Two-Step Aqueous Polymer Dispersion Process
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Solution Overview
Problem
Current two-step aqueous polymer dispersion processes for coatings face challenges in achieving both low film-forming temperatures and good mechanical properties without using volatile organic solvents, while also dealing with issues of polymer leaching and environmental concerns.
Innovation Solution
A process involving a first polymerization step with an acidic low molecular weight polymer, followed by neutralization and a second polymerization step in the presence of the neutralized polymer, using specific monomers to create a stable aqueous polymer dispersion with improved mechanical properties and reduced leaching, utilizing monomers such as ethyl acrylate, butyl methacrylate, and styrene, and incorporating a base for neutralization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a two-step aqueous emulsion polymerization is used to achieve low film-forming temperatures and good mechanical properties, then the coating performance is improved, but polymer leaching occurs causing loss of mechanical properties and environmental issues
Solution Approach 1:
The patent converts the harmful hydrophilicity of the first polymer (which causes leaching) into a beneficial property by utilizing its hydroplasticization capability. The carboxylic groups in the first polymer enable it to soften under alkaline conditions, facilitating film formation, while the subsequent neutralization and second polymerization steps prevent leaching. This transforms the potential harm (hydrophilicity) into a benefit (hydroplasticization for low Tg film formation).
Solution Approach 2:
The patent changes the chemical state of the first polymer from acidic to neutralized form, and then incorporates it into a crosslinked network structure in the second polymerization step. This parameter change (from soluble/leachable to crosslinked/integrated) prevents polymer leaching while maintaining the low Tg properties needed for film formation.
2Strength
If hydroplasticization is used to achieve higher glass transition temperatures and improved mechanical properties, then coating strength is enhanced, but filming properties deteriorate due to increased Tg
Solution Approach 1:
The patent segments the polymer system into two distinct phases with different Tg values: a first polymer phase with low Tg (from hydroplasticizable polymer) providing filming properties, and a second polymer phase with high Tg (from crosslinked network) providing mechanical strength. This segmentation allows both low Tg and high strength properties to coexist in the same coating system.
Solution Approach 2:
The patent creates a composite polymer system combining a hydroplasticizable first polymer (low Tg component) with a crosslinked second polymer (high Tg component). The first polymer provides flexibility and low-temperature film formation, while the crosslinked second polymer provides mechanical strength, resulting in a composite material with both low Tg and high strength properties.
3Ease of operation
If carboxylic acid functional monomers are used in the first polymerization step to enable neutralization and hydroplasticization, then film formation is improved, but polymer leaching increases causing mechanical property loss
Solution Approach 1:
The patent performs preliminary neutralization of the carboxylic acid groups in the first polymer before the second polymerization step. This preliminary action (neutralization) prepares the polymer for subsequent crosslinking, ensuring that the polymer will be integrated into the network structure and prevented from leaching, while still maintaining the ability to facilitate film formation through hydroplasticization.
Solution Approach 2:
The patent converts the harmful leaching tendency of carboxylic acid functional polymers into a benefit by using the carboxylic groups for neutralization and subsequent crosslinking. The same functional groups that could cause leaching (by making the polymer hydrophilic and soluble) are instead used to create crosslinking sites that prevent leaching while maintaining film formation capability.
4Temperature
If volatile organic film forming agents are used to achieve low film-forming temperatures, then filming properties are improved, but environmental concerns and health issues arise
Solution Approach 1:
The patent changes the mechanism of film formation from solvent-based (volatile organic compounds) to water-based with hydroplasticization. Instead of using VOCs to plasticize and enable film formation at low temperatures, the patent uses water-soluble hydroplasticizable polymers with carboxylic groups that can be neutralized, providing a non-VOC alternative that achieves the same low-temperature film formation effect.
Solution Approach 2:
The patent substitutes the chemical mechanism of VOC-based plasticization with a water-based hydroplasticization mechanism. The carboxylic acid functional groups in the first polymer, when neutralized, provide hydroplasticization capability that replaces the function of volatile organic film forming agents, enabling low-temperature film formation without harmful VOC emissions.
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 aqueous polymer dispersions with low film-forming temperatures, enhanced mechanical properties like blocking resistance and scratch resistance, and reduced leaching, particularly in waterborne coatings, without the use of volatile organic solvents.
Implementation Method 1
a first polymerization step as an aqueous radical emulsion polymerization of a first monomer composition M.a
Implementation Method 2
neutralized by addition of a base before the second polymerization step is performed
Implementation Method 3
a subsequent further polymerization step as an aqueous radical emulsion polymerization of a second monomer composition M.b
Implementation Method 4
two stage aqueous polymer dispersions combining a first polymer phase having a comparatively low glass transition temperature and a second polymer phase having a comparatively high glass transition temperature
Data Source
AI summary
The present invention relates to a process for producing an aqueous polymer dispersion of polymerized ethylenically unsaturated monomers, where the process comprises a first polymerization step as an aqueous radical emulsion polymerization of a first monomer composition M.a and a subsequent further polymerization step as an aqueous radical emulsion polymerization of a second monomer composition M.b, where the monomers M comprise at least one monomer M0 which is selected from compounds of formula (1), wherein X is Cl, Br or OS(O)2R3, Y is H, Cl, Br, OS(O)2R4, C1-C10-alkyl, or C(=O)OR5, R1 is H or C1-C10-alkyl, R2 is H or C1-C10-alkyl, R3 is C1-C10-alkyl, R4 is C1-C10-alkyl, R5 is C1-C20-alkyl. The invention also relates to an aqueous polymer dispersion obtainable by such a process as well as the use of such dispersions.