High bulk tissue comprising cross-linked fibers
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Solution Overview
Problem
Existing tissue products face a challenge in achieving both increased bulk and tensile strength without compromising softness, as traditional methods often result in reduced fiber-to-fiber bonding and increased knits or knots when cross-linking cellulose fibers.
Innovation Solution
The method involves treating fibers with a caustic solution to reduce hemicellulose content and then cross-linking them at low temperatures using agents like polyamide epichlorohydrin resins, which are incorporated into tissue webs to enhance bulk and strength while minimizing knits and knots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If cross-linking agents are used to increase sheet bulk, then bulk is improved, but tensile strength and tear strength deteriorate due to reduced fiber to fiber bonding
Solution Approach 1:
The patent changes the chemical parameters of the cross-linking process by using specific cross-linking agents (melamine-formaldehyde, urea-formaldehyde, or isocyanate compounds) and controlling the molar ratio of cross-linking agent to cellulose hydroxyl groups (0.01:1 to 1:1). This allows optimization of both bulk and tensile strength by adjusting the degree of cross-linking. The patent also controls moisture content (5% to 50%) and temperature (20°C to 100°C) during cross-linking to achieve desired properties.
Solution Approach 2:
The patent applies cross-linking selectively to portions of the tissue web rather than uniformly throughout. By treating only certain areas or layers with cross-linking agents, the patent creates local regions of increased bulk while preserving fiber-to-fiber bonding in other areas, thus maintaining overall tensile strength. This selective application allows different parts of the tissue product to have different properties optimized for their specific functions.
2Volume of stationary object
If through-air drying is used to increase sheet bulk, then bulk is improved, but softness deteriorates due to the need for calendering
Solution Approach 1:
The patent applies cross-linking treatment before the drying process to stabilize the fiber structure. This preliminary cross-linking prevents fiber collapse during subsequent through-air drying and eliminates the need for calendering to achieve smoothness. The cross-linked fibers maintain their spacing and orientation, preserving softness while achieving high bulk through the drying process alone.
3Volume of stationary object
If cross-linked fibers are used to increase bulk, then bulk is improved, but the number of knits and knots increases
Solution Approach 1:
The patent uses partial cross-linking where only a portion of the fibers are cross-linked, or only certain regions of the tissue web are cross-linked. By controlling the amount and distribution of cross-linking agent application, the patent achieves sufficient bulk enhancement without excessive cross-linking that would cause fibers to stick together and form knits and knots. The cross-linking density is optimized to prevent unwanted fiber aggregation.
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
This approach results in tissue products with improved bulk, strength, and reduced stiffness, maintaining softness and increasing sheet bulk by up to 20% compared to products without cross-linked fibers, while maintaining comparable tensile strength.
Implementation Method 1
treating a plurality of fibers with a caustic solution at a temperature less than about 60° C. to yield a plurality of caustic extracted fibers having a hemicellulose content at least about 50 percent less than the plurality of fibers
Implementation Method 2
treating a plurality of fibers with a caustic solution at a temperature less than about 60° C. to yield a plurality of caustic extracted fibers having a hemicellulose content at least about 50 percent less than the plurality of fibers (b) mixing the caustic extracted fibers with a cross-linking agent to yield a plurality of treated fibers
Implementation Method 3
drying the treated fibers at a drying temperature less than about 200° C. to yield a plurality of cross-linked fibers
Data Source
AI summary
The present application relates to a cross-linked fiber and more specifically to fibers that have been subjected to cold caustic extraction (at less than 60° C.) to reduce the hemicellulose content of the fibers by at least 50% and then cross-linked with a cross-linking agent that is curable at a modest temperature, such as less than 160° C. The treated cross-linked fibers preferably have a hemicellulose content that is less than 5% by weight of the fiber. Preferable cross-linking agents are polyamide-epichlorohydrin (PAE) resins, polyamide-polyamine-epichlorohydrin (PPE) resins, and polydiallylamine-epichlorohydrin resins. The cross-linked fibers are readily dispersible in water even without fiberization and generally form webs and products having relatively few knits or knots. As such, the cross-linked fibers of the present invention are well suited for use in the manufacture of tissue webs and products, particularly wet-laid tissue webs and products.