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screen printing => Newbie => Topic started by: Gilligan on October 18, 2011, 02:11:20 AM
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Ok... as you guys know, I'm extremely ignorant to coating screens and exposing them.
Well... I need to get a job going and I decided to go for it. I coated 3 screens with Chromaline blue... 2 passes on the shirt side followed by 1 pass on the squeegee side (rounded edge). It went ok... no mess, does that count for anything. ;)
Now I'm gonna expose using a vacuum storage bag and a 400w metal halide bulb (technically on a HPS ballast). I'll put the light about 4' above the screen (in it's stock hood... it was a grow light given to me).
What I'm wondering is what do you guys think my exposure time will be? I don't have an exposure calc or anything. With the vacuum bag I'll have a hard time doing a exposure test by uncovering at intervals. I do have a fixxon sample pack that came with a sample of half tones and text exposed on one of their films. Not sure if that could be useful.
Any advice to get me a decent exposure as quickly as possible... I promise I'll fine tune it later. The design I need to print is only 20 toddler shirts 2 color spot color with EXTREMELY loose registration (no colors touching).
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4 feet is quite the distance. 30-36" would be more in the neighborhood.
As for your exposure time, anything I threw out would be a total guess.
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Yeah, you are right... my math was wrong. I'd thought it seemed far but I didn't put pencil to paper, just off the cuff in my head at 1am ;)
So 3' distance not 4'.
Honestly, your guess will probably be a LOT better than my guess. ;)
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You need to crack your wallet for the $7 or so for a Stouffer scale from Victory Factory or anyone else who sells them. Takes the guesswork out of calculating exposure times. Or ask Andy to rouse "Step-Wedge Man" from his premature retirement, although serious alcoholic fortification is strongly advised before looking upon the dazzling visage of Step-Wedge Man . . .
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Here's a video from Roger Jennings that explains the step wedge thing pretty good"
http://youtu.be/29g2uHkdC_c (http://youtu.be/29g2uHkdC_c)
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To find a good distance, (starting point at least) take the diagonal of the area you are exposing and try that
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Ok... as you guys know, I'm extremely ignorant to coating screens and exposing them.
Yeah we know, but we have also seen that, as in other facets of the process, you will listen (at least sometimes)
As noted, your initial distance was much greater than necessary, and greatly affects time. Doubling the distance quadruples the time, tripling it increases it nine
fold. I guess the time is a factor of the distance difference squared. Here is a simple table from one emulsion to use just to see the distance/time relationship.
DISTANCE FACTORS
20 inches /50 cm. 0.25 44 inches /110 cm. 1.21
24 inches /60 cm. 0.36 48 inches /120 cm. 1.44
28 inches /70 cm. 0.49 52 inches /130 cm. 1.69
32 inches /80 cm. 0.64 56 inches /140 cm. 1.95
36 inches /90 cm. 0.81 60 inches /150 cm. 2.25
40 inches /100 cm. 1.00 72 inches /180 cm. 3.2
That said, I do have experience with 400 watt bulbs, though used with the proper ballast, along with a similar Chromaline emulsion.
At 26", a yellow 160 coated similarly to your description, achieving the "glisten" described in Douglas Grigar's article on the Home Page, exposures were in the 90 second range.
So, with all of this, and the information on how to perform a manual step wedge test (or a one step calculator version), as a starting point for you, I'd pick a range that halves and doubles my numbers. Remember that each mesh requires testing and adjustment.
And, as Tom brought up, remember that though he will not do your grunt work, Step Wedge Man is watching you!
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Hello inverse square law. Well familiar with it from all other aspects of my life (video, photo and stage lighting).
In a sense the more distance I have the more "latitude" I have? Is that right? If I am close enough to expose at 1 minute than 50 seconds would be fairly under and 1:10 would be fairly over. But if I need 3 minutes to expose than 2:50 is significantly less under exposed and 3:10 is significantly less over exposed... am I correct in assuming that?
In a sense that will be better for me, starting off right (more room for error)? I know it's not a fix for doing it right... but I could use all the leeway I can get.
Btw, Andy... I do listen... my wallet just doesn't cooperate sometimes. You think it's tough running one business, try spreading yourself thin across several. Bank accounts went from being 900, 1500, 150 one day to 900, 8k, 4k the next day! Of course all that money is already spent somewhere... just have to find the best place to put it and budget till next set of invoices come in.
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Couple things here vaccum storage bag? I,m thinking will bounce some of your light not being really clear #2 double coat with the round edge is going to give you a very thick screen (EOM). Not having proper vac and light will cause you some undercutting with what your doing now, I would use the sharp edge to coat 1/1 until I got a better setup.
You know you can build a exposure unit for a few dollars and use blacklights or hang a photoblub over top with a pc of glass pressing your film down tight to the mesh.
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Well... from what I've seen that vacuum bag looks pretty slick and tight. Sure it might not be AS transparent as glass... but then again it's much thinner so maybe that offsets some of it?
He was using a foam pad in the back of the screen but it was being sucked down so hard that he just stopped using it.
(http://i10.photobucket.com/albums/a122/jaythomson/screen%20printing/DSCF6953.jpg)
Here it is in action:
vacuum top.wmv (http://www.youtube.com/watch?v=MSu4joIaELc#)
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I just realized I can easily do the stepped exposure test with my setup (I changed the way I WAS going to do it and never revisited the idea again).
So what would be best to print out as an exposure calculation film? Anyone got a file they wouldn't mind sharing?
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I just realized I can easily do the stepped exposure test with my setup (I changed the way I WAS going to do it and never revisited the idea again).
So what would be best to print out as an exposure calculation film? Anyone got a file they wouldn't mind sharing?
Ulano sells an exposure kit. I have this one from them:
(http://www.texsourceonline.com/images/Product/medium/1769.jpg)
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Just seems pricey... I'm sure it's good I just wish there was a PDF that one could print and accomplish the same results.
Yeah, I'm cheap, what can I say! ;)
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I just realized I can easily do the stepped exposure test with my setup (I changed the way I WAS going to do it and never revisited the idea again).
So what would be best to print out as an exposure calculation film? Anyone got a file they wouldn't mind sharing?
With a manual step wedge test, you need no special film for exposure, just one of your typical films, perhaps with various sizes of a simple type like Arial starting really small, like 4 pts.The advantage of a manual test with your own film is that you are testing what you will actually be using, rather than a more perfect professionally produced film.
So, the film, and a piece of cardboard or other opaque material to slide (or a series of overlapping strips) and seven or so measured marks, and you're good to go. On a yellow 160, I'd go from 30 seconds to four minutes to get a wide range of visual guidelines.
Then you can fine tune it in with another test in the sweet spot.
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The advantage of a manual test with your own film is that you are testing what you will actually be using, rather than a more perfect professionally produced film.
That was one of my thoughts also... a professional calculator only shows you EXACTLY what's up IF you can match their quality and transparency. I mean if we are worried about what my vacuum bag will transmit vs glass then difference in transparent films will be "drastic" also. Then lets not even begin to talk about vellum(sp). ;)
Thanks, I'll give giving this a whirl tonight... we shall see!
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Alright... any last minute advice? In about an hour I'm gonna give this a whirl.
I'm using this wedge test:
http://www.smrsoftware.com/vellumexposure.php (http://www.smrsoftware.com/vellumexposure.php)
If I do 30 second intervals from 30 to 4 mins as Andy suggested will that give me a rough enough estimate? I really got one shot at this as I only coated 3 screens and I need two for the job. :)
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The cheap Stouffer scale is like a neutral-density filter that has 21 steps, and you adjust your exposure to get a solid step 7 on the scale. It also comes with the formula for calculating time adjustments to hit that step 7 after your first test. It also comes in handy to throw on a screen periodically to gauge the declining strength of your light source. Some recommend using it on every exposure. It's pretty small, so you can just do a small swipe of emulsion on your screen to perform the test instead of testing fully-coated screens.
Just sayin' . . .
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My advice actually called for two volunteer screens for this suicide mission. The first being a little rough and the second, really zeroing in with 10 or 15 second steps for fine tuning.
You are flirting with "settling"
Tom, your suggestion is fine, but we have already established that he is using a manual test with his own film, and should learn a lot from it.
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Andy, I totally understand what you are saying... I'm just kind of under the gun and want to get this spot job done and out of the way. The more confident I am at this entire process the more likely I am to do some more testing.
I also have NO darkroom or REAL washout booth setup. It s a good thing it is night time as it makes for easier washout. ;) Once everything is PROPERLY setup then it will also be a LOT easier to test everything out.
So... here is what I got from my first run. Looks like about 2.5 minutes was getting me a pretty decent 1pt line. Nothing got me a .5pt line and at 2 minutes I lost some entire grid blocks from the 2pt grid (this COULD be because of an improperly prepared screen too.) EVERYTHING at 2pt exposed well, even at 4 mins. I guess my vacuum storage back system worked out ok in the end. ;)
Is .5pt really reasonable on most setups? Or is that reserved for really good single point vacuum lid (nuarc) setups?
I'll take some pics later and post them.
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1/2 point should hold with even most decent compression type set-ups with a single point light (and a properly prepared screen). You may even have better detail ability with your space bag.
I have never needed an outline smaller than that, and would never even count on holding a one point reversed line.
Now, did you also get to see the gradual change from under exposed to good to over exposed? That's the added benefit to this, having it all laid out in front of you.
Make sure that you document this and use it as a stepping off point when changing coating techniques, emulsions, or different colors or mesh counts.
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Ok... so here are the pics.
First off... 2:1 rounded edge is SO much better (thicker) than 1:1 sharp edge. Wow... I mean, I can FEEL the EOM vs the ones my buddy's guy did for me. Just Wow!
Ok, so First pic is wide shot of the Wedge test. Oh, and I guess I really need to note that I really F'd it up. I put the film on backwards LOL in the dark I guess I missed that. ;) So that is probably why my 1pt and .5 pt didn't hold very well... it was probably severely undercut through the film! LOL
2nd pic is a close up of the wedge test. Obviouysly 3,4 and 5... which were 1.5mins 2mins and 2.5mins.
3rd is my screen that I shot. I did it for 2.75 mins... actually I did that one for almost 3 mins because I forgot to pull off a part of my shutter so it was only getting like 20% for the first 20 seconds. :)
4th is the close up of the smallest text. I'd say that text is comprised of CLOSE to 1pt lines. SO that's pretty damn good if I do say so myself. ;)
Overall VERY pleased and I bet my next test will be awesome when I actually put the film on correctly. LOL I only noticed that I did this when I saw the ink residue on the vacuum bag as I shot the actual screen after the test. Felt pretty smart. But felt pretty confident on pushing the exposure past the 2.5 by the extra 15 seconds. Especially on the first screen (not pictured) as it was MUCH larger spaces.
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LOL... so I realized today that I was COMPLETELY doing the step test wrong, but doing the math right... which was giving me completely the wrong answer.
I was doing some 200 mesh stuff for the first time and figured I needed to redo my test anyway to fine tune it as well as get the times for the 200 mesh.
So I cover everything but the 8 and start exposing. Wait till 2mins and then start moving it every 15 seconds. But half way through I realize that was doing it all wrong and then at the end I would have a 15 second exposure and then +15 seconds on each one up till the 8th one which would be like 4 mins.
BAAAHHH... so last time I did the same thing... thinking I needed 2.5 mins well... obviously I was WAY wrong and was WAY over exposing the screens that I did. Surprisingly that small "E" still worked out (guess that vacuum bag REALLY worked well).
So anyway... I realized today that 45 seconds to 1min was good enough... closer to 45 seconds as 1 min started closing up the .5 pt line... probably could have forced the line with a pressure washer but obviously that's not doing it right.
Guess I need to do it again and time it correctly. I'll just start at 30 seconds (I guess) and start adding up 10 seconds at a time. *shrug*
1st pic is full shot, 2nd one is 2 through 6. (30 seconds, 45 seconds, 1min, 1:15, 1:30).
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Just seems pricey... I'm sure it's good I just wish there was a PDF that one could print and accomplish the same results.
Yeah, I'm cheap, what can I say! ;)
Whan you get a real live working exposure unit, call a Ulano rep and ask for a sample of emulsion and an exposure calc kit. It will come in handy.
If you want a not-so-fussy way of calculating the exposure with the light source you have, buy a small can of 3m Artist's Adhesive spray. It's a removable, positionable adhesive.
Print out a film with some detail lines, dots, text and some thick lines and shapes. Maybe some halftones too.
Spray a light coat of the adhesive on the film, wait a half a minute, then stick it straight to the emulsion. This will give you the contact of glass/vacuum without having to cycle the vacuum off and on and you won't knock the film out of position on the screen when blocking and unblocking the light. (you can even burn a screen in the sun in a pinch this way...)
Do your step wedge. Try 10-15 second increments and do several above and below your estimated exposure time. Most of the step tests I ever did were about 10 exposures total.
Now take the one exposure that looks the MOST exposed and still holds the finest lines and detail, and do another test with 5 second increments above and below. Again, look for the MOST exposed (as in the one with the emulsion that is exposed all the way through) that still holds the detail without pinching dots and lines.
Now you have your first screen and a starting point.
Now do this once more for each mesh count and/or mesh color.
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I also have NO darkroom or REAL washout booth setup. It s a good thing it is night time as it makes for easier washout. ;) Once everything is PROPERLY setup then it will also be a LOT easier to test everything out.
Remember it's screen printing. First things first: make sure you can make good screens. Your printing will never be better than the stencils you can produce.
Money isn't an issue btw. You just need a clean space that can be made dark and is easy to mop.
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I've been doing ok so far Evo. Even coating I haven't made too much of a mess.
Exposing wise I do have the vacuum bag and they are working very well... so far it's holding it's vacuum for a long time and it's very tight. No chance of it moving and it's very tight to the screen. I have a hard time getting the little kinks out it's so tight of a vacuum, and that closing the valve and removing the vacuum unit.
The test sheet I'm using (pictured) has some .5pt stuff which to me looks pretty fine but I'm pretty ignorant on these things.
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Ok... now that I re-evaluate my first test I realized I did calculate it right. I just screwed up my second one.
So this brings me to a question. Do LOWER mesh counts result in LONGER exposure times due to essentially a thicker coat?
I'm completely talking out of my arse here because I of course don't know... I did change the setup completely so the distance might have been less (but if it is, we are talking about 1-2 inches out of 30 inches.)
Also if anything I THOUGHT I put more emulsion on. With the 158's I did 2:1 with the 200's I did 3:1 (both rounded edge).
Either way that seems like a large difference in time 2.5 mins down to 50 seconds. Even if both 2 inches closer and thinner emulsion (though more passes) that seems like too large of a difference.
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Ok... now that I re-evaluate my first test I realized I did calculate it right. I just screwed up my second one.
So this brings me to a question. Do LOWER mesh counts result in LONGER exposure times due to essentially a thicker coat?
I'm completely talking out of my arse here because I of course don't know... I did change the setup completely so the distance might have been less (but if it is, we are talking about 1-2 inches out of 30 inches.)
Also if anything I THOUGHT I put more emulsion on. With the 158's I did 2:1 with the 200's I did 3:1 (both rounded edge).
Either way that seems like a large difference in time 2.5 mins down to 50 seconds. Even if both 2 inches closer and thinner emulsion (though more passes) that seems like too large of a difference.
Yes, the coarser mesh typically will have a thicker filament which equals a thicker mesh which will have more void in the open areas which means a much thicker stencil. Thicker stencil means longer exposures.
Keep in mind also that amber/yellow mesh will require slightly longer exposure times for a given mesh count as well. The yellow dye inhibits the UV energy from creeping along the filaments and causing undercutting and loss of detail. The trade off is longer exposure.
This is why in the above post I suggested getting a very narrowed down exposure for one mesh count, then follow the exact same exposure calculation procedure for each mesh count you use.
The light units required for the range of mesh counts I use ranges from 125 to over 200. I also use 3 different kinds of emulsion, polyester and nylon mesh, and on the coarser mesh screens I may do additional coats on the print side when a thick ink film is desired. All this means test, test and test again, MAKE A CHART and hang it on the exposure area wall.
Also, it's a good idea to standardize your coating procedure, (example 1+2 on all screens) that way you don't need to do an exposure for each mesh count AND coating method combination.
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By the way, if the testing seems like it will take forever, it doesn't. You can do it while dealing with other chores around the shop. All the exposure test screens will reclaim super easy as they won't have any ink muck to deal with.
On the other hand, dealing with bad exposures wastes a ton of time and money. Dial it all in from the start and the rest of your screen making becomes a cakewalk.
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Absolutely... I definitely want to get the process down better and more accurately.
I lost a little detail in the last design I did (granted it was a distressed thing so only I can tell)... but it was odd... lost some detail here because too much emulsion washed away but only an inch away the opposite happened and I lost detail because the emulsion didn't wash away.
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Absolutely... I definitely want to get the process down better and more accurately.
I lost a little detail in the last design I did (granted it was a distressed thing so only I can tell)... but it was odd... lost some detail here because too much emulsion washed away but only an inch away the opposite happened and I lost detail because the emulsion didn't wash away.
Could it be uneven coating?
I remember my first few coated screens LOL
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Definitely! I've done well coating my screens (no big mess or anything) but "even"... ha! probably not. I try my best but when you are fumbling through with no real teaching... well, I know I must be doing somethings wrong. :)
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I do it twice on the shirt side and once on the squeegee side
Emulsion - How to coat your screen! (http://www.youtube.com/watch?v=d3lIMfYg70s#)
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Basically same process. I do it one handed while manipulating the screen with the other hand.
I'm doing it 3:1 I did the first run 2:1 on the 158's and someone suggested it would need 3:1 to get to the "glisten point".
I'm also using the round edge vs sharp edge.
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2/1 sharp works for me.
Build that little stand, that will free your other hand (that is why I attached that video)
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Yeah, I was looking at that and trying to figure out how to incorporate that into my setup.
Only issue I have with using a stand is that it's nice to lean the screen forward to help with flow back of emulsion when you get to the top.
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I do it twice on the shirt side and once on the squeegee side
Emulsion - How to coat your screen! ([url]http://www.youtube.com/watch?v=d3lIMfYg70s#[/url])
Hmm.
I coat once on the print side and twice on the squeegee side. I find this "pushes" the emulsion through to the print side more effectively. I've been using an old Black and Decker Workmate as my coating stand. I clamp a 2x2 in it as a stop block and hold the other end of the frame.
Then of course, I dry it in a de-humidified, filtered room, horizontally, print side down.
If I need a thicker stencil, (for a thicker ink film) I add more coats to the print side, drying in between each coat.
Gilligan, you dry em print side down, right?
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LOL... umm... my drying method is as you guys can imagine... "unique".
I load them on my press and pull the heads down (platens out of the way) so they are ALMOST horizontal but print side down. Then I run a big box fan to quickly "dry" them. Then after they are basically dry (30 mins?) I load them into the cardboard box they came in. I cover this up to keep it as light tight as possible (I also leave them print side down in there).
The method of coating is the one described by Douglas Grigar though I don't really see the glisten, I just go with a few coats and move on... I THINK it's glistening but it's hard to see it next to my glistening body. ;)
That last squeegee side is apparently the key to all of this coating stuff... it pushes all the emulsion through to the print side.
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LOL... umm... my drying method is as you guys can imagine... "unique".
I load them on my press and pull the heads down (platens out of the way) so they are ALMOST horizontal but print side down. Then I run a big box fan to quickly "dry" them. Then after they are basically dry (30 mins?) I load them into the cardboard box they came in. I cover this up to keep it as light tight as possible (I also leave them print side down in there).
The method of coating is the one described by Douglas Grigar though I don't really see the glisten, I just go with a few coats and move on... I THINK it's glistening but it's hard to see it next to my glistening body. ;)
That last squeegee side is apparently the key to all of this coating stuff... it pushes all the emulsion through to the print side.
You are going to bust your springs, do not keep the print head down for a long time.
Buy a rack, or build a rack.
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Never thought of that.
It is definitely in the plans... Just been swamped with everything.
A printer/embroider friend of mine also runs an ice cream truck business and he uses large broken chest freezers (he stands them on end)... he has several broken ones (as you can imagine he probably goes through a few of these in his business... running those compressors on generators is probably bad for them ;) ). So he said I could have one. I'll be building my rack out of one of those. Just trying to figure out how to circulate some air in and out of it.... I'm guessing some baffles built in or around it. Maybe cut out some offset holes through the insulation and such.
Don't hate me because I'm an evil thrifty genius. ;)
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I dry in my cabinet using furring strip blocks between the screens. I remember years ago, someone said that they use clothes pins as spacers.
At any rate, stack and dry a dozen or so at a time this way.
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Never thought of that.
It is definitely in the plans... Just been swamped with everything.
A printer/embroider friend of mine also runs an ice cream truck business and he uses large broken chest freezers (he stands them on end)... he has several broken ones (as you can imagine he probably goes through a few of these in his business... running those compressors on generators is probably bad for them ;) ). So he said I could have one. I'll be building my rack out of one of those. Just trying to figure out how to circulate some air in and out of it.... I'm guessing some baffles built in or around it. Maybe cut out some offset holes through the insulation and such.
Don't hate me because I'm an evil thrifty genius. ;)
Even a bakers rack with a light proof blanket draping over it would work till you have something more effient. The first thing I though of was man this guy must get a lot of pin holes with that method, as presses collect some dust over time.
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I only leave them there 15-30 mins... After that they are tucked away.
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I load them into the cardboard box they came in. I cover this up to keep it as light tight as possible (I also leave them print side down in there).
Believe it or not this is the worst part. (maybe even more than a fan blowing lint and dust bunnies onto wet screens...)
Once they are dry to the touch, they are still far from totally dry. Putting them in a box just traps any remaining moisture in a small space. Screens need dry air. Lots of it.
Here's some suggestions:
Small room. Maybe even a closet. Don't worry about light leaks unless you plan on storing dried screens for more than a few days. (which is a bad idea anyway)
Buy some 1x2 wood and screw strips of it to the walls on two sides, making a corner rack. If you use 23x31 screens for example, cut the strips 24" and 32" respectively. You only need support the screen from two edges.
Buy a dehumidifier from Goodwill or some other thrift store. Mine costs a whopping $20.00. You can find them free on Craig's List occasionally.
Buy a small air filter from Goodwill as well. This will be your air circulation. People buy them new them chuck em to Goodwill all the time when they find out how much the replacement filter elements cost. Don't sweat it, you're only trying to get the big dust out of the air, so you can most likely leave any expired filter in there indefinitely.
Now, once all of this is together, DUST, SWEEP AND MOP THE ROOM, then leave the filter and dehumidifier running for a couple hours.
Then go coat and rack some screens.
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Not possible/practical at this point. I have a completely open shop 30x30 building. It is unattached from any other building.
I do have a dehumidifier already from a different project.
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Not possible/practical at this point. I have a completely open shop 30x30 building. It is unattached from any other building.
I do have a dehumidifier already from a different project.
Do what I did at my last place...pick a corner, build 2 walls with a plywood top.
Throw on a $100 door from home depot. Takes a couple afternoons.
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I might do that... I might use some black plastic sheeting that I have laying around too... at least to "prototype" it out and see if it's a good fit/feel.
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Basically same process. I do it one handed while manipulating the screen with the other hand.
I'm doing it 3:1 I did the first run 2:1 on the 158's and someone suggested it would need 3:1 to get to the "glisten point".
I'm also using the round edge vs sharp edge.
Same here I feel like I have better control holding the screen with one hand and coating with the other , no akward back bending that could be a pain after coating 30 screens as I do at a time. I do 2:1 with the round side. 1:1 if I'm using the screen for 1/2 tone work.
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I do 2:1 with the round side. 1:1 if I'm using the screen for 1/2 tone work.
You may find actually better dot edge definition with proper EOM (which is unlikely with your coating method)
Remember that EOM is not just a specific thickness, but a relationship to the mesh. If you are having trouble
Then again, number of coats really means less than actual deposit, relatively easily identified by the "glisten".
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I might do that... I might use some black plastic sheeting that I have laying around too... at least to "prototype" it out and see if it's a good fit/feel.
\
Gilligan, here is my drying cabinet.
Made in the corner with 2x4's, and some old paneling for walls. It has a "Fart Fan" on the top and few holes on the bottom.
I used silicone to close up any openings and weather stripping around doors to block any light when the door is closed.
Cost, $30-$40 for all (I had paneling)
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One slight improvement modification that I may suggest would be some simple brackets to allow a standard filter panel to be placed by your intake holes.
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One slight improvement modification that I may suggest would be some simple brackets to allow a standard filter panel to be placed by your intake holes.
It is filtered air :)