Low Shrinkage PET Support for Rapid Flexographic Plate Drying
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Solution Overview
Problem
Flexographic printing plates require lengthy drying times at temperatures below the glass transition temperature of polyester support sheets to prevent thermal shrinkage, leading to inefficient production and registration issues, while attempts to accelerate drying result in quality problems due to dimensional instability.
Innovation Solution
A photopolymerizable flexographic printing element with a polyethylene terephthalate (PET) support sheet having low thermal shrinkage, bonded to a photopolymerizable layer and a laser-ablatable mask layer, allowing for drying at temperatures above 60°C without register problems, achieved by annealing the PET sheet to ensure minimal shrinkage and using a method where the supporting sheet is bonded to the photopolymerizable layer at a temperature below 60°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If drying is carried out at temperatures below the glass transition temperature of polyester support sheets, then thermal shrinkage is prevented and dimensional stability is maintained, but drying time becomes excessively long (at least 60 minutes up to 3 or 4 hours)
Solution Approach 1:
The patent changes the fundamental parameter of the support sheet material from conventional polyester to a polymer with a glass transition temperature above the drying temperature. This allows drying at temperatures above 60°C while maintaining dimensional stability, as the support sheet remains below its glass transition temperature and does not undergo thermal shrinkage.
Solution Approach 2:
The patent uses composite material construction with a support sheet made of specific polymers (polyacrylic acid, polyacrylamide, carboxymethyl cellulose, or starch) that have inherently low thermal shrinkage properties. This composite approach combines the washout properties of the photopolymerizable layer with the dimensional stability of the specialized support sheet.
2Productivity
If drying temperature is increased above 60°C to reduce drying time, then productivity is improved, but register problems occur due to thermal shrinkage of polyester support sheets
Solution Approach 1:
The patent raises the glass transition temperature parameter of the support sheet material above the drying temperature range. This allows the drying process to be conducted at higher temperatures (above 60°C) without causing thermal shrinkage, thereby maintaining registration accuracy while improving productivity.
Solution Approach 2:
The patent prepares the support sheet in advance by selecting materials with inherently low thermal shrinkage properties and appropriate glass transition temperatures. This beforehand selection cushions against the potential harmful effects of thermal shrinkage during the drying process, allowing high-temperature drying without register problems.
3Ease of manufacture
If conventional polyester support sheets are used, then ease of manufacture is maintained, but thermal shrinkage occurs during drying leading to register loss
Solution Approach 1:
The patent changes the material parameter of the support sheet from conventional polyester to polymers with suitable glass transition temperatures and low thermal shrinkage characteristics. These alternative materials maintain ease of manufacture through standard coating and processing techniques while eliminating the thermal shrinkage problem that causes registration loss.
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
Enables flexographic printing plates to be dried at higher temperatures, significantly reducing drying time without compromising dimensional stability or registration accuracy, thus improving the efficiency and quality of the printing process.
Implementation Method 1
PET support sheet of low thermal shrinkage
Implementation Method 2
achieved by annealing the PET sheet to ensure minimal shrinkage
Implementation Method 3
The photopolymerizable layer undergoes polymerization in the areas no longer concealed by the mask, whereas no polymerization occurs in the concealed areas
Implementation Method 4
a mask is written into the laser-ablatable layer by using an IR laser
Implementation Method 5
the unpolymerized portions of the relief-forming layer dissolve in the solvent
Implementation Method 6
The polymerized portions of the layer do not dissolve and remain after the washout step to form the printing relief. But they do nonetheless swell in the washout media.
Data Source
AI summary
Photopolymerizable, preferably digitally imageable photopolymerizable, flexographic printing elements having a PET support sheet of low thermal shrinkage, methods of preparing such flexographic printing elements and their use for making flexographic printing plates by imagewise exposure to light, washing out with organic solvents and drying, wherein said drying is carried out at temperatures of more than 60° C.