TSB
screen printing => Screen Making => Topic started by: Gilligan on August 11, 2012, 12:57:12 PM
-
I've noticed a couple of reasons why I was getting drips and poor screens.
My coating technique and my "flawed" coater was definitely to blame for the heavier deposits on the outside... but I've gotten better and even figured out how to kind of work with the coater I have (till I get my AWT in). I just move faster and try to concentrate pressure on that back edge. I realized that my screens looked better before I realized you could come all the way over and have the end caps lay flat... this made me realize that in chasing the emulsion up the screen I moved faster as well as had all the pressure on that back edge. I had gotten "sloppy" with my technique (how is that possible when you have no technique!)
So that made them a bit better... but I also noticed another thing I had changed. I was putting the frames out and putting a box fan on them to quickly dry them and then come back later and store them in a more light safe environment. Well, I made a quasi light safe cabinet and was using that and putting screens directly in there and putting the same box fan on them, but I don't think I was getting NEAR the air flow around them and out of that "box" like I was in the wide open spaces (at one point I was putting the screens in the press heads and putting them down to make the screens "flat").
I recently had to stack them opposite of what I was coating them so I was stacking them up outside the "box" as I coated them and put the fan on them. I noticed that the emulsion was "skinning" over quite quickly which was going to help prevent pooling and therefor drips. Of course it needs more time to dry completely but this would help it from creating drips.
Now I finally built a proper storage cabinet/drying cabinet. It will hold 27 M3's and is pretty darn light tight. I planned on putting my dehumidifier in the bottom (taking up a LOT of screen slots but probably a necessary concession). My questions (finally I know), are will that circulation with that dehumidifier be enough to skin over the emulsion quickly like a box fan on high did? Should I or could I effectively move the dehumidifier outside the box and "plumb" the intake and exhaust through the cabinet?
Till I get it unloaded and pictures of it (finished it at 1:30am last night at a buddy's house) the best way to describe it is like 55" wide and 33"(or so) deep with two columns that are 25" wide with slats every 3" or so for the screens to sit on. Very much modeled after Mooseman if anyone remembers his, just not NEARLY as elegant... next one will be better, I just happened to have a pile of 1/2" OSB laying around that I could easily stand to get rid of. Figured this was proof of concept/prototype and I'd spend the money on some nice plywood on the next one.
-
All you need is a bathroom exhaust fan in the top of your cabinet. These are designed to remove moisture from the air as well as odors. :P No fans are needed.
-
yep, a bathroom vent fan on top, a hole in the bottom with a good filter over it to keep nasty stuff out and you should be good to go
-
But here in south louisiana isn't that just defeating the purpose of the dehumidifier? Isn't this just pulling humid air right back into the box?
-
But here in south louisiana isn't that just defeating the purpose of the dehumidifier? Isn't this just pulling humid air right back into the box?
Ideal temp for drying is just below 100 and 75 for storage with humidity at or below 40%
Yep.. a large closet with a rack inside, room for a small dehumidifier and a fan will work perfect. The de-humid will generate enough heat to dry the emulsion pretty quickly. In the winter, one of those small ceramic fan driven heaters you can get from Target for 20 bucks will make it plenty hot.
Here in Cali where the yearly average humidity is around 40% is the ideal screen drying weather so we can just leave a box with screens in the middle of the room with a fan on top like Nick said.
-
Over here... It's humid outside all day almost every day. 60 - 90 on any given day depending on time... Averages mid 70's.
I will be storing this cabinet in an ac'd environment, 75 - 80 degrees in summer, same room as washout booth adding to the humidity of the room.
-
If it's an AC's enviro the ambient humidity should be plenty low enough to skip the dehumidifier. AC does a great job drying out the air. I have a rack very similar to what you described just building and all we've ever needed is a fan gently pulling air out of it and filtered intake, mind you it's damn near desert dry around here. My guy stays on top of the screens and we really don't need to rush dry freshly coated screens very often either.
Whats the relative humidity inside the AC'd shop?
-
The fan blowing is going to blow lint or crap into your wet emulsion or into your dry screen before coating. A big NO NO, from experience.
Good you changed.
Shane
-
I need to get a hygrometer still.
Yeah, the fan was just a quick fix bandaid approach to a really bad setup.
-
I had a dehumidifier in the room where i dry and keep my coated screens..It was a pantry to an old kitchen, so i assume it would be same as a box..
The dehumidifier broke...so i turn on a heater, yes its idle of summer and already high 80's in there..I do have a little digital thingy that tells the temp and humidity.. So the heater gets it to about high 90's -low 100's...and the humidity drops to under 30%...So maybe just add a heater to the box for a bit...
After i coat i let the screens sit there for like 20 minutes and then turn a fan on them and the fan has a furnace filter taped to the back for dust.....i've had no problems...
-
I guess if I do go heat only, I can vent to atmos via the duct system for the dryer. I don't want to pump hot air out of the cabinet into the room.
What I want is the emulsion to skin over as quick as possible so as to not have pooling and dripping. Maybe I'm over thinking this but I'm gun shy after such a poor coating/drying experience I've been having.
-
yeah, i didnt take your ambient humidity into consideration, so a dehumidifier in your cabinet would be a good idea for sure.
-
If it's an AC's enviro the ambient humidity should be plenty low enough to skip the dehumidifier. AC does a great job drying out the air.
This is true when the air is circulated via a closed central household system but in the case of window or thru wall mounted that pulls in outside air, the humidity level can stay in the 50-60 range.
A good habit to get into is exposing first thing in the morning, reclaiming early afternoon and coating just before you go home for the night. This way your screens dry overnight and you never have to think did it dry long enough. Now if you're in a rush or need that screen coated and dry in 20 minutes, then get that cabinet nice and hot with lots of circulating clean air.
-
This is true when the air is circulated via a closed central household system but in the case of window or thru wall mounted that pulls in outside air, the humidity level can stay in the 50-60 range.
That's not how "window units" work.
They still circulate inside air, the outside part is the condenser coil just like a regular split unit. It pushes air over the compressed freon to cool it down because compression naturally heats it up. This allows the system to work (efficiently).
It is technically still a split system just the split is all self contained in the box.
A "Packaged unit" is basically a large window unit in that the "split" is all self contained but your air flow is completely separated. It pulls air from inside via ducts and then returns it after being cooled.
No system strictly pulls air in from outside, this would be insanely inefficient and pretty much ineffective. They do have a few units that will mix air like that if you put it in "fresh air" mode, but that isn't a way to really cool down your house, it's just to introduce some fresh air into the home/room.
-
No system strictly pulls air in from outside, this would be insanely inefficient and pretty much ineffective. They do have a few units that will mix air like that if you put it in "fresh air" mode, but that isn't a way to really cool down your house, it's just to introduce some fresh air into the home/room.
That's what I was referring to, the fresh air option
-
Even if they did pull 100% outside air it would be considerably lower in humidity once it had been passed over the cooling coil, that's where all the water/condensate comes from.
-
But they don't and in fact not many window units even have a fresh air option.
-
Over here in New Orleans we built a box and have a dehumidifier in it. After coating screens we turn on the dehumidifier for 30 minutes and then the screens are ready to go.
-
Over here in New Orleans we built a box and have a dehumidifier in it. After coating screens we turn on the dehumidifier for 30 minutes and then the screens are ready to go.
Other than that it's pretty sealed up?
How long did that massive EOM screen take to dry?
-
we built a screen drying cabinet using a standard wall thermostat and a small fan driven electrical heater.
We wired it up so the fan is always on and the heating element only kicks in when the temp in the cabinet drops below 85deg F. We run it at abouit 95 deg f on the high side .
takes about 35 - 45 minutes to dry a heavily coated screen.
mooseman