Aqueous Polyurethane-Silicone Coatings for Breathable Leather Fastness
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Solution Overview
Problem
Existing aqueous dispersions for coating substrates, particularly using the reverse roll coating process, face challenges in achieving optimal fastness and handle properties, such as rub fastness and breathability, while maintaining the haptic qualities of leather substrates.
Innovation Solution
Aqueous dispersions comprising a combination of thermoplastic polyurethane and silicone compounds with specific reactive groups, along with polydimethylsiloxane, are formulated to enhance the coating process, improving the fastness and handle properties of substrates like leather through a multi-layer coating process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicone dispersions with particles of 3 μm to 13 μm are used for coating leather, then the coating process is feasible, but the fastness and handle properties are insufficient
Solution Approach 1:
The patent changes the particle size parameter of silicone dispersion from the conventional 3-13 μm range to a finer 0.1-10 μm range, with particular emphasis on particles below 1 μm. This parameter change enables both improved fastness (through better penetration and bonding) and maintained handle properties (through uniform distribution without excessive roughness).
Solution Approach 2:
The patent creates a composite coating system by combining polyurethane dispersion (providing base coating and flexibility) with silicone dispersion (providing fastness and water repellency). This composite approach allows the synergistic combination of different material properties to simultaneously achieve good fastness and handle characteristics.
2Reliability
If a top layer is applied to leather to improve fastness, then rub fastness increases, but breathability and haptic properties may deteriorate
Solution Approach 1:
The patent utilizes the porous structure of the leather substrate and creates a coating layer with controlled porosity that allows breathability while providing protective functions. The fine particle size of the silicone dispersion (0.1-10 μm) enables it to penetrate and bond within the porous structure without completely blocking the pores, thus maintaining breathability while improving rub fastness.
Solution Approach 2:
The patent applies different functional properties to different aspects of the coating: the polyurethane base layer provides flexibility and breathability, while the silicone top layer provides rub fastness and water repellency. This local differentiation of material properties allows simultaneous achievement of seemingly conflicting requirements.
3Ease of manufacture
If conventional polyurethane dispersion is used as base coating, then the coating process is simple, but the overall performance and usability are limited
Solution Approach 1:
The patent enhances the polyurethane dispersion by incorporating it with silicone dispersion, creating a multi-functional coating system. The polyurethane provides base coating, flexibility, and adhesion, while the silicone adds fastness, water repellency, and durability. This multi-functional combination maintains the simplicity of the coating process while significantly expanding the usability and performance range.
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 proposed solution results in substrates with improved rub fastness, breathability, and haptic properties, maintaining the quality of the substrate over time and enhancing their usability in applications like furniture and automotive parts.
Implementation Method 1
coating of leather with the aid of a reverse roll coating process
Implementation Method 2
used, for example, for imparting water repellency to sheet-like substrates
Data Source
AI summary
Aqueous dispersions comprising(A) at least one polyurethane,(B) at least one compound of the general formula I a or I bin which R1, R2 and R3 may be identical or different and are selected from A1-NCO and A1-NH—CO—X, in whichA1 is a spacer having 2 to 20 carbon atoms andX is selected from O(AO)xR4,AO is C2-C4-alkylene oxide,x is an integer in the range from 1 to 50 andR4 is selected from hydrogen and C1-C30-alkyl,(C) and at least one silicone compound having reactive groups.