Multistage Emulsion Polymer Core-Shell Structure for Low VOC Coatings
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Solution Overview
Problem
Existing aqueous coatings struggle to maintain a balance of desirable properties such as scrub resistance and film formation when using low levels of coalescent, particularly in low VOC coatings, as current emulsion polymers do not effectively utilize molecular weight and acid number optimization to enhance these properties.
Innovation Solution
A multi-stage emulsion polymer is developed, comprising a first polymer shell with an acid number of 5 to 100 and a calculated molecular weight of 1000 to 4500, and a second polymer core with an acid number of 0 to half that of the first polymer and a molecular weight greater than 20,000, optimized for use in low VOC coatings to improve scrub resistance and water resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If low levels of coalescent are employed in aqueous coatings, then VOC levels are reduced, but scrub resistance deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the molecular weight (Mn: 1,000-10,000) and acid number (5-100) of the shell polymer, and molecular weight (Mn: 5,000-50,000) and Tg (≥100°C) of the shell polymer. These parameter optimizations enable the coating to achieve good scrub resistance even with reduced coalescent levels, thus resolving the contradiction between low VOC and maintained scrub resistance.
Solution Approach 2:
The patent employs a core-shell composite polymer structure where the core provides structural integrity and the shell provides surface properties. This composite material approach allows the coating to maintain desirable properties including scrub resistance at low VOC levels by combining polymers with specifically optimized characteristics rather than using a single polymer type.
2Loss of energy
If low levels of coalescent are employed in aqueous coatings, then VOC levels are reduced, but film formation deteriorates
Solution Approach 1:
The patent utilizes parameter changes by optimizing the Tg of the shell polymer to be at least 100°C, which influences film formation characteristics. This parameter optimization allows the coating to form good films even with low coalescent levels, resolving the contradiction between low VOC and reliable film formation.
Solution Approach 2:
The patent applies preliminary action by pre-optimizing the polymer structure (core-shell configuration with specific molecular weights and acid numbers) before coating application. This preliminary structural preparation ensures that film formation occurs effectively even when coalescent levels are subsequently reduced for low VOC compliance.
3Strength
If the molecular weight and acid number of the first polymer are optimized, then scrub resistance increases, but water resistance may be compromised
Solution Approach 1:
The patent applies local quality by creating distinct functional zones within the polymer particle: the core with specific properties (Mn: 5,000-50,000, Tg: ≥100°C) provides structural integrity for scrub resistance, while the shell with controlled acid number (5-100) and molecular weight (Mn: 1,000-10,000) provides surface properties including water resistance. This spatial differentiation of properties resolves the contradiction between scrub resistance and water resistance.
Solution Approach 2:
The patent employs composite materials by combining two polymer components with different optimized properties into a core-shell structure. The core polymer provides mechanical strength for scrub resistance while the shell polymer with controlled acid number provides water resistance, allowing both properties to coexist without compromising either.
Data Source
AI summary
A multi-stage aqueous emulsion polymer, an aqueous coating composition including the emulsion polymer, and a method for providing a coating including the emulsion polymer are provided. The multistage emulsion polymer includes from 10% to 30% by wt., based on the wt. of the multistage emulsion polymer, of a first polymer shell having an acid number of from 5 to 100, the first polymer having a calculated Mn of from 1000 to 4500 and a calculated Tg of lower then 100° C.; and from 70% to 90% by wt., based on the wt. of the multistage emulsion polymer, of a second polymer core having an acid number of from 0 to one-half the acid number of the first polymer, the second polymer having a calculated Mn of greater than 20,000.