GB2637768A

GB2637768A - A heat-sealable flexible packaging material, a method of making suchand a use thereof

Info

Publication number: GB2637768A
Application number: GB2401424.3A
Authority: GB
Inventors: Vincent Dethloff Jan; Jensen Mara
Original assignee: One Five GmbH
Current assignee: One Five GmbH
Priority date: 2024-02-02
Filing date: 2024-02-02
Publication date: 2025-08-06
Also published as: WO2025163188A1; GB202401424D0

Abstract

Methods of forming heat-sealable flexible packaging material comprising: compounding a lignin and a plasticiser to form a plasticised lignin, and applying a layer of the plasticised lignin to a surface of a flexible substrate to form a heat seal layer thereon, by extruding the plasticised lignin or from an aqueous dispersion of the plasticised lignin. Preferred plasticizers are dicarboxylic acids and the lignin may be preferably derived from miscanthus grass.

Description

A HEAT-SEALABLE FLEXIBLE PACKAGING MATERIAL, A METHOD OF

MAKING SUCHAND A USE THEREOF

Field

The present invention relates to a heat-sealable flexible sheet material, to a method of making such, and to a use of such. The heat-sealable flexible sheet material comprises a flexible sheet material and a heat seal layer on a surface thereof, the heat seal layer comprises a lignin and a plasticiser; wherein the heat seal layer has been deposited on the flexible sheet material from an aqueous dispersion or an extrusion.

Background

Traditional plastics, derived from fossil fuels, have given rise to environmental concerns, including pollution, resource depletion, and climate change. The longevity of plastic waste in landfills and ecosystems poses threats to biodiversity and human health, necessitating a shift toward more sustainable packaging materials. Consumer demand for eco-friendly products, coupled with evolving regulations aimed at curbing plastic pollution, is causing industries to adopt more sustainable packaging materials.

Flexible packaging refers to a type of packaging that is made from materials that can easily conform to the shape of the product being packaged. Flexible packaging can be easily bent, folded, or shaped, providing versatility in design and functionality. Flexible packaging is widely used for products across different industries due to its numerous advantages. It is typically a thin sheet or film material able to be bent or folded into the desired form.

Many flexible packaging materials comprise a heat seal layer, also known as a heat-sealable layer, which is a component in packaging materials to bond or seal when subjected to heat. This layer creates secure closures for various types of packaging such as pouches, bags, and sachets. The heat seal layer is typically positioned between layers of packaging material, and when heated, it adheres to itself to another heat-sealable surface, forming a tight seal.

The choice of materials for the heat seal layer depends on the specific requirements of the packaging application, including the type of product being packaged and the desired level of seal strength. Conventionally, non-biodegradable, fossil fuel-derived polymers are used as heat seal layers, including Polyethylene (PE), Polypropylene (PP) and Polyester (PET). Consequently, conventional heat seal layers may reduce a packaging material's biodegradability and increase the carbon dioxide emissions associated with its use.

The present invention aims to provide improvements generally over the prior art methods and apparatus. In addition, the present invention may optionally seek to provide one or more of the following advantages: i) to provide a biodegradable heat seal; fi) to provide a low-cost heat seal; and/or iii) to provide a heat seal having high heat seal strength.

Summary

In the first aspect of the present disclosure, there is a method of making a heat sealable flexible packaging material, the method comprising: compounding lignin and a plasticiser to form a plasticised lignin, and applying a layer of the plasticised lignin to a surface of a flexible substrate to form a heat seal layer thereon, by extruding the plasticised lignin or from an aqueous dispersion of the plasticised lignin.

In a second aspect of the present disclosure, there is a heat sealable flexible packaging material, comprising a flexible substrate and a heat seal layer on a surface thereof, the heat seal layer comprising: lignin and a plasticiser; wherein the heat seal layer has been deposited on a surface of the flexible substrate from an aqueous dispersion or extrusion.

In a third aspect of the present disclosure, there is provided the use of a heat sealable flexible packaging material according to the second aspect. The use may be for sealing a portion of the heat sealable flexible packaging material to a portion of further packaging material with the application of heat and pressure.

Lignin is a naturally occurring biopolymer which forms the support structure in plants. It can be readily broken down by microorganisms meaning it does not contribute to plastic pollution. Lignin is also a waste material from the paper industry, where it is often burned as a heat source. This means the heat seal of the present invention is made from low-cost components.

The present disclosure does not modify the lignin or react it with agents to form an adhesive, instead, the heat seal layer of the present invention is a lignin-based layer with thermoplastic characteristics. By not modifying the lignin or reacting it with agents, the biodegradability is improved.

Description

Flexible packaging may refer to packaging made of non-rigid materials. Flexible packaging may be considered any packaging material or part of a package whose shape can readily be changed during conversion into a packaging product when filled or during use. Flexible packaging is different to rigid packaging which is a preshaped product that has sufficient rigidity to hold a three-dimensional shape.

Flexible packaging may typically have a bending resistance of from 1 to 95 mNm (CD), and/or 3 to 130 mNm (MD), or from 3 to 50 (CD), and/or from 7.5 to 75 (MD), or any range made from any of these endpoints. Bending resistance may be determined by ISO 2493.

Flexible packaging may predominantly be thin and planar in form i.e. before conversion to a three-dimensional packaging product. Flexible packaging may have a thickness from 0.01 mm to 0.5 mm, or from 0.05 mm to 0.25 mm, or from 0.07 to 0.015 mm or any range made from any of these endpoints.

The flexible packaging may be a multilayered material. The flexible packaging may comprise a flexible substrate, and any number of barrier layers, metallised layers, tie layers, primer layers, print layers, heat seal layers, and/or over-print varnish layers, amongst others.

The heat-sealable flexible packaging material is a flexible packaging material comprising a heat-seal layer. The heat seal layer is typically a layer that exhibits thermoplastic properties which enables the flexible packaging material to be bonded to itself or further packaging material with the application of heat and pressure.

The heat-sealable flexible packaging material of the present disclosure may meet one or more of the following compostability standards: EN 13432, ASTM D6400. The heat-sealable flexible packaging material of the present disclosure may meet one or more of the following Biodegradability standards: ASTM D6691-09 (marine), ASTM D5988-12 (soil). The heat-sealable flexible packaging material of the present disclosure may meet one or more of the following Recycling standards CEPI (Confederation of European Paper Industries) Recyclability Test Method Version 2 Lignin, a heterogeneous material with up to three phenyl propane monomers, varies based on the source. Softwood lignins are mainly coniferyl alcohol-based, hardwood lignins have a higher syringyl alcohol content, while grass lignins have a higher paracoumaryl alcohol content.

The lignin may derive from softwoods, hardwoods, and perennial plants (including grasses amongst others). In some preferred embodiments, the lignin may comprise lignin derived from perennial plants or annual plants, including but not limited to grasses, wheat straw and bagasse. Optionally this may be lignin derived from grasses, optionally miscanthus grasses, optionally from Miscanthus giganteus. In some embodiments, the lignin may have a paracoumaryl alcohol content of greater than 5 %, or 10 %, or 15 %, or 20 %, or 25%, or 30%, or 35%. In some embodiments, the lignin may have a paracoumaryl alcohol content not exceeding 50%, or 45%, or 40%, or 35%, or 30% or 25% or 20%. The inventor of the present disclosure has found that lignin derived from grasses, and/or lignin with a high paracoumaryl alcohol content may result in further improved heat seal properties. The lignin may comprise a blend of lignin from different sources. Preferably a blend of lignin will have an overall paracoumaryl alcohol content as stated above or comprise predominantly lignin from grasses. The lignin may have weight average molecular weight of from 2000 to 12000 Daltons, or from 4000 to 10000 Daltons, or from 5000 to 8000 Daltons, or from 6000 to 7000 Daltons.

Market-available technical lignins fall into four main groups, lignosulphate lignin, kraft lignin, organosolv lignin and soda lignin. A fifth group, Biorefinery lignin, differs in origin, linked to biorefining processes. In some embodiments, the lignin may comprise any of: biorefinery lignin, lignosulphate lignin, kraft lignin, organosolv lignin or soda lignin. In some preferred embodiments, the lignin comprises lignin from the soda pulping process, i.e. soda lignin.The lignin may comprise at least 20%, at least 40%, at least 80%, at least 90%, at least 95%, at least 99%, or comprise entirely soda lignin. The inventor of the present disclosure has found that soda lignin may result in further improved heat seal properties.

The lignin may have a particle size of 40 pm or less, or 30 pm or less, or 20 pm or less, or 10 pm or less. Optionally the lignin may comprise a particle size greater than 1 pm, or 5 pm, or 10 pm. This may be measured by passing the particles through sieves of known hole sizes. Smaller particle sizes may be measured using laser diffraction or dynamic light scattering.

The plasticiser may comprise one or more selected from the group of polyethylene glycols, polyethylene glycol ethers, polyethers, hydrogenated sugars, phthalates and/or acids (including carboxylic acids such as adipic acid, vanillic acid and lactic acid), acrylic polymers, polyvinyl alcohol, polyurethane dispersions, ethylene carbonate, propylene carbonate, lactones, lactams, lactides, acrylic-based polymers, carbonates (such as ethylene carbonate and propylene carbonate), lactones, lactams, lactides, compounds with a structure similar to lignin like vanilin or vanilic acid, acetosyringone and/or solvents used as coalescing agents like alcohol ethers or polyvinyl alcohol. In some embodiments, the plasticiser may comprise an acid. The plasticiser may optionally comprise a dicarboxylic acid. The plasticiser may comprise a saturated dicarboxylic acid. The plasticiser may comprise an acid with the structure HOOC(CH2)xCOOH where Xis 1-50, or 3-30, or 4-15, or 5-10, or 6-8, or 7.

The inventor of the present disclosure has found that carboxylic acid plasticisers result in better heat seal properties when used in an aqueous dispersion. This result is surprising as hydrophobic plasticisers were initially favoured as plasticisers for lignin in aqueous dispersions.

The plasticiser may be non-reactive and may not form covalent bonds with the lignin. The plasticiser may be hydrophilic and/or may be polar. The plasticiser may be miscible with water and optionally soluble in water.

The flexible substrate may be any flexible substrate commonly used in flexible packaging. This may include polymeric films or cellulosic substrates. Preferably the flexible substrate is a cellulosic substrate. A cellulosic substrate may be any substrate that predominantly comprises cellulose. The cellulosic substrate may comprise paper and/or paper board. The basis weight of the cellulosic substrate may range from 20 g/m2 to 1000 g/m2. The higher end of this range may be deemed paper board for the purposes of this present disclosure, i.e. a cellulosic substrate in the thickness range of 200 g/m2 to 1000 g/m2. A basis weight from 20 g/m2 to 200 g/m2 may be deemed paper.

In some embodiments, the basis weight of the flexible substrate may be from about 20g/m2 to 200 g/m2, or from about 40 g/m2 to about 120 g/m2, or from about 50 g/m2 to about 100 g/m2, or from about 60 g/m2 to 85 g/m2. Or a range formed from any combination of these endpoints. The basis weight may also be referred to as areal weight or grammage and is a measure of mass per unit area. Basis weight may be determined according to ISO 536. The thickness of a substrate may be determined using ISO 534. Unless specified the basis weight will be determined in ambient conditions, after drying if necessary.

A paper substrate may comprise kraft paper, uncoated paper, blotting paper, bond paper, gloss paper, copy paper, matte paper, silk paper or book paper.

A paper board substrate may comprise a coated unbleached kraft board, solid bleached sulphate board, clay-coated news backboard or folding box board.

The lignin and plasticiser may be compounded to form the plasticised lignin. This may occur prior to dispersing into an aqueous dispersion or extrusion. The inventor has found compounding may improve the interaction between the plasticizer and lignin prior to dispersion, resulting in an improved heat seal layer after drying. Compounding may comprise the mixing of the plasticiser and lignin under heat and/or pressure and shear forces. Compounding may convert the lignin and plasticiser to a single phase. Compounding may occur in a heater chamber and the mixing may comprise, amongst others, mixers, rollers, kneaders or screws. Optionally compounding may be performed by twin-kneading apparatus or twin-screw apparatus. The kneaders or screws may be co-or counter-rotating. Compounding may occur at a temperature of at least 120°C, or at least 110°C, or at least 100°C, or at least 90°C, or at least 70°C or at least 50°C. Compounding may occur at a temperature of not exceeding 190°C, or 170°C, or 150°C or 130°C or 120°C or 100°C. The compounded lignin and plasticiser may be extruded following compounding or as part of the compounding process. Extrusion may be defined as pushing the plasticised lignin through a die. The plasticised lignin may be formed into pellets or elongate strings.

During compounding, water may be present in the lignin or added. to decrease the viscosity of the lignin. Typically 0-15%, or 1-12%, or 5-10%, or 0-5% of water to lignin by weight may be present before compounding, or any range formed from any of these endpoints. Optionally the lignin may be dried to reduce water content prior to compounding.

The compounded lignin and plasticizer form a plasticised lignin. The plasticised lignin may be a lignin that exhibits thermoplastic properties. For example, it may be a rigid and hard material below a Tg (glass transition temperature) and above that temperature it may be rubbery, viscous and/or flowable. The transition between these two states may be flowable. Thus a plasticised lignin may also be capable of being extruded.

A plasticised lignin may have a Tg of at least 120°C, or at least 110 °C, or at least 100 °C, or at least 90°C or at least 80 °C, or at least 60 °C. The plasticised lignin may have a Tg not exceeding 120 °C, or 130 °C, or 140 °C, or 160 °C or 180 °C.

The percentage by mass (wt. %) of the lignin in the compounded lignin and plasticiser (i.e. the plasticised lignin) may be from 60 wt. % to 95 wt. % or from 70 wt. % to 90 % or from 75% to 85%. The plasticised lignin may comprise a ratio of lignin to plasticiser from 3:5 to 19:20, or from 7: 1 0 to 9:10, or from 15:20 to 17:20. The plasticised lignin may comprise only lignin and a plasticiser.

The plasticised lignin may be applied to the surface of the flexible substrate. The surface of the flexible substrate may refer to a planar surface on a sheet of flexible substrate. The plasticised lignin may be applied to one or both surfaces of the flexible substrate. The plasticised lignin may be applied directly to the flexible substrate or may be applied onto a layer previously deposited on the flexible substrate.

In some preferred embodiments, the plasticised lignin may be applied to the surface of the flexible substrate by an aqueous dispersion of the plasticised lignin. Alternatively, the plasticised lignin may be applied directly, or by extruding the plasticised lignin onto the surface of the flexible substrate.

The method may comprise heating and extruding the plasticised lignin to apply a layer of the plasticised lignin to the surface of the flexible substrate to form a heat seal layer.

The heat seal layer when the plasticised lignin has been extruded onto the surface of the flexible packaging may have a thickness of from 5 to 50 yM, or from 7 to 40 Rm or from 10 to 30 yin, or 12 to 20 ym, or any range formed from any of these endpoints. The thickness of the layer may be measured after cooling to 23°C (ambient temperature). Measurement may be done by deducting the known thickness of the substrate and any preceding layers. Or it may be measured from a section of the packaging material with microscopy.

The plasticised lignin may be extruded by any known appropriate extrusion method, in particular one that produces sheets appropriate for direct application to packaging materials. Extrusion may comprise guiding thermoplastic material under heat and/or pressure through a die with a hole. In particular, the plasticised lignin may be extruded via slot die extrusion. Alternatively, the plasticised lignin may be subject to blown film extrusion, calendering, injection moulding, compression moulding or solvent casting, amongst other known hot melt or thermoforming methods e.g. a hot melt roller coater.

The application of the plasticised lignin to a surface of the flexible substrate by an aqueous dispersion of the plasticised lignin may comprise dispersing the plasticised lignin in an aqueous liquid to form the aqueous dispersion. In some embodiments, the plasticised lignin may be dispersed in water and no other solvent to form the aqueous dispersion. No other solvent may refer to an absence in the water of organic solvents, alcohols, ketones ammonia, polar aprotic solvents, including but not limited to dimethyl sulfoxide (DMSO), dimethylformamide (DMF), N-Methyl-2-pyrrolidone (NMP), Tetrahydrofuran (THF) and other commonly used solvents. Thus, the aqueous dispersion may be free from any non-aqueous solvents. Specifically, the dispersion may be free of ammonia, ammonia hydroxide and formaldehydes. The lignin may be insoluble in the aqueous dispersion. The aqueous liquid into which the plasticised lignin is dispersed may be weakly acidic, weakly alkaline or neutral before the addition of the lignin. Preferably the aqueous liquid has a pH from 5 to 9, or 6 to 8, or 6.5 to 7.5, or 6.75 to 7.25, or 7.1 to 7.25, or 6.9 to 6.75, or is 7, or any range formed from any combination of any of these endpoints. The plasticised lignin may be added to an aqueous liquid at ambient temperature (optionally 23°C). The aqueous dispersion may not undergo any heating.

The aqueous dispersion may be applied to the flexible substrate by any of the following, non-limiting exemplary methods: gravure printing, flexographic printing, offset printing, inkjet printing, Mayer bar coating, air knife coating, reverse roll coating, size press, curtain coating or dip coating.

The presence of a layer of plasticized lignin that has been deposited via a dispersion to a flexible substrate can be determined with a microscopy examination. Particles of the milled plasticised lignin can be seen under a microscope after evaporation of the aqueous liquid. The size of the particles visible under microscopy examination accords with the milled size of the plasticised lignin. Because dispersions of the present invention retain the lignin as a dispersion and do not dissolve the lignin into a solution, particles are retained in the heat seal layer, rather than presenting as a uniform film as would occur from a solution. This may advantageously improve heat seal properties because the particles may increase the surface area of the heat seal layer compared to a film deposited from a solution. The increase in surface area may result in further improved heat seal performance from faster thermal softening and increased heat seal strength. Thus, the plasticised layer may not be formed as a uniform film after drying of the dispersion but as a layer of particles.

The method may comprise the step of drying the aqueous dispersion. Drying may take place once the aqueous dispersion has been applied to the surface of the flexible substrate. Drying may be performed using air drying, infrared drying, hot air drying,(microwave drying, rIR radiation, a heated air source, and microwave radiation, amongst others. Drying may be performed by directing the heat source at the surface of the flexible substrate with the aqueous dispersion on, or on the reverse side of the flexible substrate, or both.

After a first layer of plasticised lignin has been applied to the flexible substrate and dried, subsequent layers may be applied using the same process. Thus, a method of making a heat-sealable flexible packaging material may comprise applying and drying two, three, or more layers of an aqueous dispersion to form the heat-seal layer. Consequently, the heat-sealable flexible packaging material may comprise a bulk layer of plasticised lignin that has been deposited from multiple individual layers of an aqueous dispersion. Individual layers may be visible in the bulk layer by microscopy inspection of a section through the packaging material.

The aqueous dispersion may comprise at least 10 wt.%, or at least 20 wt.%, or at least 30 wt.%, or at least 40 wt.% or at least 50 wt.%, or at least 60 wt.%, or at least 70 wt.%, or at least 80 wt.% of lignin and plasticiser (i.e the plasticised lignin).

The aqueous dispersion may have a pH of from 5 to 10, or from 6-9, or from 7-8 or any range formed from any combination of any of these endpoints. A basic substance may be added to the aqueous liquid to neutralise it. Basic substances may include, amongst others oxides, for example, metal hydroxides such as sodium hydroxide, potassium hydroxide, aluminium hydroxide and magnesium oxide. Strongly acidic or alkaline aqueous dispersions may increase wear on the apparatus for handling the dispersion. The dispersion may comprise a basic substance at from 0.01 to 10 wt.%, or from 0.05 10 5 wt.%, or from 0.1 to 2.5 wt.%, or from 0.5 to 1 wt.% or any range formed from any combination of these endpoints.

The plasticised lignin may be converted into micron-scale particles for dispersing in an aqueous liquid. The compounded lignin and plasticiser, i.e the plasticised lignin, may be milled, to produce small particles. This may produce a particulate from the compounded plasticised lignin suitable for dispersion. Milling may take place after compounding/extruding. Milling may comprise any mechanical method where solid polymer material is subjected to grinding or shearing forces to break it into micron-sized particles. Milling may produce micron-sized particles of the plasticised lignin of not exceeding 100 pm, or 80 pm, or 60 pm, or 40 WTI, or 30 pm, or 20 pm, or 10 pm. Milling may produce micron-sized particles of the plasticised lignin greater than 0.1 pm, or 0.5 pm, or 1 pm, or 2 pm, or 5 WTI, or 10 pm, or 15 pm, or 20 pm. Preferably milling of the plasticised lignin produces particles greater than 2 pm and not exceeding 40 pm. The size of a milled particle may be determined by passing the particles through sieves of known spacing sizes. Smaller particle sizes may be determined by laser diffraction or dynamic light scattering.

Milling may be performed by any appropriate milling apparatus capable of achieving the desired particle size. Milling may be performed by, amongst others, ball milling, basket milling, hammer milling, jet milling/fluid energy milling, attrition milling, roller milling, colloid milling, cone milling, vibratory milling, knife milling, pin milling, cryogenic milling or rotary cutter milling. Some of the methods above may be performed either wet (i.e. in the presence of a liquid) or dry (i.e. in the absence of a liquid). Wet milling in an aqueous liquid may have the advantage the milled plasticised lignin may be dispersed into the aqueous liquid during the milling process.

Alternatively, the compounded plasticised lignin may be converted to micron-sized particles by using spinning (including electrospinning) to create micron-sized fibers that can later be processed into particles; or by laser ablation, hydrodynamic cavitation, high-pressure homogenization or ultrasonication.

After milling, the milled particles may be dispersed in an aqueous liquid. Alternatively, the milled particles may be applied directly to the flexible substrate. This may be directly by spreading, or the particles may be combined with a polymeric binder (e.g. PVA) and then applied, or may be deposited by any known particle deposition method (for example spraying, fluidised bed deposition, or electrostatic powder coating). The milled particles may alternatively be melted and applied to the substrate using known hot melt or thermoforming techniques e.g. a hot melt roller coater.

The method of making a heat-sealable flexible packaging material may comprise dispersing the compounded and milled lignin and plasticiser (i.e. the milled, plasticised lignin) in an aqueous liquid. For example, the milled plasticised lignin is dispersed, or scattered, in water-based liquid. This is different to a solution where the particles are dissolved in a liquid solvent.

Mechanical agitation may be employed to disperse the particles in the aqueous liquid. Any appropriate stirrer, mixer or homogeniser known in the art may be used. Examples include but are not limited to ultrasonic homogenizers, rotor-stator mixers and magnetic stirrers. Alternatively, mechanical agitation may be done as part of wet milling when used, as explained above.

Stabilizing agents may be added to the dispersion. These are often used to prevent the agglomeration or coalescence of particles and to maintain the stability of the dispersion. Stabilizing agents may include the following non-limiting examples: surfactants: such as nonionic surfactants (e.g. Triton X-100, Tween 80), or anionic surfactants (e.g. sodium dodecyl sulfate (SDS), sodium lauryl sulfate), cationic surfactants (e.g. cetyltrimethylammonium bromide (CTAB), benzalkonium chloride); polymeric stabilizers: such as polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyethylene glycol (PEG)); electrostatic atabilizers (including polyelectrolytes such as polyacrylic acid (PAA) or polydiallyldimethylammonium chloride (PDADMAC)); steric stabilizers (including hydrophilic polymers (e.g. hydroxyethyl cellulose (HEC); hydrophobic polymers (poly(methyl methacrylate) (PMMA), polyethylene oxide (PEO); particulate stabilizers such as silica nanoparticles, and clay nanoparticles (e.g. bentonite, montmorillonite); biopolymers, such as starch and gum arabic; alcohols: ethanol, isopropanol; polymeric surfactants, such as pluronic series, polymer-coated nanoparticles; such a polymer-coated metal or oxide nanoparticles or any combination of the above. The dispersion may comprise a stabilizing agent at from 0.1 to 20 wt%, or from 0.5 to 15 wt.%, or from 1 to 10 wt%, or from 2 to 5 wt.% or any range formed from any combination of these endpoints.

Dispersants may be added to the aqueous dispersion to facilitate the uniform distribution of particles or components throughout the dispersion. Suitable dispersants may include but are not limited to surfactants, polymeric dispersants, phosphates, amino polymers, cellulose derivatives, acrylic polymers, silica dispersants, sulfonates and carboxylates. Specific examples may include but are not limited to sodium dodecyl sulfate (SDS), polyacrylic acid, sodium tripolyphosphate, polyethyleneimine, hydroxyethyl cellulose, tetramethylammonium hydroxide, dodecylbenzenesulfonic acid and disodium EDTA.The dispersion may comprise a dispersant from 0.01 to 10 wt.%, or from 0.05 10 5 wt.%, or from 0.1 to 2.5 wt.%, or from 0.5 to 1 wt.% or any range formed from any combination of these endpoints.

Buffers may be added to the dispersion to resist changes in pH. Suitable buffers may include phosphate buffers, acetate buffers, citrate buffers, tris buffers, Good's buffers, and phthalate buffers amongst others. The dispersion may comprise a buffer from 0.01 to 10 wt.%, or from 0.05 10 5 wt.%, or from 0.1 to 2.5 wt.%, or from 0.5 to 1 wt.% or any range formed from any combination of these endpoints.

Antioxidants may be added to the dispersion to delay the oxidation of the dispersion by reacting with free radicals. Suitable antioxidants may include but are not limited to, ascorbic acid (vitamin C), butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tocopherols (vitamin E), quercetin, propyl gallate, trolox, gallic acid and catechins. The dispersion may comprise an antioxidant from 0.01 to 10 wt.%, or from 0.05 to 5 wt.%, or from 0.1 to 2.5 wt.%, or from 0.5 to 1 wt.% or any range formed from any combination of these endpoints.

Anti-bacterial agents may be added to the dispersion to inhibit the growth or kill bacteria. Suitable anti-bacterial agents may include but are not limited to: Silver Nanoparticles, Triclosan, Quaternary Ammonium Compounds, Chlorhexidine, Iodine Compounds, Zinc Pyrithione, Trisodium Nitrilotriacetate, Isothiazolinones, Benzoyl Peroxide and Polyhexamethylene Biguanide. The dispersion may comprise an antibacterial agent from 0.01 to 10 wt %, or from 0.05 10 5 wt.%, or from 0.1 to 2.5 wt.%, or from 0.5 to 1 wt % or any range formed from any combination of these endpoints.

Rheology modifiers may be added to the dispersion to achieve specific viscosity, stability, and texture properties. Rheology modifiers may include polysaccharides (e.g. Xanthan Gum, Guar gum, alginate, carrageenan), polymers (e.g. Carbomers, acrylics, PVA), cellulose derivatives (e.g. Methylcellulose, Hydroxypropyl Methylcellulose, Hydroxyethyl Cellulose) and Polyethers (e.g. Polyethylene Glycol, polypropylene glycol), amongst others. The dispersion may comprise a rheology modifier from 0.01 to 10 wt.%, or from 0.05 10 5 wt.%, or from 0.1 to 2.5 wt.%, or from 0.5 to 1 wt.% or any range formed from any combination of these endpoints.

In some embodiments, the lignin has not been reacted with an oxidising agent prior to dispersing in an aqueous liquid to form an aqueous dispersion. Lignin is acidic and can result in an acidic dispersion. The aqueous liquid may be neutralised by the addition of a basic substance as explained above. The basic substance may cause some incidental oxidation of the lignin but oxidation of the lignin may have minimal effect on the functioning of the present disclosure.

The lignin may not have undergone a chemical modification. Chemical modification may comprise oxidisation by an oxidization agent, grafting of functional groups or any other reaction between the lignin and a reactive agent intended to substantially change the properties of lignin such as I.A. solubility. Preferably, the lignin does not undergo any covalent reaction to alter its molecular structure. Preferably, the lignin may not undergo any covalent reaction to alter its molecular structure prior to addition into the aqueous dispersion.

In embodiments where a basic substance is added to the aqueous dispersion to alter the pH, may not be considered a covalent reaction to alter the lignin molecular structure as any reaction with a basic substance of this nature may result in an incidental change to the lignin molecular structure.

The heat seal layer may have a thickness after drying of from 2 to 30 pm, or from 3 to 25 pm, or from 4 to 20 um, or from 5 ym to 15 pm, or any range formed from any of these endpoints. As explained above the heat seal may be deposited on the flexible substrate via extrusion or from an aqueous dispersion The heat seal layer may have a basis weight of 2 to 35 g/m2, or from 3 to 30 g/m2 or from 4 to 25 g/m2 or from 5 g/m2 to 20 g/m2 after drying, or any range formed from any of these endpoints.

The heat seal layer may be deposited on the flexible substrate in one, two, three, or more layers. Each layer may be dried before a subsequent layer is applied on top. The thickness of a heat seal layer when deposited in multiple layers may be calculated after the final layer has dried.

The heat sealable flexible packaging material may be sealed via the heat seal layer to a further packaging material with a heat seal strength greater than 2.5 N/15mm, or 2.9 N/15mm, or 3.4 N/15mm, or 3.9 N/15mm. Heat seal strength may be measured using ASTM F88.

A heat seal may provide a seal from the melting and solidifying of the heat seal layer. This is distinct from curing where covalent bonds form over time, or a pressure-sensitive adhesive where bonds form from contact with a tacky surface.

A heat sealable flexible packaging material may be capable of being sealed with high throughput. Therefore, the heat seal may be sealable with heat and pressure applied for less than 10 seconds, less than 8 seconds, less than 6 seconds, less than 5 seconds, less than 4 seconds, less than 3 seconds or less than 1 second. The heat and pressure may be applied for greater than 0.25 seconds, greater than 0.5 seconds, greater than 0.75 seconds or greater than 1 second. This may be necessary to allow for a large number of packaging items to be sealed on a production line.

A further packaging material may comprise a separate packaging material or a further portion of the heat-sealable flexible packaging material. The separate packaging material may include paper, paper board, polymeric sheets or films, polymeric, wood, fibre or pulp rigid packaging products. The separate packaging material may include additional functional layers thereon, which may include primers, barrier layers and/or a heat seal layer thereon. Where the heat sealable flexible packaging material may be sealed to a further portion of the heat-sealable flexible packaging material, this may be to either a surface with the heat seal layer or a surface free from the heat seal layer.

The heat sealable flexible packaging material may be sealed with the application of heat of at least 90°C, 110°C, 130°C, or 150°C. The heat sealable flexible packaging material may be sealed with the application of heat of no greater than 200°C, 170°C, 140°C, or 110°C.

The heat sealable flexible packaging material can be sealed with the application of pressure of 50 kPA, or 150 kPA, or 250 kPA, or 350 kPA, or 400 kPA or greater. The application of pressure may not exceed 1500 kPa, or 1000 kPA, or 800 kPA, or 600 kPA, or 500 kPA, or 400 kPA, or 300 kPA.

The heat seal layer may be free from cross-linking agents. Cross-linking agents may be defined as any agent that is capable of forming a plurality of covalent bonds with the lignin. Cross-linking agents may include p-hydroxyalkylamide-cross-linkers, oxazoline-cross-linkers, aldehydes, isocyanates, phenolic hydroxyls, epoxy-based cross linkers and/or novolacs.

The method may comprise bringing a portion of a heat-sealable flexible packaging material in contact with a further portion of a flexible packaging material and applying heat and pressure, to seal the further flexible packaging material to the heat-sealable flexible packaging material via the heat seal layer.

Heat seal apparatus may comprise, amongst others, an impulse heat sealer, constant heat sealers, hot bar sealers, jaw sealers, vacuum sealers, ultrasonic sealers and induction sealers where the heat sealable packaging material comprises a metallic or otherwise inducible component.

The use may comprise cutting a series of blank shapes from a roll of the heat-sealable flexible packaging material. The reverse side of the heat sealable flexible packaging material may be printed on and/or varnish may be applied. The heat sealable flexible packaging material may be used to form an overwrapper, a pouch, a sachet, a doy pack, a pillow bag, a gusseted bag, quad seal bag, a shaped pouch, a zipper bag or any other packaging form requiring heat sealing in the manufacture thereof. Assembling any of these packaging forms may require arranging one or more blanks of the heat sealable flexible packaging material, and/or folding one or more blanks of the heat sealable flexible packaging material and heat sealing to retain the desired shape. The packaging forms may be assembled around a product, or an intermediate form may be created (e.g. a tube), filled with a product, and then sealed.

The preceding description is provided for the purposes of summarizing some embodiments to provide a basic understanding of aspects of the subject matter described herein. Accordingly, the above-described features are merely examples and should not be construed to narrow the scope or spirit of the subject matter described herein in any way. Moreover, the above and/or proceeding embodiments may be combined in any suitable combination to provide further embodiments. Features described in one aspect of the disclosure are to be construed as applicable to other aspects of the disclosure.

Examples

Before describing examples of the present disclosure, it is to be understood that the present disclosure is not limited to the details of construction or process steps set forth in the Examples below. It will be apparent to those skilled in the art having the benefit of the present disclosure that the embodied examples are capable of being practised or being carried out in various ways.

Materials: Lignin 1: Soda lignin, from WEPA, Germany, a lignin derived from miscanthus grass.

Plasticiser 1: Technical grade Azelaic acid containing 80% Azelaic acid (Azelainsaure tech.

80%, technische Qualitat VWR, Germany).

Plasticiser 2: Polyethylenglycol 400 (GPR RECTAPUR®I VWR, Germany).

Paper 1 is an 80 gsm bleached, coated paper from Brigl & Bergmeister, Germany.

Paper 2 is a 50 gsm bleached and uncoated paper from GrUnewaldt, Germany.

Paper 3 is a 150 gsm paper made from agricultural waste from PaperWise, Netherlands.

Method: Plasticised lignin was produced by compounding the lignin with the plasticizer. Compounding was performed using a Nortek filament single-screw extruder (Nortek Touch, Nortech Extrusion Systems, UK). The plasticizers and the lignin were added to the single-screw extruder. Extrusion took place at 115°C. Two plasticized lignins were produced: Plasticised lignin 1: comprising 80 wt.°/o lignin 1 and 20 wt.°/o plasticiser 1. Plasticised lignin 2: comprising 75 wt.% lignin 1, 15 wt.% plasticiser 2 and 10 wt.% plasticiser 1.

Plasticised lignin was milled using a blade mill (Multidrive, IKA, UK). This produced a typical particle size of < 45 (mesh size of the utilised sieve).

To make the dispersion, the milled lignin particles were added to water at 50 wt%. A dispersant (DOW Acumer 9210) was added to the water at 0.1 wt%. The lignin particles were dispersed in the aqueous using a disperser (T-18 Ultra-Turrax, IKA, UK).

The plasticised lignin was applied to papers 1 to 3. The plasticised lignin was applied from the dispersion described above at 9-16.5 gsm or was laminated at 40 gsm. Dispersion was performed using a SUMET roll-to-roll coater in filmpress or rod mode at ICP in Ljubljana, Slovenia. Lamination was performed by applying the milled lignin directly to paper by weighting an amount calculated for a defined surface to reach a certain grammage and spreading the milled lignin particles onto the defined surface by hand.

The coated paper was sealed to itself using a Labthink heat sealer (Labthink GmbH, Germany) at 130°C for 3s at 450kPa. The resulting heat seal strength was analysed using a Labthink tensile tester (Labthink Gmbh, Germany) and ASTM F88. The results of the heat seal testing are shown in Table 1 below.

Formulation Deposition Paper GSM Seal Strength (ASTM F88) St. dev.

Plasticised lignin 1 Milled particles by hand 3 40 1.60 N/15mm 0.08 Milled particles by hand 2 40 1.79 N/15mm 0.10 Milled particles by hand 1 40 1.59 N/15mm 0.21 Dispersion 2 9 2.35 N/15mm* 0.31 Dispersion 1 16.5 3.69 N/15mm* 0.05 Plasticised lignin 2 Dispersion 2 9 2.26 N/15mm* 0.13 Dispersion 1 16.5 0.28 N/15mm 0.2 Milled particles by hand 3 40 3.83 N/15mm* 0.10 Milled particles by hand 2 40 1.30 N/15mm 0.10 Milled particles by hand 1 40 2.60 N/15mm* 0.23 Table 1. * denotes failure by fibre tear.

The results of Table 1 show that the plasticised and milled lignin provides an effective heat seal to paper In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word 'comprising' does not exclude the presence of other elements or steps than those listed in a claim. Furthermore, the terms "a" or "an," as used herein, are defined as one or more than one. Also, the use of introductory phrases such as "at least one" and "one or more" in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an." The same holds true for the use of definite articles. Unless stated otherwise, terms such as "first" and "second" are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

Unless otherwise explicitly stated as incompatible, or the physics or otherwise of the embodiments, example or claims prevent such a combination, the features of the foregoing embodiments, examples, and of the following claims may be integrated together in any suitable arrangement, especially ones where there is a beneficial effect in doing so. This is not limited to only any specified benefit and instead may arise from an "ex post facto" benefit. This is to say that the combination of features is not limited by the described forms, particularly the form (e.g. numbering) of the example(s), embodiment(s), or dependency of the claim(s). Moreover, this also applies to the phrases "in one embodiment", "according to an embodiment" and the like, which are merely a stylistic form of wording and are not to be construed as limiting the following features to a separate embodiment to all other instances of the same or similar wording. This is to say, a reference to 'an', 'one' or 'some' embodiment(s) may be a reference to any one or more, and/or all embodiments, or combination(s) thereof, disclosed. Similarly, the reference to "the" embodiment may not be limited to the immediately preceding embodiment.

The preceding description of one or more implementations provides illustration and description but is not intended to be exhaustive or to limit the scope of the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from the practice of various implementations of the present disclosure.

Claims

Claims 1. A method of making a heat-sealable flexible packaging material, the method comprising: compounding a lignin and a plasticiser to form a plasticised lignin, and applying a layer of the plasticised lignin to a surface of a flexible substrate to form a heat seal layer thereon, by extruding the plasticised lignin or from an aqueous dispersion of the plasticised lignin.
2. A method of making a heat-sealable flexible packaging material according to claim 1, wherein the plasticised lignin is dispersed in an aqueous liquid to form the aqueous dispersion.
3. A method of making a heat-sealable flexible packaging material according to claim 1 or claim 2, wherein the aqueous dispersion comprises at least 10 wt.%, or at least 20 wt.%, or at least 30 wt.%, or at least 40 wt.% or at least 50 wt.%, or at least 60 wt.%, or at least 70 wt.%, or at least 80 wt.% of lignin and plasticiser.
4. A method of making a heat-sealable flexible packaging material according to any preceding claim, comprising the step of drying the aqueous dispersion.
5. A method of making a heat-sealable flexible packaging material according to any preceding claim, comprising applying and drying two, three or more layers of an aqueous dispersion to form the heat seal layer.
6. A method of making a heat-sealable flexible packaging material according to claim <above>, wherein the heat seal layer has a thickness of from 2 to 30 pm, or from 3 to 25 pm or from 4 to 20 pm or from 5 pm to 15 pm after drying.
7. A method of making a heat sealable flexible packaging material according to any preceding claim, wherein the heat seal layer has a basis weight of 2 to 35 g/m2, or from 3 to 30 g/m2 or from 4 to 25 g/m2 or from 5 g/m2 to 20 g/m2 after drying.
8. A method of making a heat-sealable flexible packaging material according to claim 2 or any claim dependent thereon, wherein the lignin and a plasticiser are dispersed in water and with no additional solvents to form the aqueous dispersion.
9. A method of making a heat-sealable flexible packaging material according to claim 2 or any claim dependent thereon, wherein the aqueous dispersion is free from any non-aqueous solvents.
10. A method of making a heat-sealable flexible packaging material according to claim 2 or any claim dependent thereon, wherein the aqueous dispersion has a pH of from 5 to 10, or from 6-9, or from 7-8.
11. A method of making a heat-sealable flexible packaging material according to any preceding claim, comprising milling the compounded lignin and plasticiser.
12. A method of making a heat-sealable flexible packaging material according to claim 11, comprising dispersing the compounded and milled lignin and plasticiser in an aqueous liquid.
13. A method of making a heat-sealable flexible packaging material according to claim 2 or any claim dependent thereon, wherein the lignin is not reacted with an oxidising agent prior to dispersing in an aqueous liquid to form an aqueous dispersion.
14. A method of making a heat-sealable flexible packaging material according to claim 1, comprising extruding the plasticised lignin to apply a layer of the plasticised lignin to a surface of the flexible substrate to form a heat seal layer.
15. A method of making a heat-sealable flexible packaging material according to claim 14, wherein the heat seal layer has a thickness of from 5 to 50 pM, or from 7 to 40 rim or from 10 to 30 ym.
16. A method of making a heat-sealable flexible packaging material according to any of claim 14 or claim 15, wherein the plasticised lignin is extruded via slot die extrusion.
17. A method of making a heat-sealable flexible packaging material according to any preceding claim, comprising bringing a portion of a heat-sealable flexible packaging material in contact with a further portion of a flexible packaging material, and applying heat and pressure, to seal the further flexible packaging material to the heat-sealable flexible packaging material via the heat seal layer
18. A heat-sealable flexible packaging material, comprising a flexible substrate and a heat seal layer on a surface thereof, the heat seal layer comprising: lignin and a plasticiser; wherein the heat seal layer has been deposited on a surface of the flexible substrate from an aqueous dispersion or an extrusion.
19. A heat sealable flexible packaging material according to claim 18, wherein the heat seal layer has been deposited on the flexible substrate from an aqueous dispersion and has a thickness of from 2 to 30 pm, or from 3 to 25 pm or from 4 to 20 pm or from 5 pm to 15 pm after drying.
20. A heat sealable flexible packaging material according to claim 18 or claim 19, wherein the heat seal layer has been deposited on the flexible substrate in one, two, three, or more layers.
21. A heat sealable flexible packaging material according to claim 20, wherein the heat seal layer has been deposited on the flexible substrate as an extrusion, and has a thickness of from 5 to 50 pm, or from 7 to 40 pm or from 10 to 30 pm after cooling.
22. A method or a heat sealable flexible packaging material according to any previous claim, wherein the heat sealable flexible packaging material can be sealed via the heat seal layer to a further packaging material with a heat seal strength greater than 2.5 N/15mm, or 2.9 N/15mm, or 3.4 N/15mm, or 3.9 N/15mm, measured with ASTM F88.
23. A method or a heat sealable flexible packaging material according to claim 22, wherein the heat sealable flexible packaging material can be sealed with the application of heat of 130°C for 4 seconds.
24. A method or a heat sealable flexible packaging material according to claim 23, wherein the heat sealable flexible packaging material can be sealed with the application of pressure of 450 kPa for 4 seconds.
25. A method or a heat sealable flexible packaging material according to any previous claim, wherein the flexible substrate is a cellulosic substrate, optionally wherein the flexible substrate is a paper or paper board.
26. A method or a heat sealable flexible packaging material according to any preceding claim, wherein the flexible substrate has a basis weight of 20g/m2 to 200 g/m2, or from 40 g/m2 to 120 g/m2, or from 50 g/m2 to 100 g/m2, or from 60 g/m2 to 85 g/m2.
27. A method or a heat sealable flexible packaging material according to any previous claim, wherein the lignin comprises lignin from the soda pulping process.
28. A method or a heat sealable flexible packaging material according to any previous claim, wherein the lignin comprises lignin derived from grasses, optionally wherein the lignin is derived from miscanthus grasses.
29. A method or a heat sealable flexible packaging material according to any previous claim, wherein the lignin has a paracoumaryl alcohol content of 10% or more.
30. A method or a heat sealable flexible packaging material according to any previous claim, wherein the plasticiser comprises an acid.
31. A method or a heat sealable flexible packaging material according to claim 30, wherein the plasticiser comprises a dicarboxylic acid.
32. A method or a heat sealable flexible packaging material according to claim 31, wherein the plasticiser comprises a saturated dicarboxylic acid.
33. A method or a heat sealable flexible packaging material according to any previous claim, wherein the plasticiser comprises an acid with the structure HOOC(CH2)xCOOH where Xis 1-50 or 3-30 or 4-15 or 5-10 or 6-8 or 7.
34. A method or a heat sealable flexible packaging material according to any previous claim, wherein the % of lignin in the compounded lignin and plasticiser is from 60% to 95% or from 70 % to 90 % or from 75% to 85%.
35. A method or a heat sealable flexible packaging material according to any previous claim, wherein the lignin comprises a particle size of 40 pm or less, or 30 pm or less, or 20 pm or less, or 10 pm or less.
36. A method or a heat sealable flexible packaging material according to any preceding claim wherein the heat seal layer is free from cross-linking agents.
37. A method or a heat sealable flexible packaging material according to any preceding claim wherein the lignin has not undergone a chemical modification, optionally wherein the chemical modification includes oxidisation by an oxidization agent or grafting of functional groups.
38. A method of making a heat-sealable flexible packaging material according to any of claims 1 to 17 or any claim dependent thereon, wherein the plasticised lignin is not dissolved or dispersed with a non-aqueous solvent.
39. method of making a heat-sealable flexible packaging material according to any of claims 1 to 17 or any claim dependent thereon, wherein the lignin is not reacted with an oxidising agent.
40. Use of a heat sealable flexible packaging material according to any of claims 18 to 37 or any claim dependent thereon, for sealing a portion thereof to a portion of further packaging material with the application of heat and pressure.