CA1281977C

CA1281977C - Controlled temperature film sealing apparatus

Info

Publication number: CA1281977C
Application number: CA 501497
Authority: CA
Inventors: Konrad Joseph Mrowiec
Original assignee: Polysar Ltd
Current assignee: Polysar Ltd
Priority date: 1986-02-10
Filing date: 1986-02-10
Publication date: 1991-03-26
Anticipated expiration: 2008-03-26
Also published as: NL8700308A; FR2594094A1; BE1001631A5; FR2594094B1

Abstract

CONTROLLED TEMPERATURE FILM SEALING APPARATUS
Abstract of the Disclosure An improved apparatus to form seals in flexible plastic polymer wrapping film is provided. The improved apparatus contains a controlled temperature heating wire which provides the heat required to form the seals. The temperature of the heating wire is controlled by a controller which responds to the electrical resistance of the heating wire. The apparatus is energy efficient in comparison to prior film sealing devices, and may be readily adjusted to provide suitable sealing conditions.

Description

7~

B~CKG~OUND OF_THE INVENTIUN
I~ is known to form sealed packages from flexible plastic film ~y sealing the film wit'n heat and pressure.
Some of the more important techniques to seal plastic film include:
1) "hot bar" or "jaw" sealing, 2) "impulse" sealing, 3) "rotary" sealing or "roller welding".
Hot bar or jaw sealing is a process in which plastic film is sealed under pressure between sealing bars (or "jaws"). At least one of the sealing bars is heated, usually with electric power. Normall~, either the temperature or the electrical power supplied to the apparatus is controlled. An apparatus supplied with a controlled, constant source of power may be described as a "constant heat" sealing device. Alternativelyg the temperature of the sealing bar may be the parame~er t'nat is controlled, and the sealing appara~us is thPn termed a "constant temperature" sealing apparatus. When the temperature is the controlled parameter, a sealing device of the prior art normally incorporates a separate temperature sensing device, such as a thermocouple, and a separate temperature controller. The ~h~rmocouple senses the temperature of the sealing bar and provides a feedback signal to the temperature controller. There is a time lag inherent in such a control scheme which tends to limit its effectiveness. In order to dampen the effect of the time lag, the sealing bar is often designed to be of substantial mass ~such as a heavy stèel bar). This causes the heated bar to function as a radiator, wasting heat into the working environment of the opera~or of the sealing device.
Impulse sealing is a film sealing process in which layers of plastic film are subjected to an impulse ~' of heat while being sealed under pressure betwe~n sealing bars. Heat is provided to the sealing bars only for a short period during the sealing cycle. One use of an impulse sealing device is in a packaging apparatus used to package bales o~ synthetic rubber with flexible plastic film. Using this apparatus, bales of synthetic rubber are pac~aged between two layers of plastic Eilm by sealing the layPrs of plastic film together with sealing bars constructed ~rom me~al tubing approximately 1/4" - 1/2" in dia~eter. An impulse of high current electricity is passed through the tubing ~o provide the heat used for sealing. A-fter the seal is formed, the sealing bars are cooled by flushing a cooling fluid, such as water or air, through tlle tubing. A large amount of energy is wasted into the cooling fluid and thus this apparatus is not highly energy efficient. Furthermore, the apparaLUS is prone to temperature fluctuations due to changes in the quality of the cooling fluid or changes in the ambient environment. The apparatus also is known to severely overheat if problems are encountered with the supply of cooling fluid.
Roller sealing or roller welding incorporates the use of pressure rollers to seal plastic film. The plastic film may be heated prior to being passed through the rollers or alternatively the rollers may be heated.
Temperature control systems, if incorporated into a rotary welding apparatus, normally contain an external thermocouple and feedback system.
The above film sealing techniques all require the application of heat and pressure to the plas~ic film to form a seal. The sealing devices are usually constructed from heavy materials capable of withstanding the rigorous heat and pressure conditions used in heat sealing processes.

~x~

The properties o~ the plastic used in the ~ilm can ~reatly a~fec~ the sealing operation. It is known that such characteristics as the molecular weight and crystallinity of the plastic af~ect the temperature at which the plastic ~ilm softens and the tem-perature at w~ich the plastic film degrades sufficiently to cause the film to fail. There is a ran~e of temperatures suitable for sealing plastic film, above t'ne temperature at which the plastic softens but below the temperature at which the plastic degrades. If tle sealing process is undertaken at too low a temperature, a proper seal will not be Eormed and the improper seal will break apart. If the sealing temperature is too high, the plastic fi'lm will s~ick to the sealing bar and/or be degraded rather than sealed.
The sealing time is also important. It is known that longer sealing tim~s are generally required at lower sealing temperatures. Alternatively stated, for a given sealing temperature and pressure, there is a minimum sealing time that is required for the film being sealed, or else the ~ilm will not become properly sealed.
The productivity o~ a film sealing apparatus, as measured by the number of seals formed, may obviously be improved by reducing the time required to form a seal.
However, a reduction in the sealing time normally must be accomp~nied by an increase in the sealing temperature because it is known that time required to seal the plastic is affected by the temperature of ~he sealing operation.
The increase in sealing temperature which accompanies the reduction in sealing time causes the sealing operation to be conducted at a temperature closer to the degradation temperature of the plastic. It is therefore apparent that excellent temperature control is required at minimum sealing times to ensure that the film is 'heated enough to form a seal but not subjected to a temperature that will degrade the plastic. Thus i~ is apparent that a film sealing apparatus that provides excellent control of the sealing temperature should be a useful addi~ion to the art.
OBJECT OF THE II~NENTION
It is an object of the invention to provide an improved apparatus for sealing flexible plastic polymer wrapping film. The improvement relates to the excellent temperature control achieved by the present apparatus.
SUMMARY OF THE INVENTION
__ There is provided an apparatus for sealing flexible plastic polymer wrapping film, which comprises:
(i) means for supplying an upper layer and a lower layer of said wrapping film to a sealing station;
(ii) means for film sealing comprising separately an upper component located above the upper layer o-f film and a lower componen-~ located below the lower layer of filmj (iii) wherein said upper component comprises a sealing bar, said sealing bar comprising a frame support, a high temperature resistant polymeric layer detachably attached to tne bottom of said support, a circular cross-section hea~ing wire detachably attached to essentially the centre of the bottom of said polymeric layer, and a high temperature resistant covering tape detachably at~ached to the frame support and covering the polymeric layer and the heating wire;
(iv) wherein said lower component of said film sealing means comprises a seal forming bar, sald seal forming bar matching the size and shape of said sealing bar of said upper component, said seal forming bar comprising a frame support and located on or within said frame support a high temperature resistant low compression set rubber _ 5 _ ~ ~7t7 bar, (v) means for supplying electrical power to said heating wire of said upper sealing bar, ~he electrical power supplied being controll2d by a controller to maintain an essentially constant pre-set tempera~ure of said heating wire by proportional supply of power in response to the electrical resistance of said heating wire;
(vi) means for moving said upper component of said film sealing means downwardly into contact with said lower component whereby the upper layer of film is ~rought into contact with the lower layer of film a~ the area for forming the seal, whereby the two layers of wrapping film are sealed together.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE l is a film sealing device according to the prior art;
FIGURE 2 is a side view of a film sealing 0 apparatus according to ~he presen~ invention;
FIGURE 3 is a side view of a preferred embodiment of the present invention;
FIGURE 4 is a top -view o-f the upper sealing component of a preferred em`bodiment of the present invention;
FIGURE 5 is a sectional view of the transve:rse sealing bar of the upper component of a preferred embodiment of the present invention;
FIGURE 6 is a top view of the lower sealing component of a preferred embodiment of the present invention;
FI&URE 7 is a sectional view of ~he transverse sealing bar of the lower component of a preferred embodiment of the present invention.

'7 DETAILED DESCRIPTION OF THE _NVENTION
The heat for the sealing apparatus of the present lnvention is provided by a controlled temperature electrical resistance heating wire. By careful choice of the material of constructlon, the electrical resistance of the wire in the heating wire is a known function of the temperature of the heating wire. rne electrical resistance of the heating wire is used as a control signal by a controller whlch controls the electrical resistance.
As the elec~rical resistance is a known func~ion of the temperature, the temperature oE the wire may be indirectly controlled by using a suitable controller to directly control the electrical resistance. Thus the control signal to the controller comes directly from changes in the electrical resistance of the heating wire. This eliminates the use of an e~ternal sensing device, such as a thermocouple, to provide control signals. By eliminating the requirement for a separate temperature sensing device~ excellent feedback response to the controller is obtained such that the temperature of the heating wire may be controlled to an essentially constant temperature.
~ le heating wire may be constructed -from a relatively light gauge wire. This is an advantage as the heating wire has a relatively low radiant heat loss in comparison to the more massive steel sealing bars used in the sealing devices of ~he aforesaid prior art.
The use of a change in electrical resistance to provide a control signal for a controlled temperature wire 30 heater is known. For example, ~atlow Winona, Inc.
manufactures a controlled temperature heating wire of ~his type, which is suitable for use in the appara~us of the present invention. This controlled temperature heating wire device has been previously used to trace piping to ~X~9~

prevent ~e pipes from freezing in cold ~eather. It 'nas also been used ~o control the ~emperature oE fluid ~ontained in a storage vessel, but :it has not previously been used in an apparatus to seal plastic film.
One type of con~rolled temperature heating wire manufactured by Watl~w Winona Inc. is capable of maintaining temperature control in the heater wire to within about +1/2% of the temperature scale of the heater. A heater of this type with a 0 to 600~F
~o temperature scale is suitable for the apparatus of the presellt invention.
The apparatus of the presen~ invention may be used to form seals between two layers of flexible plastic film by bringing the layers o~ film into contact with one anotl~er between the sealing components of the apparatus under suitable conditions of pressure and temperature.
Suitable conditions of pressure and temperature are those conditions which form a satisfactory seal during t'ne time period of the sealing step.
Suitable conditions for specific film are normally not known to the operator of the apparatus until some trial and error sealing step attempts have been made.
The apparatus of the present invention allows the operator to establish suitable conditions as follows. The sealing time and pressure are set by the operator and then are held constant for each seal forming step. (The pressure and sealing time controls of sealing machines known in the art are adequate to provide reasonably reproducible sealing time and pressure between different seal forming steps). The operator estimates a suitable sealing temperature for the film being sealed and sets ~he temperature o the controlled temperature heating wire of the present apparatus accordingly. ~1 attempted sealing step is then made. If the seal is too weak or incomplete, the opera~or increases the sealing temperature ~or the next attempt by increasing the temperature of t~e controlled temperature heating wire. Conversely, if the plastic film is degraded, the operator decreases the sealing temperature for the next attempt by decreasing t1ne temperature o-f the controlled ~emperature sealing wire.
It will be apparent that adjustable tempera~ure control of the sealing temperature will thus help ~o establish suitable sealing conditions. It will be further apparent that reproducible sealing control, in cooperation with reproducible time and pressure control, will contribute to the formation of reproducible sealing steps.
An apparatus used to seal plastic film is subject to strenuous operating conditions due to the heat and pressure required for forming seals. Thus i~ is necessary to protect the heating wire from being damaged during the sealing process. Through experimentation, it has been determined that the heating wire used in the apparatus of the present invention may be reasonably well protected from damage by using a low compression set rubber mat~rial in the construction of at least one of the sealing bars.
Figure 1 illustrates a schematic drawing showing a film sealing device of the type known in the art.
~ayers of plastic film (1 and 1') are sealed between heated sealing bars (2) and (3).
Figure 2 is a schematic drawing showing a side view of one embodiment of the apparatus of the present invention. Two layers of flexible plastic polymer wrapping film (10 and 10') are supplied to the sealing station9 one supplied below the upper sealing component and the other supplied above the lower sealing component.
The upper seallng component is a sealing bar which comprises a frame support (11), a high temperature resistant polymeric layer (12) detachably attached to the _ 9 _ bot~om of said support (11), a circular cross-section heating wire (13) detachably attached to essentially the centre of -~'ne bottom of said polymeric layer (12) and a high temperature resistant covering tape (14) detachably attached to said frame support (11) and covering sald polymeric layer (12) and said heating wire (13).
Polytetrafluoroethylene (PTFE) and fiberglass are suitable materials of construction Eor said high temperature resistant tape (14). Fiberglass bar stock is a suitable material of construction for said high temperature resistant polymeric layer (12).
Said heating wire (13) is connected to means t~
supply electrical power such that the electrical power supplied to said heating wire (13) is controlled by a controller (17) to maintain an essentially constant pre-set temperature of said heating wire (13) by proportional supply of power in response to the electrical resistance of said heating wire (13). The temperature of said heating wire (13) may be adjusted by adjusting the set point on the controller ~17).
The lower sealing component matches the size and shape of said upper sealing component. Said lower sealing component is a seal forming bar which comprises a frame support (16) and located on or wlthin said frame support a high temperature resistant low compression set rubber bar ~15). Silicone rubber is a preferred material of construction for said bar (lS). It is preferred that said lower frame support (16) and said upper frame support (ll) be constructed from a material of sufficient stiffness to prevent gross distortion during the sealing process~
Metal channel, such as steel or aluminum channel, is an excellent material of construction for said frame support (11 and 16~.
It should be apparent to a person skilled in the ~2~ 7 art that the relatively simple procedures used to construct the sealing bars of the present apparatus have several advantages, including ease of construction and ease of repair.
Suitable means are requi-red to move the sealing bars together, thus sealing the layers of plastic film together with heat from the controlled temperature heating wire ~13) and pressure from the sealing bars. It is apparent to a person skilled in ~he art that the upper sealing bar may be moved downwardly or the lower seal forming bar may be moved upwardly or the two sealing bars may both be moved towards each other to achieve the desired result. Known means to move the sealing hars together are suitable for the present apparatus. For example, the mechanical means used to move the sealing components of a known device to package synthetic rubber are suitable for the present apparatus.
It ~ill be apparent to a person skilled in the art that ~he sealing device of the present invention may be readily incorporated into some of ~he sealing devices of the prior art. This may be done, for example, by replacing the "jaws" o~ a jaw sealer or the impulse bars of an impulse sealing device of the prior art with the aEoresaid upper sealing component, lower sealing component and temperature controlled heating wire of the present invention. Thus, a sealing device of the prior art may ~e retrofitted with the present invention to produce a sealing device with e~cellent temperature control. The relatively simple construction procedures used to fabricate the present sealing device allow such "retrofits" ~o be easlly completed.
Figures 3, 4, 5~ 6 and 7 illustra~e a preferred embodiment of the present invention which is suitable ~or enclosing produc~ into a sealed package o~ flexible plastic film. Bales oE synthe~ic rubber may suita'bly be packaged with this apparatus.
Figure 3 illustrates a side view of said apparatus. Suitable means (20 and 20') supply 1exible plastic film to the wrapping station. The lower layer of plastic film (21) is supplied 'below the product to be wrapped but above the lower sealing component and the upper layer of plastic film (22) is supplied above the location of the product to be wrapped but below the lower sealing component.
Conveyor means (23) convey the product to the wrapping station such tha~ the product is conveyed to a position located essentially centrally above the lower layer of film. (Conveyor means 23' convey the package forwardly out of the wrapping station.) ~ e upper sealing component comprises, sequentially in the dlrection of movement of the product to be packaged, a transverse sealing bar (24) of suEficient leng~h to provide ~he forward seal of the sealed package, and spaced forward of said transverse sealing bar (24) a wrapping film cu~ting means (25) and spaced forward of said cutting means a second sealing bar (26) shaped such as ~o provide the remainder of the seal in con~unction with said forward seal. The sealing bars are further described below.
The lower sealing component comprises, sequentially in the direction of movemen~ of the product to be packaged, a ~ransverse seal -forming bar (27) and forward of sa~d transverse seal forming bar (27), a second seal forming bar (28), 'both said seal forming bars matching the size and shape of said sealing bars of said upper sealing componen~.
Means are provided (29) fo-r moving said upper component of said apparatus downwardly into contact with said lower component whereby the upper layer of film is brought about ~he product to be wrapped and into contact with the lower layer of film at the area for forming a seal, whereby the two layers of wrapping film are sealed together about the product to be wrapped. Known means for moving said upper component are sui~able for the apparatus of the present invention. For example, the means for moving the components of t'ne film sealing devic~s of the prior art are suitable for the present apparatus.
Figure 4 is a top view showing only the upper sealing component. The upper sealing component comprises a transverse sealing bar (24), a second sealing bar (26) and film cutting means (25). ~e transverse sealing bar (24) is of sufficient length to provide the forward seal of the sealed package. The plastic film cutting means ~25) are of a type well known in the art. A hot wire is suitable for said plastic film cutting means.
Figure 5 is a view through a section of the transverse sealing bar (24) of the upper component at the plane represented by a-a' in Figure 4. Figure 5 also represents a view through a section oE the second sealing bar (26) of the upper component at the plane represented by b-b' in Figure 4. A high temperature resistant polymeric layer (34) is detachably attached to a frame support (35). Fiberglass bar stock is suitable for said polymeric layer (34). Heating wire ~36) is detachably attached to essentially the centre of the bottom of said polymeric layer (34). A high temperature resistant tape ~37) is detachably attached to the frame suppor~ (35) and covers the polymeric layer (34) and the heating wire (36).
The electrical resistance of the temperature heating wire (36) is a known function of the temperat-ure of the heating wire (36). The heating wire is connected to means to supply electrical power such that the electrical power supply is controlled by a controller to - 13 ~

maintain an essen~ially constan~ pre-set temperature in said heating wire ~35) by proportional supply of electrical power in response to the electrical resistance of said heating wire (36). The heating wire temperature may be adjus~ed by adjusting the se-t point temperature on tne controller.
Said frame support is constructed from a mat~rial of suitable s~iffness to prevent gross distortion during the sealing operation. Metal c'nannel, such as steel or ~luminum channel, is a preferred material for said frame support (35). PTFE or fiberglass is a suitable material o construction for said high temperature resistant tape (37).
Figure 6 is a top view of the lower sealing component of Figure 3. The lower sealing component comprises a transverse seal -forming bar (27) and a second seal forming bar (28). The seal forming bars of the lower sealing component match the size and shape of the sealing bars of the upper sealing component. Thus the transverse seal forming bar (27) of the lower sealing component cooperates with ~he transverse sealing bar of the upper sealing component to provide the forward seal of a sealed package. Similarly, the second seal forming bar (~8) o-f the lower sealing component cooperates with the second sealing b~r o the upper sealing component to form a seal which is the remaining part of a sealed package (in conjunction with the forward seal).
Figure 7 is a cross-section view through transverse seal forming bar (27) o the lower component at the plane represented by y-y' in Figure 6. Flgure 7 also represents a cross-section view ~hrough the second seal ~orming bar (28) of the lower sealing component at the plan represented by z-z' in Figure 6. A high temperature resistant low compression set rubber (43) is detachably attached to support frame means (44). Low compression set silicone rubber is a suitable material for said layer of high temperature resistant material (43). Said support ~rame means ~44) is constructed ~om a material of sufficient stiffness to prevent gross distortion during the application of pressure during the sealing process.
~letal channel, especially steel or aluminum channel, is a suitable material of construction for said support ~ame means (44).
The film sealing apparatus shown in Figures 3, 4, 5, 6 and 7 may be conveniently described as a film wrapping station. This film wrapp;ng station may be used in a process to enclose a produc~ into a sealed package of flexible plastic polymer wrapping film.
The process of forming an enclosed package with said film wrapping station starts with t'ne formation of a straight seal in the film. The product is then introduced into tl~e wrapplng sta~ion. A second seal, which cooperates with the initial straight seal to form a 20 package which encloses the product, is then formed. The film is cut between the enclosed package and the straight seal and then the package is removed from the wrapping station.
The process may be e~plained in more de~ail by referring to Figure 4. The shape of the seals formed during each sealing step corresponds to the shape of sealing bars 24 and 26. T~e film is cut be~ween the seals by film cutting means 25 during each sealing step.
One set of seals is formed before the first 30 package is made. Two layers of plastic film are inserted into the film wrapping station in the direction moving from right to left (with reference to Figure ~) and then the layers of film are sealed. The film to t~e let of film cut~ing means 25 is removed from the film wrapping '~

station, but thP straight seal formed in the s'nape of sealing bar 24 remains. Thus, the first set of seals formed produces only one useful seal, namely the straight seal .
Subsequently formed seals are all utllized, as explained below. Product is then conveyed into the film wrapping station, again moving in a right -~o left direction (with reference to Figure 4). The product pushes against tne straight seal, thus drawing the two 10 lnyers o wrapping film into the wrapping station suC'LI
that the straight seal is -forward of the product. Thus the straig~t seal formed during the previous sealing step becomes the Eorward seal of the sealed package. Seals are then formed wi th the product in the wrapping s tation . The seal shaped according to sealing bar 26 cooperates wit'n tl~e straight seal formed during the previous step to form a package which encloses the product. Simultaneously, a straight seal is formed, behind the package, in the shape oE sea`ling bar 24. This straig'nt seal will become the 20 forward seal of the next package. The :Eilm cutting means ~5 cuts the film between the package and the straight seal. The enclosed package is then forwardly removed from the film wrapping station, leaving behind the straighc seal. Conveyor means are suitable for removing -the enclosed package from the wrapping station.
It is important to note tnat the s traight seal formed during each sealing cycle becomes the orward seal for the following enclosed package. Means are t~erefore required for bringing the two layers~of film having the 30 forward seal formed into the wrapping station. This may be simply done by conveying the product into t'ne wrapping s tation such that the product pushes agains t the s trai ght seal and the movement of the product draws the two layers of film into the wrapping station such that the straight seal ls forward of the product.
Polyethylene is a commonly used material for said flexible plastic polymer wrapping ~ilm. Other sui~able materials include poly(ethylene vinyl acetate), polystyrene and polybutadiene.
Example The film sealing apparatus illustrated in Figures 2, 3, 4, 5 and 6 is used in a process to package synthetic rubber with flexible plastic film.
To start the process, two layers of flexible plastic polyethylene film, approximately 1.7 mil thick, are provided to the wrapping station. The temperature of the controlled ~emperature heating wire is set at 175C.
The upper and lower sealing components are brought together so that a pressure of approximately 40 pounds per square inch is exerted between the sealing bars, for a period oE 0.5 seconds, thus sealing the film. The cutting means cuts the sealed plastic film between the seal formed by the transverse sealing bars and the seal -Eormed by the second sealing barsO ~le result is that the film is sealed together only at the seal formed by the transverse sealing bar. The plastic film ahead of the seal formed by the transverse bars is removed by the operator of the packaging apparatus, thus leaving the two layers of plastic film ~oined together by the seal formed by the transverse sealing bars.
A bale of rubber is then conveyed into the wrapping station. Ihe rubber bale pushes the film into the wrapping station such that ~he seal from ~he initial step becomes the forward seal of the package, ahead of the rubber bale. The sealing and cutting components are then brought together again in the manner described above. The second sealing bars form a sealed plastic film package around the rubber bale, in cooperation with the front seal formed by the initial sealing step. rne transverse sealing bars form a seal behind the packaged rubber baleg which will become the forward seal of the next package.
Simultaneously, t~e cutting means cut ~he plastic film betw~en the packaged rubber bale and the seal formed by the transverse sealing bar. The packaged rubber bale is then conveyed out of the wrapping station9 leaving the plastic fi.lm sealed together only a~ ~he seal ~ormed by the transverse sealiLlg bars. The process described in thLs paragraph may -then be repeated to form further packages.

Claims

1. An apparatus for sealing flexible plastic polymer wrapping film, which comprises:
(i) means for supplying an upper layer and a lower layer of said wrapping film to a sealing station;
(ii) means for film sealing comprising separately an upper component located above the upper layer of film and a lower component located below the lower layer of film;
(iii) wherein said upper component comprises a sealing bar, said sealing bar comprising a frame support, a high temperature resistant polymeric layer detachably attached to the bottom of said support, a circular cross-section heating wire detachably attached to essentially the centre of the bottom of said polymeric layer, and a high temperature resistant covering tape detachably attached to the frame support and covering the polymeric layer and the heating wire;
(iv) wherein said lower component of said film sealing means comprises a seal forming bar, said seal forming bar matching the size and shape of said sealing bar of said upper component, said seal forming bar comprising a frame support and located on or within said frame support a high temperature resistant low compression set rubber bar, (v) means for supplying electrical power to said heating wire of said upper sealing bar, the electrical power supplied being controlled by a controller to maintain an essentially constant pre-set temperature of said heating wire by proportional supply of power in response to the electrical resistance of said heating wire;
(vi) means for moving said upper component of said film sealing means downwardly into contact with said lower component whereby the upper layer of film is brought into contact with the lower layer of film at the area for forming tile seal, whereby the two layers of wrapping film are sealed together.

2. An apparatus for enclosing product into a sealed package of flexible plastic polymer wrapping film, which comprises:
(i) means for supplying two layers of said wrapping film to a wrapping station, a lower layer of said film being supplied below the location of the product to be wrapped and an upper layer of said film being supplied above the location of the product to be wrapped, (ii) means for forwardly conveying product to the wrapping station whereby product is essentially centrally located on top of the lower layer of film;
(iii) means for film sealing and cutting comprising separately an upper component located above the upper layer of film and a lower component located below the lower layer of film;
(iv) wherein said upper component comprises, sequentially in the direction of movement of the product to be packaged, a transverse sealing bar of sufficient length to provide the forward seal of the sealed package, spaced forward of said transverse sealing bar a wrapping film cutting means, and spaced forward of said cutting means a second sealing bar shaped such as to provide the remainder of the seal in conjunction with said forward seal, said sealing bars comprising a metal frame support, a high temperature resistant polymeric layer detachably attached to the bottom of said support, a circular cross-section heating wire detachably attached to essentially the centre of the bottom of said polymeric layer, and a high temperature resistant covering tape detachably attached to the metal frame support and covering the polymeric layer and the heating wire;
(v) wherein said lower component of said film sealing and cutting means comprises, sequentially in the direction of movement of the product to be packaged, a transverse seal forming bar and forward of said transverse seal forming bar a second seal forming bar, both said seal forming bars matching the size and shape of said sealing bars of said upper component, said seal forming bars comprising a metal frame support and located on or within said metal frame support a high temperature resistant low compression rubber bar, (vi) means for supplying electrical power to said heating wires of said sealing bars, the electrical power supplied being controlled by a controller to maintain an essentially constant pre-set temperature of said heating wire by proportional supply of power in response to the electrical resistance of said heating wire;
(vii) means for moving said upper component of said film sealing and cutting means downwardly into contact with said lower components whereby the upper layer of film is brought about the product to be wrapped and into contact with the lower layer of film at the area for forming the seal, whereby the two layers of wrapping film are sealed together about the product to be wrapped, whereby the two layers of film are cut by said cutting means, and whereby the two layers of film are sealed together by the transverse sealing bar to form the forward seal for the next package; and (viii) means for forwardly removing the sealed package from the wrapping station and bringing the two layers of film having the forward seal formed forward into said wrapping station.

3. A process for forming seals in flexible plastic polymer wrapping film using the apparatus of Claim 1 wherein:
(i) said upper layer and said lower layer of said wrapping film are supplied to said apparatus such that said upper component is located above said upper layer of film and said lower component is located below said lower layer of film, and (ii) the temperature of said heating wire is controlled at an essentially constant pre-set temperature, and (iii) the upper component of said apparatus is moved downwardly into contact with said lower component whereby the upper layer of said wrapping film is brought into contact with said lower layer of said wrapping film and whereby the two layers of film are sealed together.

4. A process for enclosing product into a sealed package of flexible plastic polymer wrapping film using the apparatus of Claim 2 wherein:
(i) said upper layer and said lower layer of said wrapping film are supplied to said apparatus such that said upper component is located above said upper layer of film and said lower component is located below said lower layer of film, and (ii) the temperature of said heating wire is controlled at an essentially constant pre-set temperature, and (iii) the upper component of said apparatus is moved downwardly into contact with said lower component whereby the upper layer of said wrapping film is brought into contact with said lower layer of said wrapping film and whereby the two layers of film are sealed together to form a straight seal and a second seal and whereby the film is cut between the straight seal and the second seal with said film cutting means, and (iv) the film located forward of the straight seal is removed from wrapping station, and (v) said product is conveyed into said apparatus such that said product pushes said layers of film forward into said apparatus such that said straight seal is forward of said product and such that said product is essentially centrally located on top of said lower layer of film, and (vi) the upper component of said apparatus is moved downwardly into contact with said lower component whereby the upper layer of said wrapping film is brought into contact with said lower layer of said wrapping film and whereby the two layers of film are sealed together about the product to be wrapped and whereby the two layers of film are sealed together by said transverse sealing bar to form a straight seal which becomes the forward seal of the next package and whereby the two layers of film are cut by said cutting means, and (vii) the sealed package is removed from said apparatus, and (viii) steps (v), (vi) and (vii) are repeated to form subsequent sealed packages.