U.S. patent application number 10/323173 was filed with the patent office on 2003-07-03 for formable thermoplastic laminate heated element assembly.
Invention is credited to Arx, Theodore Von, Laken, Keith, Schlesselman, John W..
Application Number | 20030121140 10/323173 |
Document ID | / |
Family ID | 24575681 |
Filed Date | 2003-07-03 |
United States Patent
Application |
20030121140 |
Kind Code |
A1 |
Arx, Theodore Von ; et
al. |
July 3, 2003 |
Formable thermoplastic laminate heated element assembly
Abstract
A semi-rigid heated element assembly and method of manufacturing
semi-rigid heated element assemblies is provided. A heated element
assembly includes a first thermoplastic sheet, a second
thermoplastic sheet, and a resistance heating element laminated
between the first and second thermoplastic sheets. The resistance
heating element includes a supporting substrate having a first
surface thereon and an electrical resistance heating material
forming a predetermined circuit path having a pair of terminal end
portions. The circuit path continues onto at least one flap portion
that is capable of rotating about a first axis of rotation. The
reformable continuous element structure may be formed into a final
element assembly configuration whereby at least the flap portion is
rotated along its axis of rotation to provide resistance heating in
at least two planes. Semi-rigid heating elements may be formed into
heated containers, heated bags, and other objects with complex heat
planes.
Inventors: |
Arx, Theodore Von; (La
Crescent, MN) ; Laken, Keith; (Winona, MN) ;
Schlesselman, John W.; (Fountain City, WI) |
Correspondence
Address: |
DUANE MORRIS, LLP
ATTN: WILLIAM H. MURRAY
ONE LIBERTY PLACE
1650 MARKET STREET
PHILADELPHIA
PA
19103-7396
US
|
Family ID: |
24575681 |
Appl. No.: |
10/323173 |
Filed: |
December 18, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10323173 |
Dec 18, 2002 |
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09642215 |
Aug 18, 2000 |
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6519835 |
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Current U.S.
Class: |
29/611 ; 219/544;
219/548; 29/610.1 |
Current CPC
Class: |
B29K 2079/08 20130101;
B29K 2081/04 20130101; B29K 2081/06 20130101; B29K 2079/085
20130101; B29K 2023/12 20130101; B29C 66/71 20130101; B29K 2027/18
20130101; B29C 65/1445 20130101; B29C 66/729 20130101; B29C
66/91218 20130101; B29L 2031/779 20130101; B32B 2310/0806 20130101;
B32B 1/02 20130101; H05B 2203/017 20130101; B29C 65/346 20130101;
B29C 65/3488 20130101; B29C 66/4326 20130101; B29C 66/71 20130101;
B29C 65/1458 20130101; B29C 66/71 20130101; B29C 66/81871 20130101;
B29C 66/83413 20130101; B65D 81/3476 20130101; B29K 2069/00
20130101; B29K 2023/10 20130101; B29K 2071/00 20130101; B29K
2023/0683 20130101; B29C 65/3448 20130101; H05B 2203/037 20130101;
B29C 65/1464 20130101; B29C 65/1406 20130101; B29C 66/45 20130101;
B29C 51/02 20130101; B29C 66/91645 20130101; B29C 65/3444 20130101;
H05B 2203/003 20130101; B29C 66/82661 20130101; B29C 66/431
20130101; B29C 65/342 20130101; B29C 66/432 20130101; B29C 66/433
20130101; B29K 2023/12 20130101; B29C 65/3492 20130101; B29C 66/71
20130101; B29C 66/91421 20130101; B29C 66/91655 20130101; Y10T
29/49083 20150115; B29C 66/71 20130101; B29C 66/73921 20130101;
B32B 3/06 20130101; B29C 66/81831 20130101; B32B 37/206 20130101;
B65D 2581/3428 20130101; B29C 66/4312 20130101; H05B 3/36 20130101;
B29C 66/71 20130101; B32B 3/08 20130101; H05B 2203/002 20130101;
B29C 65/348 20130101; B29C 66/71 20130101; B29C 2793/0081 20130101;
B32B 2305/34 20130101; A47J 36/2483 20130101; B29C 65/3412
20130101; B32B 37/06 20130101; H05B 2203/013 20130101; B29C 51/00
20130101; B29C 66/91214 20130101; H05B 2203/014 20130101; B29C
51/12 20130101; B32B 27/00 20130101; Y10T 29/49082 20150115; Y10T
29/49085 20150115; B29C 66/91221 20130101; B32B 2310/022 20130101;
B29C 65/3428 20130101; B29C 66/71 20130101; B29C 70/885 20130101;
B29C 65/02 20130101; B29C 65/3468 20130101; B29C 66/133 20130101;
B29C 66/71 20130101; B29C 66/71 20130101; B29C 66/91411 20130101;
B29C 70/82 20130101; B29C 53/04 20130101; B29C 66/71 20130101; H05B
2203/004 20130101 |
Class at
Publication: |
29/611 ;
29/610.1; 219/544; 219/548 |
International
Class: |
H05B 003/44 |
Claims
What is claimed is:
1. A heated element assembly, comprising: (a) a first thermoplastic
sheet; (b) a second thermoplastic; and (c) a resistance heating
element secured between and to said first and second thermoplastic
sheets, said resistance heating element comprising: (i) a
supporting substrate having a first surface thereon; (ii) an
electrical resistance heating material fastened to said supporting
substrate, said electrical resistance heating material forming a
predetermined circuit path having a pair of terminal end portions;
and (iii) a first flap portion capable of rotation about a first
axis of rotation, said circuit path continuing onto at least a
portion of said flap portion wherein said thermoplastic sheets and
resistance heating element are laminated together to form a
reformable continuous element structure, said reformable continuous
element structure formed into a final element assembly
configuration whereby at least said first flap portion is rotated
about said first axis to provide resistance heating in at least two
planes.
2. The heated element assembly of claim 1, wherein said
thermoplastic sheets are affixed with an adhesive.
3. The heated element assembly of claim 1, wherein said reformable
continuous element structure is thermoformed into said final
element assembly configuration.
4. The heated element assembly of claim 1, wherein said reformable
continuous element structure is cut into a foldable profile, said
foldable profile including at least one joining tab, said joining
tab mated to an adjacent surface of said reformable continuous
element structure when said reformable continuous element structure
is formed into said final element assembly configuration.
5. The heated element assembly of claim 1, wherein said electrical
resistance heating material is glued, sewn, fused, or a combination
thereof to said supporting substrate.
6. The heated element assembly of claim 5, wherein said electrical
resistance heating material is sewn to said supporting substrate
with a thread.
7. The heated element assembly of claim 1, wherein said supporting
substrate comprises a woven or non-woven fibrous layer.
8. The heated element assembly of claim 1, wherein said supporting
substrate is a thermoplastic sheet.
9. The heated element assembly of claim 1, wherein said supporting
substrate includes thermally conductive additives.
10. The heated element assembly of claim 1, wherein at least one of
said thermoplastic sheets includes a thermally conductive
coating.
11. The heated element assembly of claim 1, further comprising a
secondary device secured between said first and second
thermoplastic sheets.
12. The heated element assembly of claim 1, wherein one of said
thermoplastic sheets is thicker than the other thermoplastic
sheet.
13. The heated element assembly of claim 1, wherein said heated
element assembly is over molded with a thermoplastic such that said
over molded thermoplastic and thermoplastic sheets form a
substantially homogenous structure.
14. The heated element assembly of claim 1, wherein said supporting
substrate is shaped as a foldable profile of a container, said
foldable profile including said first flap portion.
15. A sheet of heated element assemblies, comprising: (a) a first
thermoplastic sheet; (b) a second thermoplastic sheet; and (c) a
sheet of resistance heating elements secured between and to said
first and second thermoplastic sheets, said sheet of resistance
heating elements comprising: (i) a supporting substrate having a
first surface thereon; and (ii) a plurality of spaced circuit
paths, each of said spaced circuit paths comprising an electrical
resistance heating material fastened to said supporting substrate
to form a predetermined circuit path, said circuit path having a
pair of terminal end portions, each of said circuit paths
continuing onto a first flap portion of a resistance heating
element capable of rotation about a first axis of rotation; and
wherein said first and second thermoplastic sheets and resistance
heating elements are laminated such that said sheet of resistance
heating elements is secured between and to said first and second
thermoplastic sheets to form a continuous element structure.
16. The sheet of heated element assemblies of claim 15, further
comprising an adhesive affixing said first and second thermoplastic
sheets.
17. The sheet of heated element assemblies of claim 15, wherein
said electrical resistance heating material is glued, sewn, fused,
or a combination thereof to said supporting substrate.
18. The sheet of heated element assemblies of claim 17, wherein
said electrical resistance heating material is sewn to said
supporting substrate with a thread.
19. The sheet of heated element assemblies of claim 15, wherein
said supporting substrate comprises a woven or non-woven fibrous
layer.
20. The sheet of heated element assemblies of claim 15, wherein
said supporting substrate is an extruded thermoplastic sheet.
21. The sheet of heated element assemblies of claim 15, further
comprising a plurality of secondary devices, each of said secondary
devices disposed between said first and second thermoplastic sheets
and associated with one of said circuit paths.
22. The sheet of heated element assemblies of claim 15, wherein at
least one of said thermoplastic sheets includes a thermally
conductive coating.
23. A combination containment bag and heater with sidewalls,
comprising: at least two heated element assemblies fused to each
other along mating edges to form a containment bag with flexible
sidewalls, each of said heated element assemblies comprising: (a) a
first thermoplastic sheet; (b) a second thermoplastic sheet; and
(c) a resistance heating element secured between and to said first
and second thermoplastic sheets, said resistance heating element
comprising: (i) a supporting substrate having a first surface
thereon; (ii) an electrical resistance heating material joined to
said supporting substrate, said electrical resistance heating
material forming a predetermined circuit path having a pair of
terminal end portions; and (iii) a pair of electrical connectors
fixed to said terminal end portions of said electrical resistance
heating material, said thermoplastic sheets and resistance heating
element laminated together to form a continuous structure.
24. The heated container of claim 23, further comprising a nozzle
secured to said container, said nozzle providing access to an area
defined within said container.
25. A heated container, comprising: a heated element assembly,
comprising: (a) a first thermoplastic sheet; (b) a second
thermoplastic sheet; and (c) a resistance heating element secured
between and to said first and second thermoplastic sheets, said
resistance heating element comprising: (i) a supporting substrate
having a first surface thereon; (ii) an electrical resistance
heating material sewn to said supporting substrate with a thread,
said electrical resistance heating material forming a predetermined
circuit path having a pair of terminal end portions; (iii) a pair
of electrical connectors fixed to said terminal end portions of
said electrical resistance heating material; and (iv) a plurality
of flap portions capable of rotation about a first axis of
rotation, said circuit path continuing onto at least a portion of
at least one of said flap portions, wherein said thermoplastic
sheets and resistance heating element are laminated together to
form a reformable continuous element structure, said continuous
element structure formed into a final element assembly whereby said
flap portions are rotated about said first axes to provide
resistance heating in a plurality of planes.
26. The heated container of claim 25, wherein said supporting
substrate is shaped as a foldable profile of a container, said
foldable profile including said plurality of flap portions.
27. The heated container of claim 26, wherein said reformable
continuous element structure substantially conforms to said
foldable profile shape.
28. The heated container of claim 27, wherein said continuous
element structure includes at least one joining tab, said at least
one joining tab mated to an adjacent surface of said continuous
element structure in said final element assembly.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This Application is a divisional application of U.S. patent
application Ser. No. 09/642,215, of Theodore Von Arx, Keith Laken
and John Schlesselman, filed Aug. 18, 2000, and is related to U.S.
application Ser. No. 09/369,779 of Theodore Von Arx, filed Aug. 6,
1999, now U.S. Pat. No. 6,392,208, issued on May 21, 2002, entitled
"Electrofusing of thermoplastic heating elements and elements made
thereby"; U.S. application Ser. No. 09/416,731, of John
Schlesselman and Ronald Papenfuss, filed Oct. 13, 1999, now U.S.
Pat. No. 6,415,501, issued on Jul. 9, 2002, entitled "Heating
element containing sewn resistance material"; U.S. application Ser.
No. 09/275,161 of Theodore Von Arx, James Rutherford and Charles
Eckman, filed Mar. 24, 1999, now U.S. Pat. No. 6,233,398, issued on
May 15, 2001, entitled "Heating element suitable for
preconditioning print media" which is a continuation in part of
U.S. application Ser. No. 08/767,156 filed on Dec. 16, 1996, now
U.S. Pat. No. 5,930,459, issued on Jul. 27, 1999, which in turn is
a continuation in part of U.S. application Ser. No. 365,920, filed
Dec. 29, 1994, now U.S. Pat. No. 5,586,214, issued on Dec. 17,
1996; U.S. application Ser. No. 09/544,873 of Theodore Von Arx,
Keith Laken, John Schlesselman, and Ronald Papenfuss, filed Apr. 7,
2000, entitled "Molded assembly with heating element captured
therein"; U.S. application Ser. No. 09/611,105 of Clifford D.
Tweedy, Sarah J. Holthaus, Steven O. Gullerud, and Theodore Von
Arx, filed Jul. 6, 2000, entitled "Polymeric heating elements
containing laminated, reinforced structures and processes for
manufacturing same"; and U.S. application Ser. No. 09/309,429 of
James M. Rutherford, filed May 11, 1999, now U.S. Pat. No.
6,263,158, issued on Jul. 17, 2001, entitled "Fibrous supported
polymer encapsulated electrical component" which are all hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] This invention relates to electrical resistance heating
elements, and more particularly to formable thermoplastic laminate
heated element assemblies.
BACKGROUND OF THE INVENTION
[0003] Electric resistance heating elements composed of polymeric
materials are quickly developing as a substitute for conventional
metal sheathed heating elements, such as those containing a Ni--Cr
coil disposed axially through a U-shaped tubular metal sheath. Good
examples of polymeric heating elements include those disclosed in
Eckman, et al., U.S. Pat. No. 5,586,214 issued Dec. 17, 1996 and
Lock, et al., U.S. Pat. No. 5,521,357 issued May 28, 1996.
[0004] Eckman et al. '214 discloses a polymer encapsulated
resistance heating element including a resistance heating member
encapsulated within an integral layer of an
electrically-insulating, thermally-conductive polymeric material.
The disclosed heating elements are capable of generating at least
about 1,000 watts for heating fluids such as water and gas.
[0005] Lock, et al. '357 discloses a heater apparatus including a
resistive film formed on a substrate. The first and second
electrodes are coupled to conductive leads which are electrically
connected to the resistive film. The heater also includes an over
molded body made of an insulating material, such as a plastic.
Lock, et al. '357 further discloses that its resistive film may be
applied to a substrate, such as a printed circuit board
material.
[0006] Laminated heaters are also disclosed in Logan, et al., U.S.
Pat. No. 2,710,909, issued Jun. 14, 1955 and Stinger, U.S. Pat. No.
3,878,362, issued Apr. 15, 1975. These laminated structures include
partially cured rubber-like substances, backed with layers of glass
cloth, such as disclosed in Logan, et al. '909, or the use of a
discontinuous layer of electrically conductive elastomeric material
containing conductive carbon adhered to a pair of spaced-apart
conductor wires bonded to a durable plastic material, such as
Stinger's polyethylene terephthalate film.
[0007] Other laminated heaters are disclosed in U.S. Pat. No.
2,889,439 to Musgrave, issued Jul. 29, 1955, and U.S. Pat. No.
3,268,846 to Morey, issued Aug. 23, 1966. Musgrave discloses a
laminated heating panel including a resistance wire laminated
between two sheets of asbestos paper impregnated with a phenolic
resin or plastic. Morey discloses a flexible tape heating element
and method of manufacturing the same. A resistance ribbon is
sandwiched between a film of teflon, silicon rubber, or plastic
material. There still remains a need, however, for a reformable but
robust electrical resistance heated element which is easily
adaptable to a variety of end uses and manufacturing processes.
There also remains a need for a resistance heating element which is
capable of capturing intricate circuit paths and which is
reformable to provide efficient heating in complex heat planes.
SUMMARY OF THE INVENTION
[0008] The present invention comprises a heated element assembly
and method of manufacturing heated element assemblies. A heated
element assembly includes a first thermoplastic sheet, a second
thermoplastic sheet, and a resistance heating element disposed
between the first and second thermoplastic sheets. The resistance
heating element comprises a supporting substrate having a first
surface thereon and an electrical resistance heating material
fastened to the supporting substrate, where the electrical
resistance heating material forms a predetermined circuit path
having a pair of terminal end portions. The resistance heating
element also includes a first flap portion capable of rotation
about a first axis of rotation where the circuit path continues
onto at least a portion of the flap portion. The thermoplastic
sheets and resistance heating element are laminated together to
form a reformable continuous element structure. The continuous
element structure is formed into a final element assembly
configuration whereby at least the first flap portion is rotated
about the first axis to provide resistance heating in at least two
planes.
[0009] The present invention as described above provides several
benefits. An intricate resistance circuit path of a resistance
heating element may be secured to a planar supporting substrate and
then laminated between thermoplastic sheets, whereby the planar
resistance heating element may then be reformed with the laminated
structure to provide heat on a plurality of heat planes. The heated
element assembly may also be secured to a second heated element
assembly to form, for example, a heated containment bag or a heated
container. These heated structures provide intimate contact between
the contents of the heated structures and the heat source, thereby
providing inherent energy consumption advantages as well as the
ability to intimately locate secondary devices such as thermistors,
sensors, thermocouples, etc . . . , in proximity to the contents
being heated or conditions being observed or recorded.
[0010] The heated element assembly also allows for an infinite
number of circuit path shapes, allowing the circuit path to
correspond to the general shape of a desired end product utilizing
the heated element assembly. The heated element assembly may be
folded to occupy a predefined space in an end product and to
provide heat in more than one plane, thermoformed into a desired
three dimensional heated plane, or stamped or die cut into a
predetermined flat shape which may, then, be folded or thermoformed
into a desired three dimensional heated shape. The heated element
assembly thereby emulates well known sheet metal processing or
known plastic forming processes and techniques.
[0011] The heated element assembly according to the present
invention may also be over molded in a molding process whereby the
resistance heating element is energized to soften the thermoplastic
sheets and the heated element assembly is over molded with a
thermoplastic to form a detailed molded structure. The energizing
and overmolding steps may be timed such that the thermoplastic
sheets and over molded thermoplastic form a substantially
homogenous structure accurately capturing and positioning the
resistance heating element within the structure. Alternatively, the
heated element assembly may soften during mold flow without
additional energizing.
[0012] In another embodiment of the present invention, a sheet of
heated element assemblies comprises a first thermoplastic sheet, a
second thermoplastic sheet affixed to the first thermoplastic
sheet, and a sheet of resistance heating elements secured between
and to the first and second thermoplastic sheets. The sheet of
resistance heating elements includes a supporting substrate having
a first surface thereon and a plurality of spaced circuit paths,
each of the spaced circuit paths comprising an electrical
resistance heating material fastened to the supporting substrate to
form a predetermined circuit path having a pair of terminal end
portions.
[0013] Each of the circuit paths continue onto a first flap portion
of a resistance heating element capable of rotation about a first
axis of rotation. The thermoplastic sheets are laminated together
such that the sheet of resistance heating elements is secured
between and to the first and second thermoplastic sheets to form a
reformable continuous element structure.
[0014] The sheet of heated element assemblies provides several
benefits. The sheet may be inexpensively and efficiently produced
using mass production techniques. The sheet may be collected into a
roll, allowing the later separation and use of individual heated
element assemblies or group of heated element assemblies as
described above. The sheet, rather than being collected into a
roll, may be further processed using various secondary fabrication
techniques, such as stamping, die cutting, or overmolding.
[0015] The above and other features of the present invention will
be better understood from the following detailed description of the
preferred embodiments of the invention which is provided in
connection with the accompanying drawings.
A BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The accompanying drawings illustrate preferred embodiments
of the invention, as well as other information pertinent to the
disclosure, in which:
[0017] FIG. 1 is a front plan view of a resistance heating element,
including a resistance wire disposed in a circuit path on a
supporting substrate and joined to a pair of electrical
connectors;
[0018] FIG. 1A is a front plan, enlarged view, of a portion of the
resistance heating element of FIG. 1, showing the preferred
cross-stitch attachment to the supporting substrate;
[0019] FIG. 2 is a rear plan view of the resistance heating element
of FIG. 1;
[0020] FIG. 3 is a front perspective view of a preferred
programmable sewing machine and computer for manufacturing
resistance heating elements;
[0021] FIG. 4 is a top plan view of a heated element assembly
including a resistance heating element according to the present
invention;
[0022] FIG. 5 is a cross-sectional view of the heated element
assembly of FIG. 4 taken along lines 1-1;
[0023] FIG. 6 is a cross-sectional view of a multilayered heated
element assembly according to the present invention;
[0024] FIG. 7a is a top plan view of a tubular shaped thermoplastic
body for providing thermoplastic sheets according to the present
invention;
[0025] FIG. 7b is a side elevational view of a tubular shaped
thermoplastic body for providing thermoplastic sheets according to
the present invention;
[0026] FIG. 8 is a front plan view of an exemplary heated
containment bag according to the present invention;
[0027] FIG. 9 is a cross-sectional view of the containment bag of
FIG. 8;
[0028] FIG. 10 is a top plan view of an exemplary heated
containment bag according to the present invention;
[0029] FIG. 11 is a top plan view of two affixed but partially
separated heated element assemblies according to the present
invention shaped to provide a heated containment bag with a
nozzle;
[0030] FIG. 12 is a diagram of an exemplary method of manufacturing
a sheet of heated element assemblies according to the present
invention;
[0031] FIG. 13 is a diagram of a sheet of resistance heating
elements shown in partial according to the present invention;
[0032] FIG. 14 is a top plan view of a resistance heating element
which may be folded to form a three dimensional heater
assembly;
[0033] FIG. 15 is a top plan view of a heating element including
the resistance heating element of FIG. 14 where the laminated
structure has been cut to form a profile for a heated container;
and
[0034] FIG. 16 is a perspective view of a heated container formed
from the cut heating element of FIG. 15.
DETAILED DESCRIPTION OF THE INVENTION
[0035] The present invention provides thermoplastic laminate heated
element assemblies including resistance heating elements. As used
herein, the following terms are defined:
[0036] "Laminate" means to unite laminae via bonding them together,
usually with heat, pressure and/or adhesive. It normally is used to
refer to flat sheets, but also can include rods and tubes. The term
refers to a product made by such bonding;
[0037] "Serpentine Path" means a path which has one or more curves
for increasing the amount of electrical resistance material in a
given volume of polymeric matrix, for example, for controlling the
thermal expansion of the element;
[0038] "Melting Temperature" means the point at which a fusible
substance begins to melt;
[0039] "Melting Temperature Range" means the temperature range over
which a fusible substance starts to melt and then becomes a liquid
or semi-liquid;
[0040] "Degradation Temperature" means the temperature at which a
thermoplastic begins to permanently lose its mechanical or physical
properties because of thermal damage to the polymer's molecular
chains;
[0041] "Evacuating" means reducing air or trapped air bubbles by,
for example, vacuum or pressurized inert gas, such as argon, or by
bubbling the gas through a liquid polymer.
[0042] "Fusion Bond" means the bond between two fusible members
integrally joined, whereby the polymer molecules of one member mix
with the molecules of the other. A Fusion Bond can occur, even in
the absence of any direct or chemical bond between individual
polymer chains contained within said members;
[0043] "Fused" means the physical flowing of a material, such as
ceramic, glass, metal or polymer, hot or cold, caused by heat,
pressure or both;
[0044] "Electrofused" means to cause a portion of a fusible
material to flow and fuse by resistance heating;
[0045] "Stress Relief" means reducing internal stresses in a
fusible material by raising the temperature of the material or
material portion above its stress relief temperature, but
preferably below its Heat Deflection Temperature; and
[0046] "Flap" or "Flap Portion" means a portion of an element which
can be folded without damaging the element structure.
Resistance Heating Element
[0047] With reference to the Figures, and particularly FIGS. 1, 1A
and 2 thereof, there is shown a first embodiment of a resistance
heating element 10 having a diameter of about 11 cm. The preferred
resistance heating element 10 may include a regulating device for
controlling electric current. Such a device can include, for
example, a thermistor, or a thermocouple, for preventing
overheating of the polymeric materials disclosed in this invention.
The resistance heating elements 10 of this invention can take on
any number of shapes and sizes, including squares, ovals, irregular
circumference shapes, tubes, cup shapes and container shapes. Sizes
can range from less than one inch square to 21 in..times.26 in.
with a single sewing operation, and greater sizes can be available
if multiple elements are joined together. Greater sizes are also
available with continuous sewing where a substrate is fed from a
roll of substrate.
[0048] As shown in FIG. 1, the resistance heating element 10
includes a resistance wire 12 disposed in a helical pattern or
circuit path 18. The ends of the resistance wire 12 are generally
riveted, grommeted, brazed, clinched, compression fitted or welded
to a pair of electrical connectors 15 and 16. One circuit path is
illustrated in FIGS. 1 and 2. The circuit includes a resistance
heating material, which is ideally a resistance heating wire 12
wound into a serpentine path containing about 3-200 windings, or, a
resistance heating material, such as ribbon, a foil or printed
circuit, or powdered conducting or semi-conducting metals,
polymers, graphite, or carbon, or a conductive coating or ink. More
preferably the resistance heating wire 12 includes a Ni--Cr alloy,
although certain copper, steel, and stainless-steel alloys could be
suitable. A positive temperature coefficient wire may also be
suitable. The resistance heating wire 12 can be provided in
separate parallel paths, or in separate layers. Whatever material
is selected, it should be electrically conductive, and heat
resistant.
Substrates
[0049] As used herein, the term "supporting substrate" refers to
the base material on which the resistance material, such as wires,
are applied. The supporting substrate 11 of this invention should
be capable of being pierced, penetrated, or surrounded, by a sewing
needle for permitting the sewing operation. Other than this
mechanical limitation, the substrates of this invention can take on
many shapes and sizes. Flat flexible substrates are preferably used
for attaching an electrical resistance wire with a thread.
Non-plastic materials, such as glasses, semiconductive materials,
and metals, can be employed so long as they have a piercable
cross-sectional thickness, e.g., less than 10-20 mil, or a high
degree of porosity or openings therethrough, such as a grid, scrim,
woven or nonwoven fabric, for permitting the sewing needle of this
invention to form an adequate stitch. The supporting substrate 11
of this invention need not necessarily contribute to the mechanical
properties of the final heating element, but may contain high
strength fibers. Such fibers could contain carbon, glass, aramid
fibers melt-bonded or joined with an adhesive to form a woven or
non-woven mat. Alternatively, the supporting substrate 11 of this
invention may contain ordinary, natural, or synthetic fibers, such
as cotton, wool, silk, rayon, nylon, polyester, polypropylene,
polyethylene, etc. The supporting substrate may also comprise a
synthetic fiber such as Kevlar or carbon fibers that have good
thermal uniformity and strength. The advantage of using ordinary
textile fibers, is that they are available in many thicknesses and
textures and can provide an infinite variety of chemistry, porosity
and melt-bonding ability. The fibers of this invention, whether
they be plastic, natural, ceramic or metal, can be woven, or
spun-bonded to produce non-woven textile fabrics.
[0050] Specific examples of supporting substrates 11 useful in this
invention include non-woven fiberglass mats bonded with an adhesive
or sizing material such as model 8440 glass mat available from
Johns Manville, Inc. Additional substrates can include polymer
impregnated fabric organic fabric weaves, such as those containing
nylon, rayon, or hemp etc., porous mica-filled plate or sheet, and
thermoplastic sheet film material. In one embodiment, the
supporting substrate 11 contains a polymeric resin which is also
used in either the first thermoplastic sheet 110 or second
thermoplastic sheet 105, or both of a heated element assembly 100
described below. Such a resin can be provided in woven or non-woven
fibrous form, or in thin sheet material having a thickness of 20
mil. or less. Thermoplastic materials can be used for the
supporting substrate 11 which will melt-bond or liquefy with the
thermoplastic sheets 110, 105, so as to blend into a substantially
uniform structure.
Sewing Operation
[0051] With reference to FIG. 3, the preferred programmable sewing
machine 20 will now be described. The preferred programmable sewing
machine is one of a number of powerful embroidery design systems
that use advanced technology to guide an element designer through
design creation, set-up and manufacturing. The preferred
programmable sewing machine 20 is linked with a computer 22, such
as a personal computer or server, adapted to activate the sewing
operations. The computer 22 preferably contains or has access to,
embroidery or CAD software for creating thread paths, borders,
stitch effects, etc.
[0052] The programmable sewing machine 20 includes a series of
bobbins for loading thread and resistance heating wire or fine
resistance heating ribbon. Desirably, the bobbins are prewound to
control tension since tension, without excessive slack, in both the
top and bottom bobbins is very important to the successful
capturing of resistance heating wire on a substrate. The thread
used should be of a size recommended for the preferred programmable
sewing machine. It must have consistent thickness since thread
breakage is a common mode of failure in using programmable sewing
machines. An industrial quality nylon, polyester or rayon thread is
highly desirable. Also, a high heat resistant thread may be used,
such as a Kevlar thread or Nomex thread known to be stable up to
500.degree. F. and available from Saunders Thread Co. of Gastonia,
N.C.
[0053] The programmable sewing machine of this invention preferably
has up to 6-20 heads and can measure 6 foot in width by 19 feet
long. The sewing range of each head is about 10.6 inches by 26
inches, and with every other head shut off, the sewing range is
about 21 inches by 26 inches. A desirable programmable sewing
machine is the Tajima Model No. TMLG116-627 W (LT Version) from
Tajima, Inc., Japan.
[0054] The preferred method of capturing a resistance heating wire
12 onto a supporting substrate 11 in this invention will now be
described. First, an operator selects a proper resistive element
material, for example, Ni--Cr wire, in its proper form. Next, a
proper supporting substrate 11, such as 8440 glass mat, is provided
in a form suitable for sewing. The design for the element is
preprogrammed into the computer 22 prior to initiating operation of
the programmable sewing machine 20. As with any ordinary sewing
machine, the programmable sewing machine 20 of this invention
contains at least two threads, one thread is directed through the
top surface of the supporting substrate, and the other is directed
from below. The two threads are intertwined or knotted, ideally
somewhere in the thickness of the supporting substrate 11, so that
one cannot view the knot when looking at the stitch and the
resulting resistance heating element 10. As the top needle
penetrates the substrate 11 and picks up a loop of thread
mechanically with the aid of the mechanical device underneath, it
then pulls it upward toward the center of the substrate 11 and if
the substrate is consistent and the thread tension is consistent,
the knots will be relatively hidden. In a preferred embodiment of
this invention, the resistance heating wire 12 is provided from a
bobbin in tension. The preferred programmable sewing machine 20 of
this invention provides a third thread bobbin for the electrical
resistance wire 12 so that the programmable sewing machine 20 can
lay the resistance wire 12 down just in front of the top needle.
The preferred operation of this invention provides a zig zag or
cross stitch, as shown in FIG. 1A, whereby the top needle
criss-crosses back and forth as the supporting substrate 11 is
moved, similar to the way an ornamental rope is joined to a fabric
in an embroidery operation. A simple looping stitch with a thread
14 is also shown. Sewing by guiding the top needle over either side
of the resistance heating wire 12 captures it in a very effective
manner and the process is all computer controlled so that the
pattern can be electronically downloaded into the computer 22 and
automatically sewn onto the substrate of choice.
[0055] The programmable sewing machine 20 can sew an electrical
resistance wire 12, 5 mil-0.25 inch in diameter or thickness, onto
a supporting substrate 11 at a rate of about 10-500 stitches per
minute, saving valuable time and associated cost in making
resistance heating elements.
[0056] The ability to mechanically attach resistive elements, such
as wires, films and ribbons, to substrates opens up a multitude of
design possibilities in both shape and material selection.
Designers may mix and match substrate materials by selecting their
porosity, thickness, density and contoured shape with selected
resistance heating materials ranging in cross-section from very
small diameters of about 5 mil to rectangular and irregular shapes,
to thin films. Also, secondary devices such as circuits, including
microprocessors, fiberoptic fibers or optoelectronic devices,
(LEDs, lasers) microwave devices (power amplifiers, radar) and
antenna, high temperature sensors, power supply devices (power
transmission, motor controls) and memory chips, could be added for
controlling temperature, visual inspection of environments,
communications, and recording temperature cycles, for example. The
overall thickness of the resistance heating element is merely
limited by the vertical maximum position of the needle end, less
the wire feed, which is presently about 0.5 inches, but may be
designed in the future to be as great as 1 inch or more. Resistive
element width is not nearly so limited, since the transverse motion
of the needle can range up to a foot or more.
[0057] The use of known embroidery machinery in the fabrication of
resistance heating elements allows for a wide variety of raw
materials and substrates to be combined with various resistance
heating materials. The above construction techniques and sewing
operation also provide the ability to manufacture multi-layered
substrates, including embedded metallic and thermally conductive
layers with resistance wires wrapped in an electrically insulating
coating, so as to avoid shorting of electric current. This permits
the application of a resistance heating wire to both sides of the
thermally conductive metallic layer, such as aluminum foil, for
more homogeneously distributing resistance heat.
Thermoplastic Laminate Heated Element Assembly and Heated Container
Construction
[0058] FIG. 4 is a top plan view of a heated element assembly 100
according to the present invention. The heated element assembly 100
includes a first thermoplastic sheet 110 and a second thermoplastic
sheet 105 laminated to the first thermoplastic sheet 110. For
illustrative purposes, second thermoplastic sheets 105 is shown
partially removed from first thermoplastic sheet 110. A resistance
heating element 10, described above, is laminated between and to
the first and second thermoplastic sheets 110, 105 such that the
thermoplastic sheets 110, 105 substantially encompass the circuit
path 18, which includes resistance wire 12.
[0059] The supporting substrate of the resistance heating element
10 is preferably not thicker than 0.05 inch, and more preferably
0.025 inch. The supporting substrate should be flexible, either
under ambient conditions or under heat or mechanical stress, or
both. A thin semi-rigid heated element assembly 100 allows for
closer proximity of the resistance heating wire 12 to an object to
be heated when the heated element assembly is formed into a final
element assembly, such as a combination containment bag and heater.
Thin element assemblies according to the present invention provide
the flexibility to choose materials with lower RTI (Relative
Thermal Index) ratings because less heat needs to be generated by
the resistance heating element 10 to provide heat to the outer
surfaces of the heating element assembly 100.
[0060] The thermoplastic sheets 110, 105 are laminated to each
other to secure resistance heating element 10 and to form a
reformable continuous element structure. The thermoplastic sheets
110, 105 may be heated and compressed under sufficient pressure to
effectively fuse the thermoplastic sheets together. A portion of
this heat may come from energizing the resistance heating element
10. Alternatively, a resistance heating element 10 may be placed
within a bag-shaped thermoplastic body (not shown) where the top
layer of the bag may be considered a thermoplastic sheet and the
bottom layer of the bag may be considered a thermoplastic sheet
(e.g., two thermoplastic sheets secured along mating edges, but
providing an opening for insertion of the resistance heating
element 10). Air from within the bag may be evacuated, e.g., by
pulling a vacuum, thereby collapsing the bag around the resistance
heating element 10, and then heat and/or pressure may be applied to
the collapsed structure to create a single heated element assembly
100. Also, heated element assembly 100 may be formed by extruding a
tubular shaped thermoplastic body 107 (FIGS. 7a and 7b), disposing
a resistance heating element 10 within the thermoplastic body 107,
and heating and compressing the body 107, particularly along edges
108, to secure the heating element 10 within the thermoplastic
body. Regardless of the initial form the thermoplastic sheets take,
thermoplastic sheets are preferably laminated such that a flexible
continuous element structure is created, including a resistance
heating element 10 and preferably with little air trapped between
the thermoplastic sheets.
[0061] Preferred thermoplastic materials include, for example:
fluorocarbons, polypropylene, polycarbonate, polyetherimide,
polyether sulphone, polyaryl-sulphones, polyimides, and
polyetheretherkeytones, polyphenylene sulfides, polyether
sulphones, and mixtures and co-polymers of these
thermoplastics.
[0062] It is further understood that, although thermoplastic
plastics are most desirable for fusible layers because they are
generally heat-flowable, some thermoplastics, notably
polytetraflouroethylene (PTFE) and ultra high-molecular-weight
polyethylene (UHMWPE) do not flow under heat alone. Also, many
thermoplastics are capable of flowing without heat, under
mechanical pressure only.
[0063] Good results were found when forming a heated element
assembly under the conditions indicated in TABLE 1 as follows:
1TABLE THICKNESS OF SHEET PRESSURE TIME TEMP. MATERIAL (mil) (PSI)
(minutes) (.degree. F.) Polypropolyne 9 22 10 350 Polycarbonate 9
22 10 380 Polysulfune 19 22 15 420 Polyetherimide 9 44 10 430
Polyethersulfone 9 44 10 460
[0064] where no vacuum was pulled, "thickness" is the thickness of
the thermoplastic sheets in mils (1 mil=0.025 mm=0.001 inch),
"pressure" represents the amount of pressure applied to the
assembly during lamination, "temperature" is the temperature
applied during lamination, and "time" is the length of time that
the pressure and heat were applied.
[0065] The first and second thermoplastic sheets 110, 105 and
resistance heating element 10 of the heated element assembly 100
may also be laminated to each other using an adhesive. In one
embodiment of the present invention, an ultraviolet curable
adhesive may be disposed between the resistance heating element 10
and the first thermoplastic sheet 110 and between the resistance
heating element 10 and the second thermoplastic sheet 105, as well
as between areas of the thermoplastic sheets 110, 105 which are
aligned to be in direct contact. An ultraviolet curable adhesive
may be used that is activated by ultraviolet light and then begins
to gradually cure. In this embodiment of the present invention, the
adhesive may be activated by exposing it to ultraviolet light
before providing the second of the thermoplastic sheets 110, 105.
The thermoplastic sheets 110, 105 may then be compressed to
substantially remove any air from between the sheets 110, 105 and
to secure resistance heating element 10 between the thermoplastic
sheets 110, 105.
[0066] FIG. 6 illustrates that a heated element assembly 100a
according to the present invention may include a plurality of
heated layers. A second resistance heating element 10a may be
laminated between and to thermoplastic sheet 110 and a third
thermoplastic sheet 115.
[0067] The thicknesses of thermoplastic sheets 110, 105 and the
thickness of supporting substrate 11 and resistance heating
material 12 are preferably selected to form a reformable continuous
element structure that maintains its integrity when the element is
formed into a final element structure. The heated element assembly
100 according to the present invention, then, is a semi-rigid
structure in that it may be reformed, such as by simply folding or
folding under heat, pressure, or a combination thereof as required
by the chosen thermoplastics, into a desired shape without
sacrificing the integrity of the structure.
[0068] FIG. 8 is a side elevational view of an exemplary
combination heated containment bag and heater 150 with flexible
walls according to the present invention. The containment bag 150
includes at least a first and second heated element assemblies 100.
FIG. 9 is a cross-sectional view of the containment bag 150, and
FIG. 10 is a top plan view of the containment bag 150. Two or more
heated element assemblies 100 may be aligned along mating edges
120, and the edges 120 may be fused or otherwise sealed to form a
heated containment bag 150 having an enclosed area, designated
generally as area 123, for holding contents. Alternatively, a
single heated element assembly 100 may be folded into a bag or
container shape and its mating edges may be fused to form a heated
containment bag. The assembly 100 may also be heated to facilitate
folding into the containment bag shape and enable the assembly to
maintain the containment bag shape after cooling. The containment
bag 150 preferably has flexible sidewalls formed from heated
element assemblies 100 which are capable of substantially
conforming to the contents contained in area 123, thereby
efficiently heating the contents of the containment bag 150.
[0069] The heated containment bag 150 preferably includes a
dispensing means 125, i.e., a nozzle or spout, that allows the
contents of the heated containment bag 150 to be inputted and
expelled. The nozzle 125 may be included as a separate structure
captured and sealed along an edge 120 or other area on a
containment bag 150. Alternatively, each heated element assembly
100a may be shaped to include a portion of the nozzle, as shown in
FIG. 11. A nozzle 125a may then be formed when the heated element
assemblies 100a are mated and fused along edges 120a. The
dispensing region 135 can either be fused along with edges 120a and
later punctured or otherwise be left open or be plugged. This
alternative of forming a nozzle from appropriately shaped heated
element assemblies 100a provides the added benefit of allowing the
circuit path 18 of the resistance heating element 10 of at least
one of the heated element assemblies 100a to continue into the
nozzle shaped area in order to provide heat to the nozzle area,
thereby preventing blockages from forming and providing a uniformly
heated container. This embodiment may be used, for example, for a
containment bag as used in a hot cheese dispenser where the
dispenser is not used for lengthy, and irregular, periods of
time.
[0070] Heated containers 150 according to the present invention
provide several advantages over non-rigid and rigid containers
which do and not include a heat source according to the present
invention. The heat source, i.e., the resistance heating element
10, intimately surrounds the contents of the container 150, which
may be, for example, blood plasma, food product, or other contents,
whether they be gaseous, liquid, solid, or semi-solid. The
product's packaging is capable of effectively doubling as its heat
source, thereby removing layers of material or air space between
the contents and its heat source as well as eliminating the need
for an external heat source. Also, secondary devices as described
above, such as temperature gauges, may be disposed more intimately
with the contents or conditions that are being monitored.
[0071] A heated element assembly 100 may also be positioned in a
mold and over molded to form a selected molded heated structure. A
heated element assembly 100 may optionally be thermoformed to
conform to at least a part of the mold structure and to
preferentially align the resistance heating element within the
mold. Once the heated element assembly is positioned within a mold,
the resistance heating element 10 of the heated element assembly
100 may be energized to soften the thermoplastic sheets, and the
heated element assembly may be over molded with a thermoplastic.
The energizing and overmolding may be timed such that the
thermoplastic sheets and over molded thermoplastic form a
substantially homogenous structure when solidified. Alternatively,
the thermoplastic sheets may be allowed to soften as a result of
mold flow alone. The thermoplastic materials of the sheets and over
molded thermoplastic are preferably matched to further facilitate
the creation of a homogenous structure. The supporting substrate 11
may also be selected to be a thermoplastic to better promote the
formation of a homogenous structure. The energizing may be timed to
soften the thermoplastic sheets before, after, or during the
overmolding process, depending upon the standard molding
parameters, such as the flow characteristic of the selected
thermoplastics, the injection molding fill time, the fill velocity,
and mold cycle. The assembly is also amenable to other molding
processes, such as injection molding, compression molding,
thermoforming, and injection-compression molding.
[0072] FIGS. 14, 15, and 16 illustrate an exemplary heated element
assembly which may be formed into a heated container final element
assembly. FIG. 14 is a top plan view of an exemplary resistance
heating element 400. The resistance heating element 400 includes a
supporting substrate 405 shaped in the profile of a flattened
container. The profile may either be initially shaped in this
profile shape or cut to the profile shape from a larger supporting
substrate. Resistance heating material is affixed to the supporting
substrate 405 and is preferably resistance wire 410 sown to
supporting substrate 405.
[0073] The resistance heating element 400 shown in FIG. 14 includes
a plurality of flap portions 420 capable of rotation about a first
axis of rotation indicated generally at joints 425. The circuit
path 415 formed by resistance wire 410 continues onto flap portions
420 and terminates at terminal end portions 412.
[0074] FIG. 15 is a top plan view of a heating element assembly
500. The resistance heating element 400 is laminated between two
thermoplastic sheets, only the top sheet 510 of which is shown, to
form a reformable continuous element structure. A portion of the
thermoplastic sheet 510 is shown removed in order to show the
resistance heating element 400.
[0075] The dashed lines 530 indicate portions of the laminated
structure that may be removed, such as by stamping or die cutting,
from the laminated structure to leave a foldable profile which may
be formed into the a non-planar container 600 shown in FIG. 16. The
remaining dashed lines of FIG. 15 indicate fold lines. The heating
element assembly 500 preferably includes joining tabs 540 which may
be used to help form the heated container 600 final element
assembly shown in FIG. 16 and described below.
[0076] Heated container 600 may be formed by folding the heating
element 500 along the dashed lines of FIG. 15 and in the direction
of the arrows shown in FIG. 16. The flaps 420 of the resistance
heating element 400 are laminated between thermoplastic layers and
are folded into the container shape shown in FIG. 16. The folding
step may include rethermalizing the thermoplastic structure while
folding in order to thermoform the structure into the desired heat
planes. The thermoplastic joining tabs 540 may then be folded to
mate with an adjacent surface of the continuous element structure.
The joining tabs 540 are preferably heated to fuse them to the
adjacent surfaces. The container 600 may even be made fluid tight
if each mating edge is fused or if the joining tabs 540 cover all
seams between adjacent surfaces.
[0077] It should be apparent that the container 600 provides heat
on five different interior planes may, but is formed from an easily
manufactured planar heating element 500. It should further be
apparent that the present invention is not limited in any way to
the container structure 600 or heating element 500 described above.
Rather, the above describe method of manufacturing and heating
element structure may be used to forms cups, enclosed containers,
boxes, or any other structure which may be formed from a planar
profile.
[0078] A sheet of heating elements and a method of manufacturing
the same is described hereafter. In another exemplary embodiment of
the present invention, a sheet of heated element assemblies 225 is
provided, as shown in FIG. 12. The sheet of heated element
assemblies 225 includes a first and second affixed thermoplastic
sheets, as described above, and a sheet of resistance heating
elements 200 (FIG. 13) secured between and to the first and second
thermoplastic sheets. Essentially, the sheet of resistance heating
elements 200 comprises a plurality of connected resistance heating
elements 10. The sheet of resistance heating elements 200 comprises
a supporting substrate 205 and a plurality of spaced circuit paths
207, each of the spaced circuit paths comprising an electrical
resistance heating material fastened to the supporting substrate
205 to form a predetermined circuit path having a pair of terminal
end portions 209, 210. The shape of the circuit path 207 is merely
illustrative of a circuit path shape, and any circuit path shape
may be chosen to support the particular end use for a heated
element assembly included in the sheet of heated element assemblies
225. The dashed lines of FIG. 13 indicate where an individual
resistance heating element may be removed from the sheets of
resistance heating elements 225.
[0079] A sheet 225 of heated element assemblies may be manufactured
using conventional mass production and continuous flow techniques,
such as are described in U.S. Pat. No. 5,184,969 to Sharpless et
al., the entirety of which is incorporated herein by reference. For
example, as illustrated in FIG. 12, first and second thermoplastic
sheets 211, 212 may be provided from a source, such as rolls 214,
216 of thermoplastic sheets, or extruded using known extrusion
techniques as a part of the manufacturing process. One manufacturer
of such thermoplastic sheet extruders is Killion Extruders inc. of
Cedar Grove, N.J. Likewise, a sheet of resistance heating elements
200 may be provided from a source, such as roll 218. Sheet 200 may
be manufactured as described above in the "Sewing Operation"
section. The sheets 200, 211, 212 may be made to converge, such as
by rollers 224, between a heat source, such as radiant heating
panels 220, to soften the thermoplastic sheets 211, 212. A series
of rollers 222 compresses the three sheets 200, 211, 212 into a
sheet of heated element assemblies 225, thereby also removing air
from between the sheets 200, 211, 212. The rollers 222 may also
provide heat to help fuse the sheets 200, 211, 212 and/or may be
used to cool freshly laminated sheets 200, 211, 212 to help
solidify the heated sheets into the sheet of heated element
assemblies 225 after compression.
[0080] It should be apparent that a sheet of a plurality of
multiple-layered heating element assemblies, such as a sheet
including a plurality of heating element assemblies 100a of FIG. 6,
may also be manufactured simply by including a third thermoplastic
sheet and a second sheet of resistance heating elements to the
process-described above.
[0081] A sheet of heated element assemblies may also be
manufactured using blown film processes and techniques. Blown film
extruders are available from the Windmoeller & Hoelscher
Corporation of Lincoln, R.I. A sheet of resistance heating elements
200 may be introduced within a blown cylindrical extrusion mass
before the mass is collected into a thin film. In this manner, a
sheet of resistance heating elements is effectively laminated
between a first and second thermoplastic sheets, i.e., between the
two halves of the cylindrical extrusion mass.
[0082] Regardless of the specific manufacturing technique, the
sheet of heated element assemblies 225 may be collected into a roll
230. The roll 230 may then be used by an original equipment
manufacture (OEM) for any desired manufacturing purpose. For
example, the OEM may separate or cut individual heated element
assemblies from the roll and include the heated element assembly in
a desired product, e.g, a container or molded product. An
individually manufactured heated element assembly as mentioned
above or a heated element assembly removed from a sheet of heated
element assemblies 225 is amenable to secondary manufacturing
techniques, such as die cutting, stamping, or thermoforming to a
desired shape or combination thereof as described above. Each
heated element assembly may be cut or stamped into a preselected
shape for use in a particular end product even while still a part
of sheet 225 and then collected into a roll 230. The circuit path
of the resistance heating element of the heated element assembly
may be appropriately shaped to conform to the desired shape of a
selected product and heat planes in which the heated element
assembly is to be included or formed.
[0083] The formable semi-rigid feature of the heated element
assemblies of the present invention provides a designer the
opportunity to include the assembly in complex heat planes. The
assembly may be cut to a desired formable shape, and the circuit
path is preferably designed to substantially conform to this shape
or the desired heat planes. The assembly may then be rethermalized
and folded to conform to the heat planes designed for the assembly
to occupy.
[0084] A preferred thermoplastic sheet may range from approximately
0.004 inch to 0.100 inch. Thus, the thickness of the thermoplastic
sheets of a heated element assembly may be chosen to effectively
bias heat generated by a resistance heating element in a selected
direction. For example, referring to the heated containment bag 150
discussed above, the outer thermoplastic sheets of the heated
element assemblies 100 may be chosen to be thicker than the
interior thermoplastic sheets (those sheets contacting any contents
of the containment bag 150) of the heated element assemblies 100.
In doing so, heat generated by the heating element assemblies 100
may be effectively biased toward the contents of the containment
bag 150 and away from the container's surroundings. The supporting
substrate itself may provide an insulation barrier when the circuit
path is oriented towards, for example, contents to be heated and
the supporting substrate is oriented toward an outer or gripping
surface.
[0085] Similarly, one or both of the thermoplastic sheets of a
heated element assembly 100 or heated element assembly 500 may be
coated with a thermally conductive coating that promotes a uniform
heat plane on the heated element assembly. An example of such a
coating may be found on anti-static bags or Electrostatic
Interference (ESI) resistive bags used to package and protect
semiconductor chips. Also, thermally conductive, but preferably not
electrically conductive, additive may be added to the thermoplastic
sheets to promote heat distribution. Examples of such additive may
be ceramic powders, such as, for example, Al.sub.2O.sub.3, MgO,
ZrO.sub.2, boron nitride, silicon nitride, Y.sub.2O.sub.3, SiC,
SiO.sub.2, TiO.sub.2, etc . . . A thermally conductive layer and/or
additive is useful because a resistance wire typically does not
cover all of the surface area of a resistance heating element
10.
[0086] As described above, the heated element assembly of the
present invention lends itself to many automated and secondary
manufacturing techniques, such as stamping, die cutting, and
overmolding, to name a few. Designers can easily choose
thermoplastics and other materials for their designs that meet
required RTI (relative thermal index) requirements for specific
applications by following standard design techniques and parameters
set by materials manufacturers Also, heated containers such as
described above allow the food industry to efficiently and
effectively reheat prepared foods, as is often required of
businesses that operate large or small food service venues or that
purchase from distributors of prepared foods. Also, among the many
advantages of the present invention is the ability to intimately
locate a secondary device captured between the thermoplastic
sheets, such as a memory device or other data collector within
close proximity to a food product, thereby allowing more accurate
data collection. This data, as an example, may be used to prove
that a food was prepared at a temperature and for a time period
sufficient to kill the E. coli bacteria.
[0087] Although various embodiments have been illustrated, this is
for the purpose of describing, but not limiting the invention. For
example, a heated container could be formed from more than two
heated element assemblies. The heated containers of the present
invention, also, are by no means limited to food products, but may
have utility in many industries, such as the medical industry.
Further, the assembly line described above is merely illustrative
of one means of forming a sheet of heated element assemblies. More,
the supporting substrate shapes and circuit paths described above
and shown in the drawings are merely illustrative of possible
circuit paths, and one of ordinary skill should appreciate that
these shapes and circuit patterns may be designed in other manners
to accommodate the great flexibility in uses and number of uses for
the heated element assembly of the present invention. Therefore,
various modifications which will become apparent to one skilled in
the art, are within the scope of this invention described in the
attached claims.
* * * * *