FIELD OF THE INVENTION

The invention relates generally to a security feature for printed products. In particular, the present invention provides a printed product and method of printing/metallization to produce a print/image in registration with metallization, for use in printed security documents including but not limited to driver’s licenses, passports, and banknotes.

BACKGROUND

Security documents and printed products such as identification cards, data pages, driver’s licenses, passports and banknotes may include one or more images or elements formed by printing or applying a printed image. For example, a security document in the form of an identification card, a driver's license or personal identification sheet of a passport may be made of a thermoplastic substrate and may bear an image comprising a security design feature that is printed onto the thermoplastic substrate. Additional features such as metallization may increase the difficulty of copying the security design feature.

Metallization by PVD (physical vapor deposition) or chemical deposition is common in the commercial world. A flood coat comprising a thin metal layer is applied on the surface of polymers to use as a vapor barrier. Selective or pattern metallization is also used for commercial purposes, especially in decorative packaging. This is commonly achieved in the following ways.

1. Pattern etching a. Chemical etching by caustic solution after mask is applied b. Print a concentrated caustic solution over metallized surface followed by a wash-up

2. Surface treatment before metallization a. Print thin oil layer which prevents metal from adhering The pattern etching uses a corrosive material which must be removed from the polymer. The process will be quite expensive due to the nature of the chemicals used.

The surface treatment process uses oil over the polymer surface b. It is difficult to remove the oil completely after metallization. The contamination would interfere with the process use for card/data page manufacturing.

Vast Films Ltd applies selective or pattern metallization by a different process (US20180282551 A1 ). A release agent is applied to the surface of a transparent film by a flexographic or other suitable process, forming a negative image. After the release agent dries, a flood metallization is applied over the coated film. The release agent is removed after metallization to obtain the final metalized film - the positive image.

As taught in US20180282551 , the release agent comprises a polymer such as PVP or PVOH or a copolymer thereof that is soluble in water and/or alcohol and is solid at temperatures about 50 °C. The release agent may further comprise a dye and an anti blocking agent comprising silica. The release agent is removed by washing with water and/or alcohol. This may be achieved by passing the film through a tank, or by spraying. After washing, the film may be dried by, for example, an air knife or hot air.

There is teaching in the prior art in respect of a security device with a reflective surface at a first side of a transparent film and an opaque surface at the second side. However, the process used to achieve such security device may be complicated and/or it may be difficult to achieve a perfect registration between the image/pattern on the two sides.

For example, DE102017011917A1 to Hoffmuller discloses a method for producing a multilayer film security element. In HoffmQller’s process, the printing of a colour motif takes place first, followed by application of a water-soluble coating and metallization. The registration of the colour motif to water-soluble coating is dictated by the printer. For example, the color motif may be printed on the first print unit of a printer and the water-soluble coating may be printed on the second unit to achieve tight registration. The unit-to-unit mechanical tolerance of the press will make it more difficult for the colour motif and coating to be in perfect registration. US20090220750A1 to Hill discloses partial printing of a substrate using metallization. Hill’s invention uses four different methods to produce a device.

1 . Solvent etch: Harsh solvent is used to etch both colour motif sits at the bottom of the etch and the metal sits at the top of the etch. The process will be costly and environmentally not too friendly due to the nature of chemicals involved.

2. Water activated stencil method: Thick stencil layer is used for this application as a mask. Metallization form discontinuities at the edge of the thick stencil. The process is too complicated and the using thicker stencil would not give high resolution image (>1200dpi).

3. Release layer stencil method: A release layer is printed on the substrate followed by a colour motif and metallization. The unwanted marking material is removed by an external force applied to the exposed surface of the superimposed layers. The resolution of the print is determined by the cleaning unit/how it applies the external force.

4. Direct method: A receptive layer applied over the transparent film. The colour motif only adheres to the receptive film. The metallization following the colour motif only adheres over the colour motif. After washup, the colour motif printed over the receptive layer will exist and the rest will wash away. Polymers discussed in the article (PVC, PET, PC, etc) have the correct surface property to receive metal during metallization. Therefore, any area that is uncoated with the receptive layer somehow needs to be masked to prevent metallization. Otherwise to achieve this, the colour motif must be flood coated. The flood coat would add cost to the process due to ink usage, clean up and disposal.

Accordingly, a security device and method of making such security device is needed, where the security device comprises a selectively reflective or metallized surface on a first side of a transparent film and an opaque surface on the second side. In particular, the security device would be simple and relatively low cost to make, and would result in excellent registration between the images and/or patterns on the two sides of the security device.

SUMMARY

Provided herein is a security device for a printed product, the security device comprising a selectively reflective or metallized surface on a first side of a transparent or semi-transparent polymer film and an opaque surface on the second side. In order to render the security feature or device more difficult to copy or counterfeit, metallization, including selective or patterned metallization, is applied to a printed image on a transparent/semi-transparent substrate, such that the image is visible from the second side of the substrate and is in registration with the patterned metallization.

Also provided herein is a method for making a security device for a printed product or security document. The method comprises the steps of: a) applying a water-soluble coating over a first portion of a first side of a transparent/semi-transparent polymer (PVC, PC, PET, PETG, Nylon, etc); b) applying a print image on a second portion the first side, wherein the first portion partially overlaps the second portion; c) metallizing the first side by way of physical vapor deposition; and d) washing the first side to remove the water-soluble coating from the polymer.

In step a, the first portion may be a negative image of the print image in step b.

In step b, the inks used to print the image may be inks with high surface energy after curing.

In step d, washing will also remove anything (e.g. metal, print image, etc that has been applied over the water-soluble coat).

The water-soluble coating may be applied by any suitable technique including but not limited to flexographic, inkjet, laser, gravure and silk-screening.

Unlike other methods described in the art (see Hoffmuller above), the water-soluble coating in the presently described process is applied first, prior to applying the print image, which may be in colour. The print image and metallization are done thereafter. Furthermore, the print image is printed so as to overlap the water-soluble print which prevents the printer from dictating the quality of the registration. After the wash-up step, the print image and metallization found over the water-soluble coating will wash away. This would allow for a tighter registration of the print image to metallization than Hoffmuller’s invention.

The method provided herein results in a >1200dpi high resolution image. In contrast to Hill (discussed above), the whole system is exposed to external force and only where the water-soluble coat exists, are the print image and metallization removed - other areas without the water-soluble coat are unaffected. This allows for a high-resolution image.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 illustrates a first step wherein a water-soluble coating is applied on a transparent or semi-transparent film, according to one embodiment.

Fig. 2 illustrates a first part of a second step wherein a non-water-soluble ink is used to apply an image, according to one embodiment.

Fig. 3 illustrates a second part of a second step wherein a second color is applied over the image, according to one embodiment.

Fig. 4 illustrates a third step wherein metallization is applied over the printed side of the film, according to one embodiment.

Fig. 5 illustrates an alternative third step wherein metallization is applied over the printed side of the film, according to one embodiment.

Fig. 6 illustrates face and back sides of a final product, according to one embodiment.

DETAILED DESCRIPTION

By the term “about” as used herein, it is meant that a figure or range of figures can vary plus or minus up to 10%. So in this embodiment if a figure of “about 1 ” is provided, then the amount can be up to 1 .1 or from 0.9.

STEP 1 : To obtain a perfectly registered metalized film to an image on a polymer surface, a negative image is printed with water-soluble coating on a transparent or semi-transparent film/layer. The film may be a thermoplastic polymer and may be made of any suitable substance including, but not limited to PVC (polyvinyl chloride), PC (polycarbonate), PET (polyethylene terephthalate), PETG (polyethylene terephthalate glycol) and Nylon. In an exemplary embodiment, a water-soluble coat (white) is applied on a transparent/semi-transparent film as shown in Figure 1.

Step 2: For the second step, an image, preferably a colour image, will be printed. The ink used to print the image will not be soluble in water. To allow metal to bind to the surface of the image, the inks used for this process would have a surface energy after curing of >25dynes/cm. Lower surface energy ink will deflect the metal from binding to the surface - this may be desirable in some embodiments. To obtain a tighter registration with metal to print, the print must overlap the water-soluble ink.

As illustrated in Figure 2, in an exemplary embodiment, a first colour (in this example, red) applied over the film is shown. The registration of the print image to the water- soluble coating is not important as the print image or printed matter shall be printed so as to overlap the water-soluble coat (i.e. in this example, the flags are slightly larger than the blank spaces created by step 1). The overlap would wash away during washup cycle and provide a perfect registration between to the printed image and the metallized portion.

As illustrated in Figure 3, in an exemplary embodiment, a second color (in this example, white) is applied over the flag. The flag will be visible on the opposite side though the transparent/semi-transparent film. The red part of the flag printed beneath the white will be slightly visible through the white due to lower opacity of that coating.

STEP 3: In step 3, after the printing of images or other matter is completed, the metallization will be applied. Water-soluble coat, ink and uncoated area will get metallized.

As illustrated in Figure 4, in an exemplary embodiment, metallization is applied over the printed side of the film.

When the water-soluble coat and inks used for visible print have a higher surface energy, this allows for metallization to adhere. Using visible ink with lower surface energy after curing, such as UV curable hard coat, would prevent metal from adhering and will form a following artifact. As illustrated in Figure 5, metallization over the printed sheet is shown wherein the ink with lower surface energy after curing repels metallization and produces an unmetallized area.

STEP 4: After metallization (figure 4) the film goes for wash-up where the water- soluble coat (applied in first step) and everything on top of it will get washed away. The resulting product will be as shown in Figure 6.

As illustrated in Figure 6 (face and back side of the printed and metallized film according to an exemplary embodiment), the water-soluble coat is washed away where the film is transparent.

The method described herein constitutes an improvement over the previously described method developed by Vast Films Ltd. The improvement consists of adding one or more steps of printing a visible and/or invisible image in order to obtain a security feature that will produce a visible and/or invisible print in registration with metallization at high resolution.

Vast Film's selective/pattern CBN's Security Feature metallization

As shown in the above flow diagram, to obtain print in registration to metallization, at least one additional step would be necessary - the addition of a visible and/or invisible print/image. The designer’s creativity can make the process more complex and the security device more difficult to counterfeit. The following elements, including two or more elements in combination, may be included to create a suitable security device using the methods described herein.

A. Transparent region

B. Metallized region

C. Visible print

D. Invisible fluorescent print

E. Visible/invisible print in registration over the metallization a. Metal receptive ink (high surface energy ink)

F. Visible/invisible print in registration around metallization a. Metal non-receptive ink (low surface energy ink)

To metallize a surface, the surface should have a surface free energy of greater than about 25 dyes/cm. If the surface energy is lower than about 25 dynes/cm, the metal will be deflected away from the surface. Using this characteristic, the ink can be chosen to allow and disallow metallization (compare Figs. 4 and 5, for example).

Typically, the energy curable inks are known to produce hard/cured surface which makes the surface energy of the cured ink to lower than 25dyes/cm. This would prevent metallization. Conventional inks would accept metallization, as the surface energy of the cured ink is typically higher.

The design of the security device with a large surface of metallization would allow for personalization of the security document. The metal applied over the film will be <1 pm in thickness, preferably ~ 500 angstroms. Using YAG (yttrium aluminum garnet) or YV04 (yttrium orthovanadate) laser, the metal can be ablated. This can be achieved, for example, in an embedded form in an ID card (in the window) or at the surface of a passport hinge (typically transparent/semi-transparent nylon).

The embodiments of the invention disclosed herein are exemplary only, and various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.