One Hit White -- the Good, the Bad, and the Ugly

[alan802]

I agree in principle to most everything Sonny, except you have to use significantly more pressure on a 230 versus a 110 and when you use higher mesh counts, you end up pushing the ink into the garment because there aren't enough inks out there that will clear higher mesh counts with very little pressure.  It takes approximately 18psi for us to shear white ink from a 135/48,  yet it takes almost 30 for it to clear a 195/55.  So less ink is going to pass through the 195, plus the added pressure it takes to shear the ink from the stencil and you have a huge loss of opacity.  I wish I knew the exact psi on our press that ink begins to penetrate the garment but I don't have the time or the tools to figure that out right now, but I'd take a wild ass guess and say it's in the upper 20's and anything over that and you have too much garment penetration with a good opaque white ink.  Obviously, some inks will penetrate at a much lower pressure point and some higher, so the ink rheology plays a huge role in that.

A few things that I don't see mentioned very often on the forums is the mesh specification sheets and what some of those numbers on them really say about the mesh and what it's capable of.  Now some of the specs don't raise my attention all that much, but I like to look at thread diameter, percentage open area, tension level and then the big one, theoretical ink volume.  Thread diameter is obvious, percentage open area will give you an idea of how much pressure you'll need to apply to shear the ink through the mesh, and then theoretical ink volume will tell you how much ink you can expect to deposit with a standard stencil.  You can really change that T.I.V. of a mesh count when you start playing with stencil thickness.  I know that with a large percentage open area and a decently thick stencil, I can look at the TIV of a mesh and get a great idea of what I can achieve with it. 

You can see that most of the thicker thread mesh will theoretically deposit more ink, but with the right art/design, you can make a thinner thread mesh with a higher % open area deposit the same amount of ink with far less pressure if you make your stencil thicker to make up the difference in thread thickness between the two mesh counts.  You can also make that thicker thread mesh with a very thick stencil and get a lot of ink on the shirt but you have to find that line where you don't have to use too much pressure to print with or you will lose opacity because of ink penetration into the garment. 

I don't know about any of you, but I'm always looking at the manufacturers mesh spec sheets for those numbers I mentioned.  I have put those numbers I see into production and they really do tell you all you need to know about how a mesh will perform.  And you can also manipulate those numbers with the stencil thickness and make a mesh count that might not look like it has much potential into a great tool for your shop. 

Well this is all fine and dandy but what about underbase on a manual? I still don't know what is exceptable, one hit white flash then color or pfpf the white then color. My single hit whites are not even close to most of you guys, maybe it's my stencil thickness at 1/1 is not thick enough. Imh coating screens today and I will try more hits of emulsion to see.

I'll tell you that you should not have to pfpf an underbase before you put on top colors.  We've done it at our shop from time to time on a low piece job so we wouldn't have to burn another screen for a highlight white, and we've had to do it on occasion for very transparent top colors like neon's and your occassional blue.  But for every day printing, it's print the underbase, flash it and on come the top colors.  You need to use a thicker stencil and perhaps a lower mesh count.  Instead of a 1/1, coat everything with a 2/2, round edge of the coater and then observe very carefully what you get on the garments.  I know lots of shops do the pfpf underbasing but it's totally avoidable.  Get a few screens of the same mesh count, coat one 1/1, then another 2/2 then the third one 3/3 then put them on your manual and set them up the same and put the same ink and use the same squeegee to print with.  Put some test shirts on your pallets and just start printing and comparing the ink deposit between the three screens.  Now make sure they are all around the same tension level and try to use as little pressure as possible to clear the screen with one stroke.  I think you'll be surprised at the difference in ink deposit between the 1/1 and 3/3 and maybe you'll not ever have to pfpf your underbases again. 

[ScreenFoo]

Great points--to me, the count, thread thickness, and tension level are THE three--open area and theoretical ink volume are both calculated from the Mc and Td. 

I'm interested in the example though--in that example, then you're increasing mesh count, as well as thread diameter--wouldn't a more subjective test be between something more like a 110/80 and a 220/40?
Although I would suppose even with a near-equal open area, the 220 may still require a little more pressure, having four times more threads per area, and so more thread surface area?

I'm not disagreeing with the reasoning, by any means--I've made similar observations in practice.  I get forced into putting white on 230's and 305's on a regular basis, and have not ever been able to do anything close to an acceptable one hit with them.

As to comparing thicknesses on the same mesh--if you're not familiar with it, there's a great little blurb about 'step coating' on page four of this: 
http://www.kiwo.com/Articles/Getting%20the%20most%20out%20of%20direct%20emulsion%20stencils.pdf
Exposing it is the trick.   

[Printficient]

The pressure that is true is the mechanical pressure and not the psi.  The psi readings on any press are not close to being true or for that matter measurable.  “Pressure” equals force divided by area [F/A].  The ideal pressure on the T-Shirt platen [or press bed] is zero.  The goal therefore is equilibrium between blade pressure [F/A] and mesh tension AT ZERO GAP. 
Ink is "one" of the "All" parameters I mentioned.  I guess that what I am saying is that while it is good to know "how" to do something, it is better to know the "why" of what you are doing.
As to "eom" and "tension", these are the two that when changed affect the "whole" in a greater way, yet these are the two that are bandied about as the end all of problem solving.  Yet these two probably cause more problems because of not knowing the "why".

[alan802]

The pressure that is true is the mechanical pressure and not the psi.  The psi readings on any press are not close to being true or for that matter measurable.  “Pressure” equals force divided by area [F/A].  The ideal pressure on the T-Shirt platen [or press bed] is zero.  The goal therefore is equilibrium between blade pressure [F/A] and mesh tension AT ZERO GAP. 
Ink is "one" of the "All" parameters I mentioned.  I guess that what I am saying is that while it is good to know "how" to do something, it is better to know the "why" of what you are doing.
As to "eom" and "tension", these are the two that when changed affect the "whole" in a greater way, yet these are the two that are bandied about as the end all of problem solving.  Yet these two probably cause more problems because of not knowing the "why".

Well, unfortunately that's all we have to go by on our autos is "presumed" psi and although the actual pressure being applied is different from one press to another, even within the same company and model, it can still be relative and compared once there are baselines achieved for each machine.  I have figured that 20psi on our RPM is equivalent to 22psi on another RPM in our area that I'm familiar with.  I also think that a 25psi readout on our press is about 30psi on a sportsman that is down the road from our shop.

I personally think that the psi/force or whatever you want to call it is measurable, although it's not very accurate or "true" in a purely physical sense like we can measure how much I weigh or how much I can bench press.  It's all we have and is pretty much standard on most autos out there for a reason, it does serve a purpose for those who want it to.

[brandon]

The pressure that is true is the mechanical pressure and not the psi.  The psi readings on any press are not close to being true or for that matter measurable.  “Pressure” equals force divided by area [F/A].  The ideal pressure on the T-Shirt platen [or press bed] is zero.  The goal therefore is equilibrium between blade pressure [F/A] and mesh tension AT ZERO GAP. 
Ink is "one" of the "All" parameters I mentioned.  I guess that what I am saying is that while it is good to know "how" to do something, it is better to know the "why" of what you are doing.
As to "eom" and "tension", these are the two that when changed affect the "whole" in a greater way, yet these are the two that are bandied about as the end all of problem solving.  Yet these two probably cause more problems because of not knowing the "why".

Well, unfortunately that's all we have to go by on our autos is "presumed" psi and although the actual pressure being applied is different from one press to another, even within the same company and model, it can still be relative and compared once there are baselines achieved for each machine.  I have figured that 20psi on our RPM is equivalent to 22psi on another RPM in our area that I'm familiar with.  I also think that a 25psi readout on our press is about 30psi on a sportsman that is down the road from our shop.

I personally think that the psi/force or whatever you want to call it is measurable, although it's not very accurate or "true" in a purely physical sense like we can measure how much I weigh or how much I can bench press.  It's all we have and is pretty much standard on most autos out there for a reason, it does serve a purpose for those who want it to.

This has turned into a great thread. I want to ask a question but I know it is veering off topic. So for presumed PSI what is everyone's point where deflection steps in? Our Sporty E  is right around 40 to 45 PSI, but as stated above it can vary from mesh count/ink and sometimes head to head (sigh).

On a side note that certain long haired Texan has helped me a lot in the past. Not personally but if you give him the chance about being efficient and thinking ahead and ROI he has some very, very good points

[Printficient]

The pressure that is true is the mechanical pressure and not the psi.  The psi readings on any press are not close to being true or for that matter measurable.  “Pressure” equals force divided by area [F/A].  The ideal pressure on the T-Shirt platen [or press bed] is zero.  The goal therefore is equilibrium between blade pressure [F/A] and mesh tension AT ZERO GAP. 
Ink is "one" of the "All" parameters I mentioned.  I guess that what I am saying is that while it is good to know "how" to do something, it is better to know the "why" of what you are doing.
As to "eom" and "tension", these are the two that when changed affect the "whole" in a greater way, yet these are the two that are bandied about as the end all of problem solving.  Yet these two probably cause more problems because of not knowing the "why".

Well, unfortunately that's all we have to go by on our autos is "presumed" psi and although the actual pressure being applied is different from one press to another, even within the same company and model, it can still be relative and compared once there are baselines achieved for each machine.  I have figured that 20psi on our RPM is equivalent to 22psi on another RPM in our area that I'm familiar with.  I also think that a 25psi readout on our press is about 30psi on a sportsman that is down the road from our shop.

I personally think that the psi/force or whatever you want to call it is measurable, although it's not very accurate or "true" in a purely physical sense like we can measure how much I weigh or how much I can bench press.  It's all we have and is pretty much standard on most autos out there for a reason, it does serve a purpose for those who want it to.

Do you not have a mechanical adjustment on the squeegee bar?  This should be 99% of your adjustment with the other 1% being the air pressure.

[ScreenFoo]

Again... aren't these single measurement tangents not seeing the forest but the tree?

Variations in mesh tension and off contact (obviously changing mesh tension as well) will make even a properly calibrated pressure measurement just another factor...  Everyone running the same bore chopper?  Exact same squeegee size? 
Everyone's squeegee new?  If you're sharpening, the free length, deflection, and applied force are changing.   Ceteris paribus....

[Inkworks]

Again... aren't these single measurement tangents not seeing the forest but the tree?

Variations in mesh tension and off contact (obviously changing mesh tension as well) will make even a properly calibrated pressure measurement just another factor...  Everyone running the same bore chopper?  Exact same squeegee size? 
Everyone's squeegee new?  If you're sharpening, the free length, deflection, and applied force are changing.   Ceteris paribus....

Yup, and getting back to the original posters print, in this case EOM is a non-factor.

I'd start with:
#1 - Mesh choice
#2 - Ink choice
#3 - Squeegee durometer/angle/pressure/speed

The light-touch final stroke is the key to not having to p/f/p.

[Printficient]

Again... aren't these single measurement tangents not seeing the forest but the tree?

Variations in mesh tension and off contact (obviously changing mesh tension as well) will make even a properly calibrated pressure measurement just another factor...  Everyone running the same bore chopper?  Exact same squeegee size? 
Everyone's squeegee new?  If you're sharpening, the free length, deflection, and applied force are changing.   Ceteris paribus....

Bingo.  You get it.  All I was saying in my original answer is that "all" the parameters have to be taken in to account and that no two shops are the same.  Also understanding "why" something does what it does will help you know what changes are needed in other parameters.  You sir get it.  No 1 parameter is the fix all for any printing issue.  The goal is to place the ink "ON" the garment and if all the stars line up in your shop then you can and you will not see any problems.
On a side note...a troubleshooting technique that has helped me throughout my career is Do the opposite of what you think you should do and you will fix your problem 99 times out of 100.

[alan802]

Do you not have a mechanical adjustment on the squeegee bar?  This should be 99% of your adjustment with the other 1% being the air pressure.

I've done it both ways where I relied on the mechanical sq. adjustment more than worrying about psi and the other way of setting the sq. all the way down and never touching them and using your air pressure regulator (psi) to adjust print pressure.  I stayed with the latter and if anyone would like to compare the two methods, do them both for several weeks at a time and let me know which one actually assures you are printing with the least amount of print pressure.  So do you set your squeegee regulators all the way up, or at a pressure that you know even the thickest ink will go through the highest mesh?  That method doesn't work the best at our shop for what I'm trying to achieve, and that is maximizing opacity by putting as much ink on the shirt and not in the shirt.  For a while I used both, 50/50, thinking that I would be maximizing all the adjustments and it was basically a waste of time.  Just set the sq mechanical adjustment one time and forget about them and if you set everything up correctly, you'll never be printing with too much pressure.

I don't recall anyone saying that one parameter is the fix for all printing problems, I'm sorry if someone got the idea that I was saying that in any way.  I think I understand as much as anyone how all the parameters interact to achieve the final print, but I think many don't understand the importance of EOM and stencil thickness.  You have to be careful when talking about EOM and just because a screen has 100% EOM, doesn't necessarily mean it's going to lay down a crap load of ink.  You can lay down a tremendous amount of ink with 10% EOM if the thread thickness of that mesh count is way up there.  In comparison, you can have 100% EOM with a 10 micron thick thread mesh and not have much of an ink deposit at all.

If you really want to only use the bare minimum pressure to shear ink from a screen, you set up your screen and put a few shirts on your pallets, set your sq all the way down, then set the squeegee regulator to a psi where you know it won't clear, then print.  Look at how much ink is left and make the adjustment based on what you think will get the ink to "almost" clear the screen and print a completely different/fresh shirt.  Printing on a wet shirt will throw you off and the wet ink will actually help pull ink from the stencil and you'll think that you have the pressure set correctly and the next clean shirt you print on the ink won't clear completely.  Increase your psi on the printhead until you reach that pressure where the ink clears, then you can do the same with squeegee speed to get the fasted print speed therefore maxing out ink opacity.

I guess I don't understand what your asking Foo.  I suggested a few things knowing the guy runs the same exact press as I do, maybe that's where the confusion is coming from?     

And I'm just gonna say it... Sonny, but that is pretty awful advice in my opinion.  I guess if you are so far off with your thinking that the opposite of what you were doing actually works, then perhaps more knowledge and experience is needed in a bad way.

[Printficient]

Do you not have a mechanical adjustment on the squeegee bar?  This should be 99% of your adjustment with the other 1% being the air pressure.

I've done it both ways where I relied on the mechanical sq. adjustment more than worrying about psi and the other way of setting the sq. all the way down and never touching them and using your air pressure regulator (psi) to adjust print pressure.  I stayed with the latter and if anyone would like to compare the two methods, do them both for several weeks at a time and let me know which one actually assures you are printing with the least amount of print pressure.  So do you set your squeegee regulators all the way up, or at a pressure that you know even the thickest ink will go through the highest mesh?  That method doesn't work the best at our shop for what I'm trying to achieve, and that is maximizing opacity by putting as much ink on the shirt and not in the shirt.  For a while I used both, 50/50, thinking that I would be maximizing all the adjustments and it was basically a waste of time.  Just set the sq mechanical adjustment one time and forget about them and if you set everything up correctly, you'll never be printing with too much pressure.

I don't recall anyone saying that one parameter is the fix for all printing problems, I'm sorry if someone got the idea that I was saying that in any way.  I think I understand as much as anyone how all the parameters interact to achieve the final print, but I think many don't understand the importance of EOM and stencil thickness.  You have to be careful when talking about EOM and just because a screen has 100% EOM, doesn't necessarily mean it's going to lay down a crap load of ink.  You can lay down a tremendous amount of ink with 10% EOM if the thread thickness of that mesh count is way up there.  In comparison, you can have 100% EOM with a 10 micron thick thread mesh and not have much of an ink deposit at all.

If you really want to only use the bare minimum pressure to shear ink from a screen, you set up your screen and put a few shirts on your pallets, set your sq all the way down, then set the squeegee regulator to a psi where you know it won't clear, then print.  Look at how much ink is left and make the adjustment based on what you think will get the ink to "almost" clear the screen and print a completely different/fresh shirt.  Printing on a wet shirt will throw you off and the wet ink will actually help pull ink from the stencil and you'll think that you have the pressure set correctly and the next clean shirt you print on the ink won't clear completely.  Increase your psi on the printhead until you reach that pressure where the ink clears, then you can do the same with squeegee speed to get the fasted print speed therefore maxing out ink opacity.

I guess I don't understand what your asking Foo.  I suggested a few things knowing the guy runs the same exact press as I do, maybe that's where the confusion is coming from?     

And I'm just gonna say it... Sonny, but that is pretty awful advice in my opinion.  I guess if you are so far off with your thinking that the opposite of what you were doing actually works, then perhaps more knowledge and experience is needed in a bad way.

Alan, I can see you might get that conclusion.  I'll give you an example.  I was helping a friend get a print looking better.  He started with a 110 mesh for his underlay.  He was doing pfp and he was not happy with the result.  It was uneven and rough.  I asked what he thought the problem was with printing one pass instead of pfp.  He said there was not enough ink and needed more for coverage.  His solution...pfp.  I took the shirt off and turned it inside out and there was a lot of ink coming through the shirt from his first pass.  I explained that the problem was not not enough ink on the first pass but in actuality the exact opposite was true.  He had way too much ink.  We went to a 230 mesh pfp and the shirt was beautiful.  The exact opposite of what he thought he needed to do was the correct thing to do.  All I am saying is if you think you need more pressure the maybe you have too much and the screen is pulling the ink back. 
If I was to ask which print stroke would get the best deposit of ink all things being equal, fast or slow, what would your answer be.
Joe Clarke's answer would be: High shear is ONLY possible with high stroke speed.

[ScreenFoo]

Sonny beat me to it on carriage speed--I had it beaten into my head for years by many people that screens clear by slowing down the squeegee.  In a way, it's true, but it's almost always a consequence of other factors that likely need to be changed.

Perhaps it was partially misunderstanding--pressure I only questioned because to me, it's the last link in the chain.  Once all other factors are decided, the screen is in, loaded with ink, floodbar, squeegee, etc.  then you set pressure at the smallest amount that will clear the screen properly.  I questioned it not only in the respect that it is not a calibrated adjustment, but that other factors not mentioned could change the amount of pressure, whatever the setting, irregardless of the possibility of settings between presses being exactly the same.

I wasn't trying to say pressure is unimportant to the process, it's critical--just like every other link in the chain is.  It was just my take that if we can go under the assumption that the screen, mesh, stencil, ink, and off contact are fine, squeegee pressure may be too high, but why is that?  Is the squeegee trying to fill the stencil when the floodbar did not?  Is the squeegee too dull or moving too slow to properly shear the ink?  Is there a factor like the ink, planar calibration, or head linear that is being taken for granted to be OK that isn't?   

These are just some thoughts--and another nice break from cranking out shirts on the press.    (Is it the weekend?  I can't tell anymore    )

[alan802]

I was lucky to discover how print speed can affect ink deposit/opacity when I first met Mr. Clarke at the ISS in Ft. Worth a few years back and I took home a few of his smiling jack blades.  I wish I would have known something other than slow=more ink, fast=less ink much sooner in my printing career but just like every other parameter and variable, I learned a little at a time.  I also started reading anything I could find from Joe and it was a lot like when I discovered Bill's articles and it opened up a lot more info that I could use to my advantage.  It was one of the last print parameters that I found had a profound influence in maximizing an inks opacity.  I had always been told that slower squeegee speed equals more ink, but just because we deposit a large amount of ink, doesn't mean the print will look good or be opaque.  I know I'm not saying anything that a lot of us don't already know, but it might help some of the pups that haven't learned this yet, but printing faster helps in shearing the ink on top of the garment, possibly depositing less ink but maximizing opacity.

[ScreenPrinter123]

So am I tracking with you, Raincloud: open the print speed valve up all the way and add just enough pressure for all the ink to clear -- even with a triple duro or is this really only optimal with something like a smilin' jack?  You're always printing wide open on the print speed valve with plastisols? -- or in your case, as fast as the motor will move the squeegee?  I'll be flinging ink all over the stinkin' place.

[alan802]

We've rarely been able to print at 30, but considering most shops print white ink very slowly, 3-6"/sec, we print white at 10-14"/sec and some other inks will shear at 20-25.  Triple duros are great, but you can print faster with the smiling jacks.  It's not a ton faster but it's noticeable.  With regular spot colors on lights, you should be at 10-20"/sec and if you're not already printing at 8-12 with your white, go ahead and try to increase your squeegee speed.  You might have to increase print pressure slightly as you increase print speed so you have to balance those two parameters to get the most opacity.