Aqueous Microsphere–Polyurethane Coating for Crack-Resistant Leather
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Solution Overview
Problem
Existing leather coatings, particularly those using inorganic matting agents, suffer from film integrity issues leading to cracking and reduced flexibility under stress, while polymeric microspheres do not provide adequate protection.
Innovation Solution
A composition comprising an aqueous dispersion of film-forming polyurethane particles with a z-average size of 50 nm to 500 nm and a Tg of less than 10°C, combined with non-film-forming single phase crosslinked polymeric microspheres with a median size of 2 μm to 30 μm and a Tg of not greater than 10°C, applied in a multilayered structure to provide flexibility and protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If inorganic matting agents (silica, calcium carbonate) are used to provide a dull finish, then matting effect is improved, but film integrity deteriorates leading to cracking and reduced flexibility
Solution Approach 1:
The patent changes the material parameters from inorganic to organic polymeric microspheres, and further optimizes by controlling the glass transition temperature (Tg) to be at or below the substrate's Tg. This parameter change allows the microspheres to remain flexible and prevent cracking while still providing the desired matting effect.
Solution Approach 2:
The patent uses composite polymeric microspheres made from specific polymer compositions (e.g., acrylics, styrenes, or their copolymers) that combine matting properties with flexibility. These composite materials integrate both the matting function and the flexibility requirement into a single material system.
2Reliability
If multistaged polymeric microspheres are used instead of inorganic agents, then film integrity is improved, but flexibility under stress deteriorates
Solution Approach 1:
The critical parameter change is setting the microsphere Tg at or below the substrate Tg (typically ≤25°C, preferably ≤10°C). This ensures the microspheres remain soft and flexible at service temperatures, allowing the coating to flex with the leather substrate without cracking, while still providing robust film integrity.
3Strength
If the coating provides robust protection and matte finish, then durability is improved, but flexibility and resistance to cracking under stress deteriorates
Solution Approach 1:
By controlling the Tg of the polymeric microspheres to be at or below the substrate's glass transition temperature, the coating maintains softness and flexibility at service conditions while providing robust protection. This parameter optimization allows the coating to flex with the substrate without cracking.
Solution Approach 2:
The use of specifically designed polymeric microsphere composites provides both the protective function and flexibility. These composite materials integrate durability with adaptability to substrate movement.
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 composition achieves a flexible matte finish on leather that retains integrity and flexibility under stress, demonstrating superior resistance to cracking in accelerated testing.
Implementation Method 1
film-forming polymer particles comprising polyurethane polymer particles
Implementation Method 2
provides a flexible matte finish to a flexible substrate such as leather
Data Source
AI summary
The present invention relates to composition comprising an aqueous dispersion of single phase crosslinked low Tg microspheres and film-forming polyurethane particles. The composition of the present invention is useful as a basecoat layer for a multilayered leather article.