Method for making a security document comprising a thermoplastic substrate and UV-cured image and security document formed thereby
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.
1. A method of forming an image comprising ultraviolet light cured ink embedded in a thermoplastic substrate of a security document, the method comprising:
(a) providing a stack of multiple thermoplastic layers;
(b) applying an ultraviolet light cured image to an interior thermoplastic layer surface of the stack, thereby forming a non-thermoforming ink layer on the interior thermoplastic layer surface of the stack, wherein the ultraviolet light cured image comprises a plurality of sub-portions having gaps between them sufficient to permit relative movement of individual sub-portions during lamination of the stack of multiple thermoplastic layers, and a portion of the stack of multiple thermoplastic layers between the ultraviolet light cured image and an exterior surface of the stack is sufficiently see-through that the image is visible upon viewing the security document; and,
(c) laminating the stack of multiple thermoplastic layers to form the thermoplastic substrates;
wherein integrity of the non-thermoforming ink layer is preserved during the laminating step.
2. The method of claim 1 wherein the thermoplastic layer to which the ultraviolet light cured image is applied has a higher Tg value than an adjacent thermoplastic layer of the stack.
3. The method of claim 1 wherein the sub-portions of the ultraviolet light cured image have a size of less than 50 square millimeters.
4. The method of claim 1 wherein linear or rectangular sub-portions of the image have a length to width ratio of not more than 8.
5. The method of claim 1 wherein sub-portions of the image have a concave angle greater than 80 degrees.
6. The method of claim 1 wherein the image is sandwiched between two intermediary elastomeric polymeric layers.
7. The method of claim 6 wherein the intermediary elastomeric polymeric layers comprise polyurethane, polyethylene or PVC film.
8. The method of claim 6 wherein the intermediary elastomeric polymeric layers comprise screen printed aqueous polyurethane dispersion ink.
9. The method of claim 1 wherein the image is formed by screen printed optically variable, magnetic ink.
10. The method of claim 1 wherein the image is applied by screen printing.
11. A security document comprising a thermoplastic substrate having an embedded image comprising ultraviolet light cured ink and formed by the method of claim 1 .
12. A method of forming an image comprising ultraviolet light cured ink embedded in a thermoplastic substrate of a security document, the method comprising:
(a) providing a stack of thermoplastic layers configured to form the thermoplastic substrate upon lamination of the stack of thermoplastic layers;
(b) applying the image to an interior surface of an outermost thermoplastic layer of the stack adjacent an intermediate thermoplastic layer of the stack, thereby forming a non-thermoforming ink layer on the interior surface of the outermost thermoplastic layer of the stack, wherein the outermost thermoplastic layer is sufficiently see-through that the image is visible upon viewing the security document; and,
(c) laminating the stack of multiple thermoplastic layers to form the thermoplastic substrate;
wherein integrity of the non-thermoforming ink layer is maintained during the laminating step.
13. The method of claim 12 wherein the outermost layer of the stack has a higher Tg value than an adjacent intermediate thermoplastic layer of the stack.
14. The method of claim 12 wherein the image comprises a plurality of sub-portions having gaps between them sufficient to permit relative movement of individual sub-portions.
15. The method of claim 12 wherein the surface of the outermost thermoplastic layer to which the image is applied has a surface roughness value of Ra≤5 microns.
16. The method of claim 12 wherein the image is sandwiched between two intermediary elastomeric polymeric layers.
17. The method of claim 16 wherein the intermediary elastomeric polymeric layers comprise polyurethane, polyethylene or PVC film.
18. The method of claim 16 wherein the intermediary elastomeric polymeric layers comprise screen printed aqueous polyurethane dispersion ink.
19. The method of claim 12 wherein the image is formed by screen printed optically variable, magnetic ink.
20. The method of claim 12 wherein the image is applied by screen printing.