Questions for Screen Printers and Prepress

[Rudstar]

Hi,

I am interested in how other screen printers and their prepress depts handle incoming files, and how they measure/monitor film and print quality.
Even if you feel you could do better, I would still be interested in how you handle things, even if you think it's not quite correct.
I am trying to see how others do it, and how I can improve on how I do it too.

BRIEFLY ABOUT US
We are screen printers, printing Stationery Products and Point of Sale. Mostly PMS colours, but we do some CMYK work. We print at 65lpi.
I am in prepress. I check incoming files for obvious errors, fix them if needed, get approval from client then output the film positives.
I manually trap my files and use Cibercat Digiser5 for our films on an epson 9880. It's a basic rip to output film separations. This was setup to output films with tone for tone (eg: 30% tone on file is 30% tone on film etc) (I understand this needs to be changed, as i want to aim for ISO standards)
The file is saved as an .eps as Cibercat can have troubles with PDFs and leave things out!
We don't have a densitometer so print quality is just by eye, and this is how it's been done for years here.
I wouldn't be able to tell you (for eg) if our 50% halftone, when printed, was 30%, 50% or 70% on the sheet etc.
This is obviously a problem when printing CMYK, as you may only notice your cyan is too heavy when you are laying down your 2nd colour.
It's even a problem when printing 1 colour, as you want your tones to be correct, but it's more obvious in CMYK.
Obviously with colour bars, you would pick this up right away and adjust as necessary, even easier if we had a densitometer.
We use Marabu UV ink.

WHAT WE ARE AIMING TO DO

• I want to aim for ISO 12647-2 Standards (or 12647-5 for screen print). Our CMYK inks are ISO 2846-4 compliant, so we should be able to get close to ISO specs. Anything at the moment will be better.
• I have ISO 12647-2 (and 12647-5) Standards sheet and Idealliance Guide to Print Production Version 12, as guides for specs to aim to.
• I have borrowed a densitometer and a transmission densitometer to measure the films.
• I am doing some initial print trials by printing a set of 1 colour black halftones, and measuring the results on film and the printed sheet.
• I can then see which halftone is printing at which value (Taking Dot gain into account).
• I can then adjust the linerisation curve when i output our films so i can then make sure our halftones print on the sheet as per ISO 12647-2.
• I am still in the process of doing this, also waiting for other valuable info before continuing.

QUESTIONS FOR YOU!

• Colour Management - How do you handle files with CMYK profiles. Do you just keep it the same profile, and preserve numbers, do you re-assign the profile, or do you just ignore what profile they have used and just output using the file's CMYK values?
• Have you measured your film's halftones, if not, how have you set up your rip/printer and how did you control what halftone came out on the film?
• Do you print and measure a colour bar for density, dot area etc. with a densitometer.
• If not, how are you judging that you are printing the correct colour and tone?
• Are you aiming at any print standards/ dot gain targets, or just a good looking print? How do you judge it?
• How do you trap files? Manual, Indesign trapping or ripping software.
• What rip are you using to make film positives?
• What brand of film are you using for your positives?
• Do you print at the best resolution on your printer (eg: 1440dpi) or does 720dpi do a good enough job.

SUGGESTIONS AND TIPS FOR ME!
There are many things I want to do (down the track), but as a starting point, I just want to know a few things from other screen printers out there.
I would love to hear of any other suggestions and tips you may have for us, or anything else you think you could share with me to improve our screen printing and film production.

Thanks
Brett

 

[silversurfer]

ABOUT US:
Large-format screen and digital. Our screenprinting is mostly 4CP, we have a Thieme 5070 4 colour inline, as well as several other one colour presses. Our film is output on an OYO Liberator XE54 thermal imagesetter using a Harlequin RIP. We run 50lpi, 65lpi, or 80lpi based on size and substrate (larger gets lower line screen, registration gets tricky with the 64" x 102" screens).

[*]Colour Management - How do you handle files with CMYK profiles. Do you just keep it the same profile, and preserve numbers, do you re-assign the profile, or do you just ignore what profile they have used and just output using the file's CMYK values?

We are running to G7 standards, so the default "US Web Coated (SWOP) v2" that most people use works well for us. If we are supplied files that are something other than that profile, we usually convert.

[*]Have you measured your film's halftones, if not, how have you set up your rip/printer and how did you control what halftone came out on the film?

Yes, we have a Barbieri SpectroLFP that we use to linearize the film, before we apply the G7 curves. This is done in the Harlequin RIP.

[*]Do you print and measure a colour bar for density, dot area etc. with a densitometer.

Yes, we have a G7 colour bar that we put on every job.

[*]If not, how are you judging that you are printing the correct colour and tone?

We read the colour bar (usually SID, and NPDC when something's out), but we also output a proof with our Epson 4800 running Colorburst RIP.

[*]Are you aiming at any print standards/ dot gain targets, or just a good looking print? How do you judge it?

We aim for the G7 standard, but we use our Epson proofs as reference. We normally have campaigns that span screen print, digital flatbed and roll to roll printers, so we keep things consistent by matching everything to the Epson proofs.

[*]How do you trap files? Manual, Indesign trapping or ripping software.

Mostly using the in-RIP trapping (TrapPro) in the Harlequin RIP, but when that doesn't work out we do it manually. We've been trying to find something better than TrapPro, and have had good results with Esko's Powertrapper plug in for Illustrator. Just not that excited about the price.

[*]What rip are you using to make film positives?

Harlequin RIP-KIT.

[*]What brand of film are you using for your positives?

There's only one supplier for the OYO: OYO.

[*]Do you print at the best resolution on your printer (eg: 1440dpi) or does 720dpi do a good enough job.

We only use the 1200dpi setting on the imagesetter.

SUGGESTIONS AND TIPS FOR ME!

Make sure you've got your exposures worked out well. Overexposure will lose your highlights with the higher line screens.

The dot gain curve with screen printing is not at all the same as litho. Screen tends to have dot loss (or negative dot gain, however you want to put it), at least we do up until the shadow region where you can gain quite quickly. The best way to calibrate that I've found is using the G7 method. It's pretty simple and effective.

 

[rich apollo]

Hey, Silversurfer, do you hit the target colors for primaries and overprints?

 

[silversurfer]

We don't really try. Which specification would you use for styrene? Corrugated B-flute cardboard? Polypropylene-based synthetic paper (MXM)? Coroplast? This is the majority of our printing, we rarely print on paper. We count ourselves lucky when we get two batches of styrene that have roughly the same white point, or corrugated that lays flat.

But as an exercise, if we were to get some Grade 1 paper I'm sure we would be close to correct on the primaries. The secondary overprints I don't know, because our ink order/film thickness is different compared to litho. I would doubt it.

We use the G7 method for press calibration, but we don't claim to be 'G7' or have plans to be certified. The thing with screen print is there's just so many variables, it's hard to have a lot of really tight process control.

Which is not to say that colour is all over the map, there's not rigid controls, but there is the flexibility to get to the visual match with the proof. The inks can be mixed stronger or based-out more, they can sharpen or sand squeegees to modify the halftone printing.

Basically my calibration gets them on the green, and its up to the press operators to putt it in.

 

[Stephen Marsh]

[*]Colour Management - How do you handle files with CMYK profiles. Do you just keep it the same profile, and preserve numbers, do you re-assign the profile, or do you just ignore what profile they have used and just output using the file's CMYK values?

For RGB work, honour the embedded profile, most of the time it is valid. If the file looks strange or you believe that basing a CMYK conversion off the profile will lead to substandard results, you can always assign a different profile to see if this fixes the issue.

Based on our previous discussion linked below, for CMYK, I would recommend that you either ignore the embedded profile and assume your “house” CMYK setup (Fogra9 or Fogra39, GRACoL or a custom profile) - or assign your “house” setup to the file. This way you can see how the supplied CMYK values will print in your house conditions. If the proofing or preview suggests that using the files numbers with your conditions may lead to substandard results, you can then try converting from the customer’s supplied ICC profile to your house profile.

http://printplanet.com/forums/color-management/31184-conflicting-lab-color-values


Stephen Marsh

 

[Rudstar]

Silversurfer,

Thanks for your reply and detailed answers... I thought i would never hear from anyone!

This is very useful to me so i can aim at improving all our areas (film, printed halftones etc.), and show what instruments etc. we should invest in! Been flying blind for too long. Fine with simple PMS work but not with 4CP.

I have asked 3 other screen printers that print 4CP and none of them use densitometers or have checked their films since having their equipment installed (just like us!). I will be visiting them soon so it will be interesting to see how they judge their prints! 1 of them print colour bars but it's just a visual reference. They can see if the 95% tone is filling in too much or if they are losing dot on the 5% tone, but everything else must just be by eye and a judgement if it's acceptable or not.

I have tested our exposure using KIWO EXPOSURE CHECK so all is ok there... STEP 1 COMPLETE... many more to do!

Thanks
Brett

 

[Rudstar]

Stephen,
Thanks!
Brett

 

[rich apollo]

Thanks for the info, silversurfer.

 

[Stephen Marsh]

Not having the specification in front of me, what substrate is Fogra9 using? The results of this screen print condition are very close to Fogra39 in gamut size and shape, if not gray balance.


Stephen Marsh