WO2021084464A1

WO2021084464A1 - Recyclable polyethylene-based packaging material for use on horizontal form-fill-seal machines and a method of its manufacture

Info

Publication number: WO2021084464A1
Application number: PCT/IB2020/060149
Authority: WO
Inventors: Dieter KREISSEL; George Francis LAHOUD
Original assignee: DIEDLOFF, Manley
Priority date: 2019-10-30
Filing date: 2020-10-29
Publication date: 2021-05-06
Also published as: ZA202205917B

Abstract

The invention relates to a polyethylene-based blown film comprising three co-extruded layers, comprising a core layer, with an inner seal layer on one side of the core layer, and an outer layer on the other side of the core layer. The invention also extends to a method of manufacturing a clear recyclable packaging film for use on horizontal form-film-seal machines using the polyethylene-based blown film.

Description

RECYCLABLE POLYETHYLENE-BASED PACKAGING MATERIAL FOR USE ON HORIZONTAL FORM-FILL-SEAL MACHINES AND A METHOD OF ITS MANUFACTURE

FIELD OF THE INVENTION

This invention relates to a recyclable polyethylene-based packaging material for use in horizontal form-fill-seal packaging processes, commonly used in the packaging of fresh, dry and prepared foods.

BACKGROUND TO THE INVENTION

Fresh, dry and prepared foods (the “Products”), such as grains, fruit and vegetables, are commonly packed in various forms of plastics material packaging that allow customers to visually inspect the Products without opening the packaging. This improves the presentation, preservation and/or integrity of the Products and create customer confidence that they are purchasing products of a reliable quality. Commonly, the process of packaging the Products is done on horizontal form-fill-seal machines, which are machines that in a single process form the final packaging from input packaging material provided in reel form, fill it with a wet or dry product, and then seal it closed.

A problem with certain polymer substrates used for the manufacture of such input packaging material is that it is not easily recyclable or widely recycled. With the current focus on sustainability and limiting the impact of plastic packaging material on the environment, there is significant pressure on producers and marketers of the Products to use only recyclable material or widely recycled packaging substrates and materials.

Conventional packaging for horizontal form-fill-seal packaging processes are commonly comprised of so-called biaxially-oriented polypropylene (“BOPP”) and Oriented Polypropylene (“Opp”) material substrates. These specific substrates have a degree of clarity, stiffness and surface texture that is suitable for the packaging and marketing of the Products and it allows for easy surface decoration. To package the Products, specific horizontal form-fill-seal machines, dedicated to the handling of BOPP and OPP substrates, have been developed and deployed by the industry at large, at significant cost, prior to BOPP and OPP becoming less desirable substrates due to sustainability and recycling challenges and requirements. There is a need for a recyclable input packaging material that can be used in form-fill-seal processes of existing BOPP and OPP type manufacturing equipment, being horizontal form- fill-seal lines, which will fulfil the requirement for a recyclable and widely recycled material. This will avoid industry having to re-invest in new equipment or having to perform expensive modification of existing equipment to enable the processing of packaging derived from recyclable or more widely recyclable substrates other than BOPP and OPP.

In this specification the following terms have the following meanings:

• MFI - means the ‘melt flow index’ of a polymer, which is a measure of the amount of a polymer that flows through a die in 10 minutes, and it is measured in g/10min;

• Slip Additive - means fatty acid amides (Oleamide, Erucamide and Stearamide) normally used during processing of the polymer and they are solubilized in the amorphous melt, and as the polymer cools and crystallizes the fatty acid amides migrates out to the polymer surface and lubricates the outer layer of the film thus changing the coefficient of friction. Slip additives reduce friction and allow ease of polymer handling in processes;

• Processing Aid - means fluoro-elastomers designed to improve the melt processability and handling of high molecular weight polymers. The fluoro-elastomer has an affinity for the metal surface of the screw and barrel and die of an extruder and therefore coats the surface of the metal providing a non-stick metal surface for the flow of molten polymer. Their functions are therefore: elimination of melt fracture, improvement of film transparency and clarity, improvement of smoothness and surface aspect, improvement of product appearance, improvement of mechanical properties and the reduction of gels; and

• Nucleating agent - means a substance that provides a nucleation site for the HDPE polymer crystals to grow on, forming small crystalline spherulites, thus improving the optical properties and both water and oxygen barrier properties.

OBJECTIVE OF THE INVENTION

It is an objective of the invention to provide a recyclable input packaging material which overcomes the abovementioned problem. SUMMARY OF THE INVENTION

In accordance with this invention there is provided a polyethylene-based blown film comprising three co-extruded layers, comprising:

• a core layer, with

• an inner seal layer on one side of the core layer, and

• an outer layer on the other side of the core layer.

There is further provided:

• for the core layer to be comprised of a polyethylene resin composite, with the core layer having a thickness that comprises about 70% of the total thickness of the co-extruded polyethylene-based blown film;

• for the inner seal layer to be comprised of a polyethylene resin composite, with the inner seal layer having a thickness that comprises about 15% of the total thickness of the co-extruded polyethylene-based blown film; and

• for the outer layer to be comprised of a polyethylene resin composite, with the outer layer having a thickness that comprises about 15% of the total thickness of the co- extruded polyethylene-based blown film.

The invention further provides for the core layer to preferably comprise about:

• 20% low-density polyethylene resin with an MFI of about 0.75g/10min and a density of about 923kg/m³;

• 20% medium-density polyethylene resin with an MFI of about 0.9g/10min and a density of about 940kg/m³;

• 57% high-density polyethylene resin with an MFI of about 0.7g/10min and a density of about 961 kg/m³;

• 1% Slip Additive; and

• 2% Nucleating agent with an MFI of about 6g/10min.

The invention further provides for the inner seal layer to preferably comprise about:

• 88% metallocene linear low-density polyethylene resin with an MFI of about 1.0g/10min and a density of about 912kg/m³;

• 10% low-density polyethylene resin with an MFI of about 0,75g/10min and a density of about 923kg/m³; and

• 2% Processing Aid. The invention further provides for the outer layer to preferably comprise about:

• 86% metallocene linear low-density polyethylene resin with an MFI of about 1.3g/10min and a density of about 927kg/m³;

• 10% low-density polyethylene resin with an MFI of 2g/10min and a density of 922kg/m³;

• 2% Nucleating agent with an MFI of about 6g/10min; and

• 2% Processing Aid.

There is still further provided for the outer layer to be corona treated to a 38 dyne/cm level, operatively to allow for the adhesion of printing inks and coatings on the outer layer.

There is still further provided for the polyethylene-based blown film to include printing on the outer layer and a thermal coating comprised of a layer of a suitable commercially available lacquer overcoated onto the printing.

There is further provided for the thermal coating to contain cellulose nitrate with a solids content of between 25 - 26%, to have a viscosity of between 38 to 40” Zahn#2 at 25°C, and preferably to have a dry coating weight of between 1.0 to 2.0 gsm.

According to a still further aspect of the invention there is a provided a method of manufacturing a clear recyclable packaging film for use on horizontal form-film-seal machines using the co extruded polyethylene-based blown film as defined above, the method including the steps of:

• co-extruding a sheet of the polyethylene-based blown film on a 3-layer blown film extruder;

• corona treating the outer layer of the co-extruded polyethylene-based blown film to a 38 dyne/cm level;

• printing desired printed content on the outer layer of the co-extruded polyethylene- based blown film; and

• applying a thermal coating layer over the printing on the outer layer of the co-extruded polyethylene-based blown film.

These and other features of the invention are described in more detail below. DETAILED DESCRIPTION OF THE INVENTION

As mentioned in the background, BOPP and OPP packaged Products are produced using form-fill-seal equipment that has specifically been developed for the processing of BOPP and OPP substrate-based input packaging materials.

BOPP is an acronym biaxially oriented polypropylene and OPP is an acronym for oriented polypropylene. To manufacture BOPP and OPP based films, a thick polypropylene (“PP”) sheet is produced by a blown tubular extrusion process, and the thick PP sheet is then heated to its softening point and stretched by up to 300%-400% into either two directions (bi-axially- orientated) or one direction (orientated). This process creates the thin BOPP or OPP film. Depending on its grade, BOPP and OPP plastics materials have material processing temperatures in the region of around 200°C-220°C, and melting points of about 160°C.

The horizontal form-fill-seal machines designed to specifically handle and process BOPP or OPP packaging materials are not suitable for processing a material substrate such at polyethylene which has a much narrower window for sealing in terms of temperature as well as very high levels of stretch/elongation when compared to BOPP and OPP substrates.

Conventional wisdom therefor teaches against using plastic substrate and materials with a significantly lower softening point and yield tensile strength and elongation in the BOPP or OPP based horizontal form-fill-seal machines. The forces exerted onto such plastics substrates or materials will be too great and will tear them and/or the plastics materials will melt or become deformed as a result of the high temperatures at which these machines operate. Also, these horizontal form-fill-seal machines use thermal sealing along the edges and between bags and uses wide seals and the heat sealing is accordingly configured specifically for BOPP or OPP and material based on the performance characteristics of the substrate. The sealing applied to a film on a horizontal form-fill-seal machine designed for BOPP or OPP substrates will accordingly melt and deform any substrate or material that has a significant lower softening point in terms of temperature.

Polyethylene inherently has a much lower softening point and much lower yield tensile strength than BOPP or OPP. Polyethylene has a melting point in the region of around 105 to 115 °C and a softening point typically in the range of about 85°C. As mentioned above, depending on its grade BOPP and OPP plastics materials have melting points in the region of around 160°C to 165°C, and a softening point of about 150°C. The combination of lower softening point and lower yield tensile strength for polyethylene renders it, conventionally, unsuitable for use on horizontal form-fill-seal machines designed to specifically handle BOPP and/or OPP substrates. These machines are not configured to operate at the lower temperatures at which polyethylene already softens, and also tears polyethylene apart from the tensile forces on it during the form-fill-seal process.

This invention has overcome these traditional limitations of polyethylene film and allows for the polyethylene film developed to be used on these horizontal form-fill-seal machines. Traditionally, polyethylene films used on these machines - for the reasons described above - would soften or melt or become deformed or torn and cause issues with registration and/or result in obstructions in the production line causing the line to fail, thus preventing further form- fill-seal activities from taking place. The resulting properties of the film created in accordance with this invention - softening point and elongation - means that the polyethylene film created in accordance with the invention does not melt or become deformed in these horizontal form- fill-seal machines, and the form-fill-seal process can therefore continue without interruption and within the correct registration.

The applicant has therefore succeeded in creating as an invention a 3-layer co-extruded polyethylene-based packaging material, resulting in a material that is fully and widely recyclable, and which is processable on existing horizontal form-fill-seal machines designed to process only BOPP and OPP input packaging materials. The advantage of this is that producers and marketers of the Products can now switch to the new 3-layer co-extruded polyethylene-based input packaging material with only minor operating temperature adjustments (which adjustments are still well within the normal operating parameters of these horizontal form-fill-seal machines) on their existing horizontal form-fill-seal machines, which enables them to manufacture and use fully recyclable input packaging material that meet the quality and performance requirements of the traditional BOPP and OPP alternatives. No re investment in new equipment or expensive modifications of existing equipment is accordingly required.

The fully recyclable co-extruded 3-layer polyethylene-based blown film comprises of three co- extruded layers, being:

• a core layer, with

• an inner seal layer on one side, and

• an outer layer on the other side. The core layer is comprised of a polyethylene resin composite and in thickness measures about 70% of the total thickness of the co-extruded 3-layer polyethylene-based blown film. The core layer comprises, in its preferred embodiment about:

• 20% LDPE (a commercially available low-density polyethylene resin with an MFI of about 0.75g/10min and a density of about 923kg/m³);

• 20% MDPE (a commercially available medium-density polyethylene resin with an MFI of about 0.9g/10min and a density of about 940kg/m³);

• 57% HDPE (a commercially available high-density polyethylene resin with an MFI of about 0.7g/10min and a density of about 961 kg/m³);

• 1% Slip additive (a commercially available lubricant); and

• 2% Nucleating agent with an MFI of about 6g/10min.

The inner seal layer is comprised of a polyethylene resin composite and in thickness measures about 15% of the total thickness of the co-extruded 3-layer polyethylene-based blown film. The inner seal layer comprises, in its preferred embodiment about:

• 88% mLLDPE (a commercially available metallocene linear low-density polyethylene resin with an MFI of about 1.0g/10min and a density of about 912kg/m³);

• 10% LDPE (a commercially available low-density polyethylene resin with an MFI of about 0,75g/10min and a density of about 923kg/m³); and

• 2% Processing Aid.

The outer layer is comprised of a polyethylene resin composite and in thickness to measure about 15% of the total thickness of the co-extruded 3-layer polyethylene-based blown film. The outer layer comprises, in its preferred embodiment about:

• 86% mLLDPE (a commercially available metallocene linear low-density polyethylene resin with an MFI of about 1.3g/10min and a density of about 927kg/m³);

• 10% LDPE (a commercially available low-density polyethylene resin with an MFI of about 2g/10min and a density of about 922kg/m³);

• 2% Nucleating agent with an MFI of about 6g/10min; and

• 2% Processing Aid. The outer layer is corona treated to a 38 dyne/cm level to allow for the adhesion of the print and thermal coating on the outer layer. The outer later is facing outward.

The co-extruded 3-layer polyethylene-based blown film may be produced in any suitable thickness. For the purpose of horizontal form-fill-seal packaging it would typically be produced in a thickness range of about 25 to 50 micron.

During the process of producing the co-extruded 3-layer polyethylene-based film on a 3-layer blown film extrusion line, the extrusion temperature profile of the three layers are:

• Extruder C (inner seal layer): hopper 175°C to screw end 200°C, Screen changer 200°C;

• Extruder B (core layer): hopper 180°C to screw end 190°C, Screen changer 190°C;

• Extruder A (print and thermal coating): hopper 175°C to screw end 200°C, Screen changer 200°C; and

• Die: bottom 200°C to die lip 220°C.

The die cool ring is operated at about 6°C.

The co-extruded 3-layer polyethylene-based film has an effective material processing temperature melting point of around 195°C and a softening point in the range of about 80°C to 95°C.

Once the co-extruded 3-layer polyethylene-based film has been produced on a 3-layer blown film extrusion line, the customer’s chosen design is printed onto the outer layer, and a thermal coating in the form of a lacquer is overcoated onto the print on the outer layer for appearance and protection of the finished product and invention in downstream horizontal form-fill-seal processes. In a preferred embodiment, the thermal coating is comprised of a commercially available lacquer suitable for this purpose, where the thermal coating contains cellulose nitrate with a solids content of 25 - 26%, has a viscosity of 38 to 40” Zahn#2 at 25°C and a dry coating weight of 1.0 to 2.0 gsm.

The thermal coating provides an excellent heat seal release, heat resistance, water and wet rub resistance, gloss, flexibility, adhesion to a wide range of olefin films, abrasion resistance, a low coefficient of frication value, oil and grease resistance to the final packaging product. Through this process the applicant is able to produce a printed co-extruded 3-layer polyethylene-based film, manufactured using existing equipment, which is fully and widely recyclable and which can be used by producers and marketers of the Products on horizontal form-fill-seal machines, designed specifically to process BOPP and OPP substrates, without any production issues or having to re-invest in new equipment or incur expensive modifications of existing equipment.

The heat sealing of the co-extruded 3-layer polyethylene-based film on the horizontal form-fill- seal machines no longer presents a problem since the invention results in the inner seal layer on the one side and the outer layer on the other side having higher melting points. The inner seal layer then forms the seal, while the core and outer layer neither deforms nor melts. When the material is sealed in the form-fill-seal process, the inner layer melts between the two protective outer layers. This produces a seal, without compromising the integrity of the co- extruded 3-layer polyethylene-based film and accordingly no melting or deforming of the packaging material occurs when the film is processed on the horizontal form-fill-seal machines designed specifically to process BOPP and OPP substrates.

It will be appreciated that the embodiment described above is given by way of example only and is not intended to limit the scope of the invention. It is possible to alter aspects of the embodiment without departing from the essence of the invention.

It is notably possible to alter components of the various layers with different commercially available products and/or to produce the invention on blown film extrusion lines with different layer configurations (for example, 5, 7 or 9 layers) by adjusting the combination or formulation of the inputs specified. The relative thicknesses of the layers comprising the co-extruded film may also be adjusted, depending on the exact choice of input components and the exact required characteristics of the required co-extruded polyethylene-based blown film (for example the specific setup of a BOPP or OPP machine).

The percentages of the various components to the composites forming each of the three layers may also be varied, within reason, to achieve the same or similar technical results for each layer and the film in its entirety. The relative ratios of the thicknesses of the three components of the film may also similarly be varied.

Claims

1. A polyethylene-based blown film comprising three co-extruded layers, comprising:

• a core layer, with

• an inner seal layer on one side of the core layer, and

• an outer layer on the other side of the core layer.

2. A polyethylene-based blown film as claimed in claim 1, in which:

• the core layer is comprised of a polyethylene resin composite, with the core layer having a thickness that comprises about 70% of the total thickness of the co-extruded polyethylene-based blown film;

• the inner seal layer is comprised of a polyethylene resin composite, with the inner seal layer having a thickness that comprises about 15% of the total thickness of the co-extruded polyethylene-based blown film; and

• the outer layer is comprised of a polyethylene resin composite, with the outer layer having a thickness that comprises about 15% of the total thickness of the co-extruded polyethylene-based blown film.

3. A polyethylene-based blown film as claimed in claim 2 in which the core layer is comprised of about:

• 1% Slip Additive; and

• 2% Nucleating agent with an MFI of about 6g/10min.

4. A polyethylene-based blown film as claimed in claim 2 in which the inner seal layer is comprised of about:

• 2% Processing Aid.

5. A polyethylene-based blown film as claimed in claim 2 in which the outer layer is comprised of about:

• 2% Nucleating agent with an MFI of about 6g/10min; and

• 2% Processing Aid.

6. A polyethylene-based blown film as claimed in claims 3 to 5.

7. A polyethylene-based blown film as claimed in any one of claims 1 to 6 in which the outer layer is corona treated to a 38 dyne/cm level, operatively to allow for the adhesion of printing inks and coatings on the outer layer.

8. A polyethylene-based blown film as claimed in claim 7 which includes printing on the outer layer and a thermal coating comprised of a layer of a suitable commercially available lacquer overcoated onto the printing.

9. A polyethylene-based blown film as claimed in claim 8 in which the thermal coating contains cellulose nitrate with a solids content of between 25 - 26%, has a viscosity of between 38 to 40” Zahn#2 at 25°C, and preferably has a dry coating weight of between 1.0 to 2.0 gsm.

10. A method of manufacturing a clear recyclable packaging film for use on horizontal form-film-seal machines using the polyethylene-based blown film as claimed in claim 1 to 9 above, including the steps of:

• printing desired printed content on the outer layer of the co-extruded polyethylene-based blown film; and

• applying a thermal coating layer over the printing on the outer layer of the co- extruded polyethylene-based blown film.