NCO-Terminated Polysiloxane Prepolymer for Coating Hydrophobicity
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Solution Overview
Problem
Existing polysiloxane-based coatings face issues with surface hydrophobicity durability and compatibility within the paint matrix, leading to potential loss of hydrophobic properties upon water contact or scratching.
Innovation Solution
Development of an NCO-terminated polysiloxane prepolymer with a specific molecular structure, produced through reacting polysiloxane polyols with diisocyanates and polyisocyanates, which enhances surface hydrophobicity and matrix compatibility, ensuring the polysiloxane chains are well-integrated within the coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polysiloxane units are incorporated into coating materials to increase surface hydrophobicity, then the hydrophobic properties of the surface are improved, but the compatibility within the paint matrix deteriorates and siloxane chains accumulate on the surface
Solution Approach 1:
The patent modifies the chemical structure of polysiloxane by introducing NCO-terminated groups and controlling the distribution of siloxane units within the polymer chain. This parameter change in molecular architecture improves both matrix compatibility and surface hydrophobicity simultaneously, resolving the contradiction between these two properties.
Solution Approach 2:
The invention creates a composite polyurethane structure incorporating polysiloxane units with NCO-terminated groups. This composite material approach allows the siloxane chains to be integrated within the polyurethane matrix while maintaining surface hydrophobicity, thus improving both matrix compatibility and surface properties.
2Reliability
If siloxane chains are present on the surface of the coating, then surface hydrophobicity is enhanced, but the durability deteriorates due to removal upon water contact or scratching
Solution Approach 1:
The NCO-terminated polysiloxane prepolymer is designed to react in advance with polyol components during coating formulation, creating strong chemical bonds between siloxane chains and the polyurethane matrix before the coating is applied. This preliminary bonding action ensures that siloxane chains remain firmly attached to the matrix, preventing their removal upon water contact or scratching while maintaining surface hydrophobicity.
Solution Approach 2:
The patent creates a differentiated structure where siloxane units are strategically positioned within the polymer chain to concentrate hydrophobic properties at the surface while maintaining strong matrix bonding throughout. This local quality differentiation allows the surface to exhibit hydrophobicity while the bulk provides durable attachment, resolving the contradiction between surface performance and durability.
3Reliability
If polysiloxane-based hardeners are used to improve surface hydrophobicity, then hydrophobic properties are enhanced, but the bonding strength with the matrix deteriorates
Solution Approach 1:
The invention merges the hydrophobic properties of polysiloxane with the bonding capabilities of NCO-terminated prepolymers into a single integrated molecule. The NCO-terminated polysiloxane prepolymer combines siloxane units for hydrophobicity with isocyanate groups for strong chemical bonding to polyols, thus simultaneously achieving both surface hydrophobicity and strong matrix bonding.
Solution Approach 2:
The NCO-terminated polysiloxane prepolymer acts as an intermediary between the polyurethane matrix and the surface environment. The isocyanate groups mediate strong bonding to the polyol-containing matrix, while the siloxane units mediate surface hydrophobicity, thus resolving the contradiction between bonding strength and hydrophobic properties.
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 NCO-terminated polysiloxane prepolymer significantly improves the surface hydrophobicity and durability of coatings, maintaining hydrophobic properties even under water exposure and scratching, while reducing the need for leveling additives and enhancing residual gloss and reflow characteristics.
Implementation Method 1
NCO-terminated prepolymers can be used as curing components in polyurethane paint or coating systems. These prepolymers are generally obtained by reacting polyols with di- or polyisocyanates. As a curing component, the prepolymers then react with other polyols, such as polyacrylate polyols, in the paint or coating system to form the corresponding polyurethanes.
Implementation Method 2
It is desirable for the surfaces of these coating materials to exhibit hydrophobic properties, for example, to minimize the adhesion of water and/or dirt. It is already known from the state of the art to incorporate siloxane units into the coating materials in order to increase the hydrophobicity of the corresponding surface.
Data Source
AI summary
The present invention relates to an NCO-terminated polysiloxane prepolymer of the general formula (I) [(Q)q]-[(M)m-(P)p-(R)r]t, in which R, P, M, Q, r, p, m, q and t are defined as follows: R in each case independently is at least one polyisocyanate unit and/or at least one diisocyanate unit, P in each case independently is at least one polyol unit, M in each case independently is at least one diisocyanate unit and/or at least one polyisocyanate unit, Q is at least one polysiloxane unit, r in each case independently is a number from 1 to 10, p in each case independently is a number from 1 to 10, m in each case independently is a number from 1 to 10, q in each case independently is a number from 1 to 10, t is an integer from 2 to 5, and the M units present are attached directly to the unit Q; to a process for producing said prepolymer; and to use as curing agent in a coating formulation.