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July 08, 2005
Registration to Pre-Printed Webs
What's the difference between registering a new patterned feature (print, die cut, laminate) to an upstream integrated pattern vs. registering to a pre-patterned web?
How about putting it another way? If you have a choice of developing a new Excel spreadsheet (or other computer program) or modifying a spreadsheet someone else has written, which is easier?
It is almost always harder to work on something that someone else has started. It was hundreds of years between the beginning of manufacturing processes to the creation of the assembly line. Having to modify someone else's work requires an initial step of figuring out where they left off. When you do a job yourself, you know what's been done (unless you put it on the shelf for too long, then it's like starting over).
Let's get back to registration.
Whenever possible, always integrate multiple printing, die cutting, and laminating steps in a single process. It may seem that creating a complex integrated process will lead to more waste (it often does), but in the case of registration, a great deal of startup and process variation waste is actually reduced by integration.
More...
Printing and die cutting can be relatively easy to get a new print or die cut to match an incoming pattern, if there is some chance to slide into registration.
Registration can have three errors.
1) a shape error, where the existing pattern doesn't match the new pattern.
2) a lateral shift (easy to correct)
3) a machine direction phase shift.
Of these, the shape error is the most annoying and potentially difficult to correct for. In printing, you can potential smear the ink transfer process slower or faster to get a MD shape match. You can increase or decrease tension to create some widthwise necking and get the TD shape to match. In die cutting, you have little room to change the size of the actual cut (the untensioned web shape will be relative to tension, but the geometry of the "live" cut is fixed by the die).
Lateral shifts are easy. You may want to guide off of the pattern rather than assume the pattern to web edge is constant.
The MD phase shift can be easy or tough. If the new process has potential for MD slippage, either by smearing the ink or changine rpm during a short non-contact portion pattern, then the phase can be adjusted between each individual pattern.
If there is no slip, such as continuous embossing or laminating to pre-patterned web together, you may only have web tension to advance or retard one of the web relative to the other. This has a limited ability to more the web and may create a curled product in laminating, but it can be used to advance or retard one pattern relative to another.
Let me now if you have questions or have other registration "tricks" worth sharing.
tjw
Posted by Tim Walker at July 8, 2005 02:00 PM
