.010" Process trap vs .015" Line trap...why the difference?

[Brad38CMU]

Can anyone give me a good solid reason why many printers run with a .010" trap for process colors and a .015" trap for spot colors? What is the reason for the difference? If the presses are capable of holding .010" registration on jobs with process inks, why are they not capable of holding .010" registration on ALL jobs? I've exhausted all resources in my building trying to come up with a good answer and I get a lot of "Hmm, I'm not sure" answers. Any insight would be appreciated.

Thanks!

[Cmd-P]

I've seen some printers use their high-end presses (or press) for process jobs only, and the rest are done on their older presses, which usually require more trap.
Also, spot color line art jobs, with lots of trap, can be run without the painstaking registration concerns that process jobs demand. That extra .005" can make a difference.
Also, Also, too much trap between a process image and a neighboring flat-toned area can create an additional unwanted color or image like a border line.

[rich apollo]

Trap is generally dictated by the paper type, sheet size and production process. Wider sheets (or webs) will exhibit more "fan out"; as will pliable, compressible and/or absorbent substrates. I believe the physical properties of flexo "plates" require a greater amount of trap, too.

The only time I've used different trap widths for different colors was to minimize the trap to metallics (in sheetfed offset) - which, by the way, is totally unnecessary if you change the ink sequence.

What type of process is this? .01" and .015" seem like really large trap widths to me.

[Lukas Engqvist]

Can think of a variety of reasons. Usually CMYK colours are find in % mixes, where as spot colours are adjacent and will generally knock out the shape, therefore more sensitive to miss registration. One other issue could be if you are printing the spot colour in a 4- colour press, it mean the spot is printed in a separate pass.
Mind you having said that we usually print gold or silver with no trapping since we have had some bad experiences with trapping metallic, and they seem to trap themselves.

[Cmd-P]

What type of process is this? .01" and .015" seem like really large trap widths to me.

These amounts are common in wide-web flexography for printing on thin plastic substrates.
It hasn't been that long since .02" to .03" was the trapping norm.
The proofing was lots of fun, trying to explain the trap-created elements and artifacts.

[Brad38CMU]

Thank you for your replies.

Wide-web flexo print, non-metallic inks. I guess I'm still not fully understanding on a job that prints with 4-color process along with 4 additional spot colors, why the plants are requesting a .010" trap for the process and 015" trap for he spot colors on the same job?

[Luc St-Pierre]

In flexo for sure, and I would need my fellow printplaneters feedback for offset, the register seem to fall out gradually as the substrate crosses the decks and is submitted to repeated drying cycles. So process is run first where the register is at peak and spots and lacquers at the end will require more trapping.

[prepression]

Lukas is correct. Underlying mixes of percentages of CMYK allow for less trap allowance. Normally, trap allowances are set to the same value whether they are CMYK or spot. It must be a requirement for the type of flexo press you're using.

Check out this resource for more info:

http://www.amazon.com/Exploring-Digital-PrePress-Delmar