Dirty Printing

[vaugh6288]

I've asked about this topic a few times already and we're still experiencing some unsatisctory results on our sheetfed presses.

We operate two SM presses from Heidelberg: an SM74 and an SM102 both 5 color plus coated presses.

I've noticed that we tend to see a lot of trash or marking in a lot of our prints in light screens and color builds and especially in color gradients. It almost looks like the dots get squished, but our dot gain is typically within what you'd expect. It's hard to explain but I have seen the same issues on publications printed on high speed web presses. We've tried several things like different blankets, screening methods, paper, etc and still are not getting rid of some of these issues.

Has anyone got any ideas as to what it might be? Could the powder have anything to do with these issues? Blanket packing? Impression cylinder pressure?

Thanks to all

 

[kansasquaker]

I'm not sure what you mean by 'trash or marking' a picture sure would help. When you say the dots look squished, that could be slur. Do you have slur targets on your press sheet or do you see any doubling?

Powder can definitely cause issues and I can see where that might create marking, but I don't know how it would make dots look 'squished'.

 

[gordo]

I'm not sure what you mean by 'trash or marking' a picture sure would help. When you say the dots look squished, that could be slur. Do you have slur targets on your press sheet or do you see any doubling?

Powder can definitely cause issues and I can see where that might create marking, but I don't know how it would make dots look 'squished'.

The same basic question was asked by this poster Feb 24 2014, and the same request was made then - show us some photos of the problem and don't use meaningless terms like "trash" and "squished". No photo then, no photo a year later. You gotta wonder.

 

[D Ink Man]

Moiré? Just a SWAG. D

 

[aqazi81]

Marking during sheet transfer? Another SWAG. ;-)

 

[aqazi81]

Are you using any type of anti marking system?

 

[claude72]

Hire an operator who understands the press (and printing) and knows how to troubleshoot.

Good solution... perhaps it's a plate problem and he sould also hire a pre-press operator able to burn correct plates?

But surely he should learn how to post in the right section of the forum! or ask his question with a cartoon???

 

[Alois Senefelder]

From this very poor description of the problem,

my educated guess - problem is - Ghosting


Regards, Alois

 

[gordo]

From this very poor description of the problem,

my educated guess - problem is - Ghosting


Regards, Alois

My educated guess would be incompetence.

Honestly it's disheartening to see how many many are happy to throw up solution when the problem hasn't been clearly articulated and the poster hasn't bothered over the course of a whole year to provide proper documentation about the issues they're having.

 

[D Ink Man]

Mind reading is sometimes part of our forum environment. SWAG it!

D

 

[Alois Senefelder]

The answer lies within !!!

Gentlemen



As Sherlock Holmes would say - Deduction, my dear Watson,


He did provide some cryptic "Clues"


Regards Alois

 

[claude72]

Over time, an experienced and qualified operator can figure out almost anything going wrong on press, it's part of what they do.

I'm guessing by your response to me, it isn't part of what you do.

My answer wasn't to you, but was half "extending" your answer to pre-press, and half humour ;-)

(OK, I should have add a smiley... my mistake)


That being said, wrong choice of screen angles and/or dots, or bad loading of one or several plates in the imagesetter (causing deformation of the printed image on some plates, or fuzzy dots), or poor copy of the films on the plates (if still used), or poorly revelated plates (with worn out bath) will cause problems that cannot be solved on the press, even by an experienced and qualified operator.

 

[kansasquaker]

My educated guess would be incompetence.

Honestly it's disheartening to see how many many are happy to throw up solution when the problem hasn't been clearly articulated and the poster hasn't bothered over the course of a whole year to provide proper documentation about the issues they're having.

Gordo, actually I think it's kind of cool. Here's a guy who can't or won't accurately describe his problem. Failing good information, the people on this board still try to help him with educated guesses. That's awfully generous behavior from a group of people with no tangible interest in the situation. I don't think anybody who answered was making a definitive statement. Even if they didn't qualify their responses, the paucity of information essentially implies that any answer is merely a guess.

Also, I'm sure incompetence is a huge factor. If you don't have the wherewithal to scan and upload an image to print planet, you should probably shouldn't go anywhere near a printing plant.

 

[vaugh6288]

No Title

Attached are two photographs that I consider good examples of the problem. Both pictures are of gradients that were printed in 20 micron stochastic-screening. A third picture is of a proof and our printed result. The third picture was printed in traditional screening 175 line 2400 dpi round dot shape.

I was unable to upload pictures earlier because I guess I'm simply too incompetent to run a print-shop during the day and upload pictures to this forum at night...

I appreciate the replies and I will admit that my descriptions were not exactly scientific in nature, but this issue is hard to describe and now I have a few examples and can find others if needed.

I feel like the common denominator is the plates but visual inspections and plate control strip readings show the plates are very clean and focused and are VERY consistent. We measure every day off the processor. So, I'd be surprised if it was the plates but am certainly open to suggestions.

 

[Slammer]

Guys methinks you are being a tad too judgmental, accusing somebody of incompetence for asking a question without using the correct terminology strikes me as arrogant, even if somebody uses technical terms like "Dodah" or "thingamigig" why not try to assist instead of looking down.
Just my two cents.

 

[Alois Senefelder]

Print Control Strips.


Vaugh,


NOW....... we are getting somewhere ! -- please supply us with pics of the "Print Control Strips" from a production print run,

1) Grip Edge and Leave Edge views


Regards, Alois

 

[gordo]

I believe you're dealing with slur, or marking. There are a few ways to diagnose the problem but you need to provide a little more information first. Your operator(s) should be able to help you with this information but to me (if your plates are in fact, very consistent), it does look like it's an on press issue.

Edit: After looking at your photos again, it also looks like it may be a squeeze issue, could it be that simple?

Judging by the very low resolution heavily compressed artifact filled images there is, I think, a suggestion of mottling - which could be caused, as alibryan says, by a squeeze issue or basic ink/water balance issue.

 

[Alois Senefelder]

Answers please ....

Vaugh,


1) Are the plates: Thermal, Chem-free or D.O.P. ?

Step 2) during a print run stop the Press via - Crash/Emergency Stop.

Step 3) Look at the M + C plates, with a 10X/20X loupe, in a 30%/40% tone image area ---

DO the dots have a "Halo" around them OR is there "Scum" inbetween the dots.?

Step 4) Look at the Leading edge of the plate, is there a "Thin scum line (1/2mm) wide across the width of the plate.?

Regards, Alois

 

[claude72]

Is it possible to have (much) higher definition pictures?

On these pictures, I don't know if it is the printing problem OR caused by low resolution pictures, I see low-res rasterized gradients in the 2 first and a low-res printed image in the top of the third...

You said in your first post that the problem is "especially in color gradients"... so, are you sure that your RIP is processing the gradients correctly, in vector mode, and not simply rasterizing the gradients at a (too) low resolution?
Other possibility, the gradients could have been badly made by the designer, (mis)using a transparencie effect, and somewhere in the process (PDFization or rip processing) the transparency is flattened with a low-res setting?

 

[vaugh6288]

Hey guys! Thanks for the posts!!

Im going to get with the press operators tomorrow and get back to you all.

Alibryan: Our 40in is a 2007 Heidelberg SM102. Our 29" is a 2001 SM74. Problems exist on both presses. We measure dot gain with handheld Xrite 518 densitometers (factory certified every year) we use a plate densitometer to check plates everyday too. We see these effects on both cover and text weight stocks

There is not any gum build up or scum line on the plates we output.

We aren't on the current version on our Prinergy system - in fact we're switching RIPs next week - having said that I wouldn't doubt that our PDF engine is behind and may contribute to the gradient/transparency issues but I don't think that would explain some of the "scum" we see randomly in other screens.

I'll also try and see how to get a higher resolution image uploaded to you guys.

I appreciate all the feedback - even the negative - we're simply trying to get better results from our presses