Lithographic Printing Plate Sensitizer Mixture Crystallization Control
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Solution Overview
Problem
Photopolymerizable compositions for lithographic printing plates face issues with crystallization of sensitizers, leading to decreased polymerization efficiency and poor storage stability, resulting in unacceptable printing quality due to crystallization defects during exposure and development.
Innovation Solution
A lithographic printing plate precursor with an image-recording layer containing a mixture of sensitizers, optimized for high solubility and MetaStable Zone Width (MSZW) in 1-methoxy-2-propanol at 80°C, minimizing crystallization and maintaining sensitivity, is used, along with a method involving exposure to actinic light with an energy density of 100 µJ/cm² or less and optional pre-heating before development.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single sensitizer is used to increase sensitivity for violet laser exposure, then exposure sensitivity is improved, but crystallization occurs during storage leading to poor printing quality
Solution Approach 1:
The single sensitizer is segmented into a mixture of multiple sensitizers (at least two different sensitizers) with different chemical structures. This segmentation prevents crystallization while maintaining or enhancing the overall sensitivity to violet laser light, as each sensitizer contributes differently to the absorption spectrum and polymerization initiation.
Solution Approach 2:
A composite sensitizer system is created by combining multiple sensitizers with different chemical structures in specific ratios. This composite approach leverages the complementary properties of each sensitizer to achieve both high exposure sensitivity and improved storage stability by preventing crystallization through molecular diversity.
2Productivity
If sensitizer concentration is increased to improve sensitivity, then exposure efficiency is improved, but crystallization defects increase during storage
Solution Approach 1:
The total sensitizer concentration is segmented across multiple different sensitizers rather than using a high concentration of a single sensitizer. This distribution maintains sufficient exposure efficiency while preventing the supersaturation conditions that lead to crystallization and printing defects.
Solution Approach 2:
The chemical composition parameters of the sensitizer system are changed from a single compound to a multi-component mixture. This parameter change allows optimization of both exposure efficiency and storage stability by selecting sensitizers with complementary solubility and absorption characteristics.
3Productivity
If exposure energy density is reduced to 100 µJ/cm² or less for high throughput, then productivity is improved, but sufficient polymerization may not occur with conventional sensitizers
Solution Approach 1:
The absorption spectrum parameters of the sensitizer system are optimized for the violet laser wavelength range (350-450 nm). By selecting sensitizers with high molar absorptivity at these wavelengths, sufficient polymerization can be achieved at low energy densities (100 µJ/cm² or less), enabling high throughput while maintaining complete curing.
Solution Approach 2:
A composite sensitizer system is designed with components that have complementary absorption spectra in the violet region. This composite approach maximizes the overall absorption efficiency at the exposure wavelength, enabling effective polymerization initiation at very low energy densities for high-speed processing.
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 provides printing plates with excellent lithographic properties and improved storage stability, ensuring high sensitivity and quality by preventing crystallization-induced defects during exposure and development.
Implementation Method 1
a photopolymerizable composition that is photopolymerizable upon absorption of light in the wavelength range from 300 to 450 nm
Implementation Method 2
the mixture of sensitizers has in 1-methoxy-2-propanol at 80°C a solubility of at least 30 wt.-% and preferably a MetaStable Zone Width (MSZW) of at least 8.5°C
Data Source
AI summary
A lithographic printing plate precursor comprising an image recording layer, said image -recording layer being photopolymerizable upon exposure to actinic light and containing a mixture of sensitizers characterized in that said mixture of sensitizers has in 1-methoxy-2-propanol at 80°C a solubility of at least 30 wt. %. and preferably a MetaStable Zone Width (MSZW) of at least 8.5°C, said MSZW measured at a cooling and heating rate of 0.2°C /minute.