impact of squeegee pressure on halftone ink deposit

[blue moon]

Doug,

what happens if you push harder and drive that dot in? I would imagine more dot gain, but if this i something that can be controlled, we should be able to get more ink on the garment.

When is more pressure too much pressure (on the squeegee)?

pierre

[DouglasGrigar]

Doug,

what happens if you push harder and drive that dot in? I would imagine more dot gain, but if this i something that can be controlled, we should be able to get more ink on the garment.

When is more pressure too much pressure (on the squeegee)?

pierre

Good question - the above was printed with about 25 -30 pounds of pressure (and for reasons I can go over later) - where do we go from here and is that too much pressure? I have thoughts and have tested for some results but of course that was not the point of the post - the point was the conversation about the issue.

How much can we flatten the garment substrate threads and weave before we have the blade bend over and have a loss of control?

This subject brings up loads of questions that need to be tested, studied, and if possible applied...

[blue moon]

Good question - the above was printed with about 25 -30 pounds of pressure (and for reasons I can go over later) - where do we go from here and is that too much pressure? I have thoughts and have tested for some results but of course that was not the point of the post - the point was the conversation about the issue.

well, we can fix that!

why waste a good topic? Here is a new thread . . .

soooo,where do we go from here and is that too much pressure?

[jsheridan]

Doug,

what happens if you push harder and drive that dot in? I would imagine more dot gain, but if this i something that can be controlled, we should be able to get more ink on the garment.

When is more pressure too much pressure (on the squeegee)?

pierre

Squeegee pressure is mute in relation to the ink volume being passed through the mesh. You can't put any more ink through a screen than the stencil thickness will allow. This is the single largest problem with screenprinters, they think they can get more ink on the substrate by adding more squeegee pressure. The only thing excessive squeegee pressure does is make things worse. It increases dot gain, drives the ink into the substrate, forces fibrillation and reduces the overall opacity.

The only way to get more ink ON the shirt is to make a thicker stencil.

[blue moon]

Doug,

what happens if you push harder and drive that dot in? I would imagine more dot gain, but if this i something that can be controlled, we should be able to get more ink on the garment.

When is more pressure too much pressure (on the squeegee)?

pierre

Squeegee pressure is mute in relation to the ink volume being passed through the mesh. You can't put any more ink through a screen than the stencil thickness will allow. This is the single largest problem with screenprinters, they think they can get more ink on the substrate by adding more squeegee pressure. The only thing excessive squeegee pressure does is make things worse. It increases dot gain, drives the ink into the substrate, forces fibrillation and reduces the overall opacity.

The only way to get more ink ON the shirt is to make a thicker stencil.

well, I agree with a little caveat. . . the amount of ink deposited probably resembles a bell curve. There is a max that can be deposited with the given stencil and squeegee combination. If the settings are not in the optimal position, some changes can still be made to increase the amount of ink deposited. So yes, there is usually a way to add more ink.

What I am not sure about is the impact of the softer squeegee and the really low angles. It is pretty obvious that both of those will lay down more ink, but I am not sure why. They also negatively impact the ink deposit by increasing the dot gain. Or . . . are they just spreading the ink more and thus appear to lay down more?

The question in the end is: "Where on that curve is the right balance of ink deposit, dot gain and all the other factors?"


pierre


pierre

[yorkie]

The problem is that the knit of the textile has a valley area beneath the halftone dot. More pressure reduces the depth of the valley, by pressing down the mountains.

Elliptical dots attempt to be wide enough to bridge between an mountain and a valley. The none proportional ratio screen example I attached orients the ellipse to oppose the orientation of the mountains and valleys. Of course at some some point, the ellipse is not big enough to bridge the gap.

Beyond dot shape would be to have a rip which could define a minimum dot size. When the dot size drops too small, full dots would be removed from the halftone and the density of these dots would be given to another dot which is also too small,to where the second dot would grow to a size above the minimum dot size. So the when the rip outputs a 5% screen, rather than having 100 each at 5%, there would be 50 dots at 10%. For a 1% tent, rather than 100 dots of 1%, there would be 10 dots of 10% and a 1/2% tint would have 5 dots of 10%... Any halftone above 10% would print normally.

EDIT: I should have also mentioned that underbasing is a method of smoothing the mountains and valleys.

[RichardGreaves]

How much force does it take to leave a bloody fingerprint on the wall as you leave the building? Will pressing harder, help? How much force does it require for a cross cut saw to cut?

Once you make the SEAL of the blade with the inside, and seal the bottom of the stencil with the substrate - more force is wasted.


Take your squeegee and press hard, harder to make this watch leave the hole in the stencil. Stand on it.  More force just BENDS THE BLADE. The ink in the foxhole is laughing at you.

Of course, with absorbent textiles, angle will force the ink that flows ahead of the lip through the stencil holes deep into the inside or a shirt.

How much can you charge for ink on the inside of the shirt - or the platen?


Remember, the downforce is distributed across the 6" or 14" blade lip AND much of it is invested in overcoming the 7 or 14 or 25 newton resistance of the mesh AND the blade stiffness itself.

EVERY amount of force you don't need is wasted. If you can reduce pressure and it still prints - keep backing off.

Concentrate on as much blade speed/shearing force as possible. Screen printing ink needs high shearing force to get it to move rather than force.