Holograms and optical variable devices

What is a hologram or OVD and why should I use this technology?

The term 'OVD' (Optically Variable Device) is used to describe both laser generated hologram images and electron beam generated images.

These optically variable devices are created in highly-secure facilities and are at the forefront of overt asset and brand protection programmes.

The OVD can be used as a stand-alone feature or can be combined with printed security features to create devices that are extremely difficult to replicate using conventional photocopy or scanning technologies.

 

OVD technologies

The list of technologies below is by no means exhaustive. It is simply meant to act as a guide to the most frequently used OVD technologies.

2D/3D - a laser generated holographic image that has depth and parallax. It uses two dimensional artwork to build a three dimensional picture.

3D - is a laser generated image that depicts an object in 3D. It can be computer generated or created using a micro-model.

Dot Matrix - generally flat, rather than three dimensional, but highly kinetic holographic image. It can be high resolution and is ideal for containing optical forensic features such as microtext.

Filmed Stereogram - a 3D moving image created from a filmed subject. Ideal for high security work and can also be computer generated.

Combination Images - As the name suggests, a combination of some of the above single technologies in order to create an image with increased security.

Ebeam Image - this is an image created without the use of a laser. The underlying structure of the image is written at the microscopic level with an electron beam generator. This type of image can include three dimensional and highly kinetic elements with forensic features within one image. It is highly secure, but commands a high price.

 

Designing a hologram

From your supplied artwork (line art, colour separated or a computer file) a hologram can be chosen to suit your application. This takes into account the substrate onto which the hologram will be applied and the existing graphics with which the hologram will interact.

The design proof is usually supplied as both hard copy colour print (where the security features contained within the hologram will be detailed and shown in magnification) and as a fully animated video file that can be played on a desktop PC.

Providing your supplier offers these stages it will allow them to engineer any changes whilst the OVD is still in its design stage. The OVD is not 'originated' until the hard copy colour print and video file have been agreed by you. Once you have approved the inital designs, the OVD is then originated (created) and manufacturing can commence.

 

Registered Images, continuous images and stripes

When the OVD is designed it will be either a registered image or continuous image. You will make your choice, governed by cost, application speed, security of the image and aesthetic appearance.

A registered (specific) image can be described as a single discreet picture (image a portrait of yourself). Even though the requirement may be for millions of images, all the images will be 'separate' items but each is exactly the same as the next. During application, the registered image is applied in exactly the same position on each document that passes through the application press. This is the type of OVD seen on credit cards and passports.

A continuoius image is often called a wallpaper pattern. This is because the image is designed so that wherever an impression is taken, all of the elements will be included, although not necessarily in the same position as the preceeding impression. in general, continuous images are designed for cost-effectiveness rather than overall aesthetic or security concerns.

A recent development has been the introduction of the OVD stripe. Generally the stripe is an OVD continuous pattern applied at a width of 10mm or less. The benefit of strips is that application speeds are very high and thus the unit cost is lower. This makes OVD stripe application ideal for large runs. An OVD stripe can be seen on the £20 note and the Euro banknotes.

 

Metallised, demettalised and selectively demetallised

The embossed hologram is metallised using a vacuum deposition process. This gives the hologram its silver appearance. Lacquer coatings can be used in the production process to alter the colour of the hologram, giving gold, red, blue etc.

It is also possible to use high refractive index coatings in the metallisation process instead of aluminium. This allows the OVD to be transparent at some angles of view yet fully diffractive at other angles. This type of product is ideal for ID applications where the transparent hologram is used as a security device to protect a photograph or important data.

A further process that can significantly increase the security of the OVD is selective demettalisation. In this process metal is removed from the OVD image after metallisation. Fine detail patterns can be achieved, including micro text. This process, when allied to a high security image creates a product that would be almost impossible to copy accurately.

 

Carrier Medium

The OVD's that are in general use today are created as embossed, metallised images. This is the type of OVD as seen on a bank card, cheque or bank note.

The OVD can be supplied as a pressure sensitive (self adhesive) label or as a transfer foil suitable for hot or cold stamping by rotary or platten application. The OVD images can also be supplied as a lamination film suitable for packaging applications.

In most cases, the OVD's that can be seen on bank cards, banknotes, tickets, printed documents and cheques have been produced as hot stamping foils which are applied with high-speed precision equipment.

 

Hot stamping foils

Most security printers use a large volume of security hot stamping foils. They are produced to high specifications and are applied using specialist equipment onto products that are produced in their factories. They can apply registered image, continuous image and stripe as some have platen and rotary application methods. In general, hot stamping foils are used in conjuction with paper or polymer (plastic) substrates. A pre-printed material is passed through an application press at high speed and the OVD is applied onto the surface of the material. This process is used to apply OVD's onto cheques, labels, tickets and financial documents. The application process is usually accurate to +/- 0.25mm ensuring consistency throughout the production run.

 

Hologram Labels

OVDs can also be supplied as labels that are tamper evident. These can be applied by hand, by hand-held applicator or by high speed labelling machines. The basic types of tamper evident labels that you can purchase exhibit their tamper evidence either by delaminating, voiding or by fracture/crumbling if an attempt is made to remove them.

Suppliers can also manufacture labels that combine security features with OVDs in order to enhance their products' performance and to allow the end user to perform a simple test of the label. The combination of print and OVD can offer a much more aesthetically pleasing product than an OVD only label. The labels can also be indelibly numbered and the larger labels can have variable data and barcodes printed.

 

Applications

Cheques, Event Tickets, Gift Vouchers, Lottery Tickets, Swing Tags, Labels for tamper-evident use, Labels for Brand and Asset Protection, Taxation Documents, Parking Permits, Identity Documents, Access Control Passes.