Waterborne Binder Two-Stage Polymerization Emulsifier Reduction
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Solution Overview
Problem
Existing polymer dispersion systems for coatings require high amounts of emulsifiers, leading to high foam-forming propensity and stability issues, while also failing to achieve fast drying and hardness development, especially in water-based two-component coatings systems.
Innovation Solution
A two-stage radically initiated aqueous emulsion polymerization process is employed, using specific monomer compositions and chain transfer agents to produce polymers with controlled molecular weights and glass transition temperatures, reducing the need for dispersing assistants and enhancing drying speed and hardness development.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional emulsion polymerization is used with high amounts of emulsifier to achieve stable polymer dispersions, then dispersion stability is improved, but foam-forming propensity increases and emulsifier consumption increases
Solution Approach 1:
The patent extracts the emulsifier from the system by using polymer particles with carboxyl groups that are neutralized to form carboxylate salts, which then serve as stabilizers for subsequent polymerization stages. This eliminates the need for external emulsifiers while maintaining dispersion stability and reducing foam formation.
Solution Approach 2:
The polymer particles from the first polymerization stage serve their own dual function: they act as both the polymer product and as stabilizers for the second polymerization stage through their neutralized carboxyl groups. This self-stabilizing mechanism eliminates the need for separate emulsifier additives.
2Productivity
If in-situ seed polymerization is used to achieve fast property development, then drying speed is improved, but emulsifier requirement increases significantly
Solution Approach 1:
The patent removes the emulsifier dependency from the in-situ seed polymerization process by using neutralized carboxyl groups on polymer particles as alternative stabilizers, enabling fast property development without excessive emulsifier consumption.
Solution Approach 2:
The patent changes the chemical parameter of the polymer particles by neutralizing carboxyl groups to form carboxylate salts, which fundamentally alters their stabilizing properties and enables them to function without external emulsifiers while maintaining fast drying characteristics.
3Quantity of substance
If carboxyl-rich monomer composition is used in first polymerization stage to create invert core-shell polymers, then emulsifier usage is reduced, but gloss characteristics deteriorate and haze increases
Solution Approach 1:
The patent optimizes the carboxyl group content parameter to a specific range (0.5-15 wt%) rather than using high carboxyl-rich compositions, and neutralizes these groups to create carboxylate salts that provide stabilization without the adverse optical effects of excessive carboxyl content.
Solution Approach 2:
The patent creates a composite structure where polymer particles with controlled carboxyl content are combined with neutralizing agents to form carboxylate salts, achieving a balance between stabilization capability and optical properties that neither component alone could provide.
4Strength
If high molecular weight polymer is produced to improve coating performance, then film strength is improved, but drying speed decreases
Solution Approach 1:
The patent segments the polymerization process into two stages: first producing lower molecular weight polymer particles (Mw 5,000-50,000) that dry quickly, then building up final coating performance through the second stage polymerization, achieving both fast drying and strong film formation.
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 results in polymer dispersions that achieve faster drying and hardness development with improved gloss characteristics and reduced haze, using minimal dispersing agents, suitable for a wide range of drying tests.
Implementation Method 1
radically initiated aqueous emulsion polymerization
Implementation Method 2
in the presence of at least one radical initiator and at least one chain transfer agent
Implementation Method 3
aqueous emulsion polymerization
Data Source
AI summary
The present invention relates process for preparing an aqueous polymer dispersion by radically initiated aqueous emulsion polymerization, which comprises polymerizing, in an aqueous polymerization medium a) in a first polymerization stage ≥ 0.5 and ≤ 15 wt% of at least one α,β-monoethylenically unsaturated C3 to C6 monocarboxylic or dicarboxylic acid (monomers A1), ≥ 5 and ≤ 40 wt% of at least one monoethylenically unsaturated compound having at least one hydroxyl group (monomers B1), ≥ 0 - ≤ 40 wt% of carboxyl-free (meth)acrylic esters with a cycloaliphatic structure (monomers C1), ≥ 15 and ≤ 94.5 wt% of at least one ethylenically unsaturated compound which is different from the monomers A1, B1 and C1 (monomers D1), the amounts of the monomers A1 to D1 adding up to 100 wt%, in the presence of at least one radical initiator and at least one chain transfer agent, and also, optionally, in the presence of a dispersing assistant, with the provisos that • the amount of chain transfer agent is selected such that the polymer 1 obtained from the first polymerization stage has a weight-average molecular weight in the range of ≥ 5000 and ≤ 40000 g/mol, • the nature and amounts of the monomers A1 to D1 are selected such that the resulting polymer 1 has a glass transition temperature Tg1 as measured to DIN EN ISO 11357-2 (2013-09) ≥ 15°C, and thereafter polymerizing, in the presence of the polymer 1 b) in a second polymerization stage ≥ 0 and ≤ 1.0 wt% of at least one α,β-monoethylenically unsaturated C3 to C6 monocarboxylic or dicarboxylic acid (monomers A2), ≥ 0.1 and ≤ 40 wt% of at least one monoethylenically unsaturated compound having at least one hydroxyl group (monomers B2), ≥ 0 - ≤ 40 wt% of carboxyl-free (meth)acrylic esters with a cycloaliphatic structure (monomers C2) ≥ 30 and ≤ 99.9 wt% of at least one ethylenically unsaturated compound which is different from the monomers A2, B2 and C2 (monomers D2), the amounts of the monomers A2 to D2 adding up to 100 wt%, in the presence of at least one radical initiator and at least one chain transfer agent, and also, optionally, in the presence of a dispersing assistant, with the provisos that • the weight ratio of the sum of the total amounts of monomers A1 to D1 (total monomer amount 1) to the sum of the total amounts of monomers A2 to D2 (total monomer amount 2) is in the range 25:75 to 50:50, • the amount of chain transfer agent in the second polymerization stage is selected such that the overall polymer obtained after the second polymerization stage has a weight-average molecular weight ≥ 5000 and ≤ 75000 /mol, and • the amount of the dispersing assistant is ≤ 3.0 wt%, based on the sum of total monomer amount 1 and total monomer amount 2 (total monomer amount), • that the sum of the total amounts of monomers C1 and C2 is 7 to 40 wt% based on the sum of total monomer amount 1 and total monomer amount 2; the aqueous polymer dispersion itself, its use and coating compositions comprising the aqueous polymer dispersion.