Record receiver having plural interactive leaves or a colorless – Having plural interactive leaves
Patent
1995-03-16
1996-08-20
Hess, Bruce H.
Record receiver having plural interactive leaves or a colorless
Having plural interactive leaves
283 94, 283107, 428195, 428212, 428480, 428910, 428913, 428914, B41M 535, B41M 538
Patent
active
055479162
DESCRIPTION:
BRIEF SUMMARY
The invention relates to receiver sheets for dye-diffusion thermal transfer printing, and in particular to receiver sheets for use in security laminates in which the receiver sheet after printing is laminated to protective cover sheets on both its printed side and its reverse side. The invention also relates to security laminates comprising such printed receiver sheets.
Security laminates are presently based on various types of information-carrying sheets laminated to cover sheets. These typically have at least one side carrying pictorial information in the form of a normal optical photograph, including typed script and/or signatures as appropriate. This is bonded to a cover sheet on each side. These cover sheets normally overlap to bond to each other and form a pouch, at least during manufacture, but in the final product the information carrying sheet may have raw unprotected edges, eg when cards or tags are stamped or cut out of a larger area.
An alternative to optical photography as a means of producing pictorial representations of persons, signatures, graphics and other such form of information, is thermal transfer printing. However, while this technology can provide some advantages, particularly in its versatility, it can also produce difficulties in lamination.
Thermal transfer printing is a generic term for processes in which one or more thermally transferable dyes are caused to transfer from a dyesheet to a receiver in response to thermal stimuli. Using a dyesheet comprising a thin substrate supporting a dyecoat containing one or more such dyes uniformly spread over an entire printing area of the dyesheet, printing can be effected by heating selected discrete areas of the dyesheet while the dyecoat is pressed against a receiver sheet, thereby causing dye to transfer to corresponding areas of that receiver. The shape of the pattern transferred is determined by the number and locating n the discrete areas which are subjected to heating. Full colour prints can be produced by printing with different coloured dyecoats sequentially in like manner, and the different coloured dyecoats are usually provided as discrete uniform print-size areas in a repeated sequence along the same dyesheet.
High resolution photograph-like prints can be produced by dye-diffusion thermal transfer printing using appropriate printing equipment, such as a programmable thermal print head or laser printer, controlled by electronic signals derived from video, computer, electronic still camera, or similar signal generating apparatus. A typical high speed thermal print head has a row of individually operable tiny heaters spaced to print six or more pixels per millimetre, using very short hot pulses.
Receiver sheets comprise a substrate supporting a receiver coat of a dye-receptive composition containing a material having an affinity for the dye molecules, and into which they can readily diffuse when an area of dyesheet pressed against it is heated during printing. Such receiver coats are typically around 2-6 .mu.m thick, and materials with good dye-affinity are generally thermoplastic polymers, such as saturated polyesters, soluble in common solvents to enable them readily to be coated onto the substrate from solution.
Most receiver sheets also have one or more backcoats on the side of the substrate remote from the receiver layer. These are generally based on a cross-linked polymer binder, and are provided to fulfil a number of different roles, including providing increased friction to improve printer feed, providing antistatic properties and preventing transfer of dyes from one receiver sheet to another.
Clearly, weak adhesion between any of the components of a security laminate reduces the robustness and the durability of the laminate and moreover leads to the possibility of the security laminate being tampered with.
It is desirable, therefore, that the strength of the adhesion between the components of the security laminate be as great as possible and also that delamination causes the substrate itself to tear rather than that there
Hess Bruce H.
Imperial Chemical Industries plc
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