Cationic Calcium Carbonate Dispersion Stability
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Solution Overview
Problem
Existing methods for producing aqueous dispersions of pigments for paper and cardboard applications often require separate retention agents and result in unstable mixtures, especially when transporting or storing high dry matter content dispersions, leading to issues with pigment precipitation and ink-jet printability.
Innovation Solution
A method using a cationic biopolymer, such as modified starch, to disperse inorganic pigments like cationic calcium carbonate, creating a stable aqueous dispersion with 30-75% solids content, which can be used as a filler, surface-sizer, or coating without additional retention agents, maintaining stability for several weeks and improving ink-jet printability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If PCC slurry is concentrated to high solid matter content for transportation, then transportation cost is reduced, but the slurry becomes unstable and requires separate retention agents
Solution Approach 1:
The invention changes the surface charge parameter of the PCC particles from anionic to cationic through chemical modification. This parameter change allows the slurry to remain stable at high solid matter content (50-70%) without requiring separate retention agents, resolving the contradiction between transportation efficiency and slurry stability
Solution Approach 2:
The invention creates a composite system where cationic PCC particles are combined with anionic cellulose fibres in the pulp slush. This composite structure provides inherent stability through electrostatic attraction between the cationic pigment particles and anionic fibres, eliminating the need for additional retention agents while maintaining high solids content
2Quantity of substance
If anionic dispersing agent is used to disperse PCC, then high dry matter content dispersion is achieved, but separate cationic retention agent is required
Solution Approach 1:
Instead of using the conventional anionic dispersing agent approach that requires subsequent cationic retention agents, the invention inverts the charge sequence by first creating cationic PCC particles. This inversion allows the pigment to inherently interact with anionic cellulose fibres, eliminating the need for separate retention agents while maintaining high dry matter content
Solution Approach 2:
The invention extracts the retention function from separate retention agents and integrates it into the pigment particle itself through cationic modification. The cationic PCC particles inherently provide retention to anionic cellulose fibres, eliminating the need for additional retention chemicals and simplifying the system
3Reliability
If cationic polymer is mixed into PCC slurry before adding to pulp slurry, then retention is improved, but the resulting mixture is unstable
Solution Approach 1:
The invention performs preliminary action by pre-modifying the PCC particles to have cationic surface charge before they are added to the pulp slurry. This preliminary charge modification ensures that when the cationic PCC particles encounter anionic cellulose fibres in the pulp, immediate and stable retention occurs without requiring additional cationic polymers, thereby maintaining mixture stability
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 cationic dispersion remains stable for extended periods, eliminating the need for separate retention agents, enhancing ink-jet printability, and providing excellent optical properties and rapid drying of printing ink, while simplifying logistics by maintaining cationic properties and preventing pigment precipitation.
Implementation Method 1
The resulting aqueous dispersion is stable, because the surface of the pigment particles is cationic, whereas the cellulose fibres in the pulp are anionic
Implementation Method 2
the PCC particle has a cationic surface charge, in which case it adheres well to the anionic fibre network
Data Source
AI summary
A method of producing an aqueous dispersion of a pigment, and the aqueous dispersion of the pigment and the uses of the aqueous dispersion of the pigment. In the present method, an inorganic pigment is dispersed in water, in the presence of a dispersing agent. According to the present invention, the inorganic pigment comprises cationic calcium carbonate, especially precipitated calcium carbonate, which is dispersed using a cationic biopolymer, such as starch, in order to prepare an aqueous dispersion, the solids content of which is approximately 30-75% by weight. The dispersion generated can be used, among others, as pigment or filler for ink-jet paper.