yellow ink problem

Hi fellow DI'ers

Just purchased a QMDI last fall, so im relatively new to waterless printing
I am using Toyo ink on recomendation of the previous owner.
The problem is that the yellow seems very light and transparent.. i have to crank the yellow fountain roller and the ink keys way up just to get just a decent reading on my densitometer.
Furthermore the ink is very "hard" and gum like (like when there is added to much anti tone)

The other day i tried some Hostmann-Steinberg ink at first i looked great and i got a really nice and deep yellow, but after 200 prints i started toning like mad...

The temp is set to 22 degrees celcius and i am using Heidelberg blankets and Heidelberg Caleidoplate. All rollers are adjusted spot on by the book.

Any suggestions?

Cheers /MC

 

Have you adjusted your M (1 to 9) function in service, to automatically increase the yellow ink level from the rip settings.

Which range of Toyo are you using.....MZ or LZ ?

Regards.

 

yeah maybe the low tack yellow would work better , you can swop out just the yellow , I don't know the DI press' but I used to work for Toyo and sold a boatload of that ink in NYC , never had any complaints and the Toyo is usually made with a higher pigment load...well anyway like mr.H ^ said try maybe switching tack...
also Toyo has tech people FYI
good luck...
Steve

 

I have tried both the EMZ and MZ. Haven't played with the ink curves yet.

 

almost sounds like the rollers are too cold , like your not getting a good flow? but like I said I dont know the DI press' , just a thought....
also I think I recall one of my customers reducing the yellow , I dunno it was a while back sooooo...god luck

Steve

 

I'd give the LZ a try. It runs much better on my Ryobi DI than MZ has. MZ tends to dry quickly on the blanket causing the substrate feeding through the press to tear between the grippers on the impression cylinder and the blanket, which can quickly result in paper in the rollers. Even with LZ, I have to do a blanket wash if I wait more than a couple of minutes between impressions. More so when working with heavy coverages.

 

My guess is the ink is fine but you have calibration issues from the RIP. Typically when this happens you are not getting enough dot gain from the RIP so you try to increase the amount of ink to the plate to make up for it. Since there is not enough dot to carry the ink to begin with it starts to tone. One of the ways to test this is to image a 50% screen on the yellow unit and print some sheets at density for the yellow then read the screen percentage. It should read around 63% to 67% or so, any less than that and you will have problems getting the yellow up to color. Another way to check without imaging a plate or printing is to go to the view screen and look at the dot in your 50% screen area, there is a dot reading option in the viewer where you can see what came over from the RIP. It should read 40% or thereabouts for the yellow as the ink will provide the gain to get you to the 63% you would read off the printed sheet. Any lower than 40% and you would be printing linear which does not provide enough saturation of color and would cause you to try and increas the colors on the press to make up for it.

In my experience with various inks the following is the gain you can expect from the ink:

Black, Cyan and Magenta 10% to 15%
Yellow 18% - 24%

Another issue that I have seen happen, is that the laser diodes are not set properly and they are not burning deep enough into the plate material to carry the ink. When the laser cuts a dot in the plate it is actually an ink well. The depth determines how much ink it can carry and therefore how dark the color will be. It is easy to calibrate the lasers by running the 60% screen test. I recommend running this test on at least half the plate and not by using the option to burn it on a 1/4 of the plate as you cannot get a good color reference from only using the smaller of the two options. This test should be run up to density for the respective color being tested and then adjustments to the laser diodes should be made. If the screen looks acceptable to you when all the diodes are adjusted then you should be fine. If the screen is light and difficult to get to density, then you need to increase the diode power.

Hopefully this information will help you find your problem.

 

Thanks for all your replys, i really appreciate it!

I will try the Toyo LZ ink instead i don't think it will help me with my yellow ink too light problem, but maybe it will prevent the paper from sticking to the blankets an eventully end up in the rollers.. or smash the blankets... I find it quite challenging to master the waterless nature og the QMDI compared to traditional water litho..

To Paul: the calibration of the machine and the rip seems to be OK. My observations is based on the density of the colorbar, im simply almost unable to get it up to the desirede density in the 100% yellow patch. I cranked the yellow ink curve up to 200% and i am only able to get about 1.00 - 1.10 density out of the yellow. Could the issue still be that the laser not is burning deep enough?

/Morten

 

An easy way to tell if it is the ink is to just swap inks in the units. If you are satisfied with the way the Magenta is working just put Magenta in the Yellow unit and see if you can get it to density. If the diodes are are set to light then you would also have an issue with the Magenta in the Yellow unit.

 

Sounds like the tack in your ink, i had the same problem when i first started shopping around for a good set of inks. try the LZ ink, ive been running it for a few years now in both my old QM46 and now my Ryobi and i haven't had any issues as far as tone out and and gum up.

 

The Toyo Yellow should be able to get a 1.0 to 1.10 but my take on this is, is that much needed? The other question is do you have a ir drier on the press? If so, the lz ink will probably tone up due to the hot air rising. You didn't say if you were toning in the begining, but with the lz, you might have that problem in warmer weather. What is the room temperature? If that much ink is needed in density to achieve color visually, I agree with Paul that the curve from the rip needs to be adjusted so you can hit .95 to 1.00. Are the traps in the red and green acceptible? If so that would be a rip problem. Remember, this press was supposed to be for pleasing color and short runs. Too much ink in the roller train causes different types of toning problems. Here in the states Toyo has a EX Yellow that was formulated for a different type of press. It would work on your press also, but I don't know if you can get it over there.

 

Have you tried using inks from Classic Colour in the UK?
I know that they are based in Reading, near London and export to Europe and America.
I used to work for KBA and Classic make some very good inks for all waterless presses.
The guy to speak to is Paul and their number is 0118 975 0017 - tell him Jamie said hi.
I think they are agents for VIM plates as well.

 

Paul, I'm trying out your trick about checking the densities of a 50% screen on the press computer. Do you also know what the values should be for Cyan, Magenta, and Black?

 

Along with that, how do I edit the dot gain? I have Prinect Metadimension 7.5 as my RIP, for what it's worth. I assume it's not as easy as changing a percentage under "Dot Gain" since I don't see something like that.

 

The values of C,M,K will vary based on the dot gain of the ink. When the press is first set up you are supposed to run linear plates at all the screen values from 0 - 100% then read the printed sheet Dot Gain so you know what your ink gain is (There is a form that comes with the RIP for this.). Then in the RIP you input those values and you should be good to go. Example: You output a 50% screen on the plate (Linear means a 50% screen outputs at 50%) you print a sheet and read the value at 67%, that means the ink gained 17%.

I personally never worked on that side so I am only partially familiar with the process. I do know that I worked on many a press where this was set up incorrectly and operators were not able to turn the ink up enough to get the color they were looking for.

I do remember there is something in the RIP that has to do with Linear and Non-Linear output. In one of those you have the ability to change the screen values which are output on the plate during imaging.

Possibly someone else on this forum could explain it in more detail.

 

Thanks Paul.