Core-shell polymeric particles for aqueous coating opacity
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Solution Overview
Problem
Aqueous coating compositions with low or no volatile organic compounds (VOC) content face challenges in achieving improved film integrity and opacity, as existing film-forming binder particles with voids often result in poor opacity due to void collapse during film formation.
Innovation Solution
The development of an aqueous dispersion of polymeric particles comprising a first polymer with voids, encapsulated by a second polymer with a specific glass transition temperature range, which provides superior opacity and film integrity through a multi-stage emulsion polymerization process, including the use of mono-ethylenically unsaturated monomers and swelling agents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If particles with voids are used to reduce mass and improve film integrity, then film integrity (scrub resistance) is improved, but opacity deteriorates because voids collapse during film formation
Solution Approach 1:
The patent applies nested doll by placing a core polymer inside a shell polymer, creating a core-shell structure where the core contains voids for film integrity and the shell encapsulates it to maintain void structure and provide opacity through light scattering. The shell acts as a protective layer that prevents void collapse while maintaining the beneficial effects of the void-containing core.
Solution Approach 2:
The patent uses composite materials by combining two different polymers with complementary properties: a core polymer containing voids that provides film integrity and scrub resistance, and a shell polymer with appropriate Tg that encapsulates the core, maintains void structure, and contributes to opacity. This composite structure resolves the contradiction between film integrity and opacity.
2Ease of operation
If a second shell polymer with low Tg is used to encapsulate the first shell, then particle flexibility and film formation improve, but manufacturing complexity increases due to multi-stage polymerization
Solution Approach 1:
The patent applies segmentation by dividing the polymerization process into distinct stages: first forming the core polymer, then forming the first shell polymer, and finally forming the second shell polymer. Each stage uses specific monomers and conditions optimized for that layer, allowing precise control over particle structure and properties while managing manufacturing complexity through systematic process division.
Solution Approach 2:
The patent uses preliminary action by pre-forming the core polymer and first shell polymer before adding the second shell polymer. This sequential approach allows each layer to be optimized independently, with the core and first shell providing a stable foundation before the final encapsulating shell is formed, thereby improving film formation while managing manufacturing complexity.
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 enhanced opacity and consistent hiding power in coatings while maintaining low VOC levels, improving film integrity and reducing material and energy usage by utilizing particles with strategically designed voids and polymer structures.
Implementation Method 1
Particles having one or more voids provide such coating compositions, while concurrently reducing the mass of the particles, and thereby reducing the materials and energy which would have been expended in providing that mass. Particles, including one or more voids may also contribute to the opacity of dry coating films.
Implementation Method 2
The particles comprise from 10 to 80% by weight, based on total polymeric weight of the particle when dry, of a first polymer, and at least one second polymer comprising, as polymerized units, at least one ethylenically unsaturated monomer.
Implementation Method 3
adding a swelling agent to the aqueous dispersion prior to, during, or after the polymerization of the mono-ethylenically unsaturated monomers of the second shell stage polymer.
Data Source
AI summary
An aqueous dispersion of polymeric particles and process for forming thereof is provided. The particles comprise a first polymer comprising, when dry, at least one void; and, substantially encapsulating the first polymer, at least one second polymer comprising, as polymerized units, at least one ethylenically unsaturated monomer.