Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to heat recoverable articles,
particularly self heating, heat recoverable articles.
Our copending Canadian patent application Serial No.
258,297 filed August 3, 1976 describes articles comprising
electrically resistive heat recoverable material and a pliable
fabric electrode in contact with such material.
Our copending Canadian patent application Serial No.
267,269 filed December 7, 1976 describes a heating element com-
prising laminar flexible electrodes, e.g. o~ metal, and an
electrically resistive polymeric layer between the electrodes,
the heating element having a plurality of apertures through the
thickness thereof to render it readily deformable; the heating ;
element is not itself heat recoverable but can be secured to a -~
heat recoverable article to effect recovery thereof.
The present invention provides a heat-recoverable
article which comprises: a heat-recoverable member which com-
prises an organic polymer having sufficient finely divided
electrically conductive particles dispersed therein to render
the member conductive; and at least two electrodes which are ~-
secured to and in contact with said member and which when con-
nected to a source of electrical power cause current to flow
through said member, at least one of said electrodes being a ~`
deformable electrode which is a metallic laminar member having -
a plurality of apertures therein, the apertures being of elongate
closed cross-section and overlapping one another, the laminar
member being such that when at least one of its dimensions is ~ ;
changed, the shape of th~ apertures is changed, the portion of ;
the member defining the perimeter of each aperture after defor-
mation being the same portion that defined the perimeter of that
aperture before deformation.
There is also provided a process for covering a sub-
strate by placing adjacent thereto an article as described in ~;
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the immediately preceding paragraph and connecting its electrodes
to a source of electrical power whereby the article is caused
to recover.
The deformable electrode is preferably composed of a
metal of good ductility~ e.g. aluminum, which is preferred,
copper or lead. The thickness of the metal and the apertures
should be such that the electrode provides the desired current- ;
carrying capacity. Typically the electrode will be 3 to 10 ~
mils (0.0075 to 0.025 cm.) thick. The apertures may be, for j-
example, diamond-shaped, e.g. with a major dimension of 0.2 to
0.5 inch (0.5 to 1.2 cm.) and a minor dimension of 0.07 to 0.15 ~
inch (0.18 to 0.4 cm.) prior to expansion, or hexagonal. The ~ ~-
width of the metal between the apertures will generally be at
least 0.01 inch (0.025 cm.), e.g. 0.01 to 0.04 inch (e.g. 0.025
to 0.1 cm.), at the narrowest point. The electrode is preferably -
prepared by perforating a metal sheet, e.g. by piercing, which
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is preferred, or stamping. CQmmercially available expanded metal
sheets provide suitable electrodes, especially if they are rolled
after they have been pierced in order to flatten them. Alter-
natively a plurality of metal wires can be welded or otherwise ~
secured together. ~`
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Preferably all the electrodes in the article are de- ` `
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formable metallic laminar electrodes, as defined, but other
types of electrode can be present, including non-deformable ~ -
electrodes, whose presence induces differential recovery.
Preferred articles comprise a said conductive polymer
member which is a heat-shrinkable sheet sandwiched between two
or more deformable metallic laminar electrodes as defined, which
electrodes preferably have substantially the same planar dimen-
sions as the heat-shrinkable sheet. ~
Preferably at least part of the heat recoverable - v
member exhibits PTC behaviour so that when the article is
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connected to a source of power, current is substantially -~
prevented from flowing through the member at a predetermined
switching temperature which is sufficiently high to cause
recovery of the member, and preferably not more than 25C,
especially not more than 15C, above the recovery temperature.
When using the article, it is not of course necessary that the
article be heated to a temperature such that no effective ;
current flows through the PTC layer, but only that the article
- be heated to its recovery temperature. However, the presence
of the PTC layer provides a safeguard against excessive heating. s
In one embodiment, the heat-recoverable member comprises a layer
exhibiting PTC behaviour which is sandwiched between two layers
each-of which exhibits constant wattage behaviour at temperatures
below the switching temperature of said PTC layer and has at
least one said deformable electrode in contact therewith.
Preferably the deformable electrode is entirely surrounded by
said constant wattage layer or by said constant wattage layer
and said PTC layer.
For additional details of heat-recoverable members -
suitable for use in this invention, rèference may be made to
abovementioned Canadian patent application Serial No. 258,297. `~ -
The articles of the invention can readily be made by
known methods in which the metallic laminar electrode is secured
to the heat-recoverable member preferably before the article is
rendered heat-recoverable.
The articles of the invention will normally comprise
an outer insulating jacket. Especially when the article is in
the form of a sheet (including tape), the insulating jacket is
preferably one which will adhere to itself on heating the
article to its recovery temperature, so that when the sheet is
wrapped around a substrate, auto-adhesion of overlapping parts
of the sheet will take place on heating. ;
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The invention is illustrated by the following Example,
in which percentages are by weight.
Example
A PTC composition having a switching temperature of
about 132C was prepared by blending 37-~ of carbon black, 57% `-
of high density polyethylene, 5% of an ethylene-propylene rubber
and 1% of an antioxidant. A constant wattage (CW) composition ~;
was prepared by blending 82% of an ethylene/ethyl acrylate co-
polymer, 17% of a carbon black and 1% of an antioxidant. An
insulating composition was prepared by blending 76% of an ~ ;~
ethylene/ethyl acrylate co-
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polymer, 15% of talc, 8% of pigment and 1% Of an antioxidant. Using these com-
positions and an aluminum electrode, a laminated article having the following
layers was prepared
Thickness
1. ` Insulating composition 20 mils ~0.05 cm)
2. CW composition10 mils (0.025 cm)
3. Electrode 5 mils ~0.013 cm)
4. CW composition10 mils (0.025 cm)
5. PTC composition20 mils ~0.05 cm) -
6. CW composition10 mils ~0.025 cm)
7. Electrode 5 mils ~0.013 cm)
8. CW composit1on10 mils ~0.025 cm) ;
9. Insulating composition 20 mils t0.05 cm) ` ~-
The electrode material was a commercially available expanded aluminum sheet
which had been flattened by rolling. It was 5 mil ~0.013 cm.) thick, with
diamond-shaped apertures of major dimension 400 mil ~1 cm.) and minor dimen- --
sion 100 mil ~0.25 cm.) and a bar width between the apertures Of ? mil ~0.05 -`
cm.). Transverse strips of a high-melting polyester tape were placed either
side of the electrodes at intervals, so that in subsequent use of the article
~2Q the tape could he separated from the electrode to provide an exposed port1on
thereof for connection to a source of electrical supply. -
The laminate was irradiated to a dosage of 10 Mrad to cross-link
the po~ymeric layers. It was then heated, expanded 2 X in the longitudinal
direction, and cooled in the expanded state to render it heat-shrinkable.
The laminate was slit to provide a tape 4 inch ~10 cm.) wide.
The heat-shrinkable tape was used to seal the junction between a ;~
lead sleeve and a cable having a polyolefin insulating jacket. The junction
was wrapped with a tape of hot-melt adhesive. The adhesive tape was then
wrapped with the heat-shrinkable tape. The electrodes of the heat-shrinkable
tape were connected to a 12 volt DC power supply. After about 8 minutes, ~;
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during which time the tape reached a temperature of about 120C,
the tape had shrunk down, melting the adhesive, and bonding to
the cable jacket and to itself.
The invention is illustrated by the accompanying drawing !~
of which the single figure is an isometric view of a portion of
a planar laminated article of the following construction:
A PCT composition as described in the Example is formed
into a flat sheet 1, and flattened expanded aluminum sheets 2
and 3 of the construction described in the Example are laminated
to each major surface. The sheet may be rendered heat-recoverable
by the method described in ~e Exe~ple.
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