Screen Printing Casting Lacquer with Shear-Dependent Viscosity
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Solution Overview
Problem
Existing radiation curable compositions for creating surface relief structures face challenges in achieving the right viscosity for successful replication of microstructures, particularly in high-speed processes like rotary screen printing, as they require low viscosity for filling recesses and high viscosity to prevent leakage and ensure uniform application.
Innovation Solution
A radiation curable screen printing composition with a shear rate-dependent viscosity, comprising compounds with radiation curable groups, photoinitiators, rheology modifying agents, and optional defoaming and adhesion promoters, designed to have a viscosity of 15 to 40 Pa·S at 0.1 s−1 and less than 0.15 Pa·S at 1000 s−1, facilitating both filling and uniform application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the composition has low viscosity, then it can effectively fill recesses in the relief structure, but it causes leakage during screen printing and prevents uniform application
Solution Approach 1:
The composition exhibits dynamic viscosity changes based on shear rate: high viscosity at low shear rates (preventing leakage during application) and low viscosity at high shear rates (enabling filling of recesses during casting). This dynamic rheological behavior resolves the contradiction between preventing leakage and filling microstructures.
Solution Approach 2:
The patent specifies precise viscosity parameters at different shear rates (15-40 Pa·s at 0.1 s⁻¹ and <0.15 Pa·s at 1000 s⁻¹). By controlling these viscosity parameters through rheology modifying agents, the composition achieves both leakage prevention during application and effective filling during high-speed casting.
2Object-generated harmful factors
If the composition has high viscosity, then it prevents leakage and ensures uniform application, but it cannot effectively fill recesses in the relief structure
Solution Approach 1:
The composition's viscosity is not static but dynamically adjusts to process conditions. During screen printing application (low shear), it maintains high viscosity to prevent leakage. During casting in the relief structure (high shear), it transitions to low viscosity to effectively fill recesses, thus resolving the contradiction.
Solution Approach 2:
The patent defines specific viscosity parameter ranges at different shear rates to achieve the desired dual behavior. Rheology modifying agents are used to control these parameters, enabling the composition to exhibit high viscosity at 0.1 s⁻¹ (preventing leakage) and low viscosity at 1000 s⁻¹ (enabling filling).
3Manufacturing precision
If the viscosity is optimized for filling recesses, then surface relief structures can be replicated, but the composition leaks during high-speed screen printing
Solution Approach 1:
The shear rate-dependent viscosity enables the composition to adapt to different process speeds. During high-speed screen printing, the high viscosity at low shear rates prevents leakage even at production speeds. During the casting step, the low viscosity at high shear rates enables complete filling of relief structures, thus resolving the contradiction between replication quality and productivity.
Solution Approach 2:
The patent specifies viscosity parameters that optimize both high-speed printing and relief replication. The viscosity at 0.1 s⁻¹ (15-40 Pa·s) prevents leakage during high-speed printing, while the viscosity at 1000 s⁻¹ (<0.15 Pa·s) enables complete filling of relief structures, achieving both productivity and manufacturing precision.
4Ease of operation
If the viscosity is optimized for uniform application, then leakage is prevented, but the composition cannot fill fine microstructures
Solution Approach 1:
The composition displays dynamic viscosity behavior that facilitates both uniform application and microstructure filling. During application, high viscosity ensures uniform coating and prevents leakage. During casting into microstructures, low viscosity enables the composition to flow into and fill fine features, resolving the contradiction between ease of operation and manufacturing precision.
Solution Approach 2:
The patent defines viscosity parameter ranges that optimize both application uniformity and microstructure filling. The viscosity at 0.1 s⁻¹ (15-40 Pa·s) ensures uniform application and leakage prevention, while the viscosity at 1000 s⁻¹ (<0.15 Pa·s) enables filling of fine microstructures, achieving both ease of operation and manufacturing precision.
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 composition effectively forms and retains surface relief structures on substrates, enabling high-speed replication and preventing leakage during screen printing, suitable for producing security documents and other articles with micro-optical features.
Implementation Method 1
Radiation curing the coating composition such that the surface relief structure formed of the radiation curable composition is retained on the substrate
Implementation Method 2
A radiation curable screen printing composition with a shear rate-dependent viscosity
Data Source
AI summary
The present invention relates to a radiation curable screen printing composition for cast-curing comprising one or more compounds comprising radiation curable groups, one or more photoinitiators and one or more rheology modifying agents, which composition has a specific shear rate dependent viscosity; an article comprising a substrate and a coating comprising the radiation curable composition in cured form, wherein the coating is in form of a surface relief structure, a method for producing the article comprising the steps: (i) Providing a casting tool having a relief structure defined in a surface thereof, the relief structure corresponding to the surface relief structure; (ii) Applying to the substrate and/or the relief structure of the casting tool the radiation curable composition; (iii) Cast curing the radiation curable composition by bringing the substrate into contact with a casting tool comprising a relief structure and forming the surface relief structure in the coating composition; and (iv) Radiation curing the coating composition such that the surface relief structure formed of the radiation curable composition is retained on the substrate; a security article comprising at least one inventive substrate; the use of the inventive radiation curable composition for the preparation of a surface relief structure on a substrate; the use of the radiation curable composition for screen printing, preferably rotary screen printing, and preferably subsequent cast curing; and a printing press comprising the radiation curable composition, wherein the printing press is adapted to carry out printing on a web-like or sheet-like substrate, in particular for the production of security articles such as banknotes, comprising a printing unit, preferably a screen-printing unit, the printing press further comprises an in-line casting device comprising a casting tool, wherein the printing unit is designed to apply the radiation curable composition to the substrate and/or the casting tool and the inline-casting device is adapted to replicate and form a surface relief structure in the radiation curable composition.