Paper Retention System Using Segmented Cationic Polymers
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Solution Overview
Problem
Conventional papermaking processes face challenges in achieving an optimal balance between retention, drainage, and formation, especially at high machine speeds, often requiring multiple retention aids and leading to increased drainage that can negatively impact water release and formation quality.
Innovation Solution
A retention system comprising a blend of cationic polymers with specific charge densities and intrinsic viscosities, combined with microparticulate materials, is applied to the cellulosic thin stock, where one polymer is dosed before the final shearing stage and the other after, to enhance retention and formation without increasing drainage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single polymeric retention aid is added to increase drainage rate, then drainage is improved, but formation is damaged
Solution Approach 1:
The retention aid system is segmented into two distinct components: a high molecular weight polymeric retention aid (for drainage enhancement) and a low molecular weight polymeric retention aid (for formation preservation). This segmentation allows each component to perform its specific function optimally without the negative effects of the other, resolving the contradiction between improved drainage and maintained formation quality.
Solution Approach 2:
The invention uses a composite retention aid system combining two polymers with different molecular weights and properties. The high molecular weight polymer provides drainage improvement while the low molecular weight polymer protects formation, creating a composite system that achieves both objectives simultaneously rather than using a single material that must compromise between the two functions.
2Productivity
If multiple polymeric retention aids are added in sequence to balance retention and drainage, then retention and drainage are improved, but device complexity increases
Solution Approach 1:
The invention merges the functions of multiple retention aids into a coordinated two-component system. Rather than adding multiple separate chemicals at different stages, the patent combines a high molecular weight polymer and a low molecular weight polymer that work together synergistically, simplifying the overall process while maintaining the benefits of multiple retention mechanisms.
3Productivity
If machine speed is increased to boost output, then productivity is improved, but retention and formation quality deteriorate
Solution Approach 1:
The low molecular weight polymeric retention aid is added preliminarily to the cellulosic suspension before the high molecular weight polymer and microparticulate material. This preliminary action prepares the suspension by enhancing retention and formation early in the process, creating a stable base that can withstand the increased mechanical stresses and reduced residence times associated with higher machine speeds, thereby maintaining formation quality at elevated productivity levels.
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 allows for increased machine speed, improved retention, and enhanced formation and strength of paper and board products, decoupling retention from drainage and increasing productivity.
Implementation Method 1
a water soluble substantially linear cationic polymer is applied to the paper making stock
Implementation Method 2
combined with microparticulate materials
Data Source
AI summary
The present invention relates to a process of making paper or paperboard in which a cellulosic thin stock is provided and subjected to one or more shear stages and then drained and a moving screen to form a sheet which is dried, wherein the process employs a retention system which is applied to the thin stock, said retention system comprising as components i) a blend of different cationic polymers and ii) a microparticulate material, in which the blend of cationic polymers comprises, a) a cationic polymer having a charge density of at least 3 mEq per gram and a molar mass of greater than 700,000 Da, b) a cationic polymer having a charge density of below 3 mEq per gram and an intrinsic viscosity of at least 3 dl/g, wherein one of the components of the retention system is dosed into the thin stock after the final shearing stage and the other is dosed into the thin stock before the final shearing stage.