Excessive dot gain (or other) - please give me the advice!

gordo
Thank you! I have just received a basic lesson! :(
I mean excessive dot gain when 80% in the plate becomes 97-98% in the printout.
Yes, your point shows me an idea that I should check the dampening solution again; it seemed to be able to clean the halfttone area but not able to clean the shadow.

Your dot gain compensation curve may be wrong in the shadows or you're "in the noise" of the instrument - i.e. it's not giving you accurate readings at that tone value.

I thought someone would mention it, but the problem might be revealed in the photo of the black.

Click image for larger version  Name:	image_7241.jpg Views:	1 Size:	236.3 KB ID:	272029


I didn't understand it so I was hoping someone smarter than me would explain it. Then I could take credit for knowing it all along ;-)

What are those lines between the dots?

Note there are many more of them in the "After" pic. They would result in a higher dot gain reading.

Normally if you have slinging/misting the ink threads would be in line with the direction of the paper through the press. But in this case they are in line with the angle of the halftone dots - which should be at 45°. This makes no sense.

As far as I can see from these photos, you have good ink lay down, no over emulsification, no ink/water issues, etc.
 
The specification is, AFAIK, that at K 1.70 (dry, non-polarized) you should have L 15, a 0, b 0

If you're not getting that then that suggests that:
A: your polarized instrument is affecting the reading
B: your instrument's calibration may be off

Gordo, it's not one instrument. We have 5 scanning densitometers, 2 scanning spectrodensitometers, one i1pro2, one exact advanced, one densitometer from techkon and all shows same density.
most of them show polarized density but do you honestly believe that polarization can affect reading by .30 D?
 
Gentlemen,


I have already said in my first Post - The Black 40% image is "Showing" signs of low dampening level, WHY because the growth patterns of INK GRAINS forming between the dots.

A) Low Dampening Level B) Plates poorly "Desensitzed" C) Chemistry of the F.S.


Regards, Alois
 
Gordo, it's not one instrument. We have 5 scanning densitometers, 2 scanning spectrodensitometers, one i1pro2, one exact advanced, one densitometer from techkon and all shows same density.
most of them show polarized density but do you honestly believe that polarization can affect reading by .30 D?

No, I,’m just WAGging.
 
Gentlemen,


I have already said in my first Post - The Black 40% image is "Showing" signs of low dampening level, WHY because the growth patterns of INK GRAINS forming between the dots.

A) Low Dampening Level B) Plates poorly "Desensitzed" C) Chemistry of the F.S.


Regards, Alois

if delta experience smth we do, then increase in dampening levels won't help neither cheking and recheking plates desensitization.
As for fs chemistry - I would suggest checking doser system. Technotranse for example can be weird sometimes
 
Tell me how the printing press is called and the model ? What is the procedure for applying paint ? What kind of printed material ? Maybe the paper is wavy ? Can slide slur ?
 

Attachments

  • 11.jpg
    11.jpg
    58.7 KB · Views: 282
Last edited:
Dear All,

I am sorry for the delay. I have spent last 3 days for trying to fix this. And we did it.
Now the printout is good as usual. We had drained dampening solution (which I just found too much alcohol - refractometer showed > 15%), and mix the new one with careful dosing the dampening additive and alcohol.
Measure the dampening solution parameter: pH = 5.2, conductivity = 850 microSimen, temp = 12 degree Cel, IPA = 10% (checked by refractometer)
And I replaced the dampening form roller, adjusted to the standard setting.
Then we printed this job again. The result is good, the dotgain returns as usual.
The condition of the dampening form roller was not good; I do not have the hardness indicator so I can not measure but it was hard when compared to the new roller.

I still do not have the conclusion but the issue was solved.

Thank you very much for your support!
Have a good day!

Regards,
DeltaE
 
If I make a dosage of 12% alcohol then I will have problems with the paint, a great deal of imbedding will begin.If alcohol is 15%, then there will be a large increase in the point, even spotted printing on the background.
 
Dear All,

I am sorry for the delay. I have spent last 3 days for trying to fix this. And we did it.
Now the printout is good as usual. We had drained dampening solution (which I just found too much alcohol - refractometer showed > 15%), and mix the new one with careful dosing the dampening additive and alcohol.
Measure the dampening solution parameter: pH = 5.2, conductivity = 850 microSimen, temp = 12 degree Cel, IPA = 10% (checked by refractometer)
And I replaced the dampening form roller, adjusted to the standard setting.
Then we printed this job again. The result is good, the dotgain returns as usual.
The condition of the dampening form roller was not good; I do not have the hardness indicator so I can not measure but it was hard when compared to the new roller.

I still do not have the conclusion but the issue was solved.

Thank you very much for your support!
Have a good day!

Regards,
DeltaE

Please post pics of your dots.
 
gordo Please find in the enclosed! Regards / DeltaE
 

Attachments

  • photo7253.jpg
    photo7253.jpg
    154.1 KB · Views: 297
  • photo7254.jpg
    photo7254.jpg
    130 KB · Views: 320
Dear All,

Can I explain this case like this:
Due to very high IPA rate (>15%) because one of stupid printer had put into the dampening solution. Our "water" is too strong.
Then he had to put more ink to keep ink/water balance. Then too much ink leads higher dotgain then before.

What do you think?

Regards,
DeltaE
 
Hello DeltaE,


15% addition of IPA is not excessive apart from the COST ! --- your pH is High.

Regards, Alois


P.S. POST PICS of the same Plate Areas
 
Last edited:
The bridging of the dots (which I think is a problem) is now similar to the original before pics. You may be solving the symptom but not the disease.
 
gordo Yes, you are right!
Maybe I should try another ink or blanket But now it is not suitable time for a trial, I will try it when I have chance.
Regards,
DeltaE
 

PressWise

A 30-day Fix for Managed Chaos

As any print professional knows, printing can be managed chaos. Software that solves multiple problems and provides measurable and monetizable value has a direct impact on the bottom-line.

“We reduced order entry costs by about 40%.” Significant savings in a shop that turns about 500 jobs a month.


Learn how…….

   
Back
Top