KCMY then CMYK

[Prepper]

We normally run our covers on our 6-color HEI in this order KCMY+2 spots, when we change to a regular 4-color job we move the KCMY inks from units 1-4 into units 2-5 to use the first unit on impression and help clean off the paper some. Would it be possible to just leave the CMY in 2-4 and move the K from 1 to 5 so they'd only be cleaning up 1 unit each time instead of 4? I know the tack will have to be different but wondered how or if it would affect our curves or profiles enough that we would need a different set of curves for the 2 setups, we're running G7.

Any thoughts appreciated,
Thanks

 

[PeterA]

In ISO Black can be run at the front or back - however all you can do is try it and see

 

[meddington]

I doubt that you'll see significant, deal breaking differences, though perhaps small changes in max density or color in some areas due to trapping differences. The critical portion of the sequence is CMY. There's an article addressing differences in K first or last in the latest TestTargets 8.0 from RIT.
TestTargets

 

[gordo]

[SNIP]There's an article addressing differences in K first or last in the latest TestTargets 8.0 from RIT.

Unfortunately that article and its related tests leave out some important factors. For one, the actual form of the two separations that were visually evaluated (i.e. how done and level of GCR or UCR). For another, it's likely that the separations that went offset retained their CMYK integrity, however the separations that went to the digital press likely may have been reseparated by the RIP to optimize for the digital process - i.e. no longer comparing apples to apples.

best, gordo
my print blog: Quality In Print

 

[meddington]

Unfortunately that article and its related tests leave out some important factors. For one, the actual form of the two separations that were visually evaluated (i.e. how done and level of GCR or UCR). For another, it's likely that the separations that went offset retained their CMYK integrity, however the separations that went to the digital press likely may have been reseparated by the RIP to optimize for the digital process - i.e. no longer comparing apples to apples.

Being that the digital press was an Indigo5500, I can confirm that the 5000 model does allow for unadulterated CMYK to pass through unless you specify otherwise, and does allow for ink sequence changes in the manner stated. I'm not familiar enough with other digital presses (iGen/Nexpress) to say if one would have this level of control, but its there on the indigo for what its worth. However, I don't think I would refer to this as "wet trapping" as the article does. I believe the 1st ink is effectively "fused" by the time the next is imaged.

 

[Vee]

You cannot change the order the CMYK inks... I mean toner are laid down on the iGen3-110. All four colors are laid down back to back, and then passed on to the fuser area of the press.

 

[gordo]

Being that the digital press was an Indigo5500, I can confirm that the 5000 model does allow for unadulterated CMYK to pass through unless you specify otherwise, and does allow for ink sequence changes in the manner stated. [SNIP] However, I don't think I would refer to this as "wet trapping" as the article does. I believe the 1st ink is effectively "fused" by the time the next is imaged.

My concern is that they did not describe the nature of the original separations used - and that can impact the results obtained.
I don't know enough about the Indigo to comment. Would you consider it as representative of digital presses - i.e. generic "digital" press appropriate for this kind of study?

best, gordo

my photography here: Gordon Pritchard's Photography

 

[meddington]

Would you consider it as representative of digital presses - i.e. generic "digital" press appropriate for this kind of study?
]

Good point. No I wouldn't consider this device representative of a generic "digital press" if there is such a thing. Though its one of the few digital imaging devices that actually implements an "impression" of sorts. With indigos and toner based devices and inkjet devices all being coined as "digital presses" things can get confusing.

 

[Sfdp2300]

We use to run the middle 4 units on our Heidelberg leaving 1 and 6 open for Pms inks . Today we use the standard KCMY most of the time but we have ran K last with success.

 

[nhprinter]

Don't forget the ink...

Don't forget the ink...

Hi Prepper,

In theory I don't think you'll see that big of a difference, but I would worry about how low of a tack you'll have to get for your black. Most people that run a "last down" black run a "first down" yellow so the tack of the black only needs to be lower than the tack of the magenta. You're going to have to run a tack lower than your yellow which might cause an unknown set of problems.

Please post results if you decide to do it. I'll take facts over theory any day.

Dave

 

[rich apollo]

It's anecdotal, but was once told by an old hand that if you run last down black you'll end up with more chromatic blacks. The black will "take on" the color of the underlying inks. Never have confirmed this. The guy sent me out to find the paper stretcher right after he told me about this.

 

[gordo]

Running Y down first and K down last is quite common in newspaper printing (yellow helps seal the paper as discussed in other posts here)
Running K down last is sometimes used in sheetfed when printing silver - SCMYK sequence helps the silver dry before overprinting it with K. Saves printing 2 Ks or a dry trap K on a second pass.
YCMK MAY be a better sequence on sheetfed if heavy/max GCR is used - but I've never seen this tested.
A YCMK or CMYK sequence in standard sheetfed work can provide more "chromatic" shadows due, IMHO, to poor K trapping. I think the results (that I've seen) look pretty poor (weird even).

gordon p

my print blog here: Quality In Print
my photos here: Gordon Pritchard's Photography

 

[Prepper]

CMYK sequence

CMYK sequence

Well, we are going to try it, probably tomorrow or Monday. I was wondering if using MaxGCR like we do may help because the black would be going down on less ink than a "normal" separation? One other thought we had was to run the last down K in unit 6 so there's more time between Y in 4 and the K going down in 6 than if the last down K was in 5 right after the Y.

I guess we'll see what happens!

 

[Bret Hesler]

We just did some testing with rotation today, although it was with hybrid UV inks. We had a job with heavy coverage of a rich black background (100k60c50m40y) and the CMY inks were contaminating with the first down black. First attempt was to dry the black, which cured the contamination. but turned to rich black into a brown. Then we put the black last and dried the CMY, and the rich black turned back to neutral. The best part was not having to reduce the tack of the black because it was UV.

I plan to do a similar test with conventional inks and heavy GCR images.

Bret

 

[rich apollo]

Running K down last is sometimes used in sheetfed when printing silver - SCMYK sequence helps the silver dry before overprinting it with K. Saves printing 2 Ks or a dry trap K on a second pass.

It's really a different thread, but I have to comment on what Gordo said here. If you run the metallic down last, do not overprint on it, and spread everything under the metallic; you don't have to go through the kind of backbends you describe here.

Every pressman wants to run the metallic first down because they don't want to wash up the units and move the colors.

 

[gordo]

We just did some testing with rotation today, although it was with hybrid UV inks. We had a job with heavy coverage of a rich black background (100k60c50m40y) and the CMY inks were contaminating with the first down black. Bret

If I understand you correctly, since KCMY is the defacto standard sequence - the most common solution (simplest) to dealing with a large area of black is to remove the CMY from the rich black - run it straight at normal density (it'll end up dark gray) then run a black on a 5th unit (KCMYK) that only applies to the linework areas (not images)

best, gordo

 

[gordo]

It's really a different thread, but I have to comment on what Gordo said here. If you run the metallic down last, do not overprint on it, and spread everything under the metallic.

Sorry, I don't understand your post. If you run metallic last, how do you overprint on it?

best, gordo

 

[Bret Hesler]

If I understand you correctly, since KCMY is the defacto standard sequence - the most common solution (simplest) to dealing with a large area of black is to remove the CMY from the rich black - run it straight at normal density (it'll end up dark gray) then run a black on a 5th unit (KCMYK) that only applies to the linework areas (not images)

best, gordo

We could not split the background to run a second black because the images blend into the background with the same color build. What made this easy for us was that the same black plate and ink were used, and trapping was not a concern because of the interdeck UV curing of the CMY inks before the black was laid on top.

To do the same thing with conventional inks would require a lower tack black ink, and possibly a curve to compensate for increased gain. I plan to test this soon because we do not always have the luxury of running UV when there is a large area of rich black.

Bret

 

[nhprinter]

Gordo,

I know what Rich is saying. We do the same thing. We knock-out the black(or any other color) in the metallic rather than overprint it, but we always make sure that the type is spread and the metallic is "right reading" so to speak. The metallic will hide any trap and you get a much more crisp look. We never overprint on a metallic.

Dave

(sorry to answer for Rich, but I didn't know if he'd check back to respond).

 

[MHS]

The only two problems that I see are the tack's of the inks and the time seperation of the printing sequence. On our Shinohara we have a perfector between the 2nd and 3rd units and sometimes we will have a fit issue on the back of the page. We have checked all of the grippers, packing, and cylinder pressure numerous times and have found nothing wrong. The paper does make a difference, if we are running 70# and up the fit is pretty tight anything less and the fit goes out. This leads me to think that the extra time the sheet has is a water problem.