Waterborne Polyurethane-Acrylic Waterproof Coating for Low-VOC Flexibility
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Solution Overview
Problem
Existing waterproof coatings lack simultaneous performance in low heat shrinkage, good low-temperature flexibility, good acid resistance, and mechanical properties, while also posing environmental pollution risks due to volatile organic compounds and poor weather resistance.
Innovation Solution
A polyurethane-acrylic composition comprising aqueous acrylic and polyurethane dispersions without a coalescing agent, achieving low VOC and improved mechanical properties, flexibility, and weather resistance through the use of self-emulsified polyurethane dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If coalescing agent is added to acrylic emulsion to improve low-temperature flexibility, then flexibility at low temperature is improved, but VOC increases and environmental pollution occurs
Solution Approach 1:
The patent changes the chemical composition parameters by replacing traditional coalescing agents with a specifically designed polyurethane dispersion containing hydrophilic groups and carboxyl groups. This parameter change achieves film formation at low temperatures without relying on high-boiling-point coalescing agents, thereby reducing VOC emissions and environmental pollution while maintaining low-temperature flexibility.
Solution Approach 2:
The patent creates a composite waterproof coating system by combining acrylic emulsion with polyurethane dispersion. This composite material approach allows the polyurethane components to provide both the film-forming capability traditionally achieved by coalescing agents and the additional benefit of reduced VOC emissions, resolving the contradiction between low-temperature flexibility and environmental protection.
2Temperature
If coalescing agent is used to achieve low-temperature flexibility, then flexibility is improved, but coating film shrinks and becomes brittle over time
Solution Approach 1:
The polyurethane dispersion contains built-in hydrophilic groups and carboxyl groups that enable it to self-regulate the film formation process without external coalescing agents. The carboxyl groups facilitate hydrogen bonding and cross-linking that stabilize the coating film structure over time, preventing shrinkage and brittleness while maintaining low-temperature flexibility through the inherent properties of the polyurethane molecules.
Solution Approach 2:
The patent modifies the chemical parameters of the coating system by introducing polyurethane dispersion with specific functional groups (hydrophilic groups and carboxyl groups). These parameter changes create a more stable molecular network in the coating film that resists shrinkage and maintains flexibility over time, eliminating the degradation issues associated with traditional coalescing agents.
3Strength
If traditional one-component polyurethane waterproof coating is used, then elasticity and tensile strength are improved, but weather resistance deteriorates
Solution Approach 1:
The patent merges the advantages of polyurethane (elasticity and tensile strength) with acrylic (weather resistance) by combining polyurethane dispersion with acrylic emulsion. This merging creates a hybrid coating system where the acrylic component provides UV stability and weather resistance while the polyurethane component contributes elasticity and tensile strength, resolving the contradiction between mechanical properties and weather resistance.
Solution Approach 2:
The patent creates a composite coating material by combining polyurethane dispersion and acrylic emulsion in specific proportions. This composite material approach allows the acrylic portion to protect against UV degradation and weathering while the polyurethane portion provides the desired mechanical properties, achieving both high strength and excellent weather resistance simultaneously.
4Strength
If acrylic emulsion with higher glass transition temperature is used to improve mechanical properties, then tensile strength is improved, but low-temperature flexibility deteriorates
Solution Approach 1:
The patent changes the glass transition temperature parameter of the coating system by introducing polyurethane dispersion with low Tg characteristics. This parameter change allows the overall coating to achieve high tensile strength from the acrylic component while the polyurethane component maintains low-temperature flexibility by lowering the effective Tg of the film, resolving the contradiction between strength and low-temperature performance.
Data Source
AI summary
A polyurethane-acrylic composition, and particularly, a polyurethane-acrylic composition that is environment friendly and exhibits low heat shrinkage, which is suitable for use as a waterproof coating for a construction structure, especially for a roof. The polyurethane-acrylic composition includes:—at least one aqueous acrylic polymer dispersion, preferably in an amount of 17-56 wt %, preferably 20-45 wt %, based on the total weight of the composition; and—at least one aqueous polyurethane dispersion, preferably in an amount of 4-30 wt %, preferably 4-10 wt %, based on the total weight of the composition; wherein the composition is free of a coalescing agent.