Thermal transfer printing receiver sheet

Details Thermal transfer printing receiver sheet Thermal transfer printing receiver sheet

1995-09-05

1997-12-23

Hess, Bruce H.

Record receiver having plural interactive leaves or a colorless

Having plural interactive leaves

428195, 4283044, 428913, 428914, B41M 5035, B41M 538

Patent

active

057007551

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a thermal transfer printing receiver sheet, and in particular to a receiver sheet having a porous substrate.
Thermal transfer printing is a printing process in which a dye is caused by thermal stimuli to transfer from a dye sheet to a receiver sheet by diffusion and/or sublimation. In such processes the dye sheet and receiver sheet are placed in intimate contact, the thermal stimuli are applied to pre-determined areas of the dye sheet and the dye is selectively transferred to the receiver to form the desired image. The dye sheet and receiver sheet are then separated.
Receiver sheets conventionally comprise a substrate with a dye receiving surface on one side into which a dye is thermally transferable and retainable. The dye-receiving surface may be provided by one side of the substrate, however, receiver sheets typically comprise a substrate supporting a receiving layer which layer presents a dye-receiving surface. The receiving layer typically comprises a dye-receptive polymer, a cross-linking agent and a release system.
Substrates conventionally employed in thermal transfer printing include thermoplastic films, for example polyethylene terephthalate, and laminated paper substrates.
Receiver sheets, for example in the form of a card, have found wide usage in security applications, for example credit cards, charge cards, identification cards, driving licences and passports.
Where the receiver sheet comprises a solid plastics substrate problems with security may be encountered where, on attempting to replace a layer on the sheet by delaminating the layers within the recording sheet, fracture tends to occur at the boundary between adjoining layers rather than through the substrate itself. Consequently there may not be significant evidence that the receiver sheet has been tampered with and thus a significant security risk my be presented. Laminated paper substrates also have a drawback in that they have relatively poor durability when exposed to solvents or water as may occur in for example flush cut card applications, that is where the edge of a card is removed during the production process and presents an exposed cross-section of the layers in the card.
U.S. Pat. No. 4,861,644 discloses the use of a micro-porous material as a printing substrate for printing inks. There is however no disclosure of such substrates being suitable for use with thermally transferable dyes in thermal transfer printing.
We have now found that drawbacks associated with prior art receiver sheets may be reduced by providing substrate comprising a porous plastics material.
According to a first aspect of the invention, there is provided a thermal transfer printing receiver sheet comprising a substrate having on one side thereof a dye receiving layer wherein the substrate comprises a porous plastics material having a network of interconnecting pores communicating throughout the substrate.
Such a substrate provides excellent durability and resistance to solvents or water as compared with laminated paper substrates. A significant practical benefit of these advantages is that the wear, ageing and handling characteristics of the receiver sheet are significantly improved.
Furthermore, the porous structure of the substrate employed in the present invention reduces the possibility of fracture occurring between adjacent layers of the receiver sheet in the event that delamination is attempted as the substrate itself may fracture internally before delamination occurs. Thus a greater degree of security is provided due to the reduced possibility of delamination of the layers of the receiver sheet, and also due to the evidence of tampering with the receiver sheet provided by the fracture substrate of the receiver sheet.
The substrate is preferably a single layer rather than a multi-layer laminate although a laminate may be employed as the substrate if desired. The preferred single layer substrate may comprise one porous plastics material or, if desired, a plurality of porous plastics materials which are suitably mixed or bl

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