Multi-Stage Emulsion Polymer Coatings Low VOC Scrub Resistance
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Solution Overview
Problem
Existing aqueous coatings face challenges in achieving a balance of good film formation and scrub/stain resistance while using low levels of coalescent, particularly in low VOC coatings, as high scrub resistance often compromises film formation or requires undesirable high coalescing solvents.
Innovation Solution
A multi-stage aqueous emulsion polymer with a first polymer having a calculated Hansch parameter >2.0 and a second polymer with limited acid monomer content, where the second polymer constitutes 50-85% of the total weight, and the Tg difference between the two polymers is from 0°C to less than 20°C, is developed to enhance coating properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a hard polymer is used to achieve high scrub resistance, then scrub resistance is improved, but film formation deteriorates or environmentally undesirable high levels of coalescing solvents are required
Solution Approach 1:
The invention divides the polymer system into two distinct polymers with different functions: a hard polymer providing scrub resistance and a soft polymer ensuring film formation. This segmentation allows each polymer to specialize in one function, resolving the contradiction between scrub resistance and film formation that plagues single-polymer systems.
Solution Approach 2:
The invention creates a composite polymer system by combining two polymers with complementary properties in a multi-stage emulsion polymer. The hard polymer (with higher Tg and Hansch parameter) provides durability and scrub resistance, while the soft polymer (with lower Tg and acid monomer content) ensures proper film formation and adhesion, achieving both functions simultaneously.
2Reliability
If high levels of coalescing solvents are used to improve film formation, then film formation is improved, but VOC levels increase making the coating environmentally undesirable
Solution Approach 1:
The invention extracts the film formation function from coalescing solvents and transfers it to the soft polymer component. The soft polymer, with its lower Tg and specific acid monomer content, provides the necessary flexibility and adhesion for proper film formation without requiring high levels of volatile organic coalescing agents, thus reducing VOC content while maintaining film quality.
Solution Approach 2:
The invention changes the chemical composition parameters of the polymer system by incorporating a soft polymer with specific properties (lower Tg, controlled acid monomer content) that inherently provides film formation capabilities. This parameter change eliminates the need for high VOC coalescing solvents, as the polymer composition itself enables proper film formation at low VOC levels.
3Object-generated harmful factors
If low levels of coalescent are used to reduce VOC, then VOC levels are reduced, but the balance of film formation and scrub resistance deteriorates
Solution Approach 1:
The invention applies local quality by giving different regions of the polymer system different functions: the hard polymer region provides scrub resistance while the soft polymer region provides film formation. This local differentiation of properties within the composite system maintains the balance of coatings properties even at low VOC levels, as each polymer component is optimized for its specific function.
Solution Approach 2:
The composite polymer system combines two polymers with complementary properties, where the hard polymer contributes scrub resistance and the soft polymer contributes film formation capabilities. This composite approach maintains the desirable balance of coatings properties at low VOC levels, eliminating the trade-off that exists in single-polymer or low-coalescent systems.
Data Source
AI summary
A multi-stage aqueous emulsion polymer including a first polymer having a calculated Hansch parameter >2.0, the first polymer including 0.5-5 wt. % copolymerized acid monomer, based on the weight of the first polymer, and a second polymer including from zero to less that half the wt. % of acid monomer in the first polymer, based on the weight of the second polymer, the second polymer being from 50% to 85% of the total weight of the first polymer and the second polymer, wherein the difference between the calculated Tgs of the first and the second polymer is from 0° C. to less than 20° C. is provided. Also provided is an aqueous coating composition including the multi-stage emulsion polymer and a method for providing a coating.