Note: Descriptions are shown in the official language in which they were submitted.
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THERMOPLASTIC FILM FOR USE IN T~E MANUFACTURE OF
FORGERY-RESISTANT IDENTIFICATION DOCUMENTS
The present invention relates to a coated
film which is suitable for use as a protective film in the
manufacture of forgery-resistant identification documents
carrying a photograph.
Background of the Invention
Identification documents, such as identity
cards, passports, drivers licenses etc. are sometimes
tampered with by exchanging the photograph and/or by
altering the information contained in the documents.
Great ef~or~s are therefore undertaken to render such
identification documents forgery-resistant.
British Patent 888,359 discloses applying a
cover sheet and a back sheet of polyester film to
identification cards in which a photograph is mounted
on a paper core sheet. The polyester film is provided
with a coatiny of thermoplastic adheslve, by which it
is then bonded to the paper core. The adhesion of
this film is, however, not verY high, and it is
consequently still relatively easy to peel the cover
film off the support without damaging the support.
To improve adhesion, it has been proposed in
U.S. Patent 3,413, 171 to coat the paper support with a
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thermoplastic adhesive layer of the same kind. But
also in this case, it is apparent tha-t the thermoplastic
bonding material adheres poorly to the surface of the
photograph, and the protective covering still comes
off the support or can be removed by unau-thorlzed
persons without leaving any noticeable trace on the
photograph. ~ ~ ~ ~ 9 ~ 7
German Auslegeschrift 2,736,852~discloses
protective coverings for identification cards, in which
the thermoplastic adhesive layer of the cover sheet is
provided with an additional coating to improve bonding,
the coating being applied in the form of a pattern.
There is, however, no indication as to the adhesion of
the protective covering, in particular under thermal
stress or upon treatment with solvents. It is also a
disadvantage of this film that it is technically
difficult and expensive to manufacture. The protective
covering is apparently intended for bonding only to
photographs which are still moist.
U.S. Patent 4,093,489 describes protective
coatings for photographs, which consist of thermosetting
catalyst-containing melamine/formaldehyde condensation
products. The coatings are cured at high pressure for
a period ranging between 3 and 10 minutes, depending
on the circumstances of each particular case.
This process has the disadvantage that, due to the long
pressing times required, it is unsuitable for a con-
tinuous operation in which the material is continuously
taken off a roll.
U.S. Patent 4,115,618 discloses protective
sheets for identification cards which compri~e a
cellulose triacetate layer which is hydrolized on one
surface and, bonded thereto, a layer consisting of a
mixture of polyYinyl alcohol and polyvinyl acetate.
3~ A drawback of this film is that lamination must be
effected wnile the photograph is moist.
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A film which is intended to be used as a protective covering in the
manufacture of forgery~resistant ldentification documents must meet numerous
requirements. The laminated protective film should withstand any attempt to
detach it from the support at room temperature or even UpOII heat treatment. It
should be readily weldable and resistant to delamination, even when treated with
conventional organic solvents. Foremost, however, it must adhere so firmly to
the gelatin layer of the photograph that it cannot be detached under the above-
specified conditions without destroying the photograph. In addition, the film
must be scratch-rasistant, fast to light, free of yellowing and ageing-resistant.
If the information carriers are contained in the identification card in the form
of an embossing, the protective film must additionally be capable of being
embossed satisfactorily, i.e. quickly and with sharp outlines, and embossing must
not lead to cracks or fissures.
None of the coa-tings described hereinabove mee-t all these requirements
simultaneously.
Accordingly it is one purpose of the present invention to provide a
film for manufacture of identification documents which adheres strongly to a
core sheet.
Another purpose of the present invention is to provide a film for
manufacture of identification documents which cannot be removed from a photograph
without destroying the photograph.
A further purpose of the present invention is to provide a film for
manufacture of identification documents which adheres well even at elevated
temperatures.
It is also a purpose of the present invention to provide a film for
manufacture of identification documents which resists separation when treated
with solvents.
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An additional purpose oE the present invent:lon is to provide a film
for manufacture of identification documents which is relatively easy and ;nexpen-
sive to manufacture.
Yet another purpose of the presen~ invention is to provide a film for
manufacture of identification documents which can be applied in a short period
of time and facilitates continuous production techniques.
A still further purpose of the present invention is to provide a film
for manufacture of identification documents which can be readily applied over
a photograph even after the photograph is dry.
Another purpose of the present invention is to provide a film for
manufacture of identification documents which is readily weldable or heat-seal-
able.
It is also a purpose of the present invention to provide a film for
manufacture of identification documents which is scratch-resistant, light stable,
resistant to ageing and does not yellow.
A further purpose of the present invention is to provide a film for
manufacture of identification documents which can be satisfactorily embossed.
In accordance with this invention there is provided a forgery-resistant
identification document comprising a core carrying identifying information, said
core having laminated thereto the cover layer side of a thermoplastic protective
film comprising a base layer and a cover layer comprising a partially hydrolyzed
olefin-vinyl ester copolymer, the degree of hydrolysis of said copolymer lying
in the range from 20 to 99 percent, said laminated protective film being
impossible to detach from said document at temperatures up to and as high as
120C. without destroying said document.
In accordance with this invention there is additionally provided a
method of protecting an identification document against forgery comprising
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laminating to said document the co~er layer side of a thermoplastic protective
film comprising a base layer a~nd a cover layer comprising a partially hydrolyzed
olefin/vinyl ester copolymer, the degree of hydrolysis of said copolymer lying
in the range from 20 to 99 percent, said laminated protective film being
impossible to detach from said document at temperatures up to and as high as
120C. without destroying said document.
In the manufacture of the forgery~=resistant identification document,
the cover layer side of the protective film is laminated under the action of
heat to the identification document. The clocument suitably comprises a core
carrying identifying information and, optionally, a photograph. If desired, the
resulting laminate can be hot embossed under pressure~
The cover layer preferably comprises a partially hydrolyzed ethylene/
vinyl ester copolymer. A partially hydrolyzed ethylene/vinyl acetate copolymer
is particularly preferred because it is readily available. In particular,
polymers have proved suitable, in which the olefin content, preferably the
ethylene content, amounts to at least 29 mole percent.
The degree of hydrolysis of the cover-layer polymer is preferably in
the range between 20 and 99 percent. The selec*ion of polymers which can be
used for the cover layer depends principally on the sealing conditions and
on the mechanical strength of the protective film and the base.
In addition to the pure, partially hydrolyzed olefin/vinyl ester
copolymers, mixtures of such copolymers with compatible polymers can also be
used for the cover layer. Preferably, the polymers to be admixed carry carbonyl
groups. Typical examples include ethylene/vinyl acetate copolymers, ethylene/
acrylic acid or ethylene/acrylic acid ester copolymers, polyesters, polyamides
and polyurethanes. It is also
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possible to add resins, such as terpene resins.
The base layer and also the cover layer rnay contain
the usual additivies, for example, anti~oxidants,
pigments, dyes etc. The choice and the amount of
the additives depends largely on the desired trans-
parency of the final film, the compatibility, e.g.
under thermal stress, and the unimpaired sealability
of the cover layer.
As the base layer any films are actually suitable
whi.ch are scratch-resistant and ageing-resistant
~nd which do not yellow, even after a prolonged period
of time. Preferred base layers comprise films of
polyvinyl chloride, polyester, polycarbonate, poly-
amide, cellulose acetobutyrate and cellulose acetate.
Polyester films are preferred, particularly polyethylene
terephthalate films~
The films may be employed in the non-oriented
state. Preferably, however, they are used in the
stretched and heat-set state because such films
exhibit a higher mechanical strength and little or no
shrinkage under thermal stress.
The total thickness of the protective film can
be varied and depends substantially on the require-
ments of the particular case. If the identification
document is intended to be embossed after lamination
of the protective film,the layer thickness must
additionally be adapted to the embossing conditions
including temperature, pressure~ and required ~epth of
embossing. Films of soft-flowing and readily deformable
polymers, such as poly~inyl chloride, require only
small pressing pads, while embossing of films such as
oriented polyester films becomes difficult with
increasing layer thickness,
t'arious methods may be used to produce the
protective film. Film can be prepared from pa~tially
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hydrolyzed olefln/vinyl ester copolymer and then
laminated to the base layer, preferably by means of
an adhesion-promoting layer, It is also possible to
start with the base film and, preferably after the
application of an adhesion-promoting layer, melt-coat
the base film with the olefin/vinyl ester copolymer.
Alternatively, the protective film may be produced
by coextruding the polymers and uniting the layers in
the thermoplastic state.
If adhesion-promoters are usec, such products are
preferabl~ employed which, after cross-linkiny, still
exhibit a sufficient adhesion under thermal stress
acting on the protective film. Suitable examples
include urethane prepolymers cross-linked with expoxides
or similar products,
If desired, the cover layer of the partially
hydrolyzed olefin/vinyl ester copolymer may be provided
with an additional layer, for example, to further
improve the adhesion on the base or on the photgraph.
This layer is preferably printed on in a discontinuous
pattern, the pattern beiny especially designed in such
a way that tearing lines cannot form in any attempt to
detach the protective film from the identification
document.
As the additional layer, polymer solutions of
polyamides, polyesters, polyurethanes or ethylene vinyl
acetate may be applied. Polymers which adhere to the
cover layer without further intermediate layers,which
form a layer which does not tend to blocking, and which
do not substantially affect the transparency of the
protective film, are preferred,
The protectivefilm is preferably subjected -to a
corona treatment, either immediately after manufacture
or shortly before it is laminated to the identification
document~ It has been found that such a treatment may
further enhance the adhesion between the base and the
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protective film.
Further details of the invention will become
apparent from a consideration of the following non-
limiting examples,
Exam~le 1
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A protective film made up of the following layers
was prepared by melt-coating:
a. biaxially stretched and heat-set poly-
ethylene terephthalate layer50~m
10 b. polyurethane adhesive (UK 3645/UK 6200
supplied by HENKEL GmbH) 4~m
c. layer comprising 97 percent of a
hydrolyzed ethylene/vinyl acetate
copolymer having an ethylene
content of about 45 ~ole percent 120~m
After a corona treatment, the protective film was
laminated at 130C under pressure with its cover-
layer side to normal photographic paper and was then
embossed at the same temperature under high pressure.
It was impossible to detach the protective film
at room temperature or even at 120C, without
destroying the photographic paper. Even after keeping
the material for several days in water and in various
customary organic solvents, such as ethyl alcohol,
methanol, benzene etc., the protective film could
only be detached by destroying the base.
Example 2
A protective film made up of the following layers
was prepared by melt-coating:
a, biaxially stretched and heat-set
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polyethylene terephalate film 50~m
b. polyurethane adhesive of Example 1 ~m
c. layer composed of a blend of 90 percent
by weight of the copolymer of Example 1
and 10 percent by weight of an
ethylene copolymer containing carbonyl
groups
($ Lupolen A 2910 M supplied by
BASF AG3 lOO~m
The protective film was corona-treated and -tested
as described in Example 1. The same results as in
Example 1 were also obtained with this film.
Example 3
The cover layer of the protective film of
Example 1 was partially printed in the form of a
pattern with a sealable polyamldelayerO and ~he
printedlayer was subjected to a corona treatment.
The tests carried out and the results obtained
corresponded to Example 1.
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Example 4
A protective film composed of polyamide 6 (50~m)
and of the copolymer of Example 1 (150~m) was prepared
by coextrusion.
After corona treatment, the tests of Example 1
were performed.
The results obtained corresponded to those given
in Example 1.
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Example 5
The procedure of Example 1 was repeated, with
the exception that the Gover layer was composed of a
blend of 60 percent by weight of the partially
'nydrolyzed ethylene/vinyl acetate copolymer of Example
S 1 and 40 percent by weiyht of a cooolyamide (~ Durethan
C 38F supplied by ~AYER AG),, The test results obtained
were the same as in Example 1.
The foregoing embodiments have been described
merely as examples of the invention and are not
intended -to be limiting~ Since modifications of
the disclosed embodiments incorporating the spirit
and subs-tance of the invention may occur to persons
skilled in the art, the scope of the invention is
to be limited solely with respect to the appended
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