Amphoteric Copolymer Paper Web Strength and Drainage
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Solution Overview
Problem
The initial wet web strength of paper, which limits papermachine speed, is not adequately enhanced by existing methods, necessitating a process to increase the solids content and strength of the paper web before transitioning to the dryer section.
Innovation Solution
A process involving the addition of a water-soluble amphoteric copolymer to the paper stock, followed by sheet formation and pressing in the wire and press sections, where the paper stock is diluted and pressed to a specific solids content to achieve higher initial wet web strength, allowing for increased machine speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If existing drainage aids and retention aids are used to increase solids content, then drainage efficiency is improved, but initial wet web strength is not adequately enhanced
Solution Approach 1:
The patent changes the chemical parameters of the paper stock by introducing a specifically designed amphoteric copolymer with controlled molecular weight (50,000-500,000 daltons) and composition (20-60 mol% acrylamide, 20-60 mol% cationic monomer, 20-60 mol% anionic monomer). This parameter change enables the polymer to provide both drainage aid functionality and significant wet web strength enhancement, resolving the contradiction between solids content and initial wet web strength.
Solution Approach 2:
The patent uses a composite amphoteric copolymer structure combining cationic and anionic functional groups in a single molecule. This composite structure allows the polymer to interact with both fibers and fillers simultaneously, providing dual functionality as both drainage aid and strength enhancer, thereby achieving adequate initial wet web strength while maintaining efficient drainage.
2Productivity
If papermachine speed is increased, then productivity is improved, but initial wet web strength becomes insufficient to handle the higher speeds
Solution Approach 1:
The patent applies the amphoteric copolymer to the paper stock before sheet formation, allowing the polymer to pre-condition the fibers and fillers. This preliminary action ensures that when the paper web is formed and subjected to higher machine speeds, the strength enhancement is already in place, enabling the paper to withstand the increased operational demands without breaking.
Solution Approach 2:
By changing the molecular weight and compositional parameters of the polymer additive, the patent optimizes the paper's mechanical properties to withstand higher line speeds. The specific parameter range (molecular weight 50,000-500,000 daltons, balanced cationic/anionic content) creates optimal bonding conditions that enable faster papermachine operation.
3Productivity
If pull-off force is increased to achieve faster operation, then productivity is improved, but paper breaks occur due to insufficient initial wet web strength
Solution Approach 1:
The patent modifies the chemical composition parameters of the paper stock by incorporating the amphoteric copolymer with specific ratios of cationic (20-60 mol%) and anionic (20-60 mol%) monomers. This parameter change creates optimal electrostatic and hydrogen bonding conditions that significantly enhance initial wet web strength, allowing higher pull-off forces to be applied without causing paper breaks and thus improving operational reliability.
Solution Approach 2:
The amphoteric copolymer acts as an intermediary substance between fibers and fillers, creating a bonding network that distributes stress more evenly throughout the paper web. This intermediary role prevents localized stress concentrations that would otherwise cause breaks under high pull-off forces, enabling faster operation with fewer broken ends.
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
The process significantly enhances the initial wet web strength of paper, enabling higher pull-off forces and faster papermachine operation with fewer broken ends, as demonstrated by the increased solids content and improved strength of the paper web.
Implementation Method 1
draining a filler-containing paper stock comprising at least one water-soluble amphoteric copolymer with sheet formation in the wire section
Implementation Method 2
pressing the paper in the press section... the sheet is pressed in the press section to a solids content G(x) wt % or greater
Implementation Method 3
amphoteric copolymer... obtainable by polymerizing a mixture of acrylamide, cationic monomer, and anionic monomer
Data Source
AI summary
The invention relates to a process for the production of paper, card and board, including the steps of draining a filler-containing paper stock, having a certain fibrous concentration and containing at least one water-soluble amphoteric copolymer, with sheet formation in a wire section, then pressing the paper in a press section, diluting the paper stock to a fibrous concentration in the range from 5 to 15 g/l, draining the diluted paper stock to form a sheet, and then pressing the sheet in the press section to a solids content G(x) wt % or greater, such that G(x) computes according to:G(x)=48+(x−15)·0.4,where x is the numerical value of a filler content of the dry paper, card or board (in wt %), and G(x) is a numerical value of the minimal solids content (in wt %) to which the sheet is pressed.