2D/3D Hologram directed by Colin Kaminski
An embossed hologram is a rainbow transmission hologram with a mirror (aluminized layer) laminated to the back. Much like the traditional vinyl record printing process, the pattern is embossed by heat and pressure from a metal stamp onto a thermoplastic medium.
There are many types of embossed holograms.
2D Embossed Holograms are made from two dimensional artwork, usually a transparency.
2D/3D Embossed Holograms are made from a stack of two dimensional artworks so each layer is a different distance from the film plane.
3D Embossed Holograms are made from three dimensional models.
Multiplexed Embossed Holograms are made from many pieces of artwork, often from a LCD screen.
Once the original artwork is ready, a transmission master hologram (H1) is made, usually with Silver Halide holographic film or plates. The H1 is a slit hologram which will provide the geometry for a Rainbow copy. This Slit is then used to make a Rainbow transmission hologram (H2) into Photoresist. The H2 is processed with an etching solution so that the recorded fringes become a relief pattern of grooves on the hologram surface.
The Resist is then silverized, which preserves the relief pattern while alowing the surface of the hologram to be electrically conductive. This silverized hologram is then placed in an electroforming tank and nickel plated, becoming a Mother Shim. The Mother Shim is peeled off, rejigged, placed back into an electroforming tank and another shim is grown on top of the Mother shim which becomes the Child shim. Many Child shims can be made from one Mother shim. The Child shim is placed in a Holographic Printer or embossing machine. Using heat and pressure the releif pattern on the shim is pressed against thermoplastic and the pattern is transferred to the plastic. shown at the top of the page. As many thousands of stampings can be made from one Child shim and quite a few Child shims can be made from one Mother shim, it is very possbile to make hundreds of thousands of embossed images from one Mother Shim.
Because holograms are impossible to make without a giant laboratory and millions of dollars, they are often used for security purposes. You probably have one on the credit card in your wallet. Feel more secure?
Making Embossed Holograms
There are a number of steps required to make embossed holograms. Thus the costs are quite high for the first embossed hologram but as the processes allows 100's of thousands of hologram to be stamped in plastic, the costs per hologram gets reduced to pennies with the increase in the number of holograms wanted.
First artwork needs to be made. This can be a 3D model, some 2D litho "pictures" or computer generated artwork. The artwork needs to be rather shallow in depth because the nature of the embossed process requires the hologram to be a surface relief hologram utilizing only the fringes on the surface of the hologram.
A special kind of transmission master needs to be made from this artwork. It is called a slit master (H1) or rainbow transmission master hologram and can consist of more then one slit. For a final embossed rainbow hologram that has the foreground or object roll through the rainbow colors while the background rolls through different colors (shifted) at the same time, two slits can be made on the same plate separated by the color shift distance. Most of the time this H1 is made in silver halide.
Once the transmission master (H1) is made a transmission copy (H2) is made from the H1 master. If there are two slits on the master they can both be imaged onto the H2 copy with one exposure. This is usually done on photoresist. Photoresist is most sensitive to the UV but is less sensitive to the deep blues and blue lines. The HeCd laser is most used for this exposure but the 457 line of and Argon Ion can be used. Exposure times of 30 or more minutes are not uncommon.
Once the resist copy rainbow hologram is made, it is put in an etching solution that etches away the areas that have not been exposed to light (the destructive interference parts of the fringes) and leaves the exposed regions of the fringes (there are some etching solutions that work opposite and remove the exposed parts and leave the unexposed parts). The hologram can now be seen in on the resist.
The resist is then covered with an electrically conductive layer, usually silver. A two part silverizing process used to make mirrors can be adapted to use for this process. It is important to maintain the surface relief structure of the fringes so a process that lays down an atom at a time is necessary. To simply coat the resist with silver would "level" out the fringes.
The silverized hologram is then placed in an electroforming tank and a layer of nickel is deposited (grown) onto the silverized hologram. This is called the mother nickel shim. The mother nickel shim is then peeled away from the resist which degrades and destroys the resist which is no longer any good. The mother nickel shim is placed back in the electroforming tank and another layer of nickel is deposited onto the mother shim. This layer is then peeled off mother shim and is called the daughter shim. Many daughter shims can be made from a single mother shim by reintroducing the mother shim back into the electroforming tank and growing a subsequent daughter shim from it.
The daughter shim is then placed into an embossing printer which "stamps" the relief fringes maintained in the shim onto the surface of a plastic film using heat and pressure. This printer can print out hundreds of hologram per minute. After thousands of holograms are stamped from a single daughter shim the daughter shim starts to degrade. The printer can then be loaded with another daughter shim and the process can continue.
As the final hologram is a transmission hologram a reflective backing, usually Mylar, needs to be present such that the light can pass through the hologram, reflect off the backing and illuminate the embossed hologram from the back. The reflective backing can be part of the original stock plastic that passes through the printer or added during or after the embossing process. Also, other qualities like an adhesive backing can also be accommodated for with the stock plastic material.
As you can see, it is quite elaborate to make the first embossed hologram but after thousands, the cost can be reduced 10,000 to 100,000 fold. It is not uncommon to see mass produced embossed holograms retail sell for $0.05 (US) a piece.