Hybrid structured tissue is a term that has risen to describe the latest iterations of structured tissue machines which forego the through air dried sections of the dominant structured platform approach. There are many reasons why a tissue maker would want to create a structured base sheet without having to dry it via evaporation as with a TAD (Through Air Dryer).
The two most obvious are the inherent energy inefficiency of evaporative drying and the cap on production imposed on the machine due to this inefficiency. This is particularly problematic at this time in Europe with the tissue industry heavily reliant on natural gas for hood operation. An advantage that hybrid structured technology brings versus the conventional tissue production is increased bulk to basis weight. This allows creation of high quality base sheets at lower basis weights which is particularly advantageous given the rising cost of pulp.
A hybrid structured machine uses more efficient dewatering processes including vacuum, belt pressing and shoe presses combined with methodologies that protect the sheet structure during the dewatering. The resultant sheet being transferred to the Yankee contains a significantly higher moisture level when compared to the TAD process and is much closer to conventional tissue making. With this method, the Yankee and hood sections’ capacities are utilized much more compared to many TAD machines, which in some cases are installed with no hoods at all. Being able to do this, while still generating the desired sheet structure and absorbency capacity increases, provides a significant potential for cost savings and profit opportunities generated by the new platforms.
Several approaches to the hybrid structured platform have been launched by various OEMs (Original Equipment Manufacturers) as well some proprietary technology approaches developed by tissue companies. NTT and QRT by Valmet, ATMOS by Voith and eTAD by Georgia Pacific are possibly the most well-known iterations of hybrid structured technologies. Each of these has faced their own challenges in producing quality tissue/towel at high speed, and they all tend to share two common challenges:
- Intimate transfer of the web.
- Temperature intolerance of the prevailing Yankee coating chemistry.
The solution for both the OEM and chemistry provider is to find a chemistry that can manage the moisture levels and inherent variability at the nip with hybrid structured machines. In so doing, uniform attachment results in uniform creping energy across the sheet. Failing to achieve this, the rolls produced will suffer from highly variable reel build across the roll width.