This invention relates generally to security devices incorporated into paper banknotes, in particular the use of a xe2x80x9cthreadxe2x80x9d which is made part of the paper banknote.
Threads have been used as a security device in paper banknotes for some time. A typical conventional thread is composed of metallized PET (Polyethylene Terephthalate), i.e. a PET carrier layer supporting a metallic layer. The thread is typically either woven into the paper of the banknote, or hot foil stamped onto the banknote. In this specification, the word xe2x80x9csubstratexe2x80x9d will be used to refer to the web or other receiving sheet, including paper banknotes.
In one prior application where the thread is stamped onto the substrate under the application of heat and pressure, the PET carrier layer is stripped away from the metallized film after the thread has been applied. Alternatively, the PET carrier layer and the metallized film may, as a final step, be applied together to the substrate under the application of heat and pressure. In the first case the PET carrier layer is stripped away after the metallized film has been applied to the substrate, while in the second case it is not. The foregoing two alternatives have certain disadvantages. In the first, the heat sensitivity of the substrate may make it impossible to hot foil stamp the thread reliably. And in the second case, where the PET carrier layer and the metallic film are applied together to the substrate as a final step, the added thickness due to the PET carrier layer may cause web winding and sheet stacking problems if it is applied, for example, to a roll of paper or plastic film.
The present invention provides key improvements in the make-up of the thread, and to a standard thread application machine used previously to apply adhesive-coated threads to a substrate. With these improvements, the machine becomes capable of applying pressure-sensitive security threads onto a plastic or paper substrate, without the application of heat and without the PET carrier layer being applied.
Accordingly, this invention provides, for application to a substrate, a security thread comprising:
a carrier layer having opposed surfaces,
a first release layer on one of said surfaces,
a second release layer on the other of said surfaces,
a metallic layer outward of said first release layer, and
an adhesive layer outward of said metallic layer.
Further, this invention provides a method of securing a metallic layer to a substrate, comprising:
providing a security thread which consists of
a carrier layer having opposed surfaces,
a first release layer on one of said surfaces,
a second release layer on the other of said surfaces,
a further layer outward of said first release layer, said further layer being said metallic layer, and
an adhesive layer outward of said metallic layer;
bringing said substrate into contact with said adhesive layer and causing the adhesive layer to bond the metallic layer to the substrate, and
peeling the carrier layer away, so that it separates from the metallic layer at said first release layer.
Finally, this invention provides an apparatus for securing a metallic layer to a substrate, the metallic layer being part of a security thread which includes:
a carrier layer having opposed surfaces,
a first release layer on one of said surfaces,
a second release layer on the other of said surfaces,
a further layer outward of said first release layer, said further layer being said metallic layer, and
an adhesive layer outward of said metallic layer;
the apparatus comprising:
means for bringing said substrate into contact with said adhesive layer in order to cause the adhesive layer to bond the metallic layer to the substrate, and
means for peeling the carrier layer away, so that it separates from the metallic layer at said first release layer.