UV-Curable Acrylate Inkjet Ink with Norrish Type I Photoinitiators
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Solution Overview
Problem
Existing solvent-based and radiation-hardening inkjet inks face challenges such as environmental unfriendliness, high drying energy requirements, poor wetting properties, and instability, particularly in long-term storage and high temperatures.
Innovation Solution
Development of a UV-hardening inkjet ink on an acrylic basis, characterized by the use of at least two radical photoinitiators of the Norrish type I and a UV-hardening monomer in the form of a poly-functional alkoxylated and/or polyalkoxylated acrylic monomer, with a specific mole ratio of acrylates to initiators and a viscosity range of 5 to 15 MPa.s.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If solvent-based inkjet inks are used, then the ink can be applied to various substrates, but the drying process requires high energy consumption and the solvents are environmentally unfriendly
Solution Approach 1:
The invention employs UV irradiation to induce photopolymerization, causing the ink composition to transition from a liquid state to a cured solid film state. This phase transition eliminates the need for thermal drying of solvents, thereby reducing energy consumption and eliminating harmful solvent emissions into the environment.
Solution Approach 2:
The invention replaces the thermal drying mechanism (heating and evaporation) with a photopolymerization mechanism (UV light-induced chemical reaction). This substitution transforms the drying process from a thermally-driven physical process to a light-driven chemical process, eliminating the need for high energy input and harmful solvent evaporation.
2Productivity
If radiation-curable inkjet inks with high polyfunctional acrylate content are used, then curing speed is improved, but the viscosity becomes too high for inkjet application
Solution Approach 1:
The invention uses different types of photoinitiators with distinct absorption characteristics to create local optimization in the curing process. Type I photoinitiators (e.g., Irgacure 127, Irgacure 369) absorb at specific wavelengths and provide rapid surface curing, while Type II photoinitiators (e.g., Irgacure 184, Irgacure 819) absorb at different wavelengths and ensure complete bulk penetration, achieving both fast curing and appropriate viscosity characteristics.
Solution Approach 2:
The invention creates a composite photoinitiator system combining Type I and Type II photoinitiators in specific ratios (0.1-10 wt% Type I and 0.1-5 wt% Type II). This composite approach allows the ink to exhibit optimized rheological properties for inkjet application while maintaining high curing efficiency, as each photoinitiator type contributes different functional characteristics to the overall system.
3Productivity
If high proportions of photoinitiators are used to achieve fast curing, then curing efficiency is improved, but the ink stability during storage deteriorates
Solution Approach 1:
The invention optimizes the concentration parameters of photoinitiators to achieve the desired balance between curing efficiency and storage stability. By maintaining Type I photoinitiator content at 0.1-10 wt% and Type II photoinitiator content at 0.1-5 wt%, the system achieves sufficient curing speed while minimizing premature polymerization during storage. The specific ratio and concentration ranges are carefully selected to prevent excessive reactivity that would compromise stability.
Solution Approach 2:
The invention introduces a balanced photoinitiator system that acts as an intermediary between the UV radiation and the acrylate monomers. The dual photoinitiator approach ensures that radiation energy is efficiently absorbed and converted into polymerization activity only when needed, rather than causing premature reactions during storage. This intermediary system provides controlled activation that maintains both efficiency and stability.
4Ease of operation
If the ink formulation is optimized for low viscosity to improve inkjet flow, then printability is improved, but the long-term stability at elevated temperatures deteriorates
Solution Approach 1:
The invention carefully controls the viscosity parameter within the range of 5-15 mPa·s at 45°C, which is optimized for inkjet printing performance. This viscosity range ensures adequate flow through the inkjet system while maintaining sufficient stability at elevated temperatures. The balanced photoinitiator system and controlled monomer composition work together to prevent excessive thinning or premature curing at higher temperatures, achieving both printability and thermal stability.
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 solution achieves minimal energy drying on various substrates, provides wipe-resistance after curing, maintains low photoinitiator content, and ensures long-term stability with minimal changes in physical properties even after four weeks at elevated temperatures.
Implementation Method 1
UV-curable ink, in particular UV-curable inkjet ink, based on acrylate... containing at least two radical photoinitiators of Norrish type I... and at least one UV-curable monomer in the form of a polyfunctional alkoxylated and/or polyalkoxylated acrylate monomer
Implementation Method 2
at least one of the radical photoinitiators of Norrish type I is a bifunctional initiator containing two potential cleavage sites
Data Source
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AI summary
The invention relates to an acrylate-based UV-curable ink, in particular ink jet ink, having a content of pigments, radical photoinitiators, dispersing agent(s) and optionally additional additives, characterized in that said ink contains at least two radical photoinitiators of the Norrish type I and at least one radically curable monomer in the form of a polyfunctional alkoxylated and/or polyalkoxylated acrylate monomer, which comprises one or more diacrylates and/or triacrylates, wherein the mol ratio of all acrylates to all initiators is approximately 5:1 to 19:1. The invention further relates to a method for producing a UV-curable ink, in particular an ink jet ink of the aforementioned type, wherein 1) a ground product or an ink base is produced by grinding one or more radically curable monomers in the form of a polyfunctional alkoxylated and/or polyalkoxylated acryl monomer, which comprise one or more diacrylate(s) and/or triacrylate(s), with one or more pigments and dispersing agents, in particular optionally additionally with synergists, stabilizers and further additives, in a high-performance mill, in particular in a pearl mill, until a constant viscosity and/or constant particle size develops, and 2) the resulting ground product is mixed with further acrylate monomers and the radical photoinitiators in the form of the Norrish type I, and optionally other additives. Said ground product exhibits advantageous physical properties at elevated temperatures and in long-term storage.