UV-Curable Ink Composition for Internal Curability
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Solution Overview
Problem
Ultraviolet-curable ink compositions containing thioxanthone-based photopolymerization initiators exhibit poor internal curability and adhesion when used with semiconductor light sources, particularly LED-based systems, due to inhibited light transmission, leading to issues with the adhesiveness of coatings, especially when yellow or black coloring materials are used.
Innovation Solution
An ultraviolet-curable ink composition for ink jet recording that includes a thioxanthone-based photopolymerization initiator, acylphosphine-oxide-based photopolymerization initiator, and yellow or black coloring materials, optimized for use with ultraviolet radiation in the range of 380 to 405 nm from a semiconductor light source, ensuring a product of light transmissivity and irradiation energy that is 2 or more, thereby enhancing internal curability and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thioxanthone-based photopolymerization initiator is used to ensure curability, then surface curability is improved, but internal curability deteriorates due to inhibited light transmission
Solution Approach 1:
The patent combines a thioxanthone-based photopolymerization initiator with a yellow coloring material that has specific light absorption characteristics. This composite approach allows the thioxanthone initiator to provide surface curability while the yellow coloring material's selective light absorption profile enables sufficient light transmission at 395 nm wavelength, thereby maintaining internal curability. The synergistic combination resolves the contradiction between surface curability and internal light transmission.
2Quantity of substance
If yellow or black coloring materials are added to achieve predetermined OD, then color strength is improved, but adhesion deteriorates due to severely inhibited inward light transmission
Solution Approach 1:
The patent specifies precise parameters for the yellow coloring material: it must have a light absorption percentage of 5% or less at 395 nm wavelength. This parameter control allows the formulation to achieve sufficient optical density for color strength while maintaining adequate light transmission for internal curability and adhesion. By carefully selecting and controlling the light absorption parameters of the coloring material, the patent resolves the contradiction between color strength and adhesion.
3Quantity of substance
If high light absorption at 395 nm is achieved for color strength, then OD is improved, but internal curability deteriorates
Solution Approach 1:
The patent applies the local quality principle by selecting a yellow coloring material with specific spectral characteristics - low light absorption (5% or less) at the critical 395 nm wavelength used for curing. This localized optimization at the specific curing wavelength allows the formulation to achieve sufficient optical density for color strength in the visible range while maintaining high light transmission for internal curability at the UV curing wavelength. The coloring material's absorption profile is optimized locally at different wavelengths to satisfy different requirements.
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 ink composition achieves excellent adhesiveness and internal curability, even with thick films, by ensuring that the ultraviolet radiation penetrates deep into the ink composition, improving the adhesion of the cured coatings on substrates while maintaining a strong color and reduced surface tackiness.
Implementation Method 1
an ultraviolet-curable ink composition for ink jet... contains a thioxanthone-based photopolymerization initiator... irradiating the ultraviolet-curable ink composition for ink jet applied to a substrate with ultraviolet radiation... to obtain a cured coating
Implementation Method 2
the use of a thioxanthone-based photopolymerization initiator, which exhibits a high percentage of light absorption at wavelengths around 395 nm, causes the ink composition to be lacking in curability inside, particularly in light curing with a semiconductor light source, such as an LED, as a result of inhibited transmission of light into the ink composition
Data Source
AI summary
An ultraviolet-curable ink composition for ink jet is for use in an ink jet recording method that includes irradiating the ultraviolet-curable ink composition for ink jet applied to a substrate with ultraviolet radiation that has a peak wavelength in the range of 380 to 405 nm from a semiconductor light source to obtain a cured coating. The product of the light transmissivity (%) of the cured coating at a wavelength of 395 nm and the irradiation energy of the ultraviolet radiation (mJ/cm2) is 2.0 or more. The ink composition contains a thioxanthone-based photopolymerization initiator and at least one of yellow coloring material and black coloring material. The OD of the cured coating made from the ink composition is 1.8 or more.