Thread: qmdi printing issue

We have recently installed a qmdi plus and having an issue on the yellow unit.
When running a full size sheet the yellow unit prints a stripe across the sheet approximately 1/4" width half way back on the sheet (about 8.5" back). It is more like a tone than solid.
It cannot be a heat issue as it starts right away even on the first job in the morning.

Sounds like you need to check your roller pressures stripes, especially on the form rollers to the plate. The third form roller is the biggest culprit to this. This should be more noticeable on uncoated stocks than coated, but can and will show up on both. Heidelberg service techs will tell you to back off the pressure on the 3rd form roller and sometimes completely back it off from making contact, but I find that as a lame fix, as that affects your ability to handle any type of decent coverage in that unit. I usually set 1 & 2 form rollers at 3mm and back 3rd to about 1.5mm. It sucks that you can't run the pressures at what the manual recommends, but that is one of the downfalls to owning a QMDI.
If your press room temperature is over 75 degrees, it could most certainly be a partial cause.
One thing you could also try is that it is possible that the tact on your yellow ink is not enough. You can add Heavy Water Fighting Varnish to it to thicken it up just a bit, like add maybe about 5% and that should help.

Heavy Water Fighting Varnish is the additive that is used that makes ordinary oil based ink DI compatible. You can take any manufacturers ink and add about 10% - 15% of the varnish to it to use on your DI. It works on every color I have ever tried, including metallics. I have tried to do spot varnish work with DI varnish supplied from Superior Inks, but cannot get dense enough coverage without it scumming the entire plate. That is where Heavy Water Fighting Varnish comes into play. Once I added it to the other varnish...BINGO, spot varnish without the scumming.

Cheers

Tracy

You should also check your ink oscillation timing.

Regards.

One of the most frequent problems I used to encounter on the QMDI is the adjustment of the ink rollers.
In most instances, it is done incorrectly. Typically the stripes to the plate are adjusted perfectly, what is not done is to stripe them to the distributor/ oscillator rollers first. This is extremely important, as this is the point that the rollers pivot, like a door hinge, for the adjustment to the plate cylinder. If this stripe is not performed first, it is impossible to stripe them correctly to the plate.

Prior to checking the stripes you must do as mrheidelberg mentioned and check to see the oscillation timing is correct. The the 6mm holes in the track cams for the oscillators should be as follows: 1st and 2nd unit 6 o’clock position, 3rd unit 12 o’clock and 4th unit 7 o’clock. If they are not I would recommend having a technician come in and put these back in position. When these are out of position it will change the charge of ink causing color fluctuations in the run.

Also check the room temperature as mentioned by 2ampress. Temperature of the room should be a maximum of 23 Celsius (74 F). Anything over this will cause toning/tinting. Usually in this instance it is apparent in the 2nd unit first, as it is the highest unit and heat rises. Then the other units start to exhibit the problem.

The problems caused by rollers not being striped to the distributor/ oscillator rollers first are numerous, they include the following:

1. Toning or banding on the press sheet. 70% of the time that we get toning complaints it is due to the rollers being striped incorrectly to the distributors/ oscillators.

2. Color fluctuations throughout the run. By this I mean that the ink densities drop off over 50 sheets or so, then spike back up for 10 or 20 sheets and slowly drop back off again. This is because the ink builds up on the distributor/ oscillator rollers and has no place to go because the stripe is too small. Once enough ink builds up on the distributor it fills the gap to the form rollers and floods the plate with ink until the ink is used up. Then the cycle starts again.

3. Mottled looking solids.

4. Slurring of text, due to the form rollers not being driven properly.

5. Continuous hickey problems. This is typically coming from the 3rd form roller because it has never been adjusted to the distributor roller. Because of this the roller is not even touching and collects all kinds of trash which eventually ends up on the plates.

6. Extended periods of time for roller wash up at the end of the day. When the rollers are adjusted properly it should only take 4 passes to wash up the rollers and about a 1/4 of a bottle of wash up solution. This could also happen due to wash blades being worn, mostly it is due to rollers settings.

The following attachment explains step by step how to adjust the rollers. The operators manual is also very clear on how to do this also, it has illustrations showing what color screws adjust what rollers.

Roller settings - See diagram in the operators manual. Spread yellow ink onto ink roller, idle press to smooth. Stop press and REMOVE ROLLERS 6,7 AND 8, to see settings of 2nd form to oscillator. Set forms to oscillators before setting forms to plate. Turn adjusting screws counter clockwise for wider stripe on all settings. Exception, item m. below, roller 4 to oscillator is clockwise for wider stripe.

a. Yellow screw - 1st ink form roller to oscillator 3.5 - 4 mm.

b. Blue screw - 2nd form roller to oscillator 3.5 - 4 mm.

c. Red screw - 3rd form roller to oscillator 3.5 - 4 mm.

d. If roller 7 has fixing screw on operators side through roller shaft, follow steps e. - m. If roller7 does not have fixing screw, follow steps i. - m.

e. Install roller 7, tighten screws (pin to operators side.)

f. Check stripes with rollers engaged to plate between roller 7 and form rollers 1 and 2. Adjust so that the stripe between roller 7 and form roller 1 is the same as the stripe between roller 7 and form roller 2. Stripes should be same width fig. 17/1 p. 124 operators manual. Turning clockwise makes stripe to form roller 2 wide and to form roller 1 narrow.

g. Adjust roller 7 so that there is a 3.5 - 4 mm stripe between both form rollers 1 and 2. Fig. 17/2 p. 124 operators manual. Turning clockwise makes both stripes narrow.

h. Remove roller 7.

i. Install rollers 6, 7 and 8. Stripes from rollers 6 to oscillator and roller 8 to oscillator are pre-set from factory.

j. Violet screw - form roller 2 to plate 3 mm

k. Orange screw - form roller 1 to plate 3 mm

l. Silver screw - form roller 3 to plate 2.5 mm

m. Roller 4 to oscillators at 3.5 - 4 mm

Roller stripes should be checked every other month. Rollers should be removed from the press every 3 months and hand cleaned, especially the 3rd unit as magenta ink causes calcium build up in the rollers due to the pigments. (This is what causes the magenta to "tone" more than the other colors.)

By doing this you greatly improve the print quality of your press, while reducing waste and speeding up make-ready times.

Originally Posted by 2ampress

One thing you could also try is that it is possible that the tact on your yellow ink is not enough. You can add Heavy Water Fighting Varnish to it to thicken it up just a bit, like add maybe about 5% and that should help.

Heavy Water Fighting Varnish is the additive that is used that makes ordinary oil based ink DI compatible. You can take any manufacturers ink and add about 10% - 15% of the varnish to it to use on your DI. It works on every color I have ever tried, including metallics. I have tried to do spot varnish work with DI varnish supplied from Superior Inks, but cannot get dense enough coverage without it scumming the entire plate. That is where Heavy Water Fighting Varnish comes into play. Once I added it to the other varnish...BINGO, spot varnish without the scumming.

Cheers

Tracy

Am I reading this correct? You were able to do spot varnish, and metalics using a QMDI?

Originally Posted by ScotJ

Am I reading this correct? You were able to do spot varnish, and metalics using a QMDI?

That is correct.

You can use ANY standard oil based ink from any manufacturer and add about 10% - 15% Heavy Water Fighting Varnish and it will run flawlessly on your DI.
Add that varnish to standard gloss varnish and you can then print spot varnish as well. Without the added viscosity, you'll most likely get major scumming.
On top of that, I just ran a job that they wanted dull varnish on, and I didn't have enough of my DI dull varnish, so I grabbed some of the 40" press dull varnish and did not add anything to it. It ran beautifully, as I didn't have to worry about scumming, as it was flood coverage, so scumming was not an issue.

Another note about varnish on the DI...I always run it as a second pass, as the other inks will contaminate it fairly quickly if ran all on the same pass. Of course, to varnish process printing has to be a second pass, but for 3 PMS colors or less, the option could be to run all as a single pass, but I highly recommend against it.

Cheers,

Tracy

Interesting - I'm slightly new to offset as a whole and wasn't aware there were non-UV cured varnishes. Does it create the same effect as a UV varnish, or not as dominant?

Unfortunatly non uv varnishes wether it be duct oil based or water based coating do not have as high a gloss level as a uv cured varnish.

Originally Posted by mrheidelberg

Unfortunatly non uv varnishes wether it be duct oil based or water based coating do not have as high a gloss level as a uv cured varnish.

But it would yeild a gloss finish to some extend though?

Also - do you go through 4 plates doing this (even if it is just a single pass?)

Oh yes you will still get a good gloss and only one plate is required.