UV-Cured Ink Splitting in Thermoplastic Security Documents
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Solution Overview
Problem
Security documents with UV light curable images on thermoplastic substrates face ink splitting issues during lamination due to the inelastic nature of the ink and high temperature/pressure processes, leading to undesirable cracks in the image.
Innovation Solution
Applying UV light cured images to an interior thermoplastic layer with small gaps between sub-portions or to an outermost layer with a higher glass transition temperature, and using elastomeric polymeric layers or specific inks like optically variable magnetic ink to reduce stress and distortion during lamination, ensuring the image is visible and minimizing ink splitting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick layer of UV light curable ink is applied by screen printing to embed security images within thermoplastic substrates, then security against tampering is improved, but ink splitting and cracking occur during lamination due to the inelastic nature of the ink under high temperature and pressure
Solution Approach 1:
The patent changes the physical-chemical parameters of the ink by incorporating elastomeric polymers that undergo phase transition at lamination temperatures. The ink formulation is modified to include polymers with glass transition temperatures matching the lamination process, transforming the ink from a rigid, inelastic state to a flexible, elastic state during lamination, thereby preventing cracking while maintaining security features
Solution Approach 2:
The patent creates a composite ink material combining UV-curable components with elastomeric polymers. This composite formulation integrates the security properties of UV-curable ink with the thermal flexibility of elastomeric materials, allowing the ink to resist cracking during lamination while maintaining its security function after curing
2Illumination intensity
If clear or transparent thermoplastic layers are used to allow visibility of the embedded image, then image visibility is improved, but the lamination process at high temperature and pressure causes the layers to soften and reform, damaging the relatively inelastic UV light cured image
Solution Approach 1:
The patent modifies the thermal parameters of the ink system by incorporating elastomeric polymers with glass transition temperatures coordinated to the lamination process. During lamination, the ink softens to match the flexibility of the transparent thermoplastic layers, preventing damage while maintaining visibility through the clear layers
3Quantity of substance
If screen printing is used to apply thick UV light curable ink layers for security embedding, then security feature thickness is improved, but the inelastic ink is more likely to result in ink splitting upon lamination of thermoplastic layers
Solution Approach 1:
The patent changes the rheological parameters of the ink by formulating it with elastomeric polymers. This allows the ink to be applied as a thick layer via screen printing while maintaining elasticity during lamination, preventing splitting despite the increased thickness that would normally make the ink more prone to cracking
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 method effectively reduces ink splitting in UV light cured images within thermoplastic substrates, maintaining image integrity and visibility while allowing for successful lamination of security documents.
Implementation Method 1
The ultraviolet light cured image is applied to an interior thermoplastic layer surface of the stack, the image comprising numerous small sub-portions having small gaps between them sufficient to permit relative movement of individual sub-portions during lamination of the stack of multiple thermoplastic layers
Data Source
AI summary
A method is provided by the invention for making a security document comprising a thermoplastic substrate with a UV light cured printed image that is less likely to result in splitting of the ink of the UV light cured printed image during the lamination step of forming the thermoplastic substrate. The UV light cured image is applied to an interior thermoplastic layer surface of a stack of thermoplastic layers configured to form a thermoplastic substrate upon lamination of the stack and comprises numerous small sub-portions having small gaps between them sufficient to permit relative movement of individual sub-portions during lamination, the thermoplastic layer(s) from the ultraviolet light cured image to an exterior surface of the stack being sufficiently see-through that the image is visible upon viewing the security document. Alternatively, or additionally, the image is applied to an interior surface of an outermost thermoplastic layer of the stack adjacent an intermediate thermoplastic layer of the stack wherein the outermost thermoplastic layer has a higher melting point than the melting point of at least the adjacent intermediate thermoplastic layer.