|
Question
#11
Subject: While coating and nipping release paper we are getting a curl.
While coating release paper and then subsequently nipping it to .006" PVC, we are getting a curl in the product. The paper and PVC are not curly, they are flat. The Paper with the PSA is flat as well. It seems that when we nip these two together the material wants to curl. If you cut off a two foot long section and let it sit, it curls up into a nice tube. I have played with tensions, temperatures, speeds, and nip pressure, none of which get rid of this curl. The PSA consists of an acrylic adhesive and solvent.
Answers (links jump to full text of answer below)
|
#12
Author: Edward Cohen, AIMCAL
Email:
Subject: One of the main causes of curl in paper is the paper drying out.
One of the main causes of curl in paper is the paper drying out because low relative humidities in the surrounding air. The moisture content of the paper is a function of the relative humidity in the air. As the humidity is lowered, the paper looses moisture and starts to dry out. During this process the paper shrinks and the forces developed cause it to curl. Conversely, as the relative humidity increases, moisture is absorbed and the forces causing the curl are dissipated and the paper will lay flat. Therefore moisture control is key process variable which must be controlled to insuring flatness. This is typically done at the end of the coater or laminator using a variety of remoisiturizing techniques, from a simple sparger to steam injection. There is a paper at the October AIMCAL meeting which deals with this subject. The title is Is Steam Remoisturization and Flatness Control soon a problem from the past? Wolfgang Schaps, Black Clawson Converting Machinery.
Back to top
|
|
|
