Paper Moisture Control to Reduce Curling
During the paper manufacturing process, many scientific processes are manipulated to control the physical properties of the paper such as weight, thickness, color, strength, and moisture. While most of these variables remain fixed after the paper is made, the moisture content begins to change almost immediately.
The primary impact to the moisture content of a new paper roll comes from the atmosphere and how the paper is handled and stored during its transition from a parent roll to final product. Humidity causes the paper roll to “cure,” either absorbing or releasing moisture depending on surrounding conditions. Since the paper is wound onto rolls or stacked on pallets, the cure rate is different from the outside to the inside which results in the paper being wavy or curled (dry in one area or moist in another). When paper with these conditions is processed into final product, it creates numerous problems such as paper jams in the processing machines, uneven cutting or sheeting, misalignment of folding processes, and off sets in the printing and graphics. All of these issues are unacceptable when processing the final product. Crisp, high quality packaging is what most producers and consumers prefer.
There are numerous ways to approach the correction of paper moisture content. Adding a controlled amount of moisture back into the sheet by applying steam in precise amounts to selected areas of the paper web has proven to be most effective. Low-pressure, high-velocity steam applied counter flow to the web path allows the paper sheet to quickly absorb the steam. As the steam cools, condensate is formed which is absorbed by the fibers in the paper allowing the fibers to relax releasing the stored energy or curl producing a “lay-flat” product that will easily feed through various phases of processing machinery.
Kadant’s Steam-Foil® profiling system has successfully used for paper curl control and moisture correction for all types of paper products in the converting industry. The Narrow Web DeCurler™ and Steam-Foil profiling systems use a Coanda® nozzle to precisely apply steam to paper webs for accurate control of moisture content.