U.S. patent application number 14/101798 was filed with the patent office on 2014-04-10 for iron.
This patent application is currently assigned to Morphy Richards Limited. The applicant listed for this patent is Morphy Richards Limited. Invention is credited to George Ralph Adkins, Richard Gregory, Mike James, Jamie Michael Sellors.
Application Number | 20140097170 14/101798 |
Document ID | / |
Family ID | 40862848 |
Filed Date | 2014-04-10 |
United States Patent
Application |
20140097170 |
Kind Code |
A1 |
James; Mike ; et
al. |
April 10, 2014 |
Iron
Abstract
The invention relates to an electrical iron. An iron comprises a
sole plate, of a glass or ceramic substrate bearing an electrical
heating element. The electrical heating element comprises a
transparent or translucent antimony tin oxide thin film which
directly heats the glass or ceramic substrate.
Inventors: |
James; Mike; (Rotherham,
GB) ; Sellors; Jamie Michael; (Rotherham, GB)
; Adkins; George Ralph; (Rotherham, GB) ; Gregory;
Richard; (Cambridge, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Morphy Richards Limited |
Rotherham |
|
GB |
|
|
Assignee: |
Morphy Richards Limited
Rotherham
GB
|
Family ID: |
40862848 |
Appl. No.: |
14/101798 |
Filed: |
December 10, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13321727 |
Nov 21, 2011 |
|
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PCT/GB2010/001010 |
May 19, 2010 |
|
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14101798 |
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Current U.S.
Class: |
219/254 |
Current CPC
Class: |
D06F 75/24 20130101;
D06F 75/38 20130101 |
Class at
Publication: |
219/254 |
International
Class: |
D06F 75/24 20060101
D06F075/24 |
Foreign Application Data
Date |
Code |
Application Number |
May 22, 2009 |
GB |
0908860.0 |
Aug 19, 2009 |
GB |
0914503.8 |
Claims
1-56. (canceled)
57. An iron comprising: a sole plate; a secondary layer spaced
apart from said sole plate and disposed over said sole plate, said
secondary layer being disposed substantially in parallel with said
sole plate, said secondary layer providing electrical and thermal
insulation from said sole plate; and a cavity formed between said
sole plate and said secondary layer; said sole plate comprising: a
glass or ceramic substrate having a glass or ceramic surface for
placing in contact with a garment to be ironed; and an electrical
heating element formed as a layer on said glass or ceramic
substrate for heating said glass or ceramic substrate.
58. The iron according to claim 57, wherein said electrical heating
element comprises a substantially transparent film coating of
conducting or semiconducting material.
59. The iron according to claim 57, wherein said electrical heating
element comprises a substantially transparent layer of doped tin
oxide.
60. The iron as claimed in claim 57, wherein said cavity comprises
a sealed cavity which provides a thermal and electrical insulation
barrier from said substrate.
61. The iron according to claim 57, further comprising a cover
layer over said secondary layer, there being an air gap between
said cover layer and said secondary layer, wherein said cover layer
is thermally insulated from said secondary layer and said sole
plate by said air gap.
62. The iron according to claim 57, further comprising a cover
layer over said secondary layer, there being an air gap between
said cover layer and said secondary layer, wherein said cover layer
is thermally insulated from said secondary layer and said sole
plate by said air gap, said cover layer being formed of a heat
resistant polymer material.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to electrical irons.
BACKGROUND TO THE INVENTION
[0002] Domestic irons consists of a heated metal sole plate onto
which water from a reservoir is dripped to generate steam, which is
then emitted through holes in the sole plate. The clothes are then
pressed by an action of heat and steam. This method produces a
small and varying amount of steam and is really only suitable for
small amounts of clothes.
[0003] An improvement has been made through the introduction of
separate water reservoir and steam generators. In this embodiment,
a water tank and steam generator is separate from the iron, which
also consists of a heated sole plate.
[0004] The generated steam is then sent down a pipe to the iron,
where a constant stream of steam is then released onto the clothes.
This method has the advantage of a large water tank for heavy use
and a constant flow of steam. The main disadvantage is that the
steam can cool down in the pipe and the system is very inefficient
and takes a long time to warm up.
[0005] With the latter system, one option would be to pump water up
a pipe and generate steam in the iron. However, current nichrome
heating technology has a power density limitation, because if the
heater becomes too hot, then it will oxidize or burn out. Thus
without making the iron much larger and having a dramatic impact on
the sole plate temperature, the volume of steam generation is
limited. Making the heater separate from the iron allows for a
large heater sub-assembly and hence a large rate of steam without
the requirement for a large heater power density at the expense of
heat up time and efficiency. A further disadvantage of this method
is that the steam has to be re-heated at the iron and this can
impact on the sole plate temperature at higher flow rates initially
when the iron is cold, until the iron is at the correct working
temperature. In particular, if a sole plate with poor thermal
conductivity is used, then this will become a potentially large
problem.
[0006] We have therefore appreciated the need for an improved iron
and steam generation system.
SUMMARY OF THE INVENTION
[0007] According to a first aspect, there is provided an iron
comprising a sole plate, the sole plate comprising a glass
substrate bearing an electrical heating element. In preferred
embodiments, said heating element comprises a substantially
transparent film coating of conducting or semi-conducting
material.
[0008] Preferably, said film coating comprises a semi-conducting
oxide, more particularly a doped tin oxide, for example antimony
tin oxide (Sb.sub.3O.sub.4/SnO.sub.2), fluorine-doped tin oxide or
some other substantially transparent conducting doped oxide
material. Thus although the use of antimony tin oxide (ATO) film
coatings has been found to be especially advantageous due to
temperature stability, embodiments of the invention also
contemplate substitution of an ATO film coating by a film of a
different, electrically conducting material, for example, an
alternative substantially transparent conducting oxide film,
preferably a tin oxide film, for example Indium Tin Oxide, or a
mixture of doped oxides.
[0009] Use of a high thermal conductivity material or substrate for
the tubes facilitates a relatively low temperature for the heated
ATO films, for example less than 200.degree. C.
[0010] In embodiments the ATO film coatings are substantially
covalently bonded to their substrates, which reduces the risk of
lift-off or delamination from the substrate. This can be achieved
by cleaning and passivation of the substrate surfaces on which the
ATO coatings are deposited.
[0011] In embodiments the ATO film coatings are substantially
transparent and in combination with a transparent substrate, such
as glass, this enables the fabrication of an iron through which
clothes being ironed are visible during ironing. This can provide
benefits in that such an arrangement facilitates monitoring of the
clothes being ironed such that creases to be ironed out are more
easily seen by the user.
[0012] The use of an antimony tin oxide film also provides other
advantages since, in embodiments, such films are scratch resistant,
oxidation resistant, substantially chemically inert.
[0013] In preferred embodiments, the iron comprises a secondary
layer of glass or ceramic laminated over said glass substrate with
a gap there between. The secondary glass layer over the glass
substrate provides a thermal and electrical insulation barrier from
the glass substrate.
[0014] There is also provided a layer of transparent polymer
disposed over said secondary layer of glass, such that a gap is
formed between said transparent polymer and said secondary glass
layer for thermally insulating the transparent polymer from the
glass substrate.
[0015] This structure enables the clothes to remain visible to the
user even during ironing, whilst insulating the user from the heat
of the heated glass sole of the iron. The gap between the glass
substrate and the secondary layer may be filled with an inert gas,
for example krypton, for additional insulation.
[0016] However, in other embodiments the secondary glass or ceramic
layer and/or the upper polymer layer may be opaque, in which case
the user would not be able to see through those layers to the
material underneath the sole plate in use.
[0017] In embodiments, the iron comprises a hub for attaching said
sole plate to a handle, wherein the electrical connections from the
power supply, and switches/controls to the heating element which
are in the handle are routed through said hub. The outer casing of
hub itself is electrically isolated from the internal electrical
connections, so as to avoid risk of electric shock to the user.
Preferably, the hub comprises one or more conduits for guiding
steam to a surface of said sole plate.
[0018] In another embodiment, there is provided an iron having a
vapour outlet positioned at a front of the iron, which emits water
vapour or mist onto a region immediately in front of the tip of the
sole plate, or through the sole plate face.
[0019] In preferred embodiments, the glass substrate of the iron is
patterned with electrically and thermally conducting power rails in
the form of metal tracks, for providing additional, localised,
heating of said glass substrate. Preferably, the metal is
silver.
[0020] In an embodiment of the iron, the power rails are formed of
stripes along a substantial length of each of the longer edges of
said glass substrate and one or more stripes along a substantial
length of a central region of said glass substrate.
[0021] In an alternative embodiment, said power rails are formed of
a rear portion disposed at a trailing end of said glass substrate,
and a forward portion disposed at a leading end of said glass
substrate, said rear portion covering substantially the width of
the glass substrate and tapering towards the outer edges of the
glass substrate, and said forward portion comprising one or more
triangular portions and a bridging portion, said bridging portion
covering a stripe across substantially the width of said glass
substrate.
[0022] In a further alternative embodiment, said power rails are
formed of edge portions along the long edges of said glass
substrate, and wherein a forward portion of said edge portions
located at a leading end of said glass substrate has a greater
width than said edge portions along the remaining edge portion.
[0023] In yet a further embodiment, there may be provided a metal
or metal oxide layer formed as an area over the sole plate between
two edges of the sole plate. In this embodiment, there may be at
least a pair of oppositely facing power rails, positioned one on
each side of the sole plate, and extending between said pair of
power rails, a continuous area of thin film metal oxide heating
element. The thin film metal oxide heating element may extend
across almost the full width of the sole plate, and may extend
substantially along the whole length of the sole plate.
Alternatively, a small number of separate areas of thin film, each
independently controlled and each extending across a full width of
the sole plate may be provided.
[0024] The shape of the sole plate need not be a conventional
arched or bullet shaped sole plate area, but in other embodiments,
elliptical, ovoid or other geometric shapes for the sole plate
footprint may be formed. The shape of the sole plate footprint may
influence whether the metal oxide heating element formed as a
series of individual elements, or as a single film extending across
the whole of the sole plate, or as a plurality of areas of film
heating element extending across the sole plate.
[0025] In an embodiment of the iron, the electrical heating element
is patterned to maintain a substantially constant heat profile
across said glass substrate. This provides a substantially constant
level of heat across the glass substrate, which leads to a
substantially constant power rating.
[0026] Preferably, the pattern of said electrical heating element
comprises a plurality of heating element tracks, and wherein each
of said heating element track has substantially the same
length.
[0027] Preferably, the glass substrate is patterned with first and
second electrically conducting power rails for providing power to
said heating elements, and wherein each of said heating elements is
electrically connected between said first and second power rails.
In this embodiment, the first power rail runs substantially along a
central portion of the length of said glass sole plate and said
second power rail runs substantially along one or more edges of
said glass substrate. Preferably, the pattern of said heating
elements comprises one or more turns in direction such that the
heating element tracks follow a zig-zag or serpentine path between
said first and second power rails.
[0028] In embodiments, the sole substrate bears a layer of
semiconducting material, wherein said heating element is formed
from said semiconducting material, and wherein said iron includes a
temperature sensor comprising a portion of said layer of
semiconducting material.
[0029] In some preferred embodiments the film coating comprises a
semi conducting material and a switch for the heating element is
fabricated within part of a layer of the same material (either
within the heating element itself or as a separate device, for
example patterned in a common layer of semiconducting material.
[0030] In some preferred embodiments, the iron comprises a steam
generator for generating steam for applying to said sole plate,
said steam generator comprising: a first tube; a second tube
located within a bore of said first tube to define a first space
between an inner wall of said first tube and an outer wall of said
second tube, said second tube being coupled to a water input and
having a plurality of conduits for communicating input water to
said first space; a steam output coupled to said first space for
expelling generated steam; a film coating of doped tin oxide on an
outer wall of said first tube; and electronic connections to said
film coating to enable electricity to be passed through said film
coating to thereby heat water flowing through said first space to
generate steam.
[0031] The term "tube" is not intended to be restricted to a
circular cross-section. In embodiments, the tube cross-section may
instead be elliptical, oval, rectangular, square, triangular,
polygonal and the like.
[0032] In embodiments, the film coating comprises ATO (antimony tin
oxide). Preferably, the first tube comprises a glass substrate.
Alternatively, the first tube comprises a ceramic substrate.
[0033] In embodiments, the second tube comprises a first sub-tube
located within the bore of a second sub-tube to define a second
space between an outer wall of said first sub-tube and an inner
wall of said second sub-tube, and wherein said first and second
sub-tubes comprise a plurality of conduits for communicating input
water to said first and second spaces. Preferably, the first and
second sub-tubes are rotatable relative to one another about an
axial axis of said tubes.
[0034] In embodiments, the film coating of the steam generator
includes a temperature sensor comprising a portion of said film
coating.
[0035] In some embodiments, the said steam generator further
comprises: an electrical power input; and an electrical power
control device electronically connected between said electrical
power input and said film coating; wherein said electrical power
control device is a semiconductor device; and wherein at least a
portion of said semiconductor device comprises a portion of said
film coating.
[0036] In embodiments, the steam generator comprises a non-return
or one-way valve between the second tube and the water input to
prevent water returning to the input. Preferably, the steam
generator comprises a priming mechanism for providing an initial
amount of water to the steam generator. Alternatively, the steam
generator comprises a pump for providing water to the steam
generator. Preferably the pump is a mechanical, electrical or heat
pump.
[0037] The steam generator may form part of the iron, or may be
separate from the iron. In embodiments where the steam generator is
separate from the iron, the steam generator is connected to the
iron by means of a connecting tube.
[0038] In embodiments the electrical heating element, in particular
where it comprises a thin film, for example a layer of
semiconducting material, may itself be used as a temperature
sensor. In this case a signal maybe modulated onto the electrical
power, typically DC or low-frequency AC, supplying the heating
element, to enable this signal to be detected by demodulation. For
example a higher frequency AC signal than a frequency of an AC
current providing power for heating the heating element may be
employed. Additionally or alternatively a region of the film maybe
defined to be dedicated to temperature sensing and being provided
with at least one separate electrode connection (optionally sharing
one electrode connection with the heating element).
[0039] In an iron as described above an electrical power control
device or switch maybe incorporated into a layer semiconducting
material forming the heating element itself. For example by
applying a gate electrode over an insulating layer on a portion of
the semiconducting layer an FET (Field Effect Transistor) switch
may be fabricated. Such a device may be fabricated in a dedicated,
separately defined region of the semiconducting layer or may be
incorporated into the heating element, for example extending along
the length of an electrode connection to the heating element.
[0040] Thus in a further aspect an iron comprises: an electrical
power input; an electrical heating element, and an electrical power
control device electronically connected between said electrical
power input and said electrical heating element; whereas said
electrical heating element comprises a layer of semiconducting
material on a substrate; wherein said electrical power control
device is a semiconductor device; and wherein at least a portion of
said semiconductor device comprises a portion of said layer of
semiconducting material.
[0041] In embodiments the portion of the layer of semiconducting
material comprising the electrical power control device is
connected in series the material defining the electrical heating
element, and in embodiments the semiconductor device and heating
element may be part of the same, substantially continuous layer of
semiconducting material (rather than needing to be defined in a
separate, dedicated region of the semiconducting layer).
[0042] The device may comprise a diode, in particular a diode using
a metal-semiconductor junction. Alternatively p-type and n-type
doped regions of the layer maybe employed to fabricate a bipolar
transistor. Alternatively, as previously described, an insulated
gate FET (or junction FET) maybe fabricated. In general the power
controlled semiconductive device comprises an FET, bipolar
transistor, IGBT, thyristor, SCR rectifier, TRIAC, or other device.
In embodiments the device and heating element and substrate may be
substantially transparent.
[0043] Suitable materials include, but are not limited to, tin
oxide, for example doped with antimony or fluorine, indium tin
oxide, and silicon carbide.
[0044] In a second aspect there is provided a method of controlling
electrical power to the electrical heating element of an iron
comprising a layer of semiconducting material, the method
comprising forming a semiconductor device in said semiconducting
material comprising said heating element to control said electrical
power.
[0045] Embodiments include a steam generator for generating steam
said steam generator comprising:
[0046] a first tube;
[0047] a second tube located within said first tube to define a
first space between an inner wall of said first tube and an outer
wall of said second tube, said second tube being coupled to a water
input and having a plurality of conduits for communicating input
water to said first space;
[0048] a steam output coupled to said first space for venting
generated steam;
[0049] a film coating of doped tin oxide on an outer wall of a said
tube; and
[0050] electrical connections to said film coating to enable
electricity to be passed through said film coating to thereby heat
water flowing through said first space to generate steam.
[0051] The steam generator can be located in the hand iron itself,
or in a steam station which supplies steam to an iron. Where the
steam station supplies steam to an iron having a glass or ceramic
soleplate, the iron may have a further such steam generator used to
reheat the steam at the iron.
[0052] Another embodiment comprises an iron comprising:
[0053] a glass or ceramic sole plate; and
[0054] a semi-conductor heating element formed directly on said
glass or ceramic sole plate;
[0055] wherein said heating element is formed in a substantially
serpentine path.
[0056] According to a further embodiment, there is provided an iron
comprising:
[0057] a substantially transparent or translucent glass or ceramic
sole plate;
[0058] a substantially transparent semi-conductor film heating
element formed on said glass or ceramic sole plate;
[0059] a secondary glass or ceramic layer positioned adjacent and
spaced apart from said substantially transparent film heating
element; and
[0060] a further transparent cover layer positioned over and spaced
apart from said secondary layer, such that a heat insulating gap is
formed between said cover layer and said secondary layer for
thermal insulating said cover layer from said sole plate.
[0061] According to yet a further embodiment, there is provided an
iron comprising:
[0062] a glass or ceramic sole plate;
[0063] a plurality of heating elements formed on said glass or
ceramic sole plate;
[0064] wherein said plurality of heating elements are arranged into
a first region, in which a said heating element has a first power
dissipation; and
[0065] a second area in which a said heating element has a second
power dissipation,
[0066] wherein said first power dissipation is higher than said
second power dissipation.
[0067] Said first, higher power dissipation area is positioned at
or in a region of a tip of said sole plate.
[0068] The embodiments include an iron comprising:
[0069] a glass or ceramic sole plate;
[0070] a semi-conductor thin film heating element formed directly
on said sole plate; and
[0071] a semi-conductor thin film fuse element formed directly on
said sole plate, and connected in series with said heating
element,
[0072] said fuse arranged to terminate a current flow when a
current taken by said heating element exceeds a pre-determined
threshold current.
[0073] In other embodiments, there may be provided a semiconductor
thin film heating element with no semiconductor thin film fuse, but
with a mechanical fuse in series with the thin film heating
element. In yet other embodiments there may be provided a
mechanical fuse in series with a semiconductor thin film fuse on
the direct power to the heating element to provide additional
safety.
[0074] The embodiments includes an iron comprising:
[0075] a glass or ceramic sole plate; and
[0076] a semi-conductor thin film heating element formed on said
glass or ceramic sole plate;
[0077] wherein said heating element comprises a plurality of tracks
of semi-conductor thin film extending between a first power rail
positioned on a first side of said sole plate and a second power
rail position on a second side of said sole plate,
[0078] wherein said plurality of tracks are arranged such as to
provide a substantially uniform power dissipation across
substantially a whole area of said sole plate.
[0079] Each of said plurality of heating elements may extend
between said a first and second sides of said sole plate; and
[0080] each said heating element extends from said first and second
power rails, towards a tip of said sole plate.
[0081] Other aspects are as recited in the claims herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0082] For a better understanding of the invention and to show how
the same may be carried into effect, there will now be described by
way of example only, specific embodiments, methods and processes
according to the present invention with reference to the
accompanying drawings in which:
[0083] FIG. 1 shows an embodiment iron according to a first
specific embodiment of the invention;
[0084] FIG. 2 shows a side view of the iron of FIG. 1;
[0085] FIGS. 3a to 3c show embodiment irons with different patterns
of power rail on the sole plate;
[0086] FIG. 3a shows in view from underneath a second iron
according to a second specific embodiment, having a transparent or
semi-transparent glass or ceramic sole plate having a first heating
element track layout;
[0087] FIG. 3b illustrates schematically in view from underneath a
third iron having a transparent or semi-transparent glass or
ceramic sole plate having a second heating element track
layout;
[0088] FIG. 3c illustrates schematically in view from underneath a
fourth iron having a transparent or semi-transparent glass or
ceramic sole plate having a third heating element track layout;
[0089] FIG. 3d illustrates schematically in view from underneath
fifth iron having a transparent or semi-transparent glass or
ceramic sole plate having a fourth heating element track layout,
having a relatively higher power output at the tip of the sole
plate compared to the main body of the sole plate;
[0090] FIG. 4 shows a sixth embodiment iron with an alternative
pattern of heating element and power rail on the sole plate;
[0091] FIG. 5 shows a cross section through a steam generator
according to a seventh specific embodiment disclosed herein;
[0092] FIG. 6 shows a distribution of current across a sole plate
having a uniformly coated thin film heating element, showing build
up of hot spots;
[0093] FIG. 7 illustrates schematically one possible approach to
reducing the hot spots on the iron sole plate shown in FIG. 6
herein;
[0094] FIG. 8 illustrates schematically a graph of sheet resistance
against width for the sole plate as shown in FIG. 7 herein;
[0095] FIG. 9 illustrates schematically a second approach to
reducing the build up of hot spots on the iron sole plate of FIG. 6
herein;
[0096] FIG. 10 illustrates schematically a plot of heated area
fraction against width for the heating elements as shown in FIG. 9
herein;
[0097] FIG. 11 illustrates schematically a seventh iron according
to an eighth specific embodiment, having a sole plate patterned
with thin film heating elements to achieve a substantially uniform
power density;
[0098] FIG. 12 illustrates schematically a one time thermal fuse
formed from a thin film coating according to a ninth specific
embodiment;
[0099] FIG. 13 illustrates schematically in perspective view an
eighth iron according a tenth specific embodiment herein;
[0100] FIG. 14 illustrates schematically in view from above, the
eighth iron as shown in FIG. 13 herein; and
[0101] FIG. 15 herein illustrates schematically in cross sectional
view a glass sole plate having a recessed glass plate surrounded by
an aluminium outer rim or frame;
[0102] FIG. 16 herein illustrates in view form underneath a metal
rimmed glass sole plate; and
[0103] FIG. 17 herein shows in cross sectional view an embodiment
of layers of a glass sole plate iron.
DETAILED DESCRIPTION
[0104] There will now be described by way of example a specific
mode contemplated by the inventors. In the following description
numerous specific details are set forth in order to provide a
thorough understanding. It will be apparent however, to one skilled
in the art, that the present invention may be practiced without
limitation to these specific details. In other instances, well
known methods and structures have not been described in detail so
as not to unnecessarily obscure the description.
[0105] In specific embodiments disclosed herein, there is provided
an iron having a glass or ceramic sole plate, which is heated
directly by a thin film semi-conductor material, for example an
antimony tin oxide coating, or an equivalent semi-conductor
coating, for example doped indium tin oxide (ITO) or doped fluorine
tin oxide (FTO).
[0106] In this specification, where the term antimony tin oxide is
used, this encompasses materials including antimony oxide and tin
oxide, and including materials with the chemical formula
Sb.sub.3O.sub.4*SnO.sub.2, as well as materials with the formula
Sb.sub.2O.sub.3*SnO.sub.2, including such compounds which are doped
with donor or acceptor materials so as to affect the resistivity or
conductivity of the antimony tin oxide material. The material may
be formed on a glass or ceramic substrate by sputtering,
evaporation, chemical vapor deposition (CVD), or by other known
processes for forming or depositing a semi-conductor layer on to a
glass or ceramic substrate.
[0107] In this specification, where the term "heating element" is
used, this generally describes a doped metal oxide film through
which electricity is passed to generate heat. The heating elements
may be divided into elongate straight, curved or meandering tracks,
or may be formed as areas of different geometric shapes.
[0108] Where the term "power rail" is used, this generally refers
to a metal strip, track, film or coating used to supply power to
one or more heating elements.
[0109] The Iron makes use of clear thin film resistive coating
(e.g. ATO) on a glass substrate as the heating element to provide
the mechanism for heating a sole plate to facilitate crease removal
from fabrics.
[0110] Iron with Central Hub
[0111] Referring to FIGS. 1 and 2 herein, an iron comprises a glass
sole plate (1); an upper transparent portion (2); a handle (4)
attached to the upper transparent handle; and a hub (3) connecting
the sole plate to the handle.
[0112] Steam is delivered to the garment being ironed through the
hub (3), which also forms the fixing point for the glass panels and
electrical contact to the film coating on the glass sole.
[0113] The sole plate assembly is thermally and electrically
insulated from the handle assembly (4) by a combination of a
secondary glass sheet (8) laminated over the ATO coating (dotted
line 10), an air gap (potential to fill with inert gas, such as
krypton, for extra insulation) and a transparent moulded polymer
(7).
[0114] In the iron of FIGS. 1 and 2, a steam generator as described
with reference to FIG. 5 herein may be incorporated within the
handle of the iron, as a tubular heating element, so that water may
flow from a base reservoir unit through a feed tube connecting the
base unit to the hand iron, and passes through the tubular heating
element within the handle so as to be ejected as steam or heated
spray at the sole plate. Water is heated continuously, as it flows
through the inline tubular heating element contained within the
handle.
[0115] In FIG. 2, the laminated construction of the first iron is
shown in cross sectional view. The layers include a glass or
ceramic plate (9) which forms a main structural body of the sole
plate; formed directly on top of the glass sole plate, a thin film
heating element coating for example an ATO coating; on top of the
ATO coating, secondary transparent glass or ceramic sheet (8),
which is in direct contact with and bonded to the sole plate (9)
and the ATO coating (10); above the sole plate/secondary plate
laminate (8, 9, 10) is provided an upper casing (7) which may be
ceramic, or of a moulded transparent polymer or plastics material.
Between the transparent casing (7) and the secondary sheet (8) is a
void cavity (11), the purpose of which is to provide thermal
insulation from the secondary glass sheet (8) which may heat up to
a temperature similar to that of the glass sole plate (9). The
upper transparent casing (7) prevents a user from burning
themselves on the underlying sole plate and secondary glass or
ceramic plate (8) and provides an acceptable touch temperature,
whilst its transparent properties allows the user to see through
the casing, secondary glass sheet and sole plate to see the fabric
underneath the sole plate as it is being ironed and pressed.
[0116] Key benefits have been identified when using thin film
technology as heating mechanism, these include: [0117] Visibility
through to the fabric to be ironed (avoiding ironing in creases and
for navigation around garment fixings (zips, buttons etc)). [0118]
Improved manoeuvrability due to the surface quality of the glass
(minimal drag) and lightweight assembly.
[0119] Zonal Heating
[0120] Referring to FIGS. 3a to 3c herein, the ATO coating (12) and
printed silver tracking (11) can be configured to optimise the base
plate efficiency and bring intelligence in zonal heating to the
soleplate for different ironing tasks.
[0121] The structure of FIG. 3a, this pattern will create an even
horseshoe band of heat on the soleplate.
[0122] The structure of FIG. 3b will create a consistent even heat
to the main plate and allow the front tip to be tweaked for
`intense` heat if required to iron out stubborn creases.
[0123] The structure of FIG. 3c will create a graduated heat
profile to the main plate (hotter towards front) and allow the
front tip to be tweaked for `intense` heat if required.
[0124] Key benefits have been identified when using thin film
technology as heating mechanism, these include energy savings due
to `heat zoning`, when the electrodes can be designed to be
switchable and allow shut off or pulsing of particular areas of the
heating surface. This helps with cost savings in the Bills of
Materials (BOM) and manufacturing process.
[0125] Referring to FIG. 3d herein, there is illustrated
schematically a fifth iron sole plate having a zoning of heating
elements so as to provide a relatively higher power density heating
element (300) at a tip of the iron compared to the relatively lower
power density heating element (301) in the main body of the sole
plate. Higher power density may be required at the tip of the iron
particularly where the iron is a steam iron or has a spray which
emits water from the front of the iron. Where the iron moves in a
forward direction and encounters wet or damp cloth, extra energy is
required to evaporate moisture or dampness in the cloth at the tip
of the iron, compared to in the main body of the iron. When the
sole plate is moving in a forward direction, the fabric encountered
by the main mid region of the sole plate may be relatively dryer,
the moisture having been predominantly evaporated as the tip of the
iron moves over the fabric. If the sole plate had a uniform power
density across its area, the tip of the iron would become cooler
than the main body of the iron, since it has more "work" to do,
i.e. must dissipate more energy, because it is the first part of
the sole plate which encounters moist or damp fabric. This can be
compensated for by providing two different power density zones on
the iron with a higher power density heating zone at the tip of the
iron compared to the remainder of the sole plate. Since the glass
sole plate does not have good thermal latency, the tip may need to
have a higher power density heating element to give a faster
response time to re-heat after ironing damp fabric.
[0126] In FIG. 3d, each heating zone may be provided with its own
temperature control in the form of its own corresponding respective
thermister or other temperature control circuit, so that each of
the two heated regions may have their temperatures maintained
substantially independently from each other, subject to thermal
transmission through the glass or ceramic material of the sole
plate between adjacent differently heated regions.
[0127] The sole plate is not restricted to having two separately
temperature controlled and separate temperature heated regions, but
rather a plurality of more than two such reasons may be provided on
the same sole plate, each having its own corresponding respective
heating element and temperature control circuitry. Each heated
region may be provided with its own metallic power rails, for
example (302, 303) for the tip region (300), or live and neutral
power rails (304, 305) for the central region (301) as shown in
FIG. 3d herein.
[0128] Referring to FIG. 4 herein, an alternative scheme is shown.
The ATO coating (or other doped oxide coating) (2) and/or
conducting power rails (3, 4) can be configured to maintain a
substantially constant power rating (and therefore heat profile) on
an irregularly shaped heating or sole plate of the iron.
[0129] As shown in FIG. 4, the ATO coating is patterned into a
plurality of heating elements (2) on the glass sole plate (1). The
heating elements span between, and are electrically connected to
electrically conducting power rails (3, 4). The conducting power
rails (3, 4) provide power to the plurality of heating elements
(2).
[0130] In order to achieve a substantially constant power rating
(and therefore heat profile), each of the heating elements (2) are
designed to be substantially the same length. In this embodiment,
the heating elements are shown to turn direction in a zig-zag or
serpentine manner between the power rails (3, 4), with the distance
between each turn varying dependent on the position of the
individual heating element track on the glass sole plate such that
the same track length of heating element is achieved across the
whole of the glass sole plate.
[0131] Whilst a zig-zag pattern is shown, it would be apparent that
other shapes could be considered, with the heating element tracks
(2) running in a length-ways configuration, arcs or other geometric
shapes. It is also envisaged that the patterned heating element
track (2) of FIG. 4 could be used in conjunction with the patterned
metallic tracks for localised heating described above and with
reference to FIG. 3 for controlled heating.
[0132] Steam Generator
[0133] Referring to FIG. 5 herein, we will now describe a steam
generator which makes use of a high power density clear thin film
resistive coating (ATO) on a glass/ceramic substrate as the heating
element to provide compact steam generation. The steam generator
may be used in conjunction with the iron described above, either
integral to the iron, or as a stand-alone unit connected to the hub
of the iron.
[0134] An internal sub assembly of perforated tubes (5) (6) can be
rotated relative to each other to give a variable fine spray/jet of
water through aligned holes (7) directly on the internal surface of
an outer (ATO) coated (4) tube heater (1). Steam is created in the
internal chamber (8) and forced out under is own pressure through
the nozzle (9). Electrical connection to the resistive coating is
made via 2 printed silver contact strips at distal ends of the tube
heater (2).
[0135] If necessary, a non-return or one way valve can be located
at (3) to prevent back pressure into the water reservoir. Under
such a scheme it is possible for the mechanism to self pump with an
initial priming mechanism.
[0136] Alternatively the water would be pumped into the steam
generator using an electrical, manual or heat pump.
[0137] Key benefits include the ability to create the steam at
source (within the iron build) or within a steam generating
base/stand and therefore assist with current issues found in
current steam generator products i.e.: [0138] Reduced heat up time
of initial steam in cold tube set from generator to iron (at source
version) [0139] Reduced limescale build up within tube set, since
limescale does not adhere well to either ceramic or glass (at
source version) [0140] Minimise the size and cumbersome nature of
current generators allowing for more water storage and possible
reconfiguration/appeal of stand unit (Upright docking station, see
through water container, etc)
[0141] Another configuration is that this system can be just used
as a secondary heat source in the iron component to keep the steam
being delivered at high temperature on exit.
[0142] The coating itself can be used to sense the temperature of
the element and/or the amount of water present in the heater as
well as switching the heating zones or sections of the element,
which we shall now describe.
[0143] The steam generator may be provided in a self contained
steam iron. In other embodiments, the steam generator may be
located in a steam station separate from the hand iron, and the
steam is fed to the hand iron via a tube.
[0144] In a conventional steam iron being supplied with steam from
steam station, the steam passes into a chamber above the soleplate,
and heat stored in the metal soleplate serves to reheat any
condensate in the steam received from the steam station. However,
if the iron is a glass or ceramic soleplate iron, there is no
reheat chamber above the soleplate, and so a further heater or
steam generator may be necessary in the iron itself as a reheat to
remove any condensate in the steam supplied from the base station.
Therefore, in a separate embodiment there is provided a steam
station and station comprising a base station and a steam iron
having a glass soleplate, where the base station comprises a steam
generator as described in FIG. 5, and the steam iron also has a
steam generator as described in FIG. 5.
[0145] Thermal Sensor
[0146] Typical thin film coatings are intrinsic semiconductors. For
example, SiC and tin oxide are both semiconductors with large band
gaps (typically .about.3.2 eV). By doping the semiconductor can be
made to be n-type or p-type. Typically, impurities make the thin
film an n-type semiconductor. For example, ATO is an n-type
semiconductor. However p-type semiconductors can also be
produced.
[0147] Typical thin film materials hence have a reversible
resistance--temperature characteristic and thus the heating element
itself can be used as a thermal sensor to measure the temperature
of the heating element or substrate. Alternatively, a separate area
of thin film which does not constitute part of the heating element,
but placed on the same substrate close to the element can be used
to measure the temperature using a separate low voltage/low current
circuit. The area can be manufactured using a masking process when
the main heating element is being created.
[0148] It is preferred to detect the resistance change using a low
voltage/low current so that the sensitivity is improved and the
semiconductor is not saturated, hence a separate area for thermal
detection is preferred rather than using the bulk element itself.
Should the bulk element need to be used, then a high frequency
signal multiplexed on to the DC or low frequency AC bias can be
used to detect variation in resistance, without the requirement to
measure high voltages or currents.
[0149] The thermal sensor can also be used to detect the
temperature of the water.
[0150] Switching Mechanism
[0151] In embodiments the heating elements are required to be
switched on and off. This may achieved using a manual switch, a
relay or a solid state switching device, generally separated from
the heating element itself. However this can add extra cost to the
overall system.
[0152] Hence, it is desired to create a system by which the heating
element switch is included within the heating element. Given that
the thin film technology is a semiconductor, it is possible to
create at the same time as the heating element different types of
semiconductor switch or rectifier. In particular, one can produce a
FET device by overlaying a thin insulator, such as mica or silicon
dioxide on top so an area of the thin film element (typically where
the current enters or leaves the element). On top of the insulator
a metallisation layer is created to which a voltage can be applied
to switch the element. Further devices are possible: for example,
at the metal--thin film junction a Schottky diode is created,
further using n-type and p-type variants of silicon carbide or tin
oxide it is possible to create a rectifying diode or bipolar
transistor. Because the material can withstand high temperatures,
there is no need for a heat sink and any heat losses are directly
used in the heater, thus increasing efficiency as well as reducing
cost. Many of these devices can be transparent and hence can be
used within the iron to switch the elements to provide different
heating levels and control.
[0153] In embodiments the element may be switched by TRIAC
switching, with differential choke filtering (for example, a
differential mode filter of 18 mH) for EMC capability.
[0154] Uniform Heat Distribution
[0155] Whilst the serpentine heating element track pattern as shown
in FIG. 4 herein is aimed at achieving a substantially constant
power rating and therefore heat distribution across the surface of
the sole plate, the pattern shown in FIG. 4 is subjected to draw
backs.
[0156] Firstly, the configuration of FIG. 4 requires a central
power rail (4) down a centre line of the sole plate, acting as a
live or neutral power supply line, and first and second peripheral
power supply lines, one on each side of the sole plate. The central
power supply track (4) may interfere with an even heat distribution
down the centre line of the sole plate.
[0157] Secondly, the central power supply rail is visually
unattractive to the user, being relatively wider than the
serpentine heating elements (2).
[0158] Thirdly, the zig-zag or serpentine heating elements
extending between the central power rail track (4) and the lateral
power rail track (3) are shaped such as to have sharp corners and
relatively sharp angles. Sharp corners give rise to high electric
field values at the apexes of the corners, which can cause hot
spots, and reduce reliability.
[0159] An alternative arrangement would be to have one power rail
(for example live) on one side of the sole plate, and another power
rail (for example neutral) extending along the other opposite side
of the sole plate, with a resistive ATO doped semi-conductor film
extending across the centre of the sole plate between the two power
rails.
[0160] Referring to FIG. 6 herein, there is illustrated
schematically a sole plate comprising a constant thickness doped
semi-conductor resistive film capable of acting as a heating
element between first and second power rail tracks (600, 601)
respectively one on each side of the sole plate. The doped
semi-conductor film is formed on a glass or ceramic sole plate. The
arrows shown in FIG. 6 represent current direction between the two
power rails (600, 601). The power rails (600, 601) are formed of a
material which is more conductive than the doped antimony tin oxide
resistive film. For example the first and second power rails (600,
601) could be formed from antimony tin oxide which is doped to act
as an efficient electrical conductor.
[0161] However, using a constant thickness electrically resistive
film which generates heat between the two power rails leads to a
non-uniform heat distribution across the sole plate, due to the
irregular non-rectangular shape of the sole plate. In particular,
as the width of the sole plate reduces at the tip (602) and the
rear of the sole plate (603), the current density in the ATO film
increases relative to its density in the centre of the sole plate,
leading to hot spots at the tip and rear of the sole plate relative
to the centre of the sole plate. Power density is proportional to
the square of the current density, and so the power density is even
less uniform than the current density. The tip of the sole plate
and the rear of the sole plate receive much more power than the
centre of the sole plate and will get much hotter than the centre
of the sole plate.
[0162] Consequently, a uniform resistive thin film between two
electrodes either side of the sole plate would result in an iron
having a relatively hot tip and rear, and with the centre of the
sole plate being relatively cool.
[0163] Referring to FIG. 7 herein, one possible solution to the
problem of hot spots on the sole plate would be to vary the sheet
resistance of the ATO film. For example as shown in FIG. 7 herein,
the sole plate of the iron could be divided into a plurality of
substantially rectangular ATO film sections each having a width W
across the width of the sole plate, and each having a height H,
being the height of the strip extending between the tip and the
rear of the sole plate. Each of the rectangles of ATO thin film has
a different sheet resistance. The power density within each strip
of ATO film varies according to the relationship:
P A = V 2 .sigma. s 1 W 2 ##EQU00001##
[0164] However, this approach has the drawback that, for a constant
5.5 W/cm.sup.2, the sheet resistance needs to vary enormously in
order to give constant power density, and therefore constant heat
distribution within each strip. For example, the resistance would
need to be 100 Ohms/per square (.OMEGA./sq), for a trip of width 10
cm. For a strip of width 3 cm, the sheet resistance needs to be
1000 Ohms/per square (.OMEGA./sq) and for a strip of film 1 cm
wide, the sheet resistance would need to be 10,000 Ohms/per square
(.OMEGA./sq) in order to achieve a constant power density.
[0165] Referring to FIG. 8 herein, there is illustrated
schematically a graph of resistive element width in centre metres,
against the required sheet resistance in ohms per square to achieve
constant power density.
[0166] The sheet resistance cannot be varied widely enough to make
this approach practicable. This approach is unlikely to work
because the sheet resistance of the ATO film needs to vary too much
(by a factor of 100) in order to give a constant power density
across a sole plate area having curved sides.
[0167] Another approach to even out the power density may be to
vary the height of the rectangular strips of thin film heating
elements between the front and the rear of the sole plate.
[0168] Referring to FIG. 9 herein, there is illustrated
schematically in plan view from above, a glass or ceramic sole
plate having a plurality of ATO heating elements each extending
across the width of the sole plate, each heating element having a
width W and a height h, where each heating element is contained
within an area of width W and height H. Each heating element does
not necessarily fill the whole of the rectangular area with
dimension W.times.H.
[0169] In this approach, the power density of each heating element
is determined by the equation
P A = V 2 .sigma. s 1 W 2 h H ##EQU00002##
[0170] In this case, for a constant power density of 5.5
W/cm.sup.2, the heated proportion of each area (h/H) needs to vary
widely. For example, for a width W of 10 cm, the height h of the
ATO strip needs to be 100% of the height of the area H. For a 3 cm
wide strip, the height h of the heating element needs to be 10% of
the height of the rectangular area, and for a heating element 1 cm
wide, the height h of the heating element needs to be 1% of the
height H of the rectangular area.
[0171] Referring to FIG. 10 herein, there is illustrated a graph of
track width in cm against the proportion of the area heated, for
heating element track widths in the range approximately 0.5 cm to
10 cm.
[0172] Even if the resistance of the thin film coating is varied as
well, the dimensions of the heating element still vary too widely
to make this approach a practical solution. At the front of the
iron, the height of the strips would be impractically small, for
example 0.1 mm high strips, spaced 1 cm apart.
[0173] Referring to FIG. 11 herein, there is illustrated
schematically in view from underneath a fifth iron having a
transparent or semi-transparent glass or ceramic sole plate, having
a fourth heating element track layout. The sole plate has formed on
it a first ATO power rail track (1101) extending around one side of
the sole plate, and a second ATO power rail track (1102) extending
around a second, opposite side of the sole plate. Between the two
power rails are positioned a plurality of thin film semi-conductor
resistive heating elements such as antimony tin oxide, fluorine tin
oxide or indium tin oxide film resistors. Each heating element
extends between the first power rail and the second power rail in a
path which veers towards the tip of the front plate, extending from
a power rail relatively at the rear of the sole plate, towards a
peak position towards the tip of the sole plate, and then returning
back to join the other opposite power rail towards the rear of the
sole plate.
[0174] In view from underneath, each heating element follows a
substantially part sinusoidal path between the first and second
power rails, wherein an element towards the rear most of the sole
plate has a relatively highest sine wave spatial frequency, and
individual elements towards the centre of the sole plate, at the
position where the sole plate is widest have a relatively lowest
spatial period or frequency. From a position at the widest point of
the sole plate towards the tip, each of the elements has a
successively reduced spatial period towards the tip, the period
frequency of the substantially sinusoidally shaped elements being
determined by the distance between the ends of the element where
they meet the corresponding respective first and second power
rails.
[0175] The arrangement of elements is designed such that for a
constant thickness film and constant width of the element, the
shape of the elements, the spacing's between the elements and the
positions of the elements relative to each other give rise to a
substantially uniform power density and substantially uniform power
dissipation across the sole plate, avoiding localised hot spots.
The heating elements have the appearance of a set of ribs running
across the area of the sole plate.
[0176] At the rear of the sole plate, are provided a pair of
contact regions (1104, 1105), for contact of the respective first
and second power rails to live and neutral power supplies.
[0177] Thermal Fuse
[0178] Referring to FIG. 12 herein, there is illustrated
schematically in close up view, a portion of a power rail (1200) of
the sole plate of FIG. 12, positioned between a contact pad (1201)
for connecting to a live electrical power supply, and a plurality
of heating elements connected further along the power rail. The
power rail section contains a narrowed portion (1202) of relatively
reduced track width, the width of the power rail being selected so
as to overheat and evaporate or otherwise burn out, at a
pre-determined current density and therefore to self destruct as a
one time thermal fuse in the event of overheating of the sole
plate.
[0179] If, for example there is a short circuit between the first
and second power rails, increased current will flow through the
reduced width section of the power rail, thereby increasing current
density and causing the reduced section of power rail to "blow"
thereby cutting the power rail. The narrowed fuse section may be
doped slightly differently to the rest of the power rail, for
example with a slightly higher resistance, in order to give it
different conductivity properties to the power rail, in addition
to, or instead of having a reduced width.
[0180] In other embodiments, instead of or as well as having a
reduced width, the thickness of the film may be varied, to a
reduced thickness compared to other parts of the power rail, so
that in any event, the fuse section of the power rail is
electrically and physically the weakest part of the power rail, and
is designed to self destruct as a pre-determined current flows
through the power rail. Once the fuse section is blown, it is not
repairable and the sole plate or iron requires replacement. The
fuse section of the thin film power rail is designed to be
relatively weaker, having relatively reduced dimensions compared to
the rest of the power rail, and/or having relatively lower
conductivity compared to the rest of the power rail, so that it
acts as the electrically weakest part of the power rail.
[0181] The embodiments may have a further fuse between the power
cable and the controls as well as a fuse between the controls and
the heating element.
[0182] In addition, there may be provided a further mechanical fuse
on the heating element side of the controls and switches as well as
or instead of the semiconductor thin film fuse. Thermal fuses may
be provided on each side of the controls.
[0183] Iron with Rear Connected Handle and Separate Reservoir
[0184] Referring to FIG. 13 herein, there is illustrated
schematically in perspective view from one side and above, an
eighth iron according to a tenth specific embodiment herein. The
iron comprises a light weight electric hand iron component (1300),
and a base component (1301) which also provides a reservoir for
water supply to the hand iron.
[0185] The hand iron comprises a substantially transparent sole
plate having a transparent or translucent thin film heating
element, for example an antimony tin oxide heating element; an
upper casing (1302) which surrounds a periphery of the sole plate
and is positioned on top of the glass or ceramic sole plate, the
casing curving up and being formed into a handle portion (1303)
which lies parallel to and above the sole plate, with a gap there
between allowing a user to grasp the handle; and positioned between
the glass sole plate and the handle, a transparent upper casing
portion (1303) which lies above the glass or ceramic sole plate.
The handle is connected to the sole plate and upper casing by a
rigid rear connecting portion (1304) and there is no connection
between the front of the handle and the tip of the upper casing.
The upper casing being transparent, allows the user to see through
the casing, and through the glass sole plate to see the material
being ironed directly underneath the glass sole plate. The
substantially transparent upper casing (1303) also provides the
function of protecting the users hand and fingers from the upper
surface of the heated glass sole plate and thermally insulates the
user from the heated glass sole plate.
[0186] A space or cavity between the convex shaped upper window
(1303) and the substantially flat planar glass or ceramic sole
plate may be filled with an inert or thermally insulating gas, in
order to reduce the thermal conductivity between the glass sole
plate and the window, or may be filled with air. The cavity may be
sealed unit to prevent escape of the gas.
[0187] Referring to FIG. 14 herein, there is illustrated
schematically the sixth iron and its base in view from above,
showing how a user can see through the transparent upper cover,
through the glass sole plate and underneath to the base unit. In
the iron of FIGS. 13 and 14, water is sprayed from a position at
the front of the iron, at the front of the handle, rather than
through the glass sole plate. A vapour outlet may be provided at a
front position of the iron, which emits water vapour or mist onto a
region immediately in front of the tip of the sole plate. In the
embodiment shown, the vapour outlet is positioned at the front of
the handle, overhanging the tip of the sole plate, or alternatively
through the face of the sole plate.
[0188] Referring to FIGS. 15 and 16 herein, there is illustrated
schematically in cross sectional view, an alternative embodiment
sole plate 1500 comprising a glass inner plate 1502 and an outer
metal e.g. aluminium rim or frame 1501. The aluminium frame may
provide shock resilience on dropping the iron accidentally. Sharp
blows to the edge of the sole plate are absorbed by the aluminium
edge which extends around a periphery of the glass sole plate. The
glass or ceramic inner sole area 1502 is protected from direct
impact in a direction along the plane of the sole plate, and from
impact around the edge of the glass/ceramic portion.
[0189] Additionally, the glass/ceramic inner sole area 1502 is
slightly recessed from the outer metal frame so that if the iron is
accidentally dropped so as to land with the sole plate flat or near
parallel to the floor, the inner glass/ceramic sole area 1502 is
protected by the outer metal rim. In the best mode, the outer rim
may project or protrude beyond the outer surface of the glass or
ceramic portion by a distance of the order of up to 0.4 mm and
preferably 0.2 to 0.3 mm. The exact amount of recess is determined
as a trade off between the protecting the glass plate from impact,
and the need to have the sole plate in contact with the surface to
be ironed. The inner periphery 1503 of the rim or frame may be
chamfered to provide a smooth transition to the glass portion of
the sole plate. Other profiles of metal frame are possible, with
the effect that a portion of the outer metal frame extending around
the glass sole plate extends in a direction perpendicular to the
planar surface of the glass sole portion by an offset distance of
the order up to 0.4 mm, and preferably 0.2 to 0.3 mm beyond the
outer cloth contacting plane of the glass sole portion.
[0190] Referring to FIG. 17 herein, there is illustrated
schematically in cut away view from one side an embodiment glass
sole plate iron showing the layers of construction. A glass sole
plate 1700 forms the underside of the iron. Spaced apart from and
on top of the sole plate is an adjacent secondary layer 1701, with
a gap between the sole plate and the secondary layer. The secondary
layer is preferably transparent or see through, but in some
embodiments may be opaque.
[0191] The secondary layer may form a sealed unit with the sole
plate and an inert gas may be contained within the cavity between
the sole plate and the secondary layer. The secondary layer
provides thermal insulation and electrical insulation to the upper
side of the sole plate onto which are formed the ATO heating
elements 1702.
[0192] Over the secondary layer is formed a further cover layer
1703, which forms the upper part of the case. This layer is
preferably transparent, but in some embodiments may be opaque.
There is preferably an air gap between the upper layer 1703 and the
secondary layer. The upper layer provides an acceptable touch
temperature to the user, being thermally insulated form the
secondary layer and the sole plate by an air gap. The upper cover
layer may be formed of a heat resistant polymer material e.g.
polycarbonate.
[0193] In this specification, where resistive heating elements,
fuses or other semi-conductor components have been described
utilising antimony tin oxide thin film, such components may be
substituted by appropriately doped indium tin oxide (ITO) or
fluorine tin oxide (FTO) coatings, as are known in the art or
mixtures of such oxides.
[0194] It will be understood that the invention is not limited to
the described embodiments and encompasses modifications apparent to
those skilled in the art lying within the scope of the claims
appended hereto.
* * * * *