Troubleshooting the Glue Line: A Guide to Common Corrugation Defects
On a high-speed corrugator, many things can go wrong, but a significant number of board quality issues can be traced back to a single, critical area: the glue line. A perfect adhesive bond is strong, consistent, and nearly invisible. A faulty one can lead to a host of defects, causing waste, downtime, and customer complaints. Learning to 'read' the board and diagnose these issues is a key skill for any successful corrugator operator or quality manager. This guide will help you troubleshoot some of the most common defects related to the adhesive application process.
One of the most common problems is a weak or 'dry' bond, which often leads to delamination. If you can easily pull the liner away from the medium and see very little adhesive or torn paper fiber, you have a starved bond line. The most likely cause is an insufficient amount of adhesive being applied. This could be due to a glue roll gap (nip) that is set too tight, or an adhesive viscosity that is too high, preventing it from transferring properly. It could also be that the paper is too absorbent, wicking away the water before the bond can form. The solution is to first check and, if necessary, increase the glue roll gap. You should also verify that the adhesive's viscosity is within its specified range. If the paper is the issue, you may need to switch to an adhesive with higher water retention.
Another frequent issue is 'delamination at the score line.' This is when the board looks perfect until it is folded to make a box, at which point the liner pops off along the crease. This is a classic sign of a brittle bond line. The adhesive has created a bond, but it is too hard and inflexible to withstand the stress of folding. This is often caused by applying too much adhesive or using an an adhesive with an incorrect formulation for that paper type. The excess adhesive forms a thick, glassy layer that simply cracks upon bending. The first step in troubleshooting is to reduce the amount of adhesive being applied. If the problem persists, it may be necessary to consult your supplier for a more flexible adhesive formulation.
Finally, there's the problem of 'wash-boarding' or a visible 'flute-print' on the single-face liner. This happens when too much adhesive is applied and/or the adhesive has too much water content. The excess moisture is absorbed by the liner, causing the paper fibers to swell in the areas where the glue was applied, creating a corrugated pattern on the flat surface. This not only looks bad but can also cause problems during printing. The solution is to minimize the amount of adhesive applied to the absolute minimum required to get a good bond. Using a higher-solids adhesive, which contains less water, is also a very effective way to combat this issue. By systematically diagnosing these defects, you can make targeted adjustments to your process, leading to higher quality board and a more efficient operation.