U.S. patent application number 12/655856 was filed with the patent office on 2011-07-14 for heat-seal device.
This patent application is currently assigned to Sealed Air Corporation (US). Invention is credited to Vincent A. Piucci, JR., Michael J. Schamel.
Application Number | 20110167772 12/655856 |
Document ID | / |
Family ID | 43618859 |
Filed Date | 2011-07-14 |
United States Patent
Application |
20110167772 |
Kind Code |
A1 |
Piucci, JR.; Vincent A. ; et
al. |
July 14, 2011 |
Heat-seal device
Abstract
A heat-seal device generally includes a heat source, a thermal
conductor, which encapsulates at least a portion of the heat source
and is capable of transferring heat from the heat source, and a
thermal insulator, which substantially surrounds the thermal
conductor but leaves a portion thereof exposed, the exposed portion
of the thermal conductor providing a heat-seal contact surface,
which is adapted to be brought into contact with a material to be
sealed.
Inventors: |
Piucci, JR.; Vincent A.;
(Spencer, MA) ; Schamel; Michael J.; (Wilmont,
NH) |
Assignee: |
Sealed Air Corporation (US)
|
Family ID: |
43618859 |
Appl. No.: |
12/655856 |
Filed: |
January 8, 2010 |
Current U.S.
Class: |
53/477 ;
53/329.2 |
Current CPC
Class: |
B29C 66/71 20130101;
B29C 66/8122 20130101; B29C 66/81831 20130101; B29C 66/81422
20130101; B29C 66/8167 20130101; B29C 66/919 20130101; B29C 66/439
20130101; B29K 2023/06 20130101; B29C 66/0062 20130101; B29C 66/71
20130101; B29C 66/932 20130101; B29C 66/91641 20130101; B29C
66/7352 20130101; B29C 66/91421 20130101; B29C 66/939 20130101;
B29C 66/43 20130101; B29C 66/8122 20130101; B29C 66/91431 20130101;
B29K 2995/0073 20130101; B32B 41/00 20130101; B29C 66/8161
20130101; B29C 66/436 20130101; B29C 66/81261 20130101; B29C
66/91651 20130101; B29C 66/8122 20130101; B29C 66/836 20130101;
B29C 65/305 20130101; B29C 66/73921 20130101; B29C 66/91212
20130101; B29C 66/962 20130101; B29C 66/81821 20130101; B29C
66/91231 20130101; B29L 2031/7138 20130101; B29K 2863/00 20130101;
B29C 65/222 20130101; B29C 66/961 20130101; B29C 66/1122 20130101;
B29K 2909/02 20130101; B29C 65/18 20130101; B29C 66/934 20130101;
B29K 2909/02 20130101; B31D 5/0073 20130101; B29C 66/876 20130101;
B29K 2863/00 20130101; B29K 2023/06 20130101 |
Class at
Publication: |
53/477 ;
53/329.2 |
International
Class: |
B65B 51/10 20060101
B65B051/10 |
Claims
1. A heat-seal device, comprising: a. a heat source; b. a thermal
conductor, which encapsulates at least a portion of said heat
source and is capable of transferring heat from said heat source;
and c. a thermal insulator, which substantially surrounds said
thermal conductor but leaves a portion thereof exposed, said
exposed portion of said thermal conductor providing a heat-seal
contact surface, which is adapted to be brought into contact with a
material to be sealed, wherein, said thermal conductor has a higher
degree of thermal conductivity than said thermal insulator.
2. The heat-seal device of claim 1, wherein said heat source is
encapsulated by said thermal conductor such that substantially no
portion of said heat-source is exposed at said heat-seal contact
surface, whereby, said heat source does not come into direct
contact with the material to be sealed.
3. The heat-seal device of claim 1, further including a
temperature-measuring device, at least a portion of which is
encapsulated with said heat source in said thermal conductor.
4. A heat-sealing method, comprising the steps of: a. providing the
heat-seal device of claim 1; b. causing said heat source to produce
heat; and c. bringing said heat-seal contact surface into contact
with a material to be sealed, whereby, the heat produced by said
heat source transfers through said thermal conductor and into the
material to be sealed via said contact surface.
5. A heat-sealing method, comprising the steps of: a. providing the
heat-seal device of claim 3; b. causing said heat source to produce
heat, thereby effecting a change in temperature within said thermal
conductor; c. measuring the temperature within said thermal
conductor; d. bringing said heat-seal contact surface into contact
with a material to be sealed, whereby, the heat produced by said
heat source transfers through said thermal conductor and into the
material to be sealed via said contact surface.
6. The heat-seal device of claim 3, wherein the encapsulated
portion of said temperature-measuring device is positioned between
said heat source and said heat-seal contact surface.
7. A heat-seal device, comprising: a. a heat source; b. a thermal
conductor, which encapsulates at least a portion of said heat
source and is capable of transferring heat from said heat source
via a heat-seal contact surface on said thermal conductor, wherein
said contact surface is adapted to be brought into contact with a
material to be sealed; and c. a temperature-measuring device, at
least a portion of which is encapsulated with said heat source in
said thermal conductor.
8. A heat-seal system, comprising: a. a heat-seal device,
comprising 1) a heat source capable of producing heat, 2) a thermal
conductor, which encapsulates at least a portion of said heat
source and is capable of assuming a temperature that corresponds,
at least in part, to the heat produced by said heat source, and 3)
a thermal insulator, which substantially surrounds said thermal
conductor but leaves a portion thereof exposed, said exposed
portion of said thermal conductor providing a heat-seal contact
surface, which is adapted to be brought into contact with a
material to be sealed; b. a temperature-measuring device, at least
a portion of which is encapsulated with said heat source in said
thermal conductor; and c. a controller in operative communication
with said heat source and with said temperature-measuring device,
said controller adapted to 1) receive input from said
temperature-measuring device, which is indicative of the
temperature of said thermal conductor, and 2) send output to said
heat source, which causes said heat source to produce more heat,
less heat, or an unchanged amount of heat, whereby, said controller
determines the temperature of said thermal conductor.
9. The system of claim 8, wherein said controller maintains said
thermal conductor at a temperature that falls within a range of a
selected temperature.
10. The system of claim 8, wherein a. said system further includes
a conveyance mechanism for conveying a web of material to be sealed
against said heat-seal contact surface of said heat-seal device,
said conveyance mechanism being adapted to convey the web at
varying speeds; and b. said controller is adapted to change the
temperature of said thermal conductor based on changes in the speed
at which the web is conveyed.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a device for sealing
materials such as plastic film and, more particularly, to an
improved heat-sealing device having a heat-source encapsulated
within a thermal conductor.
[0002] Various types of machines exist for forming containers from
plastic films. In such machines, one or more heat-sealing devices
are included for sealing together the plastic films in such a
manner as to create and/or seal-closed the containers.
[0003] In the field of packaging, for example, many types of
machines form inflated packaging cushions by inflating a flexible
container, e.g. a bag, with air, and then sealing closed the
inflated container. The inflatable containers may be pre-formed and
arranged in series in a flexible web, with only a longitudinal
closure seal being formed at the opening of the containers by the
heat-sealing device, wherein "longitudinal" refers to the direction
in which the web moves as it is conveyed through the machine.
Alternatively, the containers may be formed from a pair of
juxtaposed film plies, wherein one heat-seal device forms a
longitudinal seal between juxtaposed edge regions of the films to
form a closed longitudinal edge, while leaving the opposing
longitudinal edge open; another heat-seal device creates transverse
seals between the two film plies to form the containers, with the
open longitudinal edge providing openings in the containers for
inflation; and a third heat-seal device forms a longitudinal seal
at the open longitudinal edge to seal-closed the openings after the
containers have been inflated. Alternatively, a single film ply may
be used, which is `center-folded` in the longitudinal direction
such that the fold forms the closed longitudinal edge; in this
case, only one longitudinal heat-seal device is required. Examples
of such machines may be found, for example, in U.S. Pat. Nos.
6,598,373, 7,220,476, and 7,225,599.
[0004] Another method for producing packaging cushions is known as
`foam-in-place` packaging, wherein a machine produces flexible
containers, e.g., bags, from flexible, plastic film, and dispenses
a, foamable composition into the containers as they are being
formed. As the composition expands into a foam within the
container, the container is sealed shut and typically dropped into
a carton, e.g., a box, which holds the object to be cushioned. The
rising foam expands into the available space within the carton, but
does so inside the container. Because the bags are formed of
flexible plastic, they form individual custom foam cushions around
the packaged objects. As part of the container-forming mechanism, a
heat-seal device is generally provided for forming a longitudinal
heat-seal. Exemplary types of such packaging apparatus are
described, for example, in U.S. Pat. Nos. 4,800,708, 4,854,109,
5,027,583, 5,376,219, 6,003,288, 6,472,638, 6,675,557, and
7,607,911, and in U.S. Pub. No. 2007-0252297-A1.
[0005] While the foregoing machines for making air-filled and
foam-filled packaging cushions have been widely used and
commercially successful, improvement is continually sought. One
particular aspect wherein improvement is desired concerns the
manner in which the film plies are sealed together, especially in
the longitudinal direction, i.e., the direction in which the film
plies move as they are conveyed through the machine.
[0006] The inventors hereof have determined that an important
factor in making good heat seals is consistency in the temperature
at which heat is applied to the films during the formation of the
seal. The selection of the correct temperature to be applied during
heat-sealing is commonly carried out by operators of cushion-making
machines through routine experimentation, e.g., by trial and error.
If the temperature is too high, the heat-seal device may melt
through the films without sealing them together; if the temperature
is too low, no seal or an incomplete/weak seal may be formed. The
correct temperature to be selected will vary from application to
application, based on a number of operational factors, including
the composition and thickness of the film plies to be sealed, the
pressure at which the film plies and the heating device are urged
together, the speed at which the film is conveyed, etc.
Mathematical algorithms may also be used to select to optimum
temperature, e.g., based on operator input and/or sensor input of
the foregoing factors.
[0007] In addition to the selection of the proper heat-sealing
temperature, a factor that is equally important to the formation of
good, consistent heat seals is the ability of the heat-seal device
to maintain the selected temperature during the formation of the
heat seals. A number of factors can influence the temperature of
the heat-seal device, including the speed at which the film is
conveyed through the machine. In many packaging-cushion machines,
the film is driven at varying speeds through the machine. As the
film is driven faster, it has more ability to remove heat from the
heat-seal device, necessitating higher wattage (electrical power)
to maintain the proper temperature. Conversely, as the film drives
more slowly, it does not use the heat as fast, requiring less power
to make the seal. Other factors involved in determining the power
necessary to make a sufficient seal include ambient temperature,
latent heat build-up in the sealing components, the thickness of
the film material, and the temperature of the film itself, e.g., a
new roll of film may be taken from a cool storage room and
installed on the machine, where it will slowly raise to ambient
temperature.
[0008] While conventional packaging-cushion machines typically have
means for controlling the temperature of the heat-seal device to
achieve consistency, improvement is sought in order to obtain a
higher degree of precision, i.e., a lower degree of temperature
variation from a selected temperature.
[0009] Another aspect of conventional heat-seal devices for which
improvement is sought concerns the structure of such devices.
Conventional heat-seal devices employ, as a heat-source, an
electrically-resistive heating element, which generates heat upon
the passage of electricity therethrough. Such heating elements are
typically fully exposed, and brought into direct contact with the
film to be sealed, which can result in melt-throughs of the film
plies. When the heat-seal device melts through the film plies, an
outer strip from one or both film plies very often separates from
the rest of the film and wraps around the heat-seal device. This
problem, which is known as `ribbon cutting,` results in the
necessity of shutting down the cushion-making machine and
extricating the film strip from the heat-seal device. Typically,
the strip is tightly wound around the device and/or partially
melted such that removal of the strip is a difficult and
time-consuming process. Another disadvantage of `open-air` heating
elements is that such configuration limits the service life of the
heating element due to frictional contact with the film and
oxidation due to exposure to the air while heated.
[0010] Therefore, the need exists for an improved heat-seal device
that is suitable for forming heat-seals in packaging-cushion
machines, and which avoids the foregoing disadvantages.
SUMMARY OF THE INVENTION
[0011] That need is met by the present invention, which, in one
aspect, provides a heat-seal device, comprising:
[0012] a. a heat source;
[0013] b. a thermal conductor, which encapsulates at least a
portion of the heat source and is capable of transferring heat from
the heat source; and
[0014] c. a thermal insulator, which substantially surrounds the
thermal conductor but leaves a portion thereof exposed, the exposed
portion of the thermal conductor providing a heat-seal contact
surface, which is adapted to be brought into contact with a
material to be sealed, wherein the thermal conductor has a higher
degree of thermal conductivity than the thermal insulator.
[0015] Another aspect of the invention pertains to a heat-sealing
method, comprising the steps of:
[0016] a. providing the heat-seal device described above;
[0017] b. causing the heat source to produce heat; and
[0018] c. bringing the heat-seal contact surface into contact with
a material to be sealed,
[0019] whereby, the heat produced by the heat source transfers
through the thermal conductor and into the material to be sealed
via the contact surface.
[0020] Another aspect of the invention pertains to heat-seal
device, comprising:
[0021] a. a heat source;
[0022] b. a thermal conductor, which encapsulates at least a
portion of the heat source and is capable of transferring heat from
the heat source via a heat-seal contact surface on the thermal
conductor, wherein the contact surface is adapted to be brought
into contact with a material to be sealed; and
[0023] c. a temperature-measuring device, at least a portion of
which is encapsulated with the heat source in the thermal
conductor.
[0024] A further aspect of the invention pertains to a heat-seal
system, comprising:
[0025] a. a heat-seal device, comprising [0026] 1) a heat source
capable of producing heat, [0027] 2) a thermal conductor, which
encapsulates at least a portion of the heat source and is capable
of assuming a temperature that corresponds, at least in part, to
the heat produced by the heat source, and [0028] 3) a thermal
insulator, which substantially surrounds the thermal conductor but
leaves a portion thereof exposed, the exposed portion of the
thermal conductor providing a heat-seal contact surface, which is
adapted to be brought into contact with a material to be
sealed;
[0029] b. a temperature-measuring device, at least a portion of
which is encapsulated with the heat source in the thermal
conductor; and
[0030] c. a controller in operative communication with the heat
source and with the temperature-measuring device, the controller
adapted to [0031] 1) receive input from the temperature-measuring
device, which is indicative of the temperature of the thermal
conductor, and [0032] 2) send output to the heat source, which
causes the heat source to produce more heat, less heat, or an
unchanged amount of heat,
[0033] whereby, the controller determines the temperature of the
thermal conductor.
[0034] These and other aspects and features of the invention may be
better understood with reference to the following description and
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a schematic view of heat-seal system 10 in
accordance with the present invention, including a heat-seal device
12 and controller 16;
[0036] FIG. 2 is a perspective view of the heat-seal device 12
illustrated in FIG. 1, showing the top of the device;
[0037] FIG. 3 is a perspective view of the heat-seal device 12
illustrated in FIG. 1, showing the bottom of the device;
[0038] FIG. 4 is a perspective view of a heat-source 24, which is a
component of heat-seal device 12;
[0039] FIG. 5 is a perspective view of a step in the assembly
process for heat-seal device 12, in which the heat-source 24 is
inserted into the housing 18 of the device;
[0040] FIG. 6 is a perspective view of a step in the assembly
process for heat-seal device 12, in which temperature-measuring
device 48 is inserted into the housing 18 of the device;
[0041] FIG. 7 is a partial, perspective view of the device as shown
in FIG. 6, following the insertion of the temperature-measuring
device 48;
[0042] FIG. 8 is cross-sectional view of the device 12, taken along
lines 8-8 in FIG. 2; and
[0043] FIG. 9 is a schematic view of a heat-seal process employing
system 10 as shown in FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0044] FIG. 1 illustrates one embodiment of a heat-seal system 10
in accordance with the present invention. As illustrated, heat-seal
system 10 may include a heat-seal device 12, a support member 14,
and a controller 16. Heat-seal system 10 may be employed in any of
the above-described types of machines for making packaging
cushions, e.g., either air-filled cushions or foam-filled cushions,
by securing the support member 14 to the machine in such a manner
as to bring the heat-seal device 12 into sliding contact with the
film plies to be sealed together, i.e., to form a longitudinal seal
as described above.
[0045] In this embodiment, heat-seal device 12 is in the form of a
replaceable cartridge, which is removably affixed to support member
14. The advantage of this embodiment is ease of maintenance and
replacement of the heat-seal device 12 when necessary, without
having to remove the entire support member 14 from the machine in
which the heat-seal system 10 is employed. The components of the
heat-seal device may thus be contained within a cartridge housing
18, with grip members 20a, b included on either side of the
cartridge housing to facilitate manual grasping thereof. As shown,
the grip members 20a, b may be shaped to fit within corresponding
slots 22a, b in support member 14.
[0046] Referring collectively to FIGS. 1-4, it may be seen that
heat-seal device 12 may comprise a heat source 24, a thermal
conductor 26, and a thermal insulator 28. As shown in FIG. 4, heat
source 24 may comprise a heating element 30 and a pair of contact
posts 32a, b, wherein the heating element 30 is in physical and
electrical contact with the contact posts 32a, b. Contact posts
32a, b may extend through and out of housing 18 in such a manner as
to provide electrical contact with supply and return wires 34a, b,
respectively. As shown in FIG. 1, support member 14 may be
configured such that supply wire 34a extends through the support
member, and terminates at contact well 36a, into which contact post
32a may be inserted to make electrical contact with wire 34a.
Similarly, return wire 34b may also extend through the support
member 14, and terminate at contact well 36b, into which contact
post 32b may be inserted to make electrical contact with wire 34b.
In this manner, when wires 34a, b are connected to a source of
electricity, e.g., via controller 16, electricity may be supplied
to the heat source 24 when heat-seal device 12 is inserted into
support member 14. As explained in further detail below, system 10
may be arranged such that controller 16 controls the amount of
electricity supplied to heat source 24, and thereby controls the
amount of heat generated by the heat source.
[0047] Heating element 30 may be any device capable of heating to a
temperature sufficient to heat-seal, i.e., melt bond or weld, two
film plies together. Such temperature, i.e., the "sealing
temperature," may readily be determined by those of ordinary skill
in the art, without undue experimentation, for a given application
based on, e.g., the composition and thickness of the film plies to
be sealed together, the pressure at which the film plies and the
heating device are urged together, the speed at which the film
plies are conveyed, etc., as noted above.
[0048] Suitable types of devices for heating element 30 include one
or more wires, ribbons, bands, etc., comprising metal and/or other
electrically conductive materials. FIG. 4 illustrates heating
element 30 in the form of a wire. When heating element 30 assumes
such a form, the wire may have any desired cross-sectional shape,
including round, square, oval, rectangular, etc.
[0049] In a preferred embodiment of the invention, heating element
30 has a higher degree of electrical resistance than the contact
posts 32a, b. In this manner, the transmission of electrical
current through the heat source 24 results in the heating element
30 heating to a higher temperature than the contact posts 32a, b
due to the higher resistance of the heating element. Thus,
depending upon the difference in resistance between the heating
element 30 and contact posts 32a, b, only the heating element 30,
and not the contact posts 32a, b, may be heated to the sealing
temperature. Such arrangement is advantageous in that it results in
less overall heat generated by the heat source 24, and therefore
less energy usage. Further, when only the heating element portion
30 of the heat source 24 is heated to the sealing temperature, the
relatively small thermal mass of the heating element 30 may be
heated to the sealing temperature from room temperature very
quickly, usually in less than 1 second. Thus, the heat source 24
does not have to be kept warm during pauses in sealing operations
by maintaining a low or "idling" current through the heat source.
Instead, current is sent through the heat source 24 just prior to
initiation of a sealing operation, and is then stopped immediately
thereafter.
[0050] The difference in electrical resistance between the heating
element 30 and the contact posts 32a, b may be accomplished by
constructing heating element 30 from a material having a higher
degree of electrical resistance and/or a smaller cross-section than
that from which the contact posts 32a, b are constructed. Suitable
materials from which heating element 30 may be constructed include
nickel/chromium alloy (nichrome), cobalt/chromium/nickel alloy,
copper/manganese alloy, nickel/iron alloy, copper/nickel alloy, and
other metals having a relatively high degree of electrical
resistance. Contact posts 32a, b may be constructed from
lower-resistance materials, such as stainless steel, brass, copper
and copper alloys, materials such as steal with an external
cladding of copper, gold, or highly conductive metal, and other
metals having a relatively low degree of electrical resistance.
[0051] Heating element 30 may be in the form of a wire having a
diameter ranging from about 0.003 inch to about 0.040 inch, e.g.,
between about 0.005 to about 0.015 inch. Contact posts 32a, b may
have diameter ranging from about 0.015 inch to about 0.125 inch,
e.g., between about 0.030 to about 0.060 inch.
[0052] The heat source 24 as illustrated in FIG. 4 may be
constructed by providing grooves 38 at a first end 40 of each of
the contact posts 32a, b, placing the heating element 30 in such
grooves, and affixing the heating element 30 to contact posts 32a,
b within the grooves 38, e.g., via laser welding, electron beam
welding, etc. As an alternative to grooves 38, holes may be drilled
into the contact posts 32a, b near first end 40, into which
opposing ends of the heating element 30 may be placed. The second
ends 42 of the contact posts 32a, b may be shaped as necessary to
facilitate the making of good electrical contact within contact
wells 36a, b in support member 14.
[0053] As perhaps best shown in FIGS. 2 and 8, thermal insulator 28
substantially surrounds the thermal conductor 26, but leaves a
portion 44 thereof, i.e., a surface portion, exposed, wherein the
exposed portion 44 provides a heat-seal contact surface. In some
embodiments, the entire cartridge housing 18 may function as the
thermal insulator, e.g., by being constructed from a thermally
insulating material. In other embodiments, the thermal insulator 28
may be omitted altogether. In still other embodiments, cartridge
housing 18 may be constructed largely from a relatively low-cost,
non-insulating material, e.g., plastic, metal, etc., with a
thermally-insulating sub-housing or liner in direct contact with
all or most of the thermal conductor 26.
[0054] In the drawings, the latter embodiment is illustrated,
wherein thermal insulator 28 is in the form of a liner or
sub-housing within cartridge housing 18. As shown, thermal
insulator 28 is configured such that it is substantially positioned
between the thermal conductor 26 and the cartridge housing 18,
thereby insulating the housing 18 from the conductor 26,
particularly those portions of the conductor 26 that are adjacent
to the heating element 30. In this manner, most of the heat
generated by the heat source 24 will be transferred through the
thermal conductor 26 and out of the conductor at surface portion
44, rather than into the cartridge housing 18. This improves the
efficiency of the heat-sealing process and allows cartridge housing
18 to be constructed, e.g., from a low-cost plastic material having
a melting point lower than the sealing temperature reached by the
heat source 24.
[0055] With continuing reference to FIGS. 2 and 8, it may be seen
that thermal conductor 26 encapsulates at least a portion of heat
source 24. For example, as shown, the heating element 30 of heat
source 24 may be substantially completely encapsulated by the
thermal conductor 26. In this manner, the heating element 30 may be
physically protected by the conductor 26, which extends the service
life of the element, e.g., by preventing the heating element from
coming into direct contact with the films to be sealed.
Encapsulation in this manner also minimizes the exposure of the
heating element to air, which thereby prevents or reduces oxidation
of the heating element and further extends the service life
thereof.
[0056] The thermal conductor 26 is capable of transferring heat
from the heat source 24. Thus, in addition to encapsulating the
heating element 30, the thermal conductor 26 also functions as a
heat transfer medium to deliver heat from the heat source 24 to the
film being sealed. In this manner, the conductor 26 further
protects the heating element 30 by serving as a heat sink, which
helps to prevent the heating element from overheating.
[0057] Accordingly, the thermal conductor 26 preferably has a
relatively high degree of thermal conductivity while the thermal
insulator 28 has a relatively low degree of thermal conductivity.
Thermal conductivity is a measure of the ability of a material to
transmit heat, and is defined as the rate at which heat will flow
through the material. The lower the thermal conductivity of a
material is, the better the material is at resisting the flow of
heat therethrough. Conversely, the higher the conductivity, the
better the material is at allowing heat to flow through it. One
common unit of measurement is Btu in./ft..sup.2 hour .degree. F.,
which is the rate of heat flow, in BTU's per hour, through a square
foot of material one inch thick whose surfaces have a temperature
differential of 1.degree. F. For reference, water has a
conductivity of 4 Btu in./ft..sup.2 hour .degree. F., fiberglass
insulation is approximately 0.04, and stainless steel is 111.
[0058] The specific thermal conductivity of the materials chosen
for the thermal conductor 26 and thermal insulator 28 is not
critical; however, it is preferred that the thermal conductivity of
the material chosen for the conductor 26 is higher than that of the
material selected for the insulator 28 such that the thermal
conductor 26 has a higher degree of thermal conductivity than the
thermal insulator 28.
[0059] Preferably, the thermal conductor 26 will have a relatively
high degree of thermal conductivity in order to transfer heat as
efficiently as possible, e.g., greater than about 1 Btu
in./ft..sup.2 hour .degree. F. In addition, the material employed
for the thermal conductor 26 preferably also has a sufficiently low
degree of electrical conductivity that the electrical current sent
through the supply/return wires 34a, b will pass through the
heating element 30, and not through the thermal conductor 26. The
material used for the thermal conductor 26 will ideally also have a
sufficiently high operating temperature to withstand the heat
produced by the heat source 24. A further factor in the selection
of materials for thermal conductor 26 is abrasion resistance. As
described in further detail below, when the heat-seal device 12 is
in operation, the surface 44 of the conductor 26 is in sliding
contact with the film being sealed, and sufficient abrasion
resistance to provide a reasonable life span is thus a desirable
feature.
[0060] A number of suitable compounds for thermal conductor 26 are
available, including high-temperature epoxies and ceramic cements.
Many epoxies have a maximum temperature rating of around
500.degree. F., while ceramic cements have maximum temperature
ratings ranging from about 1500.degree. to 4000.degree. F. A
specific material that was found to work well as a thermal
conductor is an alumina ceramic cement sold by Cotronics
Corporation of Brooklyn, N.Y. under the tradename Resbond 989FS.
This alumina ceramic cement has a temperature rating of
3000.degree. F., a thermal conductivity of 15 Btu in./ft..sup.2
hour .degree. F., good abrasion properties, and a relatively low
degree of electrical conductivity. Other suitable materials include
zircon-based cements, and aluminum-nitride-filled ceramic potting
compounds.
[0061] The thermal insulator 28 preferably has a relatively low
degree of thermal conductivity, i.e., in comparison to the thermal
conductor 26, in order to insulate the cartridge housing 18 from
the heat generated by the heat source 24, and to direct such heat
into the film being sealed. For example, the thermal conductivity
of the material from which the thermal insulator 28 is constructed
is preferably less than about 5 Btu in./ft..sup.2 hour .degree. F.
Many suitable materials exist, e.g., ceramics, such as zirconia and
alumina silicate, high temperature plastics such as poly ether
ether keytone (PEEK) or polyphenylsulfone, glass, glass ceramics,
etc. A specific example of a suitable thermal insulating material
is a general purpose alumina silicate ceramic, such as Grade
GCGW-5110, manufactured by Graphtek, LLC, which has a thermal
conductivity of 0.003 Btu in./ft..sup.2 hour .degree. F.
[0062] As noted above, the thermal insulator 28 substantially
surrounds the thermal conductor 26, but leaves a surface portion 44
thereof exposed. In this manner, the exposed surface portion 44
provides a heat-seal contact surface, which is adapted to be
brought into contact with a material to be sealed, e.g., a pair of
juxtaposed film plies. The exposed portion 44 may be adapted in
this regard, e.g, by applying thereto a surface finish, which both
smoothes and rounds the exposed portion so that it may be brought
into sliding contact with film material to be sealed with minimal
abrasion thereto and/or frictional resistance therewith. If
desired, the entire contact surface 46 of the heat-seal device 12
may be rounded and smoothed in this manner.
[0063] The heat source 24 is preferably encapsulated by thermal
conductor 26 such that substantially no portion of the heat-source,
and particularly the heating element 30 thereof, is exposed at the
exposed/heat-seal contact surface 44. In this manner, the heat
source 24 does not come into direct contact with the material to be
sealed. Instead, the heat generated by the heat source 24 is
transferred into the thermal conductor 26. By substantially
surrounding the thermal conductor 26 with the thermal insulator 28
as described above, a significant portion of the heat transferred
into the thermal conductor 26 by the heat source 24 may be
transferred through the thermal conductor 26 and into a material to
be sealed via the exposed/heat-seal contact surface 44.
[0064] As may be appreciated, the foregoing configuration in
accordance with the present invention results in a highly efficient
transfer of the energy supplied to heat source 24, e.g., electrical
energy via wires 34a, b, into the film or other material to be
sealed. In addition, this configuration avoids the above-noted
difficulties associated with conventional heat-sealing devices,
which generally employ direct contact between the film and the
heat-source. That is, by encapsulating the heat-source, the
problems of `ribbon cutting` of the film and shortened service life
of the heating element are avoided.
[0065] In accordance with another aspect of the present invention,
heat-seal device 12 may further include a temperature-measuring
device 48, at least a portion of which is encapsulated with heat
source 24 in thermal conductor 26, as shown in FIG. 8. In the
illustrated embodiment, a thermocouple is used as the
temperature-measuring device 48, which includes two wires 50, 52 of
dissimilar metals welded together at a junction 54. As is well
known to those of ordinary skill in the art, thermocouples operate
based on the principle that when a junction of two dissimilar
metals is heated, a voltage is created that corresponds to the
temperature. Typically, the junction size is 1.5 times the wire
diameter. For instance, if the wires 50, 52 are both 0.005 inches
in diameter, the junction 54 will be 0.0075 inches in diameter.
[0066] There are numerous, commercially-available thermocouple
types using various materials which are chosen for their
temperature ranges and response time. Almost any type will work in
heat-seal device 12, e.g., a `type J` thermocouple comprising, as
the two dissimilar metals, iron and constantan, with a temperature
range of 32-1382.degree. F. In most cases, the temperature needed
to seal two polymeric film plies together is in the range of
250-400.degree. F. The output of a type J thermocouple in this
temperature range is approximately 6 to 8 millivolts. Since this
output is small, the controller 16 will preferably include an
instrument amplifier that will increase and filter the signal from
the thermocouple.
[0067] As shown in FIG. 8, both the heating element 30 of heat
source 24 and the thermocouple junction 54 of temperature-measuring
device 48 may be encapsulated in the thermal conductor 26, which is
surrounded by the thermal insulator 28 in the cartridge housing 18.
As shown, the heating element 30 and thermocouple junction 54 may
be physically separated from each other within the thermal
conductor 26. When the thermal conductor 26 is formed from a
material having a relatively low degree of electrical conductivity,
this arrangement results in the heating element 30 and thermocouple
junction 54 being electrically insulated from one another, which
makes for a clearer output signal from the thermocouple.
[0068] The encapsulated portion of the temperature-measuring device
48 may be positioned between the heat source 24 and heat-seal
contact surface 44. For example, as also shown in FIG. 8, the
thermocouple junction 54 can be placed between the heating element
30 and the heat-seal contact surface 44. This configuration has
been found to result in a high degree of accuracy in the
measurement of the temperature of the thermal conductor 26 at the
surface 44. The encapsulation of the junction 54 and heating
element 30 in the thermal conductor 26 ensures that such
configuration will be maintained, e.g., will not be disturbed due
to movement of the film against the heat-seal device 12.
Alternatively, the encapsulated portion of the
temperature-measuring device 48, e.g., the junction 54 thereof when
device 48 is a thermocouple, may be positioned beneath or beside
the heat source 24 within the thermal conductor 26.
[0069] Referring now to FIGS. 5-7, a method for assembling the
heat-seal device 12 will be described. FIG. 5 shows the beginning
of the assembly process, with thermal insulator 28 having already
been inserted into cartridge housing 18. As shown, the thermal
insulator 28 has an open channel 56 to accommodate the heat source
24.
[0070] The thermal conductor 26 may be provided in the form of an
uncured liquid or paste, which may subsequently be cured into a
solid. For example, alumina ceramic cement, e.g., Resbond 989FS,
has the ability to flow when in uncured/liquid form, and then
accept a smooth finish when in cured/solid form. Curing may be
accomplished by simply allowing the material to air dry.
[0071] Accordingly, a small quantity of uncured thermal conducting
material may first be poured or otherwise placed into the channel
56, e.g., in an amount sufficient to cover the bottom 58 of the
channel 56 (FIG. 8). The heat source 24 is then inserted in the
direction of arrows 60 into channel 56 (FIG. 5), and pressed down
into the channel until the second ends 42 of the contact posts 32a,
b protrude from the bottom 62 of the housing 18 (FIG. 3) and the
heating element 30 is buried into the thermal conducting material
placed at the bottom 58 of the channel 56.
[0072] In FIG. 6, the heat source 24 has been fully installed, with
only the second ends 42 of the contact posts 32a, b visible, as
extending from the bottom 62 of the housing 18. Additional thermal
conducting material, indicated at 64, is then added into the
channel 56, on top of the heating element 30 to bury the element
30.
[0073] FIG. 6 also depicts the installation of the
temperature-measuring device 48. In the presently-illustrated
embodiment, thermal insulator 28 may include a second channel 66 to
accommodate the temperature-measuring device 48. Second channel 66
may be disposed at an angle relative to the channel 56, e.g.,
substantially transverse as shown. Both channels 56 and 66 may
extend beyond thermal insulator 28 as needed, e.g., into housing 18
as shown.
[0074] The temperature-measuring device 48 may be inserted into the
second channel 66 as shown, i.e., by moving the device 48 into the
channel 66 in the direction of arrow 68, such that it is embedded
into the thermal conducting material 64. As a result, the
temperature-measuring device 48 and heat source 24 will have the
respective positions shown in FIG. 7 (the thermal conducting
material 64 is not shown in FIG. 7 for clarity).
[0075] After installation of the temperature-measuring device 48,
additional thermal conducting material 64 is added on top of the
device 48, so that the material 64 covers the device 48 and fills
the channels 56, 66. If desired, the thermal conducting material 64
may be mounded above the top of the channels 56, 66 to insure
complete fill. The conducting material 64 may then be allowed to
cure completely until hardened (with the rate and conditions of the
cure depending upon the specific material selected), thereby
resulting in the thermal conducting material 64 transforming into
thermal conductor 26. Any excess material may be removed by
sanding, and the heat-seal contact surface 44 may be alternatively
or additionally polished to provide a desired degree of smoothness,
e.g., to minimize the coefficient of friction between the surface
44 and the films to be sealed.
[0076] The result of the foregoing assembly process is the
heat-seal device 12 as shown in FIG. 2.
[0077] Referring back to FIG. 1, it may be seen that the
temperature-measuring device 48 may be brought into electrical
communication with controller 16 in the same manner as is heat
source 24, i.e., via support member 14. Support member 14 may thus
be configured such that sensing wire 70a extends through the
support member, and terminates at contact pin 72a, while sensing
wire 70b extends through the support member, and terminates at
contact pin 72b as shown. Within heat-seal device 12, thermocouple
wire 50 terminates at, and is electrically connected to,
thermocouple contact 74, which, as shown in FIG. 3, is positioned
at the bottom 62 of housing 18, e.g., as a step in the assembly
process for heat-seal device 12. Similarly, thermocouple wire 52
terminates at, and is electrically connected to, thermocouple
contact 76. In this embodiment, the thermocouple contacts 74, 76
are included to ensure good electrical communication between the
relatively small-diameter thermocouple wires 50, 52 and the sensing
wires 70a, b, by electrically connecting the thermocouple wires 50,
52 to the relatively large contact surfaces 78, 80, against which
the contact pins 72a, b abut when the heat-seal device 12 is
inserted into support member 14 as shown in FIG. 1.
[0078] Referring now to FIG. 9, a heat-sealing method in accordance
with the present invention will be described. FIG. 9 illustrates
system 10, as shown in FIG. 1, in a process for sealing a web of
material, e.g., for sealing together two juxtaposed film plies 82a,
b via a continuous longitudinal seal, e.g., at juxtaposed edges of
the film plies to thereby form an inflatable or Tillable packaging
material 85 with a closed longitudinal edge (closed edge not
shown). As is conventional, film plies 82a, b may be supplied from
separate film rolls 84a, b. Sealing may be facilitated by providing
a backing member 86, which may be movable relative to heat-seal
device 12, or simply biased against the heat-seal device, such that
film plies 82a, b may be compressed between device 12 and member 86
during sealing as shown.
[0079] The system may further include a conveyance mechanism for
conveying a web of material to be sealed, e.g., juxtaposed film
plies 82a, b, against the heat-seal contact surface 44 of heat-seal
device 12, wherein the conveyance mechanism is adapted to convey
the web at varying speeds. As shown, the conveyance mechanism may
be embodied by a pair of driven, counter-rotating nip rollers 88a,
b. As an alternative, the conveyance mechanism may be embodied by a
single drive roller, which is used in place of backing member 86 to
both drive the conveyance of the web and compress the web against
the heat-seal device 12.
[0080] In its most basic form, the method illustrated in FIG. 9
includes the steps of:
[0081] a. providing heat-seal device 12;
[0082] b. causing the heat source 24 to produce heat; and
[0083] c. bringing the heat-seal contact surface 44 into contact
with the material to be sealed, i.e., film ply 82a, which is
juxtaposed with film ply 82b as shown. In this manner, as explained
above, the heat produced by heat source 24 transfers through the
thermal conductor 26 and into the film plies 82a, b via contact
surface 44 of heat-seal device 12.
[0084] When the heat-seal device 12 includes temperature-measuring
device 48, the foregoing method would include the further step of
measuring the temperature within the thermal conductor 26. Such
method may be carried out by system 10, as shown in FIGS. 1 and 9,
wherein controller 16 is in operative communication with both heat
source 24 and with temperature-measuring device 48, i.e., via
respective wires 34a, b and 70a, b as described above. Controller
16 may thus be adapted, e.g., programmed, to:
[0085] 1) receive input from temperature-measuring device 48, which
is indicative of the temperature of thermal conductor 26, and
[0086] 2) send output to heat source 24, which causes the heat
source to produce more heat, less heat, or an unchanged amount of
heat, e.g., depending upon a selected/target temperature that is
provided to, or calculated by, controller 16.
[0087] In this manner, controller 16 determines the temperature of
the thermal conductor, which will generally vary within a
temperature range that is centered on a selected temperature, which
becomes a target temperature that the controller tries to maintain.
Controller 16 may thus include an operator interface 90 (FIG. 9),
e.g., a control panel, which allows an operator to select a
temperature for the thermal conductor 26. Alternatively, controller
16 may be programmed with a mathematical algorithm that calculates
the selected/target temperature, based on various factors such as
film speed, film type, etc.
[0088] As may be appreciated, the controller 16,
temperature-measuring device 48, and heat source 24 together form a
temperature-control feedback loop, in which the controller will
continuously vary the power input supplied to the heat source,
based on temperature feedback provided by the temperature-measuring
device, in order to maintain the temperature of the thermal
conductor 26 as closely as possible to the operator-selected or
controller-calculated temperature. As with all such
temperature-control feedback loops, there will generally be an
inherent off-set between the selected temperature and the actual
temperature, with the controller 16 continually `driving` the
actual, sensed temperature toward the set-point temperature, in
response to changes in the actual temperature due to operational
changes during the sealing process. Controller 16 will thus
maintain the thermal conductor 26 at a temperature that falls
within a range of the selected temperature.
[0089] Many types of controllers are suitable for use as controller
16. Controller 16 may be an electronic controller, such as a
printed circuit assembly containing a micro controller unit (MCU),
which stores pre-programmed operating codes; a programmable logic
controller (PLC); a personal computer (PC); or other such control
device which allows the temperature of the thermal conductor 26 to
be controlled via local control, e.g., via operator interface 90;
remote control; pre-programmed control, etc.
[0090] Various modes of control may be employed by controller 16,
including proportional, derivative, integral, and combinations
thereof, e.g., PID (proportional-integral-derivative) control, to
achieve a desired degree of accuracy in the control of the
temperature of thermal conductor 26, e.g., a desired maximum degree
of off-set between the set and actual temperature. The electrical
power output to heat source 24 from controller 16 may be regulated
via analog power control or digital power control, e.g., pulse
width modulated power control.
[0091] In some embodiments, the film web to be sealed is conveyed,
i.e., driven, through the system at variable speeds. See, e.g., the
foam-in-place system disclosed in U.S. Pat. No. 7,607,911, the
disclosure of which is hereby incorporated entirely herein by
reference thereto. In such systems, as the film drive speed is
increased, the time of contact between the sealing surface and the
film becomes shorter. As the contact time decreases in this manner,
the temperature of the sealing surface may be raised in order to
ensure that good seals continue to be made, i.e., in order to put
sufficient heat into the film to ensure that its temperature
remains above the melting point thereof. Conversely, when the film
speed is decreased, the contact time between the sealing surface
and the film increases. In this case, the temperature of the
sealing surface may be lowered to ensure that the sealing surface
does not put so much heat into the film that it melts therethrough.
Accordingly, controller 16 may be adapted, e.g., programmed, to
change the temperature of the thermal conductor 26 based on changes
in the speed at which the film web is conveyed.
[0092] As an example, the heat-seal device 12 was used as a
longitudinal sealing device in the foam-in-place apparatus
disclosed in the above-referenced U.S. Pat. No. 7,607,911, by
mounting the device 12 on shaft 48 of the '911 apparatus such that
the heat-seal contact surface 44 of the device 12 was urged into
contact with drive roller 40 of the '911 apparatus near an end of
the drive roller such that the unsealed longitudinal edges of a
pair of juxtaposed film plies were sealed together when conveyed
between the contact surface 44 of the device 12 and drive roller 40
of the '911 apparatus. The film plies comprised polyethylene and
had a thickness of about 0.75 mil.
[0093] The drive roller 40 of the '911 apparatus was driven by a
gear motor that included an encoder. A controller, similar to
controller 16 as described above, was in communication with the
encoder and gear motor, such that the controller monitored the film
drive speed (based on input from the encoder) and drove it at a
desired rate in accordance with the '911 patent. The encoder
produced 3900 counts per inch of film travel. Thus, for example, if
the controller read 3900 counts per second, this meant that the
film was being driven at 1 inch per second.
[0094] The controller may be programmed to simply increase the seal
temperature by a predetermined amount in response to a given speed
increase, e.g., a temperature increase of 10.degree. F. for each 1
inch/second speed increase, and visa versa. Alternatively, optimal
`seal-temperature vs. film-speed` values may be determined
experimentally, and then programmed into the controller. The latter
was accomplished by driving the film plies through the '911
apparatus at various speeds throughout the speed range of the gear
motor, and determining the lowest and highest temperatures at each
speed at which a good seal was made. A "good seal" at the lowest
temperature was the point at which the film plies exhibited some
degree of stretch prior to the seal breaking when the film plies
were pulled apart, indicating that the seal was strong enough to
withstand at least some amount of applied tensile force. A "good
seal" at the high temperature was the point just below the
temperature when ribbon cutting began.
[0095] Table 1 below is a summary of the resultant data:
TABLE-US-00001 TABLE 1 Film drive Low temp High temp Temp
Calculated speed for good for good midpoint temp: (inch/min.) seal
(.degree. F.) seal (.degree. F.) (.degree. F.) Y = mX + b 1 200 230
215 218 2 220 260 240 236 3 220 280 250 253 4 230 310 270 270 5 240
350 295 288 6 240 360 300 305 7 260 390 325 323 8 260 410 335 340 9
290 430 360 357 10 300 450 375 375
[0096] The film plies were driven from 1 to 10 inches/minute in
increments of 1 inch/minute. The temperature values shown in Table
1 were obtained experimentally at each speed. To determine the low
temperature for a good seal, the seal temperature was lowered until
the seal failed. The temperature was then raised until ribbon
cutting occurred to determine the high temperature for a good seal.
The values shown in Table 1 are the average results of numerous
seal tests. The temperature midpoint is the value midway between
the low and high values. This midpoint value may be used by the
controller to determine the target temperature for each speed value
since it offers the largest range to account for inconsistencies in
the operation of the apparatus.
[0097] There are several ways that the foregoing data can be used
by the controller to determine the target temperature for the
heat-seal device 12. In one embodiment, the data from Table 1 or
the like may be programmed into the controller, which uses the data
to select the proper temperature value, e.g., the temperature
midpoint, based on the selected/detected film drive speed. For
instance, if the film drive speed is 5 inches/minute, the
corresponding midpoint heat-seal temperature is 295.degree. F.
[0098] In an alternative embodiment, a liner regression formula may
be used to determine the target temperature, given that the values
in Table 1 represent a substantially straight line. Thus, the
formula
Y=mX+b
may be used by the controller, where "Y" is the target temperature,
"m" is the slope, "X" is the drive speed, and "b" is the Y
intercept. In a situation where the speed vs. temperature plot is
not linear, a higher order equation can be used. For the data set
forth in Table 1, the slope is 1.742 and the intercept is 200.67.
These values may be used by the controller to calculate target
temperature as a result of film drive speed. The film drive speed
may be determined by the controller based on feedback from the gear
motor encoder. The last column in Table 1 above shows the target
temperature as calculated in this manner.
[0099] Accordingly, the controller may monitor and/or control the
film drive speed, and continuously calculate and update the target
temperature based on the drive speed. Thus, as the drive speed
changes, so does the temperature of the seal element. When the
controller both monitors and controls the drive speed it can, as an
alternative, use its target drive speed rather than measured drive
speed for temperature calculations.
[0100] The controller may also be programmed to anticipate changes
in drive speed and, therefore, temperature, for those embodiments
in which the controller determines drive speed, given that the
controller will thus "know" when a speed change will occur, and
what the next drive speed and target temperature will be. Such
anticipation can be used during a cycle whenever the drive speed
changes. If, for instance, the drive speed increases from 2
inches/minute to 8 inches/minute, the controller can take the
heating element 30 to the requisite target temperature, e.g.,
increase the temperature from 236.degree. F. to 340.degree. F., at
a time prior to changing speeds, which may help to maintain the
consistency and integrity of the seal, e.g., by not allowing
unsealed gaps to form immediately following the speed increase.
Conversely, the controller can lower the target temperature prior
to slowing or stopping the film drive. This may prevent the
heat-seal device 12 from burning through the film due to having too
much heat for the slower speed.
[0101] The foregoing description of preferred embodiments of the
invention has been presented for purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed, and modifications and
variations are possible in light of the above teachings or may be
acquired from practice of the invention.
* * * * *