Solid Ink Density (SID) and Dot Gain (TVI) relativity and troubleshooting

[MassPrepressGuy]

Hello Print Planet. I’ve got a question from a Prepess guy (me) who is learning the ropes of sheet-fed offset.
We all know that SID affects TVI. Usually when SID is on the low side then most likely TVI is low as well. Conversely, when SID is high, then so might be the TVI. Well what happens when this isn’t the case? What if SID is high but TVI is much lower than where it should be. Also the opposite…what if SID is low but TVI is high? What should be looked at on press that causes this and how can it be corrected so that the SID and TVI remain in harmony?

Thanks

 

[Cornishpastythighs]

Check for slurring or doubling and check condition of printed dots for signs of excessive emulsification

 

[MassPrepressGuy]

Check for slurring or doubling and check condition of printed dots for signs of excessive emulsification

Thanks. I understand what emulsification is, however what are tell tale signs of excessive emulsification?

 

[gordo]

Thanks. I understand what emulsification is, however what are tell tale signs of excessive emulsification?

Emulsification is normal and the ink is formulated to accept a molecule thin film of fountain solution.
Over-emulsification is not normal.
Fountain solution/water is a solvent.
Large areas of ink (solids) can somewhat resist the solvent effect while small areas of ink are less able. The effect is a washing out of the ink film in those small areas. Hence the solids retain more ink film density than the small dots.
Your measuring device doesn't know about dot size so it reports low dot gain.
A visual examination of the halftone dots vs the solids will reveal the loss of ink density on the halftone dots vs the solids.

It can be helpful at the end of a run to have the press operator force over emulsification, slur and doubling to give you a visual reference for future preass runs.

 

[SheetSqueezer]

Unfortunately troubleshooting and corrective measures aren’t easily accomplished or explained in an internet discussion forum. Correct SOPs however, when established and followed, can minimize or completely eliminate many to most issues on press. And with that, help reduce the need for any ….troubleshooting.

 

[MassPrepressGuy]

Unfortunately troubleshooting and corrective measures aren’t easily accomplished or explained in an internet discussion forum. Correct SOPs however, when established and followed, can minimize or completely eliminate many to most issues on press. And with that, help reduce the need for any ….troubleshooting.

Agreed. Hence the importance of procedures, consistent process control, and data collection (to look for trends).

 

[gordo]

Agreed. Hence the importance of procedures, consistent process control, and data collection (to look for trends).

And it helps to really understand the process so that the procedures, consistent process control, and data collection are based on a solid foundation.

 

[danremaley]

Hello Print Planet. I’ve got a question from a Prepess guy (me) who is learning the ropes of sheet-fed offset.
We all know that SID affects TVI. Usually when SID is on the low side then most likely TVI is low as well. Conversely, when SID is high, then so might be the TVI. Well what happens when this isn’t the case? What if SID is high but TVI is much lower than where it should be. Also the opposite…what if SID is low but TVI is high? What should be looked at on press that causes this and how can it be corrected so that the SID and TVI remain in harmony?

Thanks

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