Need some help from the offset press experts...

[Alith7]

this has been an ongoing battle between me (color manager & Prepress Manager) and the Pressmen and the Owner.

WHERE ARE THE COLOR CONSISTENCY ISSUES COMING FROM!?!?!?! and who's "fault" is it?

So we've finally settled on that prepress and the CTP are stable and manages, and that issues are coming from the press; ie: inconsistent dot gain, inconsistent inks, roller lines, color problems, and generally the inability to match a job we printed even just a few days ago.

We are running a Heidelberg SM74 - 1985, and a Ryobi 524 - 2010.

here's where I would like some help. Without going into detail (I don't want you to think you have to tell me HOW to fix things and not share cause you don't have time)... Can someone give me a laundry list of the different variables that could go wrong causing the most common press issues. then I can take this to my boss and start the battle of how to start investigating all these things.

ATM, he's fixated on the dot gain being so high - generally over 75-79% - and instead of figuring out why, he just wants me drop the press curve. When the pressmen actually take time and clean the water tank and do some general maintenance (maybe once a month if I'm lucky), the dot gains drop to around 67% where we want them for a few days then go back up.

***PLEASE I'm aware that there is part of the problem right there, and I KNOW that, but that's not what I need help with.

Thank you in advance!
- Seriously Frustrated Tech!

[DanB]

There are many variables that affect a press some of which are outside the control of a press operator. Here is a list of some and by no means all.

Temperature of the ambiant air
Humidity of the ambiant air
Temperature of the fountain solution
Conductivity of the fountain solution
PH of the fountain solution
Temperature of the ink train
Temperature of the paper
Inks and Ink additives
Paper conditioning
Blankets (new versus old)
Roller Pressures
Roller Condition
Conditon of Plate and Blanket Packing
Type Plate

One way to find out what might be the issue is to keep a log recording the things that you can measure such as air temp, PH of the fountain solution and so on and then you can try to get these to the same levels each time. It is hard to do.

[Kaoticor]

Very brief list of some things to get you started.

(1) Speed and temperature. If you run a job at a set speed and obtain a good dot gain, running the same densities at a different speed/time of day will give you a completely different result depending on atmospheric conditions.

(2) Why is your dot gain so high??? 67% is very high. I don't know if you use ISO or a different means of standardizing, but ISO 12647-2 says that your 40% screen should be 22% dot gain and that your 80% should be 13% dot gain for a UWF paper providing you are running 60cm-1.

Since I work as the press operator and in pre-press, I thought I'd give you those two things to start out looking at. I'm sure there will be some other informative comments as well.

[Alith7]

Thanks Dan!

That'll be a help to start.

Some of the other things I know we're battling is our ink supplier - who the owner has used for almost 20 years - is inconsistent with pigment. we can open to cans of Cyan from the same order and visibly SEE the pigment difference. not always, but often enough. And the owner won't concede that that may be a problem. as he says "ink pigment is ink pigment, it doesn't change". *eye roll*

but thank you!

[Cornishpastythighs]

I would start by getting your suppliers to come in and give some training seminars to your press people(and the owner) the important suppliers would be Blankets, Plates, Fountain Solution, Rollers and of course the ink people. This training would be free and it would give everyone a solid foundation on which to effect changes. There is no value in ordering the pressmen to change the Tanks every week if they really dont understand why?
After and during the training I would put down everything that can and needs to be measured and controlled on the press. pH/Conductivity, Roller Durometer and Stripe settings, Roller Temperature, Fountain Solution Temperatures, Blanket/Plate Packings and squeezes and Ink.
If you have Spectro/Densitomers make sure the press people know how to use them and what the numbers mean. Your ink supplier has to use them to make sure you are receiving the same colour ink day in day out, if they cannot supply you with Spectral Data on their inks make them.
If you dont have a roller maintenance program build one, your roller supplier will be only too happy to help. If you are not checking and recording fountain solution pH/Conductivity readings then start doing it and convince someone to clean the tanks once a week at least in the beginning.
If the pressmen are still controlling ink density manually then invest in some Scanning Densitometers like an Intelitrac and make sure the operators are fully trained on how to use it.
Start a program of checking rollers/Stripes once per week and if the settings are drifting you may want to call the roller people in and suggest a different compound.
Get a packing guage and measure your printing squeezes.
Get a durometer guage and check the hardness of your inking rollers.
Get a infra red temperature guage and check roller and fountain solution temperatures.
Only when you have these things in place can you really fingerprint your press to give you a base line and if you are measuring and controlling the variables then you have half a chance of correcting them.
Sorry if this is a long winded answer but your question was a big one.
I'm sure I forgot many other points and others will join in and help
Good Luch

[Alith7]

Very brief list of some things to get you started.

(1) Speed and temperature. If you run a job at a set speed and obtain a good dot gain, running the same densities at a different speed/time of day will give you a completely different result depending on atmospheric conditions.

(2) Why is your dot gain so high??? 67% is very high. I don't know if you use ISO or a different means of standardizing, but ISO 12647-2 says that your 40% screen should be 22% dot gain and that your 80% should be 13% dot gain for a UWF paper providing you are running 60cm-1.

Since I work as the press operator and in pre-press, I thought I'd give you those two things to start out looking at. I'm sure there will be some other informative comments as well.

just to address this quick and thank you for the help!

1- I didn't know about the speed, but I'm aware temp and humidity can change things pretty drastically.

2- We're measuring a 50% patch. so 17% gain based off the numbers you threw out is about right. We only running a 4-up press and don't have the length to put all the measuring patches in I would like.

I try to run to G7 spec with my limited tools, and we're pretty close. I had a tech in installing our Techkon scanner and just for curiosity sake, he took the test sheets and my epson proof back with him to his shop to test and he said that both were within G7 spec and would pass testing. So that's good I guess. now If only I can get us to stay there consistently.

It doesn't help that while the owner is trying to convince me to adjust press curves so that our dot gains are lower for when everything is "dirty" and not worry about being in spec when it's "clean", and as I'm trying to explain to him why to fix the symptom won't cure the problem, the pressman walks up and goes "yeah, that should work just do that..." after the boss walked off irritated at me because I wouldn't "just fix it" I asked the pressman why he said that since he KNOWS why the dot gains are a problem and he said that it would work, but then agreed it wouldn't fix the problem....

This is what I'm battling with!!!

[Alith7]

wow..thanks for the great responses everyone!!

this will be a big help to try to talk to him about these problems!

[gordo]

@DanB & Cornishpastythighs

All good points to which I would add: the condition of the press operator.

@ Alith7

When you say: "he's fixated on the dot gain being so high - generally over 75-79%" do you mean 25% - 29% dot gain (50% + 25% - 50% + 29%)?

What is a good idea is to document as many the variables as possible - the print condition - and print a "Golden Reference" press sheet. I.e. a press sheet that represents a snapshot of the print condition when everything was working correctly. Then, when things go sideways, it can be used as a reference point to compare with a live job. If that's done, then most problems with live jobs can be very easy to figure out.

If your shop cannot produce a Golden Reference then it can be used to help diagnose what the problems are that are preventing you from producing it.

Hope that makes sense.

best, gordo

[Alith7]

Gordo~
on the dot gain, yes, that is what I'm saying. Scary huh!?

and thank you for your input too!

[gordo]

Gordo~
on the dot gain, yes, that is what I'm saying. Scary huh!?

and thank you for your input too!

What's the tone value on your plate at 50%? Do you have a microscope that can take photos of the halftone dots (25%, 50%, 75%) and solids (100%) that you could post?

best, gordo