[theory] What makes white ink so hard to print? Part 4

[Underbase37]

I have found for us the right short body ink will sheer better & at a quicker speed. This means for us we can get a better fiber mat-down & as Colin stated letting the ink sit on top of the garment, resulting in better opacity.
I feel you can get the long body to do the same but with slower speed & sometimes higher pressure, or some modifications to make it less stringy/long bodied. I also feel that the long body inks have better opacity if you can get them to sit on top of the garment with low pressure. & I feel they have better bridging/stretch capabilities too.

Murphy37

[blue moon]

How would one test if the ink long or short bodied?

What about the fact that we are shearing on the top?

Pierre

[ScreenFoo]

We all keep saying it prints better and shears better, but what does that mean? The shearing is happening on the top of the screen and the print is underneath. That sounds like we are not really shearing it! Or are we?

Depending on your print speed, you may be 'ejecting' it.   (Someone will come up with who came up with that   )

[Underbase37]

How would one test if the ink long or short bodied?

What about the fact that we are shearing on the top?

Pierre

I guess my hippie non technical way would be dip my spatula in the ink & if the string of ink follows me half way to the press, its long. If I pull my spatula out & it is more of a clean break its short. But I don't think that is the test you are talking about.

On the shearing, i guess I'm unsure what you mean by "on the top" are you saying that if the screen is flooded/primed with ink correctly you are shearing the ink from the screen instead of though the screen. Giving you the ability for less pressure & therefore needing less body?

Murphy37

[starchild]

OK, so many good points, but I am going to try to reel this in and return to the less practical and more theoretical discussion.

We all keep saying it prints better and shears better, but what does that mean? The shearing is happening on the top of the screen and the print is underneath. That sounds like we are not really shearing it! Or are we?

Pierre

To share the ink is to apply force to the ink.. A low share is to stir, a high share is blade pressure applied as during a print stroke. A high share is needed to thin the ink to it's plastic viscosity level to allow the ink to flow into the mesh.

A "better" share will be indicative of an ink that flows readily with minimum- high share force..
A "better" printing ink will rapidly return to it's original body (it's relative viscosity) only after it exists the shirt side of the mesh opening and wets the shirt fibers and hold's the image shape.

How would one test if the ink long or short bodied?

What about the fact that we are shearing on the top?

Pierre

A long bodied ink will be stringy and will not want to separate.
A short bodied ink will separate easily.

A short bodied ink is preferable for better shearing and printing.

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[abchung]

I was thinking today about spaghetti on a fork while printing today.

If we are shearing with the squeegee, it means we are shearing at where the emulsion touches the squeegee. Which means there is an ink thickness from the mesh to the top of the emulsion. Now would this ink thickness be thick enough to give us ink release problem?

If it does for long bodied ink, wouldn't it be better to have a low EOM on the ink side of the screen, so the spaghetti ink is thin enough to just break apart.

[blue moon]

I was thinking today about spaghetti on a fork while printing today.

If we are shearing with the squeegee, it means we are shearing at where the emulsion touches the squeegee. Which means there is an ink thickness from the mesh to the top of the emulsion. Now would this ink thickness be thick enough to give us ink release problem?

If it does for long bodied ink, wouldn't it be better to have a low EOM on the ink side of the screen, so the spaghetti ink is thin enough to just break apart.

this is where I was going with the questions! After the shear, there is a layer left that still has the mesh embedded in it and after the squeegee leaves out of the way, the off contact makes the mesh move up and out of the ink deposit. This, it seems, is where the body of the ink comes into play. If it is long, the mesh will pull the ink apart and it will not release cleanly (long strings drawn from the mesh to the shirt). Short bodied ink will actually release (break off) quicker and should leave a cleaner deposit.

So what makes one ink short and another long?

pierre

[starchild]

I was thinking today about spaghetti on a fork while printing today.

If we are shearing with the squeegee, it means we are shearing at where the emulsion touches the squeegee. Which means there is an ink thickness from the mesh to the top of the emulsion. Now would this ink thickness be thick enough to give us ink release problem?

If it does for long bodied ink, wouldn't it be better to have a low EOM on the ink side of the screen, so the spaghetti ink is thin enough to just break apart.

Getting the ink thin enough has to do with the amount of force applied to the ink to get it at it's fluid state. (It's plastic viscosity).

Your thought towards lower eom will suggest distance the ink has to travel to transfer (it's shortness ratio-how it resists flow) if it's too low then higher force will also have to be applied for transfer to occur but the ink may not hold it's shape once it's deposited on to the shirt.

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[starchild]

I'm trying to understand what makes it long or short.. Do you mean the ingredients? Or the measurement?

Is it the difference in too high or just right viscosity of the ink?

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[blue moon]

I'm trying to understand what makes it long or short.. Do you mean the ingredients? Or the measurement.

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how about both?

pierre

[blue moon]

I was thinking today about spaghetti on a fork while printing today.

If we are shearing with the squeegee, it means we are shearing at where the emulsion touches the squeegee. Which means there is an ink thickness from the mesh to the top of the emulsion. Now would this ink thickness be thick enough to give us ink release problem?

If it does for long bodied ink, wouldn't it be better to have a low EOM on the ink side of the screen, so the spaghetti ink is thin enough to just break apart.

Getting the ink thin enough has to do with the amount of force applied to the ink to get it at it's fluid state. (It's plastic viscosity).

Your thought towards lower eom will suggest distance the ink has to travel to transfer (it's shortness ratio-how it resists flow) if it's too low then higher force will also have to be applied for transfer to occur but the ink may not hold it's shape once it's deposited on to the shirt.

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I think he was talking about the dimensional thickness rather than density thickness.

Which brings up another point, will the thinner deposit be longer or shorter than the thick deposit of the same ink?

pierre

[starchild]

If the ink is deposited then it's at it's relative viscosity so it's just sitting there doing nothing. So how would there be a stress test reading on an already deposited ink?  How would we test long vs short?

When the ink transfers into the mesh it retains it's fluid form while the blade's edge is still in contact with the mesh opening and only deposits onto the shirt when the mesh snap happens... So if the ink is clinging on mesh snap then that indicates that the ink is reverting back to it's relative viscosity too quickly- a reading of too high a value of a thixotropic index measurement.

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[ScreenFoo]

Seen the 'pulling the ink through' the screen trick.
How many people here can wipe a finger across the top of a white screen on the auto that's just pulled, and not pick up any ink?  Not me.
Dynamics change a lot with speed and angle, not to mention viscosity and changes in it...

How about this:  It's thixotropic, i.e. will stay put until you push it around, it would have as little tack as possible (under the circumstances with the pigment involved,) it will have a minimum of shear thickening, and all these properties will stay stable between 70-120 degrees.

Does this sound like what we are going for?
Sounds tough.  I feel sorry for the ink guys.   

[3Deep]

Pierre, after reading some of your post I see what your asking about whats going on at the bottom of the screen.  From what I see it all depends on whats happen at the top..short body long body don't matter if the inks are not warm,correct squeegee, squeegee angle, print pressure, print speed, tight mesh, mesh count to me all that plays a big factor in how a ink will work.  I would almost bet you and I could use the ink and it might be the root to boot in your shop and might print like crap in my shop from the way I set it up, I know all this still does not explain a long and short body ink and why it happens, but I know some inks print great for me and some don't.

Darryl

[blue moon]

Pierre, after reading some of your post I see what your asking about whats going on at the bottom of the screen.  From what I see it all depends on whats happen at the top..short body long body don't matter if the inks are not warm,correct squeegee, squeegee angle, print pressure, print speed, tight mesh, mesh count to me all that plays a big factor in how a ink will work.  I would almost bet you and I could use the ink and it might be the root to boot in your shop and might print like crap in my shop from the way I set it up, I know all this still does not explain a long and short body ink and why it happens, but I know some inks print great for me and some don't.

Darryl

Darryl, your comment is the reason I am down this path. Why should the inks print different?

My thinking is that if we take the lab readings on the inks and understand 99% of what is going on with them, we should ALL be able to set up our presses to get the most out of the ink. Without really understanding the ink properties we are all guessing what to do and how to print. We all find ways to make it happen, but I would rather understand the viscosity, density, tack and body and then go and set up the press to match those. I think if we truly understood those, we would all have the presses set up the same!!!

does that make sense?

pierre