Amphoteric Polymer Dewatering for Paper Wet Strength
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Solution Overview
Problem
The existing paper production methods face challenges in achieving high initial wet structural strength, which limits machine speed and filler usage, as rapid dewatering can lead to poor strength and optical properties in the paper.
Innovation Solution
A method involving an aqueous slurry containing a water-soluble amphoteric polymer and microparticles, specifically copolymerized with N-vinylcarboxamide and monoethylenically unsaturated monomers, is added to the paper stock, allowing dewatering to a dry content of at least 18% before pressing and drying, enhancing the initial wet structure strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If rapid dewatering is performed to increase productivity, then machine speed can be increased, but initial wet structure strength deteriorates
Solution Approach 1:
The patent applies preliminary action by adding specific chemical additives (anionic polymers followed by cationic polymers) to the paper stock before dewatering occurs. These additives pre-condition the fiber-filler-water system to maintain strength during subsequent rapid dewatering operations, enabling higher machine speeds without sacrificing initial wet structure strength.
Solution Approach 2:
The patent changes chemical parameters by introducing a two-stage polymer treatment system with specific charge densities and molecular weights. This chemical parameter modification allows the system to tolerate faster dewatering rates while maintaining strength properties, effectively decoupling the trade-off between productivity and strength.
2Quantity of substance
If filler content is increased to reduce material costs, then quantity of substance improves, but initial wet structure strength deteriorates
Solution Approach 1:
The patent uses polymeric additives as intermediary substances that mediate between filler particles and fiber matrix. These polymers act as binding agents that hold filler particles together and to the fiber network, allowing high filler content to be maintained without compromising the structural integrity and initial wet strength of the paper.
Solution Approach 2:
The patent creates a composite system combining fiber, filler, and polymeric additives. This composite approach allows the beneficial properties of high filler content (cost reduction) to be combined with the strength-providing properties of the polymer-filler-fiber matrix, resolving the contradiction between quantity and strength.
3Device complexity
If conventional dewatering methods are used to simplify the process, then device complexity is reduced, but initial wet structure strength deteriorates
Solution Approach 1:
The patent applies self-service by using chemical additives that automatically perform the strength-enhancing function during the normal dewatering process. The polymers self-organize around filler particles and fibers during dewatering, providing strength enhancement without requiring additional equipment or complex process modifications.
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 initial wet structure strength of the paper, enabling higher machine speeds and increased filler usage without compromising paper quality.
Implementation Method 1
the suspension is flocculated using a flocculation system comprising a siliceous material and organic microparticles
Implementation Method 2
the water is separated from the paper material by gravity alone or by a combination of gravity and centrifugal forces and drains through the openings of the sieves
Implementation Method 3
the water is separated from the paper material by gravity alone or by a combination of gravity and centrifugal forces
Implementation Method 4
WO-A-04/087818, WO-A-05/012637 and WO-A-2006/066769 describe aqueous slurries of finely divided fillers that have been treated with water-soluble amphoteric copolymers based on polyvinylamine
Data Source
AI summary
The invention relates to a method for producing paper and cardboard, having the steps of providing an aqueous suspension containing filler, at least one water-soluble amphoteric polymer, and microparticles; adding said aqueous suspension to a paper material, dewatering the obtained paper material, thereby forming sheets in the wire section, until the dry matter content of the paper sheet is at least 18 wt.%; and subsequently pressing and drying the paper sheet. The water-soluble ampoteric polymer can be obtained by copolymerizing a monomer mixture comprising a) at least one N-vinyl carboxylic acid amide of the general formula, in which R1 and R2 independently of each other represent H or C1- to C6-alkyl, b) at least one monoethylenically unsaturated monomer with at least one free acid group or at least one acid group in salt form, c) optionally at least one monoethylenically unsaturated monomer which differs from components (a) and (b), and d) optionally at least one compound which has at least two ethylenically unsaturated double bonds in the molecule, and subsequently partly or completely hydrolyzing the groups -CO-R1 of the polymerisate, wherein the difference between the contents of the cationic and the anionic monomer units in mol.% absolutely maximally equals 10, in each case based on the total number of moles of all monomer units.