Core-Shell Latex with Copolymerized Polyether for Low VOC Coatings
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Solution Overview
Problem
Low VOC aqueous architectural coatings face challenges with freeze-thaw stability and open time due to reduced organic solvents, leading to compromised properties like scrub resistance and stain removal, as existing additives migrate and have limited efficacy.
Innovation Solution
Aqueous latex composition with a core-shell structure, where a water-retaining monomer is copolymerized into the shell of the latex, providing improved binding and stability, and a two-stage sequential polymerization process is used to form distinct phases with tailored glass transition temperatures and particle sizes for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If freeze-thaw and open time additives (alkyl or aralkyl polyethers) are introduced into low VOC coating formulations to improve freeze-thaw stability and open time, then freeze-thaw stability and open time are improved, but the additives migrate because they are not bound to the film-forming binder, and other problems such as water sensitivity and scrub resistance occur
Solution Approach 1:
The patent combines the film-forming binder and polyether monomer into a single integrated polymer structure through copolymerization. The polyether monomer is incorporated into the binder molecule itself, eliminating the need for separate additive molecules that would migrate. This merging of functions resolves the contradiction by ensuring the freeze-thaw active species remain bound to the film-forming binder while still providing the desired stability improvement.
Solution Approach 2:
The patent creates a composite polymer structure where the film-forming binder and polyether monomer are chemically combined in a single polymer chain. This composite approach ensures that the freeze-thaw active polyether groups are permanently bound to the binder, preventing migration while maintaining the functional benefits of both components.
2Stability of the object's composition
If polyether monomers are copolymerized with binder monomers to chemically bind polyethers to the film forming resin and prevent migration, then additive migration is prevented, but the resulting paint films have insufficient ability to resist mechanical scrubbing and stains
Solution Approach 1:
The patent modifies the chemical structure parameters of the polymer by incorporating specific monomer units with different functional groups. The binder monomer contains both film-forming functional groups and hydrophobic groups that enhance scrub resistance. This parameter change in the polymer structure allows simultaneous achievement of binding stability and mechanical strength without requiring separate additives.
Solution Approach 2:
The patent introduces hydrophobic groups at specific locations within the polymer chain (in the binder monomer structure) to provide localized scrub resistance. This local quality enhancement is integrated into the polymer structure itself, allowing different regions of the polymer to serve different functions: binding stability from the polyether-containing segments and scrub resistance from the hydrophobic segments.
3Loss of substance
If organic solvents are significantly reduced in low VOC aqueous coatings to meet environmental requirements, then VOC content is reduced, but freeze-thaw stability and open time are compromised
Solution Approach 1:
The patent replaces the traditional role of organic solvents (which provided freeze-thaw stability through physical solvation) with a chemical mechanism where polyether monomers are copolymerized into the binder. This substitution eliminates the need for high VOC content while achieving the same functional outcome through chemical bonding rather than physical dissolution.
Solution Approach 2:
The patent changes the fundamental parameter of how freeze-thaw stability is achieved: from physical solvation by organic solvents to chemical incorporation of polyether groups into the polymer binder. This parameter change allows the system to achieve freeze-thaw stability in a low-VOC aqueous formulation by making the polyether groups an integral part of the binder structure.
4Duration of action of moving object
If existing freeze-thaw and open time additives are used in low VOC formulations, then open time is extended, but the additives have limited efficacy and impose other problems such as water sensitivity
Solution Approach 1:
The patent merges the open time extension function with the film-forming binder structure through copolymerization. The polyether monomer incorporated into the binder provides both film formation and open time extension functions simultaneously, eliminating the need for separate additive molecules that would have limited efficacy and caused water sensitivity problems.
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 achieves improved freeze-thaw stability, longer open time, better scrub resistance, and effective stain removal, maintaining desirable coating properties without the need for additional additives.
Implementation Method 1
a water-retaining monomer is copolymerized to the shell
Implementation Method 2
The Tg of the core ranges from about 0° C. to about 12° C., and the Tg of the shell ranges from about 13° C. to about 40° C.
Data Source
AI summary
Disclosed herein is an aqueous latex composition comprising a substantially acrylic core-shell latex, wherein a water-retaining monomer is copolymerized to the shell. The Tg of the core ranges from about 0° C. to about 12° C., and the Tg of the shell ranges from about 13° C. to about 40° C. The mean volume average particle size of the latex ranges from about 125 nm to about 200 nm. The core-shell latex comprises at least one acrylic monomer having a solubility that ranges about 10 g/L to about 30 g/L at 30° C., and this at least one acrylic monomer is present in the shell polymer in an amount greater than about 50 wt. % of all monomers in the shell. Preferably, the at least one acrylic monomer is methyl methacrylate.