Fighting warp from the inside – Flattening effect with Exilva
Synnøve Holtan | October 5, 2021
To wrap up this corrugated boards application series we finish with a focus on warp. Warp is one of the most common problems that corrugated board manufacturers face. Producing bent or twisted boards results in excessive scrap, waste and reduced production rates. There may be a number of factors that contribute to this problem; leaving out the machinery and focusing on the moisture control in the bonding process, what happens when we add Exilva (Microfibrillar Cellulose, MFC) to the adhesive?
Before we continue, have you checked out the other blog posts in the corrugated boards series? If not, you can find them here:
Figure 1: F-microflutes run at 200 m/min on a combined BHS and Fosber corrugator of 2.8 meters width.
Exilva, like starch, is a polymer of glucose with the same functional OH-groups capable of interacting with starch and the paper surface by hydrogen bonding. Moreover, Exilva being non-soluble, the cellulose fibrils will form a 3D- network ‘embedding’ the starch polymers and granules within. This novel texture provides improved application of the glue onto the flute tips, extended open time and moisture control between the top and bottom papers.
To measure the effect of Exilva on warp, production data were collected over a period of two months (reference period) in regular manufacturing of boards in a combined BHS/Fosber corrugator of 2.8 m width, equipped with an Escada laser measurement system. Thereafter Exilva was added to the glue and the measurements were repeated for two new months (see Table). The difference in acceptable warp numbers per meter per net machine hour, demonstrated a warp reduction of 11% upon adding Exilva. Moreover, the ‘Good Production’ numbers with the glue comprising Exilva increased by 14% measured as m2 board per net machine hour compared to the reference period.
Table 1: Production and waste summary from corrugator; % difference to reference glue in 2 months test period
PRODUCTION & WASTE SUMMARY CORRUGATOR
GLUE WITH EXILVA
DELTA WARP M PER NET MHOUR
DELTA GOOD PRODUCTION M2 PER NET MHOUR
With Exilva, the improved glueability and application enables low glue consumption and moisture control through an extended open time. This has shown to facilitate flatter boards production. Moreover, as described earlier in my post about how to reach prolonged stability of starch adhesives and how to bring your corrugated starch adhesive robustness to a new level, Exilva brings robustness to the glue towards mechanical impacts, which potentially could be advantageous when fighting warp caused by tension differences or other corrugator issues. Being able to run flat boards for all grades at high corrugator speed, is increasing the productivity in the converting department and of the whole plant. Thanks to Exilva, the factory in this trial could reduce its glue related waste and increase its productivity considerably.
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Synnøve Holtan has worked with microfibrillated cellulose MFC since 2005 and has developed an in-depth understanding of the product characteristics, as well as production processes and application innovation. As a senior scientist at Borregaard she focuses on the analyses and performance of Exilva in industrial applications, such as coatings and adhesives. Synnøve has a PhD in biopolymer chemistry from the Norwegian University of Science and Technology.