Flexo dot gain compensation

[gordo]

Can you use dot gain compensation curves in flexo like you use them in offset? Or is your only option to lower the lpi to lower dot gain?

 

[Slammer]

Dot gain in flexo can be a problem from the quarter tones to the highlights and your main weapon is the bump-up curve, however as in offset some people are in the two curve camp and some in the one curve, I know you like a one curve solution, at least in offset, I found it easier to level the playing field with the bump-up first and then use a plate curve to compensate for dot gain if needed. Having said that if the plate making procedure was done correctly you should not need to compensate much for dot-gain.

 

[Deleted member 16349]

Can you use dot gain compensation curves in flexo like you use them in offset? Or is your only option to lower the lpi to lower dot gain?

A related issue with how a flexo type plate prints is that the squeeze tends to push ink out from under the dots and forms a ring of ink. This ink ring can be thicker than the normal ink of the dot especially if the substrate is non absorbing and depending on the amount of squeeze. The thicker ink of this ring will often change the hue of the printed dot. So compensating for only dot gain might not get the results one might want.

 

[Slammer]

A related issue with how a flexo type plate prints is that the squeeze tends to push ink out from under the dots and forms a ring of ink. This ink ring can be thicker than the normal ink of the dot especially if the substrate is non absorbing and depending on the amount of squeeze. The thicker ink of this ring will often change the hue of the printed dot. So compensating for only dot gain might not get the results one might want.

The doughnut of dread.

 

[Cornishpastythighs]

Something like this

 

[Slammer]

Something like this

they are actually not the worst I have seen.

 

[gordo]

My question was prompted by this statement made by an EG solution:

"Ink film thickness is directly correlated to density. The higher the density, the thicker the ink film. For example, to achieve PANTONE 485 Red @ 1.80d (single layer) density in Flexo you would need to use an anilox range 360#~440# @5.0~6.0bcm. Of course, then you run into dot-gain issues and are forced to lower your screen to 85#~100# to maintain a minimum 4:1 anilox/screen ratio."

It just didn't sound right. Comments?

 

[Deleted member 16349]

My question was prompted by this statement made by an EG solution:

"Ink film thickness is directly correlated to density. The higher the density, the thicker the ink film. For example, to achieve PANTONE 485 Red @ 1.80d (single layer) density in Flexo you would need to use an anilox range 360#~440# @5.0~6.0bcm. Of course, then you run into dot-gain issues and are forced to lower your screen to 85#~100# to maintain a minimum 4:1 anilox/screen ratio."

It just didn't sound right. Comments?

OK, this helps. I would not say that there is a direct correlation of density to ink film. One could modify the strength of the ink and therefore get the same density with a different ink film. In flexo, the modification of ink strength used to be done all the time to maintain density during a run. I am guessing it still is done. This is just me being picky about their description.

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I think their comment seems quite OK. I think the problem is that when they say dot gain issues, you are thinking of the "amount" of dot gain. I think they are really talking about the issue of the "consistency" of the dot gain.

Imagine if the ratio is 1:1. This means that the cell spacing in the anilox roller is basically the same size as the dot spacing. Inking an individual dot would be a hit or miss situation, where some dots of the same size could get more ink and other dots of the same size could get less ink depending on how they happen to align with dot and cell. By having a higher resolution of the anilox roller than the dots have on the plate will tend to provide a more even amount of ink applied to the dots.

If one has a high lpi screen for the flexo plate, then one needs a higher screened anilox roller in order to consistently ink the screen dot. This I would say is where the 4:1 ratio applies.

As I understand, although I have limited knowledge of flexo, cmy process printing can have very high anilox screen values (over 1000) to be able to ink high screen values of the process flexo plates. The cmy inks need to be suitable for that.

In the case above, the pantone ink needs a high density and its strength might also be an issue, therefore I can see the need for the anilox roller above that can provide that extra amount of ink for the plate and since that anilox roller has a lower screen value, the plate dot screen value must follow it down to lower values using that ratio as a guide.

I may be wrong, but that is how I understand their comment. They could have made it a bit clearer.

 

[gordo]

I could understand the screen lpi and anilox cell frequency relationship but what confused me was the use of a coarser halftone frequency to moderate dot gain rather than just altering the plate curve.

 

[Deleted member 16349]

I could understand the screen lpi and anilox cell frequency relationship but what confused me was the use of a coarser halftone frequency to moderate dot gain rather than just altering the plate curve.

Gordon, I think you missed my point unless I am reading too much in your comment. There are two very different issues.

In their comment, they are not specifically talking about the issue of moderating dot gain. They poorly state that there would be a dot gain issue without describing what that issue would be. I would think anyone who has experience in flexo would understand their comment to be related to the ratio issue and not moderation of a plate curve. Moderating the plate curve IMO is a given. It has to be done. I think the issue they are implying is a problem is the consistency of the printed dot gain. It will vary a lot during the run if the ratio is not suitable. They imply the ratio needs to be at least 4:1.

They are not going to the coarse halftone because they think it will print better. Going to the coarse halftone will actually print with less quality. But they are forced to go there so they won't get into the problem of variation of how the halftone will print during the run. It is kind of like a moire problem with the interference of the anilox screen pattern with the plate dot pattern, which would be constantly changing.

Anyhow, that is the way I see it and their comment makes sense to me.

 

[gordo]

Thanks for the clarification.