Low-Gloss Polyurethane Coatings Without Matting Agents
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Solution Overview
Problem
Existing aqueous radiation-curable polyurethane coatings achieve low gloss surfaces by using matting agents, which degrade coating performance and resistances to stains, and are prone to migration and undesired coloration.
Innovation Solution
A process involving UV irradiation with specific wavelengths and E-beam to cure aqueous radiation-curable polyurethane dispersions without matting agents, utilizing a composition with urea groups and radiation-curable diluents to achieve low gloss coatings with improved stain resistance and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If matting agents are used to achieve low gloss surfaces, then the aesthetic effect and natural appearance are improved, but the stain resistance and surface performance deteriorate
Solution Approach 1:
The invention extracts and eliminates matting agents from the coating formulation entirely. Instead of using silica-based matting agents that compromise stain resistance, the patent achieves low gloss through a dual-irradiation process using UV light at ≤220 nm followed by UV light at ≥300 nm or E-beam irradiation, which modifies the coating surface morphology without requiring external matting agents.
Solution Approach 2:
The invention replaces the mechanical/physical approach of adding matting agents (solid particles suspended in coating) with a radiation-based chemical/physical process. The dual-irradiation method uses electromagnetic radiation to induce crosslinking and surface modification, substituting the need for mechanical matting agents with a radiation-driven surface transformation process.
2Illumination intensity
If matting agents are used to create matte surfaces, then the visual sensation of low gloss is improved, but the resistance to household chemicals and long-term durability are reduced
Solution Approach 1:
The invention removes matting agents from the coating system, eliminating their negative impact on chemical resistance. The low gloss effect is achieved through radiation-induced surface modification that creates a matte appearance while maintaining the integrity and chemical resistance of the polymer matrix.
Solution Approach 2:
The invention uses a composite approach combining UV irradiation at ≤220 nm with UV irradiation at ≥300 nm or E-beam irradiation. This multi-stage radiation process creates a composite structure in the coating: a crosslinked network providing chemical resistance and a modified surface layer providing low gloss, achieving both properties simultaneously without compromise.
3Illumination intensity
If silica-based matting agents are used, then the low gloss effect is achieved, but undesired coloration occurs due to absorption of organic dyes from stains
Solution Approach 1:
The invention extracts and eliminates silica-based matting agents from the coating formulation. Without these porous inorganic particles that absorb and retain organic dyes from household stains, the coating maintains its original color and does not exhibit undesired coloration over time, while still achieving low gloss through radiation processing.
4Illumination intensity
If matting agents are used to achieve low gloss, then the aesthetic appearance is improved, but the matting agent migrates to the surface and is lost upon mechanical deformation
Solution Approach 1:
The invention removes matting agents from the coating system, eliminating migration and loss issues. The low gloss effect is generated in-situ through radiation-induced surface modification, creating a stable matte surface that is an integral part of the cured coating rather than a separate additive that can migrate or be lost.
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 method produces low gloss coatings with enhanced resistance to stains like coffee, red wine, and mustard, improved smoothness, and better intercoat adhesion, while eliminating the need for matting agents and ensuring stable application on complex shapes.
Implementation Method 1
irradiating the at least partially dried coating composition with UV light having a wavelength ≤220 nm under inert atmosphere
Implementation Method 2
irradiating with UV light having a wavelength ≥300 nm or with E-beam
Implementation Method 3
irradiating with UV light having a wavelength ≥300 nm or with E-beam
Data Source
AI summary
The present invention relates to a process for producing a coating from an aqueous, radiation-curable coating composition, wherein the process comprises the steps in the sequence (1) to (4):(1) applying an aqueous, radiation-curable coating composition on a surface of a substrate,(2) drying the aqueous, radiation-curable coating composition, affording an at least partially dried coating composition,(3) irradiating the at least partially dried coating composition with UV light having a wavelength s 220 nm under inert atmosphere, followed by(4) irradiating with UV light having a wavelength 300 nm or with E-beam,wherein the aqueous, radiation-curable coating composition is a dispersion comprising:(A) at least one water-dispersible polyurethane (A), wherein the polyurethane (A) has a urea group (—NH—CO—NH—) concentration of at least 0.1 milli-equivalents per g of polyurethane (A) and of at most 2.6 milli-equivalents per g of polyurethane (A) and the polyurethane (A) is essentially free of radiation-curable, ethylenically unsaturated bonds,(B) at least one radiation-curable diluent (B) with a molar mass less than 750 g/mol and with an acrylate functionality of from 2 to 5, and(C) water and optionally organic solvent, whereby the optional organic solvent is present in an amount of at most 30 wt. %, based on the total amount of water and organic solvent,whereinthe amount of (A) is from 30 to 85 wt. % and the amount of (B) is from 15 to 70 wt. %,based on the total amount of (A) and (B).