Water Absorption

Definition
Water absorption is the rate at which water is absorbed by corrugating medium.

Influence
Absorptivity influences the ability of corrugating medium to accept water, from either the steam showers or the corrugating adhesive.

Potential Problems
Extremely high absorptivity (low numerical test value) can cause poor bonding due to excess absorption of water from the adhesive into the medium before the gel temperature is reached, leaving insufficient water to swell starch granules completely. High adhesive consumption results from attempts to compensate, leading to warp, blisters, soft board, etc.

Extremely low absorptivity (high numerical test values) can cause poor bonding due to lack of penetration into the substrate. Low absorptivity can also inhibit penetration of shower steam, causing potential problems with proper flute formation (high-low).

Converters can obtain good bonding and flute formation on mediums of either high or low absorptivity by tailoring adhesive properties or shower steam quality and volume to those conditions, as long as the medium is fairly consistent. Wide variations in absorptivity within a roll, or from roll to roll, cannot be tolerated, however, because adhesive properties for a given batch are fixed and operators may not become aware of problems soon enough to take appropriate corrective action before a quantity of rejectable board is run.

Source
McGrattan, W. "Key characteristics of linerboard, corrugating medium, and roll stock mechanical condition and their influence on the manufacture of corrugated products, part 1." Tappi Journal (1990): 99-108.

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