Paper curl is big problem for paper maker. To know where possibility of paper curl happened, following article from Charles Green. If you interest with this articels, please email techman@papercurl.com.
There are currently four steps in manufacture that are understood as where curl or the potential for curl can be introduced into paper. These are the wet end, size press, dryers and windup. In end use heat, wetting, bending, etc. interact with the manufactured properties.
Wet end. Sheet formation, such as differences in fiber orientation between the top and bottom layers, is a major factor in curl. The adjustment of wet end variables such as jet to wire speed is important. Some wet ends, such as gap formers tend to do a better job of keeping top to bottom fiber orientation more equal. Impingement point apparently controls two sidedness of fiber orientatation. Composition difference can also be a factor, including differences in moisture diffusion rates, filler and fines.
Size press. Low percent solids starch sizing of itself has not been cited as a problem. On the other hand, metering size presses with high solids application seems to be a factor. The sizing stays on the surface instead of penetrating and saturating like conventional sizing. Starch has a high shrinkage compared to the base sheet. The restraint of this shrinkage when the sheet is dried builds in recoverable shrinkage (internal strain), which can be released by heating or wetting.
Drying. Unbalanced top to bottom drying will result in curl paper coming off the dry end. The extreme of this is when single tier dryers are used in the last section. Moisture content is important to printing processes.
Wound rolls. Paper at the core can become curled from the narrow radius bend. It can be enhanced or reduced by the top vs. bottom unbalanced fiber orientation.
There are currently four steps in manufacture that are understood as where curl or the potential for curl can be introduced into paper. These are the wet end, size press, dryers and windup. In end use heat, wetting, bending, etc. interact with the manufactured properties.
Wet end. Sheet formation, such as differences in fiber orientation between the top and bottom layers, is a major factor in curl. The adjustment of wet end variables such as jet to wire speed is important. Some wet ends, such as gap formers tend to do a better job of keeping top to bottom fiber orientation more equal. Impingement point apparently controls two sidedness of fiber orientatation. Composition difference can also be a factor, including differences in moisture diffusion rates, filler and fines.
Size press. Low percent solids starch sizing of itself has not been cited as a problem. On the other hand, metering size presses with high solids application seems to be a factor. The sizing stays on the surface instead of penetrating and saturating like conventional sizing. Starch has a high shrinkage compared to the base sheet. The restraint of this shrinkage when the sheet is dried builds in recoverable shrinkage (internal strain), which can be released by heating or wetting.
Drying. Unbalanced top to bottom drying will result in curl paper coming off the dry end. The extreme of this is when single tier dryers are used in the last section. Moisture content is important to printing processes.
Wound rolls. Paper at the core can become curled from the narrow radius bend. It can be enhanced or reduced by the top vs. bottom unbalanced fiber orientation.
0 comments:
Post a Comment