Hot stamping is a rather old process. In general terms, it is used to selectively transfer portions of a previously prepared foil or other layer from a film to the surface of a substrate by the application of heat under pressure. This transfers a portion of the film onto the substrate in the form of alphanumeric characters, graphic designs, etc. This transfer is of the well defined physical characteristics of the specially prepared hot stamping film.

In recent years, with modern technical improvements, hot stamping has become an alternative method of printing and is successfully performed on a very wide variety of substrates, such as, paper, textiles, leather, plastic, wood, metal, etc.

The hot stamping process has evolved from ancient times where thin gold leaves were stamped on high value bookbindings or furniture. Presently, highly sophisticated stampings using properly structured hot stamping films, allows for the transfer of highly sophisticated and complex patterns and film structures that can even result in colorful diffraction gratings and holographic prints onto a wide variety of surfaces.

Since hot stamping is often associated with relatively highly priced and high profile products, it has become desirable to introduce security features into hot stamping films in such a way that an authentic product that is carrying the specially treated hot stamp element can be authenticated simply by verifying the authenticity of the hot stamped element itself.

SUMMARY OF THE INVENTION The object of the present invention is to provide a security system and a method that can be integrated into the manufacturing steps of hot stamping films or foils in such a way that it will allow an easy and convenient authentication of legitimate hot stampings obtained from those films.

A number of features are considered to be particularly desirable for an authentication system to be commercially acceptable for large volume utilization. For example, it is important that the method of identification be simple, i. e., will require no complex devices or high technical skills from the user. This is important in view of the need for an inspector to be able to perform the verification task easily, and often in the field, away from his desk and from any special equipment. It is also important that the authentication system be covert, so that a counterfeiter will not be able to readily identify its presence and attempt to duplicate it with any success. A particularly desirable quality of the covertness is its ability to be transparent, meaning that the presence of the system does not modify or disturb in any manner the visual appearance that the hot stamping element would have had before the introduction of the authentication system.

Another object of the present invention is to provide a very effective solution to fulfill the above- mentioned needs. The authentication system according to the present invention provides not only a method to rapidly verify the authenticity of the hot stamping in a simple way and thus the authenticity of the product that carries it, but also provides a way to impart, when needed, a covert message to the hot stamping which, when needed, can be revealed on demand.

This message can include information, such as, for example, the intended and legitimate source and/or destination of a product and thus would allow one to track the product to its original, intended destination from which it was diverted.

These and other features of the present invention are achieved in accordance with the present invention by a method of authenticating a hot stamping film or foil which comprises the steps of applying a hot stamp film or foil to a surface, wherein the hot stamp film includes an authenticating layer comprising a lacquer and a colorless chemically activatable or a photochromic authenticating agent dissolved therein. The chemically activatable authenticating agent is reactable with an activator to produce a reaction product which is visible. Alternatively, the photochromic agent is exposed to light to make it visible. The activator is applied and the visible reaction product indicates authenticity.

Another object of the present invention is to provide a method of producing an authenticatable hot stamping film comprising the steps of providing a support layer, applying a release coating on one surface of the support layer, applying an authenticating layer between the release coating and a hot stamping layer and applying an adhesive layer on the hot stamping layer. In one embodiment of the present invention, the authenticating layer is a lacquer coating comprising a colorless chemically activatable or photochromic authenticating agent dissolved therein. The chemically activatable authenticating agent is reactable with an activator to produce a reaction product which is visible or the photochromic authenticating agent is exposed to light to make it visible. In an alternative embodiment of the present invention, a special lacquer coating is placed between the release coating and the protective lacquer coating. The special lacquer coating comprises the authenticating agent dissolved therein. In still a further embodiment of the present invention, information is printed over the release coating with lacquer and the authenticating agent dissolved therein. In another embodiment of the present invention, information is printed over the protective coating with a lacquer and the authenticating agent dissolved therein.

Still another object of the present invention is to provide an authenticatable hot stamping film. The film preferably comprises a support layer, a release coating on the support layer, an authenticating layer between the release coating and a hot stamping layer and an adhesive layer on the hot stamping layer. In accordance with one embodiment of the present invention, the authenticating layer is a lacquer coating having a colorless chemically activatable or a photochromic authenticating agent dissolved therein. In another embodiment of the present invention, between the release coating and a lacquer coating is a special lacquer coating comprising the authenticating agent dissolved therein.

In a further embodiment of the present invention, between the release coating and the lacquer coating, a printed information layer is provided which comprises lacquer and the authenticating agent dissolved therein. In another embodiment of the present invention, between the lacquer coating and the hot stamping layer, a printed information layer is provided comprising lacquer and the authenticating agent dissolved therein.

These and other features and advantages of the present invention will be described in more detail with reference to the following detailed description of the invention and the attached drawings wherein: BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-section of a prior art hot stamping film; Figs. 2A-2D show four embodiments of a hot stamping film according to the present invention; Fig. 3 shows the hot stamping film of Figs. 2A-2D hot stamped onto a substrate; and Figs. 4A-4D show the cross-sectional view along line IV-IV in Fig. 3 of the hot stamping from the films of Figs.

2A-2D respectively.

DETAILED DESCRIPTION OF THE INVENTION Fig. 1 shows a hot stamping film 10 that is typical of the prior art. The size of the layers have shown are depicted for the sake of clarity and are not the actual sizes nor are they to scale. The film includes a support or carrier film or layer 11 which acts as a supporting structure of the multi-layer hot stamping film or foil. A release coating 12 is applied to one surface of the support 11 and when heat is applied from the top of layer 11, the release coating permits the transfer of the remaining composite structure of the film onto the substrate. The remaining composite structure includes layers 14,15 and 16. Layer 16 is an adhesive layer which provides the adhesion of layers 14 and 15 to the substrate. Layer 15 is the actual hot stamped element, i. e., it provides the visual features of the hot stamping. It can be a film of a plain color, a film with a particular pattern, a metalized layer that provides a plain gold leaf or a silver leaf looking metalized appearance, a diffraction grating appearance or a holographic appearance. This all depends upon the specific features imparted to the layer 15. The layer 14 is a lacquer which is used to provide a protective coating to the hot stamped layer 15.

During the manufacturing process, the different layers 12-16 are successively applied to the carrier film 11 using standard printing or coating techniques; typically, multi-station flexographic or gravure printing equipment is used.

The hot stamping film 10 can be typically of a customary type with a structure well known in the industry and described in several patents, such as, U. S. P. 4,232,077, 5,393,590 and 5,674,580. For example, the support layer or film 11 is typically composed of a polyester film, but also can be an aluminum foil or coated papers having a thickness of from 10 to 50 um. The release layer or coating is typically composed of wax and has a thickness of about 0.025 to 1 um.

The lacquer layers are composed of acrylic, styrene acrylonitrile, polyethylene-terephthalate or nitrocellulose and have a thickness of about 0.5 to 3.0 um. The hot stamping layer typically has a thickness of from about 500 A to 4 microns thick. The hot stamping layer can be a color layer composed of cellulose inks, polyvinyl chloride inks, polyurethane inks and acrylic links, or when a metal is preferably a metal applied by vacuum metal deposition, sputtering or electron beam deposition. The adhesive layer is typically composed of polyvinyl alcohol copolymers, nitro- cellulose, and methacrylate/butyl methacrylate copolymers and may have a thickness of about. 75 to 5 um.

In accordance with the invention, the customary method of manufacturing the hot stamping film 10 and the resulting hot stamping film is modified in order to make the hot stamping film authenticatable.

Different embodiments of the present invention are shown in Figs. 2A-2D.

In Fig. 2A, a film 20 is produced by providing the protective layer 24 with a chemically identifiable authenticating agent solubilized in the lacquer solution which is applied by conventional techniques. The layer 24 will be the top lacquer layer of the final stamping when the hot stamping is obtained. Since layer 24 contains the authenticating agent, the latter will be easily accessible for verification as will be discussed hereinafter.

In the embodiment of Fig. 2B, before the protective layer 14 is applied, a first protective layer 34 is applied which has the authenticating agent solubilized in the lacquer solution and applied using conventional techniques. When a hot stamping is obtained from the film structure 30 of the Fig. 2B, the layer 34 which contains the authenticating agent remains at the top of the stamping and thus is easily accessible for authentication purposes. The lacquer layer 14 also isolates the chemically active layer 34 from the actual hot stamping layer 15 and thus allows the authentication process through the detection of the authenticating agent to take place without affecting the visually significant component 15.

In the embodiment of Fig. 2C, the authenticating agent is again solubilized in a lacquer solution to provide a modified chemically active lacquer solution. The hot stamping film is manufactured by, after coating the polyester film 11 with the release coating 12, information 44 is printed in a repetitive pattern using the modified chemically active lacquer solution. This is then followed with the lacquer coating 14 and the application of layers 15 and 16. The information can be a repetitive pattern, such as a logo, the word original or authentic, a source or destination country identification, such as USA or Mexico or any other message.

The hot stamping which is obtained from the film structure 40 of Fig. 2C has the message 44 which contains the authenticating agent on the very top of the film and is therefore accessible for authentication purposes.

Fig. 2D shows a film structure 50 which has the same elements of Fig. 2C, except that the modified chemically active lacquer solution is used to print information 54 on the protective layer 14. When the hot stamping is obtained from the film structure of Fig. 2D, the information 54 which contains the authenticating agent is still close to the top of a final stamping. However, it is now protected by the top coating 14 and this configuration has the advantage of, on the one hand, protecting the authenticating information 54 and, on the other hand, to provide a way of hiding this critical authenticating information. These advantages are of course offset by the need to penetrate through the layer 14 in order to have access to information 54 for authentication. It is, however, possible to choose the nature of the lacquer used in layer 14 such that it is relatively easy to use an appropriate solvent to penetrate through it and have access to the printed information 54.

Fig. 3 shows a hot stamping of the letters A, B, C and D on a substrate 60. The hot stamping is obtained from the hot stamping films or foils made in accordance with Figs.

2A-2D. Taking the section IV-IV through the letter D in Fig.

3, gives the resulting hot stamp structure shown in Figs. 4A- 4D, respectively.

In each of the four cases of Figs. 4A-4D, the verification of authenticity consists of using a convenient method to show the presence of the authenticating agent in layers 24,34,44 and 54.

The authenticating agent (Chemical A) according to the present invention has a chemically reactive activating agent (Chemical B) which reacts therewith to produce a reaction product which is visible. The Chemicals A and B must be such that reasonable concentrations of the Chemical A can be solubilized in the lacquer structures normally used in the manufacturing process of commercial hot stamping films. It is also necessary that Chemical A, in solution, be clear, colorless and therefore transparent. When the hot stamping is completed as shown in Fig. 3, the verification of authenticity will consist of using a convenient applicator, typically a highlighter, to apply Chemical B which itself is solubilized in a solvent that is also a solvent for the Chemical A and the solids that constitute the lacquer layers 24,34,44,14 and 54.

It is also necessary that the reaction product of Chemicals A and B will be visible to the unaided eye, so that the observation of the reaction product will ascertain the presence of the authenticating agent and hence the authenticity of the hot stamping.

Thus, Chemical A must be one of a pair of chemicals, such as described above, which take into account the lacquer system that is utilized in the manufacturing process of the hot stamping film, so that authentication can be effected.

Examples of such pairs which are found to be practical and efficient to carry out the present invention are set forth hereinafter, however, it is understood that other pairs can be used in accordance with the teachings of the present invention.

In many commercially used hot stamping foil or film systems, the lacquers use MEK or similar strong solvents, such as acetone, or others, to solubilize the solids. In such cases, a very convenient reactive chemical pair of Chemicals A and B can be chosen from color developers and leucodyes. The color developer can be either the Chemical A or Chemical B with the other of the two being the leucodye. When the leucodye and color developer are reacted, they produce a reaction product which has a distinctive color that can be easily identified.

A number of color developers lend themselves very appropriately to the requirement specified for Chemical A.

For example, bisphenol hydroxybenzoates, multi- hydroxybenzoates, phenolsulfonates, and particularly, zinc salicylate and zinc phenosulfonate are useable as Chemical A, since they can be solubilized in the lacquer as described above. In this case, Chemical B that is used can be applied with a highlighter carrying it dissolved in a solvent, such as, for example, MEK or acetone and can be chosen from one of a relatively large group of available leucodyes, some examples of which are the Hilton Davis Copikem 4, Copikem 1, the Ciba- Geigy Pergascript blue and others.

When the two chemicals react, a characteristic optically observable effect, such as a distinctive color, will dramatically develop over the surface of the hot stamping wherever the reactive lacquer 24,34,44 and 54 is present.

Clearly in the cases illustrated in Figs. 4A and 4B, the color change occurs over the entire surface of the hot stamping, whereas in the cases of Figs. 4C and 4D, the originally colorless and even preferably hidden and invisible messages represented by 44 and 54 will acquire a visible color and will thus become alive and will be identifiable to the authenticating person who is applying the highlighter carrying the activator. On the other hand, when the authenticating agent is absent, the application of the activator will result in no reaction, thus indicating that the hot stamping and hence the product that carries it is suspect and may be counterfeit.

It should also be clear that the chemicals used as the authenticating agent and activator can be easily interchanged as long as the activator fulfills the conditions of being soluable in the lacquer and acting essentially as a colorless and transparent additive to the lacquer. In such a case, the highlighter will correspondingly carry the other of the pair for authentication purposes.

With regard to the embodiments disclosed hereinabove, when a choice is possible between using the reactive lacquer in the configuration 24 or 34 in Figs. 2A and 2B or the configuration 44 and 54 in Figs. 2C and 2D, the use of the configuration of Figs. 2C and 2D is preferred for the following reason. Given the choice of any pair of chemicals for use as the authenticating agent and the activator, where Chemical A is the authenticating agent and Chemical B is the activator, if there is a possibility that traces of Chemical A may be naturally present in the original commercial lacquer, it is clear that in such a case that the application of Chemical B on an unmodified lacquer would result in a weak but finite reaction possibly leading an observer to the false conclusion that the lacquer is properly modified to contain the authenticating agent. On the other hand, when the authentic lacquer is properly modified and loaded with a distinct amount of Chemical A, i. e., typically more than 1% of its liquid weight and printed as 44 or 54, the application of Chemical B through a highlighter will produce a very distinctive differential optical effect between the reaction at 44 and 54 compared to a possible spurious or faint reaction on the background surrounding areas 44 and 54, thus establishing without a doubt that the Chemical A is present.

The present invention is also useful in situations where the presence of the authenticating agent does not have to be ascertained through a chemical reaction with an activator. Indeed, there are situations where the need to use an authenticating tool, as described above, carrying the activator may be considered to be cumbersome and therefore it may be desirable in such cases that the reactivity of the hot stamping surface be identified with a more universally available stimulus. In such cases, this can be achieved by solubilizing in the lacquer layer 24,34,44 or 54, a photochromic material, such as Chromadye 2 from Chroma- Chemicals of Dayton, Ohio. When the top lacquer is doped with typically 1% by weight of this photochromic material, there is no perceptible color change in the lacquer. However, when the hot stamped film is exposed to strong sunlight or a source of ultraviolet light, the photochromic molecules and hence the lacquer undergoes a distinct color change which in this case is purple, thus indicating the authenticity of the stamping.

When the stamping is brought back to a regular ambient lighting environment, the lacquer reverses into its normal colorless state within several minutes. This color change is reversible several times.

It is understood that the embodiments described herein according to the present invention are merely illustrative and are not intended to limit the scope of the invention. It is realized that various changes, rearrangements and modifications can be made by those of ordinary skill in the art without departing substantially from the spirit and scope of the present invention.