Handle With Care
The process requires each cover layer to overlap using a wooden top to weight the top layer to maintain flatness. For successful brick stacking key elements are:
a) Maintaining a consistent stack height that provides minimal weight build on the cover turn-in area,
b) Placing cover stacks so their weight is distributed to the outer edges of the stack below, and
c) Overlapping layers to stabilize the pallet for movement to the next operation.
If made covers are not controlled during equilibrium and there are dissimilarities between the bonded substrates, cover curl can result.
The rate of moisture intake and dissipation between cover material and cover board represents one consideration.
The other is the adhesive. The more adhesive that is applied, the more that moisture can affect substrate interaction. If the adhesive-solids content is low, additional moisture is added, and that moisture must eventually dissipate. Proper and timely stabilization of made covers reduces these variables.
In-line case-making and case-in operations pose slightly different equilibrium issues. As long as there is minimal time between case-making and case-in, the made cover won't have time to react to the moisture intake, reducing the chance of the cover curling before it reaches the case-in cover hopper. Problems occur when the case-in portion of the in-line operation is down and product continues to run .
This is prevented when made covers are brick-stacked, stabilized and fed back in-line without presenting problems to the case-in cover hopper.
LIMITING MOISTURE EVENTS
During case-in, application rollers apply adhesive onto the outer end leaf. As the adhesive on the end leaf makes contact with the exposed surface of the cover board, another opportunity for a moisture event exists.
In this case, the moisture from the water-based adhesive will begin penetrating the end leaf fibers and the board fibers. Another 12- to 24-hour period is necessary to dissipate the moisture and for the substrates