment's effectiveness exceeded my expectation by a country mile - and I am serious.
I treated an A4 sheet of acetate (from my local craft store) and the difference between the treated and non-treated areas is amazing - refer to the images below.
I used plain filtered water to check and compare the wettability.
CONCLUSION - I will treat all membranes prior to coating for sure. - thanks for the advice SY !!!
The treated section has a uniform film of water over the whole area.
The treater in action (feediing diriver with 20V dc & 5 amps)
We have a number of threads related to (various) coatings applications but I decided to start a new thread as it is related to preparation for coating application only.
Recent coatings are more environmentally friendly and based on (I think) water-soluble acrylics or polyurethanes which is great.
However, regardless of the type of coating, there is always a question of how easy/difficult coating application is and the wettability of the used diaphragm film.
A long, long time ago (could be a decade ago
) SY mentioned that corona treatment prior to application of coatings should be beneficial.SY also said that a corona or plasma treatment could be done using a small Tesla coil.
There are small commercial corona treaters like BD-20AC Lab Corona Treater, however, I'm not prepared to pay $US 1,000 (my wife would kill me).
So before I refurbish my old ESLs, the challenge was to corona treat a sample film.
TAKE 1 - Build and use Tela coil - FAILURE
The idea was to build a small Tesla coil and replace the HV coil load (sphere or doughnut) with something suitable for film treatment - something like a coat-hanger.
So I built this "small" Tesla coil and it was great fun (for my kids) as it produced copious sparks - to be honest, I was a little bit scared, it was also very noisy.
TAKE 2 - Use AC flyback to make a treater - SUCCESS
Build a driver for AC flyback and use a 300mm long 19mm Dia (3/4in) copper pipe as an electrode.
This is a small treater that does 100W at approximately 30kHz and the photos of the unit in action are below.
To my surprise, this treatment's effectiveness exceeded my expectation by a country mile - and I am serious.
I treated an A4 sheet of acetate (from my local craft store) and the difference between the treated and non-treated areas is amazing - refer to the images below.
I used plain filtered water to check and compare the wettability.
CONCLUSION - I will treat all membranes prior to coating for sure. - thanks for the advice SY
!!!The treated section has a uniform film of water over the whole area.
The treater in action (feediing diriver with 20V dc & 5 amps)
Barrier discharge treatment is well known procedure in printing and coating. There is pretreated film as well. This was mentioned here before. There is ready to use device called D'Arsonval used in beauty industry like that
https://www.aliexpress.com/item/2251832674002995.html?sku_id=65663352806&gatewayAdapt=4itemAdapt
Cheers!
https://www.aliexpress.com/item/2251832674002995.html?sku_id=65663352806&gatewayAdapt=4itemAdapt
Cheers!
On a more serious note, thank you for your comments. You are correct, corona treatment has been mentioned on this forum. It is common in the plastics & printing industry.
The effects of corona treatment deteriorate over time, so pre-treated films should be procured with care. Also, a reasonable amount of power is required to achieve surface tensions between 45-50 dynes/cm required for an acceptable wettability of PET.
The AliExpress high frequency facial machine in your link appears under powered for ESL film treatments (or would take a very long time to treat). My little treater electrode (copper pipe) becomes very hot after a couple of minutes of treatment.
Nevertheless, I would be grateful if you point me to a reasonably priced (not more than $100-$200US) corona treater available on Ebay, AliExpress, Amazon, …
Note:
I am not a chemical engineering and don’t have hands-on experience in (industrial) corona treatment. My knowledge is based on general engineering and online educational material and information on Vetaphone, Tantec and Enercon websites.
Regards
The effects of corona treatment deteriorate over time, so pre-treated films should be procured with care. Also, a reasonable amount of power is required to achieve surface tensions between 45-50 dynes/cm required for an acceptable wettability of PET.
The AliExpress high frequency facial machine in your link appears under powered for ESL film treatments (or would take a very long time to treat). My little treater electrode (copper pipe) becomes very hot after a couple of minutes of treatment.
Nevertheless, I would be grateful if you point me to a reasonably priced (not more than $100-$200US) corona treater available on Ebay, AliExpress, Amazon, …
Note:
I am not a chemical engineering and don’t have hands-on experience in (industrial) corona treatment. My knowledge is based on general engineering and online educational material and information on Vetaphone, Tantec and Enercon websites.
Regards
Last edited by a moderator:
This seems to be quite an interesting option and a successful finding - and it might be at the same time an ingenious poor man's corona workaround, but also an everybody's electrical chair clone ... isn't it a bit risky in terms of accidental high voltage exposure, especially when there are kids around?
But despite the risks - could you please detail a bit more about the schematics (input signal generation), the transformer's specification (Voltages / Turns / DIY or Refurbished from a gear? Brand?), and the actual processing (your "user experience" such as application time, how hot in °C is "very hot", what's a "couple" of minutes? ) and the like?
Hi Daihedz,
You are correct, the corona treater voltage and currents are lethal. For that reason I will not provide you with the schematic and I would discourage anyone without a sound understanding of electronic circuits building and using one.
If you are confident in your diy electronic skills, the following description should be sufficient.
1. You will need a dc power supply 25-30V dc and 10A should be good enough. My treater is works well with 20V/5A dc feed.
2. Flyback driver - I started with a function generator & FET buffer for flyback tunning purposes. This was replaced with “el cheapo” ZVS driver (induction heater) from Ebay. It is advertised as 12-30V, 300W max.
I had to modify slightly the driver by adding additional capacitor to tune the ZVS circuit resonance.
3. AC Flyback Transformer
They are difficult to find, majority of flybacks have built-in rectifiers (diodes). I have had no luck using DC flybacks.
4. Electrode & Insulator
I started with a brass foil inside 16mm OD pyrex (glass) tube with 1mm wall thickness. This worked good, but the brass foil required cooling after each 2 minutes of use.
Better (but more dangerous) option is bare copper pipe with 1.5mm thick silicone rubber sheet insulator between the pipe and other electrode (PCB board or sheet of thin aluminium). Refer the images in my previous post.
5. Corona Treater Tuning
My AC flyback secondary has inductivity of 420mH. The capacitance between the electrodes is about 40pF, so the resonance is about 39kHz. I don’t know the number of turns on the flyback secondary.
6. Tuning of ZVS driver (= flyback primary)
To get sufficiently high secondary voltage, the primary resonace should be close to 39kHz. I used 8 turns of 18AWG, silicone insulated wire and added one HV capacitor to ZVS to get resonance around 38-39kHz.
7. I start with 13.8v power supply gradually increasing voltage until corona discharge is formed (around 15-16V). The plate electrode is properly grounded and the hot electrode (copper tube) is fixed to a PVC conduit. The process generates a fair bit of ozone, so the workplace should be well ventilated.
I have a video clip of the above operation, will try to zip and attach it to my next post. I will also measure the copper electrode temperature increase after 1 and 2 minutes of operation. One slow pass 1.2m/min of 300mm wide strip should me adequate treatment for an ESL membrane.
Regards
You are correct, the corona treater voltage and currents are lethal. For that reason I will not provide you with the schematic and I would discourage anyone without a sound understanding of electronic circuits building and using one.
If you are confident in your diy electronic skills, the following description should be sufficient.
1. You will need a dc power supply 25-30V dc and 10A should be good enough. My treater is works well with 20V/5A dc feed.
2. Flyback driver - I started with a function generator & FET buffer for flyback tunning purposes. This was replaced with “el cheapo” ZVS driver (induction heater) from Ebay. It is advertised as 12-30V, 300W max.
I had to modify slightly the driver by adding additional capacitor to tune the ZVS circuit resonance.
3. AC Flyback Transformer
They are difficult to find, majority of flybacks have built-in rectifiers (diodes). I have had no luck using DC flybacks.
4. Electrode & Insulator
I started with a brass foil inside 16mm OD pyrex (glass) tube with 1mm wall thickness. This worked good, but the brass foil required cooling after each 2 minutes of use.
Better (but more dangerous) option is bare copper pipe with 1.5mm thick silicone rubber sheet insulator between the pipe and other electrode (PCB board or sheet of thin aluminium). Refer the images in my previous post.
5. Corona Treater Tuning
My AC flyback secondary has inductivity of 420mH. The capacitance between the electrodes is about 40pF, so the resonance is about 39kHz. I don’t know the number of turns on the flyback secondary.
6. Tuning of ZVS driver (= flyback primary)
To get sufficiently high secondary voltage, the primary resonace should be close to 39kHz. I used 8 turns of 18AWG, silicone insulated wire and added one HV capacitor to ZVS to get resonance around 38-39kHz.
7. I start with 13.8v power supply gradually increasing voltage until corona discharge is formed (around 15-16V). The plate electrode is properly grounded and the hot electrode (copper tube) is fixed to a PVC conduit. The process generates a fair bit of ozone, so the workplace should be well ventilated.
I have a video clip of the above operation, will try to zip and attach it to my next post. I will also measure the copper electrode temperature increase after 1 and 2 minutes of operation. One slow pass 1.2m/min of 300mm wide strip should me adequate treatment for an ESL membrane.
Regards
Last edited by a moderator:
Look,
barrier discharge does produce ozone, which is highly toxic substance besides burning/oxidizing everything on the way.
Luckily enough it decomposes @ 52 C almost completely. In regard to process I may not be of good source cause I did ozone generator for water purification. BTW @ power you mentioned ozone production could be half an ounce per hour.
Beware... well ventilated area.
I would suggest isolator over electrode like thin wall glass tube to prevent breakdown per say so current stays only as displacement one.
barrier discharge does produce ozone, which is highly toxic substance besides burning/oxidizing everything on the way.
Luckily enough it decomposes @ 52 C almost completely. In regard to process I may not be of good source cause I did ozone generator for water purification. BTW @ power you mentioned ozone production could be half an ounce per hour.
Beware... well ventilated area.
I would suggest isolator over electrode like thin wall glass tube to prevent breakdown per say so current stays only as displacement one.
Hi Daihedz,,
My posts appear quite long, so I'll try to be short.
Photo of the copper electrode during the temperature test.
Thermal image before the test (electrode is at 22.4 degC) so lets say aboyt 20 debC
Thermal image after 60 seconds of treatment (electrode is at 41.3 deg C) so let's say the temperature rise is 20 deg C /min
This correlates well with 60 deg C after 2 minutes (which is ok to touch but too hot to hold)
Regards
My posts appear quite long, so I'll try to be short.
Photo of the copper electrode during the temperature test.
Thermal image before the test (electrode is at 22.4 degC) so lets say aboyt 20 debC
Thermal image after 60 seconds of treatment (electrode is at 41.3 deg C) so let's say the temperature rise is 20 deg C /min
This correlates well with 60 deg C after 2 minutes (which is ok to touch but too hot to hold)
Regards
Hi Alexberg,
My first prototype has a brass foil electrode inside a pyrex (borosilicate) glass tube.
The glass tube is a great electrical insulator, but also a great thermal insulator.
The brass electrode would require active cooling (small blower).
Something like blowing cold air into a silicone hose connected to one side of the pyrex tube.
Prototype Photo
Prototype Working
Also, could you please elaborate on "to prevent breakdown per say so current stays only as displacement one"
I don't really understand what are you saying there.
To those who want to replicate all or part of the above - if you have not had experience with high voltage (few kilovolts) do not do it, period. For the smarty ones who aware of a skin effect - you never know where nerves are going through body of yours and even then HF burns are quite nasty.
Be aware that i speak only from my experience - so it's not the ultimate truth.
Displacement current is the AC though the capacitor i.e. Ic=C*dUc/dt. Tube being one electrode grounded piece under working piece yet another. In between you have dielectric. In total a capacitor is formed.
My concern is breakdown of the film and occurrence of ark discharge which would make holes if additional insulator (besides air) is absent. As far as science says in case with solid insulator second capacitor plate is formed by tiny water/inpurity spots on the insulator(glass). Those small "plates" are being charged by aforementioned current and when voltage gradient becomes high enough discharge into air. Single charge is small and dicharge stops as soon as former is depleted. Making really nice pinkish glow. It is not the case with bare electrode where film itself (and the air) is the only barrier. I hat eto look for a book and provide you with exact quote but the ways dicsharge is formed are different for bare and insulated electrodes.
In regard to heating - yep it will. That said pyrex is quite durable - look at vaccum tubes and chemical glassware. Same goes for kapton tape you are using. In real life even quartz tube does not last long... I doubt it will melt the copper though.
I've been under impression that most membranes are just few feet long and there's no need to treat it in advance - it looks good enough.
Cheers!
Be aware that i speak only from my experience - so it's not the ultimate truth.
Displacement current is the AC though the capacitor i.e. Ic=C*dUc/dt. Tube being one electrode grounded piece under working piece yet another. In between you have dielectric. In total a capacitor is formed.
My concern is breakdown of the film and occurrence of ark discharge which would make holes if additional insulator (besides air) is absent. As far as science says in case with solid insulator second capacitor plate is formed by tiny water/inpurity spots on the insulator(glass). Those small "plates" are being charged by aforementioned current and when voltage gradient becomes high enough discharge into air. Single charge is small and dicharge stops as soon as former is depleted. Making really nice pinkish glow. It is not the case with bare electrode where film itself (and the air) is the only barrier. I hat eto look for a book and provide you with exact quote but the ways dicsharge is formed are different for bare and insulated electrodes.
In regard to heating - yep it will. That said pyrex is quite durable - look at vaccum tubes and chemical glassware. Same goes for kapton tape you are using. In real life even quartz tube does not last long... I doubt it will melt the copper though.
I've been under impression that most membranes are just few feet long and there's no need to treat it in advance - it looks good enough.
Cheers!
I like your iterative process and the gear you built. Sincere congratulations, and I think you had a lot of fun doing so. And also the moistening result seems very evident, such as the the even corona discharge under the copper rod. And thank you for your very illustrative FLIR images.
For me, reasonable boils down to "providing enough power to treat PET while sparing human lives in case of uintentional contacts". Did your failed tesla coil eventually deliver not enough energy instead? And finally, what would then seem to be the best compromise approach in order to be on the safe side and on the effective side all at the same time?
For me, reasonable boils down to "providing enough power to treat PET while sparing human lives in case of uintentional contacts". Did your failed tesla coil eventually deliver not enough energy instead? And finally, what would then seem to be the best compromise approach in order to be on the safe side and on the effective side all at the same time?
Hi Daihedz,
The Tesla coil I built was an old fashioned type with a non-electronic neon light transformer (7.5kV) as feed and a spark gap. It was way to much to handle, big, very heavy, with huge arcs - as I said it was fun for my kids (btw my kids are 30 and 27 years old 😂 and refused to even hold a fluo tube in poroximity of the secondary coil 😁).
The current corona treater with ZVS driver being fed 20V at 5A works great when I move the electrode approximately 1m/min (approx 15mm/sec). I will revert back to a Pyrex protected “live” electrode and grounded aluminium sheet as other electrode (as sugested by Alexberg). The Pyrex tube has 1.5mm thick wall which should ensure a breakdown FOS of 5-6. This way the HV section of the circuit will be fully contained / isolated.
One minute of treatment should be good for approximately two ESL63 panels. After that, I can take a short break to cool the Pyrex electrode.
And finally, I have to concur with Alexberg - simply don’t do it if you have no experience with high voltage RF. The voltages AND currents produced by the AC Flyback are lethal !!!
Regards
The Tesla coil I built was an old fashioned type with a non-electronic neon light transformer (7.5kV) as feed and a spark gap. It was way to much to handle, big, very heavy, with huge arcs - as I said it was fun for my kids (btw my kids are 30 and 27 years old 😂 and refused to even hold a fluo tube in poroximity of the secondary coil 😁).
The current corona treater with ZVS driver being fed 20V at 5A works great when I move the electrode approximately 1m/min (approx 15mm/sec). I will revert back to a Pyrex protected “live” electrode and grounded aluminium sheet as other electrode (as sugested by Alexberg). The Pyrex tube has 1.5mm thick wall which should ensure a breakdown FOS of 5-6. This way the HV section of the circuit will be fully contained / isolated.
One minute of treatment should be good for approximately two ESL63 panels. After that, I can take a short break to cool the Pyrex electrode.
And finally, I have to concur with Alexberg - simply don’t do it if you have no experience with high voltage RF. The voltages AND currents produced by the AC Flyback are lethal !!!
Regards
Hi,
coincidence gg I just received my same ZVS plus HV-transformer last week.
Just bent two wires into a Jacobs ladder for tests and some fun. Got sparks of easily 10cm+ @20V/10A.
My thoughts were going into using a Jacobs ladder stile electrode and compressed air for a blown cold plasma.
The problem I wanted to circumvent is a too hot corona.
Your Flir pics seem to indicate though that the corona is not burning so hot to fry the plastic.
Have You tried treating thin PET film yet?
If Your design is suitable for thin film treatment it certainly appears to be a smarter solution that also seems to allow for very even and quite fast treatment procedures.
jauu
Calvin
coincidence gg I just received my same ZVS plus HV-transformer last week.
Just bent two wires into a Jacobs ladder for tests and some fun. Got sparks of easily 10cm+ @20V/10A.
My thoughts were going into using a Jacobs ladder stile electrode and compressed air for a blown cold plasma.
The problem I wanted to circumvent is a too hot corona.
Your Flir pics seem to indicate though that the corona is not burning so hot to fry the plastic.
Have You tried treating thin PET film yet?
If Your design is suitable for thin film treatment it certainly appears to be a smarter solution that also seems to allow for very even and quite fast treatment procedures.
jauu
Calvin
Calvin, corona is not that hot, but the single discharge may be, otherwise what is glowing all about. It all depend on power density. In ozone production you need to have cooled electrodes and rather high flow rate. I've stumbled on articles here and there - basically you need a smooth cylinder over which film is moved under some tension. This way film is basically pressed to massive cold metal piece thus the former will not burn. I suspect something similar is done during metallization of film for capacitors even polypropylene by sputtering of aluminum in vacuum. Anyhow I do know few people who used D'Arsonval with good results being not that proficient in the art and perhaps having more patience or persistence.
https://www.researchgate.net/public...former/link/0922b4f830cf4dcea7000000/download
Cheers!
Alex
https://www.researchgate.net/public...former/link/0922b4f830cf4dcea7000000/download
Cheers!
Alex
Found something in this link:
Maybe a $100 12kV neon transfomer would do the job?
Another question: Is there anything known about the long-term adherence/stability of the coating on pre-treated mylar? Is it better, equal or worse than on a non-treated film? If it was substantially better, then such a pre-treatment might make some sense to me. In any other case, the risk-vs.-benefit analyis seems negative to me.
Another, quite subversive question - what is that excersise good for in practical terms? When reworking my ESL63's, moisting while coating non-pretreated-off-the-shelf mylar with the ERAudio-coating liquid was no problem at all. The best possible applicator for even results turned out to be a handheld bit of melamine foam, bought as a bit of stain remover. Maybe the very slight abrasive character of this melamine contributed to the near-perfect result. But I have to admit: Cowardly handling a bit of household stain remover sponge is certainly less spectacular than taming misteriously glowing, eery coronas as a bold tech hero ...
Maybe a $100 12kV neon transfomer would do the job?
Another question: Is there anything known about the long-term adherence/stability of the coating on pre-treated mylar? Is it better, equal or worse than on a non-treated film? If it was substantially better, then such a pre-treatment might make some sense to me. In any other case, the risk-vs.-benefit analyis seems negative to me.
Another, quite subversive question - what is that excersise good for in practical terms? When reworking my ESL63's, moisting while coating non-pretreated-off-the-shelf mylar with the ERAudio-coating liquid was no problem at all. The best possible applicator for even results turned out to be a handheld bit of melamine foam, bought as a bit of stain remover. Maybe the very slight abrasive character of this melamine contributed to the near-perfect result. But I have to admit: Cowardly handling a bit of household stain remover sponge is certainly less spectacular than taming misteriously glowing, eery coronas as a bold tech hero ...
Hi Daihedz,
I don’t consider myself “a bold tech hero” by any strech of imagination. In my younger days I was an active radio-amateur and built VHF tranceivers and transmitters. Smaller ones were with PL509’s and some had large jar size transmission tubes. During that period I developed a healthy appreciaion of HF/HV and developed a habit of checking and testing these circuits in rubber sole shoes with one hand safely in my pocket 😉.
This corona treater can be leathal just as many Tesla coil drivers available on Amazon, Ebay and AliExpress. However, when I revert back to a Pyrex enclosed “hot electrode” , with properly rated enclosures & cables it will be a reasonably safe piece of kit.
About 20 years ago I built ER Audio’s ESL III and I was frustrated with coating application (significant beading). I was so frustrated that I contacted Sheldon Stokes regarding his Tin Oxide coating formulation. Shortly after, Techspray produced Licron sprays (first tin oxide variant and then Crystal) which I find convenient to store & use. Rob has obviousy improved the formulation of his coating(s) in recent years.
This time I would like to be 100% sure that my membrane coating is well applieed and durable.
Calvin
In regard to the Calvin’s question, I have tried corona tratment of PET film with my first prototype (Pyrex enclosed electrode) - it works great. No problims with heat at all - this type of corona is treated as “cold flame”. I haven’t tried the exposed copper pipe because PET is very prone to tears and I have not polished the copper pipe to remove the ends cut burr’s.
Alexberg
Thanks for your explanation, now I understand your concerns. A single spark would certainly burn a hole (or multiple holes) in the film and make the use of corona treatment counter productive. I would never consider using my treater wih a membrane film only between bare electrodes. With the exposed copper pipe electrode there is a sheet of 1.5mm thick silicone rubber on the top of grounded PCB sheet electrode.
The electric breakdown of either Pyrex or silicone rubber (1.5mm thick both) are multiple times higher than my (estimated) flyback secondary output. I will measure the actual output as soon as I build a HV scope probe - again I can’t afford a Tectronix HV scope probe. HP 34111A 40kV probe that I have is good only between DC and up to 200-300Hz max.