Anionic Additive Retention in Multilayer Paper Headbox
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Solution Overview
Problem
Existing methods for producing paper or board products using multilayer headboxes do not adequately enhance burst strength and SCT strength, and there is a need to improve the retention of cationic polymers in the final product.
Innovation Solution
Incorporating an anionic additive, such as anionic synthetic organic polymers or anionic polysaccharides, into the feed water in a multilayer headbox to form an aqueous layer between fibre layers, which interacts with cationic polymers to create polyelectrolyte complexes, increasing drainage resistance and retention, thereby enhancing the strength properties of the final product.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If only cationic polymer is added to feed water in multilayer headbox, then some strength improvement is achieved, but retention of cationic polymer to formed web is insufficient and further strength improvement is needed
Solution Approach 1:
The patent introduces an anionic polymer as an intermediary substance that mediates between the cationic polymer and the fibre web. The anionic polymer forms a polyelectrolyte complex with the cationic polymer through electrostatic attraction, creating a larger composite structure that is more effectively retained by the web during dewatering. This intermediary mechanism solves the retention problem while maintaining strength enhancement.
Solution Approach 2:
The patent creates a composite polyelectrolyte complex by combining two different polymers with opposite charges (cationic and anionic). This composite structure has superior retention properties compared to the individual cationic polymer alone, as the complexed structure is larger and interacts more effectively with the fibre network during web formation, thereby improving both retention and strength.
2Strength
If more cationic polymer is added to increase strength, then burst strength and SCT strength improve, but loss of cationic polymer to circulating waters increases
Solution Approach 1:
The anionic polymer acts as a retaining intermediary that captures the cationic polymer through electrostatic complexation. This complexed structure is then retained by the fibre web during dewatering, preventing the cationic polymer from being lost to circulating waters. The intermediary mechanism allows effective strength enhancement without proportional increases in polymer loss.
Solution Approach 2:
The patent converts the potential harm of cationic polymer loss to circulating waters into a benefit by using the anionic polymer to create a complex that is specifically retained by the web. The electrostatic interaction between oppositely charged polymers transforms the retention problem into an opportunity for enhanced web strength and reduced chemical loss.
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 significantly increases the burst strength and SCT strength of paper or board products, allowing for lighter grammage while reducing raw material and energy usage, and minimizing the carbon footprint.
Implementation Method 1
the anionic additive forms some kind of polyelectrolyte complex with the cationic polymer present in the feed water
Implementation Method 2
the anionic additive forms some kind of polyelectrolyte complex with the cationic polymer
Implementation Method 3
the anionic additive, preferably anionic synthetic polymer, increases the viscosity of the feed water as the anionic additive interacts with the cationic polymer, and this increases the drainage resistance and shear resistance of the system
Implementation Method 4
The formed complex is efficiently retained by the adjacent stock layers during the dewatering of the web
Data Source
AI summary
The present invention relates to a method for increasing the strength properties, preferably burst strength and SCT strength, of a paper or board product. The paper or board product is manufactured from a fibrous web produced by a multilayer headbox, where an aqueous layer is formed between at least a first and a second fibre layer formed from fibrous stock suspension(s), and where feed water for the aqueous layer comprises at least one cationic polymer. The invention comprises an addition of an anionic additive, which is selected from a group comprising anionic synthetic organic polymers, anionic polysaccharides, and any of their combinations to the feed water before formation of the aqueous layer.