NSSC Pulp Fluting High Line Load Pressing
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Solution Overview
Problem
The stiffness of Neutral Sulfite Semi-Chemical (NSSC) pulp fibers makes it difficult to press paper webs to high densities, limiting the compressive strength of containerboard used in corrugated boards, as traditional presses require lower nip pressures to maintain bulk.
Innovation Solution
Using a shoe press with a high line load above 1200 kN/m to increase the density and compressive strength of containerboard, combined with steam application to elevate web temperature, allowing for higher peak nip pressures and press impulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional presses are used to press NSSC pulp web, then bulk is maintained, but density and compressive strength are limited
Solution Approach 1:
The patent applies parameter changes by significantly increasing the line load from conventional levels (typically below 500 kN/m) to above 1200 kN/m, and by increasing web temperature through steam injection from 20-30°C to 60-90°C. These parameter changes enable the stiff NSSC fibers to be pressed to high densities (above 725 kg/m³) while maintaining manufacturing feasibility.
2Volume of stationary object
If high nip pressure is applied to NSSC pulp web, then density increases, but bulk is reduced
Solution Approach 1:
The patent changes the temperature parameter by injecting steam to raise web temperature from 20-30°C to 60-90°C before pressing. This temperature increase makes the stiff NSSC fibers more pliable, allowing them to withstand high line loads (above 1200 kN/m) without excessive bulk reduction, thereby achieving high density (above 725 kg/m³) while maintaining acceptable bulk properties.
3Strength
If line load is increased above 1200 kN/m, then compressive strength increases, but energy consumption increases
Solution Approach 1:
The patent applies parameter changes in sequence: first increasing web temperature through steam injection (from 20-30°C to 60-90°C) to make fibers more pliable, then applying high line load (above 1200 kN/m). This sequential parameter change reduces the total energy required compared to applying high pressure alone, as the thermal energy enables the mechanical pressing to be more efficient and effective.
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 method results in a high-density containerboard with increased compressive strength, maintaining or improving machine speed, and achieving densities above 725 kg/m3 and geometric SCT indices above 37 Nm/g, enhancing the structural integrity of corrugated boards.
Implementation Method 1
pressing a web formed from a pulp comprising NSSC pulp in an extended nip press, such as a shoe press, wherein the line load in the extended nip press is above 1200 kN/m
Implementation Method 2
combined with steam application to elevate web temperature, allowing for higher peak nip pressures and press impulses
Data Source
AI summary
There is provided a method of producing a containerboard, comprising the step of pressing a web formed from a pulp comprising NSSC pulp in an extended nip press, such as a shoe press, wherein the line load in the extended nip press is above 1200 kN/m. Further, there is provided a corrugated board comprising a liner and a fluting, wherein the fluting is formed from a pulp comprising NSSC pulp, the density of the fluting is above 725 kg/m3 and the geometric SCT index (ISO 9895) of the fluting is above 37 Nm/g.