Holograms with discontinuous metallization including alpha-numeric shapes

Non-continuous reflective hologram or diffraction grating devices are provided in various forms for authenticating documents and things, such as those that contain visual information desired to be protected from alteration. Examples of such information include written personal data and photograph on a passport, driver's license, identity card, transportation pass, and the like. The reflective discontinuous hologram or diffraction device is formed in a pattern that both permits viewing the protected information through it and the viewing of an authenticating image or other light pattern reconstructed from it in reflection. The same master hologram or diffraction grating is made into distinct authentication devices by forming replicas thereof that have different patterns of reflective material which form distinct indicia, such as a different alpha-numeric character.

BACKGROUND OF THE INVENTION 
This invention relates generally to the optical arts of holography and 
diffraction gratings, and more particularly, to a special forms of these 
optical devices for use in authenticating documents and other items as 
genuine. 
There is a wide-spread need to authenticate written information and 
articles in order to prevent both the counterfeiting of the article and an 
alteration of a genuine article. Examples of such articles include credit 
cards, identification cards, driver's licenses, transit passes, passports, 
stock certificates, and the like. Holograms are currently being 
extensively used on credit cards and transit passes, for example. An image 
having observable three-dimensional characteristics is viewable in light 
reflected from such a hologram. 
Because holograms are difficult to make and require a high level of 
technical sophistication, the difficulty of making a counterfeit credit 
card, or other article to which a hologram is attached, is increased. A 
master hologram is made in an optical laboratory with coherent light. The 
resulting master hologram is capable of reconstructing an image of the 
object from which it is made. Low-cost replicas are then made from that 
master. Several specific replication techniques are known, the most common 
currently being to make the master in a manner that the object information 
is stored in a surface relief pattern. This surface relief pattern is then 
used to make replicas by an embossing or casting operation. A layer of 
reflective material is applied to each replica surface relief pattern so 
that the image may be viewed in light reflected from that pattern. The 
holograms are then firmly attached to the credit card or other article to 
be authenticated. The hologram is also constructed of suitable materials 
so that an attempt to remove the hologram from the article will destroy 
it, thereby eliminating the possibility of a counterfeiter transferring a 
hologram from a genuine article and onto a counterfeit article. 
An authenticating hologram of this type cannot cover printing, photographs 
and the like carried by the article to be authenticated when that 
information wants to be viewed. This is because the reflective layer of 
the hologram is substantially opaque so that any visual information on the 
article in the area to which it is attached is covered by the hologram. 
Some credit cards are authenticating some of the raised alpha-numeric 
information on them by covering at least a few of the characters with the 
hologram. But any printing, photographs or the like on a flat surface 
under the hologram is not viewable. 
There has been some effort to control the amount of reflective material 
that is applied to the surface relief hologram so that it will both 
reflect enough light in order to reconstruct an image recorded in the 
hologram and at the same time be transparent enough to make visible any 
printing, photograph or other visual information under the hologram. 
Besides authenticating the article to which the hologram is attached and 
the visual information under it, such a 
hologram has the potential of preventing alteration of that information on 
an authentic article. It has been found to be very difficult, however, to 
be able to repeatedly form a reflective layer on the hologram that gives 
it these advantageous characteristics. Aluminum is usually employed as the 
reflective material. A proper thickness of that layer can result in the 
desired partial transparency and partial reflection, but the processes 
used to date have been very difficult to control in order to provide the 
proper thickness. 
Holograms are also being used to authenticate documents, such as transit 
passes, that are reissued at frequent periodic intervals, such as monthly. 
It is often desired that the hologram be changed each month so that 
transit authorities can easily recognize a valid current transit pass from 
an expired one. This presently requires making a new optical master 
hologram for each new pass, an expensive and time consuming process. 
Therefore, it is a specific object of the present invention to provide an 
improved hologram or diffraction grating for attaching to a document or 
article over visual information that is to be protected, wherein the 
information can be observed through the hologram and an image 
reconstructed from the hologram may be observed. 
It is another object of the present invention to provide an authentication 
hologram or diffraction grating, and process for making it, that allows 
easy modification for monthly transit passes and the like without having 
to make a new optical master. 
It is a more general object of the present invention to provide novel 
holograms and diffraction gratings for authentication of documents and 
other articles. 
SUMMARY OF THE INVENTION 
These and additional objects are accomplished by the articles and processes 
of the present invention, wherein, briefly, a continuous hologram or 
diffraction grating device is provided from which an image or other 
recognizable pattern is reconstructed in light reflected from the device 
but light reflective material is discontinuously provided in distinctive 
shapes such as one or more alpha-numeric characters. The reflective 
material pattern can thus be selected to convey information which is 
independent of that recorded on the hologram or diffraction grating. In 
the case of transit passes discussed above, for example, the same hologram 
or diffraction grating can be used for each month's pass, the pattern of 
reflective material clearly indicating the current month for which the 
pass is valid. This technique is optimally combined with a noncontinuously 
reflective hologram or diffraction pattern that covers information on a 
substrate to be protected but the technique can also be used as part of an 
otherwise solid hologram that is attached to a substrate along side 
information desired to be visible. 
Additional objects, advantages and features of the various aspects of the 
present invention will become apparent from the following description of 
the preferred embodiments thereof, which description should be taken in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring initially to FIG. 1, an example is given of an article having a 
protective hologram attached that utilizes the present invention. A 
document, such as a passport, driver's license, personal identification 
card, transit pass, or the like, includes a photograph 11 of the bearer. 
Written information 13 of the bearer is also provided on the surface of 
the document. The document can be paper, plastic or some other material 
that contains visual information to be protected from alteration. Covering 
at least the photograph 11 and the written information 13 is a see-through 
hologram authentication device of a type discussed in the patent 
applications cross-referenced above. Such a hologram reconstructs in 
reflected light images recorded in it, such as reconstructed images 15. 
Thus, the information 11 and 13 to be protected is covered with a hologram 
that allows the information to be observed through it at the same time as 
allowing the authenticating reconstructed images 15 to be observed. 
A small area 17 of FIG. 1 is expanded in FIG. 2. FIG. 3 shows a sectional 
view through the expanded portion of FIG. 2. A hologram 19 is attached to 
a substrate 21 by an appropriate adhesive layer 20. The hologram 19 
includes a substantially clear plastic film 23 having a surface relief 
pattern 25 formed on an inside surface thereof. The surface relief pattern 
25 is continuous across at least a defined area of the hologram 19, 
continuing over the entire hologram in this example and thus the entire 
protected document. The surface relief pattern is formed from a master 
hologram by a standard embossing or casting technique. 
That portion of the surface relief pattern 25 to which a reflective layer 
is attached will be operative in reflecting incident light into the 
recorded image or other light pattern. In the hologram portion illustrated 
in FIGS. 2 and 3, reflective aluminum dots 27 are periodically spaced 
across the surface relief pattern 25 and attached to it in a manner to 
follow its contours. As described in considerably more detail in the 
applications cross-referenced above, this allows an image to be 
reconstructed from the hologram 19 in reflected light at the same time as 
the photograph 11 and other information attached through the substrate 21 
is viewed through the hologram. The opaque, reflective dots 27 are made of 
a size and spaced apart sufficient for this to occur. 
In addition to the reflective dots, the opaque metallization of the 
hologram surface relief patter in the embodiment of FIG. 1 is configured 
over an area of the protected document not covering the photograph 11 or 
other information 13 to provide a unique indicia that is separate, 
independent and unregistered from the images 15 reconstructed from the 
hologram. The indicia formed by the hologram metallization pattern is also 
separate and independent from the document information 11 and 13 being 
protected. In this case, that indicia is alphanumeric information, namely 
a month 29 and a year 31. The information or visual design of the 
protected document itself can also be changed each time that the hologram 
metallization pattern characters are changed but this technique allows use 
of other copies of the same document without change, if desired, for 
economics and simplicity. 
FIG. 4 shows an expanded view of another small area 33 of the protected 
document of FIG. 1. This includes a portion 35 of the "nine" of the year 
31 that is visible from the face of the protected document of FIG. 1. The 
number is formed by the shape of the reflective metallization layer that 
is applied to the surface relief pattern 25. The region 33 shown in FIG. 4 
illustrates that metallization pattern to retain the reflective dots 
around it. The metallization 35 also provides a reflective backing for 
reconstructing an image from the hologram surface relief pattern 25 
covered by it. 
This information can be a month and year of expiration of the protected 
document, of a month during which the protected document is valid, and the 
like. In such cases, new documents need to be issued periodically and it 
is quite expensive if an entirely new protective hologram needs to be 
constructed for use with each document reissue. What is most expensive is 
the making of an optical master hologram. But the technique of adding the 
indicia 29, 31 in a metallization step allows the same authenticating 
hologram to be utilized in successive reissues of the document since the 
metallization step occurs after the hologram replication step. A large 
number of such protective holograms can be manufactured for inventory with 
limited amounts periodically withdrawn and metallized with unique indicia 
29, 31, but it generally is preferable to replicate each new issue of the 
protective hologram from the beginning. This still utilizes the same 
master hologram replicating plates for each issue, only the pattern of 
metallization changing. No new optical hologram master need be made. 
Such a technique is illustrated generally in FIGS. 6-8. FIG. 6 illustrates 
the process steps for forming hologram replicas on a continuous length of 
flexible substrate material 111. There are several distinct processing 
stages through which the web 111 passes. A first stage 113 applies liquid 
resin to defined areas of the web 111. Solidified, surface relief 
holograms are formed at station 115 in these resin areas. Next, the web 
proceeds to a station 151 that prints a liquid onto the surface of the 
replica holograms in regions where reflective material is not to be 
attached. A next station 153 applies a reflective metal layer over the 
entire hologram replica surface relief pattern. A station 155 then removes 
the metallization layer from those areas that were printed at station 151 
with a liquid material. Next, at station 157, the process web is dried 
and, at an optional station 159, a protective coating and/or adhesive 
layer is placed on the metallized surface relief pattern. 
Details of the hologram replica casting stations 113 and 115 can be had 
from copending patent application Ser. No. 399,812, filed Aug. 29, 1989, 
the disclosure of which is incorporated herein by this reference. Briefly, 
a liquid bath 117 of casting resin has a first cylindrical roller 119 
rotating about its axis through the liquid. The roller 119 transfers such 
liquid to outward surfaces of pads, such as pads 125 and 127, that are 
attached to an otherwise smooth cylindrical surface 123 of a drum shaped 
roller 123. 
A third roller 131 in the station 113 guides the web 111 in a path that 
results in contact between the pad surfaces of the roller 123 and the web 
without any relative motion therebetween. Guide rollers 133 and 135 also 
determine the paths of the web 111. Thus, liquid resin is applied from the 
bath 117 to discreet areas of the web 111 as defined by the size and 
pattern of the pads carried by the roller 123. 
After leaving the station 113, the web 111 is passed in contact with the 
outside of the cylindrical drum 137 by appropriate guide rollers 139 and 
141, in the second work station 115. The drum 137 has a plurality of 
individual hologram masters, such as pieces 143 and 145, attached to its 
outside surface. This arrangement is further shown in FIG. 7. These 
hologram master pieces are arranged essentially in the same pattern as the 
pads of the drum 123. Rotation of the drums in the work stations 113 and 
115 is coordinated by a master control 147 to cause the individual 
hologram pieces 143, 145, etc. to contact areas of the web 111 that have 
been coated with liquid resin by the pads 125, 127, etc. 
The web 111 and the hologram masters attached to the outside surface of the 
drum 137 move together without any motion between them. Liquid resin is 
held between each of the surface relief master holograms 143, 145, etc. 
and the web. While being so held, the liquid resin is hardened by curing 
with actinic radiation. A source 149 of such radiation directs it through 
the web 111 to the trapped liquid resin. By the time a point on the web 
has advanced to the position of the roller 141, the liquid resin has been 
cured with the desired surface relief pattern formed therein. The web 111 
is separated from the hologram masters 143, 145, etc. at this point and 
proceeds to a next work station 151. 
The station 151 then coats each of the hologram replicas with a liquid 
material in a pattern of the desired non-continuous reflective 
metallization layer on the completed hologram. The web is directed around 
a drum shaped roller 161 and is guided away from it by rollers 163 and 
165. A bath 167 of the liquid to be printed onto the hologram replicas is 
a water soluble resin, such as polyvinyl alcohol. This liquid is 
transferred by a roller 169 to the outer surface of a roller 171 which is 
urged into contact with the web against the roller 161. As can be seen 
from FIG. 8, a cylindrical surface of the printing drum 171 contains a 
pattern 173 that corresponds with the desired pattern of metallization on 
the resulting hologram replica shown in FIG. 1. In this case, the pattern 
173 for a single hologram is constructed so that the liquid 167 is applied 
to all areas of the cast hologram relief pattern except for the regions of 
the desired metallization pattern 173. That is because the water soluble 
resin being applied will, in a subsequent step, simply be washed away and 
thus will remove any reflective material from the areas where the resin 
has been printed. The roller 171 is preferably formed from a gravure 
cylinder having liquid containing holes formed in a negative of the 
desired metallization pattern for the hologram replicas. 
After application of the water soluble resin at the work station 151, the 
web 111 proceeds to a station 153 that coats the entire web on its side 
where the holograms are formed with an opaque, reflective material layer. 
That layer is preferably made of aluminum and the work station 153 is 
preferably a standard vacuum metallization machine. 
Next, the web 111 advances to a station 155 which submerses the metallized 
hologram replicas in a water bath. The metal layer is sufficiently porous 
to allow water to penetrate through to the resin, thereby causing the 
resin applied at the station 151 to dissolve and the aluminum layer coated 
on such a resin to then be washed away. The next work station 157 simply 
dries the web by use of heat lamps and the like. Specific techniques and 
materials for use in the non-continuous metallization process of stations 
151, 153, 155 and 157 are given in U.S. Pat. Nos. 3,935,334--Narui et al. 
(1976) and 4,242,378--Arai (1980). 
As an alternative to using a water soluble resin, a resin soluble in any 
one of a wide variety of organic solvents can be printed onto the web 111 
prior to metallization. The metal layer is then removed in the pattern of 
the resin by submersing the coated web into a bath of the appropriate 
organic solvent. 
A final, optional work station 159 uniformly coats the metallized hologram 
replicas of the web 111 with a protective or adhesive layer from a liquid 
174. A transfer roller 175 carries the liquid to the web 111 surface. The 
web 111 is guided by another roller 177. After an appropriate drying step, 
the metallized hologram replicas have such a desired additional layer. The 
web is then ready for separation into individual holograms by die cutting 
and the like for attachment to a document or other substrate surface to be 
protected. If it is desired to apply the individual holograms by a hot 
stamping process, the web 111 is then alternately attached by a hot melt 
adhesive to a flexible plastic carrier. 
The example of the unique indicia 29, 31 (FIG. 1) formed during the 
reflective metallization step was described to be formed of solid 
reflective material. It is not necessary, however, that the alphanumeric 
characters be solid. That is only one of many specific implementations. 
Four additional specific implements are illustrated in FIGS. 9-12 for 
representing the letter "T" in the pattern of aluminization. 
Referring initially to FIG. 9, a regular pattern of metallized dots 181 
exists on the surface relief hologram replica. The letter "T" is formed by 
omitting dots in the region 183. This technique works well in cases where 
the size of the individual dots and the density of the background pattern 
181 are clearly visible. The dot pattern can be made to be practically 
invisible to the ordinary user but still reconstruct holographic images, 
but in the case of FIG. 9, such an invisible pattern of dots is not 
workable. The example of FIG. 9 has an advantage of being able to place 
the "T" character 183 over information to be protected, such as the 
photograph 11 or writing 13 (FIG. 1), if desired, since none of the 
protected document is blocked by it. 
FIG. 10 is an example similar to FIG. 9 except that the region 183 without 
a dot pattern is outlined in a thin continuous metal pattern 185. This 
makes the letter "T" highly visible, even when the individual dots of the 
background pattern 181 may not be very visible, but does so without 
blocking view of much area of an underlying document to which the hologram 
is attached. 
FIGS. 11 and 12 utilize the fact of a background pattern 181 of dots 
clearly visible. The letter "T" is formed in FIG. 11 by a pattern 187 of 
reflective dots that are larger than those of the regular background 
pattern 181. The pattern of the dots 187 is the same as that of the 
background dots 181 but they are more dense and thus the pattern is 
distinguishable from the background. The pattern 189 in FIG. 12 is made to 
be different from the background pattern 181, and distinguishable because 
of that feature. The density of the area covered by dots in the pattern 
189 may be the same as that of the background pattern 181. 
The examples described above result in the making of a large number of 
hologram replicas with the same alpha-numeric characters formed in the 
metal layer of each. Alternatively, these characters can be formed by use 
of a printing technique that places a unique pattern on each hologram 
replica. This is useful, for example, where each hologram replica of a 
large batch of replicas is to carry a unique identifying serial number 
that is clearly visible in the metal layer. This can be accomplished by 
jet or laser printing techniques, by use of a mechanically indexed print 
head included as part of the drum 171, etc., to form a soluble layer 
pattern that is somewhat different for each replica. 
Although the various aspects of the present invention have been described 
with respect to their preferred embodiments, it will be understood that 
the invention is entitled to protection within the full scope of the 
appended claims.