UV-Curable Inkjet Inks for Plastic Packaging Adhesion
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Solution Overview
Problem
Radiation-curable inkjet inks and coatings face challenges in achieving good adhesion to substrates, particularly flexible plastics, without using components that can migrate and contaminate food or pharmaceutical packaging, especially under UV-LED curing which often results in inefficient curing and potential health hazards.
Innovation Solution
Incorporating low molecular weight acrylic polymers and multifunctional hybrid monomers, such as those with (meth)acrylate and vinyl ether groups, into the inkjet ink compositions to enhance cure response and adhesion to plastic substrates, while minimizing migration potential by using predominantly multifunctional monomers and specific photoinitiators like thioxanthones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high concentrations of monofunctional monomers are used to improve adhesion to substrates, then adhesion is enhanced, but migration of low molecular weight components increases causing contamination
Solution Approach 1:
The patent changes the functional group composition parameters of monomers, specifically using a ratio of vinyl ether groups to (meth)acrylate groups between 1:4 and 1:1, and controlling the total functional group concentration at 2-10 mmol/g. This parameter optimization achieves both good adhesion and low migration by balancing reactivity and molecular weight characteristics.
Solution Approach 2:
The patent employs composite monomer systems combining different types of monomers with complementary properties: vinyl ether monomers for adhesion, (meth)acrylate monomers for crosslinking density, and multifunctional monomers for network formation. This composite approach allows simultaneous achievement of adhesion and low migration through synergistic effects.
2Use of energy by moving object
If UV-LED curing is used to reduce energy consumption and heating, then energy efficiency is improved, but curing efficiency decreases leading to poor adhesion
Solution Approach 1:
The patent optimizes the spectral absorption parameters of photoinitiators to match UV-LED emission wavelengths, and adjusts monomer functional group concentrations (2-10 mmol/g) to enhance curing kinetics under low-energy UV-LED irradiation. This ensures adequate curing efficiency while maintaining energy savings.
Solution Approach 2:
The patent uses specific photoinitiators with absorption maxima matching UV-LED wavelengths (e.g., 395 nm LEDs with photoinitiators absorbing at 380-420 nm), creating localized optimal curing conditions that compensate for the lower overall energy intensity of UV-LEDs compared to traditional lamps.
3Object-generated harmful factors
If multifunctional monomers are used to reduce migration, then migration is reduced, but adhesion to substrates deteriorates
Solution Approach 1:
The patent optimizes the concentration balance between different functional groups: vinyl ether groups (2-10 mmol/g) for adhesion, (meth)acrylate groups for crosslinking, and controls the ratio between them (1:4 to 1:1). This balanced composition achieves both low migration and good adhesion simultaneously.
Solution Approach 2:
The patent incorporates vinyl ether groups that provide preliminary adhesion promotion before final curing, ensuring substrate bonding occurs during the curing process even with reduced monofunctional monomer content, thereby maintaining adhesion while reducing migration.
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 inks and coatings demonstrate improved UV-LED cure response, enhanced adhesion to plastic substrates, and low migration potential, reducing the risk of contamination and maintaining print quality, suitable for single pass and multi-pass printing applications, including food and pharmaceutical packaging.
Implementation Method 1
The inkjet inks and coatings are curable by any form of radiation, such as ultraviolet (UV) or electron beam. The inks and coatings exhibit good adhesion to substrates, such as flexible plastic substrates, when cured by UV-LED radiation.
Implementation Method 2
at least one photoinitiator is thioxanthone or a derivative or a polymethine dye
Data Source
AI summary
The present invention provides radiation-curable (UV-curable) inks and coatings for inkjet printing comprising an inert thermoplastic acrylic resin and multifunctional monomers. The inks and coatings can be applied in a single pass printing operation. Furthermore, the inks and coatings are suitable for the printing of food, pharmaceutical and other sensitive packaging materials, particularly of plastic materials. The acrylic polymer (or copolymer) preferably has a molecular weight of 10,000 g/mole, or less, and the ink comprises less than 5 wt% of any blend of monofunctional monomer. The inks and coatings of the invention are particularly suitable for curing by UV-LED radiation.