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Discussion Starter · #1 ·
hi
i am trying to print my first halftone print. i am new with screen printing and have printed only one color prints till now and now i want to start doing halftones but my printing result was not so good. i have attached images of the original design, the halftone design, the film positive, and two prints i made on a shirt - one with two hard strokes and one with one soft stroke.
i have used these parameters when converting the image to bitmap halftone:
resolution: 600 pixels/inch
frequency: 40 lines/inch
angle: 55 degrees
shape: round

i have used a 196 mesh for the screen.
i use plastisol ink.

as you can see in the printing result, it is not so good. i need any advice and help you can give me to improve my results.
thanks a lot!
 

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hi
i am trying to print my first halftone print. i am new with screen printing and have printed only one color prints till now and now i want to start doing halftones but my printing result was not so good. i have attached images of the original design, the halftone design, the film positive, and two prints i made on a shirt - one with two hard strokes and one with one soft stroke.
i have used these parameters when converting the image to bitmap halftone:
resolution: 600 pixels/inch
frequency: 40 lines/inch
angle: 55 degrees
shape: round

i have used a 196 mesh for the screen.
i use plastisol ink.

as you can see in the printing result, it is not so good. i need any advice and help you can give me to improve my results.
thanks a lot!
There is an exposure/wash out issue somewhere you are not picking up all the detail in the negative you are loosing a good bit in his forehead. From the looks of it you are under exposing your screen or washing out with to much force. With halftones I slightly underexpose than use warm water and a towel to get the image to show than only use a water hose at the end for a final wash out. If you could put a pic of the screen that would help as well, part of your issue may be an off contact issue.
 

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Discussion Starter · #3 ·
thanks a lot Allygator,
i have attached images of the screen, you can see that the dots in the forehead and other places can be seen on the screen but ink did not pass through it even when i used hard pressure two strokes.
with the off contact issue do you think i need smaller off contact?
 

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thanks a lot Allygator,
i have attached images of the screen, you can see that the dots in the forehead and other places can be seen on the screen but ink did not pass through it even when i used hard pressure two strokes.
with the off contact issue do you think i need smaller off contact?
If ink is not passing through the screen it is not clear ... With halftones you have to make sure all the emulsion is out. My guess without being able to see the screen is that there is still a very thin layer of emulsion keeping it from printing. I would try the warm water trick. Its magic.
 

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You're getting a moiré pattern from the screen angle and the mesh. Use an angle of 22.5° and make sure there is a thick layer of emulsion on the shirt side of the screen to minimize this effect. Also you are getting dot gain, meaning the shadow areas are printing darker than the original. You can compensate for this by lightening up your shadows on the original halftone. If a halftone is a little too light, an extra squeegee stroke or two will darken it up. If it's too dark, there's nothing you can do besides make a new screen.
 

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I would try a finer mesh as it may be threads blocking the ink from passing through (check with a magnifying loupe). Make sure it is dried in the print position (mesh side down) after coating and expose it thouroughly, never under. You can use process black ink or regular ink with process base added to soften it or a mix of regular black and process black.
 

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another trick you may be able to use is 'dot gain' (I know corel uses it, I'm not sure about other programs) what it does, it helps with the halftones and pixels, to 'adjust' for larger/smaller bleed with the ink/screens.. it takes a LOT of practice to get it just right, and you may to need to adjust it for different viscosity inks.

something to maybe check into, after you've determined it's not an exposure wash out issue. (also, personally, I drop the exposure time a smidge on fine detail and halftones, to make it easier to wash out)

also, if you may have transparency darkness issues, one option is to change the color 'black' (c0y0m0k100) to true black (c100y100m100k100) if you're printing with a color printer (or copy shop) it darkens the black more.

only other issue I could think of, would be make sure your transparency is TIGHT on your exposure table. (preferably a single light source, vacuum sealed) multiple light sources, or even a tiny gap could cause loss of halftone detail where it doesn't quite matter as much on solid colors.. (check out 'undercutting' there's a bit of detail here. Exposure FAQ Screen Making Products how to measure exposure )

one way you can play with a bunch of different settings, without having to burn a different screen each time, is set up something similar to an exposure step test, where you have 1 screen, with a dozen (or more) settings. I made a transparency myself, with a dozen different lpi's, and dot gain settings on 1 page, I use it whenever I need to test out fine detail/exposure settings/new emulsion/different inks/etc.. I just drop that into an exposure step test, and see what washes out/prints the best. I've found doing 1 screen as a test, beats having to do test after test (especially during production) to figure out what works best.

Hope you figure it out soon! good luck!
SMU
 

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your artwork needs to be created in higher res. i always use 300 dpi and i would also us a 230 mesh. Wash out completely.. You might want to turn pressure off the water at end so you won't blow dots out. dont need a thick layer of emulsion use sharp end of coater. i hope that helps some
 

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Artwork at 300DPI for most is fine. photorealistic or photos 600-1200DPI.

What type of exposure unit do you use, emulsion type? Dual cure or photopolymer. If your using a florescent BL unit then hose pressure and maybe 15-45 sec exposure time adjustment. With a halogen or metal halide and good films no time adjustment should be needed A properly prepped screen, coated and dried properly and proper exposure will result in a stencil that can easily washed while still withstanding the pressure washer.
 
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Discussion Starter · #13 ·
Artwork at 300DPI for most is fine. photorealistic or photos 600-1200DPI.

What type of exposure unit do you use, emulsion type? Dual cure or photopolymer. If your using a florescent BL unit then hose pressure and maybe 15-45 sec exposure time adjustment. With a halogen or metal halide and good films no time adjustment should be needed A properly prepped screen, coated and dried properly and proper exposure will result in a stencil that can easily washed while still withstanding the pressure washer.
i use a self made exposure unit, i have added photos of the unit and the emulsion. Water Resistant Emulsions from Ulano 925WR QT-Discharge TZ
 

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i use a self made exposure unit, i have added photos of the unit and the emulsion. Water Resistant Emulsions from Ulano 925WR QT-Discharge TZ
Evenly space your lights. So what ever the spacing between the bulbs on the same fixture use that go space the other bulbs. You will have to add a fixture but can still get away using 3 fixtures.

As for your mesh am I correct that you are using the metric system. So you 45 is 45 threads per CM. If so you will need to use something around 120 to use the 50-55 LPI and do CMYK work.

You advised that was a simulated picture in your post or was it an actual print?

When I had mention simulated process that's where you use standard opacity inks. That would print 3 or 4 color and be much easier then doing CMYK. I have been doing this 7- 7 1/2 years. I have done less then 24 CMYK prints. I have tried more then that but the others always looked so much better simulated process vs CMYK and its a thousand times easier especially on a manual.
 

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When I first started I would have problems with inks not passing through and it was because I had emulsion muck covering the open areas. Sometimes I was able to use screen opener to clear it out.

Give that a shot before you make a new screen. Blast it with screen openener and see if you can pass ink through.
 

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I believe that light scatter from your multiple light sources is responsible for losing the finer halftones. If a point light source is not an option, try using a faster exposing emulsion like Murakami Blu.
 

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I believe that light scatter from your multiple light sources is responsible for losing the finer halftones. If a point light source is not an option, try using a faster exposing emulsion like Murakami Blu.
The only issue is that his screen show the image good. So the light scatter does not appear to have washed the image detail away. In my opinion the holes are still clogged.
 

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My thought is about your washout issues is that the backside of the emulsion isn't fully exposed and when washing out the stencil you are getting residual emulsion from the backside leaving a slimy film on parts of your mesh... In this case the backside is the side away from your UV source... I've had this happen when an apprentice of mine started getting cocky in her abilities and didn't do the extra rinsing to prevent the unexposed emulsion from bleeding into the open areas...

3 things you can do to help minimize this this without changing your setup 1) only spread emulsion slightly larger than your image... far enough you aren't getting inconstant thicknesses where you are burning/using 2) wash the heck out off all the edges of the backside and anywhere you don't risk blowing out the screen 3) dry the backside of the screen first and fast to minimize the possibility of the emulsion slime from spreading.

BTW, someone suggested Murakami Blu... I have half a gallon you can have... I can't get decent halftones or fine lines to hold with Blu... I use QT-Discharge (not sure if that the same as your 950 WR or not)... QT-Discharge gives me incredible halftones and lessons blowout issues but it does increase the risk slime as it takes significantly longer to burn
 
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