[0001] This invention relates to flexible sheeting suitable for use in forming a security
enclosure for an article, and to security enclosures formed from such sheeting.
[0002] Flexible sheeting suitable for use in forming a security enclosure is already known,
for example, from European Patent Specification No. 89306035, wherein the sheeting
incorporates electrically conductive elements which, when connected to a monitor circuit,
give rise to an indication of attempted interference by an outside agency on penetration
of the sheeting. The known sheeting provides security against penetration by a small
diameter puncture tool, such as a needle, but there is a need to provide security
against penetration by a small diameter radiant energy cutting tool, such as a laser
beam.
[0003] It is an object of the present invention to provide a new and improved form of flexible
sheeting suitable for use in forming a security enclosure for an article, and to security
enclosures formed from such sheeting.
[0004] According to the present invention there is provided flexible sheeting suitable for
use in forming a security enclosure for an article, said sheeting comprising a flexible
layer of insulant material having adherent to its opposite surfaces respective layers
of electrically-conductive low-melt material, said low-melt material being in solid
form at ambient temperatures but being rendered fluid by the energy from a small diameter
radiant energy cutting tool, so that, when the layers of low-melt material are connected
to an electrical monitor circuit a change in electrical characteristic is detectable,
in use, by flow of the fluidised low-melt material through the hole in the layer of
insulant material formed by the cutting tool.
[0005] Preferably the thickness of each low-melt material layer is approximately the same
as or slightly greater than that of the layer of insulant material, each such layer
having a thickness of less than 25 microns. Conveniently each low-melt material layer
is 8-12 microns in thickness and the insulant material layer is about 12 microns in
thickness. The low-melt material preferably fluidises at about 100°C.
[0006] Preferably the insulant material layer is made of polyester film and each low-melt
material layer is made of carbon-filled polyester, the latter being applied to the
insulant material layer by screen printing. Typically the carbon-filled polyester
is 50% filled with graphitic carbon to provide a resistivity of the order of 0.3 ohms-cm.
Other materials may be used to form the electrically-conductive low-melt material
for example certain thermoplastic resins such as polyamides, polyethers, polyurethanes,
polyvinyl acetate and certain uncured silicones loaded with carbon or conductive salts
such as caesium iodide. Primarily these materials are of low molecular weight and
fluidise at temperatures in the range 70 to 130°C.
[0007] Preferably the sheeting incorporates outer coverings bonded to the layers of low-melt
material. The outer coverings may be carbon-loaded polyester coated onto polyester
film with the carbon content selected to provide high colour (jetness) with minimum
change to electrical resistance on penetration or fluidisation due to its very high
resistivity, the latter preferably being in excess of 10¹³ ohm-cm. The outer coverings
may be adherent to the respective layers of low-melt material by an adhesive, such
as polyester, providing a patterned coverage of the outer coverings sufficient in
areal extent to laminate the sheeting. The adhesive layer may be over-printed on the
low-melt material.
[0008] According to another aspect the present invention provides flexible sheeting suitable
for use in forming a security enclosure for an article, said sheeting comprising two
flexible layers of electrically-responsive fibrous material separated by a flexible
layer of insulant material, each of said fibrous material layers being bonded substantially
throughout its entire area to said insulant material layer by a flexible layer of
electrically-responsive adhesive, said adhesive layer being a laminate comprising
a layer of carbon bound at ambient temperatures in a matrix of low-melt material,
and wherein the length of the fibres of the fibrous material is greater than the thickness
of the layers of adhesive and insulant.
[0009] Preferably the thickness of each low-melt material layer is approximately the same
as or slightly greater than that of the layer of insulant material, each such layer
having a thickess of less than 25 microns. Conveniently each low-melt material layer
is 8-12 microns in thickness and the insulant material layer is about 12 microns in
thickness. The low-melt material preferably fluidises at about 100°C.
[0010] Preferably the insulant material layer is made of polyester film and each low-melt
material layer is made of carbon-filled polyester, the latter being applied to the
insulant material layer by screen printing and over-printed with an adhesive, such
as polyester, providing a patterned coverage of the low-melt material layer sufficient
in areal extent to laminate the sheeting. Typically the carbon-filled polyester is
50% filled with graphitic carbon to provide a resistivity of the order of 0.3 ohms-cm.
[0011] Preferably the layers of fibrous material are made of unsintered carbon-loaded PTFE
having a volume resistivity in the range 1 to 10 ohm-cm and of the order of 75 microns
in thickness.
[0012] Preferably the sheeting incorporates outer coverings bonded to the layers of fibrous
material by non-conductive adhesive. The adhesive may be over-printed onto the fibrous
material layers, and may be polyester, providing a patterned coverage sufficient in
areal extent to laminate the sheeting. The outer coverings may be carbon-loaded polyester
coated onto polyester film with the carbon content selected to provide high colour
(jetness) with minimum change to electrical resistance on penetration or fluidisation
due to its very high resistivity, the latter preferably being in excess of 10¹³ ohm-cm.
[0013] According to a further aspect the present invention provides a security enclosure
formed of flexible sheeting according to the present invention, each layer of low-melt
material being connected to an electrical monitor circuit. The monitor circuit may
be an impedance monitoring bridge circuit.
[0014] By virtue of the provision of layers of low-melt material containing carbon or other
electrically-conductive filler the sheeting and the enclosure provided by the present
invention provides security against penetration by a radiant energy cutting tool such
as a laser beam.
[0015] Embodiments of the present invention will now be described by way of example with
reference to the accompanying drawings in which:
Fig. 1 is an exploded view of a first form of flexible sheeting for use in forming
a security enclosure;
Fig. 2 schematically illustrates a partly-formed security enclosure made of the Fig.
1 sheeting; and
Fig. 3 is a sectional view of a second form of flexible sheeting for use in forming
a security enclosure.
[0016] The flexible sheeting 10 which is shown in Fig. 1 in exploded form comprises various
layers each of which is flexible including layer 11 which is an insulant layer, layers
12, 13, each of which is electrically conductive having a resistivity of the order
of 0.3 to 0.4 ohm-cm and outer cover layers 14, 15, each of which is essentially an
insulating layer. Layer 11 is made of polyester film being about 12 microns in thickness
for best results but which should not be more than 25 microns in thickness. The layers
12, 13, are screen printed on either side of layer 11 and are about 8 to 25 microns
in thickness. layers 12, 13 are each composed of a polyester matrix which is loaded
with graphitic carbon to a level of about 50% by weight in order to render layers
12, 13, electrically conductive and to provide these layers with low-melt characteristics,
the latter being provided by the polyester which has a melting point of the order
of 100°C. Outer cover layers 14, 15, are also made of polyester loaded with carbon
and coated onto a polyester film carrier but the loading is selected to provide very
high resistivity (of the order of 10¹³ ohm-cm or greater) and high blackness in colour.
Cover layers 14, 15, are adherent to the layers 12, 13, by an adhesive such as polyester
over-printed onto layers 12, 13, to provide a patterned coverage of about 30% in areal
extent. By virtue of its construction sheeting 10 is a laminate and the layers 12,
13, are essentially homogeneous and complete over their entire areal extent. The areal
extent of layer 12 is substantially identical to that of layer 13, each being slightly
less in areal extent than layer 11 to provide insulation at the edges of the layers
12, 13.
[0017] Fig. 2 illustrates a partly formed security enclosure 20 made of the sheeting 10
by initially forming the layer 11 of the sheeting to a box blank shape and folding
the shaped sheeting along lines 21 to provide a box-like configuration which can envelope
or enclose an article (not shown) to be protected. The adjacent edges 22 of the folded
sheeting 10 may abut or overlap and may be held in place by a wrapping (not shown).
An electrical monitor circuit 23 is connected to the enclosure 20 to provide impedance
monitoring across the insulant layer 11 by means of the conductive layers 12, 13,
functioning as conductive termination pads. Circuit 23 may be connected to the layers
12, 13, via strip copper conductors.
[0018] Fig. 3 illustrates a modified form of flexible sheeting 30 which incorporates all
of the components of sheeting 10 but additionally incorporates layers 31, 32, of electrically-responsive
fibrous material, preferably carbon-loaded unsintered PTFE between the outer cover
layers 14, 15, and the layers 12, 13. The fibres of layers 31, 32, are of sufficient
length to extend from one of the layers 31, 32, to the other of the layers 31, 32,
when penetrated by a piercing tool. Layers 31, 32, are secured by polyester adhesive
to both cover layers 14, 15, and layers 12, 13, with the adhesive patterned to give
about 30% coverage. Layers 31, 32, are accordingly in electrical contact with layers
12, 13, and may be used as interconnectors between the layers 12, 13, and the monitor
circuit 23 in the Fig. 2 arrangement to avoid strip copper conductors. This has the
additional benefit that, in use, only a single monitor circuit is required for both
the layers 12, 13, and the layers 31, 32, the latter functioning as a security measure
against piercing.
1. Flexible sheeting for use in forming a security enclosure for an article characterised
in that the sheeting comprises a flexible layer (11) of insulant material having adherent
to its opposite surfaces respective layers (12,13) of electrically-conductive low-melt
material, said low melt material being in solid form at ambient temperatures but being
rendered fluid by the energy from a small diameter radiant energy cutting tool, so
that, when the layers (12,13) of low-melt material are connected to an electrical
monitor circuit (23) a change in electrical characteristic is detectable, in use,
by flow of the fluidised low-melt material through the hole in the layer (11) of insulant
material formed by the cutting tool.
2. Flexible sheeting as claimed in claim 1, characterised in that the thickness of each
low-melt material layer (12,13) is approximately the same as or slightly greater than
that of the layer (11) of insulant material.
3. Flexible sheeting as claimed in claim 1, characterised in that the low-melt material
layer (12,13) is made of carbon-filled polyester applied to the insulant material
layer (11) by screen printing.
4. Flexible sheeting as claimed in claim 3 characterised by further incorporating outer
coverings (14,15) bonded to the layers (12,13) of low-melt material.
5. Flexible sheeting as claimed in claim 4, characterised in that the outer coverings
(14,15) may be carbon-loaded polyester coated onto polyester film.
6. Flexible sheeting suitable for use in forming a security enclosure for an article,
characterised in that said sheeting comprises two flexible layers (31,32) of electrically-responsive
fibrous material separated by a flexible layer (11) of insulant material, each of
said fibrous material layers (31,32) being bonded substantially throughout its entire
area to said insulant material layer (11) by a flexible layer of electrically-responsive
adhesive (12,13), said adhesive layer (12,13) being a laminate comprising a layer
of carbon bound at ambient temperatures in a matrix of low-melt material, and wherein
the length of the fibres of the fibrous material is greater than the thickness of
the layers (11,12,13) of adhesive and insulant.
7. Flexible sheeting as claimed in claim 6, characterised by further incorporating outer
coverings (14,15) bonded to the layers of fibrous material (31,32) by non-conductive
adhesive.
8. Flexible sheeting as claimed in claim 7, characterised in that the outer coverings
(14,15) may be carbon-loaded polyester with the carbon content selected to provide
high colour (jetness) with minimum change to electrical resistance on penetration
or fluidisation due to its very high resistivity.
9. A security enclosure formed of flexible sheeting which is multilayered and incorporates
a layer (11) of insulant material having adherent to its opposite surfaces respective
layers (12,13) of electrically-conductive low-melt material which is solid at ambient
temperatures but fluidises at temperatures of about 100°C or less, and an electrical
monitor circuit (23) connected to said low-melt material layers (12,13) to detect
fluidisation therein.