Filler Preflocculation in Papermaking for Shear Stability
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Solution Overview
Problem
Increasing filler content in papermaking reduces sheet strength and optical efficiency, and poses challenges in maintaining even distribution and shear stability due to the limitations of current preflocculation technologies using low molecular weight coagulants or high molecular weight flocculants.
Innovation Solution
A method involving the treatment of filler particles with a combination of starch and cationic or ionic flocculants, either premixed or added simultaneously, to form filler flocs that enhance shear stability and particle size distribution, thereby improving sheet strength and uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If low molecular weight coagulants like starch are used for filler preflocculation, then the process is simple and economical, but the filler flocs have small particle size that breaks down under high shear forces of the paper machine
Solution Approach 1:
The patent combines low molecular weight coagulants (starch) with high molecular weight flocculants to create a synergistic effect. The starch provides initial floc formation and economic benefits, while the high molecular weight flocculant reinforces the flocs to resist shear forces during paper machine operation, thus resolving the contradiction between process simplicity and shear stability.
Solution Approach 2:
The invention uses composite chemical systems combining different types of polymers (coagulants and flocculants) with different molecular weights and charge characteristics. This composite approach creates filler flocs that possess both the ease of formation from simple coagulants and the shear resistance of high molecular weight flocculants.
2Reliability
If high molecular weight flocculants are used for filler preflocculation, then shear stability is improved, but particle size distribution becomes broad and difficult to control
Solution Approach 1:
The patent segments the flocculation process into two stages: first, low molecular weight coagulants create initial small flocs with controlled size distribution, then high molecular weight flocculants are added to reinforce these pre-formed flocs. This segmentation allows each chemical to perform its optimal function, maintaining particle size control while achieving shear stability.
Solution Approach 2:
The low molecular weight coagulants perform preliminary floc formation before the high molecular weight flocculants are introduced. This preliminary action creates a foundation of uniformly sized flocs that the subsequent flocculant can reinforce without creating broad size distribution, thus maintaining manufacturing precision while improving shear stability.
3Productivity
If filler content is increased to improve product quality and reduce costs, then raw material and energy costs are reduced, but sheet strength and optical efficiency are reduced
Solution Approach 1:
The patent changes the physical parameters of filler particles through preflocculation treatment, increasing their size and modifying their surface characteristics. This allows higher filler content to be incorporated while the modified floc structure maintains better bonding with cellulose fibers, preserving sheet strength despite increased filler substitution.
Solution Approach 2:
The preflocculated filler acts as an improved intermediary between cellulose fibers. By treating filler with coagulants and flocculants, the filler flocs develop better interfacial properties that enhance their ability to bond with cellulose, allowing high filler content to be used without proportionally reducing sheet strength.
4Productivity
If filler content is increased, then raw material costs are reduced, but maintaining even distribution of fillers becomes more difficult
Solution Approach 1:
The patent changes the size and surface properties of filler particles through preflocculation, creating uniformly sized flocs with modified surface characteristics. This standardization of filler parameters improves their flow and distribution characteristics in the paper machine, enabling even distribution even at high filler contents.
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 method results in larger filler particle sizes, reduced interference with cellulose-cellulose bonding, and increased sheet strength, while maintaining economic feasibility.
Implementation Method 1
The term 'preflocculation' refers to the modification of filler particles into agglomerates through treatment with coagulants and/or flocculants before their flocculation and addition to the furnish stock
Implementation Method 2
The flocculation treatment and shear forces of the process determine the size distribution and stability of the flocs before addition to the furnish stock
Data Source
AI summary
Method of papermaking comprises: treating filler with a starch and a flocculant to form a filler floc; combining the filler floc with the cellulose fiber stock; and forming a paper mat from the combination of filler floc and cellulose fiber stock. The method have been found to result in larger particle sizes for the filler flocs, improved shear stability, and improved sheet strength in the paper mat.