Transfer band

The invention relates to a multilayer foil, in particular a transfer foil. The transfer foil consists of a carrier. foil, a one- or multilayer transfer layer containing an optically variable structure, and an intermediate layer located between the carrier foil and the transfer layer, the intermediate layer being a metal oxide or semiconductor oxide layer.

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.sub.x). Since a mixture of SiO and SiO.sub.2 is deposited
 on the carrier foil in this process, SiO.sub.x layer with 1&lt;x&lt;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.

As shown in FIG. 1, one can use the inventive transfer fail to apply
 transfer element 15 a data carrier, in the present case bank note 16.
 Optically variable element 15 is executed in particular as a hologram and
 can he applied to the data carrier so as to extend from one lateral edge
 to the opposite lateral edge of the data carrier. Otherwise one can also
 employ so-called island solution, applying optically variable element 15
 at any place on the data carrier as a separate element. There are no
 restrictions on the form and size of the optically variable element so
 that the element can be adapted without difficulty to the particular
 desired design of date carrier.
 FIG. 2 shows schematically she basic principle of the inventive foil
 pretreatment for producing a transfer foil. Carrier foil 3 is wound on
 roll 2 and guided via vaporization unit 4 to second roll 1 on which the
 foil is rolled up again after application of the metal or semiconductor
 oxide layer. As a carrier foil one can use for example polyethylene
 terephthalate (PET), oriented polypropylene (OPP), oriented polyamide
 (OPA) or another sufficiently stable foil. In vaporization unit 4 the
 metal or semiconductor oxide to be applied, for example silicon monoxide,
 is heated and evaporated in a heatable pan. The SiO to be evaporated
 exists in the pan as brown powder. The particles passing into the vapor
 phase are deposited on the surface of the carrier fail, forming a thin
 film whose thickness depends an the transport speed of the carrier foil
 and the evaporation temperature. Although evaporation takes place in a
 vacuum, no pure silicon monoxide layer is deposited on the foil web. This
 is because oxygen from the existing residual air reacts with SiO to
 SiO.sub.2, so that a layer of a mixture of SiO ant SiO2, the so-called
 SiO.sub.x layer, is deposited on the surface of the foil web. Oxygen bound
 to the surface of the foil also makes a contribution to forming SiO.sub.2
 . Depending an the exide layer to be applied, the process parameters are
 selected so that layers are applied in a thickness of no more than 200 nm,
 preferably in a thickness of 60 to 100 nm. These thin layers have the
 advantage that they already form a sufficiently defined adhesion surface
 for the lacquer Layer to be applied later, on the one hand, and are
 transparent, on the other hand. They therefore do not influence the
 optical impression or be obtained by the transfer element. Unlike the
 evaporation temperatures of aluminum, those of silicon oxide are
 relatively high, i.e. generally between 1350 and 1400.degree. C., so that
 it is necessary to, cool rolls 1 and 2 during vaporizing of the oxide.
 The deposition rate of the oxide layer can be controlled for example by
 providing windows 6 and 7 in the evaporation unit. Through window 6 light
 ray 8 with intensity I.sub.0 from light source 5 is guided into the
 interior of evaporation unit 4. Depending an the quantity of particles
 rising due to evaporation, the incident light ray is scattered more or
 less diffusely so that intensity I.sub.0 is lowered by a certain amount.
 Intensity I.sub.1 emerging from window 7, or quotient I.sub.1 /I.sub.0 is
 a direct measure of the evaporation rate, which can then be regulated
 according to the particular requirements.
 Instead of using evaporation unit 4 shown in FIG. 2 one can also deposit
 the metal or semiconductor oxide layer on the carrier material from the
 vapor phase by other process techniques such as chemical precipitation.
 Evaporation unit 4 can also be executed as an electron-beam coating unit
 in which an electron beam is used as a heating source. The basically
 point-shaped electron beam is guided quickly across evaporation pan 9
 containing the oxide material to be evaporated. Electron-beam coating has
 the advantage that this technique permits coating of broad webs and the
 path speed can be increased.
 After the carrier foil is coated with the thin SiO.sub.x layer the one- or
 multilayer transfer layer is applied to this SiO.sub.x layer in a further
 operation. During production of hologram transfer layers an embossing
 lacquer layer is applied for this purpose to the SiO.sub.x layer, in which
 the particular desired holographic embossed structure is impressed. After
 that embossing lacquer layer cures of crosslinks, a metal layer is applied
 thereto in a further operation for clearly strengthening the optical
 impression of the embossed hologram. If necessary, the metal layer is
 provided with a hot-melt adhesive layer with which the transfer element
 can be glued directly to a substrate. One can dispense with this adhesive
 layer, however, if a suitable adhesive layer is applied to the substrate
 directly before application of the transfer element and the transfer
 element is transferred to the areas of the substrate coated with adhesive.
 In such cases it is favorable to use adhesives with delayed curing, i.e.
 whose curing is initiated for example by a UV lamp after application.
 The structure of the inventive transfer band is shown schematically in FIG.
 3. Thin semiconductor or metal oxide layer 11, for example a SiO.sub.x,
 magnesium oxide or aluminum oxide layer, is applied to carrier foil 10.
 This oxide layer bears transfer layer 15 to be transferred to the
 substrate, said transfer layer being executed in the present case as a
 multilayer layer. Transfer layer 15 consists of lacquer layer 12 in which
 holographic structure 14 is embossed. On the embossed site of the lacquer
 layer a metal layer is applied, preferably being vaporized. Depending on
 how the transfer layer is to be applied to the substrate, a further
 hot-melt adhesive layer not shown in FIG. 3 is applied to metal layer 13.
 The adhesive band between the carrier foil and the transfer layer is
 adjusted via oxide layer 11 in very exact and defined fashion. For a
 silicon oxide layer which is vaporized on an OPA foil, the adhesion
 coefficients an a UV lacquer layer printed an the oxide layer can be
 adjusted in the range between 15 to 50 mN/m, preferably from 30 mN/m to 38
 mN/m.
 However the invention is not restricted to providing a certain transfer
 layer, for example a hologram The inventive transfer hand can instead he
 used or transfer almost any layers to substrates. Along with the
 abovementioned holograms, one can also transfer smooth metallic surfaces,
 magnetic layers or surfaces with effect pigments to substrates such as
 paper, plastic or metal. From the point of view of security it is
 especially interesting to use layers with optically recognizable or
 optically variable properties and with machine-readable properties.
 The inventive transfer foil will be explained further by examples.
 EXAMPLE 1
 A 25 micron OPA foil is vaporized with silicon oxide (0.1 g/m.sup.2 to 0.25
 g/m.sup.2). or A UV-crosslinkable lacquer is then applied to the silicon
 oxide layer by one of the common techniques, for example printing. After
 holographic embossing and UV curing, the foil is vaporized with aluminum.
 After application of this transfer foil with a mixed adhesive the OPA
 carrier foil can be removed very easily without defects arising on the
 remaining hologram embossed layer.
 EXAMPLE 2
 A 25 micron OPA foil is vaporized with silicon oxide and coated with a
 thermoplastic lacquer. After holographic embossing with a heated embossing
 roll the foil is vaporized with A mixed adhesive is applied to the
 aluminum foil. Upon transfer of the transfer layer the CPA carrier foil
 can removed very easily without leaving any defects on the transfer layer.
 EXAMPLE 3
 A 25 micron CPA foil is vaporized with silicon oxide and coated with a
 cold-crosslinking lacquer. After the lacquer cures, the foil is vaporized
 with copper. With the help of a mixed which is applied directly to the
 substrate, the transfer element of the transfer foil is transferred to the
 substrate, whereby the CPA carrier foil Can be removed very easily. This
 produces a golden layer on the substrate.
 EXAMPLE 4
 A 12 micron PET foil is vaporized with silicon oxide and coated with a
 solvent-containing lacquer. After the lacquer dries, the foil is vaporized
 with aluminum. The application of the transfer element takes place as in
 Example 3 by applying a mixed adhesive directly to the substrate surface,
 then placing the transfer foil thereon and removing the carrier foil. This
 produces a silvery layer on the substrate.