Note: Descriptions are shown in the official language in which they were submitted.
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Hot-melt adhesive component layers for smart cards
The invention relates to a multilayer composite, to a
process for producing it, and to the use of
thermoplastic hot-melt adhesives for producing said
composite.
The present invention is concerned predominantly but
not exclusively with the production of what are known
as smart cards. By a smart card is meant a generally
multilayer article in the form of a plastic card, which
is commonly provided with information and/or
advertising imprints and/or with security features,
such as a photo of the cardholder, a magnetic strip, an
identification symbol in the form of a hologram or the
like. This smart card commonly consists of a plastic
card laminated on one or both sides. Embedded in the
body of the smart card is what is known as a module,
whose key constituent is an electronic circuit (chip).
This chip may be seated on a support plate which in one
particular embodiment is provided with a plurality of
electrically conductive surface segments. This
segmented electrical contact area is accessible from
the outside so that information, e.g. data and
identification features, may be exchanged by way of
these contacts with external computers and/or control
equipment.
Newer types of card include an antenna connected
electrically to the chip within the card body, so that
by way of this antenna there is the facility both for
contactless electronic exchange of information and for
contactless supply of energy to the chip in the card
body. Smart cards of this kind are used or envisaged as
telephone cards, authorization cards for mobile
communication devices, check cards in monetary
transactions, proofs of authorization for health
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insurance organizations, driver's licenses, train
tickets, and bus tickets. The user inserts the
contactless smart card into a card reader or moves it
at a distance past the reader, which communicates with
the electronic circuit in the smart card by way of a
corresponding antenna facility. In this way it is
possible, for example, in the case of a telephone card
or a check card or a rail ticket, to check the presence
of funds, to ascertain an identity, or to perform some
other data exchange.
Production processes for the contactless smart cards
are known in principle. For instance, WO-A-98/09252
describes a multistage production process. In that
process, the so-called component layer or card body is
provided with openings, depressions or similar
cavities, after which the electronic components to be
disposed in the card body are inserted into these
cavities, then the card body is coated with an adhesive
in such a way that the cavities are filled and the
adhesive forms a substantially planar surface.
Subsequently, a cover film is applied to the surface of
the adhesive, which has not yet set or fully cured and
which is therefore still plastically deformable. The
face of the cover film remote from the card body is
then held fixed on a shaping surface in such a way and
for sufficient time, during the curing of the adhesive,
that the external contour of the cover film and thus
the external contour of the finished smart card
corresponds to the contour of the shaping surface. The
adhesive proposed is a cold-curable adhesive, in
particular an epoxy adhesive. In order to prevent
shrinkage of this adhesive, it must be filled with a
filling material such as glass, quartz or the like.
This production process comprises many worksteps and is
time-consuming and therefore very costly.
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EP-A-0 692 770 describes a process in which the chip
and the antenna are introduced into the cavity of an
injection mold, after which a thermoplastic material is
injected into this mold, where appropriate in a
plurality of worksteps. The thermoplastic material
proposed comprises typical injection molding materials
such as PVC, ABS (acrylonitrile-butadiene-styrene
terpolymer), polyethylene terephthalate (PET),
polycarbonate (PC) or polyamide (PA). Such injection
molding materials require very high temperatures during
processing, and high pressures of, for example,
700 kg/cm2. Such high pressures and temperatures are,
however, very poorly suited to the sensitive electronic
circuits to be embedded, with the consequence that
these circuits often suffer damage.
EP-A-0 709 804 proposes, in a multistage injection
molding process, first inserting a plastic disk into
the injection mold, the antenna being placed on said
disk. Subsequently, a liquid polymer material (mention
is made specifically of ABS, PC, PET, polyamide or
reactive resins curable at higher temperatures such as
polyurethane, epoxy-phenolic resins) is spread over the
surface of the antenna, with the antenna connections
being left exposed. Subsequently, a plastic film which
closes the hole in the card is placed over the antenna.
This plastic film has an indentation into which the
electronic chip is accommodated in such a way that it
is in electrical contact with the antenna contacts.
This procedure also necessitates high temperatures and
high pressures for the injection molding steps;
furthermore, additional worksteps are necessary in
order to insert the electric circuit into the card
body, to fix it and to connect it electrically to the
antenna.
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JP-A-08 276 459 describes a production process for
contactless smart cards in which the component support
comprises a glass fiber reinforced epoxy resin which
has an indentation and, where appropriate, comprises
conductor tracks, including that for forming the
antenna. The electronic chip is introduced into the
indentation of the component layer. Subsequently, this
entire component is inserted into an injection mold
and, after the mold has been closed, a liquid,
thermosetting polymer material is injected into it at
low pressure and is cured therein. Specifically, a
thermosetting epoxy resin is proposed for this purpose.
The curing of the epoxy resin takes 4 to 5 minutes;
after the molding has been removed from the mold,
after-curing by heating at a certain temperature for a
certain time is necessary - specific details of this
aftercure are lacking.
EP-A-0 350 179 describes a production process for smart
cards and similar electronic tokens with the aid of a
reaction injection molding process. The electronic
circuit is encapsulated by a layer formed by the
reaction injection molding material. The cover films of
the two flat sides of the card are supplied to the mold
in the course of injection molding in such a way that
they serve simultaneously as mold release agents for
facilitating the removal of the cured card body from
the injection mold. Specific details regarding the
composition of the polymer for the reaction injection
molding process are not given; all that is said is that
it is possible to take any polymer material or any
polymer blend that cures under reaction injection
molding conditions. Owing to the precision metering
equipment they entail, reaction injection molding
machines are known to be expensive and complicated.
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EP-A-0 846 743 describes a thermoplastic, heat-curable,
self-adhesive sheet for implanting electric modules
into a card body which is provided with a cutout into
which it is intended an electronic module should be
arranged, said module having on the first side a
plurality of contact areas and on the opposite side an
IC chip whose contacts are connected by electrical
leads to the contact areas. The adhesive sheet is to be
composed of a thermoplastic polymer, one or more
tackifying resins and/or epoxy resins with hardeners,
and also accelerators, where appropriate. These
adhesive sheets have to be heat-cured at approximately
150°C for 30 minutes.
JP-A-05 270 173 describes a process for producing
laminated sheetlike polymer structures for blank card
bodies. For this purpose, two rigid PVC sheets are
coated with a film of a moisture-curing polyurethane
hot-melt adhesive from 5 to 50 ~m thick at from 100 to
120°C and are compressed for 10 seconds under a
pressure of 5 kg/cm2. One of these sheets has a cutout,
or a cavity produced by thermoforming, intended to
accommodate the microprocessor that is to be inserted
subsequently. Thereafter, these sheetlike structures
are left at room temperature for several hours without
pressing, so that the adhesive cures to give a card
base material which can be processed to the finished
smart card in further processing steps.
An object of the invention was therefore to develop a
gentle, quick and easy process for producing smart
cards, permitting cost-effective large-scale
manufacture of such smart cards.
The inventive achievement of the object is set out in
the claims. It essentially comprises the use of
thermoplastic hot-melt adhesives for producing the
component layers of smart cards, and a process for
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producing said smart cards wherein the thermoplastic
hot-melt adhesives can be used at low temperatures and
low pressures in the low-pressure injection molding
process.
As thermoplastic hot-melt adhesives it is preferred to
use the low-melting polyamides based on
polyaminoamides, thermoplastic polyurethanes or atactic
polypropylene, or a blend thereof, to produce the
component layer. These thermoplastic hot-melt adhesives
feature a low viscosity of from about 100 to
100 000 mPa.s at the processing temperature. As a
result, they can be used in the low-pressure injection
molding process at pressures of between 1 and 50 bar,
preferably at injection pressures of between 10 and 30
bar. The processing temperatures are guided by the
composition of the hot-melt adhesive material; they are
situated at between 80°C and 250°C, preferably between
100°C and 230°C. The polyamides to be used with
preference generally have a viscosity of less than
10,000 mPa.s at 210°C. Particularly preferred ranges of
the processing viscosities at 210°C are situated at
between 1,500 and 4,000 mPa.s, this viscosity usually
being measured using a Brookfield viscometer of the
RVDV II type with Thermose facility.
In particular cases, reactive, moisture-
postcrosslinking polyurethane hot-melt adhesives may be
used instead of the aforementioned thermoplastic hot-
melt adhesives. The moisture-reactive polyurethane hot-
melt adhesives, although involving increased effort
during application owing to their moisture sensitivity,
have an advantage which lies in the markedly lower
viscosity at processing temperatures: reactive
polyurethane hot-melt adhesives generally have
viscosities at 130°C of < 25 000 mPa.s, preferably
indeed below 15 000 mPa.s, and with very particular
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preference below 10 000 mPa.s at 130°C, the viscosity
customarily being measuring using a Brookfield
viscometer of the RVDV II type with Thermose facility.
An advantage of the use of moisture-curing polyurethane
hot-melt adhesives is their low melting point, which is
generally below 100°C, preferably below from 70 to
80°C, so that even very temperature-sensitive circuits
may be embedded using these hot-melt adhesives and even
very temperature-sensitive laminating films may be
used. Their postcrosslinking with moisture results in
the formation of a particularly resistant and
temperature-stable bond between component layer and
base film and cover film.
Through the use of the thermoplastic hot-melt adhesive
to produce the component layer, the subsequent milling
to produce the space require to accommodate the chip,
or chip and antenna, becomes unnecessary, since these
parts to be encapsulated may be placed in the
corresponding encapsulation mold prior to the finishing
of the base structure. During the subsequent
encapsulation process, chip, or chip and antenna, are
surrounded by the base body thus produced (component
support) such that there is no longer any subsequent
need either for additional fixing or for any cushioning
or surround-filling of the electronic components.
Moreover, when the printable or printed base film and
cover film are applied, it is possible to forego
additional application of adhesive to the component
support, since the latter is of course itself
manufactured of adhesive and, following appropriate
activation by heating if desired, forms a secure bond
with the base films and/or cover films.
In accordance with the invention, all thermoplastic,
reactive and nonreactive hot-melt adhesives may be used
to produce the card base body, provided they can be
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processed at temperatures between 80°C and 250°C,
preferably between 100°C and 230°C, in the low-pressure
injection molding process, i.e., their processing
viscosity should be situated at between 100 and
100 000 mPa.s. The pressure range for the low-pressure
injection molding process is situated in the range from
to 30 bar, particular preference being given to a
range for injection molding of between 10 and 30 bar.
This ensures that the inserted chips or other
10 electronic storage media used can be surrounded gently
and not damaged and destroyed as in the regular
injection molding process by means of high injection
pressures (500 to > 1 000 bar).
Depending on the nature of the base film and cover film
used for the finished card, and on the stiffness and
elasticity requirements of the card body, and the
possible temperature stresses thereon, the hot-melt
adhesives may be selected from the conventional groups
of polyamide (especially polyamidoamide based on
dimerized fatty acids), polyurethane, polyesters,
ethylene-vinyl acetate (EVA) copolymer, low molecular
mass polyethylene copolymer, atactic polypropylene
(APP), or combinations thereof. As already mentioned
above, it may be advantageous in particular cases to
use reactive hot-melt adhesives based on moisture-
postcrosslinking polyurethanes instead of the
aforementioned thermoplastic hot-melt adhesives.
As the base film and/or cover film it is possible here
to use all films known in principle for this purpose;
examples that may be mentioned include films based on
polyester, especially polyethylene terephthalate (PET),
polyvinyl chloride (PVC), acrylonitrile-butadiene-
styrene (ABS), polycarbonate (PC) or polyimide. These
films usually have thicknesses of up to 100 Vim;
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preferably, the film thicknesses are situated in the
range between 30 and 70 ~.m.
In the production process of the invention, a variety
of procedures can be adopted. Firstly, the chip and the
associated antenna, where appropriate, may first be
placed in the injection mold of the injection molding
unit, it being possible for the chip and antenna to be
in preassembled form on a support film, for example.
After the mold has been closed, the hot-melt adhesive
is then injected. After brief cooling, the mold can be
opened and the component layer thus produced removed
from the mold. No further application of adhesive is
required for the subsequent lamination with a base film
and/or cover film, since the matrix of the card body
layer acts itself as an adhesive: all that need be done
is to compress the films with the component layer, with
heating where appropriate.
Alternatively, a thin film of the hot-melt adhesive may
be placed in the injection mold, and the electronic
component and the antenna placed thereon. Subsequently,
the mold is closed and the electronic components are
completely encapsulated by the injection of further
hot-melt adhesive material. Again, no further
application of adhesive is necessary for lamination
with the base and/or cover film, since here again, with
heating where appropriate, the films can be compressed
with the component layer and so are connected
permanently to the layer. The film thickness of the
hot-melt adhesive matrix including the encapsulated
chip is presently in general between 400 and 600 Vim,
preferably 500 ~.m, but may turn out to be thinner or
thicker depending on the type of chip.
For the embedding of the electronic component and the
antenna into the matrix of the card support layer
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comprising the hot-melt adhesive, it is possible in one
particularly preferred embodiment to use a low-pressure
processing system from Optimel Schmelzgul3technik. The
preferred embodiment of the injection mold is depicted
in figures 1 to 3. Of these figures,
Fig. 1 shows a plan view of the bottom part of the
injection mold,
Fig. 2 shows a side view of the top part of the
injection mold,
Fig. 3 shows a detail of the top part.
In accordance with Fig. 1, the bottom part 1 of the
injection mold possesses a cutout 2 whose length and
width correspond to the dimensions of the top part of
the injection mold. The bottom part of the injection
mold further comprises the runner 3, which is designed
so that the hot-melt adhesive is able to fill the
entire mold, fully and without bubbles, within very
short cycle times. Moreover, the shape of the runner is
designed so that the sprue remaining on the card body
can be removed easily after the card body has
solidified.
Fig. 2 shows a cross-sectional view of the upper part 4
of the injection mold across the line A-B of Fig. 1. In
its upper marginal region this top part has a
projection 5, so that when the top part engages in the
cutout 2 of the bottom part a fully closed chamber is
formed in the injection mold. The cutout 6 of the top
part 4 corresponds in its length and width dimensions
to the card support layer that is to be manufactured;
the thickness of the cutout 6 corresponds to the
thickness of the component layer that is to be
manufactured.
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Fig. 3 shows a detailed view C of Fig. 2, which shows
in detail the cutout 6 for the card support layer.
Alternatively, in a continuous manufacturing process,
the base film and cover layer film may be supplied to
the injection mold simultaneously with the chip and,
where appropriate, the antenna, which where appropriate
may also have been applied in a copper foil on a thin
flexible film. After the mold has been closed, the hot-
melt adhesive is again injected. After brief cooling
and opening of the mold, the finished layer body may be
transported further. This procedure affords the
advantage that the base layer and cover layer may be
used simultaneously as mold release agents in the
injection mold. In all of the aforementioned production
processes, the base film and/or cover film may be
provided in an upstream or downstream manufacturing
step with customary information and/or advertising
imprints and/or security features such as a photo of
the cardholder, a magnetic strip, an identification
symbol in the form of a hologram or the like.
The advantages of the use of thermoplastic hot-melt
adhesives to produce the component layers, in
accordance with the invention, relative to the prior
art, are:
~ There is no need for support material which has to be
produced separately by normal injection molding
process.
~ Milling work to produce the cutouts for the chip and
the antenna is unnecessary.
~ Also unnecessary is the separate adhesive bonding of
chip and antenna into the cutouts.
~ Following lamination with base film and cover film
there is no "readthrough" of the unevennesses from
conventional manufacture, since the card support
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layer on the one hand possesses a very smooth surface
and on the other hand itself acts as an adhesive.
Although the principal field of application of the
invention is in the production of contactless cards
comprising electronic circuits (smart cards), this
technology may also be used to produce transponders for
the vehicle industry, in mechanical engineering and in
container construction for the control of operations.
