Durable wet-pressed tissue
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Solution Overview
Problem
Wet-pressed tissue products have limited cross-machine direction (CD) properties such as stretch, tensile energy absorption, and durability due to web densification during the wet-pressing process, which restricts the ability to impart structure and increases energy consumption for drying.
Innovation Solution
A method involving the use of cellulosic fibers with specific curl indices to form multi-layered fibrous webs, which are then pressed and dried to achieve higher CD tensile strength and stretch without compromising tensile strength, incorporating a higher percentage of curled fibers to enhance cross-machine direction properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the web is densified by wet pressing, then dewatering efficiency is improved, but cross-machine direction stretch and tensile energy absorption are reduced
Solution Approach 1:
The patent changes the physical-chemical parameters of the fibers by applying a chemical treatment that increases fiber curl. This parameter change occurs before web formation, allowing the fibers to naturally create an open structure during wet pressing that maintains cross-machine direction stretch and tensile energy absorption while still achieving effective dewatering through the pressure nip.
Solution Approach 2:
The chemical treatment to increase fiber curl is applied in advance, before the fibers are formed into a web and subjected to wet pressing. This preliminary action ensures that the fibers are pre-configured with enhanced curl characteristics that will manifest during the subsequent dewatering and drying processes, thereby improving cross-machine direction properties before the densification step occurs.
2Strength
If tensile strength is increased to improve cross-machine direction properties, then durability is improved, but product softness is compromised
Solution Approach 1:
The patent applies a chemical treatment that specifically modifies the fiber curl parameter, which indirectly influences web structure and mechanical properties. This targeted parameter change allows the web to achieve improved cross-machine direction tensile strength and durability through enhanced fiber interlocking and structure, while maintaining softness by avoiding direct strengthening treatments that would increase tensile strength excessively.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method results in tissue products with improved CD tensile strength, stretch, and durability, specifically achieving CD Tensile greater than 450 g/3″ and CD Stretch greater than 6.0%, while maintaining softness and reducing energy consumption.
Implementation Method 1
dispersing cellulosic fibers having a curl index less than about 0.10 to form a first fibrous slurry, dispersing curled cellulosic fibers having a curl index greater than about 0.20 to form a second fibrous slurry
Implementation Method 2
Free water expressed from the web in the pressure nip is absorbed and carried away by the felt as the web transfers to the Yankee surface
Implementation Method 3
The web is then final dried on the surface of the Yankee and subsequently creped to impart bulk and softness to the resulting tissue sheet
Data Source
AI summary
The disclosure provides a wet-pressed tissue product having improved cross-machine tensile, toughness and durability properties. Cross-machine properties are significant because tissue products often fail in the cross-machine direction because it is often the weaker of the two product orientations (cross and machine directions). Accordingly, in certain embodiments the present disclosure provides a conventional wet pressed tissue product having a CD Tensile greater than about 450 g/3″ and a CD Stretch greater than about 6.0 percent.