The present invention relates to a thermally insulating textile and
more particularly to a thermally insulating textile in which the degree of insulation
automatically varies in response to changes in ambient temperature.
The thermal protection offered by currently available protective garments
which employ thermally insulating textiles to trap layers of air may be altered
by varying the amount of trapped air. This may be achieved by having the wearer
add or remove garment layers. However this requires the wearer either to carry
a number of garments or to wear a garment adapted to protect against the largest
likely change in ambient temperature. As thermally protective garments tend to
be bulky both solutions are likely to prove cumbersome to the wearer. Additionally,
the wearing of a garment which provides protection against the largest potential
change in ambient temperature, for example in situations where there may be a likelihood
of fire or a risk of exposure to cold, may place thermal stress on the wearer in
the absence of these situations.
As an alternative to increasing the number of garment layers in order
to achieve an increased thermal protection the air gap between two layers of a
garment may be increased. Thus, by providing a garment in which the air gap may
be varied variable thermal protection may be achieved. One known fabric which may
be utilised to provide such a variable air gap garment is described in GB 2 234
705 A and comprises a material having two parallel material layers between which
is disposed fibres, the height of which may be manually varied by the effecting
a relative movement of the layers. This solution requires the wearer to pull on
one or other of the layers by, for example, zipping and unzipping gussets in order
to vary the thermal insulation and has the disadvantages that the wearer must stop
what he or she is doing in order to adjust the garment and in that the wearer may
not respond quickly enough to rapid environmental changes to provide timely thermal
According to the present invention there is provided a textile comprising
a laminate of two material layers having interposed a temperature sensitive bulking
layer, the bulking layer comprising a shape memory composition being adapted to
co-operate with the material layers to automatically vary the gap therebetween
upon departure in a desired direction of the textile temperature from a predetermined
Thus, as the volume of the textile automatically changes then the
thermal insulating properties of the textile changes, increasing as the volume
increases to trap more air and decreasing as the volume decreases to trap less
air. This has the advantage that garments fabricated using this textile are able
to provide a variable thermal protection for the wearer without the need for the
wearer to vary the number of garments worn or to manually make changes to the air
So called "shape memory" compositions are well known (for example:
pgs 29-31 Plastics Engineering February 1995; "Properties and Applications of Polyurethane-Series
Shape Memory Polymer" pgs 1998-2001 ANTEC '94 and "The Properties and Processing
of Shape Memory Alloys..." AD-Vol 24/AMD Vol 123, Smart Structures and Materials
Avionics Society of Mechanical Engineering (ASME) 1991) and have the property that
they can exist in two solid phases so that at certain temperatures they will exist
primarily in one phase or the other. These compositions may be incorporated into
a textile for example by depositing a coating onto a flexible substrate such as
fabric layer, which may be the internal face of the fabric envelope, or by incorporating
fibres made from such compositions into the weave of a fabric layer and may be
employed in either a reversible or irreversible process.
The reversible process exploits mainly the property of these compositions
that there is associated a specific volume change with the change between phases
while the irreversible process exploits mainly the "shape memory" property of these
compositions where a shape incorporated in one phase at a particular temperature
is altered to another shape in the second phase at a predetermined temperature
only to be recovered when the composition reverts to the original, particular temperature.
Thus, by choosing the volume of the shape to be much greater at the particular
temperature than at the predetermined temperature a textile incorporating such
a composition is capable of undergoing an irreversible increase in volume with departure
from the predetermined temperature to the particular temperature.
When used reversibly, for example when deposited onto a flexible substrate,
such as a fabric, plastics or rubber layer, so as to provide out of plane protuberances
in that substrate as the specific volume of the composition decreases, the change
in specific volume of the shape memory composition may be no more than a few percent.
Preferably the composition and substrate arrangement of the textile is therefore
made so as to magnify this change. This may be achieved by choosing a pattern made
by the deposited shape memory composition onto the substrate so as to provide a
multiple effect, such as by employing a plurality of concentric rings in a repeat
Usefully a further enhancement of this multiple effect may be achieved
by providing a textile having one or more pairs of such patterned flexible substrates
arranged such that the protuberances of each substrate of the pair will oppose
one another. As an alternative to the use of such patterns, there may be provided
a folded substrate which may be, for example, folded in concertina or spiral fashion,
the substrate having deposited on portions thereof the shape memory composition,
with the portions being selected to provide for unfolding of the folded substrate
as the specific volume of the shape memory composition decreases. As the substrate
unfolds then the size of the cross-section of the textile will increase to produce
an increase in its thermal insulation effect.
It will be obvious to those skilled in the art that through a suitable
choice of the portions on which to deposit the composition a folding of the substrate
may be effected by an increase in the volume of the composition. Reversible arrangements
such as are discussed in this paragraph have the advantage that as the temperature
changes from a predetermined temperature, typically between about 20°C and 40°C,
in a desired direction, bulking of the shape memory composite may occur by an amount
dependent on that temperature change to provide the textile with a variable thermal
insulation which reverses as the textile temperature moves back towards the predetermined
The textile may alternatively be made to undergo an irreversible change
in thermal insulation and may employ substrates substantially similar to the ones
employed for the textile which acts reversibly, that is deposited, patterned, inter-woven
or folded flexible substrates. These substrates are made to provide an increase
in the thermal insulation of the textile by being shaped into a high volume structure
at a temperature where the change in thermal insulation is required, for example
at about 60°C for high temperature protection, or at a higher processing temperature,
then after cooling as appropriate, stress applied to reduce the bulk, for example
by compressing or folding the original structure and the stress frozen in at a
predetermined temperature, typically between about 20°C and 40°C. Such textiles
have the advantage (over textiles constructed to undergo reversible thermal insulation
changes) that large retained strains can be released. This provides for a more
pronounced volume change within the textile and hence a greater change in the thermal
protection provided by such a textile. This is particularly suitable for use in
the production of thermal protection garments since such garments need to be able
to automatically react to large and rapid temperature changes.
Embodiments of the invention will now be described, by way of examples
only, with reference to the drawings in the accompanying figures of which:
- Figures 1 are schematic representations of a textile according to the
present invention having a bulking layer comprising a shape memory composition
deposited on a fabric substrate with a)
a plan view of the fabric substrate
b) a sectional view through the textile at 20°C and c) a sectional view
through the textile at 0°C.
- Figures 2 are schematic representations of a textile according to the
first aspect of the present invention capable of an irreversible change with
a) the textile at 20°C and b) the textile at 70°C.
- Figures 3 are schematic representations of a textile according to the
present invention having a bulking layer comprising a shape memory alloy incorporated
into the weave of a fabric substrate with a) a plan view of the fabric substrate
b) a sectional view through the textile at 20°C and c) a sectional view
through the textile at 70°C.
Referring to Figure 1, the bulking layer 1 of the textile 2 comprises
a pair of fabric substrates 3a,b onto which is deposited a polyurethane based shape
memory polymer in a repeat pattern. The polymer being chosen to exhibit a reversible
phase change to a phase having a decreased specific volume at about 0°C, it being
obvious to those skilled in the art that a number of suitable polymers exist which
may be substituted for the one here. One such fabric substrate 3 is shown in Figure
1a and is provided with a printed pattern of concentric rings 4 of polymer, repeated
at centres C. These rings 4 are printed at about 20°C and are made planar at that
temperature by suitable equilibration, for example pressing through release paper
at an iron temperature of approximately 110°C. The textile 2 shown in Figures 1b
and 1c comprise two fabric layers 15,15' having a pair of fabric substrates 3a,b
sandwiched between them. The substrates 3 a,b are correlated such that the protuberances
6,6', which appear in each substrate as the phase changes, oppose one another.
This correlation may be maintained by stitching the layers 3 a,b, 15,15' of the
textile 2 together at their edges.
Since the textile according to Figures 1 exploits the volume change
in the shape memory polymer to achieve a change in the thermal insulation properties
of that textile then the changes are reversible.
A variant on the textile of Figures 1 would be to choose the polyurethane
shape memory polymer to exhibit a phase change at higher temperatures, for example
at about 70°C, to provide a textile capable of high temperature thermal protection.
A textile 7 which is formed so as to undergo an irreversible increase
in thermal insulation is shown in Figures 2. The bulking layer comprises a number
of fabric strips 8 a..n on to which is deposited a polyurethane shape memory polymer.
These strips 8 a..n are made to form individual coils or "springs" which are made
and equilibrated in an extended state at 70°C. These stress free structures 8 a..n
are then coiled to exhibit the compact cross-sections, as shown in Figure 2a, and
the applied stress frozen in at 20°C. One end of each such compact coil 8 a..n
is then looped through the weave of one of the fabric layers 25,25' and fixed by
ultrasonic point welding. These coils 8 a..n form the bulking layer over substantially
all of one face of one of the fabric layers 25,25'.
On exposure of the textile 7 to a temperature of 70°C the bulking
layer responds irreversibly with the coils 8 a..n recovering their initial extended
state to push apart the layers of fabric 25,25' as shown in Figure 2b.
It will be appreciated that a similar effect may be obtained by replacing
the coated fabric strips with coiled "springs" of a suitable shape memory metals,
such as Nickel/Titanium alloys.
A further embodiment of a textile 9 according to the present invention
is shown in Figures 3. The bulking layer comprises a fabric substrate 10 onto which
are attached, in a grid pattern, Nickel/Titanium shape memory alloy wires 11 having
a 4% retained strain. The wires are fixed on the fabric substrate 10 by having
an adhesive applied at their crossing points. A number of these substrates 10 a..n,
chosen so as to be able to effect the desired change in thermal insulation, are
sandwiched between two fabric layers 35,35' to form the bulking layer of the textile
9 which is substantially flat at 20°C (Figure 3b). As the temperature of the textile
varies from the predetermined temperature towards a higher temperature the substrates
10 a..n of this bulking layer pucker to increase the gap between the layers 35,35'
as shown schematically in Figure 3c.
It will be clear to a person skilled in the art that while the above
examples utilise fabric substrates and layers any suitably flexible material may
be substituted, depending on the desired characteristics of the garments to be
fabricated from the textile.