Using HARMAN advanced multilayer coating technology, we have devised an ink jet receiving medium that provides most of the advantages of lamination without the cost of an extra stage. We call it our self-seal technology.
Prints on most commercially available inkjet materials are relatively poorly robust to handling and scratching, and are also susceptible to staining. It is possible to improve the robustness of printed images by lamination or encapsulation using a transparent laminate that acts as a physical protection for the image and completely seals it from ingress of water. Highly glossy and robust prints may be produced by suitable choice of the laminating sheets, but this is an expensive process because of the additional materials required together with extra handling and equipment.
The self-seal ink jet material comprises two essential imaging layers: a lower "pumping" layer that is similar to the receiving layer in many conventional ink jet printing materials and is designed to take up the fluid components of the ink; and an upper "sealing" layer that is porous, being formed from small particles of a thermoplastic polymer together with a binder. The material may be printed just like any other ink jet medium, and the porous construction means it is quickly dry to the touch.
However after printing the thermoplastic polymer in the upper layer may be softened or (partially) melted by application of heat. The particles fuse to form a continuous protective film on the surface, resistant to staining and handling. Further, by heating in contact with a smooth-surfaced roller it is possible to obtain high gloss, and it is also possible to pattern the surface or apply a security mark. Another security feature is that once sealed, the surface will no longer receive ink and thus the print cannot be altered.
The Scanning Electron Microscope pictures above show the surface of a self-seal material before and after printing and sealing. Before printing the particles forming the upper sealing layer are clearly visible; they are around 10 - 20 microns (µm) in size. After sealing there is a smooth glossy surface that is resistant to handling.
The accompanying image is a microscopic view of a cross-section through the printed and sealed material. It is clearly seen that the colorant is retained within the upper sealing layer, the lower pumping layer and supporting substrate are also shown.
Finally a view of a prototype system comprising a roll-fed ink jet printer (left) feeding printed material into a sealing unit (right) that incorporates a heated roller in contact with the top surface of the material to seal the surface layer. Ultimately, a single machine will print, dry, and seal.
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