Liquid light and Screenprinting

Discussion in 'Alternative Processes' started by AlexG, Nov 6, 2009.

  1. AlexG

    AlexG Member

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    I've been wanting to get into screenprinting for a while. When you do this process, an image must be projected onto a screen that has a photo-sensitive emulsion on it to create the inking mask. After reading a few online manuals, it looks like the printers are using a Liquid Light type emulsion to put on the screen to create the masks.

    Anyways, Could I use liquid light to make the masks?...or do I have to go out and buy a special emulsion mix made specially for screenprinting?

    Does anyone have experience with any of this?

    Alex
     
  2. nick mulder

    nick mulder Subscriber

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    Liquid light no, it will be too thin - special emulsion yes ...

    If you're interested in home brewing I think the process its most akin to would be Gum Bichromate.
     
  3. hrst

    hrst Member

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    In screen printing you use an emulsion that hardens in UV light. Then you contact print a very high-contrast film using a bright UV light. Then the mask is washed with strong water spray. Unhardened emulsion will loosen from the screen, leaving a positive mask.
     
  4. Ian Grant

    Ian Grant Subscriber

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    You can use an emulsion like Liquid Light for screen printing if you use the etch-bleach process. Back in the 70's when I dealt with Rockland Colloids they sold a specific enalarger speed emulsion for screen printing, Normally the screen is made of a dichromated gelatin or polymer layer that hardens with the action of UV light.

    I used the etch-bleach process commercially for a few years, it's great with RC papers, and also tried it with screen prints using the silver bromide emulsion my company manufactured, but we decided not to pursue screen printing.

    Ian
     
  5. Steve Smith

    Steve Smith Member

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  6. Ian Grant

    Ian Grant Subscriber

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    Steve, it's not common now but there were Photo-emulsions made for screen printing by enlargement, I think they never really took off because most Screen print companies didn't have the equipment or skills need.

    You're right PVA/Bichromate emulsions tend to be used now but Gelatin/Bichromate used to work just as well.

    Ian
     
  7. Steve Smith

    Steve Smith Member

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    I have never heard of those. Do you mean that the screen is positioned in place of the paper in an enlarger type of arrangement?

    This would be very tricky for us as we run to a print tolerance of +/-0.25mm and have to register prints to each other. Typically four for conductive circuits and around four to ten for graphic layers. We manufacturer flexible circuits, membrane switches and medical sensors on polyester substrate.

    http://www.parlex.com/products/ptf.php

    Stencil emulsion choice depends on the type of ink being used. Some emulsions can be removed with water and these are fine for solvent inks but we are increasingly moving over to UV cured inks which need a waterproof emulsion.


    Steve.
     
  8. Steve Smith

    Steve Smith Member

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    To answer your original question, the usual method is to have the artwork on a film. Clear areas of the film will result in solid stencil and black areas of the film will result in washed out clear areas of the stencil. Therefore the artwork is a positive image.

    It is generally contact printed to the rear of the screen and exposed to ultra violet light. This hardens the areas where the light shines through and allows the areas which were covered by black (i.e. got no UV light) to be able to be washed out. This creates a stencil with clear areas to print the ink through.


    Steve.
     
  9. AlexG

    AlexG Member

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    Yarrrrhhhhggg...


    I was hoping to just use stuff found at home, but now its looking like I have to go out and buy some special emulsion mix.

    Anyways Ian, could you shed more light on the etch-bleach process? Those chemicals don't look very hard to acquire and it might always be a possibility.
     
  10. Ian Grant

    Ian Grant Subscriber

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    Yes use under an enlarger with a high contrast line/lith negative. It was aimed at the art world rather than industry, I may still have a Rockland Colloids catalogue/price list from around 1976/7 in the UK with details of their commercial product.

    Your own field is more specialist and while+/-0.25mm sounds a tight tolerance it's nothing in comparison to photo-resists used for micro-chips.

    Ian
     
  11. Rick A

    Rick A Subscriber

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    I picked up a ton of screenprint stuff a couple of years ago thinking it would be fun, and a natural extension of my darkroom work. Now I have a ton of unused screenprint equiptment sitting in my attic. I even bought an 18"x24" repro camera to make my copywork, thats sitting in the basement. Oh well, at least my wife isn't giving me any grief about my toys. Anybody want a giant repro camera?

    Rick
     
  12. Steve Smith

    Steve Smith Member

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    That's true but it is a very tight tolerance when you are trying to cope with screen stretch on an 18" x 24" sheet.

    For really critical work we modify the artwork to compensate and on some machines it's not linear in either direction.


    Steve.
     
  13. Ray Rogers

    Ray Rogers Member

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    There is a nice short how-to outline of the process in a photography book by Michael Lang... something - I don't recall the exact name... perhaps someone will know, otherwise I can go look it up in my library later.

    Perhaps this will be all you need... but you still need the emulsion, and as has been pointed out there are two (basic) types... one orange with dichromate and the other white being a normal photographic emulsion... unfortunately, they are both called "emulsion" and even "photo emulsion", so there is some confusion... Wasn't this process called photolithography?

    Anyway, you might want to have a look at that book....
     
  14. Ray Rogers

    Ray Rogers Member

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  15. glbeas

    glbeas Member

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  16. Ray Rogers

    Ray Rogers Member

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    That seems to be a diazo based material.
    I have never used these processes, but another name that comes to mind is "Ulano" or something like that.

    But come to think of it, the OP said he had seen online manuals, and they were using a "liquid light" type product... yet he then asked if a liquid light type product can be used... (?)!

    Perhaps the OP simply wants to communicate with other people actually doing that processes... I don't, so I will get out of the way.

    Ray
     
  17. Ian Grant

    Ian Grant Subscriber

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    Ray, I suspect the confusion is because screen printers use an emulsion, albeit usually only sensitive to UV light and with no silver, but Rockland Colloids still make PRINTSCREEN which is on the same page as Liquid Light on their website and can be exposed by contact printing a Line neg using a Halogen lamp rather than UV.

    But at one time they did have an enlargement Screen-print emulsion but I don't have any details here, I may have saved the thin Catalogue in the UK.

    Ian
     
  18. Photo Engineer

    Photo Engineer Subscriber

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    There are basically 4 different ways to use these photo systems.

    The Dichromate system, painted on a screen, hardens the gelatin imagewise using UV or daylight for exposure and is developed by a hot water rinse which removes gelatin where exposure did not take place. The remaining image can be used as-is, or it can be inked and used as a resist to allow the inked image to pass through the screen to a reciever. That accounts for two possible methods.

    A silver halide emulsion can be used the same way, coating a screen and when exposed will yield an image on the substrate or screen in this case. But, since silver halide does not harden gelatin unless you use a tanning developer, if you wash with hot water, the image is lost. Therefore you can either harden the gelatin beforehand and then retain the entire image, or you can use a tanning developer to harden the gelatin imagewise to retain only the developed image.

    With the first way here, you cannot pass ink through and it will not act as a resist, only a substrate for the entire image. With the second way, you get a resist with pores created imagewise just as with the dichromate system. All of these methods yield fine images, the differences being exposure time and light type and processing method.

    We used to make 3 or 4 color decals using these methods and printing onto transferrable blank paper decal sheets. We also made multicolor t-shirts this way. That was so long ago, it was back when there was no digital at all! We kept a bolt of cheap fine silk in the shop and several types of cloth as well for achieving the different textures that customers wanted. This used to be a service of some photofinishers back then.

    PE
     
  19. Ian Grant

    Ian Grant Subscriber

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    Your 4 ways misses Etch Bleach Ron (PE) where an image is processed and the developed part of the image removed by the Etch-Bleach which is usually Acetic Acid/Cpper Chloride/Hydrogen Peroxide.

    Ian
     
  20. Photo Engineer

    Photo Engineer Subscriber

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    Well, I should add then that the post refers to the methods I have used. Sorry. I am not even remotely familiar with the method you describe. It must be an archaeological curiosity for you to know about it. :D

    PE
     
  21. Ian Grant

    Ian Grant Subscriber

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    Actually both Ilord & Kentmere published data sheets & formulae for the Etch Bleach process in the 70's, 80's etc until quite recently in the case of Kentmere. It's a wash off relief process usually used in the graphics field. With an RC paper the remaining relief is dyed, sometimes selectively using dyes. Most definitely not an archaic process, but not need in these days of large format digital printer. I'd be surprised if Kodak didn't publish a data sheet on the process, but probably in the Graphic Arts field.

    Etch Bleach also has some more creative uses, as if the bleach is used after development without fixing the remaining image can be re-exposed and re-developed.

    The process will work to make silk screens by enlargement.

    Ian
     
  22. Steve Smith

    Steve Smith Member

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    This thread has started me thinking about getting some screen emulsion coated onto paper to experiment with! I think that if I tape the paper to the underside of a screen, I can get it evenly coated by machine.


    Steve.