screen coating tips from an old bastard

[mooseman]

One of the things I love about this board is how everyone does everything differently to get to the same place.
adding to that mess of info here is waht we have learned about coating screens.

specifics
newmans MZX
155 @ 40Nm , 195 @ 35Nm , 250 mesh @ 30Nm
awt twin edge coater 18 inch wide, use the wide edge
Ulano QTX color pink wet red dry on yellow mesh
manual press
triple duro squeegees
one man shop so same monkey every time handles the process

we assume everyone  cleans and dry screens correctly.

What we have learned

take a fine bristle paint brush natural bristle and dust off the screen just before you coat especially in dryer humidity environments...dust sucks and sticks to screens no matter how careful you are .

Keep the coater about 75% full to start and refill when used down to about 40%, this allows a specific hydraulic weight to be applied to the film deposit while coating.

keep a damp towel or paper towel handy to wipe the edge of the coater as the interface of the coater edge film begins to dry out. If the coater tends to resist moving forward to any degree when you start the coating stroke it is time to clean the edge with a damp towel. the coater should easily transition from static contact to forward motion.

using a wider coater , 18inch,  we need to coat side as the coater will lock out if coating top to bottom. Trust me on this one. the advantage of the wider coater is we get a better / larger deposit of useable area as the coater tends to apply emulsion differently at the ends than in the middle of its length. Move the lesser quality coating farther out of the print area with the widest coater you can use.

coating speed should be adjusted based on screen mesh. Speed is subjective but suffice it to say that higher mesh screens should be coated at a lower forward rate than lower mesh screens.

coating pressure again subjestive we tend to start the the coater at first contact with the screen almost verticle. We immediately lower this angle to about 25 degrees above the table as we begin to move the coater. this allows us a heavy emulsion wave to be piled up at the coater screen interface taking advantage of a strong weighted supply of emulsion.

we rotate the screen back to nearly verticle at the end of the stroke and rotate the coater to wash back the emulsion as the run is complete.

Number of coates...we play it by ear, usually 2 or 3  on the shirt side and two on the ink side but again it is subjective as we simply look at the deposit and make a value judgement on the overall deposit. we are looking for a consistant color density of emulsion across the print area and lastly a strong drive through of emulsion on the shirt side when we feel we have sufficient deposits.

store your screens level as possible. While emulsion will not flow easily it will wander to a low area thinning some areas while strenghtening others. We just try to have things level as possible because gravity never sleeps.

Control the volume in your emulsion bucket. we find we get better coverage as the bucket gets to about 1/3 of the original volume. typically we find even after stirring the emulsion there is always a heavier deposit of solids in the bottom of the bucket. We tend to take the last 1/3 of a bucket and stir it up very well then refill that bucket with emulsion from a new bucket duly stirred. this tends to give us a relatively consistant emulsion density relative to solids .
 
we do not measure EOM values but use again a subjective measure of a calibrated finger tip test to decide if the exposed and wased out screen offers sufficient emulsion thickness to acheive the ink result we are expecting.
Strangely enough a quick wipe of the hand over the washed out screen will tell us what we need to know. detecting a crisp edgy feel across the image on the shirt side and a relative flat and non discript feel on the ink side tells us we are pretty good to go and should get good ink deposit results.

Another subjective review we use before exposing is simply to look at the coating density relative to the dried emulsion color and opacity.
If we are looking for a 155 for a white ink on a black shirt we look at the available screens and select the one with the heaviest (darkest color red emulsion) visually. this also give us feed back on our ability to consistantly coat screens of like mesh. we do not expect to see a a big difference in the color / density of any 155 screen for example. If we do we most likely were coating that lot of screens with a hangover or at the end of our work day...it makes  difference at least in our shop again we are a one monkey operation.

Trust some will find some value in this droll at any rate we are open to any suggestions as we are self taught and do most of our work and learning in the vacuum of our world.
mooseman
   

[Gilligan]

Trust some will find some value in this droll at any rate we are open to any suggestions as we are self taught and do most of our work and learning in the vacuum of our world.
mooseman
 

I am in the same situation so trust me, I read these post very carefully to pick up on anything and everything as it's likely the only insight into how do do things better/more correctly than what I might have seen.  I go hang at my buddy's shop a lot and I'm very thankful for all the knowledge I've gained there but his guys use the Pull stroke and coat 1:1 and have no idea of what EOM is.  Their screens have practically no EOM and you can't feel a bit of difference between the print area and the exposed area!  So as much as I appreciate what I can learn from watching those guys I do take it with a grain of salt.  Yes, they get the job done and done well!  But I know they aren't doing it "right" (technically speaking).  So post like this are where I really look to see if I can visualize and learn something.

Only thing I can really offer, as you are way a head of me, is a tip that I think Frog gave me.  Instead of a paint brush (though that's better than what I WAS doing), he suggest using Tack Cloths.  They are basically rags that have a mild tackiness to them to take off that layer of dust that inevitably collects on a sitting screen.

[Parker 1]

What is the Viscosity, and % Solids of the emulsions you are useing?  When coating 2/2

[mooseman]

What is the Viscosity, and % Solids of the emulsions you are useing?  When coating 2/2

according to Ulano 46% & 7100 to 8100 cps
more data here directly from Ulano
http://www.ulano.com/emulsn/presensitized.htm#qtx

[mk162]

question...would refrigerating emulsion up the viscosity and get a better eom?

just wondering that yesterday.

[Frog]

question...would refrigerating emulsion up the viscosity and get a better eom?

just wondering that yesterday.

Not in an unheated shop in Buffalo in December. 

[mooseman]

question...would refrigerating emulsion up the viscosity and get a better eom?

just wondering that yesterday.

Actually we can acheive a better coating when the emulsion is at 50 degrees as opposed to 70 degrees. Here in lovely upstate NY mother nature provides a natural chill but we are actually looking at something with a little more control.
We have been experimenting with altering the scoop coater to get a heavier deposit with fewer passes. So far we are getting mixed reports but we have had some interesting and promising results.
 

[jsheridan]

Great write up. Summed it rather well with methods that are time honored ways of doing it. The best EOM gauge we ever had was our thumbnail and the knowledge of those thumbnail readings from past prints.

take a fine bristle paint brush natural bristle and dust off the screen just before you coat especially in dryer humidity environments...dust sucks and sticks to screens no matter how careful you are .
 

I prefer to use the tack cloths from the local home center or paint shop as it traps that pesky dust that plagues our screen rooms.

[Prosperi-Tees]

Dont some tack cloths have some sort of oil in them?

Since I have not had any formal training could anyone see this? I coated about 12 screens yesterday and a few of them had these lighter circles on them. I clean the same way each time but these had them, admittiley my washout booth is filthy but I give each screen a generous flood rinse before setting to the side to dry.

[mooseman]

Great write up. Summed it rather well with methods that are time honored ways of doing it. The best EOM gauge we ever had was our thumbnail and the knowledge of those thumbnail readings from past prints.

take a fine bristle paint brush natural bristle and dust off the screen just before you coat especially in dryer humidity environments...dust sucks and sticks to screens no matter how careful you are .
 

I prefer to use the tack cloths from the local home center or paint shop as it traps that pesky dust that plagues our screen rooms.

we have a very dusty (tee shirt dusty ) environment but the problem with tac cloth is we need to store it somewhere, keep it clean, not use it for anything else like a snot rag. the beauty of the brush for us is it never wears out, is always handy and just seems to work and if it ain't broke i don't try to fix it more than two or 3 times.
i have been thinking of spraying it, the brush that is, with ststic guard the stuff that folks use on clothes to kill static cling but i have not got there yet. Another test for another day .

[Frog]

Dont some tack cloths have some sort of oil in them?

Since I have not had any formal training could anyone see this? I coated about 12 screens yesterday and a few of them had these lighter circles on them. I clean the same way each time but these had them, admittiley my washout booth is filthy but I give each screen a generous flood rinse before setting to the side to dry.

Tack cloths are generally impregnated with an adhesive (that does not transfer), and are designed for preparing a surface just prior to staining,finishing, or painting and work great for this "off label" use, though it's not that far off label.
To keep it clean, merely store it in a zip lock bag.

Gerry, I can only barely see your problem areas, but have to assume that the mesh resisted the emulsion in these lighter areas and that would have to be due to incomplete cleaning and/or degreasing.

[Prosperi-Tees]

I clean the crap out of my screens but maybe the ones like this were at the end of my run. I use easiest 701 if I have some stains and cci nutralyze if I don't. I just cleaned and scraped my washout booth for the first time in 3 years for about an hour. The thing looks dang near new now, maybe I was getting some contamination from that.

[mk162]

those are fisheyes.  its a small amount of grease or oil on the screen.  same thing happens in the auto paint industry.

try degreasing a little better

[Gilligan]

...we are open to any suggestions...

...if it ain't broke i don't try to fix it more than two or 3 times....

 

[Prosperi-Tees]

Maybe I will try degreasing after the 701 as well. We shall see on the next batch