NZ628728B - Method of manufacturing flexible plastic film - Google Patents

Abstract

method of manufacturing a flexible plastic film is disclosed. Plant for forming very wide plastic films is expensive and not widely available. If wide sheets are required they may be formed by joining smaller sheets rather than producing the wide sheet in one process step. The method comprises the steps of: i) Forming a length of first primary film (26) by a blown film extrusion process, wherein the first primary film comprises a first layer (26a) and a second layer (26b); ii) Forming a length of second primary film by a blown film extrusion process, wherein the second primary film comprises a first layer (26c) and a second layer (26d) ; and iii) Connecting an outer edge (24) of the second layer of the first primary film to an outer edge of the first layer of the second primary film by a substantially continuous heat sealing operation to form a secondary film having four layers, creating a join (25). steps of: i) Forming a length of first primary film (26) by a blown film extrusion process, wherein the first primary film comprises a first layer (26a) and a second layer (26b); ii) Forming a length of second primary film by a blown film extrusion process, wherein the second primary film comprises a first layer (26c) and a second layer (26d) ; and iii) Connecting an outer edge (24) of the second layer of the first primary film to an outer edge of the first layer of the second primary film by a substantially continuous heat sealing operation to form a secondary film having four layers, creating a join (25).

Description

METHOD OF MANUFACTURING FLEXIBLE PLASTIC FILM The present invention relates to a method of manufacturing flexible plastic films, and in particular, but not exclusively, to a method of manufacturing heavy duty multi-panel shrink wrap film.

Background There is an increasing requirement in New Zealand for the use of heavy duty plastic heat shrink film to wrap and/or protect large objects, up to and including residential and industrial building projects. This film is typically monolayer polyethylene, with the largest common size sheeting being around 12 metres wide, around 33 metres in length, and around 250 microns (µm) thick.

To date the majority of this product has been imported because it is beyond the size capacity of New Zealand blown film extrusion manufacturers.

It would be advantageous to create a method for producing heavy duty heat shrink film or other film which has relatively large overall dimensions, but which can be manufactured using blown film machinery which is capable only of manufacturing film sheets having a width which is much less than the required width of the film.

The reference to any prior art in the specification is not, and should not be taken as, an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge in any country.

Object of the Invention It is an object of a preferred embodiment of the invention to provide a method of manufacturing a flexible plastic film and/or a flexible plastic film manufactured by that method which will overcome or ameliorate problems with such methods or films at present, or at which will at least provide the public with a useful choice.

Other objects of the present invention may become apparent from the following description, which is given by way of example only.

Brief Summary of the Invention According to one aspect of the present invention there is provided a method of manufacturing a flexible plastic film comprising the steps of: i) Forming a length of first primary film by a blown film extrusion process, wherein the first primary film comprises a first layer and a second layer; ii) Forming a length of second primary film by a blown film extrusion process, wherein the second primary film comprises a first layer and a second layer; iii) Connecting an outer edge of the second layer of the first primary film to an outer edge of the first layer of the second primary film by a substantially continuous heat sealing operation to form a secondary film having four layers.

Preferably the first and second primary films are arranged in a centrefold configuration.

Preferably the connection between the second layer of the first primary film and the first layer of the second primary film is a flange type joint.

Preferably the method comprises connecting an outer edge of a fourth layer of the first secondary film to an outer edge of a first layer of a third primary film by a substantially continuous heat sealing operation, to thereby form a tertiary film having six layers.

Preferably the method comprises dividing the secondary film into a first length of secondary film and a second length of secondary film and connecting an outer edge of a fourth layer of the first secondary film to an outer edge of a first layer of the second secondary film by a substantially continuous heat sealing operation, to thereby form a tertiary film having eight layers.

Alternatively, the method comprises repeating steps i) to iii) to form a second secondary film having four layers and connecting an outer edge of a fourth layer of the first secondary film to an outer edge of a first layer of the second secondary film by a substantially continuous heat sealing operation, to thereby form a tertiary film having eight layers.

Preferably the first primary film and the second primary film comprise polyethylene.

Preferably the first and second primary films have a blow up ratio of at least 1.3:1, more preferably at least 2:1.

Preferably the method comprises forming a heat seal having a width of between 1mm and 15mm, more preferably between 6mm and 9mm.

Preferably each said heat sealing operation occurs at between 150°C and 220°C, more preferably between 190°C and 200°C.

Preferably each said layer is between 100 µm and 300 µm thick, more preferably substantially 250 µm thick.

Preferably each said layer is between substantially 1 and 2m wide, more preferably substantially 1.6m wide.

Preferably step i) comprises winding the first primary film onto a first reel.

Preferably step ii) comprises winding the second primary film onto a second reel.

Preferably step iii) comprises mounting the first reel above the second reel.

Preferably one or more of the primary films may be coloured or the film may be printed.

According to second aspect of the present invention, a method of manufacturing a multi-panel flexible plastic film is substantially as herein described with reference to Figures 1 to 6, Figures 1 to 8, or Figures 1 to 6 and Figure 9.

According to a third aspect of the present invention there is provided a film manufactured by the method of the first aspect or the second aspect.

The invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

Further aspects of the invention, which should be considered in all its novel aspects, will become apparent from the following description given by way of example of possible embodiments of the invention.

Brief Description of the Figures Figure 1 is a diagrammatic side view of a blown film manufacturing process according to one embodiment of the invention.

Figure 2 is a diagrammatic transverse cross-section view of the film in a layflat tube formation.

Figure 3 is a diagrammatic cross-section view of the primary film in a centrefold formation.

Figure 4 is a diagrammatic side view of a primary sealing process according to an embodiment of the invention.

Figure 5 is a diagrammatic end view of the film passing through the heat sealer of Figure Figure 6 Is a diagrammatic cross-section view of a secondary film.

Figure 7 is a diagrammatic side view of a secondary sealing process according to an embodiment of the invention.

Figure 8 Is a diagrammatic cross-section view of a tertiary film.

Figure 9 is a diagrammatic side view of a sealing process according to an alternative embodiment of the invention.

Brief Description of Preferred Embodiments Referring first to Figure 1 a first primary film 1 is created by a prior art “blown film” process. In this process a suitable polymer film 2 is extruded from an annular die 3. The die comprises at least one air port (not shown) by which pressurised air is introduced into the interior of the “bubble” 4 of film produced. The air pressure increases the diameter of the bubble and decreases the gauge of the film. In a preferred embodiment of the present invention a blow up ratio (BUR) of at least 2:1 is used, although in other embodiments BUR ratios between 1.3:1 and 2:1 may be used.

The extruded film 2 is collapsed down to a “layflat” tube 5 by a collapsing frame 6 and suitable nip rollers 7.

In the embodiment shown winder haul-off nip rollers 8 are provided to draw the film 5 through the system before it is wound onto a roll 9.

At some point between the film leaving the nip rollers 7 and being wound onto the roll 9, a suitable cutting means such as a slitting knife 10 is used to create a slit along one edge of the layflat tube 5. This slit changes the film from a tubular formation, as seen in Figure 2, to a centrefold formation 1 comprising a first layer 11 and a second layer 12, as seen in Figure 3.

Referring next to Figures 4 and 5, a sealing process according to an embodiment of the present invention is shown.

A roll of first primary film 20 and a roll of second primary film 21 are provided. The first and second primary films 20, 21 are preferably substantially identical. The films 20, 21 are preferably mounted one above the other, as shown in Figure 4.

The first and second primary films 20, 21 are fed past a continuous heat sealer 22, preferably a hot air type heat sealer, although in some embodiments a band sealer (not shown) may be used.

The film is arranged such that only the second (lower) layer 12a of the first primary film 20 and the first (upper) layer 11b of the second primary film 21 enter the heat sealer 22. The first layer 11a of the first primary film 20 and the second layer 12b of the second primary film 21 are directed away from the heat sealer 22 and so are not connected together.

The heat sealer 22 comprises a pair of parallel manifolds 23. The outer portions 24 of the layers 12a, 11b are directed between the manifolds 23 and are exposed to hot air which is blown from apertures in the manifold 23. A pair of rollers (not shown) then set the seal 25.

The seal 25 is preferably between 1mm and 15mm wide, more preferably between 6mm and 9mm. When polyethylene film is used, the sealing heat range is preferably between around 150°C and 220°C, more preferably between 190 and 200°C. Speed through the sealer is preferably between 1m/min and 15m/min, more preferably between 2m/min and 5 m/min.

When connected, the two primary films 20, 21 form a single secondary film 26 comprising two connected panels arranged into four concertinaed layers 26a-26d.

Winder haul off nip rollers 27 are provided to assist in drawing the secondary film 26 away from the heat sealer 22. Nip rollers 27 may also optionally be provided between the rolls of film 20, 21 and the heat sealer 22 to guide the film though the heat sealer 22. In some embodiments (not shown) the heat sealer 22 may be provided with opposed conveyors to guide the layers 12a, 11b through the heat sealer 22.

The rotational speed of the nip rollers 27 is preferably selected such that the nip rollers 27 draw the secondary film 26 away from the heat sealer 22 at substantially the same speed that the rollers operate within the heat sealer 22, so that the seal 25 is not compromised. The secondary film 26 is then wound onto a secondary roll 28.

Referring next to Figures 7 and 8, where the required width of the finished film is greater than can be achieved by connecting two primary films 20, 21 together, as shown in Figure 4, the width of the finished film may be doubled by sealing a fourth layer 26d of a first roll 29 of secondary film 26 to a first layer 26a of a second roll 30 of secondary film 26, thereby doubling the width of the film. The same apparatus (heat sealer 22, nip rollers 27 etc) may be used to connect the two secondary rolls 29, 30 together as was used to connect the two primary films , 21.

Once connected by the heat sealer 22 the two secondary films 29, 30 form a single tertiary film 31 comprising four panels connected by three heat seals 25, and arranged into eight concertinaed layers 31a-31h. In a variation of the sealing operation shown in Figures 7 and 8 (not shown) one of the secondary films 29, 30 may be replaced by a primary film, so that the tertiary film has six layers rather than eight.

Still wider films may be created by repeating this process to connect two or more tertiary films 31. Alternatively a tertiary film 31 may be connected to a secondary film 26. Regardless of the number of iterations of the sealing process used, the final film is arranged into a plurality of concertinaed layers which can be easily unfolded in use.

Referring next to Figure 9, a variation of the heat sealing process shown in Figures 4 and 5 is shown. In this embodiment a second heat sealer 22a is provided. A further roll of film 33 is provided. The further roll of film 33 may have any number of layers. Film from the further roll 33 is joined to the secondary film by the second heat sealer 22a in the same manner as the two films 20, 21 are joined in the first heat sealer 22. This embodiment may speed production of film having multiple layers. If still further capacity is required, additional heat sealers and rolls of film may be used.

In one embodiment the annular die 3 is substantially 500mm in diameter, with a 1 mm die gap.

Using the method of the present invention, this die may be used to produce finished film having a width of 12m or more.

For shrink wrap applications an enhanced linear low density rich resin is preferably used, with minor low density resin plus colour, ultra violet inhibitor and process additives. In one embodiment the resin mix comprises Exxon Mobil Enable 2005HH (50-75%) : Lotrene FE8000 (44-19%) : 5% Clariant White 57186 : 1% Ampacet UVI 10478 : 0.25% Clariant Slip/Antiblock 409 : 0.2% Clariant Process Aid 179. In another embodiment the resin mix comprises Borouge Borstar FB2230 (50-75%) : Lotrene FE8000 (44-19%) : 5% Clariant White 57186 : 1% Ampacet UVI 10478 : 0.25% Clariant Slip/Antiblock 409 : 0.2% Clariant Process Aid 179.

In preferred shrink wrap embodiments the film has a thickness of substantially 250 µm, although in other embodiments the film may have a thickness between 100 µm and 300 µm.

In some embodiments one or more of the primary films comprise different colouring agents, so that the finished film has at least one panel with a different colour to one or more other panels.

In some embodiments an end-user may request one or more of the primary films be coloured to match their particular branding, or the film may be printed. Off-line printing of a sheet having the dimensions of the finished sheet may prove difficult and/or expensive, whereas printing on the narrower primary film prior to the sealing process may be simpler and more economical.

In some embodiments non shrink applications may be appropriate, for example to provide general purpose sheet film, or to provide specific purpose sheet film such as “glass house EVA” sheeting.

Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of “including, but not limited to”.

Where in the foregoing description, reference has been made to specific components or integers of the invention having known equivalents, then such equivalents are herein incorporated as if individually set forth.

Although this invention has been described by way of example and with reference to possible embodiments thereof, it is to be understood that modifications or improvements may be made thereto without departing from the spirit or scope of the appended claims.

WHAT WE

Claims (22)

CLAIM 1. IS

1. A method of manufacturing a flexible plastic film comprising the steps of: i. Forming a length of first primary film by a blown film extrusion process, wherein 5 the first primary film comprises a first layer and a second layer; ii. Forming a length of second primary film by a blown film extrusion process, wherein the second primary film comprises a first layer and a second layer; and iii. Connecting an outer edge of the second layer of the first primary film to an outer edge of the first layer of the second primary film by a substantially continuous 10 heat sealing operation to form a secondary film having four layers.

2. The method of claim 1 wherein the first and second primary films are arranged in a centrefold configuration. 15

3. The method of claim 1 or 2 wherein the connection between the second layer of the first primary film and the first layer of the second primary film is a flange type joint.

4. The method of claim 1, 2 or 3, further comprising the step of connecting an outer edge of a fourth layer of the first secondary film to an outer edge of a first layer of a third primary 20 film by a substantially continuous heat sealing operation, to thereby form a tertiary film having six layers.

5. The method of any one of claims 1 to 3 further comprising the steps of dividing the secondary film into a first length of secondary film and a second length of secondary film 25 and connecting an outer edge of a fourth layer of the first secondary film to an outer edge of a first layer of the second secondary film by a substantially continuous heat sealing operation, to thereby form a tertiary film having eight layers.

6. The method of any one of claims 1 to 3 further comprising the steps of repeating steps i) 30 to iii) to form a second secondary film having four layers and connecting an outer edge of a fourth layer of the first secondary film to an outer edge of a first layer of the second secondary film by a substantially continuous heat sealing operation, to thereby form a tertiary film having eight layers. 35

7. The method of any one of the preceding claims wherein the first primary film and the second primary film comprise polyethylene.

8. The method of any one of the preceding claims wherein the first and second primary films have a blow up ratio of at least 1.3:1. 5

9. The method of claim 8 wherein the first and second primary films have a blow up ratio of at least 2:1.

10. The method of any one of the preceding claims wherein the heat sealing operation forms a heat seal having a width of between 1mm and 15mm.

11. The method of claim 10 wherein the heat seal has a width of between 6mm and 9mm.

12. The method of any one of the preceding claims wherein each said heat sealing operation occurs at between 150°C and 220°C.

13. The method of claim 12 wherein each heat sealing operation occurs at between 190°C and 200°C.

14. The method of any one of the preceding claims wherein each layer is between 100 µm 20 and 300 µm thick.

15. The method of claim 14 wherein each layers is substantially 250 µm thick.

16. The method of any one of the preceding claims wherein each layer is between 25 substantially 1 and 2m wide.

17. The method of claim 16 wherein each layer is substantially 1.6m wide.

18. The method of any one of the preceding claims wherein step i) comprises winding the 30 first primary film onto a first reel.

19. The method of claim 18 wherein step ii) comprises winding the second primary film onto a second reel.

20. The method of claim 19 wherein step iii) comprises mounting the first reel above the second reel.

21. The method of any one of the preceding claims wherein one or more of the primary films 5 may be coloured or the film may be printed.

22. A method of manufacturing a multi-panel film substantially as herein described with reference to