Ink Laydown

[BeauchampT]

Want to get feedback on the appearance of these solid laydowns. The pictures are taken at 50X magnfication of ink printed on MFC quailty paper. This is consitent on different presses, at different speeds. Sheetfed and web (more pronounced the higher speed you go). Different inks, different fount solutions, even checked on a coated paper, yet, all get the same pattern.

There are two distinct problems 1) 'voids' (actual white spaces in the print) (I know what this is from and am pursuing a solution), 2) if you look it seems like the ink lays down in a mottled pattern.

Is this just a natural limit of lithography, is it possibly from a raw supply, or am I just overthinking it....?

Thanks for your help.

 

[gordo]

Can you post a photo of a 25% 50% and 75% halftone dots. Doesn't have to be the exact percent.

Best gordo

 

[BeauchampT]

Here they are. Appear to have the same issue.

 

[BeauchampT]

Just to finish this thread myself.....

Turns out I just need to think before I speak.

AFter looking at a variety of prints from various manufacturers, I found that all offset print looks like this, I'd just never really noticed before.

It is normal that an emulsion is not going to be perfectly even (oil and water do not mix). Laydown will always have some variation to its appearnce. The goal is to minimize this difference (likely a great deal to do with how the raw materials of the ink are worked together in my opinion).

Guess I was just hunting for a perfect world that doesn't exist.

Thank you for your patience as I though out loud.

 

[gordo]

AFter looking at a variety of prints from various manufacturers, I found that all offset print looks like this, I'd just never really noticed before.

It is normal that an emulsion is not going to be perfectly even (oil and water do not mix). Laydown will always have some variation to its appearnce. The goal is to minimize this difference (likely a great deal to do with how the raw materials of the ink are worked together in my opinion).

I think that it's great that you have the equipment to take micro photos - most printers do not, and that's a problem.
A small but important correction...you wrote that "oil and water do not mix" That is incorrect. They do "mix" (actually emulsify) and they are designed to "mix". Oil and water are instead non-miscible.
The problem is when ink is over emulsified by the fountain solution. Because fountain solution is a solvent - instead of emulsifying the ink - it can attack and break down the ink. When you see voids in the solids it may indicate over emulsification. Then you check the halftone structures in screen tint areas (which is why I asked you to post those pics). You do this because every halftone dot is a miniature solid so it should look quite similar to the actual solids. However with the halftone dots you can see their edges where the greatest volume of fountain solution touches the ink and where the ink film is thinest. At the dot edges you can see more clearly if the fountain solution is eroding, washing away, or dissolving the ink. If so then you can start decoding why that's occurring. If the dot edges are fairly sharp then that indicates that the fountain solution/ink formulation are probably compatible and so the voids, or pigment clumping/mottling is probably caused by something else in the process.

Voids in the solids usually indicate over emulsification however, voids are sometimes confused with “pinholing” which is most likely due to inadequate pressure between plate and blanket rather than the ink over emulsifying.

A good idea is to collect a small library of micro photos of solids and halftone dots cataloged according to what defects they reveal as well as what they look like when the printing is good. That way you'll have a reference when things go sideways.

When I saw the pics you posted of the halftone dots they appeared to be OK (although it was a bit difficult to tell because the images are out of focus).

best, gordo