Cationic Polymer Filler Retention in Wood Free Pulp
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Solution Overview
Problem
Producers of wood free paper face challenges in retaining additional filler content, which can lead to poor sheet formation and reduced sheet bulk and stiffness, especially when incorporating mechanical fibers like bleached chemical thermo mechanical pulp (BCTMP).
Innovation Solution
Adding a cationic polymer to the mechanical pulp before mixing with other pulps to form a medium consistency stock, along with suitable filler incorporation, enhances filler retention and distribution within the paper sheet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If additional filler is added to increase opacity and smoothness, then paper quality improves, but sheet formation deteriorates and filler retention decreases
Solution Approach 1:
The patent applies preliminary action by adding the cationic polymer to the mechanical pulp stream before it enters the headbox, allowing the polymer to pre-coat the mechanical fibers and create retention sites for filler particles before sheet formation occurs. This advance preparation ensures filler retention without compromising sheet formation.
Solution Approach 2:
The cationic polymer acts as an intermediary between the mechanical fibers and filler particles. The polymer's positive charge attracts negatively charged filler particles to the mechanical fiber network, facilitating filler retention while maintaining proper sheet formation on the wire mesh.
2Ease of manufacture
If additional filler is added to reduce cost, then manufacturing cost decreases, but filler retention and sheet bulk deteriorate
Solution Approach 1:
The cationic polymer serves as a mediator that enables high filler retention even at increased filler loadings. By coating mechanical fibers with the polymer before filler addition, the system can accommodate more filler without loss, allowing cost reduction through higher filler content while maintaining retention.
Solution Approach 2:
The patent changes the chemical parameter of the pulp slurry by introducing a cationic polymer with positive charge. This parameter change enables the system to retain higher amounts of filler material that would otherwise be lost, allowing increased filler content for cost reduction without compromising retention.
3Strength
If mechanical pulp is incorporated to improve stiffness and bulk, then physical characteristics improve, but filler retention becomes more difficult
Solution Approach 1:
The cationic polymer acts as an intermediary that bridges the mechanical fibers and filler particles. By pre-coating the mechanical fibers with the polymer, the system creates effective retention sites that enable filler particles to adhere to the mechanical fiber network, solving the retention difficulty associated with mechanical pulp incorporation.
Solution Approach 2:
The patent applies preliminary action by introducing the cationic polymer to the mechanical pulp stream in advance, before the pulp reaches the headbox and sheet formation zone. This advance coating of mechanical fibers with polymer ensures that when filler is added later, it will be effectively retained by the pre-prepared mechanical fiber-polymer complex.
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 improves filler retention in paper or board manufacturing, maintaining sheet bulk and stiffness while ensuring effective filler distribution, as demonstrated by increased first pass ash retention (FPAR) measurements.
Implementation Method 1
Retention aids are (usually) polymeric additives which flocculate the small filler particles onto the papermaking fibers, so that the filler material is retained in the paper sheet.
Data Source
AI summary
The present invention relates to a process of manufacturing paper or paperboard which comprises providing (a) a mechanical pulp and (b) a wood free pulp, combining (a) the mechanical pulp and (b) the wood free pulp to form a mixed pulp comprising no more than 20 % by total dry weight of fiber of the mechanical pulp, flowing the mixed pulp as a medium consistency stock and combining the medium consistency stock with dilution water to form a low consistency stock, draining the low consistency stock through a wire or mesh to form a sheet of paper which is dried, in which additional filler and a cationic polymer are added to the mechanical pulp.