It is a well-known fact that deposition and linting in the dryer section of a paper machine negatively impact paper machine productivity and paper quality.  While many conventional control methods exist, none have been able to completely eliminate deposition and linting in the dryer section.  New technology that significantly reduces or eliminates these problems was recently introduced by Hercules.  This technology, which employs the continuous application of chemistry directly onto either dryer cylinders or dryer fabrics, establishes a protective coating on the treated surface that prevents contaminant adhesion.  The resulting surface passivation not only prevents deposition but also significantly reduces linting by improving the release of the sheet.

The technology is marketed by Hercules as Zenix® Dryer Section Passivation Technology and is available in North America, Europe, and Latin America.

Mode of Action

When applied to dryer cylinders or dryer fabrics, the passivation chemistry establishes a protective coating on the treated surface.  This coating reduces the surface energy of the treated surface, which reduces the tendency for contaminant adhesion and improves the release of the sheet.  However, this coating is too thin to interfere with heat transfer from the dryer cylinder to the wet sheet.  The heat transfer of the modified surface is actually improved because the deposition of thermally insulating material is eliminated or reduced.  The improved heat transfer allows a mill to increase its machine speed or reduce its steam usage.  Such small amounts of the passivation chemistry are applied that there is no negative impact on sheet quality.

Additionally, the passivation chemistry provides lubrication at the dryer cylinder/doctor blade interface that results in a mirror-like finish on the treated dryer cylinder surface.  Figure 1 illustrates the effect of lubrication on a dryer cylinder.  With lubrication, the doctor blade cuts away smaller pieces of the dryer cylinder, which leaves a smoother dryer cylinder surface and therefore generates less lint.

Method of Application

The passivation chemistry is applied to the surface of either a dryer cylinder or a dryer fabric roll. If deposits form on dryer cylinders, then the passivation chemistry is continuously applied to the surface of a dryer cylinder using a single traversing nozzle. If deposits form on the dryer fabrics, then the passivation chemistry is continuously applied to the surface of a dryer fabric roll using a stationary spray bar.

With dryer cylinder applications, the passivation chemistry is normally applied to the first dryer cylinder that contacts the top side of the sheet and the first dryer cylinder that contacts the bottom side of the sheet. Using these feedpoints, the passivation chemistry transfers via the sheet to several of the down-machine dryer cylinders. This is referred to as the "duplication effect." With dryer fabric applications, the passivation chemistry is applied to a dryer fabric stretch roll.  Figure 2 illustrates the typical dryer cylinder and dryer fabric application points.

Recorded Benefits

The following benefits have been recorded from practical applications of Zenix® Dryer Section Passivation Technology.  Not all benefits are realized for the applications.

Eliminated/reduced deposition
Reduced picking and linting
Fewer breaks
Increased paper production
Improved moisture profile
Improved sheet smoothness
Reduced steam consumption
Less downtime for cleaning
Reduced fiber rising
Reduced need to ramp up dryer section temperature
Improved housekeeping