Method for protecting from forgery, assuring the authenticity of or personalizing pre-printed sheets

The method provides the protection or personalization of the pre-printed sheets by impressing microengravings, on all or some of the printed portions of the sheets, through an embossing process carried out on the pre-printed sheets at a temperature higher than the softening point of the dyeing substances used for obtaining the print thereon and followed by a cooling step, said microengravings corresponding to holograms or diffraction patterns or images or words.

FIELD OF THE INVENTION 
The present invention relates to a method for protecting from forgery, 
assuring the authenticity of or personalizing pre-printed sheets (both of 
small size such as documents, etc. and of large size such as continuous 
paper or strips wound in reels) and in particular pre-printed by laser or 
ink-jet printers, plotters, airbrushes, and xerographic, typographic, 
lithographic, off-set, serigraphic, flexographic, copper-plate, 
rotogravure machines with any kind of drying, including UV and 
electron-beam reticulation. 
BACKGROUND OF THE INVENTION 
Various methods are used in order to protect from forgery or to assure the 
authenticity of printed documents. 
The use of watermarked paper and the impressing of holograms are among 
those methods which offer a greater guarantee. These are two fairly 
expensive methods either, in the case of watermarked paper, for the costs 
involved in the paper manufacturing process, or, in the second case, for 
the costs of preparation of the type plate (electrotype) and even more of 
the paper substrate in that said substrate is usually previously coated 
with a film of a material (such as PVC, polyester, polypropylene, 
polythene, coating, etc.) suitable to receive and permanently retain the 
holographic microengravings engraved by the electrotype. Moreover, in the 
case of holograms the manufacturing costs are economically sustainable 
only for mass productions (generally using substrate material in reels) 
whose plant require high investments. 
For example, WO-A-89/03760 discloses a method for impressing holograms on a 
paper or plastic sheeting by providing a coating thereon and then 
embossing the coated substrate. The coating can be applied in different 
ways according to the thermoplastic material employed in the process (e.g. 
polyethylene by extrusion). Regardless of the specific process, this 
coating step of covering the whole surface of the sheet with a uniform 
coating layer implies the above-mentioned problems. 
SUMMARY OF THE INVENTION 
The present invention is aimed at overcoming these drawbacks and 
limitations by providing a method for protecting from forgery, assuring 
the authenticity of or personalizing pre-printed sheets, which has a 
significantly low cost and is suitable not only for mass production 
applications but also and particularly for small productions. 
To this purpose, the method according to the invention provides the 
protection or personalization of the pre-printed sheet by impressing 
microengravings, on all or some of the printed portions of the sheet, said 
microengravings corresponding to holograms or diffraction patterns or 
images or words and being obtained through a hot embossing process, 
carried out at a temperature higher than the softening point of the dyeing 
substances used for obtaining the print on the pre-printed sheet. 
The features of the invention will be apparent from the following 
description of a non-limiting embodiment schematically illustrated in FIG. 
1. 
According to the method of this example, once the type and content of the 
microengraving to be transferred on the pre-printed sheets have been 
selected (e.g. the microengraving of an hologram showing a specific figure 
or producing a particular visual effect), a type plate of the hologram is 
prepared according to the processes conventionally used for the embossing 
of holograms, said plate usually consisting of a flexible metallic sheet 
having the microengraving of the hologram and designed to be applied onto 
that of the two cylinders of an embossing group which is usually called 
"embossing cylinder". 
Assuming that the treatment is to be applied to pre-printed sheets of small 
size and not in reels (this latter case being particularly simple as it 
will be said further on), the sheets have to be subjected to an embossing 
process by using said plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Obviously, a conventional sheet feeder and sheet collector may replace, 
respectively, the holding tray 1 and the collecting tray 10. Cylinder 7 
must have the characteristics usually required for embossing cylinders, 
namely it must be made from ground and lapped hardened steel of high 
surface resilience, with a very high degree of surface finish, such that 
the cylinder surface has a degree of linearity (i.e. of approximation of a 
straight line), along any generatrix of the cylindrical surface, which is 
not lower than the order of magnitude of the resolution of the 
microengravings on the plate. An acceptable value of said degree of 
linearity could be, for example, around 2000 lines per mm. 
Cylinder 8 is made from hardened steel, preferably coated with a rubber 
layer having a Shore hardness of 75.div.100, and is idle around its axis 
so that, when operating, it can be driven by the rotation of the upper 
cylinder 7. Its shaft is supported at its ends by two spring supports 
(cup-type springs) and exerts against cylinder 7 a pressure between 1 and 
60 kg/mm.sup.2, preferably around 20 kg/mm.sup.2. 
The type plate is secured onto the surface of cylinder 7 and is sized so as 
to cover substantially the whole thereof. Alternatively the cylinder 
itself could be engraved with the microengravings. 
When operating, said cylinder is heated (e.g. by means of a fluid 
circulating therein or by means of an electrical resistor) at a 
temperature such as to assure that the paper of the document passing under 
the plate reaches a temperature a little higher (e.g. by 10.degree. C.) 
than the softening temperature (e.g 80.degree. C.) of the dyeing 
substances used for obtaining the print on the pre-printed sheet. Said 
temperature of the cylinder shall be selected according to the operating 
speed, in that higher operating speeds require higher cylinder temperature 
in order to achieve the same paper temperature. For a paper temperature of 
about 80.degree. C. and an operating speed around 20 m/min, the cylinder 
temperature could be in the range of 120.degree.-140.degree. C. 
For the correct working of the machine it is necessary that, at each 
embossing operation, the document picked from tray 1 is taken to the inlet 
to the embossing group and starts passing between the cylinders with a 
proper phase, i.e. at the moment when the plate leading edge is arriving 
at the area of contact between the cylinders. The mechanism for picking 
and feeding the sheets in phase with the plate leading edge can be made 
much alike similar mechanisms already used in other machines, such as for 
example the mechanism of a xerographic machine which assures the picking 
and phased feeding of the sheets to the light-sensitive drum of the 
machine. 
It is apparent from the above how it is possible and takes place the 
transferring of the microengravings on the plate to the document in 
transit. In fact, since during the passage of the document between the 
cylinders the document reaches, in the contact area, the softening 
temperature of the dyeing substances, the plate can impress the 
microengravings on the film that said substance is forming on the paper, 
which microengravings will remain permanently retained on the pre-printed 
portions after the document has come out of the cylinders and has been 
substantially immediately cooled by the cooling group 9. 
As an alternative, the paper could be heated by a heating group (e.g. by 
hot air, IR, heated rollers 5, etc.) prior to entering the embossing 
group, and the latter could also include the cooling by having cylinder 7 
and 8 internally cooled (e.g. by water, air, oil, etc.). In this way, the 
cooling takes place almost simultaneously with the impressing of the 
microengravings, thus assuring an even better "freezing" thereof than by 
cooling rollers 9. 
It can be understood that the above-described method is suitable both for 
large series and small series treatments. In the latter case the machine 
can have a reduced size and cost, comparable with those of an office 
machine (e.g. a xerographic machine) so that it can be a useful tool for 
industries, banks, offices, etc. 
The previously mentioned advantages are apparent from the above. In fact: 
the method assures the impossibility of counterfeiting a document treated 
therewith, both for the possibility of erasing and forging (which would 
necessarily cancel in the forged portion the microengravings and their 
visual effect) and of copying (presently known copying methods are not 
able to reproduce the microengravings); therefore, the method can be used, 
for example, for issuing uncounterfeitable cheques in a quite cheap and 
reliable way; in the same way, it can be used for assuring the originality 
of any document; 
it can be used for personalizing in a very cheap way a wide range of 
documents such as headed paper, leaflets, coupons for various uses, 
shares, stocks, bank or government bonds, etc. 
As already mentioned, the above-schematized embodiment has been described 
as a mere non-limiting example and many modifications, adaptations, 
additions, changes and replacements of members with other functionally 
equivalent ones can be made thereto yet without departing from the spirit 
of the invention and from the protecting scope of the appended claims. 
A modification could concern the area of the plate which could be lower 
than that of the cylindrical surface of the embossing cylinder rather than 
being equal thereto. 
Another modification could be the application of the method to a 
xerographic machine, by inserting the embossing group immediately 
downstream from the light-sensitive drum so that each document coming out 
from the photocopying machine is automatically protected from forgery and 
personalized. Similarly, the method could be applied in line with 
lithographic, rotogravure, or flexographic machines. 
A further modification could be the application of the method to 
pre-printed sheets in reels. In this case the corresponding machine would 
have a configuration quite similar to that of current embossing machines.