Cationic Polymer Dispersion for Paper Sizing
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Solution Overview
Problem
There is a continuous need in the paper industry for novel, effective internal and surface sizing agents for paper, board, and cardboard that maintain a permanent cationic charge, as existing cationic surface sizes often lose their charge at higher pH levels, reducing their sizing efficiency.
Innovation Solution
A finely divided, cationic, aqueous polymer dispersion is obtained through emulsion polymerization using a cationic prepolymer prepared with quaternary ammonium group-containing monomers, which is then further polymerized with styrene and alkyl acrylates, ensuring a stable cationic charge even at neutral pH.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional cationic surface sizes are used, then sizing efficiency is achieved at lower pH levels, but the cationic charge is lost at higher pH levels, reducing sizing efficiency
Solution Approach 1:
The invention changes the chemical parameter of the cationic group from pH-sensitive (tertiary ammonium) to pH-insensitive (quaternary ammonium with permanent positive charge). This parameter change ensures the sizing agent maintains its cationic charge and sizing efficiency across a wide pH range (pH 3-10), resolving the contradiction between reliability and compositional stability.
2Shape
If emulsion polymerization is used to produce polymer dispersions, then fine particle size and good dispersion are achieved, but the process requires multiple stages and complex formulation
Solution Approach 1:
The invention applies preliminary action by first preparing a cationic prepolymer dispersion with controlled particle size and charge density through emulsion polymerization. This pre-formed dispersant then facilitates the second polymerization stage, simplifying the overall process by establishing stable nucleation sites and reducing the need for complex emulsifier systems in the final formulation.
Solution Approach 2:
The invention creates a composite polymer structure combining a cationic core (from quaternary ammonium monomers) with a hydrophobic shell (from styrene and alkyl acrylates). This composite architecture provides both the desired fine particle size characteristics and the permanent cationic charge, achieving multiple functions through material composition rather than process complexity.
3Stability of the object's composition
If quaternary ammonium monomers are used to maintain permanent cationic charge, then charge stability at high pH is improved, but the polymerization process becomes more challenging
Solution Approach 1:
The invention applies local quality by concentrating the quaternary ammonium groups primarily in the core region of the polymer particle rather than uniformly distributing them throughout. This localized placement maintains the permanent cationic charge stability needed for high pH performance while confining the polymerization challenges to a specific region, allowing the shell to be formed with more polymerization-friendly monomers.
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 polymer dispersion provides excellent sizing properties for paper products, maintaining efficiency across varying pH levels and fiber types, with good compatibility with starches and immediate development of sizing effects.
Implementation Method 1
finely divided, cationic, aqueous polymer dispersions... used as sizing agents for paper, board and cardboard
Implementation Method 2
obtainable by polymerisation of ethylenically unsaturated monomers in a continuous phase containing an aqueous liquid
Data Source
AI summary
Finely divided, cationic, aqueous polymer dispersion which is obtainable by emulsion polymerisation of ethylenically unsaturated monomers in an aqueous liquid containing a cationic prepolymer as a dispersant, wherein the cationic prepolymer is prepared in the presence of at least one polymerisation initiator by polymerisation of (a) from 15 to 45% by weight of at least one ethylenically unsaturated monomer comprising at least one quaternary ammonium group; (b) from 5 to 80% by weight of at least one optionally substituted styrene; (c) from 0 to 50% by weight of at least one C 1-12 alkyl (meth) acrylate; (d) from 0 to 10% by weight of at least one ethylenically unsaturated monomer comprising an acid group; (e) from 0 to 10% by weight of at least one ethylenically unsaturated monomer comprising an amine group; and (f) from 0 to 20% by weight of at least one non-ionic ethylenically unsaturated monomer differing from (b), (c) and (e), the sum of (a)+(b)+(c)+(d)+(e)+(f) being 100% by weight, in a first emulsion polymerisation in the presence of at least one non-ionic emulsifier, and thereafter, in the aqueous liquid containing the cationic prepolymer a second emulsion polymerisation is carried out, in the presence of at least one polymerisation initiator, of a monomer mixture comprising (i) from 10 to 70% by weight of at least one of an optionally substituted styrene or (meth) acrylonitrile; (ii) from 30 to 90% by weight of at least one CMS alkyl (meth) acrylate; (iii) from 0 to 30% by weight of at least one vinyl ester of linear or branched C1-30 carboxylic acids; and (iv) from 0 to 30% by weight of at least one non-ionic ethylenically unsaturated monomer differing from (i), (ii) and (iii), the sum of (i)+(ii)+(iii)+(iv) being 100% by weight, and the first emulsion polymerisation and/or the second emulsion polymerisation is optionally carried out in the presence of from 0 to 10% by weight of at least one polymerisation regulator. The polymer dispersions according to the present invention are suitable for use as sizing agents for paper, board and card board.