Layered tissue comprising long, high-coarseness wood pulp fibers
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Solution Overview
Problem
The papermaking industry faces challenges in balancing the strength and softness of tissue products due to supply pressures and environmental concerns with northern softwood kraft fibers, while southern softwood kraft fibers are unsuitable for soft tissue products due to high coarseness, leading to stiffness and harshness.
Innovation Solution
Incorporating long, high-coarseness wood pulp fibers with average lengths greater than 2.2 mm and coarseness of 20 mg/100 m or more into tissue products, particularly in outer layers, to enhance durability without compromising softness, and using a multi-layered tissue web structure with specific fiber blends in fabric and air-side layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If northern softwood kraft fibers are used to provide strength and softness, then durability and softness are improved, but supply availability deteriorates due to economic and environmental pressures
Solution Approach 1:
The patent replaces expensive, scarce northern softwood kraft fibers with more abundant, economical southern softwood kraft fibers. Although SSWK fibers have higher coarseness, the patent uses them in a multi-layer configuration where they form the bulk structure, thereby reducing dependency on limited NSWK supply while maintaining product functionality.
Solution Approach 2:
The patent creates a composite tissue structure by combining southern softwood kraft fibers (SSWK) with hardwood kraft fibers (HWK) in specific layers. This composite approach allows the SSWK to provide bulk and strength while HWK contributes to softness, achieving durability without relying on scarce NSWK fibers.
2Quantity of substance
If southern softwood kraft fibers are used to replace northern softwood kraft fibers, then supply availability improves, but softness deteriorates due to high coarseness
Solution Approach 1:
The patent applies local quality by assigning different fiber types to different layers of the tissue product. SSWK fibers with higher coarseness are placed in the air-side layer where bulk and strength are prioritized, while HWK fibers with lower coarseness are placed in the fabric-contacting layer where softness is critical. This spatial differentiation allows each layer to optimize its local function.
Solution Approach 2:
The patent uses composite materials by combining SSWK and HWK fibers in a multi-layer structure. The SSWK provides structural integrity and bulk in the air-side layer, while HWK provides softness in the fabric-contacting layer, achieving overall product softness despite using coarser SSWK fibers for availability.
3Strength
If long fiber furnish is used to provide strength, then tensile strength is improved, but stiffness increases reducing softness
Solution Approach 1:
The patent applies local quality by concentrating long SSWK fibers in the air-side layer where tensile strength is most needed for structural support. The fabric-contacting layer uses shorter HWK fibers that provide softness without excessive stiffness. This spatial separation allows each layer to optimize its mechanical properties for its specific function.
Solution Approach 2:
The patent uses composite materials with long SSWK fibers providing tensile strength in the air-side layer while HWK fibers modulate stiffness in the fabric-contacting layer. The combination achieves adequate tensile strength without the excessive stiffness that would result from using long fibers throughout the entire structure.
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 use of long, high-coarseness fibers improves durability and maintains or enhances softness in tissue products, offering comparable or better properties than those made with short, low-coarseness fibers, while reducing the need for northern softwood kraft fibers and addressing the unsuitability of southern softwood kraft fibers for premium tissue products.
Implementation Method 1
it is believed that this behavior is due to the higher number of hydrogen bonds required to produce a product of a given tensile strength with short fibers than with long fibers
Data Source
AI summary
The present invention provides multi-layered tissue webs, and tissue product comprising the same, comprising long, high-coarseness wood pulp fibers selectively deposited in one or more outer layers of the multi-layered web. Surprisingly disposing long, high-coarseness wood pulp fibers in one or more outer layers, even in relatively modest amounts, may improve certain product properties, such as durability, without negatively affecting softness. In certain instances, both the softness and durability may be improved by selectively incorporating long, high-coarseness wood pulp fibers in one or more of the outer layers.