Cross-Linked Tissue Webs for Bulk-Strength Balance
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Solution Overview
Problem
Existing tissue products struggle to achieve a balance between bulkiness and tensile strength without compromising softness, as methods like through-air drying and cross-linking often result in reduced fiber-to-fiber bonding and subsequent loss of tensile strength.
Innovation Solution
The development of non-compressively dewatered tissue webs comprising cross-linked cellulosic fibers, which are combined with conventional fibers to form homogenous or layered tissue webs, allowing for improved sheet bulk and z-directional properties without sacrificing tensile strength or softness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If cross-linking agents are used to increase sheet bulk, then sheet bulk is improved, but tensile strength deteriorates due to reduced fiber to fiber bonding
Solution Approach 1:
The patent applies local quality by treating only a portion of the papermaking furnish with cross-linking chemicals, creating regions with different properties. The cross-linked fibers provide bulk while untreated fibers maintain strong hydrogen bonding for tensile strength. This spatial differentiation allows simultaneous achievement of high bulk and strength.
Solution Approach 2:
The invention creates a composite fiber structure where cross-linked fibers (providing bulk) are blended with uncross-linked fibers (providing strength through hydrogen bonding). This composite approach combines the advantages of both fiber types to achieve improved sheet bulk without sacrificing tensile strength.
2Volume of stationary object
If through-air drying is used to increase sheet bulk, then sheet bulk is improved, but softness deteriorates requiring calendering which reduces bulk
Solution Approach 1:
The patent changes the chemical parameters of the fibers through cross-linking treatment, which fundamentally alters how the tissue responds to mechanical processing. Cross-linked fibers resist compression better, allowing the tissue to maintain bulk even after calendering while still achieving softness through controlled calendering of the blended web.
3Strength
If uncross-linked fibers are used to maintain tensile strength, then tensile strength is preserved, but sheet bulk deteriorates
Solution Approach 1:
The patent segments the fiber population into two distinct groups: cross-linked fibers (providing bulk) and uncross-linked fibers (providing strength). This segmentation allows each fiber type to fulfill its specific function without compromising the other, achieving both high sheet bulk and tensile strength in the blended tissue product.
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 approach results in tissue products with increased sheet bulk, preserved tensile strength, and enhanced resiliency, maintaining a high degree of bulk even after calendering, while maintaining low stiffness and high absorbency.
Implementation Method 1
treating a portion of the papermaking furnish with chemicals that facilitate the formation of covalent bonds between adjacent cellulose molecules
Implementation Method 2
the reaction of water soluble multi-functional molecules capable of reacting with cellulose under mildly acidic conditions
Implementation Method 3
through-air drying
Data Source
AI summary
The present invention provides tissue webs and products that are manufactured by non-compressive dewatering and/or drying methods, such as through-air drying, where the webs and products comprise cross-linked fiber. The non-compressively dewatered tissue webs and products have improved sheet bulk and z-direction properties. For example, in one embodiment, the invention provides through-air dried tissue products having good sheet bulk and resiliency, such as a sheet bulk greater than about 15 cc/g and Compression Energy (E) greater than about 1.30 N/m. Surprisingly the foregoing products have sufficient strength to withstand use, such as a GMT greater than about 600 g/3″, but are not overly stiff, generally having a Stiffness Index less than about 12.