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  1. #1
    hrst's Avatar
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    Corona discharge polyester subbing

    I have now built a working corona discharge unit in order to try subbing polyester (PET) sheets, to prevent the emulsion from loosening during processing.

    It consists of 24V DC supply, a HV source made from flyback transformer (from color CRT television), one power transistor and two resistors. Transistor's base current is taken from feedback winding and it starts to oscillate, generating 5 kV voltage (measured at 0.6 mA current). The complete unit also contains a meter for current (0 - 1 mA).

    High voltage + is then fed to a corona wire taken from a copier, and ground is connected to a copper plate under the corona wire.

    A PET sheet is placed on the ground plate. Push-button is pressed to enable HV, and then you drag the sheet.

    This seems to work: the sheet is heavily attracted by the ground plate and it needs much force to drag the sheet, when the button is pressed. During this, unit produces quite loud hiss noise from corona discharge and draws HV current of 0.2 mA, making the total corona power of 1 Watt at 5 kV. And a familiar ozone smell like with copiers & laser printers.

    I made some coatings on corona-charged sheets. I coated them in a few minutes after coronizing. I will post the results in a few days after they have dried&hardened so I can try to process them.

    I attached some images of this cool unit .
    Attached Thumbnails Attached Thumbnails corona-apug-1.jpg   corona-apug-2.jpg   corona-apug-3.jpg  

  2. #2

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    Well done! Unit looks great. Please keep us informed of how well it works.

    Did you do a test of coating using the corona discharge preparation versus coating without the preparation?

    You have set me thinking of alternative High Voltage sources that are readily available.
    -Neon sign transformer with a rectifier on the output. (5-30kV).
    -A car ignition coil with a driver circuit
    -A corona module from an older scrapped photocopier. (The one I have is 5kV)

    Emulsion.

    Quote Originally Posted by hrst View Post
    I have now built a working corona discharge unit in order to try subbing polyester (PET) sheets, to prevent the emulsion from loosening during processing.

    It consists of 24V DC supply, a HV source made from flyback transformer (from color CRT television), one power transistor and two resistors. Transistor's base current is taken from feedback winding and it starts to oscillate, generating 5 kV voltage (measured at 0.6 mA current). The complete unit also contains a meter for current (0 - 1 mA).

    High voltage + is then fed to a corona wire taken from a copier, and ground is connected to a copper plate under the corona wire.

    A PET sheet is placed on the ground plate. Push-button is pressed to enable HV, and then you drag the sheet.

    This seems to work: the sheet is heavily attracted by the ground plate and it needs much force to drag the sheet, when the button is pressed. During this, unit produces quite loud hiss noise from corona discharge and draws HV current of 0.2 mA, making the total corona power of 1 Watt at 5 kV. And a familiar ozone smell like with copiers & laser printers.

    I made some coatings on corona-charged sheets. I coated them in a few minutes after coronizing. I will post the results in a few days after they have dried&hardened so I can try to process them.

    I attached some images of this cool unit .

  3. #3
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    What you have to do for "proof of concept" is to coat on a sheet of the film before discharge and on a sheet after discharge. These both have to be identical coatings. Then you have to demonstrate the adhesion properties of one vs the other. This proves that the sheet "before" did not have some property that enabled the coating process.

    Very good work.

    PE

  4. #4
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    I coated one sheet which I coronized only for the lower half. This should allow me to compare with the same coating.

    In addition, I have coated about 3-4 or more these very same A4 PET sheets before, with same emulsion and same coating blade, and every time the emulsion has started to loosen at least at the edges, after 2-5 minutes of processing. If this seems to stick, I'll process longer and longer. If it survives a longer-than-normal process with vigorous agitation then it's probably okay. That will be my test.

    If it doesn't work, then I'll try to rise the voltage. The current design can give at least 8 kV. It's possible to do but the risk of arcing will become higher.

    My coatings still need to improve, though. Our last emulsion (the one that fogged, good for practicing though) is also way too dilute and thus hard to coat. (Of course I could add gelatin.)

    Emulsion, thanks for list of HV sources; In fact, if this works, I think that the whole unit can be found in a photocopier or laser printer; just remove the melting unit and toner unit and you have a complete product! But that would have been too easy, I had to construct something .

  5. #5

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    How about a photo of it running with the room lights turned down low so we can see the glow?!
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  6. #6
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    Failure!!

    The two identical coatings, one with corona discharge and one without, both started loosening after 5 minutes of processing. Loosening looks very identical in both samples.

    Coating thickness doesn't seem to affect much. Thin coating took 1 minute to diffuse thoroughly (darkened from the base side in developer), and thicker took 5 minutes to diffuse, but both started loosening at the same time, after 5 mins.

    But what's even more interesting, I made another coating so that I dragged the PET base four times through the coronizer. When I did this, the first time I needed much force to drag, the second time was much easier and the two last times it went through without any force. After this, I could feel the static electricity. BUT! This coating had loosened completely already during drying, which is quite interesting!

    Currently I'm giving positive corona discharge (meaning that the corona wire has the positive voltage), side to be coated facing the corona wire. Maybe I should try changing the polarity? Or then again, I could rise the voltage to give stronger corona discharge. I can't even see any glow even in dark now.

  7. #7
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    Look at some of the Kodak patents. They may have more specific information. I'm sorry I can't help, but this was way outside of my field of work.

    PE

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    Goodby R-O-O-O-SIE, Queen of Corona !
    Sorry! But when the Spirit moves me, I godda let go.
    Bill

  9. #9
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    Just an idea transposed from a process I did many years ago. What would happen if you abraded the sheet with something like diatomaceous earth. I used something similar on plastic sheet but the material I was coating was solvent based with a water base photo resist on top. It worked very well.
    Richard

    Why are there no speaker jacks on a stereo camera?

  10. #10
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    Richard;

    This should not be needed. The corona discharge, if done properly, (right polarity and voltage) will do the trick all on its own.

    PE

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