ISO 12-647 Trap

[Jam]

Hi,
I'm new here but I was hoping someone might be able to confirm what trap you should expect on a Offset press?

Thanks

J

 

[DANCCLTECH]

In 10 years in the industry, we always do trap at 0,144pt or 0,05mm on offset press.

I think this is the minimum we should take.

 

[Alois Senefelder]

Trapping

Trapping

Hello Jam, DO you mean Wet on Wet Printing Ink Trapping ??? OR Pre-press Image Trapping ???


Regards, Alois

 

[PGE]

I presume he means apparent trapping of the inks. Since the pre-press trapping is not something you "expect" , nor is it something you measure on an offset press.

Traditional values can be found in the png below :
measured with Status T and calculated with Preucil formula.
Trapping is not standardised by ISO12647, but can be a parameter that gives you a fast check on the printing quality.

Regards PGe

 

[Jam]

Absolutely right, sorry I should've been clearer when making the post but what PGE stated was correct. Thanks

J

 

[Jam]

New question sorry, I'm not a printer but something that PGE mentions "nor is it something you measure on an offset press"

Why would you not measure your Trap?

J

 

[Vee]

Because trap is only to ensure pleasing asthetics.
It doesn't mater if it's exactly .144 or 1,000 - as long as there is no "flash" of stock showing through where the two differnt colors meet.

 

[Jam]

So why would I look to measure what trap the press is achieving? Is it not necessary to see how your colours lay on each other?

 

[PGE]

some maths

some maths

So why would I look to measure what trap the press is achieving? Is it not necessary to see how your colours lay on each other?

Digital Prepress trapping is to overcome registration issues, If all press would would perfectly register, trapping would not be necessary, so when you want to define a value for your trapping, you should know what your press (as a system) is capable of. tolerances and are dependant of the line frequency , which in his turn is normally dependant of the media being use. Normally the tolerance for image register is half of the line frequency.
So eg for 175 lpi the register tolerance is 0.0028" or 0.2 pt (or 0.072 mm).
So if you really hit the lower tolerance value for register, a typical trap of 0.14 pt is not enough ! 0.2 PT is the max trap value needed for 175 lpi.
From a practical point you could measure the necessary trap that is needed for you register level, simply measure you register error, but rember the half line frequency rule.

regards

PGe

 

[Jam]

HI PGE,

Thanks for that, Is it not the case though traditionally printers would monitor their inks Trapping on each other so if they had colour mismatches it would give them an indication of what might be the problem?

J