UV LED Array Curing for Flexographic Dot Geometry Control
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Solution Overview
Problem
Flexographic printing plates struggle to maintain small graphic elements like fine dots, lines, and text due to the nature of the platemaking process, which often results in dot removal or damage during printing, affecting image quality.
Innovation Solution
The use of an array of UV LED light assemblies with alternating peak wavelengths between 360 nm to 420 nm for selectively crosslinking and curing photocurable layers in relief image printing elements, allowing for tailored geometric characteristics of relief printing dots such as planarity, shoulder angle, and edge sharpness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional UV light sources are used in the platemaking process, then the process is simple and fast, but the relief printing dots have poor geometric characteristics (irregular shape, poor edge definition, inconsistent size) leading to dot removal or damage during printing
Solution Approach 1:
The UV light source is segmented into multiple LED assemblies arranged in a specific pattern, with each assembly emitting at a different wavelength. This segmentation allows different portions of the photocurable layer to be cured to different depths, creating relief dots with controlled geometric characteristics including planarity, shoulder angle, and edge sharpness.
Solution Approach 2:
Different wavelengths of UV light are applied to different locations or depths within the photocurable layer. Shorter wavelengths (e.g., 360-380 nm) penetrate less deeply and create sharper edges, while longer wavelengths (e.g., 390-420 nm) penetrate deeper and create smoother transitions. This local differentiation of light properties enables precise control over dot geometry.
2Reliability
If the platemaking process uses standard curing methods, then the process is straightforward, but small graphic elements (fine dots, lines, text) are removed or damaged during printing
Solution Approach 1:
The patent applies preliminary curing actions using multiple wavelengths before final development. By pre-curing the photocurable layer with a sequence of wavelengths, the relief structure is established with proper geometric characteristics that prevent dot removal during subsequent printing. This preliminary structuring ensures small graphic elements maintain their integrity.
Solution Approach 2:
The invention changes the parameters of the curing process by using multiple UV wavelengths instead of a single wavelength. Each wavelength provides different penetration depth and curing characteristics, allowing optimization of the relief dot geometry to prevent damage during printing while maintaining small graphic elements.
3Manufacturing precision
If single-wavelength UV light is used for curing, then the equipment is simple, but the relief dots lack controlled geometric characteristics needed for optimal printing performance
Solution Approach 1:
The energy input is segmented into multiple wavelength components, each contributing differently to the curing process. This segmentation allows optimization of energy distribution across different depths and regions of the photocurable layer, achieving precise geometric control while managing overall energy consumption efficiently.
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
This method produces relief printing dots with improved geometric characteristics, enhancing print surface quality, edge definition, and dot structure, reducing the need for bump exposure and improving the representation of small graphic elements during printing.
Implementation Method 1
the source of actinic radiation comprises an array of UV LED light assemblies comprising at least four rows
Implementation Method 2
selectively exposing the at least one photocurable layer to a source of actinic radiation to selectively crosslink and cure the at least one photocurable layer
Data Source
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AI summary
A method of tailoring the shape of a plurality of relief printing dots created in a photosensitive printing blank during a platemaking process is provided. The photocurable layer is exposed to actinic radiation using an array of UV LED light assemblies and the use of the array of UV LED light assemblies produces relief printing dots having at least one geometric characteristic selected from the group consisting of a desired planarity of a top surface of the relief printing dots, a desired shoulder angle of the relief printing dots and a desired edge sharpness of the relief printing dots.