Sequential Cationic Anionic Treatment for High Filler Paper Strength
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Solution Overview
Problem
Existing methods for improving the dry strength of paper and board, particularly at high filler content or low basis weight, are not optimal, as they often require increased amounts of strength agents and compromise strength properties.
Innovation Solution
A method involving the sequential addition of a cationic first agent and a water-soluble anionic copolymer to fibre stock, optimizing the charge ratio between cationic and anionic charges to enhance zeta potential and fibre interaction, thereby improving strength properties without excessive foaming or retention issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If filler content is increased to reduce costs, then manufacturing cost decreases, but strength properties of the paper deteriorate
Solution Approach 1:
The patent introduces a two-stage chemical treatment system where a cationic agent first modifies fibre surfaces to create positive charges, then an anionic agent acts as a bridge between fibres through electrostatic attraction. This intermediary chemical mechanism enables high filler content to be maintained while strength properties are preserved through enhanced fibre-fibre bonding, resolving the contradiction between cost reduction and strength maintenance.
Solution Approach 2:
The patent fundamentally changes the charge parameter of fibre surfaces through sequential chemical treatment. By first introducing cationic charges and then anionic charges in a controlled sequence, the system creates optimal electrostatic conditions for fibre bonding. This parameter change enables the paper to maintain strength properties even with high filler content, as the charged fibre surfaces create strong attractive forces that compensate for the presence of fillers.
2Quantity of substance
If filler content is increased to reduce costs, then manufacturing cost decreases, but zeta potential optimization becomes more difficult
Solution Approach 1:
The patent segments the charge optimization process into two distinct stages: first adding a cationic agent to create positive charges on fibre surfaces, then adding an anionic agent to create negative charges. This segmentation of the chemical treatment process simplifies the overall optimization by breaking down the complex charge ratio control into two manageable steps, each with its own optimization parameters. The sequential addition allows independent control of each stage, making the process more manageable despite high filler content.
Solution Approach 2:
The patent applies preliminary action by first modifying fibre surfaces with a cationic agent before introducing the anionic agent. This preliminary cationic modification creates a foundation of positive charges that facilitates subsequent anionic agent attachment. By preparing the fibre surfaces in advance with the first agent, the system optimizes the conditions for the second agent's action, thereby simplifying the overall charge ratio optimization process even when filler content is high.
3Productivity
If basis weight is reduced to produce lighter board, then productivity increases, but bending stiffness deteriorates
Solution Approach 1:
The patent creates a composite structure at the fibre level through sequential cationic and anionic treatment. The two-charged fibre surfaces form a composite bonding mechanism where electrostatic attractions create strong fibre-fibre bonds. This composite approach at the micro level compensates for the reduced basis weight, maintaining bending stiffness even in lighter boards. The composite chemical structure of treated fibres provides enhanced mechanical properties that offset the lower overall weight.
Solution Approach 2:
The patent applies local quality by concentrating chemical treatment effects at the fibre surface level rather than uniformly throughout the bulk material. The cationic and anionic agents create localized charged regions on fibre surfaces that generate strong bonding forces at fibre contact points. This localized enhancement of bonding quality at critical interfaces maintains overall board stiffness even when the total basis weight is reduced, as the local bond strength compensates for the lower bulk mass.
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 maintains or enhances strength properties of paper and board at high filler content or low basis weight, offering cost-effective solutions by optimizing the charge ratio and fibre interaction, while minimizing the need for additional strength agents.
Implementation Method 1
the cationic first agent is added to the fibre thick stock... it interacts with the anionic sites of the fibre surfaces
Implementation Method 2
the anionic second agent is added, whereby it interacts with the cationic first agent attached to the fibre surface and forms 'bridges' between the fibres
Data Source
AI summary
The invention relates to a method for treating a fiber stock for making of paper, board or the like. The method comprises obtaining a fiber thick stock and adding to the fiber thick stock at least one cationic first agent, and adding separately to the fiber stock and after the addition of the cationic first agent, at least one anionic second agent, which is an water-soluble anionic copolymer of acrylamide, methacrylamide or acrylonitrile, in such amount that the ratio of the added absolute cationic charge to the added absolute anionic charge is from 1:0.1 to 1:0.95. The invention relates also to the product prepared by using a fiber stock, which is treated by using the method.