Tissue Webs High Cross-Direction Slope Durability
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Solution Overview
Problem
Papermakers face challenges in producing tissue webs with increased cross-direction slope while maintaining softness and durability, as existing methods either result in tissues that are perceived as weak or stiff.
Innovation Solution
A method involving forming a through-dried tissue web, rewetting it, pressing, and drying it again to achieve a high cross-direction slope without significantly increasing tensile strength, thereby enhancing durability and softness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If CD tensile strength is increased to increase CD slope, then CD slope is improved, but tissue becomes stiffer and less soft
Solution Approach 1:
The patent changes the physical state parameters of the tissue web by controlling moisture content during pressing (maintaining at least 5% moisture) and applying specific pressure ranges (5-50 psi). This allows achievement of high CD slope (9000-15000 g/3") while maintaining softness, as the controlled moisture prevents excessive stiffening that would occur with traditional dry pressing methods.
2Strength
If CD tensile strength is reduced to reduce CD slope, then CD slope is reduced, but tissue is perceived as weak or flimsy
Solution Approach 1:
The patent achieves high CD slope values (9000-15000 g/3") that convey durability perception without requiring high CD tensile strength. The controlled moisture pressing process creates a balance where the tissue appears durable due to high slope while maintaining lower tensile strength for softness.
3Productivity
If throughdrying is used to reduce moisture content, then drying efficiency is improved, but tissue requires additional rewetting and drying steps to achieve desired properties
Solution Approach 1:
The patent performs preliminary throughdrying to reduce moisture content below 5% before the final pressing operation. This preliminary action prepares the web for the subsequent moisture-controlled pressing that achieves the high CD slope, separating the drying function from the property-modification function.
Solution Approach 2:
The patent employs periodic action by alternating between drying phases (throughdrying to <5% moisture) and moisture-introduction phases (rewetting to at least 5% moisture before pressing). This periodic cycle of drying and moisture addition enables precise control over the final tissue properties.
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 produces tissue webs with improved durability and softness, characterized by a high cross-direction slope and moderate tensile strength, resisting stretch removal under tensile load and maintaining consumer-preferred attributes.
Implementation Method 1
rewetting the web
Implementation Method 2
pressing the rewetted web
Implementation Method 3
drying the pressed web, such that the web has a moisture content less than about 5 percent
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
The present disclosure provides tissue webs with improved durability produced by rewetting a dried tissue web, pressing the rewetted web and drying the web for a second time. This improved durability is manifested by a high cross-machine direction (CD) slope.