UV LED Ink Jet Curing with α-Hydroxyketone for Low Yellowing

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Solution Overview

Problem

Ink jet compositions using acylphosphine oxide-based initiators cure well under LED irradiation but suffer from yellowing of printed coating films, while those using α-hydroxyketone-based initiators require large, heat-generating lamps, causing heat damage to recording media.

Innovation Solution

An ink jet recording method using a radiation-curable ink composition containing a polymerizable compound and an α-hydroxyketone-based initiator, cured by LED irradiation with a peak wavelength of 250 to 310 nm, reducing heat damage and preventing yellowing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an APO-based initiator is used as a photopolymerization initiator, then the ink jet composition can be cured by LED irradiator with peak wavelength of 365 nm to 405 nm, but the printed coating film is easily turned yellow and has poor color reproducibility

Engineering Contradiction:

Improvecuring efficiencyVSAvoidcolor reproducibility

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent changes the wavelength parameter of the LED irradiator from the conventional 365-405 nm range to a shorter wavelength range of 250-310 nm. This parameter change enables the use of α-hydroxyketone-based initiators instead of APO-based initiators, achieving both effective curing and prevention of yellowing for excellent color reproducibility

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the conventional APO-based initiator system with an alternative α-hydroxyketone-based initiator system that responds to different wavelength radiation. This substitution maintains the curing function while eliminating the yellowing side effect, effectively copying the desired curing outcome without the harmful byproduct

Inventive Principle:

Principle #26Copying

2Ease of manufacture

If an α-hydroxyketone-based initiator is used as a photopolymerization initiator, then the printed coating film is hardly turned yellow, but irradiation with radiation at a peak wavelength near 280 nm is required, necessitating a lamp with large size and high heat generation

Engineering Contradiction:

Improvecolor reproducibilityVSAvoidheat damage to recording medium

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the conventional lamp-based irradiator (metal halide lamp or high-pressure mercury lamp) with an LED irradiator. This substitution eliminates the need for large, heat-generating lamps while achieving the required 250-310 nm wavelength output, thereby preventing heat damage to the recording medium

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the peak wavelength parameter of the radiation source to 250-310 nm and uses LED technology to achieve this wavelength range. This parameter change allows the system to activate α-hydroxyketone-based initiators without requiring high-heat conventional lamps, thus eliminating heat damage to the recording medium

Inventive Principle:

Principle #35Parameter changes

3Reliability

If a metal halide lamp or high-pressure mercury lamp is used as a radiation irradiator, then the ink jet composition can be cured, but the large size and high heat generation cause heat damage to the recording medium

Engineering Contradiction:

Improvecuring functionVSAvoidheat damage to recording medium

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The patent substitutes conventional high-heat lamps (metal halide or high-pressure mercury lamps) with an LED irradiator system. This replacement maintains the curing function while dramatically reducing heat generation and eliminating thermal damage to the recording medium

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces an LED irradiator as an intermediary device that converts electrical energy directly to ultraviolet radiation in the 250-310 nm range. This intermediary approach avoids the thermal conversion process of conventional lamps, preventing heat transfer to the recording medium while still providing the necessary radiation for curing

Inventive Principle:

Principle #24Intermediary (Mediator)

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 effectively cures the ink composition, minimizing heat damage to the recording medium and preventing yellowing of the printed coating film, while maintaining excellent color reproducibility.

Implementation Method 1

a LED irradiator having a peak wavelength of 250 to 310 nm

Methodology Applied

Scientific EffectLight Emitting Diode: Light Emitting Diode

Implementation Method 2

The ink jet composition contains a polymerizable compound and an α-hydroxyketone-based initiator

Methodology Applied

Scientific EffectPhotopolymerization: Photopolymerisation

Data Source

PatentUS20260084454A1Ink Jet Recording Method And Ink Jet Recording Apparatus

Publication Date: 2026.03.26 SEIKO EPSON CORP

AI summary

An ink jet recording method includes ejecting a radiation-curable ink jet composition to a recording medium from an ink jet head, and curing the ink jet composition ejected to the recording medium by irradiating with radiation from a LED irradiator having a peak wavelength of 250 to 310 nm to form a cured coating film. The ink jet composition contains a polymerizable compound and an α-hydroxyketone-based initiator.