HK1169082A - Transfer foil comprising optically variable magnetic pigment, method of making, use of transfer foil, and article or document comprising such - Google Patents

Description

Transfer foil containing optically variable magnetic pigment, methods of making, using, and articles or documents containing the same

Technical Field

The present invention is a technique in the field of transfer foils (decal transfer, decals, also known as metal foils) and its application to the protection of security documents and of such items. More particularly, it relates to optically variable decals or foils containing magnetically oriented optically variable pigment particles in an ink or coating, and their manufacture, use, and articles protected thereby.

Technical background-prior art

In 1989, optically variable transfer foils were introduced by the bank of canada on their 20$ banknotes. This foil, based on a vapor deposited multilayer thin film interference pattern, exhibits a gold to green color change when changing from a perpendicular to a tangential viewing angle. The transfer foil comprises five layers (ZrO)₂/SiO₂/ZrO₂/SiO₂/ZrO₂) Full dielectric interference films applied on dark backgrounds (Optically Variable Devices for Use on bank notes, j. rolfe, optical Variable Devices, proc. spie, volume 1210, 1990, pages 14-19; US 3,858,977; US4,626,445).

The bank in canada later replaced the five-layer all-dielectric interference film with a three-layer metal-dielectric-metal fabry-perot interference film, which was easier to manufacture, while having about the same color change, but higher light reflectance, and did not need to be applied on a dark background (US 4,705,300; US4,779,898; US5,648,165).

The multilayer thin film interference film is manufactured on a release-coated carrier, which may be a PET foil, in a roll vacuum coating machine. An adhesive layer is applied to the interference film and/or printed on the article or document at the location where the interference film is to be transferred, prior to application to the article (i.e., article or document). The interference film is then applied to the article or document by a transfer method such as hot or cold die, and the release coated carrier is then removed.

An important drawback of the optically variable transfer foil is its mechanical fragility. In fact, the applied interference film, unless specifically protected, can be easily broken and removed from the document, e.g. with the aid of a pencil eraser. For this reason, optically variable interference film transfer foils are eventually replaced by optically variable inks in currency applications.

In addition to the disadvantage of mechanical brittleness, the optically dryableFilm transfer foils also suffer from a lack of artistic design flexibility. The only possibility worth noting in this regard is to transfer a single type of interference pattern, displaying the determined "color" and "color change" properties, onto an article or document. The artistic freedom left by designers in this respect is limited to the choice of colors and color change properties, and the form of the pattern transferred. Efforts have been made to improve the limited design capabilities of optically variable interference film transfer foils by additional embossing of the applied thin film pattern (securitrafix of Security foil)^TMEquipment, uk), but the artistic effects obtainable are still not good.

The mechanical fragility of optically variable transfer foils, as well as the inherent artistic design limitations, are overcome by the use of Optically Variable Inks (OVI) in combination with suitable printing techniques (U.S. Pat. No. 4,434,010; U.S. Pat. No. 5,059,245; U.S. Pat. No. 5,084,351; U.S. Pat. No. 5,171,363; U.S. Pat. No. 5,653,792 and EP 0227423 (Phillips et al)). The optically variable ink includes Optically Variable Pigments (OVP) in a flake shape having a symmetrical type (e.g., Cr (3.5 nm)/MgF) by pulverization₂(200nm)/Al(60nm)/MgF₂(200nm)/Cr (3.5nm) layer sequence) of a vacuum deposited 5-layer fabry-perot interference film. The flake-shaped particles have a diameter typically between 10 and 50 μm and a thickness typically between 0.5 and 5 μm.

The outermost two metal layers of the interference film are implemented as semi-transparent/semi-reflective layers and the middle metal layer is implemented as a fully reflective, opaque layer. The color and color variation with viewing or incident angle of the interference film is determined by the thickness and refractive index of the dielectric layer, and the optical properties of the material used to make the interference film. The term "absorbing layer" is also used in the art to denote such a semi-transparent/semi-reflective layer.

To produce Optically Variable Inks (OVI), at least one type of Optically Variable Pigment (OVP), if desired together with other pigments and/or dyes and/or printing additives, is mixed into an ink binder containing at least one resin. The optically variable ink thus obtained, if desired in combination with other inks, can be printed in the form of an image, indicia or pattern on a substrate, which may be a security document or a general-purpose article.

Interesting artistic designs can then be realized by appropriately combining different inks to form the printed image using standard printing techniques and existing printing equipment. Optically Variable Inks (OVI) were first printed on currency in Thai (1987, 60 Thai coin monuments) and then have application in both Germany and French (1000 German Mark: 27.10.1992; 50 French Fang: 20.10.1993); it is now adopted as the standard on most currencies in the world.

Optically Variable Magnetic Inks (OVMI), including Optically Variable Magnetic Pigments (OVMP), are used in further developments in the field of optically variable security features. Such pigments have been described in e.g. US4,838,648; WO 02/073250; EP 686675; WO 03/00801; US6,838,166; is disclosed in WO 2007/131833. Optically variable pigment particles in optically variable magnetic inks can be oriented after printing by applying a suitable unstructured (i.e. homogeneous) or structured (i.e. variable in space) magnetic field and then fixing them in their respective positions and orientations by hardening the printed ink composition on the substrate. "oriented" optically variable magnetic inks are currently used on banknotes (Olympic Association 2008 Chinese memorial (10 Renminbi) and Australian memorial (20 Australian), Kazakhstan memorial (5000 Teng)).

Oriented materials and techniques for magnetic particles in coating compositions, and corresponding combined printing/magnetic orientation processes, have been described in US2,418,479; US2,570,856; US 3,791,864; DE 2006848-A; US 3,676,273; US5,364,689; US6,103,361; US 2004/0051297; US 2004/0009309; EP-A-710508, WO 02/090002; WO 03/000801; WO 2005/002866, and US 2002/0160194, and co-pending application PCT/IB2008/003406 of the same applicant.

The ink may further be used as a suitable vehicle (vector) in combination with additional, specifically designed overt (i.e. visible to the human eye) and/or covert (i.e. invisible to the human eye) security elements (markings), such as luminescent materials, or forensic tracers, which allow the authenticity determination (authentication) of documents so marked.

It is important in the security document printing industry to provide a secure supply chain to prevent counterfeiting and diversion of the security documents produced, as well as the key materials used to produce them.

For these reasons, Optically Variable Inks (OVI) and Optically Variable Magnetic Inks (OVMI) for printing banknotes and similar security documents are exclusively supplied to a limited, trusted printing house selected from the highly secure banknote printing houses established in the world.

On the other hand, optically variable security elements have considerable market potential on many documents other than banknotes, such as transportation tickets, event tickets, tax excise tickets, credit cards, access cards, certificates, tax labels, and the like, which are generally not printed by a trusted cash printer but by one of numerous other security printers that are not necessarily equipped with Optically Variable Ink (OVI) or Optically Variable Magnetic Ink (OVMI). There is therefore a long felt need to serve this market, and it is to this need that the present invention addresses.

Disclosure of Invention

The present invention provides transfer foils (decal, also known as metallic foils) containing oriented optically variable magnetic pigment particles in a binding resin, preferably in the form of optically variable magnetic inks or coatings (OVMI), as disclosed and defined in the detailed description, drawings and claims below. The transfer foil is a semi-finished product and can be manufactured in a dedicated secure printing environment (provided for the printing and orientation of optically variable magnetic inks) and it can be applied to security documents or general-purpose articles in a different environment (provided for the application of the transfer foil).

The transfer foil of the present invention provides a greater degree of customization freedom in that it can be uniquely specified and designed for each given application. The present invention also reduces the misuse (transfer) of optically variable magnetic inks that can occur outside of the private security printing environment while maintaining the potential for the application of optically variable magnetic features on documents or articles that are not typically produced in the private security printing environment.

The transfer foil of the present invention further provides a highly secure optically variable element that is easily identifiable by the individual eye and cannot be easily counterfeited with commonly available devices.

According to the invention, a transfer foil (decal transfer, decal paper, also known as metal foil) comprises a release-coated carrier (1), and a transfer coating (transferable portion) (3) in the form of a design disposed on the carrier, and is characterized in that the transfer coating (3) contains oriented optically variable magnetic ink (OVMP) particles. An adhesive layer (4) known from the prior art may additionally be provided on the transfer coating (3).

The transfer coating (3) comprising oriented optically variable ink magnetic pigment particles in a binding resin may further be a combined layer comprising a layer or part of a layer not made with optically variable magnetic ink, but an integrated part of the design (i.e. the transferable part of the transfer foil).

The transfer coating carrying the design, which may be an image, indicia or pattern, may then be transferred to a substrate, such as a security document (e.g., a banknote, passport, identification card, access card, driver's license, credit card, voucher, transportation ticket, event ticket, tax label), or a general purpose article or document (e.g., a merchandise label or commercial good) in a hot or cold die process as is known in the art. After the transferable portion of the transfer foil is transferred to the document or article, the carrier is removed from the applied transfer coating.

Detailed Description

The transfer foil of the present invention comprises oriented optically variable magnetic ink (OVMP) particles, preferably contained in a cured Optically Variable Magnetic Ink (OVMI) or coating.

Transfer foils and decals are known to the person skilled in the art of images and decoration and are used for transferring pre-manufactured marks, images or patterns onto products such as textiles, documents or the like (US 5,393,590; US5,681,644; US5,925,593, US6,808,792, EP 0538358; EP 0538376). These indicia, images or patterns are thus pre-formed as mirror images on a release-coated intermediate carrier (such as a plastic wave or transfer paper) by printing and/or other application techniques, and transferred to the target item in a second step by a suitable transfer technique, such as a hot or cold die. Finally the intermediate carrier is removed leaving a clean transferable layer carrying the indicia, image or design on the target item.

In the context of the present disclosure, design shall mean anything that can be produced by a printing or coating process (including vacuum coating, pre-or post-processing, and magnetic pigment orientation).

In the context of the present description, oriented Optically Variable Magnetic Pigment (OVMP) particles refer to pigment particles present in the image layer in an orientation that is different from the orientation that they would assume as a result of a simple printing process. In the context of the present invention, the oriented pigment particles are obtained by applying a uniform, or suitably structured, external magnetic field to the newly applied coating and then fixing the pigment particles in their respective positions by a hardening (solidifying, drying, curing) process (as disclosed in EP 1641624B 1 and WO 2008/046702 a 1).

Preferably, the pigment particle orientation represents an image, indicia, or pattern.

Preferably, the Optically Variable Magnetic Pigment (OVMP) is a magnetic thin film interference pigment selected from the group consisting of: Fabry-Perot interference pigments and all-dielectric, refractive index-modulated interference pigments. By containing at least one magnetic or magnetizable material in at least one of its constituent layers, magnetic properties can be imparted to the pigment particles.

Most preferably, the Optically Variable Magnetic Pigment (OVMP) is selected from the group consisting of: a pigment comprising 5 layers in the order of an absorbing layer, a dielectric layer, a reflective layer, a dielectric layer, an absorbing layer, wherein the reflective layer and/or the absorbing layer is a magnetic layer, and a pigment comprising 7 layers in the order of an absorbing layer, a dielectric layer, a reflective layer, a magnetic layer, a reflective layer, a dielectric layer, an absorbing layer.

The binding resin of the transfer coating (3) is advantageously selected from the group consisting of: thermoplastic resins, photocurable resins, electron beam curable resins, and thermosetting resins.

Preferably, the transfer foil additionally comprises, at least on extended portions of said transfer coating, a layer (4) of a thermally or radiation activatable (active-able) adhesive. Most preferred are heat activatable adhesive layers selected from the group consisting of: naturally occurring, and synthetic thermoplastic resins. Examples of thermoplastic resins are shellac, phenol-formaldehyde resins, vinyl acetate-vinyl resins, polyamides, polyvinyl chloride, acrylic resins, polyurethane-acrylates, polyester acrylic, polysiloxane acrylic, and the like.

In the temperature range for hot-molding applications (i.e., 65 ℃ to 180 ℃, most preferably 80 ℃ to 120 ℃), the thermoplastic resin should become tacky. It is further preferred that these thermoplastic resins irreversibly cross-linked in the fused state provide a permanent fixation of the transferred coating on the final substrate.

As known to the skilled person, the chemistry of the adhesive must be adapted to the chemistry of the substrate on which the transfer foil is applied. Although the choice of suitable glues falls outside the scope of the present invention, it is known to the skilled person that for application on a paper substrate, the binder must have hydrogen bonding capability, i.e. contain hydrogen bonding functional groups such as phenols, carboxylic esters, amino compounds, urethanes, etc.

In certain cases, an intermediate layer is required between the transfer coating (3) and the adhesive layer (4) to provide sufficient adhesion at this interface; optionally, the chemistry of the transfer coating (3) can also be modified to securely bond to the selected bonding layer (4).

Alternatively, the transfer coating (3) itself may be realized as a thermoplastic layer and transferred directly to the substrate by means of a hot stamp. However, this combination is not preferred, provided that the magnetic orientation of the pigment particles in the transfer coating (3) will be lost more or less under the effect of heat.

In another contemplated embodiment, the transfer foil additionally comprises, at least on its extension, a top coating (6) arranged between the release-coated carrier (1) and the transfer coating (3).

In another contemplated embodiment, the transfer foil additionally comprises, at least on the extension thereof, a base coating (6') provided on the transfer coating (3) or between the transfer coating (3) and the adhesive layer (4).

The transfer coating (3) of the transfer foil according to the invention is in the form of a design, preferably a composite layer, comprising layers or parts of layers which are not manufactured with optically variable magnetic inks. The combined layer thus has at least one region printed with a first ink containing oriented optically variable magnetic pigments and at least one further region printed with a second ink containing other types of pigments and/or dyes.

The other types of pigments and/or dyes may include, notably, non-magnetic optically variable pigments, transparent optically variable pigments, additive-color-mixed pigments, rainbow pigments, liquid crystal polymer pigments, metallic pigments, magnetic pigments, UV, visible or IR absorbing pigments, UV, visible or IR emitting pigments, UV, visible or IR absorbing or emitting dyes, and mixtures thereof.

The additive-color-mixed pigment is an optically opaque reflective pigment that selectively reflects a defined portion of the visible spectrum while masking all reflections from the background. Such pigments may be realized by chromatic metallic pigments or by opaque interference pigments. The color metallic pigment is not optically variable. Interference pigments that rely on high index dielectric materials (n is greater than 2) generally exhibit small, negligible color change with viewing angle and therefore do not appear to be optically variable. Interference pigments relying on low index dielectric materials (n being less than 1.65) generally exhibit a perceptible color change with viewing angle and thus appear optically variable. The optical variability of the boundary conditions between these refractive index limits must be individually judged at the sensitivity of the particular color of the pigment to the viewing angle; yellow is more sensitive than, for example, blue or red.

In the transfer foil according to the invention, the top coat (6) or the bottom coat (6') may further be a metal layer; and the metal layer may additionally represent or carry a mark.

Finally, the ink layer (3) containing optically variable magnetic pigments may further contain other types of pigments and/or dyes, such as second type of optically variable magnetic pigments, non-magnetic optically variable pigments, transparent optically variable pigments, rainbow pigments, liquid crystal polymer pigments, magnetic pigments, metallic pigments, pigments or dyes further emitting light in the visible and/or IR spectral region, absorbing pigments or dyes, and mixtures of the above. It may further carry a specially designed overt (i.e. visible to the human eye) and/or covert (i.e. invisible to the human eye) security element (marking), such as a luminescent material, or forensic tracer, which allows the authenticity determination (authentication) of a document so marked.

Further disclosed is a process for making an optically variable transfer foil, the process comprising the steps of:

a) providing a release-coated carrier (1);

b) optionally coating the carrier (1) with a top coating layer (6);

c) applying a transfer coating (3) containing magnetic or magnetizable optically variable pigment particles (5) on the release-coated carrier (1) or the top coating layer (6);

d) magnetically orienting the magnetic or magnetizable optically variable pigment particles (5) in the applied transfer coating (3) by applying an unstructured or suitably structured magnetic field;

e) hardening the transfer coating (3) containing the oriented optically variable pigment particles, thereby fixing them in their respective positions and orientations;

f) optionally coating the transfer coating (3) with a base coating (6').

In a particularly preferred embodiment, the process comprises the additional steps of:

g) applying an adhesive layer on the transfer coating (3) or the base coating (6').

Also disclosed is a process for protecting a document or article using a transfer foil according to the invention, said process comprising the steps of:

a) applying a transfer coating (3) from a transfer foil according to the invention on a document or article using an application method selected from hot or cold stamping;

b) removing the carrier (1) from the applied transfer coating (3).

The optically variable transfer foil according to the invention can be used for the protection of documents, such as banknotes (banknotes), passports, identity or access cards, driving licenses, credit cards, vouchers, transportation tickets, event tickets, tax labels, further for the protection of articles such as articles or commercial goods, etc., by applying a transfer coating (3) from the transfer foil on the document, the goods or the article.

Also disclosed is a document carrying a transfer coating (3) according to the invention, such as a banknote, passport, identification or access card, driver's license, credit card, voucher, transportation ticket, event ticket, tax label, or article such as an article or commercial good.

The transfer foil according to the invention, its production and its use will now be explained further with reference to the figures and the exemplary embodiments.

Fig. 1 shows a first embodiment of a transfer foil according to the invention, comprising a release-coated (2) carrier (1) and a transfer coating (3) containing oriented optically variable magnetic pigments (5).

Fig. 2 shows a second embodiment of a transfer foil according to the invention, additionally comprising an adhesive layer (4).

Fig. 3 shows a third embodiment of a transfer foil according to the invention, additionally comprising a top and/or bottom coating (6, 6').

Fig. 4 shows a fourth embodiment of a transfer foil according to the invention, additionally comprising a top and/or bottom coating layer (6, 6') and an adhesive layer (4).

Fig. 5 shows a further embodiment of a transfer foil according to the invention having a composition transfer coating (3) with areas printed with a first ink containing oriented optically variable magnetic pigments and areas printed with a second ink containing other types of pigments and/or dyes.

Fig. 6 shows the transfer foil of fig. 2 applied to a substrate (S), with the carrier (1) removed.

Fig. 7 shows a photograph of a transfer foil produced according to the example given below, seen from the printed side of the carrier. The cured ink sheet on the release coated substrate showed an image of the reversed letter "a".

Fig. 8 shows a photograph of a transfer foil according to the examples given below after application to a substrate.

The optically variable transfer foil according to the invention comprises, with reference to fig. 1 to 4, a carrier (1) having a release coating (2) applied on its surface, and a transfer coating (3) containing an oriented Optically Variable Magnetic Pigment (OVMP) (5) on said release coating (2). A heat-activatable or otherwise activatable adhesive layer (4) may be provided on the transfer coating (3). One or more additional top coats (6) may be provided between the release coating (2) and the transfer coating (3), i.e. on top of the transfer foil. Further, a base coat (6') may be provided on the transfer coat (3) or between the transfer coat (3) and the adhesive layer (4), respectively.

The foil is preferably applied onto the substrate (S) by a transfer method selected from hot and cold stamping, optionally in combination with a curing step. After application of the foil, the carrier (1) with the release coating (2) is removed, leaving behind the transfer coating (3), or in some cases the top coating (6), exposed at the surface of the substrate (S).

The optically variable transfer foil according to the invention may thus be a hot die foil, in which case one of the transfer coating layer (3) or the adhesive layer (4) must be a thermoplastic layer or a heat-activatable adhesive layer. The transfer coating (3) and/or the adhesive layer (4) may also include radiation-curable functionality that can be ultimately hardened (cured) by UV or electron beam irradiation of the companion following or as the transfer coating is applied to the document or object.

The support (1) may be selected from paper or plastic (e.g., PET), as known to those skilled in the art. The release coating (2) may be a siliconized coating such as known in the art. Siliconized surfaces are considered to be detachably bonded to all kinds of coatings applied to these surfaces. Siliconized papers and waxed papers are known to the skilled person as suitable substrates for the manufacture of transfer foils.

Referring to fig. 5, and in a particularly preferred embodiment, the transfer coating (3) is a composite layer comprising areas printed with "oriented" optically variable magnetic ink (9, 9 ', 9 "), and areas printed with inks (7, 7 ', 7", 7 "') containing other types of pigments and/or dyes, depending on the design of the transfer foil. A metallized surface (8, 8') may further be provided on or in the transfer coating (3), which may further carry or represent indicia. The optically variable magnetic ink (9 ") may further contain other types of pigments and/or dyes (10).

These other types of pigments and/or dyes (10), as well as other types of pigments and/or dyes in the ink (7, 7 ', 7 ", 7"') may be selected from spectrally selective absorbing pigments, spectrally selective reflecting pigments, spectrally selective emitting (luminescent) pigments in the UV (300-. These pigments may further be selected from magnetic pigments, and selective tracer pigments. For useful pigments and dyes, the skilled worker is also referred to O.L ü ckert's Pigment + F ü llstoff Tabellen, fifth edition, Laatzen, 1994, which is incorporated herein by reference.

Optically variable magnetic inks (9, 9', 9 ") preferably include those described in, for example, US4,838,648; WO 02/073250; EP 686675; WO 03/00801; US6,875,522; US6,838,166; and optically variable magnetic or magnetizable pigment particles of the type disclosed in WO 2007/131833.

The most preferred pigments to be used in the present invention are 5-layer fabry-perot interference film pigments in the form of flakes according to US4,838,648, of the symmetrical (absorption/dielectric/magnetic/dielectric/absorption) type, having e.g. Cr (3.5nm)/MgF₂(200nm)/Ni(100nm)/MgF₂(200nm)/Cr (3.5nm) layer sequence, or flake-shaped symmetrical (magnetic absorption/dielectric/reflection/dielectric/magnetic absorption) type 5-layer Fabry-Perot interference film pigment having, for example, Ni (5nm)/MgF₂(250nm)/Al(40nm)/MgF₂(250nm)/Ni (5nm) layer sequence, or a 7-layer Fabry-Perot interference film pigment in the shape of a thin plate according to US6,875,522, is of the symmetrical (absorption/dielectric/reflection/magnetic/reflection/dielectric/absorption) type, having for example Cr (3.5nm)/MgF₂(200nm)/Al(40nm)/Ni(100nm)/Al(40nm)/MgF₂(200nm)/Cr (3.5 nm).

In this 5-layer structure, the intermediate magnetic layer must also have appreciable light reflective properties to provide the light interference coloration of the pigment. Alternatively, a thin outer absorbing layer may provide magnetic properties to the 5 layers of pigment. This limits the number of useful materials for making the magnetic layer(s). In the 7-layer structure, a magnetic material can be selected irrespective of its light reflective properties, which provides a greater degree of freedom in the selection of a material having suitable magnetic properties. Of course, the pigment structure may include additional layers that provide pigments with supplemental or enhanced functionality.

In the most preferred embodiment, the colour-generating, optically variable structure of the pigment is of the reflective/dielectric/reflective fabry-perot type, wherein at least one of the reflective layers (which may be a metal layer) is partially light-transmissive to allow light to enter the fabry-perot structure from the outside and to generate interference. In an alternative embodiment, the color producing, optically variable structure of the pigment is of the all dielectric refractive index modulation type, comprising alternating layers of material having different refractive indices. An example of such a structure, the output of which is a gold-to-green change with viewing angle, comprises a layer sequence of ZrO₂(75nm)/SiO₂(302nm)/ZrO₂(75nm)/SiO₂(302nm)/ZrO₂(75nm)。ZrO₂And SiO₂Having refractive indices of 2.2 and 1.54, respectively. The skilled person may refer to "Optical Thin-Film Security Devices" by j.a.dobrowolski, in "Optical document Security", r.l.van renewse, second edition, Artech House press, london, 1998, chapter 13, page 289-. In all cases, there must be appropriate settings to impart the desired magnetic properties to the pigment particles. This can be achieved if they contain at least one magnetic or magnetizable material in at least one of their constituent layers.

A particular case of stable, index-modulated, fully dielectric color-generating structures are Cholesteric Liquid Crystal Polymers (CLCP), for example from US5,798,147, US6,899,824, WO 2008/000755 a1, EP 1213338B 1; EP 0685749B 1; DE 19922158 a 1; EP 0601483 a 1; DE 4418490 a 1; EP 0887398B 1, WO2006/063926, U.S. Pat. No. 5,211,877, U.S. Pat. No. 5,362,315 and U.S. Pat. No. 6,423,246. CLCP pigments containing magnetic materials and CLCP-coated magnetic core particles may also be used as optically variable magnetic pigments in the present invention.

Most preferably, screen printing is used to apply the optically variable ink (OVMI). It is worth noting that screen printing allows the application of the required coating thickness, in the order of 10 to 50 μm, in a simple and fast manner. However, with the required skill, other printing processes can be used for the same purpose, worth mentioning intaglio, flexographic and gravure printing processes.

The magnetic or magnetizable pigment particles in the ink are oriented by the application of an unstructured or suitably structured magnetic field, either concomitantly with or after the application or printing of OVMI, as is known in the art.

The ink containing the oriented magnetic or magnetizable particles is then hardened to fix the particles in their respective orientations and positions. Suitable curing, drying or curing mechanisms are known to those skilled in the art and the ink may be designed according to the available drying/curing equipment. Preferred curing processes in the context of the present invention are curing by radiation (i.e. photo-curing or electron beam curing), most preferably by UV-curing. UV curing has the advantage of leading to fast hardening, allowing the highest production speeds at moderate equipment costs.

The additional coating (6, 6') or adhesive layer (4) between the release coating (2) and the transfer coating (3), or between the transfer coating (3) and the substrate (S), may be of any type known and used by the person skilled in the art. In particular, the coating (6, 6') can be selected as a metal layer, which additionally represents or carries the marking. Such indicia may be implemented in the metal layer, for example, by selective etching, embossing, or printing.

Depending on the application process, the transferred pre-manufactured transfer coating (3) on the document or article may be subjected to a pre-treatment, such as an additional curing by treatment with chemicals and/or radiation (UV, electron beam) or painting with a suitable protective lacquer.

Exemplary embodiments of the invention

Transfer foil containing pulverized thin film Fabry-Perot type oriented optically variable magnetic pigment

UV-curing screen-printing inks containing optically variable magnetic pigments were formulated (by weight) as follows:

epoxy acrylate oligomer (i.e., Sartomer CN120A75)	40％
		Trimethylolpropane triacrylate (TMPTA) monomer (1)	10％
Tripropylene glycol diacrylate (TPGDA) monomer (2)	10％
		Genorad 16(Rahn)	1％
Aerosil 200(Degussa-Huels)	1％
		Irgacure 500(CIBA)	6％
Genocure EPD(Rahn)	2％
		Pigment (#)	20％
Dowanol PMA	10％

(1) Industrial commodity (e.g., Sartomer SR351)

(2) Industrial commodity (e.g., Sartomer SR306)

(#) pigment: magenta-to-green 5-layer optically variable magnetic pigments, available from FLEX Products, JDS Uniphase, Santa Rosa, Calif., USA.

(#) for making other inks, this pigment was replaced with the same weight of other pigment(s).

The pigment is stirred into the homogeneous mixture of resin and additive. Dowanol PMA/fused silica was used to adjust the viscosity to a target viscosity (Brookfield) between 500 and 800 mPa.s.

Magenta-to-green optically variable magnetic ink was screen printed in circular patches on silicone release coated paper carriers using a pore size of 70 wires/cm (openings of screen cells about 80 microns). After printing, the wet-printed ink sheet on the carrier is exposed to an engraved permanent magnet plate according to EP 1641642B 1, which permanent magnet plate is temporarily placed under the imprinted carrier for this purpose. The permanent magnet plate is a plate of "plastic to iron" (Plastoferrite), magnetized in a direction perpendicular to the engraved surface, and engraved to a depth of 0.3mm in the form of the inverted letter "a". After exposure to the magnetic field of the engraved permanent magnet plate, the ink sheet is hardened (cured) under UV light (two 200W/cm lamps), thereby irreversibly fixing the position and orientation of the optically variable magnetic pigment particles in the ink matrix.

It is noted that all printing and magnetic orientations must be done in the mirror-inverted orientation to allow the design to be properly displayed after the transferable portion of the foil is applied to the substrate.

A thermoplastic adhesive coating (commercial 1: 5 shellac in ethanol (shellac) and viscosity adjusted to 800mpa.s with ethanol/fused silica) was applied in a further step by screen printing on top of the UV-cured ink sheet. After drying, the printed sheet had the appearance shown in fig. 7.

The printed sheets were transferred to white, untreated paper under laboratory conditions (using hot iron at 120 ℃) and the release-coated paper carrier was removed. The transferred sheet has the appearance shown in fig. 8.

In a similar manner, a composition transfer coating can be made having areas printed with an "oriented" optically variable magnetic ink, and areas printed with a second ink containing other types of pigments and/or inks.

A specific example of an optically variable magnetic ink containing circular patches of "magenta to green" is oriented to display the letter "a" in the above example, but surrounded by an annular region of magenta ink, color matched, so that the same color as the optically variable ink is displayed when viewed from normal incidence. The two inks are printed in two successive screen printing processes each followed by a UV cure.

In a variation of this example, a surrounding annular region is printed with a second optically variable ink having a lower color variation as a function of viewing angle than the "magenta to green" optically variable magnetic ink, and the annular region is, for example, matched to the reflection spectrum of a letter at an oblique viewing angle of 40 °, as disclosed, for example, in co-pending application PCT/IB2008/002620 of the same applicant.

In yet another example, a metallic ink (containing aluminum pigment) may be screen printed on a silicone release coated paper carrier in the form of a signature mark. After curing the printed metallic ink, magenta-to-green optically variable magnetic ink is screen printed in the form of circular patches on the signature marker and magnetically oriented to reproduce the image of the signature marker. After UV curing, a heat activatable adhesive layer is applied over the optically variable magnetic ink and the printed flakes are thermally transferred to an uncoated paper substrate, such as disclosed above.

Claims (16)

1. Transfer foil comprising a release-coated carrier (1) and a transfer coating (3) in the form of a design on said carrier, characterized in that the transfer coating (3) contains oriented Optically Variable Magnetic Pigment (OVMP) particles.

2. The transfer foil according to claim 1, wherein the pigment particle orientation represents an image, a mark or a pattern.

3. Transfer foil according to one of claims 1 to 2, wherein the Optically Variable Magnetic Pigment (OVMP) is a thin film interference pigment selected from the group of: Fabry-Perot type interference pigments and refractive index modulation type interference pigments.

4. Transfer foil according to one of claims 1 to 3, wherein the Optically Variable Magnetic Pigment (OVMP) is selected from the group of: a pigment comprising a 5-layer sequence of an absorbing layer, a dielectric layer, a reflecting layer, a dielectric layer, an absorbing layer, wherein the reflecting layer and/or the absorbing layer is a magnetic layer, and a 7-layer sequence of an absorbing layer, a dielectric layer, a reflecting layer, a magnetic layer, a reflecting layer, a dielectric layer, an absorbing layer.

5. Transfer foil according to one of claims 1 to 4, characterised in that the binding resin of the transfer coating (3) is selected from the group: thermoplastic resins, photocurable resins, electron beam curable resins, and thermosetting resins.

6. Transfer foil according to one of claims 1 to 5, characterized in that a heat-or radiation-activatable adhesive layer is additionally included at least on a part of the transfer coating.

7. Transfer foil according to one of claims 1 to 6, characterized in that it additionally comprises, at least on a part of the transfer foil, a top coating (6) which is arranged between the release-coated carrier (1) and the transfer coating (3).

8. Transfer foil according to one of claims 1 to 7, characterized in that, at least on a part of the transfer foil, additionally comprises a bottom coating (6') provided on the transfer coating (3) or between the transfer coating (3) and the adhesive layer (4).

9. Transfer foil according to one of claims 1 to 8, characterised in that the transfer coating (3) is a composite layer having areas printed with a first ink containing oriented optically variable magnetic pigments and areas printed with a second ink containing other types of pigments and/or dyes.

10. Transfer foil according to one of claims 1 to 9, characterized in that the top coat (6) or the bottom coat (6') is a metal layer.

11. Transfer foil according to claim 10, characterized in that the metal layer represents or carries indicia.

12. A process for manufacturing an optically variable transfer foil, comprising the steps of:

a) providing a release-coated carrier (1);

b) optionally coating the carrier (1) with a top coating layer (6);

c) applying a transfer coating (3) containing magnetic or magnetizable optically variable pigment particles (5) on the release-coated carrier (1) or the top coating layer (6);

d) magnetically orienting the magnetic or magnetizable optically variable pigment particles (5) in the applied transfer coating (3) by applying an unstructured or suitably structured magnetic field;

e) hardening the transfer coating (3) containing the oriented optically variable pigment particles, thereby fixing them in their respective positions and orientations;

f) optionally coating the hardened transfer coating (3) with a base coating (6').

13. The process of claim 12, further comprising the additional step of:

g) applying an adhesive layer on the transfer coating (3) or the base coating (6').

14. A process for protecting a document or article, the process comprising the steps of:

a) use is made of a compound selected from the group consisting of: method of application of a hot or cold die, applying a transfer coating (3) from a transfer foil according to one of claims 1 to 11 on said document or article;

b) removing the carrier (1) from the applied transfer coating (3).

15. Use of an optically variable transfer foil according to one of claims 1 to 11 for the protection of documents, banknotes, passports, identification cards, access cards, driver's licenses, credit cards, vouchers, transportation tickets, event tickets, tax labels, articles of manufacture or commercial goods.

16. Document, banknote, passport, identity card, access card, driver's license, credit card, voucher, transportation ticket, event ticket, tax label, article or commercial good carrying a transfer coating (3) from a transfer foil according to one of claims 1 to 11.