Question:
What effect does the environment have on litho labels?
Answer:
Wood and wood related products (lithe labels) change as their surrounding environment changes. Paper is made from wood pulp, which begins the paper making process at about 90% water. The relative humidity (moisture) in the air causes paper fibers to expand (higher humidity) or shrink (lower humidity). This change is generally more noticeable around the fibers (diameter) rather than in the length of the fibers. Huston Patterson’s experience indicates that low humidity generally presents more of an issue with lithe labels and corrugation then periods of high humidity. Some of the main environmental effects include tunneling, cracking-fracturing, and shrinkage.
Tunneling: Although there are multiple factors that may cause a lithe label to tunnel when applied to corrugation, the most common cause is the lithe label has a lower RH (moisture content) than the corrugation. This lower RH generally occurs during dry environmental conditions, either because outside air is dry, or the air inside a facility becomes dry because we heat it and do not replace the lost moisture. Regardless of the cause, this change in moisture from the originally manufactured environment causes the fibers in the label to become dry and shrink. When we apply adhesive (moisture) to the lithe label, too much of the moisture in relation to the corrugation is absorbed by the lithe label causing an over expansion of the fibers. As the adhesive dries, the fibers continue to expand causing the tunneling.
Cracking-Fracturing: There are many factors that may cause cracking or fracturing on a corrugated box or display. Once again, one of those is a low RH or moisture content of the lithe label and/or corrugation. I believe the concept that something dry is more brittle and less pliable than something wet is easily understood.
Shrinkage: The one single issue that is extremely tough to understand is how the size of a lithe label may shrink between the time it is cut and later inspected. This change in size is more often noticed across the grain of the sheet (diameter of the fiber), rather than the long grain dimension of the sheet. This size change occurs due to environmental effects where low humidity conditions cause the fibers of the sheet to shrink as they lose moisture. We see the most dramatic changes in single sheets that are exposed individually to the environment.
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