U.S. patent application number 10/899461 was filed with the patent office on 2005-01-06 for multilayer card.
Invention is credited to Brennan, William James, Lawrence, Paul David, Rhoades, Gary Victor.
Application Number | 20050003962 10/899461 |
Document ID | / |
Family ID | 33518447 |
Filed Date | 2005-01-06 |
United States Patent
Application |
20050003962 |
Kind Code |
A1 |
Brennan, William James ; et
al. |
January 6, 2005 |
Multilayer card
Abstract
A multilayer card has (i) an opaque polyester film substrate (1)
containing 0.2 to 30% by weight, relative to the total weight of
the substrate, of at least one copolyesterether, (ii) an
ink-receptive layer (2) on at least one surface of the substrate,
and (iii) a cover layer (4) on the surface of the ink-receptive
layer and/or surface of the substrate. The presence of the
copolyesterether in the substrate reduces the tendency of the card
to delaminate in use. Suitable for use, inter alia, in
identification, magnetic, credit, pre-paid and smart cards.
Inventors: |
Brennan, William James;
(Cleveland, GB) ; Rhoades, Gary Victor;
(Middlesbrough, GB) ; Lawrence, Paul David;
(Cleveland, GB) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
33518447 |
Appl. No.: |
10/899461 |
Filed: |
July 26, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10899461 |
Jul 26, 2004 |
|
|
|
09155842 |
Apr 6, 2001 |
|
|
|
Current U.S.
Class: |
503/227 |
Current CPC
Class: |
B32B 27/20 20130101;
Y10T 428/24802 20150115; Y10T 428/2495 20150115; B32B 27/308
20130101; B32B 27/36 20130101; B32B 2307/41 20130101; B32B 27/08
20130101; Y10T 428/31855 20150401; Y10T 428/24942 20150115; B32B
2425/00 20130101 |
Class at
Publication: |
503/227 |
International
Class: |
B41M 005/38 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 10, 1996 |
GB |
9607401.8 |
Claims
1-7. (Cancelled).
8. A method of producing a multilayer card which comprises forming
an opaque substrate by extruding a layer of molten linear polyester
comprising an opacifying agent and in the range from 0.2 to 30% by
weight, relative to the total weight of the substrate, of at least
one copolyesterether, quenching the extrudate, orienting the
quenched extrudate in at least one direction, forming an ink
receptive layer on at least one surface of the substrate, applying
pictorial and/or written information on the surface of the
ink-receptive layer, and forming a cover layer on the surface of
the information carrying ink receptive layer and/or surface of the
substrate.
9. A method according to claim 9 wherein the substrate and
ink-receptive layer(s) are formed by coextrusion.
10. A method according to either one of claims 8 and 9 wherein the
multilayer card is formed by laminating together two or more
separate self-supporting film structures.
Description
[0001] This invention relates to a multilayer card such as an
identification, credit or magnetic card, and in particular to a
multilayer card comprising an opaque polyester film substrate.
[0002] Polyester films, such as polyethylene terephthalate, are of
utility in a wide range of applications including magnetic
recording media--such as tapes and discs, as supporting substrates
for light-sensitive emulsions, pressure-sensitive adhesives and
metal layers, as decorative drapes, electrical insulants, packaging
films and cards.
[0003] Polyester films have been used in the production of an
identification or magnetic card, such as a credit card, and in
particular a "pre-paid card", eg a telephone card, and a "smart
card", which is, for example, capable of storing information
relating to a number of financial transactions. Such cards are
usually constructed of multiple sheets of the same, eg all
polyester, or different materials, eg alternative sheets of
polyester, such as polyethylene terephthalate and PETG,
polycarbonate, polyolefin, polyvinyl chloride, ABS resin or paper.
A card preferably contains at least one opaque layer. We have
discovered that the presence of an opaque polyester film in a
multilayer card results in a tendency of the card to delaminate in
use, with subsequent peeling of the layers.
[0004] Copolyesterethers have been used in polyester films to
improve the flex-crack resistance thereof. EP-A-0437942 describes a
transparent polyester film containing a copolyesterether which is
suitable for use in packaging applications.
[0005] We have now devised a multilayer card comprising an opaque
polyester film substrate which exhibits improved resistance to
delamination.
[0006] Accordingly, the present invention provides a multilayer
card comprising (i) an opaque polyester film substrate comprising
in the range from 0.2 to 30% by weight, relative to the total
weight of the substrate, of at least one copolyesterether, (ii) an
ink-receptive layer on at least one surface of the substrate, and
(iii) a cover layer on the surface of the ink-receptive layer
and/or surface of the substrate.
[0007] The invention also provides a method of producing a
multilayer card which comprises forming an opaque substrate by
extruding a layer of molten linear polyester comprising an
opacifying agent and in the range from 0.2 to 30% by weight,
relative to the total weight of the substrate, of at least one
copolyesterether, quenching the extrudate, orienting the quenched
extrudate in at least one direction, forming an ink receptive layer
on at least one surface of the substrate, applying pictorial and/or
written information on the surface of the ink-receptive layer, and
forming a cover layer on the surface of the information carrying
ink receptive layer and/or surface of the substrate.
[0008] The polyester film substrate is a self-supporting film by
which is meant a self-supporting structure capable of independent
existence in the absence of a supporting base.
[0009] A polyester suitable for use in the formation of a substrate
layer is preferably a synthetic linear polyester and may be
obtained by condensing one or more dicarboxylic acids or their
lower alkyl (up to 6 carbon atoms) diesters, eg terephthalic acid,
isophthalic acid, phthalic acid, 2,5-, 2,6- or
2,7-naphthalenedicarboxylic acid, succinic acid, sebacic acid,
adipic acid, azelaic acid, 4,4'-diphenyldicarboxylic acid,
hexahydro-terephthalic acid or 1,2-bis-p-carboxyphenoxyethane
(optionally with a monocarboxylic acid, such as pivalic acid) with
one or more glycols, particularly an aliphatic or cycloaliphatic
glycol, eg ethylene glycol, 1,3-propanediol, 1,4-butanediol,
neopentyl glycol and 1,4-cyclohexane dimethanol. A polyethylene
terephthalate or polyethylene naphthalate film is preferred. A
polyethylene terephthalate film is particularly preferred,
especially such a film which has been biaxially oriented by
sequential stretching in two mutually perpendicular directions,
typically at a temperature in the range from 70 to 125.degree. C.,
and preferably heat set, typically at a temperature in the range
from 150 to 250.degree. C., for example as described in
GB-A-838708.
[0010] The polyester substrate may be unoriented, or preferably
oriented, for example uniaxially oriented, or more preferably
biaxially oriented by drawing in two mutually perpendicular
directions in the plane of the film to achieve a satisfactory
combination of mechanical and physical properties. Simultaneous
biaxial orientation may be effected by extruding a thermoplastics
polymeric tube which is subsequently quenched, reheated and then
expanded by internal gas pressure to induce transverse orientation,
and withdrawn at a rate which will induce longitudinal orientation.
Sequential stretching may be effected in a stenter process by
extruding the thermoplastics material as a flat extrudate which is
subsequently stretched first in one direction and then in the other
mutually perpendicular direction. Generally, it is preferred to
stretch firstly in the longitudinal direction, ie the forward
direction through the film stretching machine, and then in the
transverse direction. A stretched substrate film may be, and
preferably is, dimensionally stabilised by heat-setting under
dimensional restraint at a temperature above the glass transition
temperature thereof.
[0011] A copolyesterether employed in the present invention is
preferably a block copolymer comprising predominantly a polyester
block as a hard segment, and a polyether block as a soft
segment.
[0012] The hard polyester block is suitably formed by condensing
one or more dicarboxylic acids, or ester derivatives or ester
forming derivatives thereof, with one or more glycols. The
dicarboxylic acid or derivative thereof may be aliphatic,
cycloaliphatic or aromatic. Suitable aliphatic or cycloaliphatic
dicarboxylic acids include 1,3- or 1,4-cyclohexane dicarboxylic,
adipic, glutaric, succinic, carbonic, oxalic and azelaic acids.
Aromatic dicarboxylic acids are preferred and include terephthalic,
isophthalic, phthalic, bibenzoic and naphthalenedicarboxylic acids,
and the dimethyl derivatives thereof. The glycol component may also
be aliphatic, cycloaliphatic or aromatic. The glycol is preferably
aliphatic or cycloaliphatic. Suitable glycols include ethylene
glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol,
1,6-hexanediol and 1,4-cyclohexane dimethanol.
[0013] The polyester block preferably comprises at least one
alkylene terephthalate, for example ethylene terephthalate,
butylene terephthalate and/or hexylene terephthalate. Butylene
terephthalate is particularly preferred. The molecular weight of
the polyester block is preferably less than 15,000, more preferably
in the range from 440 to 10,000, particularly 660 to 3000, and
especially 880 to 1500.
[0014] The soft polyether block is a polymeric glycol suitably
formed from one or more glycols such as ethylene glycol, 1,2- or
1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol
and 1,4-cyclohexane dimethanol. The polyether block is preferably a
poly(alkylene oxide) glycol, for example poly(ethylene oxide)
glycol, poly(1,2- and 1,3-propylene oxide) glycol,
poly(tetramethylene oxide) glycol, and random or block copolymers
of ethylene oxide and propylene oxide. Poly(tetramethylene oxide)
glycol is a preferred component of the polyether block. The
molecular weight of the polyether, preferably poly(tetramethylene
oxide) glycol, block is preferably in the range from 350 to 10,000,
more preferably 600 to 5000, particularly 900 to 2000, and
especially 1200 to 1800. In a particularly preferred embodiment of
the invention, the copolyesterether comprises, as the soft
polyether block, a mixture of poly(tetramethylene oxide) glycol and
poly(propylene oxide) glycol, suitably in a ratio of from 1 to
20:1, preferably 5 to 15:1, and more preferably 8 to 12:1. The
molecular weight of the poly(propylene oxide) glycol is preferably
in the range from 1000 to 5000, more preferably 2000 to 3000.
[0015] The ratio of hard:soft block in the copolyesterether is
preferably in the range from 10 to 95:5 to 90, more preferably 25
to 55:45 to 75, and particularly 35 to 45:55 to 65 weight %.
[0016] In a preferred embodiment of the invention the
copolyesterether is dried prior to polyester film substrate
formation and/or prior to incorporation in the substrate layer
composition. The copolyesterether may be dried in isolation, or
after mixing with one or more of the other components of the
substrate layer, eg dried after mixing with the opacifying agent,
preferably inorganic filler, more preferably titanium dioxide. The
copolyesterether may be dried by conventional means, for example in
a fluidised bed, or in an oven, at elevated temperature, under
vacuum or by passing through an inert gas, eg nitrogen. The water
content of the copolyesterether prior to extrusion of the film
forming substrate layer composition and subsequent film formation
is suitably in the range from 0 to 800 ppm, preferably 25 to 600
ppm, more preferably 50 to 400 ppm, particularly 100 to 300 ppm,
and especially 150 to 250 ppm.
[0017] The amount of copolyesterether present in the polyester
substrate is preferably in the range from 1 to 20, more preferably
3 to 15, particularly 5 to 12, and especially 6 to 10% by weight,
relative to the total weight of the substrate layer. The amount of
polyether present in the polyester substrate is preferably in the
range from 0.5 to 15, more preferably 1 to 5, and particularly 2 to
4% by weight, relative to the total weight of the substrate
layer.
[0018] The copolyesterether employed in the present invention
preferably has a flexural modulus (measured at 23.degree. C.
according to ASTM D790) of 200 MPa or less, and more preferably in
the range from 50 to 100 MPa. In addition, preferred
copolyesterethers have a Shore hardness (measured at 23.degree. C.
on the D scale according to DIN 53505) of 60 or less, particularly
in the range from 35 to 45.
[0019] The copolyesterethers can be prepared by conventional
polymerisation techniques, which are well known to those skilled in
the art.
[0020] The polyester substrate is opaque, by which is meant
substantially impermeable to light, and preferably exhibits a
Transmission Optical Density (TOD) (Macbeth Densitometer; type TD
902; transmission mode) in the range from 0.6 to 1.75, more
preferably 0.8 to 1.6, particularly 1.0 to 1.5, and especially 1.1
to 1.4. The aforementioned TOD ranges are particularly applicable
to a 300 .mu.m thick substrate.
[0021] The polyester substrate is preferably white and suitably
exhibits a whiteness index, measured as herein described, of
greater than 85, more preferably in a range from 90 to 105,
particularly 92 to 100, and especially 94 to 98 units.
[0022] The polyester substrate preferably exhibits a yellowness
index, measured as herein described, of less than or equal to 3,
more preferably in the range from -10 to 0, particularly -8 to -3,
and especially -7 to -5.
[0023] The polyester substrate is conveniently rendered opaque by
incorporation into the synthetic polyester of an effective amount
of an opacifying agent. Suitable opacifying agents include an
incompatible resin filler, a particulate inorganic filler or a
mixture of two or more such fillers.
[0024] By an "incompatible resin" is meant a resin which either
does not melt, or which is substantially immiscible with the
polyester, at the highest temperature encountered during extrusion
and fabrication of the layer. The presence of an incompatible resin
usually results in a voided film, by which is meant that the film
comprises a cellular structure containing at least a proportion of
discrete, closed cells. Suitable incompatible resins include
polyamides and olefin polymers, particularly a homo- or co-polymer
of a mono-alpha-olefin containing up to 6 carbon atoms in its
molecule, for incorporation into a polyester film. For
incorporation into a polyethylene terephthalate film, suitable
materials include a low or high density olefin homopolymer,
particularly polyethylene, polypropylene or poly-4-methylpentene-1,
an olefin copolymer, particularly an ethylene-propylene copolymer,
or a mixture of two or more thereof. Random, block or graft
copolymers may be employed.
[0025] The amount of incompatible resin filler present in the
polyester substrate is preferably within the range from 2 to 30,
more preferably 3 to 20, especially 4 to 15, and particularly 5 to
10% by weight, relative to the total weight of the substrate
layer.
[0026] Particulate inorganic fillers suitable for generating an
opaque polyester substrate include conventional inorganic pigments
and fillers, and particularly metal or metalloid oxides, such as
alumina, silica and titania, and alkaline metal salts, such as the
carbonates and sulphates of calcium and barium. The particulate
inorganic fillers may be of the voiding or non-voiding type.
Suitable particulate inorganic fillers may be homogeneous and
consist essentially of a single filler material or compound, such
as titanium dioxide or barium sulphate alone. Alternatively, at
least a proportion of the filler may be heterogeneous, the primary
filler material being associated with an additional modifying
component. For example, the primary filler particle may be treated
with a surface modifier, such as a pigment, soap, surfactant
coupling agent or other modifier to promote or alter the degree to
which the filler is compatible with the substrate polyester.
[0027] In a preferred embodiment of the invention the polyester
substrate has a degree of voiding in the range from 0 to 15, more
preferably 0,01 to 10, particularly 0.05 to 5, and especially 0.1
to 1% by volume. Thus, the polyester substrate is preferably
substantially free of voids. The degree of voiding can be
determined, for example, by sectioning the film using scanning
electron microscopy, and measuring the voids by image analysis. The
density of the polyester substrate is preferably in the range from
1.2 to 1.5, more preferably 1.3 to 1.45, and particularly 1.35 to
1.4.
[0028] In a particularly preferred embodiment of the invention, the
particulate inorganic filler comprises titanium dioxide.
Substantially non-voiding titanium dioxide is preferred.
[0029] The individual or primary inorganic filler, preferably
titanium dioxide, particles suitably have a mean crystal size, as
determined by electron microscopy, in the range from 0.05 to 0.4
.mu.m, preferably from 0.1 to 0.2 .mu.m, and more preferably of
approximately 0.15 .mu.m. In a preferred embodiment of the
invention, the primary inorganic filler, preferably titanium
dioxide, particles aggregate to form clusters or agglomerates
comprising a plurality of inorganic filler particles. The
aggregation process of the primary inorganic filler particles may
take place during the actual synthesis of the filler and/or during
the polyester and film making process.
[0030] The aggregated inorganic filler particles preferably have a
volume distributed median particle diameter (equivalent spherical
diameter corresponding to 50% of the volume of all the particles,
read on the cumulative distribution curve relating volume % to the
diameter of the particles--often referred to as the "D(v,0.5)"
value), as determined by laser diffraction, in the range from 0.3
to 1.5 .mu.m, more preferably 0.4 to 1.2 .mu.m, and particularly
0.5 to 0.9 .mu.m.
[0031] The size distribution of the inorganic filler particles is
also an important parameter, for example the presence of
excessively large particles can result In the film exhibiting
unsightly `speckle`, ie where the presence of filler aggregates in
the film can be discerned with the naked eye. It is preferred that
none of the inorganic filler incorporated into the substrate should
have an actual particle size exceeding 30 .mu.m. Particles
exceeding such a size may be removed by sieving processes which are
known in the art. However, sieving operations are not always
totally successful in eliminating all particles greater than a
chosen size. In practice, therefore, the size of 99.9% by number of
the inorganic filler particles should not exceed 30 .mu.m,
preferably should not exceed 20 .mu.m, and more preferably should
not exceed 10 .mu.m. Preferably at least 90%, more preferably at
least 95% of the inorganic filler particles are within the range of
the volume distributed median particle diameter .+-.0.5 .mu.m, and
particularly .+-.0.3 .mu.m.
[0032] The amount of inorganic filler incorporated into the
polyester substrate desirably should be in the range from 5 to 25,
more preferably 10 to 25, particularly 12 to 20, and especially 14
to 16% by weight, relative to the total weight of the substrate
layer.
[0033] The preferred titanium dioxide particles may be of anatase
or rutile crystal form. The titanium dioxide particles preferably
comprise a major portion of anatase, more preferably at least 60%,
particularly at least 80%, and especially approximately 100% by
weight of anatase. The particles can be prepared by standard
procedures, such as using the chloride process or preferably by the
sulphate process.
[0034] In one embodiment of the invention the titanium dioxide
particles are coated preferably with inorganic oxides such as
aluminium, silicon, zinc, magnesium or mixtures thereof. Preferably
the coating additionally comprises an organic compound, such as
fatty acids and preferably alkanols, suitably having from 8 to 30,
preferably from 12 to 24 carbon atoms. Polydiorganosiloxanes or
polyorganohydrogensiloxanes, such as polydimethylsiloxane or
polymethylhydrogensiloxane are suitable organic compounds.
[0035] The coating is applied to the titanium dioxide particles in
aqueous suspension. The inorganic oxides are precipitated in
aqueous suspension from water-soluble compounds such as sodium
aluminate, aluminium sulphate, aluminium hydroxide, aluminium
nitrate, silicic acid or sodium silicate.
[0036] Particle size of the filler particles described herein may
be measured by electron microscope, coulter counter, sedimentation
analysis and static or dynamic light scattering. Techniques based
on laser light diffraction are preferred. The median particle size
may be determined by plotting a cumulative distribution curve
representing the percentage of particle volume below chosen
particle sizes and measuring the 50th percentile. The volume
distributed median particle diameter of the filler particles is
suitably measured using a Malvern Instruments Mastersizer MS 15
Particle Sizer after dispersing the filler in ethylene glycol in a
high shear (eg Chemcoll) mixer.
[0037] In one embodiment of the invention, the polyester substrate
comprises an optical brightener. The optical brightener is
preferably added in amounts in the range from 50 to 1500 ppm, more
preferably 200 to 1000 ppm, and especially 400 to 600 ppm by
weight, relative to the weight of the substrate polyester. Suitable
optical brighteners include those available commercially under the
trade names "Uvitex" MES, "Uvitex" OB, "Leucopur" EGM and
"Eastobrite" OB-1.
[0038] In a preferred embodiment of the invention, the polyester
substrate comprises a blue dye, preferably in amounts in the range
from 100 to 3000 ppm, more preferably 200 to 2000 ppm, and
especially 300 to 1000 ppm by weight, relative to the weight of the
substrate polyester.
[0039] The optical brightener and/or blue dye may be included at
any stage of the polyester or polyester film production. Preferably
the optical brightener and/or blue dye is added to the glycol, or
alternatively by subsequent addition to the polyester prior to the
formation of the polyester film, eg by injection during
extrusion.
[0040] The thickness of the polyester substrate is preferably in
the range from 25 to 400 .mu.m, more preferably 100 to 350 .mu.m,
particularly 250 to 320 .mu.m, and especially 280 to 310 .mu.m.
[0041] The components of the substrate layer composition may be
mixed together in conventional manner. For example, by mixing with
the monomeric reactants from which the polyester is derived, or the
components may be mixed with the polyester by tumble or dry
blending or by compounding in an extruder, followed by cooling and,
usually, comminution into granules or chips. The copolyesterether
may be fed separately to the extruder from which the linear
polyester is extruded to form the substrate layer.
[0042] The ink-receptive layer is preferably a polymeric coating
layer which functions to improve the adhesion of inks, dyes and/or
lacquers etc to the polyester substrate. The ink-receptive layer
preferably comprises at least one ink-receptive polymer. The
ink-receptive layer may carry pictorial information, such as an
ordinary photograph, and/or written information such as typed
script, a signature etc, as appropriate. The ink-receptive layer
may be printed on by means of traditional printing processes such
as off-set, gravure, silk screen, and flexographic printing, or by
writing by hand, or by thermal transfer printing (TTP), or by laser
transfer printing (LTP). The chemical composition of the
ink-receptive layer may vary over a wide range, and suitable
materials include polyesters, polyurethanes, acrylics and
styrene-containing polymers.
[0043] In one embodiment of the invention the ink-receptive layer
suitably comprises a polyester resin, particularly a copolyester
resin derived from one or more dibasic aromatic carboxylic acids,
such as terephthalic acid, isophthalic acid and
hexahydroterephthalic acid, and one or more glycols, such as
ethylene glycol, diethylene glycol, triethylene glycol and
neopentyl glycol. Typical copolyesters which provide satisfactory
properties are those of ethylene terephthalate and ethylene
isophthalate, especially in the molar ratios of from 50 to 90 mole
% ethylene terephthalate and correspondingly from 50 to 10 mole %
ethylene isophthalate. Preferred copolyesters comprise from 65 to
85 mole % ethylene terephthalate and from 35 to 15 mole % ethylene
isophthalate, and especially a copolyester of about 82 mole %
ethylene terephthalate and about 18 mole % ethylene
isophthalate.
[0044] The polyester ink-receptive layer may be applied from an
organic or aqueous solvent, to an already oriented polyester
substrate, or more preferably before or during the stretching
operation. Alternatively, the polyester ink-receptive layer may be
formed by casting the ink-receptive polyester onto a preformed
substrate layer. Conveniently, however, formation of a composite
sheet (polyester substrate and polyester ink-receptive layer) is
effected by coextrusion, either by simultaneous coextrusion of the
respective film-forming layers through independent orifices of a
multi-orifice die, and thereafter uniting the still molten layers,
or, preferably, by single-channel coextrusion in which molten
streams of the respective polyesters are first united within a
channel leading to a die manifold, and thereafter extruded together
from the die orifice under conditions of streamline flow without
intermixing thereby to produce a composite sheet.
[0045] A coextruded sheet is stretched to effect molecular
orientation of the substrate, and preferably heat-set. Generally,
the conditions applied for stretching the substrate layer will
induce partial crystallisation of the ink-receptive polyester and
it is therefore preferred to heat set under dimensional restraint
at a temperature selected to develop the desired morphology of the
ink-receptive layer. Thus, by effecting heat-setting at a
temperature below the crystalline melting temperature of the
ink-receptive polyester and permitting or causing the composite to
cool, the ink-receptive polyester will remain essentially
crystalline. However, by heat-setting at a temperature greater than
the crystalline melting temperature of the ink-receptive polyester,
the latter will be rendered essentially amorphous. Heat-setting of
a composite sheet comprising a polyester substrate and a
copolyester ink-receptive layer is conveniently effected at a
temperature within a range of from 175 to 200.degree. C. to yield a
substantially crystalline ink-receptive layer, or from 200 to
250.degree. C. to yield an essentially amorphous ink-receptive
layer. An essentially amorphous ink-receptive layer is
preferred.
[0046] In a preferred embodiment of the invention the polyester
ink-receptive layer also exhibits heat-sealing properties, ie
should be capable of forming a heat-seal bond to itself and/or to
the polyester substrate and/or to the cover layer as described
herein, by heating to soften the polyester material of the
ink-receptive layer and applying pressure without softening or
melting the polyester material of the substrate layer. The
polyester ink-receptive layer preferably exhibits a heat-seal
strength, measured by sealing the layer to itself, in the range
from 300 to 3000, more preferably 1000 to 2500, and particularly
1800 to 2200 Nm.sup.-1.
[0047] The thickness of the polyester ink-receptive layer may vary
over a wide range but generally will not exceed 50 .mu.m, and is
preferably within a range of from 0.5 to 25 .mu.m, and more
preferably from 3 to 15 .mu.m.
[0048] In an alternative embodiment of the invention, the
ink-receptive layer comprises an acrylic resin, by which is meant a
resin which comprises at least one acrylic and/or methacrylic
component.
[0049] The acrylic resin component of the ink-receptive layer is
suitably thermoset and preferably comprises at least one monomer
derived from an ester of acrylic acid and/or an ester of
methacrylic acid, and/or derivatives thereof. In a preferred
embodiment of the invention, the acrylic resin comprises greater
than 50 mole %, preferably less than 98 mole %, more preferably in
the range from 60 to 97 mole %, particularly 70 to 96 mole %, and
especially 80 to 94 mole % of at least one monomer derived from an
ester of acrylic acid and/or an ester of methacrylic acid, and/or
derivatives thereof. A preferred acrylic resin comprises an alkyl
ester of acrylic and/or methacrylic acid where the alkyl group
contains up to ten carbon atoms such as methyl, ethyl, n-propyl,
isopropyl, n-butyl, isobutyl, terbutyl, hexyl, 2-ethylhexyl,
heptyl, and n-octyl. Polymers derived from an alkyl acrylate, for
example ethyl acrylate and butyl acrylate, together with an alkyl
methacrylate are preferred. Polymers comprising ethyl acrylate and
methyl methacrylate are particularly preferred. The acrylate
monomer is preferably present in a proportion in the range from 30
to 65 mole %, and the methacrylate monomer is preferably present in
a proportion in the range from 20 to 60 mole %.
[0050] Other monomers which are suitable for use in the preparation
of the acrylic resin of the ink-receptive layer, which may be
preferably copolymerised as optional additional monomers together
with esters of acrylic acid and/or methacrylic acid, and/or
derivatives thereof, include acrylonitrile, methacrylonitrile;
halo-substituted acrylonitrile, halo-substituted methacrylonitrile,
acrylamide, methacrylamide, N-methylol acrylamide, N-ethanol
acrylamide, N-propanol acrylamide, N-methacrylamide, N-ethanol
methacrylamide, N-methyl acrylamide, N-tertiary butyl acrylamide,
hydroxyethyl methacrylate, glycidyl acrylate, glycidyl
methacrylate, dimethylamino ethyl methacrylate, itaconic acid,
itaconic anhydride and half esters of itaconic acid.
[0051] Other optional monomers of the acrylic ink-receptive layer
polymer include vinyl esters such as vinyl acetate, vinyl
chloroacetate and vinyl benzoate, vinyl pyridine, vinyl chloride,
vinylidene chloride, maleic acid, maleic anhydride, styrene and
derivatives of styrene such as chloro styrene, hydroxy styrene and
alkylated styrenes, wherein the alkyl group contains from one to
ten carbon atoms.
[0052] A preferred acrylic resin, derived from 3 monomers comprises
35 to 60 mole % of ethyl acrylate/30 to 55 mole % of methyl
methacrylate/2 to 20 mole % of methacrylamide, and especially
comprising approximate molar proportions 46146/8% respectively of
ethyl acrylate/methyl methacrylate/acrylamide or methacrylamide,
the latter polymer being particularly effective when thermoset, for
example in the presence of about 25 weight % of a methylated
melamine-formaldehyde resin.
[0053] A preferred acrylic resin, derived from 4 monomers comprises
a copolymer comprising comonomers (a) 35 to 40 mole % alkyl
acrylate, (b) 35 to 40 mole % alkyl methacrylate, (c) 10 to 15 mole
% of a monomer containing a free carboxyl group, and (d) 15 to 20
mole % of a monomer containing a sulphonic acid group and/or a salt
thereof. Ethyl acrylate is a particularly preferred monomer (a) and
methyl methacrylate is a particularly preferred monomer (b).
Monomer (c) containing a free carboxyl group, ie a carboxyl group
other than those involved in the polymerisation reaction by which
the copolymer is formed, suitably comprises a copolymerisable
unsaturated carboxylic acid, and is preferably selected from
acrylic acid, methacrylic acid, maleic acid, and/or itaconic acid;
with acrylic acid and itaconic acid being particularly preferred.
The sulphonic acid group monomer (d) may be present as the free
acid and/or a salt thereof, for example as the ammonium,
substituted ammonium, or an alkali metal, such as lithium, sodium
or potassium, salt. The sulphonate group does not participate in
the polymerisation reaction by which the adherent copolymer resin
is formed. The sulphonic acid group monomer is preferably aromatic,
and more preferably is p-styrene sulphonic acid and/or a salt
thereof.
[0054] The weight average molecular weight of the acrylic resin can
vary over a wide range but is preferably in the range from 10,000
to 10,000,000, and more preferably 50,000 to 200,000.
[0055] The acrylic resin component of the ink-receptive layer
preferably comprises at least 30%, more preferably in the range
from 40 to 99%, particularly 50 to 85%, and especially 70 to 80% by
weight relative to the total weight of the ink-receptive layer. The
acrylic resin is generally water-insoluble. The ink-receptive
coating composition including the water-insoluble acrylic resin may
nevertheless be applied to the polyester film substrate as an
aqueous dispersion.
[0056] If desired, the acrylic ink-receptive layer coating
composition may also contain a cross-linking agent which functions
to cross-link the layer thereby improving adhesion to the polyester
film substrate. Additionally, the cross-linking agent should
preferably be capable of internal cross-linking in order to provide
protection against solvent penetration. Suitable cross-linking
agents may comprise epoxy resins, alkyd resins, amine derivatives
such as hexamethoxymethyl melamine, and/or condensation products of
an amine, eg melamine, diazine, urea, cyclic ethylene urea, cyclic
propylene urea, thiourea, cyclic ethylene thiourea, alkyl
melamines, aryl melamines, benzo guanamines, guanamines, alkyl
guanamines and aryl guanamines, with an aldehyde, eg formaldehyde.
A useful condensation product is that of melamine with
formaldehyde. The condensation product may optionally be
alkoxylated. The cross-linking agent may suitably be used in
amounts of up to 70%, preferably in the range from 1 to 60%, more
preferably 15 to 50%, and especially 20 to 30% by weight relative
to the total weight of the ink-receptive layer. A catalyst is also
preferably employed to facilitate cross-linking action of the
cross-linking agent. Preferred catalysts for cross-linking melamine
formaldehyde include para toluene sulphonic acid, maleic acid
stabilised by reaction with a base, morpholinium paratoluene
sulphonate, and ammonium nitrate.
[0057] The acrylic ink-receptive layer coating composition may be
applied before, during or after the stretching operation in the
production of an oriented film. The coating composition is
preferably applied to the film substrate between the two stages
(longitudinal and transverse) of a thermoplastics polyester film
biaxial stretching operation. Such a sequence of stretching and
coating is suitable for the production of an ink-receptive layer
coated linear polyester film, particularly polyethylene
terephthalate film, substrate, which is preferably firstly
stretched in the longitudinal direction over a series of rotating
rollers, coated, and then stretched transversely in a stenter oven,
preferably followed by heat setting.
[0058] An acrylic ink-receptive layer coated polyester, especially
polyethylene terephthalate, substrate is suitably heated up to
240.degree. C., preferably up to 220.degree. C., in order to dry
the aqueous medium, or the solvent in the case of solvent-applied
compositions, and also to assist in coalescing and forming the
coating into a continuous and uniform layer. The cross-linking of
cross-linkable coating compositions is also achieved at such
temperatures.
[0059] The acrylic ink-receptive layer coating composition is
preferably applied to the polyester film substrate by any suitable
conventional technique such as dip coating, bead coating, reverse
roller coating or slot coating.
[0060] The acrylic ink-receptive layer is preferably applied to the
polyester film substrate at a dry coat weight in the range from
0.05 to 5 mgdm-2, especially 0.1 to 2.0 mgdm.sup.-2. The thickness
of the dry acrylic ink-receptive layer is preferably less than 1.5
.mu.m, more preferably in the range from 0.01 to 1.0 .mu.m, and
particularly 0.02 to 0.5 .mu.m.
[0061] In a particularly preferred embodiment, the opaque polyester
substrate has a polyester ink-receptive layer, as described herein,
on a first surface thereof, and an acrylic ink-receptive layer, as
described herein, on a second surface thereof.
[0062] The chemical composition of the cover layer component of a
multilayer card, according to the present invention may vary over a
wide range, and is suitably selected from materials which include
polyester, such as polyethylene terephthalate and PETG,
polycarbonate, polyolefin, polyvinyl chloride, ABS resin and/or
paper. The cover layer is preferably a self-supporting film.
Indeed, the cover layer may even be the major contributor to the
total thickness of the multilayer card. The function of the cover
layer, in addition to the support it provides for the overall card,
is to provide protection, including security, for example for the
ink-receptive layer and the information contained thereon. The
cover layer may have more than one layer, preferably is a
multilayer polymeric film, and for example may be an opaque
polyester substrate having an ink-receptive layer as described
herein. A multilayer card may be formed by laminating together two
or more opaque polyester films by means of heat-sealing their
respective polyester ink-receptive layers. Alternatively,
non-heat-sealing ink-receptive layers may be laminated together by
means of an additional adhesive layer. In a preferred embodiment of
the invention the cover layer is transparent in order that the
information contained on the ink-receptive layer can be visualised.
A preferred card contains an opaque polyester substrate, an
ink-receptive layer, and at least one transparent polyester cover
layer having a heat-sealable or ink-receptive layer, whereby the
card is formed by heat-sealing together the respective
ink-receptive layers. A particularly preferred card is an all
polyester film structure, having the general structure as described
in EP-A-0497483, the disclosure of which is incorporated herein by
reference. The opaque polyester support film and dye receptive or
printable receiver film of EP-A-0497483 are equivalent to the
polyester substrate and ink-receptive layer respectively of a
multilayer card according to the present invention.
[0063] The multilayer card according to the present invention
includes any of the multilayer structures disclosed in U.S. Pat.
No. 5,407,893, the disclosure of which is incorporated herein by
reference. The biaxially oriented polyester film and image
receiving layer (numbers 3 and 1 respectively in FIGS. 6 to 13) of
U.S. Pat. No. 5,407,893 are equivalent to the polyester substrate
and ink-receptive layer respectively of a multilayer card according
to the present invention.
[0064] The multilayer card according to the present invention can
be used to form any of the card structures known in the art,
including identification cards, magnetic cards such as credit cards
and pre-paid cards, smart cards which may have an electronic chip
at the surface or encapsulated, for example in epoxy material,
inside the card (a so-called contactless smart card).
[0065] The multilayer card preferably has a thickness in the range
from 150 to 1000 .mu.m, more preferably 200 to 900 .mu.m,
particularly 250 to 850 .mu.m, and especially 650 to 840 .mu.m.
[0066] The multilayer card preferably has a length in the range
from 70 to 100 mm, more preferably 80 to 90 mm, and particularly
about 86 mm, and a width in the range from 40 to 70 mm, more
preferably 50 to 60 mm, and particularly about 54.5 mm.
[0067] The multilayer card according to the present invention is
preferably formed by a lamination process, by which is meant that
two or more separate self-supporting film structures, which may
themselves contain more than one layer, are brought together and
joined by suitable means, including heat or adhesive, to form a
card. An opaque polyester substrate having an ink-receptive layer
on at least one surface thereof is a preferred first
self-supporting film structure and a cover layer a preferred second
self-supporting film structure.
[0068] For manufacturing purposes, it is generally desirable for a
card comprising substrate, ink-receptive layer and cover layer to
be coterminous along all edges. However, this is not always the
case, and for example, the ink-receptive layer may cover only part
of the substrate and the cover layer may be joined to the substrate
in the regions where there is no ink-receptive layer, generally by
means of an additional adhesive layer.
[0069] The layers of a multilayer card according to the present
invention may, if desired, contain any of the additives
conventionally employed in the manufacture of polymeric films.
Thus, agents such as dyes, pigments, voiding agents, lubricants,
anti-oxidants, anti-blocking agents, surface active agents, slip
aids, gloss-improvers, prodegradants, ultra-violet light
stabilisers, viscosity modifiers and dispersion stabilisers may be
incorporated as appropriate.
[0070] The invention is illustrated by reference to the following
drawings in which:
[0071] FIG. 1 is a schematic sectional elevation, not to scale, of
a multilayer card having an opaque polyester film substrate,
ink-receptive layer and cover layer.
[0072] FIG. 2 is a similar schematic elevation of a multilayer card
shown in FIG. 1, with an additional information carrying layer on
the surface of the ink-receptive layer, underneath the cover
layer.
[0073] FIG. 3 is a similar schematic elevation of a multilayer card
shown in FIG. 2, with an additional ink-receptive layer and cover
layer, on the second side of the substrate.
[0074] Referring to FIG. 1 of the drawings, the multilayer card
comprises an opaque polyester film substrate layer (1) having an
ink-receptive layer (2) bonded to a first surface (3) of the
substrate, and a transparent cover layer (4) bonded to the surface
of the ink-receptive layer (5) remote from the substrate.
[0075] The film of FIG. 2 additionally comprises an information
carrying layer (6) on the surface (7) of the ink-receptive layer
(2).
[0076] The film of FIG. 3 additionally comprises a second
ink-receptive layer (8) on the second surface (9) of the substrate
layer (1), and a second cover layer (10) on the surface (11) of the
second ink-receptive layer (8) remote from the substrate (1). The
second cover layer (10) is a multilayer film comprising an opaque
polyester substrate layer (12) having ink-receptive (or
heat-sealable) layers (13 and 14) on both surfaces thereof.
[0077] In this specification the following test methods have been
used to determine certain properties of the layers of the
multilayer card and/or of the card itself:
[0078] (i) Transmission Optical Density (TOD)
[0079] TOD of the film was measured using a Macbeth Densitometer TD
902 (obtained from Dent and Woods Ltd, Basingstoke, UK) in
transmission mode.
[0080] (ii) Whiteness Index and Yellowness Index
[0081] The whiteness index and yellowness index of the film was
measured using a Colorgard System 2000, Model/45 (manufactured by
Pacific Scientific) based on the principles described in ASTM D
313.
[0082] (iii) Heat-Seal Strength
[0083] A heat-seal was formed by positioning together and heating
two ink-receptive layers present on opaque polyester substrate
layers, at 140.degree. C. for ten seconds under a pressure of 275
kPa (40 psi). The sealed film was cooled to room temperature, and
the heat-seal strength determined by measuring the force required
under linear tension per unit width of seal to peel the layers of
the film apart at a constant speed of 4.23 mm/second.
[0084] (iii) Delamination Susceptibility
[0085] Delamination susceptibility was measured using the following
edge impact test. A multilayer card of dimensions 86 mm.times.54.5
mm.times.750 (or 640) .mu.m was held upright in the hand and
uniformly hit 10 times by means of one of the corner edges of the
card on to a wooden table. The card was then examined for
delamination and scored as excellent (no delamination), good (small
signs of delamination), or poor (total delamination--the layers of
the card clearly separated and could be easily peeled apart).
[0086] The invention is further illustrated by reference to the
following examples.
EXAMPLE 1
[0087] Separate streams of a substrate layer polymer of
polyethylene terephthalate comprising 15% by weight, relative to
the total weight of the substrate, of anatase titanium dioxide
having a volume distributed median particle diameter of 0.7 .mu.m,
8% by weight, relative to the total weight of the substrate, of
Lomod ST4090A (copolyester ether, supplied by General Electric
Corporation), and 460 ppm of optical brightener, and two outer
ink-receptive layer polymers comprising a copolyester of 82 mole %
ethylene terephthalate and 18 mole % ethylene isophthalate were
supplied from separate extruders to a single channel coextrusion
assembly. The polymer layers were extruded through a film-forming
die onto a water cooled rotating, quenching drum to yield an
amorphous cast composite extrudate. The cast extrudate was heated
to a temperature of about 80.degree. C. and then stretched
longitudinally at a forward draw ratio of 3.2:1. The composite
sheet was passed into a stenter oven, where the sheet was dried and
stretched in the sideways direction to approximately 3.4 times its
original dimensions. The biaxially stretched composite sheet was
heat set at a temperature of about 225.degree. C. Final film
thickness of the composite sheet was 150 .mu.m. The opaque
substrate layer was 125 .mu.m thick, the two outer ink-receptive
layers were both 12.5 .mu.m thick.
[0088] The composite sheet was subjected to the test procedures
described herein and exhibited the following properties:
[0089] (i) Transmission Optical Density CROD)=1.2.
[0090] (ii) Whiteness Index=96 units.
[0091] Yellowness Index=-0.9 units.
[0092] (iii) Heat-Seal Strength=2000 Nm.sup.-1.
[0093] Items (i) and (ii) are essentially properties of the opaque
substrate layer, as the ink-receptive layers make little or no
contribution thereto. Item (iii) is a property of the ink-receptive
layers.
[0094] Five of the composite sheets produced above were press
laminated together at a temperature of 150.degree. C. for 90
seconds to form a laminated sheet of thickness 750 .mu.m.
Multilayer cards of dimensions 86 mm.times.54.5 mm were cut out
from the laminated sheet, subjected to the edge impact test
described herein and exhibited the following property:
[0095] (iv) Delamination Susceptibility=excellent (ie no
delamination).
EXAMPLE 2
[0096] This is a comparative example not according to the
invention.
[0097] The procedure of Example 1 was repeated except that Lomod
ST4090A was omitted from the substrate layer composition. The
multilayer cards of dimensions 86 mm.times.54.5 mm which were cut
from the laminated sheet of thickness 750 .mu.m were subjected to
the edge impact test described herein and exhibited the following
property:
[0098] (iv) Delamination Susceptibility=poor (ie total
delamination--the layers of the card clearly separated and could be
easily peeled apart).
EXAMPLE 3
[0099] The procedure of Example 1 was repeated except that Lomod
TE3040A (copolyesterether, supplied by General Electric
Corporation) was used instead of Lomod ST4090A. The multilayer
cards of dimensions 86 mm.times.54.5 mm which were cut from the
laminated sheet of thickness 750 .mu.m were subjected to the edge
impact test described herein and exhibited the following
property:
[0100] (iv) Delamination Susceptibility=good (small signs of
delamination).
EXAMPLE 4
[0101] The procedure of Example 1 was repeated except that the
substrate contained a blue dye instead of optical brightener, had a
single copolyester ink-receptive layer, and the surface of the
monoaxially oriented polyethylene terephthalate substrate film was
coated with an acrylic ink-receptive layer composition comprising
the following ingredients:
1 Acrylic resin 163 ml (46% w/w aqueous latex of methyl
methacrylate/ethyl acrylate/methacrylamide: 46/46/8 mole %, with
25% by weight methoxylated melamine-formaldehyde) Ammonium nitrate
6 ml (10% w/w aqueous solution) Demineralised water to 2.5
litres
[0102] Final film thickness was 320 .mu.m. The opaque polyester
substrate layer was 295 .mu.m thick, the copolyester ink-receptive
layer was 25 .mu.m thick, and the dry coat weight of the acrylic
ink-receptive layer was approximately 0.04 .mu.m.
[0103] The film exhibited the following properties:
[0104] (ii) Whiteness Index=96 units.
[0105] Yellowness Index=-5.7 units.
[0106] Two of the composite sheets produced above were press
laminated together at a temperature of 150.degree. C. for 90
seconds to form a laminated sheet of thickness 640 .mu.m.
[0107] The multilayer cards of dimensions 86 mm.times.54.5 mm which
were cut from the laminated sheet of thickness 640 .mu.m were
subjected to the edge impact test described herein and exhibited
the following property:
[0108] (iv) Delamination Susceptibility=excellent (ie no
delamination).
* * * * *