Multiphase Emulsion Polymer Latex Binder for Low VOC Coatings
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Solution Overview
Problem
Conventional aqueous coating compositions face challenges in achieving excellent block resistance, freeze-thaw stability, and low temperature coalescence while minimizing volatile organic compounds (VOCs) and coalescing solvents, which are harmful to the environment.
Innovation Solution
A multiphase emulsion polymer latex binder is developed, comprising a hard polymer phase with a glass transition temperature 50°C higher than a soft polymer phase, achieved through multi-stage emulsion polymerization, allowing for film formation at low temperatures without the need for coalescing solvents and VOCs, and formulated into a zero or low VOC latex coating composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If coalescing solvents are used to lower glass transition temperature for film formation, then low temperature coalescence is improved, but volatile organic compound content increases
Solution Approach 1:
The invention extracts and eliminates coalescing solvents from the coating composition by using a multi-stage emulsion polymerization process that creates a multiphase polymer system. The soft phase polymer particles (with Tg of -50°C to 0°C) replace the function of coalescing solvents in enabling low-temperature film formation, while the hard phase polymer particles (with Tg of 50°C to 100°C) provide the protective properties and block resistance.
Solution Approach 2:
The invention changes the fundamental parameter of how glass transition temperature is controlled - instead of using external coalescing solvents to temporarily lower Tg, the system incorporates polymer phases with inherently different Tg values. The soft phase polymer particles provide low Tg for film formation at low temperatures, while the hard phase polymer particles provide high Tg for protective properties, eliminating the need for VOC-containing solvents.
2Reliability
If conventional freeze/thaw additives are used to improve freeze/thaw stability, then stability is improved, but volatile organic compound content increases
Solution Approach 1:
The invention extracts and eliminates conventional freeze/thaw additives (such as alcohols, glycols, and other volatile compounds) from the coating composition. Instead, the multiphase polymer structure itself provides freeze/thaw stability through the synergistic interaction between soft phase and hard phase polymer particles, which maintain film integrity and prevent phase separation during freezing and thawing cycles.
Solution Approach 2:
The coating composition achieves freeze/thaw stability through its own multiphase polymer structure without requiring external volatile additives. The soft phase polymer particles provide flexibility and the hard phase polymer particles provide structural integrity, enabling the system to self-regulate during temperature fluctuations and maintain stability without VOC-containing additives.
3Temperature
If low glass transition temperature is used for film formation, then low temperature coalescence is improved, but block resistance and hardness deteriorate
Solution Approach 1:
The invention segments the polymer system into two distinct phases with different glass transition temperatures and functions. The soft phase polymer particles (Tg: -50°C to 0°C) are responsible for low-temperature film formation and coalescence, while the hard phase polymer particles (Tg: 50°C to 100°C) are responsible for providing hardness, block resistance, and protective properties. This segmentation allows each phase to independently fulfill its specific function without compromising the other.
Solution Approach 2:
The invention applies local quality by assigning different Tg characteristics to different polymer phases based on their specific functions. The soft phase polymer particles have locally optimized low Tg for film formation at low temperatures, while the hard phase polymer particles have locally optimized high Tg for providing protective properties. This local differentiation of material properties enables simultaneous achievement of low temperature coalescence and excellent block resistance.
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 solution enables aqueous coating compositions to maintain excellent block resistance, freeze-thaw stability, and low temperature coalescence properties while significantly reducing VOC content, thus being environmentally friendly and effective.
Implementation Method 1
The binder is a polymer, in the form of latex particles, that forms a polymer film after drying and determines the film formation mechanism depending on its chemistry. Water is present as a consequence of the emulsion polymerization process used in preparing the binder
Implementation Method 2
The multiphase polymer of the polymer latex binder of the present invention includes at least one soft polymer phase and at least one hard polymer phase
Implementation Method 3
the glass transition temperature, Tg, must be very low (i.e., minimum film forming temperature). The at least one hard polymer phase comprises a hard phase polymer having a glass transition temperature in a range from 10°C to 100°C
Data Source
AI summary
A multiphase emulsion polymer for aqueous coating compositions containing little or no organic solvent includes at least one soft phase and at least one hard phase prepared by a multi-stage emulsion polymerization. The hard phase contains a hard phase polymer having a glass transition temperature in a range from I0C to 100C which is more than 50C higher than that of the soft phase polymer. The hard phase is formed as a first stage polymer and the one soft phase is subsequently polymerized in the presence of the first stage polymer. The hard phase polymer includes at least one carboxylic acid monomer and at least one ethylenically unstaturated monomer. A method of making a multiphase emulsion polymer for aqueous coating compositions containing zero or low levels of organic solvent is disclosed. Such aqueous coating compositions may simultaneously have excellent block resistance, freeze thaw stability and low temperature coalescence characteristics.