Note: Descriptions are shown in the official language in which they were submitted.
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ELECTRIC ~IEATING PANELS
DESCRIPTION
The invention relates to an electric heatiny
panel, by which term is mean-t not only an electric
blanket but also a heating pad for example a heated
carpet underlay, the panel comprising outer layers
adhesively laminated toyether with a heating element
therebetween, and also to a method of and an apparatus
for manufacturing such a heating panel.
Electric blankets conventionally comprise two
layers of fabric with a heating element, and perhaps
also a layer or layers of foamed material, received
between them. The heating element must be held at least
approximately in a desired pattern extending over the
area of the blanket, and this can be achieved by securely
~-- connecting the two fabric layers together be-tween
adjacent runs of the heating element.
When the fabric is a non-woven fabric, securement
toge-ther of the fabric layers can be effected by
~0 needling, which however requires rather elaborate and
consequently expensive machinery. To avoid the need
for such machinery, a solvent based adhesive can be
employed to secure the lavers together but this
technique has some disadvantages. The adhesive tends
to bond the hea-ting element to the fabric layers so
that the element is incapable of movement relative to
the layers, for example when the blanket is folded,
with an adverse effect on the ~orking life of the element.
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To overcome the aforementioned disadvantages of known
electric blankets, heating pads etc., the invention provides
a flexible electric heating panel comprising first and
second layers of flexible material laminated together by a
hot melt adhesive and an electric heating element received
between the layers, the adhesive being distributed substan-
tially uniformly between the layers without formation of a
permanent bond with the heating element. The element is
thus capable of limited movement within the panel, so
facilitating flexure and folding of the panel and thereby
extending its useful life.
By the term hot melt adhesive there is meant herein
an adhesive the condition of which is determined substan-
tially only by its temperature, as opposed to adhesives
which bond by a chemical action which is effectively
irreversible. Hot melt or thermoplastic adhesives as here
employed are heated to render them plastic for application
to the surfaces to be bonded, and bonding takes place by
cooling. After such cooling, the adhesives can again be
softened by the application of heat. The undesirable
release of solvent during bonding is thus completely
avoided.
; The adhesive is, of course, selected so as to have a
softening temperature above the temperature of the heating
element in normal use.
The invention also provides a method of manufacturing
a foldable electric heating panel, the method comprising
the steps oE applying a hot melt adhesive substantially
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uniformly over at least one of the first and second foldable
layers, bringing the first and second layers into overlyiny
relationship with an elongate electrical heating element
received between the layers, and applying heat and pressure
to the layers to bond the layers together by means of the
adhesive without formation of a bond with the heating
element capable of resisting folding of the panel.
The invention is further described below, by way
of example, with reference to the accompanying drawing, in
which:
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Figure 1 is ~ schematic side view of an apparatus
fox manufacturing an electric blanket in accordance
with the invention: and
Figure 2 i5 a p~rtial schematic sectional view
throuyh an electric blanket manufactured by the
apparatus of Figure 1.
The laminating apparatus illustrated in Figure 1
comprises support means for two ~upply rolls 2,4 of
fabric, The fabric can be of any suitable material,
synthetic or natural, and can be woven or non-woven;
it is however con~enient to employ a non-woven fabxic
of rayon. Webs 6,8 of the non-woven fabric are
withdrawn from the rolls 2,4 and are fed towards each
other along aligned generally horizontal paths to the
nip of pressure rollers 10,12. Suitable support or
guide rollers or the like tnot shown3 are provided to
help define these paths.
On leaving the supply roll~ each fabric web
undergoes a drying operation, to remove surplus
moisture which would absorb energy appl~ed to the web
later on for the purpose o~ softening thexmoplastic
adhesive applied thereto. For this purpose, heating
means, each conveniently as shown in the form of an
opposed pair of electric radiant heaters 14,16
between which the web travels, are positioned
immediately downstream of the supply rolls 2,4.
As shown at the right hand side of Fiyure 1, a
foam layer is secured to the upper side of the fabric
web 8 dlrectly after the drying stage to add bulk to
the blanket. The layer 18 can be of foamed plastics
material; it is fed downwardly from a supply roll 20
so as to be received in overlying relationship with
the web 8 in the nip of pressure rollers 22,24~
A heater 26 heats the underside of the layer 18
imme~iately before it en~ages the web so as to soften
the thermoplastiCS material of the layer. The
pressure of the rollers 22,24 effects an effective
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permanent bond hetween the softened foam layer and
the weh~ as the former hardens by cooling.
An adhesive 28 ~s then applied to the exposed
upper surface of the layer 18. The adhesive 28 is a
hot melt or thermoplastlc adhesiveO pre~erably a
polyethylene adhesive, hut a polyamide adhesive, or a
mixture o~ the two, can be employed. The adhesive 28
can be in particulate form and the adhesive particles
are then sprinkl~d over the surface of khe layer 18 by
a dispenser or distrlbutor 30, graYity fed from a
hopper 32. In~tead, the adhe~ive can be in the form
of a sheet or net 34. A~ shown in broken line at the
left of Figure 1, the net 34 can be applied ~o the web
6 by being drawn from a supply roll 36 thereof and fed
against the we~ by heing passed with the web between
pressure rollers 38,40. The net can instead be laid
on the web 6 under gravity.
Immediately prior to the laminating operation,
which is effected by the rolllers 10,12, the adhesive 28
is heated to a temperature at which it is capable of
bonding together the fabric web 6 and the foam layer 18,
and in the illust~ated apparatus this is done by radi~nt
heat supplied by an electric heater 42 positioned
immediately upstream of the rollers 10,12. The web 6
can also be heated immediately prior to lamination, as
by an electric radiant heater 44.
Batween the web 6 and foam layer 18, there is
~ntroduced a heati~g element 46 comprising a metallic
wire 48 in a sheath 50 of insulatinq material~ for
example a thermoplastic material. The heatin~ element
46 is introduced between the web and the layer in a
predetermined pattern by a laying up device
schematically indicated by reference numeral 52. Any
suitable pattern for the wire heating element 46 can
~e employed, depending for example on whether the
eventual blanket is to have a single or mul~i-heat
control arrangement.
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The web 6 turns downwaxdly over the pressu~e
rollex 10~ as do the web 8 and layer 18 s~er the
roller 12, 50 that the web 6 and the layer 18 are
laminated together by the adhesive 28 at the same time
as the electrical harness constituted by the heating
element 46 is introduced between them.
A reliable bond can be formed between the webs
6 and the layer 18 after these have travelled as far
downstream of the pressure rollers 10,12 as is needed
for the adhesive 28 to cool. The laminated blanket
material thus ormed is carried from the rollers
10,1~ by driving meansg for example driv~ rollers
54,56 as shown, to appropriate cutting and further
processing equipme~t ~not shown).
The adhesive 28 employed is of course selected
so that it will not soften due to the heat generated
in use by the heating element 46, that is, it has a
softening temperature well above the maximum
temperature likely to be experienced by the blanket
in normal use~ The adhesi~e 28 is preferably chosen
also so that it will not form a bond with the insulating
material of the sheath 50 of the wire 48. ~lthough
firmly restrained against lateral movement by the
adhesion between adjacent surfaces of the web 6 and
the layer 18, the element 46 is consequently capable
of longitudinal movement within the tunnel in which
it is secured, so that stresses on the blanket which
occur on folding are reduced and the life of the blanket
enhanced,
The adhesive, in any form, can be applied to the
upper surface of both the web 6 and the layer 18 if
prefexred, The applicatlon of the adhesive need not
take place immediately before thelaminating step, but
it can be applied to one or both of the surfaces to
be bonded, with ~ubsequent application of heat to
secure it in place, and the intermediate product thus
obtained kept for lamination subsequently.
The apparatus described can be modified further
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so that the foam layer ~ is n~t included in the
product, the webs 6,8 being then bonded dlrectl~
together with the element 46 be~ween them. A ~oam
layer can be applied to each of the webs 6,8 i~
desired, and may be convenient to form ~he or each
foam-fabric laminate as a prior operation separate
from the other steps described herein.
Although reference has been made throughout the
specific description to electrlc blankets, it will be
evident that the invention can also be applied to and
embodied in heatiny pads for supplying heat in
situations other than those in which electric blankets
are employed.
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