AU2015200362A1 - Production of flexible films - Google Patents

Abstract

A method for creating lines or areas of weakness 5 in a multilayer flexible film is disclosed. The method comprises creating small cracks in a layer or layers of a film by feeding the layer or layers through a nip between a pair of rolls, where one of the rolls in the nip has a series of raised features, and where the size, shape, or 10 planar position of the raised features are accurately controlled. The method also comprises laminating the weakened layer or layers to one or more than one other film layer to create the multilayer film. 6153890_1 (GtHattrs) P72088.AU.2 KRYSTALM 27/01/15 C'e) (CO Cyc

Description

- 1 PRODUCTION OF FLEXIBLE FILMS The present invention relates to the production 5 of flexible films for packaging products. The present invention also relates to containers that include the packaging films. 10 It is important for consumers and manufacturers of certain products made from polymeric films to be able to easily tear the films along predetermined lines or alternatively to be able to easily open the films in certain areas. This is important for a range of products, 15 including food products and medical products. While notches are known in the art to initiate tearing, there is often little control of the tearing once it has started. This lack of control can be detrimental to 20 the end user. Another weakness with notches is that the tearing may happen inadvertently, for example due to the stresses placed on the packaging during handling and 25 transportation, and this may lead to product loss and health risks. Notching films also fails to address circumstances where the tear strength of a material 30 remains too high for consumer comfort, even though tearing is initiated at a notch. International publication WO 03/035504 in the name of Hosokawa discloses another solution to the easy 35 opening problem, namely the roughening of a portion of a polymer film (the "Hosokawa method") using areas of sandpaper. The roughened area is then more likely to tear. 6153890_1 (GH tter) P72088.AU.2 KRYSTALM 27/01/15 - 2 The Hosokawa method is commonly used in conjunction with a notch to initiate tearing. However the Hosokawa method has some major 5 limitations. The first limitation is that use of sandpaper limits the precision of the method. The grains of sand on the sandpaper used to create the weakened area are 10 randomly positioned. It is also difficult to use this method for very small areas while retaining its effectiveness. The second limitation is that quite high 15 pressures are required in the nip where the sandpaper is applied against the polymer film to achieve an acceptable level of weakening. This causes unintended other consequences, including premature wear of the other parts of the nip. 20 A third limitation is that packaging made using the Hosokawa method can be damaged by the high pressures and random nature of the sandpaper. This can lead to increased gas transmission through the weakened or damaged area. 25 It is also known in the art to promote controlled tearing of materials by laser ablation of part or all of one or more layers of the film. Laser ablation provides excellent control of tear propagation. However, the use 30 of lasers also has limitations. One limitation is the cost of laser apparatus. Although the cost of laser technology has reduced, the requirement in packaging for multiple tear lines in a web 35 of material, sometimes in the machine direction, but more commonly across the machine direction of the web, and even 6153890_1 (GH tter) P72088.AU.2 KRYSTALM 27/01/15 - 3 with shaped contour, means the capital cost of laser systems remains high. Another limitation of the laser ablation system 5 is that available lasers are not suitable for all types of substrates. Specifically, lasers cannot ablate reflective materials like metal foils at high rates. A third method of creating controlled tear in a 10 flexible substrate is disclosed in International publication WO 02/40250 in the name of the applicant. The method disclosed in the International publication is based on the use of a particular tool geometry to control tearing characteristics of flexible polymer films. 15 The applicant's method as disclosed the International publication is able to create tear properties in many substrates. However, one limitation o the method is that high pressures are required in a roll 20 nip and this can lead to premature failure of the system. The above description is not to be taken as an admission of the common general knowledge in Australia or elsewhere. 25 The present invention provides an alternative method of creating an easy opening area or line of weakness in a polymer film with very high precision and low mechanical wear in a roll nip and at low capital and 30 operating cost. SUMMARY OF THE PRESENT INVENTION 35 In general terms, the method for creating lines or areas of weakness in a multilayer flexible film in accordance with the present invention comprises creating 6153890_1 (GH tter) P72088.AU.2 KRYSTALM 27/01/15 - 4 small cracks in a layer or layers of a film by feeding the layer or layers through a nip between a pair of rolls, where one of the rolls in the nip has a series of raised features, and where the size, shape, or planar position of 5 the raised features are accurately controlled. The method also comprises laminating the weakened layer or layers to one or more than one other film layer to create the multilayer film. 10 According to the present invention there is provided a method for creating lines or areas of weakness in a multilayer flexible film that comprises: (a) creating small cracks in a layer or layers 15 of a film in predetermined areas or lines of the layer or layers by feeding the layer or layers through a nip between a pair of rolls, where one of the rolls in the nip has a series of raised features, and where the size, shape, or planar position of the raised features is 20 accurately controlled, and (b) laminating this weakened layer or layers to one or more than one other film layer to create the multilayer film. 25 The weakened lines or areas of the multilayered film may facilitate tearing of the multilayered film where desired. 30 Preferably the raised features of the roll are created using the method disclosed in International publication WO 02/40250 and the disclosure in the International publication is incorporated herein by cross reference. 35 The raised features could be created by any other suitable method. 6153890_1 (GH tter) P72088.AU.2 KRYSTALM 27/01/15 - 5 Preferably the cracks in the weakened area or line are less than 1 mm in a maximum dimension. 5 More preferably the cracks in the weakened area or line are less than 0.5 mm in the maximum dimension. Most preferably the cracks in the weakened area or line are less than 0.25 mm in the maximum dimension. 10 Preferably the other layer or layers in the multi-layer film is selected and/or formed to provide an acceptable level of gas and moisture barrier so as compensate for the loss of gas barrier caused by adding 15 cracks into the weakened area or line. Preferably the nip is found in an adaption of a standard gravure press is used to weaken the film layer or layers. 20 Preferably the backing roll in the nip is made from a rubber material or a polymer material or another type of material with a hardness less than the hardness of of mild steel. 25 Preferably the film substrate to be weakened provides at least 50% of the tensile strength of the multi-layer film. 30 Preferably, the weakened layer or layers is extrusion laminated to one or more than one other film layer to create the multilayer film. Preferably, one or more of the other layers to 35 which the weakened layer or layers is laminated is a metallic foil. 6153890_1 (GH tter) P72088.AU.2 KRYSTALM 27/01/15 - 6 Preferably the weakened lines or areas are invisible or nearly invisible to the naked eye. Preferably sections of the laminated films 5 incorporating the weakened areas or lines are unable to be distinguished by feel compared other non-weakened areas of the laminated film. It is understood that the layer or layers to be 10 weakened can be formed from any commercial film - this will not affect the working of this invention. It is also understood that the remaining layer or layers of the multi-layer film can be joined by any known 15 lamination method, as again the lamination process will not affect the working of this invention providing that areas or lines that are weakened by the method remain weaker than the non-weakened areas, even after the lamination process has increased the tear strength of both 20 of these types of areas. It is also understood that the invention can potentially produce films where the weakened areas or lines are exposed to the outside of packaging formed from 25 the films and so easily seen, or hidden by other layers, and either scenario will not reduce the effectiveness of the invention. It is also within the scope of the invention to 30 create weakened areas in a straight line to create a preferred tear line or alternatively create other types of weakened areas to achieve other objectives. These could comprise parallel lines, zig-zag lines, circles that can be punched out, and any combination suitable to give a 35 commercial advantage to this invention. 6153890_1 (GH tter) P72088.AU.2 KRYSTALM 27/01/15 According to the present invention there is also provided a multi-layer film made by the above-described method. 5 According to the present invention there is also provided a packaging product made from the above-described multi-layer film. BRIEF DESCRIPTION OF THE DRAWINGS 10 One embodiment of the present invention is now described with reference to the accompanying drawings, of which: 15 Figure 1 shows a schematic layout of one embodiment of a process used to produce the multilayer film in accordance with the present invention; Figure 2 shows a schematic of the cross section 20 of the film produced in one embodiment of this invention; and Figure 3 shows an example of a raised feature or projection included in the process layout shown in Figure 25 1. DETAILED DESCRIPTION 30 Figure 1 shows a schematic of a process layout that can be used to produce one embodiment of this invention. It should be noted that that layout is an example only and many other layouts can be used. 35 A preprinted PET film 1 enters a nip between a roll containing raised projections 3 and a rubber backing roll 2. The perforated film 4 passes around a tension 6153890_1 (GH tter) P72088.AU.2 KRYSTALM 27/01/15 - 8 rolls 5 and 6 before being coated with a co-extrusion jet 10. This coextrusion jet 10 is formed within a first coextrusion unit 7 which has two chambers 8 and 9, with the larger chamber 9 used for extruding a HDPE/LDPE 5 copolymer and the smaller chamber 8 used for extruding an ethylene acrylate acid resin tie layer. The combination of perforated PET film and the first co-extruded material is transported to a nip formed 10 between two rolls 13 and 14, where it is joined to an aluminum foil 12 to make a laminate of perforated PET film and aluminium foil 15. This laminate passes around a further tension 15 roll 16 before being coated with a second co-extrusion jet 20. Thi second co-extrusion jet 20 is formed with a second co-extrusion unit 17. This second co-extrusion unit 17 has two chambers, a larger chamber 19 for extruding a LDPE coating using for sealing the aluminium foil, and a 20 smaller chamber 18 used for extruding an ethylene acrylate acid resin tie layer. The final combination of materials 21 is wrapped around a final tension roll 22 before passed onto further 25 processing (not shown), or being rolled up for transport to customer plants or other separate conversion operations. Figure 2 shows a laminate formed in one 30 embodiment of the present invention. The base layer 30 is formed from PET film, with perforations 36. This next layer 31 is a LDPE/HDPE polymer blend, which is adjacent to an ethylene acrylate acid resin tie layer 32. This resin is used to join the co-polymer blend 21 to an 35 aluminium foil 33. A second ethylene acrylate acid resin tie layer 24 is joined to join the aluminum foil to the LDPE sealing layer 35. 6153890_1 (GH tter) P72088.AU.2 KRYSTALM 27/01/15 - 9 Figure 3 is an example of the raised projection used on roll 2 in Figure 1. The raised projection can be used to create the cracks used to form the weakened lines 5 or areas. The raised projection 45 has two pairs or sets of arms being 45' and 45", and 46' and 46". The projection in the shape of a cross can be defined by the width of the arms of the cross 41, the height of the cross 42, the total width of the walls 40 of the cross. In one example 10 the width of the arms of the cross 41 was 50 um, the height of the cross 42 was 165 um, and the total width of the projection 40 was 163 um. The slope of the walls of the cross 43 was below 6.3 degrees. 15 In this example the raised projection 44 was created using electro-forming. It has been found that optical means can be used to create reverse images of the desired raised features in 20 rigid polymeric substrates, and that with appropriate care, micro-scale electroforming of the tool can be performed. The tool can be of any electro-formable metal or alloy; sulphamate nickel as understood in the art of electroforming has been found to possess a desirable 25 balance of strength and flexibility. For wear resistance, traditional hard chrome plating has been can be applied. 30 One suitable optical means for the manufacture of the polymeric negative is excimer laser ablation. An excimer laser breaks molecular bonds of appropriate polymers, effectively evaporating the polymer at approximately one micron per laser pulse. The use of 35 patterned masks in the laser beam creates a shaped laser of controlled dimensions, which can then be reproduced in the polymer. The height of the projection, is controlled 6153890_1 (GH tter) P72088.AU.2 KRYSTALM 27/01/15 - 10 by the number of pulses used in the manufacture of any feature. The use of an NC table to control placement of 5 the polymeric negative allows multiple features to be created in a single piece of polymer, to a high accuracy (typically less than 1 micron) EXAMPLE 10 An example of a packaging film made in accordance with the present invention will now be described. The packaging film may be used for packaging any material but is particularly suitable for forming long thin pouches containing instant coffee powder. 15 The film having cracks or perforations is made from polyethylene terephthalate (PET) which has been selected for its ability to survive the high temperatures of the subsequent forming processes, and because it can be 20 used to carry a high quality high gloss print surface. In this example a 12 um film is used, but readers will understand that any film thickness capable of passing through the converting process can be used. 25 In this example the PET film is printed before it is perforated, but it will be understood that other embodiments would include printing the PET film after it has been perforated and laminated using this process. 30 The PET film is passed through a perforation nip to perforate and hence weaken the film. The raised projections are found in a 10.2 mm (cross direction) by 27 mm (machine direction) area. Hereafter these areas will be referred to as a 'block' as in a block of projections. 35 There are a number of these blocks across the machine direction of the projection roll, with these blocks spaced 86 mm from each other across the machine direction, and 6153890_1 (GH tter) P72088.AU.2 KRYSTALM 27/01/15 - 11 100 mm in the machine direction. There are 16 such blocks across the width of the nip. Each of these blocks comprise a cross shaped 5 projection, with each projection being spaced 0.3 mm apart from neighbouring projections across the machine direction, and 0.6 mm from its neighbours in the machine direction. 10 After the PET film has been perforated as described above, it is extrusion laminated to a 6.35 um aluminium foil. The function of the aluminium foil is to provide resistance to the transmission of oxygen, water vapour, carbon dioxide and other gases. The extrusion 15 process in this example comprises co-extruding a 15 um thick film comprising a laminate of the following components. (a) A melted blend of high density (LDPE) and 20 low density (LDPE) polyethylene, with the exact blend of LDPE and HDPE selected to optimize the melt resistance and flowability of this polymer blend. The function of this polymer blend is to adhere 25 to the perforated PET film. (b) Ethylene acrylate acid resin chosen for its ability to adhere to the aluminium foil, i.e. a 'tie layer' as known in the art. It 30 should be recognized that any tie layer capable of bonding to aluminium foil and other polymer blends will substitute for ethylene acrylate acid resin. 35 In this example the co-extruded laminate of LDPE/HDPE and ethylene acrylate acid resin is firstly extruded through a die onto the perforated PET film, and 6153890_1 (GH tter) P72088.AU.2 KRYSTALM 27/01/15 - 12 then the lamination of perforated film and co-extrusion is then joined to the aluminium foil in a subsequent nip. Following this first co-extrusion process the 5 lamination of PET film/LDPE-HDPE copolymer/ ethylene acrylate acid resin/aluminium foil then has a second co extrusion of LDPE and ethylene acrylate acid resin laminated to the aluminium foil. The function of the LDPE in this final co-extrusion is to provide a heat sealing 10 surface, i.e. a surface that will melt in a hot nip and join to other polymer surfaces. The function of the ethylene acrylate acid resin in this second co-extrusion is to join the aluminium foil and the LDPE polymer. 15 The material produced in this perforation and lamination process is subsequently formed into a pouch, where the PET film layer is on the outside of the pouch, and the LDPE film layer is on the inside of the pouch and used to hold the pouch together. 20 In another example of the present invention, a 23 um thick PET film is perforated to create a medical film. Some of the advantages of the present invention 25 may include creating an easy opening area or line of weakness in a polymer film with very high precision and low mechanical wear in a roll nip and at low capital and operating cost. 30 To achieve a low operating and capital costs it is preferable to use existing polymer film manufacturing equipment, and to allow very high operating speeds and volumes. Typically polymer film will manufactured at production speeds of up to 600 m/min. 35 The production units are run continuously, and the owners of the packaging process equipment would prefer 6153890_1 (GH tter) P72088.AU.2 KRYSTALM 27/01/15 - 13 a method that has a lifetime comparable to that of a standard gravure press before major maintenance is required. This can both reduce operating costs and reduce the environmental impact of the manufacturing process. 5 Another advantage of the present invention is that it may enable the production of a high number of individual packages with easy opening area or lines before needing to replace any element of the packaging 10 manufacturing equipment. Another advantage of the present invention is that a full range of perforation patterns may be used to form the weakened lines or areas including the use of 15 straight lines, circles, zig-zag patterns, circles, ovals and other shape or geometric feature selected. Another advantage of the present invention is that can produce an easy opening area or line in packaging 20 film with high precision, where the easy opening feature is imparted in one layer of a laminate using for packaging film within the simple adaption of the nip of a conventional packaging line. 25 Another advantage of the present invention is that is provides an alternative means of creating an easy opening area or line for a packaging where the weakened area or line that contributes to the easy opening area can not be easily seen, or is invisible to the naked eye, so 30 as to present the companies that use the packaging a useful option to support their marketing efforts. Another advantage of the present invention is it provides an alternative means of creating an easy opening 35 area or line for a packaging where the weakened area or line that contributes to the easy opening area cannot be felt by normal finger tips, i.e. is smooth to the touch, 6153890_1 (GH tter) P72088.AU.2 KRYSTALM 27/01/15 - 14 so as to present the companies that use the packaging a useful option to support their marketing efforts. Many modifications may be made to the embodiment 5 of the present invention described above without departing from the spirit and scope of the invention. 6153890_1 (GH tter) P72088.AU.2 KRYSTALM 27/01/15

Claims (15)

1. A method for creating lines or areas of weakness in a 5 multilayer flexible film that comprises: (a) creating small cracks in a layer or layers of a film in predetermined areas or lines of the layer or layers by feeding the layer or layers through a nip 10 between a pair of rolls, where one of the rolls in the nip has a series of raised features, and where the size, shape, or planar position of the raised features is accurately controlled, and 15 (b) laminating the weakened layer or layers to one or more than one other film layer to create the multilayer film.

2. The method defined in claim 1 wherein the cracks in 20 the weakened area or line are less than 1 mm in a maximum dimension.

3. The method defined in claim 1 wherein the cracks in the weakened area or line are less than 0.5 mm in the 25 maximum dimension.

4. The method defined in claim 1 wherein the cracks in the weakened area or line are less than 0.25 mm in the maximum dimension. 30

5. The method defined in any one of the preceding claims comprises selecting or forming the other layer or layers in the multi-layer film to have an acceptable level of gas and moisture barrier so as compensate for the loss of gas 35 barrier caused by adding cracks into the weakened area or line. 6153890_1 (GH tter) P72088.AU.2 KRYSTALM 27/01/15 - 16

6. The method defined in any one of the preceding claims wherein the film to be weakened provides at least 50% of the tensile strength of the multi-layer film. 5

7. The method defined in any one of the preceding claims wherein the weakened layer or layers is extrusion laminated to one or more than one other film layer to create the multilayer film. 10

8. The method defined in any of the preceding claims wherein one or more of the other layers to which the weakened layer or layers is laminated is a metallic foil. 15

9. The method defined in any of the preceding claims wherein the weakened lines or areas are invisible or nearly invisible to the naked eye.

10. The method defined in any of the preceding claims 20 wherein the weakened areas or lines are unable to be distinguished by feel compared other non-weakened areas of the laminated film.

11. The method defined in any one of the preceding claims 25 comprises using a standard gravure press to form the weakened film layer or layers.

12. The method defined in any one of the preceding claims wherein the other roll forming the nip is a backing roll 30 which is made from a material of a hardness less than that of mild steel.

13. A multi-layer film made by the method defined in any one of the preceding claims. 35

14. A packaging product made from the multi-layer film defined in claim 13. 6153890_1 (GH tter) P72088.AU.2 KRYSTALM 27/01/15 - 17

15. A method for creating lines or areas of weakness in a multilayer flexible film substantially as hereinbefore described with reference to the accompanying drawings. 5 6153890_1 (GH tter) P72088.AU.2 KRYSTALM 27/01/15