Radiation Curable Inkjet Inks for Flexibility and Scratch Resistance
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Solution Overview
Problem
Radiation curable inkjet inks face challenges in achieving simultaneously good flexibility, scratch resistance, low viscosity for jetting performance, high cure speed, and adhesion to a wide range of substrates, as existing compositions often compromise on these properties.
Innovation Solution
The development of a radiation curable inkjet ink formulation that includes specific ratios of monofunctional and polyfunctional monomers, such as N-vinyl lactam, vinylether acrylate, and ethoxylated or propoxylated polyacrylates, along with a photoinitiator and surfactants, to achieve optimal properties like low viscosity, high cure speed, and improved adhesion and scratch resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the ratio of polyfunctional monomers over monofunctional monomers is increased to improve curing speed and scratch resistance, then scratch resistance is improved, but flexibility deteriorates and the image cracks or peels off
Solution Approach 1:
The patent applies parameter changes by precisely controlling the ratio of polyfunctional to monofunctional monomers within specific ranges (0.05-0.50) and regulating the content of specific monomers like N-vinyl lactam (5-30 wt%) and vinylether acrylate (5-30 wt%). This quantitative control optimizes the balance between cross-linking density for scratch resistance and chain mobility for flexibility, resolving the contradiction between these two properties.
Solution Approach 2:
The patent uses composite materials by combining multiple types of monomers (N-vinyl lactam, vinylether acrylate, ethoxylated/propoxylated polyacrylates) with different functional characteristics in a single ink formulation. This composite approach allows simultaneous achievement of high scratch resistance through cross-linking and good flexibility through the specific interactions and mobility characteristics of the combined monomer system.
2Stability of the object's composition
If the ratio of polyfunctional monomers is decreased to improve flexibility, then flexibility is improved, but curing speed and scratch resistance deteriorate
Solution Approach 1:
The patent resolves this contradiction through parameter changes by establishing optimal concentration ranges for different monomer types. Specifically, it maintains polyfunctional monomer content at 5-30 wt% while controlling monofunctional monomer content at 5-30 wt%, creating a balanced composition that achieves both good flexibility and high curing speed through optimized chemical composition parameters.
3Stability of the object's composition
If specific monomers like acrylic acid are used to improve flexibility through hydrogen-bonding interactions, then flexibility is improved, but corrosion in inkjet print heads occurs
Solution Approach 1:
The patent applies the blessing in disguise principle by replacing acrylic acid monomers (which provide flexibility through hydrogen bonding but cause corrosion) with alternative monomers like N-vinyl lactam and vinylether acrylate. These alternatives maintain the desired flexibility and adhesion properties through different chemical mechanisms while eliminating the harmful corrosion effect on inkjet print heads.
4Strength
If reactive oligomers with glass transition point of 0°C to 70°C are used to achieve good flexibility and adhesion, then adhesion and flexibility are improved, but viscosity increases requiring high jetting temperatures
Solution Approach 1:
The patent resolves this contradiction through parameter changes by selecting reactive oligomers with specific glass transition points (0°C to 70°C) and controlling their molecular weight and concentration. This optimization allows achieving good adhesion and flexibility while maintaining viscosity within acceptable ranges for standard jetting temperatures, eliminating the need for excessively high heating.
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 inkjet ink formulation effectively balances flexibility, scratch resistance, and adhesion while maintaining low viscosity, enabling efficient jetting and curing performance on various substrates.
Implementation Method 1
radiation curable inkjet inks... UV-curable inks... photopolymerisation... polymerization initiator... curing speed
Implementation Method 2
highly cross-linked three-dimensional structure... scratch resistance... polyfunctional monomers... cross-linked polymers
Implementation Method 3
carboxy group in the monomer provides a hydrogen-bonding interaction... weaker bond than the covalent bond... flexibility
Implementation Method 4
surfactants... controlled spreading of the ink on the ink receiver... adhesion
Data Source
AI summary
A free radical radiation curable inkjet ink containing a photoinitiator and polymerizable compounds includes a) no more than 15 wt % of one or more monofunctional acrylates wherein the homopolymer thereof has a Tg smaller than 20° C.; and b) at least 45 wt % of a mixture of monomers consisting of b1) 10 to 45 wt % of a N-vinyl lactam and/or a vinylether acrylate; and b2) 10 to 45 wt % of an ethoxylated and/or propoxylated polyacrylate having a molecular weight of at least 450; wherein all wt % are based on the total weight of the inkjet ink; and wherein the Tg is determined by the DSC method in ISO 11357-2:1999.