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DIY LED Exposure Unit

5607 Views 9 Replies 4 Participants Last post by  sben763
I am going to build my own exposure unit and upgrade from the old painter light I've been working with.

I purchased a large piece of tempered glass and I'm very interested in using LED's as a lightsource.

I don't see many postings on this. I know I need UV LED's with a range of 360nm to 420nm. I need help selecting the right LED's in terms of wattage and ease to install

Is there anyone out there with experience with this and recommendations on sources for the UV LED's? I would prefer to buy the strips because they seem to be easier to work with.

Thanks for the help.
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There's a post on here about homegrown led exposure units. It has some links and findings.

From what I remember, the undercutting is similar to fluorescents, but they are decent.

I believe single source metal halide is preferable

Make sure your glass is not green. The iron blocks uv
I've been toying with this myself and been doing a bit of research.

Most uv led lights are used for the Disco industry, and a lot of them have a UV range that only starts at 390nm. Make sure that you specify the ones that start at 365nm or some emulsions may not expose well.
The 5 metre rolls (16.5 feet) seem to be available on ebay for less than $30. They have 30 leds per metre, and are cut-able every 9 leds. Experimentation shouldn't be too expensive.

Alternatively this technology has been used for some time to cure auto paint. There are a lot of spotlights/floodlights available on the market so some research there may be worthwhile.

It would be interesting to see how you progress. The only thing that has stopped me actively experimenting is size. I also print corroplast signs and use screens up to 84"!
Make sure your glass is not green. The iron blocks uv

Absolutely correct regarding glass.

The glass is almost as important as the light source. Even ordinary float glass filters out uv light at about 7.5% per millimetre, So 1/4inch thick glass (6mm) will result in a 38% loss in uv.
Special low Iron content glass is available but this still filters out 3% per mm (15% per 1/4 inch). It is also very much (4x+) more expensive than float glass.

It seems to me that the most useful development for screen printers would be something that eliminates the glass altogether.
I have been trying to find some form of 'low tack' water soluble adhesive to keep the transparency tight to the screen for the last year. Maybe some form of static charge would do the trick. Anybody got any suggestions?
I guess in effect this is what the new generation of 'direct to screen' systems are doing - but you are talking the difference between a $6 aerosol glue and many (many) thousands of dollars.
The low power LEDs won't work. Speaking from experience. I bought 1w and 3w Cree LEDs. They worked ok but were no better then a florescent but faster. The under cutting may have been slightly better. I also tried to get a manufacture to expose a screen and compare to my 1000W metal halide. They had a demo unit but wouldn't do for a comparison to look at under a microscope. There is nothing wrong with a florescent or LED unit and used correctly you can expose 5%-95% halftones. These units can also be used to control dot gain with the under cutting. When I used the fluorescents I never used any dot gain controls. Now with the metal halide exposure unit I have to set dot gain controls or a 5% halftone may grow to 8-10% with on press dot gain.
It seems to me that the most useful development for screen printers would be something that eliminates the glass altogether.
I have been trying to find some form of 'low tack' water soluble adhesive to keep the transparency tight to the screen for the last year. Maybe some form of static charge would do the trick. Anybody got any suggestions?
I guess in effect this is what the new generation of 'direct to screen' systems are doing - but you are talking the difference between a $6 aerosol glue and many (many) thousands of dollars.
As much as I admire your train of thought, you've also got to consider "everyday" screen print shops.

Glass really isn't a problem. Exposure times and print accuracy really isn't an issue anymore. As much as I like the idea of utilizing as much of the uv light generated as possible, exposure time isn't an issue for shops anymore. The Industry has got over the problem of lost uv by just generating more uv at the source through metal halide.

Infact, the glass is actually an asset. What we loose in filtered uv, we gain in positive contact for little to no cost.

Sometimes the problem is actually a solution!

Now, I'm not saying that the process can't be improved - I'm actually working on an international patent that will do just that, but any solution has to be either affordable or offer huge advantages. If it can do both, then that's perfect! If not, then as much as it grinds my gears, sometimes the old way is actually the "best" for most shops
I think loosing nearly 40% of your available uv is fairly problematic. If we could 'reclaim' that amount of light then the mid sized shops could all get by without spending what amounts to the price of a good Manual press on what is effectively a light bulb in a box. I know that this 'everyday' print shop would think so. I for one have more than enough invested in 'ancillary' equipment.

The whole point of the paragraph that you quoted was that there must be a way of gaining good positive contact without the use of glass. The new generation of direct to screen systems cuts out the exposure unit by printing the image directly to the emulsion.
Surely then there is a way to get a similar, low-cost effect by getting transparencies to adhere (temporarily) directly to the screen.

I've tried using 'window cling' vinyl printed on the versacamm, but it is not thick enough to get completely smooth and the vinyl doesn't have enough static cling to stick to the rough emulsion. But I think that I am heading in the right direction.
All the problem needs is a transparency film with a low tack temporary backing to stick directly to the screen. Simple, affordable and advantageous.
Maybe I should get down to the patent office?

There are other sectors of our industry that could provide us with a solution. The transfer or printable vinyl sectors should be able to develop the film, and uv conveyor dryers used by the rigid substrate and wide format solvent sector could be easily modified for exposure purposes.
All this nonsense of messing around with sheets of glass or having something the size of a deep freeze in the corner need to be a thing of the past.
After all, the only real requirement is a bit of light.
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That's true - but almost all units come with low iron glass and are not loosing 40% uv. What I'm trying to say is how fast so you really need to expose? 3 minutes? 1 minute? 15 seconds? that's what people are getting and in the relative scheme of things with metal halide bulbs, the exposure time is now mostly insignificant. Metal halide is still expensive because it is relatively new to our industry. But you can still build one for cheap yourself if you want. The size of the unit is simply a factor of the light spread. Those big units you refer to allow 2 screens to be exposed at once. 1 screen every 7.5 seconds is way quicker than I can handle - the bottleneck just isn't at exposure and I don't think glass is a problem or limiting factor. Technically, I know that it could be better, but I loose way more resolution from my print method and substrate (using poly screens and printing onto cotton fabric), than I do by having the light pass through a sheet of low iron glass.

I applaud you for looking for a different way of getting positive contact, but given that the glass isn't a problem, why not just use that since it's there?

My patent actually eliminates the big exposure units and glass so please don't think that I don't want to improve the current process. But even if you came up with a better way to get positive contact, I can almost guarantee that industry will not jump at the idea. I introduced insulated concrete swimming pools to the industry in the UK. They saved 80% of heating costs, yet they were not adopted by the industry because people like to do things the way they always have. That's why people still buy wooden screens. I mean, why on earth would you buy wooden screens? But people do because they are cheap and do the job.

Unless you have a revolutionary idea that gives a huge host of benefits (cough cough, like my patent idea ;) ), then I think that perhaps you have actually just created a screen positive contact problem by not wanting to use glass

However, if you can figure out a glass less option then it would certainly benefit the hobby market immediately and may eventually come through to the pro end. The light would need to be above, rather than below, though, because right now the glass allows me to use a variety of screen sizes without having to have a special adjustable frame to support them.
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I have two problems with current exposure systems.
Firstly I use 84" screens for the correx sign printing half of my business so exposure units are large.
Secondly my old exposure unit went 'tits up' a year ago and I don't currently want to re-invest in large unit, given the changes that are afoot regarding uv led light source. When the tech settles down I may take a different view.

I have been forced, but not too reluctantly to revert to overhead lamps, which is probably where my biggest issue with the glass comes from - hefting a 7 foot sheet is not easy. I can expose 4 31" screens at a time.
The actual light source is fine and I have no issues with the exposure time (it is just long enough to burn the next screen whilst washing the previous one out). The multi point light source I have been using is not a problem for the big screens as they don't tend to use halftones. When burning 31" screens the light source is lower and each screen is far enough apart to have its own light.

Its just that the glass seems soo superfluous. I am not even talking about technological advances here, just some sticky transparency film.

Sorry to bgtshirts for hijacking your thread..
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With the proper light and SBQ emulsion you can get a 10-30 sec exposure. After talking to a few of the DTS people they have had to change back to pure photopolymer or diazo due to too fast of exposure. Yes according to them there is. It is recommended that nothing faster than 10 sec exposure. There is a shop I visited that has DTS and using diazo and a Nuarc 3140 DTS exposure unit. 18-24 sec as they use light units so it varies to what the sensor reads. They were even having issues with photopolymer. With their volume its no problem to go through a 5 gal of diazo in a month and probably much more. I personally will buy 4-5 1gal containers of emulsion at a time to save on cost. Unopened a most photopolymer have a 2 year shelf life and opened a 1year. Diazo 30-90 days. Yes it can be extended longer buy personally I don't want to guess will it work today or not. The other thing is I use a registration system. With a adhesive the carrier sheets would get ruined. I have kicked around picking up a 24" epson and trying to make a poor mans DTS. The info isn't as available for the 24" as the 17" and under epson printers.

I have used standard glass which came with my old national exposure unit that I converted to metal halide. Then switched out to starfire glass which is the lowest iron most optically clear glass available. There are other copy cat glass similar but this is a PPG product and our local glass company has a display with some of the off brand, standard and the starfire. Visually there is a night and day difference but not so much when it comes to exposure time.

This next statement is more of my opinion from using the 2 different glass. I don't think the iron cuts the amount of UV that gets to the screen as much is it causes light to refract around the iron. I get slightly cleaner exposure with the low iron glass and 10-30 sec faster exposure depending on the mesh and stencil thickness used.

As some know here I do a lot of testing to prove or disprove what is said in this industry. I do this because I personally have found that some stuff being told in the industry doesn't apply to every shop.
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