Press Drying Mechanical Pulp Web With Overpressure And Dry Strength Additives
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Solution Overview
Problem
Existing paper and paperboard production methods face challenges in achieving strong products with high bulk and low fiber content, as pulps rich in long fibers struggle with fiber bonding, leading to compromised bulk and strength properties.
Innovation Solution
A process involving mechanical and/or chemimechanical pulp dried in a press drying process with overpressure above 40 kPa and heat, combined with at least two dry strength additives, such as cationic starch and carboxymethyl cellulose, to enhance strength without affecting bulk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If mechanical or CTMP pulp with high freeness and long fibers is used to increase bulk, then bulk properties are improved, but fiber bonding ability deteriorates
Solution Approach 1:
A dry strength additive is introduced as an intermediary substance between the mechanical/CTMP fibers to facilitate fiber bonding. The additive adsorbs to the fiber surfaces and creates strong bonds between fibers, enabling both high bulk and strong fiber bonding to be achieved simultaneously without compromising either property
Solution Approach 2:
The drying conditions are changed by applying superatmospheric pressure (above 40 kPa) during the press drying process. This parameter change in the drying environment enables the dry strength additive to function effectively, producing a bulky paper product with improved strength that would not be achievable under conventional atmospheric drying conditions
2Strength
If cationic starch is added to improve dry strength, then strength is improved, but the amount of starch retained deteriorates due to difficulty in adsorption
Solution Approach 1:
The drying process parameters are changed by applying superatmospheric pressure (above 40 kPa) during press drying. This parameter change improves the retention of cationic starch on fibers by enhancing the adsorption process and reducing starch loss, thereby achieving both strength improvement and adequate starch retention
3Volume of moving object
If fiber content is reduced to achieve high bulk, then bulk is improved, but strength deteriorates
Solution Approach 1:
The dry strength additive serves as a mediator that compensates for the reduced fiber content. By adding this substance that promotes strong fiber-to-fiber bonding, the patent achieves high bulk with reduced fiber content while maintaining or improving the overall strength of the paper or paperboard product
Solution Approach 2:
The patent creates a composite system combining mechanical/CTMP fibers with dry strength additives. This composite approach allows the use of lower fiber content for high bulk while the additive component provides the necessary strength, achieving a synergistic effect that resolves the contradiction between bulk and strength
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 produces a strong and bulky paper or paperboard product with improved strength and bulk properties, comparable to those made with chemical pulps, while reducing fiber usage and production costs.
Implementation Method 1
drying the web in a press drying process by subjecting the web to heat and an overpressure of above 40 kPa
Implementation Method 2
subjecting the web to heat and an overpressure of above 40 kPa
Implementation Method 3
It is however difficult to adsorb large amounts of starch to the fibers
Data Source
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AI summary
The present invention relates to a process for producing at least one ply of a paper or board product wherein a web comprising mechanical and/or chemimechanical pulp and at least one dry strength additive is dried in a press drying process by subjecting the web to heat and an overpressure of above 40kPa. The present invention also relates to a paper product, a paperboard product and a ply produced according to the process.