Transfer band

Details Transfer band Transfer band

1997-06-10

2001-09-04

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S142000, C428S213000, C428S446000, C428S448000, C428S451000, C428S915000, C283S072000, C283S074000, C283S081000, C283S100000, C427S248100

Reexamination Certificate

active

06284396

ABSTRACT:

This invention relates to a multilayer material, in particular a transfer band, consisting of a carrier material and a one- or multilayer transfer layer containing an optically varying structure, and an intermediate layer located between the carrier band and the transfer layer, and to a method for producing this material.
With bank notes, identity cards, passports or similar documents it is necessary to take measures to increase security. Protection from imitation can be clearly increased if these documents are equipped with transfer elements having a hologram, diffraction grid or other effect varying with the viewing angle. For this purpose it is already known to apply holograms by the transfer method to cards, bank notes or other documents which must meet a high security standard.
The optically varying element, for example hologram, is usually transferred from a transfer band using pressure and heat. The transfer bands for transferring holograms consist of a carrier foil, a heat-activable release layer, a thermo-plastic lacquer layer with holographic embossing, an aluminized layer, a protective layer and a hot-melt adhesive layer. When the transfer hologram is transferred to the substrate the thermoplastic lacquer layer including the following layers is transferred to the substrate with the help of the hot-melt adhesive layer, while the carrier foil along with the thermally activable release layer are removed during the transfer process.
For many applications it has proved useful to use instead of the thermoplastic lacquer layer a lacquer which cures with the help of radiation. These lacquers have the advantage that they are not thermally deformable upon transfer to a substrate. So-called delayed-curing lacquers are often used whose curing is initiated e.g. by UV radiation. However, curing occurs only after a certain delay time. This permits the lacquer to be irradiated directly before embossing, to retain the necessary plasticity during then embossing process and to cure irreversibly directly after embossing independently without further method steps. since the irradiation and resulting high action of heat can also activate the release layer with this mode of operation, however, there is the great danger of the carrier layer coming off the transfer layer prematurely when the diffraction structure is being embossed in the lacquer layer. One therefore usually dispenses with a release layer completely in this procedure. But release layers have the function of facilitating detachment of, the transfer element from the carrier when the transfer element is transferred to a substrate. If a release layer is dispensed with, the property then lacking in the transfer band must be obtained in a different way. For example one can integrate the properties the release layer into the embossing lacquer layer.
EP 0 502 111 B1 describes :or this purpose a lacquer whose properties are modified in such a way that it is readily possible to emboss the lacquer layer without the lacquer coming off the carrier, while the lacquer is simultaneously easy to detach from the transfer foil when the element is transferred to a substrate.
Since the adhesion of the lacquer layer to the carrier foil depends essentially on the nature and pretreatment of the foil, the lacquer layer is adapted by additives to the particular plastic film used as a carrier layer.
This means that the embossing lacquer layer and the carrier layer must be coordinated to each other in such a way a: to fulfill the described conditions difficult to reconcile with each other.
Furthermore the adhesion coefficients of the lacquer layer on the carrier are often not constant even when the same carrier materials are used. The properties of the carrier foil are subject to accidental fluctuations, which may be caused e.g. by fluctuations in the conditions of production, the storage period, aging or the like. This leads to different adhesion coefficients of the carrier foil surface so that it is necessary to adapt the adhesion of the embossing lacquer layer to the carrier used, even when the same plastic carrier foil is used.
The problem of the invention is therefore to propose a transfer and with a carrier band and a transfer layer, and a method for producing it, whereby the carrier band has a defined adhesion to the transfer layer.
This problem is solved by the features of the independent claims. Special embodiments are the object of the subclaims.
The basic idea of the invention is to provide a defined adhesion of the carrier band to the transfer layer by pre-treating the carrier band. For this purpose the carrier band is provided with a thin metal or semiconductor oxide layer to which the transfer layer is then applied.
A special advantage of the inventive solution is the fact that application of the thin oxide layer decouples the adhesion of the carrier layer to the transfer layer from the surface properties of the carrier layer. Thus the transfer layer can be selected almost independently of the carrier band properties, without the desired adhesion coefficients being adversely affected. This is of course also the case with plastic carrier bands which are made of the same plastic material but come from different production batches. Application of a metal or semiconductor oxide layer to the carrier band creates particular defined adhesion conditions with the transfer layer located thereabove. The particular adhesion coefficient achieved is thus determined only by the adhesion of the transfer layer to the oxide layer, being between 15 and 80 mN/m, preferably between 30 and 38 mN/m.
Although many materials can be used for the carrier and, such as plastic, paper or silicone paper, in a preferred embodiment a carrier foil, for example a polyethylene terephthalate foil, is vaporized with a silicon oxide layer (SiO
x
). Since a mixture of SiO and SiO
2
is deposited on the carrier foil in this process, SiO
x
layer with 1<x<2 arises on the carrier foil. The thickness of the layer is selected is as to obtain a continuous area coating of the carrier foil, on the one hand, while the vaporized layer remains transparent, an the other hand. The silicon oxide layer is then coated with an embossing lacquer in which the desired hologram is provided e.g. with the help of an embossing roll in a further operation. After the embossing lacquer cures or crosslinks, the side bearing the hologram structure is provided with a metal layer. A mixed adhesive can optionally be applied to the metal layer.
The silicon oxide layer adjusts the adhesion coefficient of the transfer hologram to the carrier material just so that the hologram can be provided in the embossing lacquer layer without the transfer layer coming off the carrier. The hologram can accordingly be easily transferred to a substrate for example with a punch or pressing roll and easily detached from the carrier foil.


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