US20110167772A1

Movatterモバイル変換

Info

Publication number: US20110167772A1
Application number: US12/655,856
Authority: US
Inventors: Vincent A. Piucci, Jr.; Michael J. Schamel
Original assignee: Sealed Air Corp
Current assignee: Sealed Air Corp
Priority date: 2010-01-08
Filing date: 2010-01-08
Publication date: 2011-07-14
Also published as: EP2543496A1; EP2543496B1; EP2521643A1; US8434536B2; ES2423839T3; US20120080133A1; US20130180643A1; WO2011085055A1

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.

Description

BACKGROUND OF THE INVENTION

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

That need is met by the present invention, which, in one aspect, provides a heat-seal device, comprising:

a. a heat source;

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

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.

Another aspect of the invention pertains to a heat-sealing method, comprising the steps of:

a. providing the heat-seal device described above;

b. causing the heat source to produce heat; and

c. bringing the heat-seal contact surface into contact with a material to be sealed,

whereby, the heat produced by the heat source transfers through the thermal conductor and into the material to be sealed via the contact surface.

Another aspect of the invention pertains to heat-seal device, comprising:

a. a heat source;

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

c. a temperature-measuring device, at least a portion of which is encapsulated with the heat source in the thermal conductor.

A further aspect of the invention pertains to 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 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
- 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;

b. a temperature-measuring device, at least a portion of which is encapsulated with the heat source in the thermal conductor; and

c. a controller in operative communication with the heat source and with the temperature-measuring device, the controller adapted to

- 1) receive input from the temperature-measuring device, which is indicative of the temperature of the thermal conductor, and
- 2) send output to the heat source, which causes the heat source to produce more heat, less heat, or an unchanged amount of heat,

whereby, the controller determines the temperature of the thermal conductor.

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

FIG. 1 is a schematic view of heat-seal system10 in accordance with the present invention, including a heat-seal device12 andcontroller16;

FIG. 2 is a perspective view of the heat-seal device12 illustrated inFIG. 1, showing the top of the device;

FIG. 3 is a perspective view of the heat-seal device12 illustrated inFIG. 1, showing the bottom of the device;

FIG. 4 is a perspective view of a heat-source24, which is a component of heat-seal device12;

FIG. 5 is a perspective view of a step in the assembly process for heat-seal device12, in which the heat-source24 is inserted into thehousing18 of the device;

FIG. 6 is a perspective view of a step in the assembly process for heat-seal device12, in which temperature-measuringdevice48 is inserted into thehousing18 of the device;

FIG. 7 is a partial, perspective view of the device as shown inFIG. 6, following the insertion of the temperature-measuringdevice48;

FIG. 8 is cross-sectional view of thedevice12, taken along lines8-8 inFIG. 2; and

FIG. 9 is a schematic view of a heat-sealprocess employing system10 as shown inFIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates one embodiment of a heat-seal system10 in accordance with the present invention. As illustrated, heat-seal system10 may include a heat-seal device12, asupport member14, and acontroller16. Heat-seal system10 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 thesupport member14 to the machine in such a manner as to bring the heat-seal device12 into sliding contact with the film plies to be sealed together, i.e., to form a longitudinal seal as described above.

In this embodiment, heat-seal device12 is in the form of a replaceable cartridge, which is removably affixed to supportmember14. The advantage of this embodiment is ease of maintenance and replacement of the heat-seal device12 when necessary, without having to remove theentire support member14 from the machine in which the heat-seal system10 is employed. The components of the heat-seal device may thus be contained within acartridge housing18, withgrip members20a, bincluded on either side of the cartridge housing to facilitate manual grasping thereof. As shown, thegrip members20a, bmay be shaped to fit within correspondingslots22a, binsupport member14.

Referring collectively toFIGS. 1-4, it may be seen that heat-seal device12 may comprise aheat source24, athermal conductor26, and athermal insulator28. As shown inFIG. 4,heat source24 may comprise aheating element30 and a pair of contact posts32a, b, wherein theheating element30 is in physical and electrical contact with the contact posts32a, b. Contact posts32a, bmay extend through and out ofhousing18 in such a manner as to provide electrical contact with supply and returnwires34a, b, respectively. As shown inFIG. 1,support member14 may be configured such thatsupply wire34aextends through the support member, and terminates at contact well36a, into which contact post32amay be inserted to make electrical contact withwire34a. Similarly,return wire34bmay also extend through thesupport member14, and terminate at contact well36b, into which contact post32bmay be inserted to make electrical contact withwire34b. In this manner, whenwires34a, bare connected to a source of electricity, e.g., viacontroller16, electricity may be supplied to theheat source24 when heat-seal device12 is inserted intosupport member14. As explained in further detail below,system10 may be arranged such thatcontroller16 controls the amount of electricity supplied to heatsource24, and thereby controls the amount of heat generated by the heat source.

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.

Suitable types of devices forheating element30 include one or more wires, ribbons, bands, etc., comprising metal and/or other electrically conductive materials.FIG. 4 illustratesheating element30 in the form of a wire. When heatingelement30 assumes such a form, the wire may have any desired cross-sectional shape, including round, square, oval, rectangular, etc.

In a preferred embodiment of the invention,heating element30 has a higher degree of electrical resistance than the contact posts32a, b. In this manner, the transmission of electrical current through theheat source24 results in theheating element30 heating to a higher temperature than the contact posts32a, bdue to the higher resistance of the heating element. Thus, depending upon the difference in resistance between theheating element30 andcontact posts32a, b, only theheating element30, and not the contact posts32a, b, may be heated to the sealing temperature. Such arrangement is advantageous in that it results in less overall heat generated by theheat source24, and therefore less energy usage. Further, when only theheating element portion30 of theheat source24 is heated to the sealing temperature, the relatively small thermal mass of theheating element30 may be heated to the sealing temperature from room temperature very quickly, usually in less than 1 second. Thus, theheat source24 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 theheat source24 just prior to initiation of a sealing operation, and is then stopped immediately thereafter.

The difference in electrical resistance between theheating element30 and the contact posts32a, bmay be accomplished by constructingheating element30 from a material having a higher degree of electrical resistance and/or a smaller cross-section than that from which the contact posts32a, bare constructed. Suitable materials from whichheating element30 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 posts32a, bmay 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.

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 posts32a, bmay have diameter ranging from about 0.015 inch to about 0.125 inch, e.g., between about 0.030 to about 0.060 inch.

Theheat source24 as illustrated inFIG. 4 may be constructed by providinggrooves38 at afirst end40 of each of the contact posts32a, b, placing theheating element30 in such grooves, and affixing theheating element30 to contactposts32a, bwithin thegrooves38, e.g., via laser welding, electron beam welding, etc. As an alternative togrooves38, holes may be drilled into the contact posts32a, bnearfirst end40, into which opposing ends of theheating element30 may be placed. The second ends42 of the contact posts32a, bmay be shaped as necessary to facilitate the making of good electrical contact withincontact wells36a, binsupport member14.

As perhaps best shown inFIGS. 2 and 8,thermal insulator28 substantially surrounds thethermal conductor26, but leaves aportion44 thereof, i.e., a surface portion, exposed, wherein the exposedportion44 provides a heat-seal contact surface. In some embodiments, theentire cartridge housing18 may function as the thermal insulator, e.g., by being constructed from a thermally insulating material. In other embodiments, thethermal insulator28 may be omitted altogether. In still other embodiments,cartridge housing18 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 thethermal conductor26.

In the drawings, the latter embodiment is illustrated, whereinthermal insulator28 is in the form of a liner or sub-housing withincartridge housing18. As shown,thermal insulator28 is configured such that it is substantially positioned between thethermal conductor26 and thecartridge housing18, thereby insulating thehousing18 from theconductor26, particularly those portions of theconductor26 that are adjacent to theheating element30. In this manner, most of the heat generated by theheat source24 will be transferred through thethermal conductor26 and out of the conductor atsurface portion44, rather than into thecartridge housing18. This improves the efficiency of the heat-sealing process and allowscartridge housing18 to be constructed, e.g., from a low-cost plastic material having a melting point lower than the sealing temperature reached by theheat source24.

With continuing reference toFIGS. 2 and 8, it may be seen thatthermal conductor26 encapsulates at least a portion ofheat source24. For example, as shown, theheating element30 ofheat source24 may be substantially completely encapsulated by thethermal conductor26. In this manner, theheating element30 may be physically protected by theconductor26, 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.

Thethermal conductor26 is capable of transferring heat from theheat source24. Thus, in addition to encapsulating theheating element30, thethermal conductor26 also functions as a heat transfer medium to deliver heat from theheat source24 to the film being sealed. In this manner, theconductor26 further protects theheating element30 by serving as a heat sink, which helps to prevent the heating element from overheating.

Accordingly, thethermal conductor26 preferably has a relatively high degree of thermal conductivity while thethermal insulator28 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.²hour ° 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° F. For reference, water has a conductivity of 4 Btu in./ft.²hour ° F., fiberglass insulation is approximately 0.04, and stainless steel is 111.

The specific thermal conductivity of the materials chosen for thethermal conductor26 andthermal insulator28 is not critical; however, it is preferred that the thermal conductivity of the material chosen for theconductor26 is higher than that of the material selected for theinsulator28 such that thethermal conductor26 has a higher degree of thermal conductivity than thethermal insulator28.

Preferably, thethermal conductor26 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.²hour ° F. In addition, the material employed for thethermal conductor26 preferably also has a sufficiently low degree of electrical conductivity that the electrical current sent through the supply/return wires34a, bwill pass through theheating element30, and not through thethermal conductor26. The material used for thethermal conductor26 will ideally also have a sufficiently high operating temperature to withstand the heat produced by theheat source24. A further factor in the selection of materials forthermal conductor26 is abrasion resistance. As described in further detail below, when the heat-seal device12 is in operation, thesurface44 of theconductor26 is in sliding contact with the film being sealed, and sufficient abrasion resistance to provide a reasonable life span is thus a desirable feature.

A number of suitable compounds forthermal conductor26 are available, including high-temperature epoxies and ceramic cements. Many epoxies have a maximum temperature rating of around 500° F., while ceramic cements have maximum temperature ratings ranging from about 1500° to 4000° 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° F., a thermal conductivity of 15 Btu in./ft.²hour ° 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.

Thethermal insulator28 preferably has a relatively low degree of thermal conductivity, i.e., in comparison to thethermal conductor26, in order to insulate thecartridge housing18 from the heat generated by theheat source24, and to direct such heat into the film being sealed. For example, the thermal conductivity of the material from which thethermal insulator28 is constructed is preferably less than about 5 Btu in./ft.²hour ° 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.²hour ° F.

As noted above, thethermal insulator28 substantially surrounds thethermal conductor26, but leaves asurface portion44 thereof exposed. In this manner, the exposedsurface portion44 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 exposedportion44 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, theentire contact surface46 of the heat-seal device12 may be rounded and smoothed in this manner.

Theheat source24 is preferably encapsulated bythermal conductor26 such that substantially no portion of the heat-source, and particularly theheating element30 thereof, is exposed at the exposed/heat-seal contact surface44. In this manner, theheat source24 does not come into direct contact with the material to be sealed. Instead, the heat generated by theheat source24 is transferred into thethermal conductor26. By substantially surrounding thethermal conductor26 with thethermal insulator28 as described above, a significant portion of the heat transferred into thethermal conductor26 by theheat source24 may be transferred through thethermal conductor26 and into a material to be sealed via the exposed/heat-seal contact surface44.

As may be appreciated, the foregoing configuration in accordance with the present invention results in a highly efficient transfer of the energy supplied to heatsource24, e.g., electrical energy viawires34a, 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.

In accordance with another aspect of the present invention, heat-seal device12 may further include a temperature-measuringdevice48, at least a portion of which is encapsulated withheat source24 inthermal conductor26, as shown inFIG. 8. In the illustrated embodiment, a thermocouple is used as the temperature-measuringdevice48, which includes two

wires

50,52 are both 0.005 inches in diameter, thejunction54 will be 0.0075 inches in diameter.

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 device12, e.g., a ‘type J’ thermocouple comprising, as the two dissimilar metals, iron and constantan, with a temperature range of 32-1382° F. In most cases, the temperature needed to seal two polymeric film plies together is in the range of 250-400° F. The output of a type J thermocouple in this temperature range is approximately 6 to 8 millivolts. Since this output is small, thecontroller16 will preferably include an instrument amplifier that will increase and filter the signal from the thermocouple.

As shown inFIG. 8, both theheating element30 ofheat source24 and thethermocouple junction54 of temperature-measuringdevice48 may be encapsulated in thethermal conductor26, which is surrounded by thethermal insulator28 in thecartridge housing18. As shown, theheating element30 andthermocouple junction54 may be physically separated from each other within thethermal conductor26. When thethermal conductor26 is formed from a material having a relatively low degree of electrical conductivity, this arrangement results in theheating element30 andthermocouple junction54 being electrically insulated from one another, which makes for a clearer output signal from the thermocouple.

The encapsulated portion of the temperature-measuringdevice48 may be positioned between theheat source24 and heat-seal contact surface44. For example, as also shown inFIG. 8, thethermocouple junction54 can be placed between theheating element30 and the heat-seal contact surface44. This configuration has been found to result in a high degree of accuracy in the measurement of the temperature of thethermal conductor26 at thesurface44. The encapsulation of thejunction54 andheating element30 in thethermal conductor26 ensures that such configuration will be maintained, e.g., will not be disturbed due to movement of the film against the heat-seal device12. Alternatively, the encapsulated portion of the temperature-measuringdevice48, e.g., thejunction54 thereof whendevice48 is a thermocouple, may be positioned beneath or beside theheat source24 within thethermal conductor26.

Referring now toFIGS. 5-7, a method for assembling the heat-seal device12 will be described.FIG. 5 shows the beginning of the assembly process, withthermal insulator28 having already been inserted intocartridge housing18. As shown, thethermal insulator28 has anopen channel56 to accommodate theheat source24.

Thethermal conductor26 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.

Accordingly, a small quantity of uncured thermal conducting material may first be poured or otherwise placed into thechannel56, e.g., in an amount sufficient to cover the bottom58 of the channel56 (FIG. 8). Theheat source24 is then inserted in the direction ofarrows60 into channel56 (FIG. 5), and pressed down into the channel until the second ends42 of the contact posts32a, bprotrude from the bottom62 of the housing18 (FIG. 3) and theheating element30 is buried into the thermal conducting material placed at the bottom58 of thechannel56.

InFIG. 6, theheat source24 has been fully installed, with only the second ends42 of the contact posts32a, bvisible, as extending from the bottom62 of thehousing18. Additional thermal conducting material, indicated at64, is then added into thechannel56, on top of theheating element30 to bury theelement30.

FIG. 6 also depicts the installation of the temperature-measuringdevice48. In the presently-illustrated embodiment,thermal insulator28 may include asecond channel66 to accommodate the temperature-measuringdevice48.Second channel66 may be disposed at an angle relative to thechannel56, e.g., substantially transverse as shown. Both

channels

56 and66 may extend beyondthermal insulator28 as needed, e.g., intohousing18 as shown.

The temperature-measuringdevice48 may be inserted into thesecond channel66 as shown, i.e., by moving thedevice48 into thechannel66 in the direction ofarrow68, such that it is embedded into the thermal conductingmaterial64. As a result, the temperature-measuringdevice48 andheat source24 will have the respective positions shown inFIG. 7 (the thermal conductingmaterial64 is not shown inFIG. 7 for clarity).

After installation of the temperature-measuringdevice48, additional thermal conductingmaterial64 is added on top of thedevice48, so that the material64 covers thedevice48 and fills the

channels

56,66. If desired, the thermal conductingmaterial64 may be mounded above the top of the

channels

56,66 to insure complete fill. The conductingmaterial64 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 conductingmaterial64 transforming intothermal conductor26. Any excess material may be removed by sanding, and the heat-seal contact surface44 may be alternatively or additionally polished to provide a desired degree of smoothness, e.g., to minimize the coefficient of friction between thesurface44 and the films to be sealed.

The result of the foregoing assembly process is the heat-seal device12 as shown inFIG. 2.

Referring back toFIG. 1, it may be seen that the temperature-measuringdevice48 may be brought into electrical communication withcontroller16 in the same manner as isheat source24, i.e., viasupport member14.Support member14 may thus be configured such thatsensing wire70aextends through the support member, and terminates atcontact pin72a, while sensingwire70bextends through the support member, and terminates atcontact pin72bas shown. Within heat-seal device12,thermocouple wire50 terminates at, and is electrically connected to,thermocouple contact74, which, as shown inFIG. 3, is positioned at the bottom62 ofhousing18, e.g., as a step in the assembly process for heat-seal device12. Similarly,thermocouple wire52 terminates at, and is electrically connected to,thermocouple contact76. 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 thesensing wires70a, b, by electrically connecting the

thermocouple wires

50,52 to the relatively large contact surfaces78,80, against which the contact pins72a, babut when the heat-seal device12 is inserted intosupport member14 as shown inFIG. 1.

Referring now toFIG. 9, a heat-sealing method in accordance with the present invention will be described.FIG. 9 illustratessystem10, as shown inFIG. 1, in a process for sealing a web of material, e.g., for sealing together two juxtaposed film plies82a, bvia a continuous longitudinal seal, e.g., at juxtaposed edges of the film plies to thereby form an inflatable orTillable packaging material85 with a closed longitudinal edge (closed edge not shown). As is conventional, film plies82a, bmay be supplied from separate film rolls84a, b. Sealing may be facilitated by providing abacking member86, which may be movable relative to heat-seal device12, or simply biased against the heat-seal device, such that film plies82a, bmay be compressed betweendevice12 andmember86 during sealing as shown.

The system may further include a conveyance mechanism for conveying a web of material to be sealed, e.g., juxtaposed film plies82a, b, against the heat-seal contact surface44 of heat-seal device12, 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 niprollers88a, b. As an alternative, the conveyance mechanism may be embodied by a single drive roller, which is used in place of backingmember86 to both drive the conveyance of the web and compress the web against the heat-seal device12.

In its most basic form, the method illustrated inFIG. 9 includes the steps of:

a. providing heat-seal device12;

b. causing theheat source24 to produce heat; and

c. bringing the heat-seal contact surface44 into contact with the material to be sealed, i.e., film ply82a, which is juxtaposed with film ply82bas shown. In this manner, as explained above, the heat produced byheat source24 transfers through thethermal conductor26 and into the film plies82a, bviacontact surface44 of heat-seal device12.

When the heat-seal device12 includes temperature-measuringdevice48, the foregoing method would include the further step of measuring the temperature within thethermal conductor26. Such method may be carried out bysystem10, as shown inFIGS. 1 and 9, whereincontroller16 is in operative communication with bothheat source24 and with temperature-measuringdevice48, i.e., viarespective wires34a, band70a, bas described above.Controller16 may thus be adapted, e.g., programmed, to:

1) receive input from temperature-measuringdevice48, which is indicative of the temperature ofthermal conductor26, and

2) send output to heatsource24, 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,controller16.

In this manner,controller16 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.Controller16 may thus include an operator interface90 (FIG. 9), e.g., a control panel, which allows an operator to select a temperature for thethermal conductor26. Alternatively,controller16 may be programmed with a mathematical algorithm that calculates the selected/target temperature, based on various factors such as film speed, film type, etc.

As may be appreciated, thecontroller16, temperature-measuringdevice48, andheat source24 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 thethermal conductor26 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 thecontroller16 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.Controller16 will thus maintain thethermal conductor26 at a temperature that falls within a range of the selected temperature.

Many types of controllers are suitable for use ascontroller16.Controller16 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 thethermal conductor26 to be controlled via local control, e.g., viaoperator interface90; remote control; pre-programmed control, etc.

Various modes of control may be employed bycontroller16, 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 ofthermal conductor26, e.g., a desired maximum degree of off-set between the set and actual temperature. The electrical power output to heatsource24 fromcontroller16 may be regulated via analog power control or digital power control, e.g., pulse width modulated power control.

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,controller16 may be adapted, e.g., programmed, to change the temperature of thethermal conductor26 based on changes in the speed at which the film web is conveyed.

As an example, the heat-seal device12 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 thedevice12 onshaft48 of the '911 apparatus such that the heat-seal contact surface44 of thedevice12 was urged into contact withdrive roller40 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 thecontact surface44 of thedevice12 and driveroller40 of the '911 apparatus. The film plies comprised polyethylene and had a thickness of about 0.75 mil.

Thedrive roller40 of the '911 apparatus was driven by a gear motor that included an encoder. A controller, similar tocontroller16 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.

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° 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.

Table 1 below is a summary of the resultant data:

TABLE 1

Film drive	Low temp	High temp	Temp	Calculated
speed	for good	for good	midpoint	temp:
(inch/min.)	seal (° F.)	seal (° F.)	(° 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

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.

There are several ways that the foregoing data can be used by the controller to determine the target temperature for the heat-seal device12. 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° F.

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.

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.

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 theheating element30 to the requisite target temperature, e.g., increase the temperature from 236° F. to 340° 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 device12 from burning through the film due to having too much heat for the slower speed.

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.