BACKGROUND OF THE INVENTION

The present invention relates generally to methods of forming, filling and sealing polymer bags or packages, and particularly to a form-fill-seal method which is capable of significantly increasing the rate of production for polymer films having a characteristically narrow temperature range over which a seal may be made.

For purposes of economy, packaging machines are typically employed to automate the form-fill-seal process. From a production viewpoint, it is advantageous to make as many packages in as short of time as possible when the machine is in operation. Ultimately, in a mass production environment, the unit cost of each package produced can be reduced if a way can be found to increase the rate of production without incurring any loss in the quality of the packages being produced.

In this regard, the type of polymer material used to form the package may affect the rate of production. For example, if the polymer chosen may only be sealed over a relatively narrow range of temperatures (e.g. , 10-15° F) , then the process time will be considerably slower when compared with other polymer materials which may be sealed over a broader temperature range (e.g., 20-50° F) . This is because the application of heat to adjacent layers of the polymer must be carefully controlled to soften, but not melt or burn the polymer layers in order to achieve a reliable and uniform seal.

Polyvinyl alcohol is one example of a polymer film which has a narrow temperature range (10-15° F) over which a seal may be made. Indeed, it should be noted that this temperature range is not necessarily constant from one batch of polyvinyl alcohol film to another. In this regard, it has been found that the narrow heat sealing range for polyvinyl alcohol film will vary over the broader temperature range of 310-360° F.

Polyvinyl alcohol film is particularly applicable to some forms of packaging due to its water soluble character. Thus, for example, polyvinyl alcohol films have been advantageously used as a packaging material for agricultural chemicals intended to be mixed or diluted in water. Since the polyvinyl alcohol film package will dissolve in water, there is no need for anyone to come into direct contact with the chemical itself. Only the polyvinyl alcohol film package needs to be handled by those distributing or applying the chemical contained in the package.

In one specific application involving polyvinyl alcohol film packaging, 4 oz. packages were formed, filled and sealed with a powdered insecticide using commercial form-fill-seal machine technology. Specifically, the polyvinyl alcohol film was formed into a cylinder where the vertical edges of the film overlapped each other and heat was applied on only one side of the film to seal this overlapping edge. However, the maximum production rate that could be achieved was on the order of 15-17 packages per minute. While this rate may appear to be reasonably rapid, in a mass production environment, this production rate is well below that which can be achieved using polymers having a broader temperature range over which a seal may be made. Accordingly, the need exists to provide a more rapid method of forming, filling and sealing packages using polymers having a narrow heat sealing range.

Thus, it is a principal objective of the present to provide an improved form-fill-seal method which is capable of more than doubling the production rate when polymer materials are used which have a narrow heat sealing range.

It is a further objective of the present invention to provide an improved form-fill-seal method which achieves a substantial increase in the production

rate without burning the polymer material or otherwise adversely affecting the integrity of the seal being made. It is a more specific objective of the present invention to provide a form-fill-seal method which is particularly advantageous for use with polymer films, such as polyvinyl alcohol.

SUMMARY OF THE INVENTION

To achieve the foregoing objectives, the present invention generally comprises a method which first forms a continuous polymer film sheet into a cylindrical shape such that the opposite ends of the film are disposed adjacent to each other so as to create a radially extending fin along the longitudinal axis of the package being formed. This cylindrical shaped film is formed coaxially over a tube through which the desired filling material will enter the package being formed. Pressure is applied to the fin along the longitudinal axis of the package by a pair of sealing blocks to force the opposite end of the film into engagement, such that a generally flat sealing surface is formed. A predetermined amount of heat is applied to both sides of this fin, concomitantly with the application of pressure, for a period of time which is sufficient to soften and bond the opposite ends of the film together. The bottom end of cylindrical package is then sealed as the film is drawn downwardly to align the film for the next package with the pair of sealing blocks. The package may also be filled as the film is drawn downwardly or filled immediately thereafter. Finally, the top end of the package is sealed, and a cut is made above this top end seal to separate the package from the next package being formed.

In one method according to the present invention, both of the vertical or longitudinal sealing blocks are heated to the same extent, so that the same amount of heat is applied to both sides of the longitudinal fin. With

the use of polyvinyl alcohol film for the packaging material, production rates on the order of 38-40 packages per minute have been achieved under the method according to the present invention. Additional advantages and features of the present invention will become apparent from a reading of the detailed description of the preferred embodiment which makes reference to the following drawing.

BRIEF DESCRIPTION OF THE DRAWING Figure 1 is a diagrammatic perspective view of a portion of a form-fill-seal apparatus capable of being used with the method according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to Figure 1, a diagrammatic representation of the relevant portion of a form-fill- seal machine 10 is shown. In this regard, Figure 1 is intended to provide a generalized representation of a vertical draw-pull type of form-fill-seal machine which is particularly useful with the method according to the present invention. One example of a specific machine of this type is a model 175 NEL, No. 7011 vertical form- fill-seal machine by Robert Bosch Corporation, South Plainfield, New Jersey. However, it should be appreciated that the method according to the present invention may be utilized with a variety form-fill-seal machines which is capable of fulfilling the requirements of this method.

It this regard, the machine 10 includes a forming tube 12 and a forming shoulder 14 for converting a continuous sheet of polymer material 16 into a specific cylindrical shape. The machine 10 also includes a filling tube 18 which is coaxially disposed within the forming tube 12 along a vertical or longitudinal axis. A funnel 20 is connected to the top of the filling tube 18 to assist the feeding of the desired filler material into the

filling tube and ultimately into the package being formed. One of the preferred requirements of the machine 10 is that the polymer sheet 16 will be formed into a cylinder having a radially extending fin 22 along the vertical or longitudinal axis. This vertical fin is opposed to a cylindrical form in which the vertically extending ends of the polymer sheet 16 overlap each other circumferentially so as to permit the application of heat to only one side of these overlapping layers. Hie radially extending fin 22 is formed by the engagement of the two opposite vertical ends of the polymer sheet 16 so as to create a generally flat sealing surface having a width of at least 5 millimeters and preferably 10 millimeters. This radially extending fin 22 advantageously permits the application of heat to both of the opposing layers of the polymer sheet 16. In one form of the present invention, the polymer sheet 16 is a polyvinyl alcohol film (2004 X) from Polymer Films Inc. , Rockville, Connecticut. In this regard, this particular polyvinyl alcohol film has a shiny side and a dull side, and it is preferred that the shiny side form the interior of the package being created. This is because the shiny side of the polyvinyl alcohol film is more smooth in comparison with the dull side, and thereby provides a better surface for creating the necessary seal.

As shown in Figure 1, the machine 10 includes a pair of vertical sealing blocks 24-26, which are used to apply a predetermined amount of heat to both sides of the fin 22. While the construction of the sealing blocks 24- 26 may be varied in accordance with the application, it is preferred that they be provided with a nichrome resistance heating element or ribbon for the purpose of controlling the heat applied to the fin 22. Any suitable actuation mechanism, such as pneumatic cylinders, may be used to bring the sealing blocks 24-26 into and out of engagement with the fin 22. In this regard, it should be appreciated

that the closing of the sealing blocks 24-26 into engagement with the fin 22 will apply pressure to the fin along the longitudinal axis to force the opposite ends of the film into engagement, while at the same time applying heat in a predetermined temperature range to both the opposite sides of the fin. Generally speaking, in accordance with the present invention the concomitant application of pressure and heat to the fin 22 will take less than one second to soften the opposite ends of the polymer sheet 16 and permit a uniform and reliable bond to be created, and thereby seal the vertical side of the package. Once this sealing step is completed, the machine 10 will draw the polymer sheet 16 down so that a pair of horizontal sealing blocks 28-30 may be used to seal the bottom of the package being formed, as well as seal the top of the package in a subsequent step. In this regard, each of the sealing blocks 28-30 include a pair of heating surfaces 32-34 and 36-38 to seal the top and bottom ends of adjacent packages. At least one of the sealing blocks 28 is also provided with a cutting mechanism, such as knife 40 for separating a completed package from the next package being formed.

In order to maximize the rate of production, the sealing blocks 28 and 30 are used to engage the vertically sealed polymer sheet 16 in order to pull the polymer sheet downwardly while performing the necessary sealing steps. As the polymer sheet 16 is being pulled downwardly, the desired filling material may be permitted to flow through the funnel 20 and the filling tube 18 into the package being formed. Once the filling step has been completed, the horizontal sealing blocks 28 and 30 may be moved upwardly to engage the next portion of the vertically sealed polymer sheet 16 to seal the top end of the package just filled and the bottom end of the next package being formed. These steps are then repeated in rapid succession to produce a multiplicity of completely sealed packages at

a desired production rate.

It should be appreciated from the above, that both the top and bottom seals of the package, as well as the vertical seal for the package are all created by the application of heat to both sides of the adjacent layers of the polymer sheet used as the packaging material. Preferably, the heat applied to all three of these sealing surfaces should be uniform across the sealing surfaces and at the same temperature within the narrow heat sealing range for which the seal may be made. The specific sealing temperature employed will, of course, be dependent upon the polymer material being used as the packaging material. However, with the use of nichrome resistance heating elements, the temperature of the heat being applied to the sealing surfaces may be carefully controlled to provide a constant temperature for each of the packages being created. In one method according to the present invention, a momentary blast of air is applied to the areas being sealed immediately after the sealing blocks have opened to avoid stretching of the polymer material. In this regard, a tube may be provided with a series of lateral holes formed along the tube to permit air to be directed onto the recently sealed area. As well known in the art, a copper coating may also be applied to the portions of the nichrome resistance heating elements which extend beyond the length of the sealing surfaces.

The embodiment which has been set forth above is for the purpose of illustration and is not intended to limit the invention. It will be appreciated by those skilled in the art that various changes and modifications may be used to the method described in the specification without departing from the spirit and scope of the invention as defined by the appended claims.