UV-LED Curing Ink Set with Composite Initiators
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Solution Overview
Problem
Actinic-ray-curable ink sets for ink-jet recording face challenges in achieving uniform curing across different colors and thick-film curability when using a UV-LED lamp as a light source, leading to non-uniform dot sizes and insufficient clearness in printed matter.
Innovation Solution
The ink set comprises cyan, magenta, yellow, and black inks with specific photopolymerization initiators, such as acylphosphine oxide-based initiators, and pigments, optimized in mass ratios and concentrations to ensure uniform curing and deep penetration of light, even in thick films, using bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide and 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide in combination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional pigment inks are irradiated with UV-LED light source, then energy consumption is reduced and eco-friendliness is improved, but the ink cannot be sufficiently cured due to absorption of ultraviolet rays by pigments and photopolymerization initiators
Solution Approach 1:
The patent changes the wavelength parameter of the light source from conventional UV ranges to specifically 380nm to 420nm peak wavelength, which matches the absorption characteristics of the photopolymerization initiator while minimizing absorption by pigments. This parameter optimization enables sufficient curing with UV-LED while maintaining energy efficiency and eco-friendliness.
Solution Approach 2:
The patent uses a composite photopolymerization initiator system comprising both an acylphosphine oxide compound and a thioxanthone compound. This composite initiator system has broad absorption characteristics that match the UV-LED wavelength range, ensuring effective curing across different pigment colors while maintaining the energy-saving benefits of LED technology.
2Productivity
If UV-LED lamp is used as light source, then curing speed is improved and productivity increases, but uniform curing across different colors cannot be achieved due to differential absorption characteristics
Solution Approach 1:
The patent applies different concentrations of photopolymerization initiators to different color inks based on their specific absorption characteristics. Cyan and magenta inks contain 3-10% and 1-5% photopolymerization initiator respectively, while yellow and black inks contain higher concentrations. This localized adjustment ensures uniform curing across all colors when using UV-LED light source.
Solution Approach 2:
The patent employs a composite photopolymerization initiator system combining acylphosphine oxide and thioxanthone compounds, which together provide broad-spectrum absorption coverage matching the UV-LED wavelength range. This composite system enables simultaneous and uniform curing of multiple colors with different absorption characteristics.
3Quantity of substance
If thick ink coating film is printed, then design flexibility and coverage are improved, but light penetration to interior is insufficient resulting in failure of rapid curing
Solution Approach 1:
The patent uses a photopolymerization initiator system with specific absorption characteristics that acts as an intermediary to transfer energy efficiently through thick ink layers. The acylphosphine oxide and thioxanthone compounds have absorption profiles that enable deep penetration of UV-LED light, allowing rapid curing even in thick coating films that would otherwise block light transmission.
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
This configuration allows for quick and uniform curing throughout the ink coating film, preventing non-uniformity across different colors and ensuring effective curing even in large thicknesses, resulting in high-quality printed images with consistent dot sizes.
Implementation Method 1
actinic-ray-curable inks can form a coating film having high strength, chemical resistance, and toughness
Implementation Method 2
pigments and the photopolymerization initiators contained in such inks generally have a nature of absorbing ultraviolet rays
Data Source
AI summary
To provide an actinic-ray-curable ink set for ink-jet recording which is excellent in thick-film curability even when a UV-LED lamp is used as a light source, and has uniform curing sensitivity across different colors. The present invention relates to an actinic-ray-curable ink set for ink-jet recording, characterized in that a cyan ink contains a phthalocyanine pigment, a radical polymerizable compound, and less than 10% by mass of a photopolymerization initiator based on the total amount of the cyan ink, a magenta ink contains a quinacridone-based pigment, a radical polymerizable compound, and less than 5% by mass of a photopolymerization initiator based on the total amount of the magenta ink, a yellow ink contains an azo pigment, a radical polymerizable compound, and less than 10% by mass of a photopolymerization initiator based on the total amount of the yellow ink, and a black ink contains a carbon black, a radical polymerizable compound, and less than 12% by mass of a photopolymerization initiator based on the total amount of the black ink.