The increase in fine particles in the furnish, linked to strategies for reducing fiber costs, can alter the behavior of the Yankee cylinder coating in tissue machines, reducing sheet elasticity and compromising runnability. Improving process stability therefore requires careful control of these interactions.
In the tissue paper production process, the interaction between the fine particles present in the furnish and the Yankee cylinder coating system can affect the optimization of operating performance. The relationship between these elements directly influences sheet quality and the overall productivity of the machine.
Solenis has focused precisely on this aspect and has developed an innovative approach to managing Yankee cylinder coating in tissue machines. “Our goal is to better understand how fines interact with coating chemicals and to develop technologies that make it possible to control these interactions,” explains Gwenael Tartarat-Bardet, Senior Tissue Applications Specialist at Solenis, who discussed these topics at MIAC 2025.
Chain Reaction
In the papermaking process, the sheet finishing phase improves its surface and functional characteristics, making the paper suitable for its final use. In the specific case of tissue, Tartarat-Bardet emphasizes that this phase takes place within the current economic context of high energy costs and a similarly strong increase in fiber prices. This forces the industry to reconsider many of its production strategies. Many paper mills have begun to reduce product basis weight, increase the use of short fibers, or increase the use of recycled fibers within the furnish.
These solutions, however, are not without consequences. “This type of intervention is not neutral, because it generates a series of chain effects that can have a negative impact on the process.”
When basis weight is reduced and the proportion of short or recycled fibers increases, the sheet tends to become weaker. To maintain mechanical strength within the required values, Tartarat-Bardet explains, it therefore becomes necessary to increase refining intensity.
This step results in greater generation of fine particles within the fibrous system. The increase in fines has direct consequences on the behavior of the Yankee cylinder coating, because these particles interact with the coating chemicals.
The result is often the formation of a harder and less elastic coating on the cylinder surface. In turn, lower elasticity leads to an increase in sheet breaks and runnability problems.
“To compensate for these effects, operators tend to increase the crepe ratio, that is, the level of deformation of the sheet during the creping process. However, this intervention involves a further trade-off: a reduction in machine productivity.”
A true chain reaction is therefore created, which can ultimately result in a loss of efficiency of the production process.
Standard practice: reducing adhesion force
Faced with these problems, the traditional approach of paper mills consists in attempting to reduce the adhesion force between the sheet and the cylinder.
One of the most common strategies involves modifying the formulation of the adhesive used in the coating, “for example, by acting on the polymerization rate or by introducing softening components.” In many cases, work is always carried out on the same type of polymer, trying to regulate its behavior when the sheet comes into contact with the Yankee surface.
Another intervention concerns the use of release agents or anti-adhesive agents. Over time, Tartarat-Bardet explains, there has been a gradual shift from vegetable oils to synthetic oils and to the use of compounds such as polyethylene glycol (PEG), used to facilitate the release of the sheet from the cylinder surface during processing.
However, these solutions have limitations and produce limited effects. “The introduction of new chemical additives often leads to an increase in dosages and therefore also in operating costs, while the results in terms of coating elasticity are not always predictable. In many cases, chemical dosages are increased without having a real guarantee of improved performance,” the expert emphasizes. Even operational interventions such as reducing reel winding tension produce limited effects.
For this reason, he says, it is necessary to change perspective and adopt a different strategy.
The idea: interacting with fines
The proposal developed by Solenis is therefore based on a different principle. It does not limit itself to modifying coating adhesion, but controls the interaction between fines and the coating chemicals themselves by minimizing it, Tartarat-Bardet explains.
“In the case of tissue paper, these fine particles are strongly anionic and during drying they easily come into contact with the chemical coating of the Yankee. When this happens, the coating polymers can be partially deactivated and lose their adhesive properties.” Under these conditions, the adhesion force between paper and cylinder no longer depends on the chemical coating but on so-called “natural adhesion,” that is, on spontaneous interactions between fibers and the metal surface of the cylinder.
Studies have been carried out on residues collected after the creping blade and the cleaning blade. “Analyses show that about 75% of the residues present on the Yankee consist of fibrous material, in particular fines, while the remaining 25% is composed of ash and phosphates, and during the process a significant part of the coating is removed by the creping blade”.
In coating formation, when chemicals are sprayed onto the cylinder surface they penetrate beneath the existing coating layer. “During contact with the wet sheet, one would expect them to migrate toward the sheet itself to facilitate release during creping. In reality, the polymer often tends to migrate in the opposite direction, that is, toward the cylinder surface.” This phenomenon promotes the accumulation of contaminants that modify coating characteristics, influencing abrasiveness, adhesion, and creping blade behavior.
Over time, the contaminated layer can become increasingly thick and, to manage the problem, in some machines—especially smaller ones with a single blade, often used in Italy, the expert points out—the Yankee surface is treated again by applying chemicals, but the situation tends to recur in a short time. In addition, when products are applied via spray systems, there is always the risk that the coating does not cover the entire cylinder surface uniformly. “Areas that are not properly coated become points of very high adhesion, creating possible sheet release problems and a consequent loss of elasticity or even potential breaks”.
A dedicated solution
The strategy developed by Solenis to address these problems aims to limit the migration of fines within the coating layer during drying.
The approach, Tartarat-Bardet further explains, involves two fundamental elements. “On the one hand, it is necessary to use an adhesive with low affinity for fines, in order to reduce the probability of interaction; on the other hand, it is necessary to introduce a release agent capable of functioning as a barrier to particle migration.” This combination has been achieved through the use of two specific products: Crepetrol 9212 and Rezosol M 6430.
Crepetrol 9212 is a proprietary polymer designed to have minimal affinity with fines while maintaining good moisture tolerance. “The objective is to ensure a stable and uniform level of adhesion of the sheet on the Yankee cylinder, regardless of process conditions or furnish composition.”
The release agent Rezosol M 6430, on the other hand, is a next-generation technology based on a synthetic oil whose formulation has been completely revised “to enable it to function also in counteracting fines migration.” This configuration makes it possible to reduce coating contamination and to maintain a softer layer. “When contamination decreases, the coating remains more elastic and machine performance improves immediately,” explains Tartarat-Bardet. Initial results already indicate an increase of about 2% in sheet elasticity.
Mill trials
Plant trials allowed Solenis technicians to evaluate the impact of this technology on tissue machine performance.
In the first case study, the application of Crepetrol 9212 was tested on a 6-meter-wide crescent former producing toilet paper with a basis weight of 15.5 g/m² at a speed of 1,800 m/min, using virgin pulp with 50% eucalyptus. “The objective of the intervention was to improve elasticity and softness of the final product,” the expert continues. “The introduction of the new polymer led to an increase of 1.5 percentage points in sheet elasticity. This improvement was subsequently converted into a 15% reduction in refining energy, with a 2% increase in production.”
At the same time, he explains, a significant improvement in softness was also recorded, equal to 5 points according to measurements carried out with the TSA (tissue softness analyzer), which evaluates the tactile properties of the sheet.
The second case study also involved a 6-meter crescent former, but even faster than the previous one, capable of operating at 2,000 m/min and intended for the production of toilet paper with a basis weight of 15 g/m² and a eucalyptus content of 60%. “In this plant,” Tartarat-Bardet continues, “the main problem was represented by a relatively low level of elasticity compared to a high crepe ratio. The combined introduction of Crepetrol 9212 and Rezosol M 6430 made it possible to achieve an increase of 3 percentage points in elasticity.” In this case as well, the improvement was translated into operational benefits: “production increased by 4% and the energy required for refining decreased by about 50 kWh per ton.” Furthermore, according to estimates carried out on the plant, this result corresponds to a reduction in emissions of about 285 tons of CO₂ per year.
Costs and raw materials
The results obtained indicate that controlling the interactions between fines and coating chemicals makes it possible to improve the operational stability of tissue machines. This approach also allows producers to optimize fiber costs, which are increasingly relevant in the economic balance of paper mills, without compromising runnability or product quality. It is precisely in an industrial context characterized by increasing cost pressures and the need to use increasingly diversified raw materials that strategies of this kind make it possible to maintain high performance levels in production lines.