Chimar: Suppressing Pre-curing in Industrial MDF Production

Formaldehyde & Resin Plant. Image: Chimar

A very well-known issue in MDF production today, is the inadequate catalysis of the adhesive(s) used, which could lead to an extension of production cycles and thus reduced productivity. The wide use of conventional catalysts all these past years and up to date, which are either pre-mixed with the adhesive or added closely to it, still presents the adverse effect of a considerable amount of the latter being cured prior to the mat entering the press. This condition, which is called pre-curing, is usually being handled by an increase to the resin consumption, a solution not always acceptable by the industry though, as the financial burdens following it are considerable.  

As requests for relevant troubleshooting were increasing on the part of the industry, CHIMAR decided to tackle the issue by developing a new method. This methodology included the addition of a patented resin activator just prior to the hot press leading to a two-fold advantage: a) as the adhesive is added separately from the catalyst, its curing is not triggered just until the mat is in the press and b) adhesives of low reactivity may also be an option for MDF production (and beyond) since there will be enough catalyst in the press to cure them in time. But it was not only the new way of applying the catalyst that solved the issue, it was also the actual latent hardener solution being used in combination with either polyamidic resins (Urea-formaldehyde, Melamine-urea-formaldehyde and Melamine-formaldehyde resins) or polymeric isocyanate adhesives. The said latent hardener is specifically designed to overcome the ineffectiveness of the ammonium-based ones used so far, while it accelerates the curing of the adhesive used by activating preliminary the core of the mat, even when applied superficially e.g. by surface sprayers.

The above innovative vapor catalyst and new methodology were successfully tested at industrial scale in MDF lines (Target board thickness and density: 16mm & 750kg/m3 accordingly) while the mechanical properties of the boards obtained were determined according to EN 319: 1993 standard (Particleboards and Fibreboards: Determination of transverse tensile strength perpendicular to the plane of the board). The superiority of the proposed bonding system can more easily be observed in the case of MDF and/or HDF production lines, simply because the ligno-cellulosic material is subjected to extensive thermal stress (Blowline, dryer, possible dry resination system) after the binder is applied, imposing precuring. By purposely buffering the resin prior to the application and reactivating the mat prior to the press entrance, significant savings on the binder used were repeatedly obtained and/or speed increase was possible.

Finally, depending on the resin and application line characteristics, 1-5% wt of solid Latent Hardener (SACOL-LH 1620) per wt resin solids is sufficient to achieve the production acceleration required while preventing surface over-and/or pre-curing.