Heat sealable packaging material

Abstract

The invention relates to a method for manufacturing a heat sealable packaging material (1). The method comprises supplying a support layer (2) comprising a paper (2a) and applying a barrier coating composition (5) in form of an aqueous dispersion on the support layer (2), the aqueous dispersion having solids content from 40 to 70 wt.%. The barrier coating layer (3) has a coat weight of 2 to 10 g / m2 and comprises mineral fillers from 50 wt.% to 70 wt.% and binding agents from 30 wt.% to 50 wt.%. A first binding agent is a polyvinyl alcohol, and a second binding agent is selected from styrene-acrylate copolymers, acrylate-vinyl acetate copolymers, styrene-butadiene copolymers, and their mixtures. The invention relates to a heat sealable packaging material (1).

Description

[0001] HEAT SEALABLE PACKAGING MATERIAL

[0002] Technical field

[0003] The specification relates to heat sealable packaging materials. The specification relates to a method for manufacturing a heat sealable packaging material.

[0004] Background

[0005] A large variety of packaging materials is manufactured in industry. For packaging materials, properties, and the desired shelf life of the products to be packaged typically determine the packaging material used for packaging each product. Further, packaging materials used for food products must have some properties that may not be needed in other applications.

[0006] Materials used for obtaining desired barrier properties can be selected so that if e.g., good water vapor barrier properties are needed, a packaging material can comprise a layer having excellent water vapor barrier properties, e.g., an aluminum foil.

[0007] In industry, however, there is still need for new packaging materials.

[0008] Summary

[0009] It is an aim of this specification to present a heat sealable packaging material. Furthermore, it is an aim of this specification to present a method for manufacturing a heat sealable packaging material.

[0010] Aspects of the invention are characterized by what is stated in the independent claims. Preferred embodiments of the invention are disclosed in the dependent claims. These and other embodiments of the invention are disclosed in the description and figures.

[0011] The heat sealable packaging material according to this specification comprises a support layer comprising cellulose-containing natural fibers. The heat sealable packaging material comprises at least one barrier coating layer.

[0012] Preferably, the heat sealable packaging material comprise or consist of a paper, optionally, a first precoating layer on a first side of the paper, optionally, a second precoating layer on a second side of the paper, only one barrier coating layer, preferably on the first precoating layer.

[0013] The first precoating layer is an optional but preferable layer on the first side of the paper, between the uncoated paper and the barrier coating layer. Technical effects include preparing the surface of the support layer for the barrier coating layer. Technical effects of the first precoating layer include improving coating holdout, hence, the later added coating layer, i.e., the barrier coating layer, does not absorb into porous paper as much, requiring less coating to make a uniform layer.

[0014] In an embodiment, the heat sealable packaging material does not have the first precoating layer. Thus, the barrier coating layer can be directly on the first side of the paper. Technical effect is to simplify the process.

[0015] The second precoating layer is an optional but preferable layer on the second side of the paper, such as between the uncoated paper and a printing. Technical effect is to prepare the surface of the support layer for a printing.

[0016] In an embodiment, the heat sealable packaging material does not have the second precoating layer. Technical effect is to simplify the process.

[0017] The optional precoating layer(s) can be directly on the paper, preparing the surface of the support layer for the barrier coating layer and / or a printing. At least one of the precoating layers can comprise or consist of a binding agent. Thus, the first precoating layer can comprise or consist of binding agent(s). Thus, the support layer can be an uncoated paper or a precoated paper. The barrier coating layer can be on the first precoating layer, or the barrier coating layer can be directly on the uncoated paper.

[0018] As discussed, the barrier coating layer is on the first precoating layer. Technical effect is that the precoating layer and the barrier coating layer create a synergistic effect, further improving barrier properties of the heat sealable packaging material.

[0019] In an embodiment, the paper is calendered or supercalendered paper. Particularly, if the support layer is an uncoated paper and the barrier coating layer is directly on the uncoated paper, the uncoated paper can be calendered paper. Thus, the uncoated paper can be treated by methods such as calendering to enable coating hold-out. Further technical effect of the calendering is to provide barrier properties for the heat sealable packaging material cost-efficiently.

[0020] A method for manufacturing a heat sealable packaging material according to this specification can comprise the following steps: supplying a support layer comprising a paper comprising cellulose- containing natural fibres, and applying a barrier coating composition in form of an aqueous dispersion on the support layer, the aqueous dispersion preferably having solids content from 40 to 70 wt.%, thereby forming a barrier coating layer, the barrier coating layer having a dry coat weight of 2 to 10 gsm and comprising mineral fillers from equal to or more than 50 wt.% to 70 wt.% of a total dry weight of the barrier coating layer, and binding agents from 30 wt.% to 50 wt.% of a total dry weight of the barrier coating layer, wherein a first binding agent is a polyvinyl alcohol, and an amount of the polyvinyl alcohol is from 15 to 30 wt.%, preferably from 17 wt.% to 25 wt.%, of a total dry weight of the barrier coating layer, and a total amount of the second binding agent is from 10 to 20 wt.% of the total dry weight of the barrier coating layer, wherein the second binding agent is selected from styrene-acrylate copolymers, acrylate-vinyl acetate copolymers, styrene-butadiene copolymers, and their mixtures.

[0021] One technical effect of the heat sealable packaging material comprising the barrier coating layer having high mineral pigment content, polyvinyl alcohol as the first binding agent, and styrene-acrylate copolymer, acrylate-vinyl acetate copolymer, and / or styrene-butadiene copolymer as the second binding agent is to improve runnability during manufacturing process of the heat sealable packaging material. For environmental and cost reasons, the heat sealable packaging material preferably comprises only one barrier coating layer, the barrier coating layer having a dry coat weight of 2 to 10 gsm.

[0022] A heat sealable packaging material according to this specification can comprise a support layer comprising a paper comprising cellulose-containing natural fibres, a barrier coating layer having a coat weight of 2 to 10 g / m2and comprising mineral fillers 50 wt.% to 70 wt.% of a total dry weight of the barrier coating layer, and binding agents from 30 wt.% to equal to or less than 50 wt.% of the total dry weight of the barrier coating layer, wherein the binding agents comprise a first binding agent and a second binding agent, wherein the first binding agent is a polyvinyl alcohol, and an amount of the polyvinyl alcohol is from 15 to 30 wt.%, preferably from 17 wt.% to 25 wt.%, of the total dry weight of the barrier coating layer, and a total amount of the second binding agent is from 10 to 20 wt.% of the total dry weight of the barrier coating layer, and the second binding agent is selected from styrene-acrylate copolymers, acrylate-vinyl acetate copolymers, styrene-butadiene copolymers, and their mixtures.

[0023] The technical effects of the heat sealable packaging material according to this specification include that there is no need to use extrusion coating or other further converting for desired barrier properties. Furthermore, the heat sealable packaging material can be recycled in regular paper wastepaper process after usage. Still further, the coating composition does not wet the paper web as much as some other water based barrier dispersions, and thus it contributes a better dimension stability of the paper web. Still further, the barrier coating composition can have good film forming and adhesive properties, excellent runnability and high-solid content capacity, providing lower energy consumption and need of equipment for drying.

[0024] Typically, mineral pigments negatively affect heat sealability. Surprisingly, the barrier coating layer according to this specification having high mineral pigment content of equal to or more than 50 wt.% (by dry weight), up to 70 wt.% (by dry weight), and a binding agent content of equal to or less than 50 wt.% is heat sealable. Still further, the heat sealable packaging material can improve production efficiency as the high mineral pigment content provides increased solids content, improving efficiency of a drying process. Furthermore, the barrier coating layer can provide desired barrier properties for many applications.

[0025] Surprisingly, runnability of the barrier coating composition having mineral pigment content of equal to or more than 50 wt.% was improved compared to barrier coatings having low mineral pigment content. The best results were obtained by using kaolin as the mineral pigment. Thus, preferably, the barrier coating layer comprises equal to or more than 30 wt.% of kaolin, more preferably the barrier coating layer comprises more than 40 wt.% of kaolin, and most preferably, the barrier coating layer comprises equal to or more than 50 wt.% of kaolin, determined as dry weight of the barrier coating layer. As discussed, the heat sealable packaging material can further comprise the first precoating layer, which precoating layer is between the paper and the barrier coating layer. A grammage of the first precoating layer can be in a range between 1 gsm and 10 gsm.

[0026] Surprisingly, for obtaining the desired properties for many applications, amount of the first binding agent should be from 15 to 30 wt.%, preferably from 17 wt.% to 25 wt.%, of a total dry weight of the barrier coating layer, and amount of the second binding agent(s) should be from 10 to 20 wt.% of the total dry weight of the barrier coating layer.

[0027] As discussed, the first binding agent is polyvinyl alcohol. Technical effects of the first binding agent include increasing elasticity of the coating layer.

[0028] As discussed, the second binding agent is selected from styrene-acrylate copolymers, acrylate-vinyl acetate copolymers, styrene-butadiene copolymers, and their mixtures.

[0029] Technical effect of this co-binder is to improve the coating color runnability by lowering viscosity and increasing solids content. Another technical effect of these binding agents is to provide heat sealable barrier paper.

[0030] Thus, the second binding agent can comprise, or be the styrene-acrylate copolymer. The technical effect of the styrene-acrylate copolymer is to provide good adhesion, water resistance, and film formation properties, smoothness, gloss, brightness, and opacity to the paper surface.

[0031] The second binding agent can comprise or be the acrylate-vinyl acetate copolymer. The technical effect of the acrylate-vinyl acetate copolymer includes high flexibility and good compatibility with other polymers, as well as resistance to cracking and peeling.

[0032] The second binding agent can comprise or be the styrene-butadiene copolymer. The technical effects of the styrene-butadiene copolymers include improved cost efficiency, high coating layer elasticity, abrasion resistance, and dimensional stability to the paper surface, as well as resistance to water absorption and surfactant migration.

[0033] The barrier coating layer comprises both, the first binding agent and the second binding agent. The barrier layer can comprise only two binding agents, i.e., only the first binding agent and the second binding agent. Surprisingly, it was possible to provide heat sealable packaging material having improved properties by replacing part of the second binding agent with the first binding agent. Surprisingly, the novel heat sealable packaging material according to this specification is heat sealable and has desired properties for many applications.

[0034] A ratio of the first binding agent of the barrier coating layer to the second binding agent of the barrier coating layer is preferably in a range from 0.5 to 3, more preferably from 0.75 to 3.0, still more preferably from 0.75 to 2.5, and most preferably from 1.0 to 2.0. Technical effects include providing environmentally friendly heat sealable packaging material having improved barrier properties as well as desired film forming, elasticity, emulsifying and adhesive properties.

[0035] In an embodiment, the barrier coating layer has a mineral pigment content from 50 wt.% to 70 wt.%. Technical effects include decreasing manufacturing costs of the product, while obtaining desired barrier properties. Further, said mineral pigment contents can increase solids content of the barrier coating layer(s), decreasing energy needed to dry the barrier coating layer. Thus, the novel heat sealable packaging material can be particularly environmentally friendly product.

[0036] Preferably, the heat sealable packaging material has a hydrocarbon barrier (n- heptane vapor transmission rate) of less than 30 g / m2*day, more preferably less than 20 g / m2*day, and most preferably less than 10 g / m2*day.

[0037] Preferably, the heat sealable packaging material has a WVTR value of less than 10 g / m2*day, determined at 23°C / 50% RH according to standard ISO 2528. A package according to this specification can comprise the heat sealable packaging material according to this specification.

[0038] Conventionally, a barrier is formed on a fiber-based substrate by using e.g. metallization, extrusion-coating or lamination using plastics. Nowadays producers and end users are looking for alternative paper and board products in various applications on a fit for purpose bases avoiding metallization, extrusion-coating, or lamination.

[0039] All coating layers of the heat sealable packaging material are preferably aluminum free. Most preferably, the heat sealable packaging material does not contain a metal-based foil. Technical effect is to obtain environmentally friendly, aluminum free route to obtain desired barrier values.

[0040] Preferably, all coating layers of the heat sealable packaging material are nanocellulose free, or at least substantially nanocellulose free, coating layers. Technical effect is to provide cost efficiently more environmentally friendly heat sealable barrier material as the production of nanocellulose, as well as drying of nanocellulose containing coatings, can be very energy consuming processes.

[0041] The heat sealable packaging material according to the specification can be manufactured in an environmentally friendly way. Dispersion coating offers a route to thinner barrier coating layers compared to extrusion coating or lamination. Further, dispersion coatings can reduce manufacturing and transportation costs. This decreases environmental load such as the carbon dioxide load. Thus, preferably, the heat sealable packaging material does not have an extrusion coated layer.

[0042] The heat sealable packaging material can provide excellent mineral oil and water vapor barrier properties for a package made of the heat sealable packaging material. The heat sealable packaging material is capable of preventing or at least limiting water vapor, and mineral oil migration through the heat sealable packaging material. Paper and board based packages are preferably recyclable. The heat sealable packaging material comprising the barrier coating layer can satisfy the recyclability requirements.

[0043] The solution according to this specification can provide flexible or rigid packaging applications for food, beverages as well as for non-food, where barrier values are needed. Preferably, the heat sealable packaging material is designed to ensure recyclability.

[0044] The packaging material according to this specification is preferably used for packaging food. Effective barriers, include resistance to water vapor, mineral oil, are often required in packaging industry to extend shelf-life of packaged food products.

[0045] Advantageously, the heat sealable packaging material is heat sealable at least at 160°C, determined at 0.6 bar sealing pressure, by using 1 .0 s dwell time so that the material has a seal strength of more than 4 N / 15 mm, with full fiber tear. Further, preferably, the heat sealable packaging material is not showing adhesion at 80°C. Technical effect is that ability of the heat sealable packaging material to be heat-sealed at 160°C while not showing adhesion at 80 °C can enhance process flexibility in the manufacturing process as well as in packaging.

[0046] Surprisingly, the combination of the first binding agent and the second binding agent was suitable for achieving desired properties. For example, for obtaining the desired properties, amount of the first binding agent should be from 15 to 30 wt.%, preferably from 17 wt.% to 25 wt.%, of a total dry weight of the barrier coating layer, and total amount of the second binding agent should be from 10 to 20 wt.% of the total dry weight of the barrier coating layer. Surprisingly, the heat sealable packaging material had, during experimental tests, a desired combination of heat sealability properties; they did not exhibit adhesion at 80 °C, but had a desired seal strength of more than 5 N / 15 mm at temperatures from 160°C up to 200°C, with full fiber tear. Furthermore, the coating composition had, during experimental tests, a desired solids content behavior. In an embodiment, the heat sealable packaging material is not an oxygen barrier material.

[0047] Brief description of the

[0048] In the following, the invention will be described in more detail with reference to the appended drawings, in which:

[0049] Figs 1 -4 illustrate examples of heat sealable packaging materials in crosssection,

[0050] Fig. 5 illustrates example method steps for manufacturing a heat sealable packaging material,

[0051] Fig. 6 shows solids content and Brookfield viscosity of coating color as a function of PVA fraction in binder mixture, determined during experimental tests, and

[0052] Fig. 7 shows seal strength curves from experimental tests.

[0053] The Figures are intended to illustrate the general principles of the disclosed solution. Therefore, the illustrations in the Figures are not necessarily in scale or suggestive of precise layout of system components.

[0054] Detailed description

[0055] In the text, references are made to the figures with the following numerals and denotations:

[0056] 1 heat sealable packaging material,

[0057] 2 support layer,

[0058] 2a paper,

[0059] 2b 1 first precoating layer on a first side of the paper 2a,

[0060] 2b2 second precoating layer on a second side of the paper 2a,

[0061] 3 barrier coating layer,

[0062] 4a first precoating composition,

[0063] 4b second precoating composition,

[0064] 5 barrier coating composition,

[0065] 6 precoating unit, and 7 barrier coating unit.

[0066] Terms and standards

[0067] Unless otherwise indicated, the following standards refer to methods which are used in obtaining stated values of parameters representing quality of the packaging material:

[0068] 1 ) Grammage ISO 536:2019

[0069] 2) WVTR ISO 2528 at 23°C / 50%RH

[0070] 3) Brookfield viscosity SCAN-P 50:84 using RV Brookfield equipment

[0071] 4) KIT Tappi T559 cm02

[0072] 5) Mineral oil barrier:

[0073] Heptane vapor transmission rate (HVTR) is determined by a gravimetric method adapted from the method described in Gaudreault et al. 2013 (R. Gaudreault, C. Brochu, R. Sandrosck, P. Deglmann, H. Seyffer and A. Tetreault. Overview of practical and theoretical aspects of mineral oil contaminants in mill process and paperboards. In Advances in Pulp and Paper Research, Cambridge 2013, Trans, of the XVth Fund. Res. Symp. Cambridge, 2013, (S.J. I’Anson, ed.), pp 907-925, FRC, Manchester, 2018. DOI: 10.15376 / frc.2013.2.907. A sponge soaked in n-heptane is placed in a test cup, that is then covered with the tested paper, barrier side down. Cup edges are then sealed with molten wax, and the filled and sealed cups are kept at standard conditions (50 % relative humidity and 23°C). The cups are weighed immediately after sealing, and then after 2h, 3h, 5h, and 25h. The HVTR is determined according to the equation in Gaudreault et al. 2013.

[0074] 6) Heat sealability test:

[0075] Unless otherwise indicated, the heat sealability is tested by cutting 15 x 120 mm specimen from the heat sealable packaging material and sealing them coating vs. coating according to ASTM F2029-16. Seal strength (N / 15 mm) can be measured with a tensile tester according to standard ASTM F88 / F88M- 15. Seal strength with said 15 mm wide specimen is preferably at least 4 N, more preferably at least 5 N. To be fully sealed, the sealed area should also show a full fiber tear.

[0076] Unless otherwise indicated, sealing parameters are dwell time of 1 .0 s and jaw pressure of 0.6 bar.

[0077] The seal of the heat sealable packaging material has preferably the seal strength of at least 4 N, more preferably at least 5 N, and full fiber tear, when the seal has been sealed at 180 °C, preferably at 160 °C. It is advantageous for the sealing process and many applications that full fiber tear and high enough seal strength are reached at 180 °C, preferably at 160 °C.

[0078] The term ‘WVTR’ refers to water vapour transmission rate. Unless otherwise indicated, the term WVTR refers to water vapour barrier at conditions of RH 50%, temperature 23°C.

[0079] The term ‘RH’ relates to relative humidity of the air.

[0080] In this specification, percentage values relating to an amount of a material are percentages by weight (wt.%) unless otherwise indicated. All the contents (percentages) are in dry weight, unless otherwise expressed.

[0081] The terms ‘gsm’ refers to grams per square meter (g / m2). Unless otherwise indicated, all the grammages (i.e., coat weights) are in dry weight.

[0082] For the purpose of the present description and the claims, unless otherwise indicated, all ranges include any combination of the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

[0083] The embodiments and examples recited in the claims and in the description are mutually freely combinable unless otherwise explicitly stated.

[0084] In this specification, the term “comprising” may be used as an open term, but it also comprises the closed term “consisting of’. Thus, unless otherwise indicated, the word “comprising” can be read as “comprising or consisting of’. The term “binder” refers to a binding agent.

[0085] The term "PVA" refers to polyvinyl alcohol. Polyvinyl alcohol is a synthetic polymer prepared e.g. by the polymerization of vinyl acetate, followed by a controlled hydrolysis of the ester in the presence of an alkaline catalyst.

[0086] Polyvinyl alcohol can be dissolved by adding the polyvinyl alcohol powder or granulates to water and by heating the slurry to 80-100°C for 20-60 minutes using steam or a heating equipment. Fully hydrolyzed PVA usually has a degree of hydrolysis (DS) of 98% to 99.8%, and can dissolve in water only at > 80 °C.

[0087] The term “latex” refers to a dispersion of polymer particles in water. Latex may be natural, for example originating from flowering plants, or be synthetic, or the combination thereof.

[0088] The term “polymer dispersion” refers to a polymer dispersed into water by a dispersion technology such as a thermal or mechanical method or combinations thereof, or created by polymerizing monomer(s) dispersed in water.

[0089] The term “dispersible polymer” refers to a polymer that can be dispersed into water by a dispersion technology such as a thermal or mechanical method or combinations thereof.

[0090] In this specification, the term “pigment” particularly refers to mineral pigments. Mineral pigments can comprise at least one of: kaolin, natural ground calcium carbonate, precipitated calcium carbonate, talc, calcium sulphate, and titanium dioxide.

[0091] In this specification the term "platy pigment" refers to pigments having a flat structure in which one dimension is substantially smaller than the two other dimensions of the structure. Examples of platy pigment include kaolin, talc, and mica. The term “coating composition” refers to an aqueous composition to be applied on to a surface of an object to form a coating layer.

[0092] The term "dispersion coating" refers to a coating technique in which a coating composition in form of an aqueous dispersion comprising polymer particles is applied to a surface of a substrate to form a solid coating layer after drying.

[0093] The term “coating layer” refers to a thin solid layer that is applied to a surface of a substrate.

[0094] Advantageously, all coating layers of the heat sealable packaging material are formed by the dispersion coating technique. Technical effect is to provide, efficiently, thinner coating layers compared to extrusion-coating or lamination. Further, dispersion-coating can reduce manufacturing and transportation costs. This decreases environmental load such as the carbon dioxide load.

[0095] Support layer

[0096] The support layer 2 comprises a paper 2a having a first side and a second side. Thus, the support layer 2 has a first side and a second side.

[0097] The support layer can comprise a first precoating layer 2b1 on the paper 2a. Technical effect is to provide improved surface for the paper before applying the barrier coating layer.

[0098] The paper 2a comprises cellulose-containing natural fibers, typically as its main raw material, and can further comprise, for example, one or more fillers and / or additives.

[0099] The term ‘cellulose-containing natural fiber’ refers to any plant material that contains cellulose.

[0100] The natural fiber can be of wood origin, and / or it may comprise other than wood-based natural fibers. Other than wood-based raw materials may include agricultural waste, grasses and / or other plant materials, such as straw, leaves, bark, seeds, legumes, flowers, tops, or fruit, which may have been obtained from cotton, corn, wheat, oat, rye, barley, rice, flax, hemp, manila hemp, sisal hemp, jute, ramee, kenaf hemp, bagasse, bamboo, and / or reed.

[0101] Preferably, the paper 2a comprises cellulose-containing natural fibers which are of wood origin. The paper 2a can comprise fibers from softwood trees, such as spruce, pine, fir, larch, douglas-fir, or hemlock, or from hardwood trees, such as birch, aspen, poplar, alder, eucalyptus, or acacia, or from a mixture of softwoods and hardwoods.

[0102] Preferably, the cellulose-containing natural fibers comprises chemically pulped natural fibre, that is, pulp made in a chemical pulping process. In an advantageous example, the content of chemically pulped natural fibres in all the cellulose-containing natural fibers used in the paper 2a is thus at least 70 wt.%, at least 80 wt.% or at least 90 wt.%, advantageously at least 95 wt.%, and more preferably at least 98 wt.%. Most preferably, all the cellulose- containing natural fibers used in the paper 2a are chemically pulped cellulose- containing natural fibers. Preferably, the paper 2a does not contain so-called mechanical pulp.

[0103] The paper 2a refers to an uncoated structure, i.e., an uncoated paper. In an embodiment, the support layer 2 is an uncoated paper.

[0104] As discussed, the support layer 2 can have, in addition to the paper 2a, precoating layer(s) 2b1 , 2b2.

[0105] Thus, the paper 2a can be coated with precoating composition(s) 4a, 4b.

[0106] The support layer 2 can have a first precoating layer 2b1 on the first side of the paper 2a and / or a second precoating layer 2b2 on the second side of the paper 2a.

[0107] If the support layer 2 comprises the first precoating layer 2b1 and the second precoating layer 2b2, the coating compositions of the first and second precoating layers preferably differ from each other. If the support layer comprises the precoating layer(s) 2b1 , 2b2 each precoating layer 2b1 , 2b2 can have a grammage in a range between 1 gsm and 10 gsm. Preferably, each precoating layer 2b1 , 2b2 has a grammage from 2 to 8 gsm, more preferably from 3 to 7 gsm, and most preferably from 4 to 6 gsm. Technical effect is to provide improved surface for the support layer in order to achieve full surface coverage with substantially low coat weight of the precoating. Another technical effect is to prepare the surface of the support layer for barrier coating composition and to work as an adhesion promoter to the barrier coating layer.

[0108] Thickness of the first precoating layer 2b1 and / or the second precoating layer 2b2 is preferably between 1 to 10 pm, and more preferably between 2 pm and 8 pm, and most preferably from 3 to 7 pm. Technical effect is to prepare the surface of the support layer 2 for barrier coating layer and / or a printing cost efficiently.

[0109] The precoating layer(s) 2b1 , 2b2 can comprise or consist of a binding agent. The precoating layer(s) 2b1 , 2b2 can have a binding agent content of at least 25 wt.%, preferably at least 32%, such as in a range between 35% and 60%, and most preferably in a range between 35% and 50%, referring to relative proportion of the binding agent(s) in the total content of the precoating(s).

[0110] The binding agent(s) of the precoating layer 2b1 , 2b2 can be selected from: starch, modified starch, enzymatically converted starch, polyvinyl alcohol, ethylene vinyl alcohol, modified cellulose, dispersions of different polyesters such as PLA, PBS, PBAT, PHAs, PCL, co- and terpolymers comprising or consisting of lactide, glycolide and caprolactone, and their mixtures. For obtaining desired properties for many applications, the first binding agent is preferably polyvinyl alcohol.

[0111] Advantageously, the binding agent(s) of the precoating layer(s) 2b1 , 2b2 comprises at least 60 wt.% or at least 70 wt.%, more advantageously at least 80 wt.% or at least 90 wt.%, and most advantageously at least 95 wt.% of the above-mentioned substances or consists of the above-mentioned substances. Technical effect is to ensure good surface coverage and film forming for the precoating. In an embodiment, the binding agent(s) of the first precoating layer 2b1 comprises polyvinyl alcohol and / or modified starch and / or enzymatically converted starch, most preferably the polyvinyl alcohol, a total amount being at least 60 wt.% or at least 70 wt.%, more advantageously at least 80 wt.% or at least 90 wt.%, and most advantageously at least 95 wt.%, up to 100 wt.%, determined from total amount of binding agents in the first precoating layer. Technical effect is to ensure good surface coverage and to provide improved film forming on to the precoating.

[0112] The precoating layer(s) 2b 1 , 2b2 can further contain pigments. The precoating layer(s) 2b 1 , 2b2 can contain mineral pigments, such as at least one of: kaolin, natural ground calcium carbonate, precipitated calcium carbonate, talc, calcium sulphate, and titanium dioxide. Advantageously, the pigments comprise at least one platy pigment, preferably clay.

[0113] The first precoating layer 2b1 can comprise mineral pigments in a range between 30 wt.% and 75 wt.%, preferably in a range between 40 wt.% and 70 wt.%, and more preferably in a range between 48 wt.% and 68 wt.%, calculated from the total dry weight of the first precoating layer 2b 1 . The usage of the mineral pigments can improve some properties of the material, improve the rheological properties in the coating process, as well as decrease the manufacturing costs of the product. However, the mineral content may not be too high.

[0114] Preferably, the binding agent(s) of the second precoating layer 2b2 comprises or consists of starch or polyvinyl alcohol, most preferably starch, amount preferably being at least 60 wt.% or at least 70 wt.%, more advantageously at least 80 wt.% or at least 90 wt.%, and most advantageously at least 95 wt.%, up to 100 wt.% determined from total amount of binding agents in the second precoating layer. Technical effect of the second precoating layer 2b2 is to improve the printability of the heat sealable packaging material.

[0115] The second precoating layer 2b2 can contain pigments. Technical effect of pigments is to provide improved surface for printing. The second precoating layer 2b2 can comprise mineral pigments, for example, in a range between 30 wt.% and 75 wt.%, preferably in a range between 40 wt.% and 70 wt.%, and more preferably in a range between 48 wt.% and 68 wt.%, calculated from the total dry weight of the second precoating layer.

[0116] Alternatively, in an advantageous embodiment, the second precoating layer 2b2 does not contain pigments.

[0117] The first side of the paper 2a can be coated with the first precoating composition 4a for obtaining the first precoating layer 2b1 . Alternatively, or in addition, the second side of the paper 2a can be coated with the second precoating composition 4b for obtaining the second precoating layer 2b2.

[0118] Advantageously, the heat sealable packaging material comprises the first precoating on the first side of the paper 2a and the second precoating on the second side of the paper, wherein the first precoating composition comprises polyvinyl alcohol, and the second precoating composition comprises starch. Technical effects include that polyvinyl alcohol in the first precoating composition improves coating holdout of subsequent coating layers and improves barrier for humidity and mineral oil after barrier coating, and the starch in second precoating composition facilitates drying of the coating layers, preventing blistering, dusting, deposits and curling of the material. Preferably, the first precoating composition comprises polyvinyl alcohol equal to or more than 50 wt.%, more preferably equal to or more than 60 wt.%, determined from dry weight of the first precoating layer. Further, preferably, the second precoating composition comprises starch equal to or more than 50 wt.%, more preferably equal to or more than 60 wt.%, determined from dry weight of the second precoating layer.

[0119] Thus, the support layer 2 can comprise the first precoating layer 2b1 on the first side of the paper 2a, and / or the support layer 2 can comprise the second precoating layer 2b2 on the second side of the paper 2a.

[0120] Preferably, the support layer 2 comprises, at the most, only one first precoating layer 2b1 and only one second precoating layer 2b2. Grammage of the support layer 2 is advantageously at least 35 gsm, more advantageously at least 40 gsm and preferably not greater than 130 gsm. The grammage of the support layer 2 may be, for example, in a range between 40 gsm and 120 gsm. In an advantageous example, the grammage of the support layer 2 is between 45 gsm and 110 gsm. Technical effect is to obtain heat sealable packaging material having good strength properties. Support layer 2 having less grammage is thinner and may have reduced strength properties, but substantially light weight material can decrease manufacturing and transportation costs and reduce environmental load. Thus, it is possible to provide good barrier, heat sealability and strength properties while the heat sealable packaging material can be environmentally friendly solution due to the minimum amount of raw materials needed for the package.

[0121] Most preferably, the support layer 2 consists of: paper 2a, optionally, first precoating layer on the first side of the paper 2a, and optionally, second precoating layer on the second side of the paper 2a.

[0122] Density of the support layer 2 can be from 800 to 1200 kg / m3. Technical effect is to provide support layer that either through high density and / or by a coating layer provides good coating hold out.

[0123] In an embodiment, density of the support layer 2 is less than 1000 kg / m3, more preferably in a range between 800 kg / m3and 990 kg / m3, still more preferably in a range between 820 kg / m3and 970 kg / m3, and most preferably equal to or less than 950 kg / m3, such as in a range between 850 kg / m3and 950 kg / m3. Technical effect is to provide particularly environmentally friendly product, wherein energy consumption in the papermaking unit processes, including refining, dewatering, and drying steps, are decreased.

[0124] In another embodiment, density of the support layer is at least 1000 kg / m3, such as in a range between 1000 kg / m3and 1200 kg / m3, more preferably in a range between 1020 kg / m3and 1170 kg / m3, and most preferably in a range between 1050 kg / m3and 1150 kg / m3. Technical effect is that high-density paper structure enables good interaction between the surface of the support layer and a coating layer added on the support layer. Roughness (Bendtsen) of the support layer 2 can be more than 40 ml / min, such as in a range between 60 ml / min and 120 ml / min, determined according to standard ISO 2494. Technical effect is that by providing such roughness of the support layer 2, substrate to be coated with the barrier coating is smooth. Low amount of surface roughness provides a good substrate for the coating process of the barrier coating composition 5.

[0125] Due to the barrier coating layers, support layer 2 does not need to provide low water vapour transmission rate. In an embodiment, WVTR (23°C / 50%RH, ISO 2528) of the support layer 2 is higher than 500 g / m2*day. Technical effect includes improved easiness of the manufacturing process as the support layer 2 (as such) does not need to provide water vapour barrier material.

[0126] Barrier coating layer

[0127] The heat sealable packaging material 1 comprises the barrier coating layer 3. The technical effect of the barrier coating layer 3 is to provide desired barrier properties as well as the heat sealability.

[0128] The barrier coating composition 5 comprises two binding agents. Thus, the barrier coating layer contains a first binding agent and a second binding agent.

[0129] The barrier coating layer 3 can have a binding agent content of at least 30 wt.% (by dry weight), preferably at least 35 wt.% (by dry weight), such as in a range between 30 wt.% and equal to or less than 50 wt.% (by dry weight), and most preferably in a range between 35 wt.% and 40 wt.% (by dry weight), referring to relative proportion of binding agents in the total content of the barrier coating layer. Technical effect is, e.g., to provide excellent runnability and high-solid content capacity, providing decreased time for drying.

[0130] The first binding agent consists of polyvinyl alcohol(s). A total amount of polyvinyl alcohol(s) can be up to 90 % (by dry weight) of the binding agents of the barrier coating composition.

[0131] The second binding agent is selected from styrene-acrylate copolymer(s), acrylate-vinyl acetate copolymer(s), styrene-butadiene copolymer(s), and their mixtures

[0132] Technical effects include improved drying efficiency of the barrier coating during manufacturing process. Further technical effect is to improve easiness of coating process compared e.g. to PVA based coatings. Another technical effect is to provide water vapor barrier properties and heat sealability for the heat sealable packaging material. Still another technical effect is that second barrier coating is capable of forming good barrier layer on a surface of a paper at typical process temperatures on paper machines.

[0133] Preferably, the second binding agent comprises the styrene-butadiene copolymer. Most preferably, the second binding agent consists of the styrene- butadiene copolymer. Technical effect is to provide improved barrier properties as well as excellent runnability and high-solid content capacity. Furthermore, styrene-butadiene copolymers can be produced cost efficiently on a large scale.

[0134] Thus, in an advantageous embodiment, the barrier coating layer 3 contains a first binding agent that is polyvinyl alcohol, and a second binding agent comprises styrene-butadiene copolymer(s). Technical effects of this combination include improved grease and humidity barrier as well as good heat sealability, suitable e.g. for foodstuff packaging.

[0135] The binding agents of the barrier coating layer can comprise polyvinyl alcohol(s) from 15 wt.% to 30 wt.%, preferably from 16 wt.% to 28 wt.%, more preferably 17 wt.% to 25 wt.%, determined of total amount of the barrier coating layer. Technical effects include improved film formation and barrier properties, especially mineral oil and water vapor barrier, and improved heat sealability.

[0136] The polyvinyl alcohol(s) can have a degree of hydrolysis in a range from 90 to 100 mol%, preferably from 95 to 99 mol%, and weight average molecular mass from 30 to 60 kDa. Technical effects include a low tendency for foaming and increased crystallinity compared to lower degree of hydrolysis. The binding agents of the barrier coating layer can comprise a total amount of at least 10 wt.% and equal to or less than 20 wt.%, more advantageously at least 15 wt.% and equal to or less than 19 wt.%, of styrene-acrylate copolymer(s) and styrene-butadiene copolymer(s), determined from the barrier coating layer. Technical effects include lowering Tg and providing higher flexibility, and lower heat sealing temperature.

[0137] Preferably, the first and second binding agents according to this specification form at least 70 wt.%, more preferably at least 80 wt.%, still more preferably at least 90 wt.%, and most preferably at least 95 wt.% (by dry weight) and up to 100 wt.% of the binding agents of the barrier coating layer. Technical effect is good basis for grease barrier and possibility to tailor the viscosity of the coating color.

[0138] Ratio of the first binding agent to the second binding agent is preferably in a range from 0.5 to 3.0, more preferably from 0.75 to 2.5, and most preferably from 1 to 2. Technical effects include providing improved barrier properties as well as excellent film forming and heat sealability properties.

[0139] The barrier coating layer further contains one or more mineral pigments. Mineral pigments can comprise, for example, at least one of: kaolin, natural ground calcium carbonate, precipitated calcium carbonate, talc, calcium sulphate, and titanium dioxide.

[0140] The barrier coating layer 3 can comprise mineral pigments from equal to or more than 50 wt.% to 70 wt.%, preferably in a range between 53 wt.% and 65 wt.%, and more preferably in a range between 56 wt.% and 63 wt.%, calculated from the total dry weight of the barrier coating layer 3. Surprisingly, the high usage of the mineral pigments, when used together with the binding agents according to this specification, improved runnability and maintained barrier properties of the heat sealable packaging material while it also decreased drying energy requirement. Furthermore, rheological properties of the barrier coating composition were improved. Pigment addition in the barrier coating was also favorable to maintain recyclability of the heat seal packaging material. Further, surprisingly, the barrier coating layer with said high pigment content had heat sealability properties suitable for the use in packaging lines. Advantageously, solids content of the barrier coating composition 5 is from 38 to 50 wt.%, preferably 41 -47 wt.%, more preferably 43-46 wt.%. Technical effects include accelerated production efficiency and reduced energy required to dry the applied coating. This solids content can be particularly easily obtained by using said high mineral pigments content together with the ratio of the first binding agent to the second binding agent.

[0141] Preferably, the barrier coating layer 3 contains

[0142] - a first binding agent, from 15 to 25 wt.% (by dry weight) of the total dry weight of the barrier coating layer,

[0143] - a second binding, from 10 to 20 wt.% (by dry weight) of the total dry weight of the barrier coating layer, and

[0144] - filler(s), preferably mineral filler(s), from more than 50 wt.% to 70 wt.% (by dry weight) of the total dry weight of the barrier coating layer, wherein total content of the first binding agent, second binding agent and the fillers is preferably from 90 to 100 wt.% (by dry weight) of the total dry weight of the barrier coating layer. Technical effects include is to maximize solids content compared to levels possible for polyvinyl alcohol approved as food contact material alone, while the presence of the second binding agent provides, e.g., the desired heat sealability.

[0145] Preferably, the main pigment of the barrier coating layer is talc, clay, or calcium carbonate, more preferably clay, or ground calcium carbonate (GCC), and most preferably kaolin. Technical effect is to provide better immobilization of the binding agent on the surface of the support layer 2. Another technical effect is to improve runnability of the manufacturing process. Still another technical effect is to obtain higher solids content cost efficiently. The higher solids content is typically environmentally friendly solution as it can decrease energy consumption of the manufacturing process.

[0146] Thus, preferably, the barrier coating composition 5 contains at least one platy pigment, preferably talc, mica and / or kaolin. As discussed, the platy pigment refers to pigment particles having a flat structure in which one dimension is substantially smaller than the two other dimensions of the structure. The platy pigment can be selected from kaolin and talc. Technical effect of the combination of binding agents and platy pigments is to further enhance the water barrier and water vapour resistance properties. Thus, the barrier coating can provide excellent water barrier and moisture barrier especially in high humidity, and therefore the packed product is protected well from the moisture outside.

[0147] Advantageously, barrier coating layer 3 comprises platy pigment(s), preferably kaolin, at least 50 wt.%, preferably at least 60 wt.%, more preferably at least 70 wt.%, and most preferably at least 90 wt.%, calculated from all mineral pigments in the barrier coating layer 3. Kaolin can be easily dispersed into water, improving easiness of the manufacturing process while providing advantages of platy pigments.

[0148] The barrier coating composition and the barrier coating layer preferably comprises the binding agents and the mineral pigments in a dry weight ratio from 30:70 to 50:50, more preferably from 35:65 to 45:55, and most preferably from 36:64 to 40:60. Technical effect is tailoring the rheological properties and decreasing the costs of chemicals. Further technical effect is to provide polymers to fill voids between e.g., pigment particles. Still another technical effect is obtaining heat sealability and improved barrier properties.

[0149] The barrier coating composition and the barrier coating layer can further comprise one or more additives, such as one or more of slip additive(s), thermal stabilizer(s), anti-block or antistatic agent(s), and UV stabilizer(s), etc. Technical effect of the additive is to modify the surface and / or optical properties of the barrier coating layer.

[0150] The barrier coating composition 5 and, hence, the barrier coating layer, can comprise a plasticizer, which is a compound or composition capable of imparting plasticity flexibility to the heat sealable packaging material. In an embodiment, the plasticizer is selected from the group consisting of glycol, glycerol, sorbitol, glucose, and mixtures thereof.

[0151] Grammage of the barrier coating layer is preferably 2 to 10 gsm, more preferably 3 to 9 gsm, and most preferably 4.5 to 7.5 gsm (by dry weight). Technical effect is to provide improved barrier properties and heat sealability for the heat sealable packaging material cost-efficiently.

[0152] A thickness of the barrier coating layer 3 can be in average in a range between 1 .5 pm and 10 pm, preferably between 3 to 9 pm, and more preferably between 4 pm and 8 pm, and most preferably from 4.5 to 7 pm. Technical effect is to obtain protection from grease cost efficiently with the barrier coating.

[0153] The barrier coating composition 5 can have a Brookfield viscosity of 400-1800 mPas, preferably 700-1200 mPas, when measured at 45°C, 100 rpm, at maximum solids content (35-45%). Technical effect is that the viscosity is suitable for pumping coating color to the storage tank and the coating units.

[0154] One technical effect of the barrier coating layer 3 is to provide improved water vapor barrier properties. Another technical effect is to provide heat sealability for the heat sealable packaging material 1 . Still another technical effect of the barrier coating layer 3 according to this specification is boosting grease barrier of the heat sealable packaging material. Yet another technical effect of the barrier coating layer according to this specification is to improve the cracking resistance of the barrier coating layers of the heat sealable packaging materials 1 .

[0155] The support layer 2 can be coated with a barrier coating composition 5 to obtain the heat sealable packaging material 1 comprising the barrier coating layer 3.

[0156] Preferably, the heat sealable packaging material 1 comprises the first precoating layer 2b1 , and the barrier coating layer 3 on the same side of the paper 2a. Preferably, the barrier coating layer 3 is on the first precoating layer 2b1. The barrier coating layer 3 can be directly on the first precoating layer 2b1. The technical effect is to obtain improved barrier properties for the heat sealable packaging material.

[0157] If the heat sealable packaging material 1 does not comprise the first precoating layer 2b1 , the barrier coating layer 3 is preferably directly on the paper 2a. Polyvinyl alcohol is a dissolving polymer and, after reaching a tipping point, builds up viscosity rapidly with increasing solids content, limiting its use in online coating processes. Viscosity is especially sensitive to temperature, and relatively small decrease in processing temperature can make the coating color having poor runnability in a coating station.

[0158] Film formation of PVA takes place by evaporation of solvent (water) and not by melting. As PVA of high degree of hydrolysis has a melting point around 200-210 C, it reduces tackiness of the coating, compared to coating colors with only latex as a binder. This enables film formation in suitable temperature range for drying in paper machines while avoiding blocking. Conventionally, some challenges have been caused due to an absence of web cooling devices at most paper machines. Thus, paper web temperature at a pope reeler of a paper machine is typically around 40°C to 60°C. Therefore, the coating layer on a paper web should not be tacky at this temperature, because otherwise it may cause reel blocking. Thanks to the novel solution, tackiness of the barrier coating can be avoided at a pope reeler.

[0159] The barrier coating can have good resistance for creasing and folding so that the barrier coating is not cracking when the heat sealable packaging material is e.g. folded into a package. Cracking may decrease barrier properties of the coating. Thus, technical effect of the resistance for creasing and folding is to maintain barrier properties of packages comprising the heat sealable material.

[0160] In an embodiment, the heat sealable material is used for producing packages at high speed packing lines.

[0161] The barrier coating layer 3 can form the topmost coating layer of the heat sealable packaging material.

[0162] In an embodiment, there may be a printing on the barrier coating layer 3.

[0163] In a preferred embodiment, the heat sealable packaging material has the barrier coating on the first side of the support layer, and the second precoating layer 2b2, preferably designed for printing, on the second side of the paper 2a. Heat sealable packaging material

[0164] As discussed, the heat sealable packaging material has the support layer 2 and the barrier coating layer 3 on the support layer.

[0165] Preferably, the heat sealable packaging material has only one side comprising the barrier coating layer 3. Preferably, the heat sealable packaging material has the barrier coating layer 3 only on the first side of the support layer 2. Technical effect is to decrease environmental load, such as the carbon dioxide load, and to provide cost efficiently environmentally friendly heat sealable barrier material.

[0166] The other side of the heat sealable packaging material may only have, for example, the second precoating layer 2b2. However, it is also possible that the barrier coating layer 3 is provided on both sides of the support layer 2.

[0167] The second precoating layer 2b2 can be a surface size layer. The second precoating layer 2b2 can consist of one or more binding agents. Alternatively, the second precoating layer can comprise binding agent(s) and pigments.

[0168] Therefore, the second side of the support layer 2 can be uncoated, such as calendered, or coated.

[0169] If the heat sealable packaging material has a coating layer on the second side of the paper 2a, the coating layer on the second side of the paper 2a is preferably the second precoating layer 2b2.

[0170] Preferably, the heat sealable packaging material is printable heat sealable packaging material.

[0171] The heat sealable packaging material can have at least one side, preferably the second side of the paper 2a, designed for printing. The printable side(s) is / are preferably printable by using at least one of

[0172] » digital printing, such as digital inkjet printing,

[0173] « flexography, ® rotogravure, and

[0174] • offset lithography.

[0175] Technical effect is to improve easiness of printing process for packages comprising the heat sealable packaging material.

[0176] In an advantageous embodiment, the heat sealable packaging material comprises the barrier coating layer 3 on the first side of the support layer, and only the second side of the support layer comprises a printing. In this embodiment, the second side of the support layer 2 preferably comprises the second precoating 2b2 on the paper 2a, which second side of the support layer is preferably configured to be printable as such. Technical effect is that the barrier layer can provide suitable barrier properties for a package having the barrier layer on the first side of the support layer, while the printing on the other side of the package can provide information for a user of the package.

[0177] Thus, the heat sealable packaging material can consist of the support layer 2 consisting of o the paper 2a, o optionally, the first precoating layer, o optionally, the second precoating layer, optionally, a printing, and the barrier coating layer 3.

[0178] A technical effect is to provide environmentally friendly heat sealable packaging material having good barrier properties.

[0179] Thanks to the novel heat sealable packaging material, there is no need to use extrusion-coated or laminated layer, nor metal layers, for the heat sealability or barrier properties.

[0180] Further, when contaminated with food residues, the heat sealable packaging material is preferably suitable for being burnt after usage.

[0181] The manufacturing process according to this specification can be a lot simplified compared to conventional manufacturing processes. Often a support layer is transported from a paper mill to a converter who adds barrier materials, for example by extruding plastic on paper, as the extruder is not necessarily available at the paper mill, and then coated paper is again transported to another converter / printer for finalizing it into a final product. In the method according to this specification, the barrier coating layers can be done at the paper mill and thus at least one converter step and transportation phase can be avoided, so that the whole process of manufacturing is more efficient.

[0182] The heat sealable packaging material can provide a combination of barrier properties against water vapor for foldable or flexible packaging products, which have been difficult to obtain conventionally without metal foils and laminated films for foldable or flexible packaging products.

[0183] Furthermore, a decreased time for drying can be achieved which consequently facilitates the manufactural efficiency.

[0184] The heat sealable packaging material can have a WVTR value of less than 10 g / (m2*day), preferably less than 6 g / (m2*day), determined at 23°C / 50%RH according to standard ISO 2528. Technical effect is to provide, cost efficiently, desired water vapour barrier properties for the obtained heat sealable packaging material.

[0185] Mineral oil barrier can be evaluated from heptane vapor transmission rate (HVTR). The heat sealable packaging material can have an improved mineral oil barrier, with HVTR value of less than 10 g / (m2*day). Technical effect is to improve, cost efficiently, mineral oil barrier properties, hence, avoid a risk of mineral oil contamination when using the packaging material e.g. for food. Mineral oil barrier of the heat sealable packaging material can be particularly useful for food products. An HVTR value below 60 g / (m2*day) generally indicates sufficient barrier, limiting migration of aromatic hydrocarbons to below 0.5 mg / kg of packed product. The barrier requirement depends on the area of packaging material needed per mass unit of packed product. The lower the HVTR, the more packaging applications the material is suitable for. Another technical effect is to provide environmentally friendly material as materials which do not comprise laminated films or aluminum layers can be used for the heat sealable packaging material. The heat sealable packaging material can have a KIT value of at least 12, determined according to standard T559 cm-12. Technical effect is to provide, cost efficiently, desired oil and grease barrier properties, and a pinhole free coating for the obtained heat sealable packaging material.

[0186] The heat sealable packaging material is preferably heat sealable according to the heat sealability test. As discussed, the heat sealability is tested by cutting 15 x 120 mm specimen from the heat sealable packaging material and sealing them coating vs. coating according to ASTM F2029-16. In this application, the term “heat sealable” particularly refers to a seal strength (N / 15 mm) of at least 4 N / 15mm, preferably over 5 N / 15mm, measured with a tensile tester according to ASTM F88 / F88M-15. In addition to said seal strength, sealed area should exhibit full fiber tear. Technical effect is to provide an airtight seal, which is required to take advantage of barrier properties of the material.

[0187] Heat sealability can be determined at 0.6 bar sealing pressure (i.e., jaw pressure), by using 1.0 s dwell time. Thus, the heat sealable packaging material is preferably heat sealable at 160°C by using jaw pressure of 0.6 bar and dwell time of 1 .0 s.

[0188] In a preferred embodiment, the heat sealable packaging material does not exhibit adhesion at 80 °C, but is heat sealable, at least, at temperatures from 160°C up to 200°C. One technical effect is to prevent tackiness at drying section of a paper machine, where coating is in contact with hot metal cylinders, or at pope reeler. Furthermore, ability of the heat sealable packaging material 1 to be heat-sealed in all temperatures from 160°C up to 200°C can enhance process flexibility in packaging.

[0189] In an embodiment, the heat sealable packaging material 1 consist of the support layer and the barrier coating layer, at least essentially.

[0190] Thanks to the heat sealable packaging material, mineral oil, and water vapor barrier can be substantially improved, compared to conventional environmentally friendly heat sealable materials. Further, the heat sealable packaging material can have good seal ability so that good barrier properties can be provided over the sealing cost efficiently. Manufacturing method

[0191] A method for manufacturing a heat sealable packaging material can comprise the following steps: providing a support layer 2 comprising a paper 2a, and applying a barrier coating composition 5 onto the support layer 2 in a form of an aqueous dispersion, thereby forming a barrier coating layer 3.

[0192] The support layer 2 can be made by a paper machine.

[0193] The paper 2a is suitably either calendered or coated by a precoating unit for applying the precoating composition(s) 4a, 4b. The precoating unit can be one of a blade coater, flooded nip coating unit, nozzle unit, short retention unit, rod coater, air brush coater, film transfer coater, curtain coating unit, or spray coating unit.

[0194] The barrier coating composition 5 can be applied onto the support layer 2 by a barrier coating unit 7 for applying the barrier coating composition 5. The barrier coating composition 5 can be applied in the form of an aqueous composition. The barrier coating unit 7 can be one of a blade coater, flooded nip coating unit, nozzle unit, short retention unit, rod coater, air brush coater, film transfer coater, curtain coating unit, or spray coating unit. Preferably, the barrier coating unit is the blade coater.

[0195] Package

[0196] Packages can be produced from the heat sealable packaging material.

[0197] A package can comprise, essentially consist of, or consist of the heat sealable packaging material. In an embodiment, the heat sealable material forms more than 50 wt.%, such as at least 60 wt.% (by dry weight) of a package.

[0198] Experimental tests Example 1 : Coating color properties

[0199] Solids content and Brookfield viscosity are key properties when defining runnability of coatings on a paper machine or high speed offline coater.

[0200] Solids content of 40% or more is generally required for good runnability with high speed coaters.

[0201] Coating comprising kaolin, polyvinyl alcohol (PVA) and styrene-butadiene copolymer was applied by a blade coating on a pre-coated paper.

[0202] Referring to Fig. 6, solids content decreased consistently when PVA fraction of binder increased. Viscosity behaved in a non-linear manner, first increasing rapidly up to 33% PVA fraction and then decreasing gradually.

[0203] PVA acts as a thickener, especially with high solids coating colors. Despite having lower viscosity at 45 °C, the rheology of formulation with only PVA as binder was most sensitive to temperature variations. Viscosity of PVA solutions is known to be affected strongly by temperature, increasing by up to 50% when temperature decreases from 45 to 35 °C, for instance. Meanwhile, formulations where PVA comprised only 50-66% of binder, were considerably more stable to run. The higher solids content also reduced the requirement for drying energy.

[0204] Using styrene-acrylate copolymer as co-binder improved the coating color runnability by lowering viscosity and increasing solids content compared to PVA coatings.

[0205] Example 2: Barrier properties

[0206] Coating recipes according to Table 1 comprising kaolin pigment, and pigments selected from polyvinyl alcohol (PVA) and styrene-butadiene copolymer was applied by blade coating on pre-coated paper. Table 1 shows amount of raw materials in the coating, as well as WVTR, KIT and HVTR values determined from the obtained heat sealable packaging material. Table 1 . List of coating formulations, percentages of PVA, latex, and clay, coat weights, and barrier properties.

[0207] Amount of PVA was gradually increased, pigment share being roughly

[0208] 5 constant. Replacing 35-50% of PVA with SB latex did not negatively impact barrier performance. KIT value was even improved. SB / clay coating without PVA had higher WVTR (water vapor transmission rate) and especially high heptane vapor transmission rate (HVTR), i.e. poor mineral oil barrier. 0 The heat sealable packaging material comprising kaolin, polyvinyl alcohol (PVA) and styrene-butadiene copolymer was heat sealable and had improved properties compared to heat sealable packaging material according to Example 1 . 5 Example 3: Heat sealability

[0209] Heat sealability of coatings described in Table 1 was studied.

[0210] Heat sealing was tested using sealing pressure of 0.6 bar and sealing time of0 1.0 s. at variable temperatures. The test results are shown in Table 2. Seal quality is an average of five test specimen.

[0211] Table 2. Heat seal quality of different coatings. Legend: 0 = no adhesion; 1 = adhesion, no tear; 2 = partial fiber tear; 3 = full fiber tear; 4 = cohesive failure5 (paper torn before seal).

[0212] Temp. (°C)

[0213]

[0214] The recipe with only SB latex as binder had lowest sealing initiation temperature, showing more than 4 N strength between 100-200 °C, despite the latex not being sold as a heat sealable product. However, the sealed area never exhibited full fiber tear, thus failing to produce an airtight seal. On the other hand, the recipe with pure PVA binder eventually reached a hermetic seal but required 180 °C for strong sealing.

[0215] Compared to pure PVA binder coating, heat sealability was improved when 35-50% parts of PVA were replaced with SB latex. Minimum temperature for full fiber tear was lowered to 160 °C, and these recipes were the only ones to exhibit a cohesive failure at seal, indicating very strong adhesion. This optimal formulation range improved runnability, barrier properties, and heat sealability. The improvement in latter two categories could be due to improved film formation, caused by PVA filling spaces between latex particles.

[0216] Recipes with slightly higher pigment content exhibited significantly weaker sealing performance. The result indicated that pigment content of 63% was probably close to the tipping point, where sealability starts to suffer significantly.

[0217] Example 4

[0218] Various barrier coatings according to this specification were applied to the support layer according to this specification. Surprisingly, by mixing the first binding agent and the second binding agent according to this specification with mineral pigments so that the coating composition had a pigment content of more than 50 wt.% (by dry weight), a binding agent content of at least 30 wt.%, preferably at least 35 wt.% (by dry weight), first binding agent content from 10 wt.% to 30 wt.% (by dry weight), preferably 17 wt.% to 25 wt.%, and second binding agent content from 10 wt.% to 20 wt.% (by dry weight), the obtained heat sealable packaging material

[0219] 1 ) was heat sealable, and

[0220] 2) had desired barrier properties including water and water vapor barrier.

[0221] Furthermore, referring to Fig. 7, seal strength of the of the novel heat sealable packaging material was as desired so that the heat sealable packaging material did not exhibit adhesion at 80 °C, but had a desired seal strength of more than 5 N / 15 mm at temperatures from 160°C up to 200°C, with full fiber tear. The reference samples only comprising first binding agent did not exhibit adhesion at 80 °C, but they did neither had the desired seal strength of more than 5 N / 15 mm at temperatures from 160°C up to 200°C. Furthermore, the reference samples only comprising the second binding agent had the desired seal strength of more than 5 N / 15 mm at temperatures from 160°C up to 200°C, but they also exhibit adhesion at 80 °C, which is not desired for the heat sealable material.

[0222] Thus, surprisingly, only the heat sealable packaging material according to this specification had both desired properties; they did not exhibit adhesion at 80 °C, but had a desired seal strength of more than 5 N / 15 mm at temperatures from 160°C up to 200°C, with full fiber tear. As discussed, surprisingly, for obtaining the desired properties, amount of the first binding agent (PVA) had to be from 15 to 30 wt.%, preferably from 17 wt.% to 25 wt.%, of a total dry weight of the barrier coating layer, and total amount of the second binding agent(s) had to be from 10 to 20 wt.% of a total dry weight of the barrier coating layer. The invention is not limited solely to the examples presented in Figures and the above description, but it may be modified within the scope of the appended claims.

Claims

Claims:

1. A method for manufacturing a heat sealable packaging material (1 ) comprising supplying a support layer (2) comprising a paper (2a) having a first side and a second side, the paper comprising cellulose-containing natural fibres, and applying a barrier coating composition (5) in form of an aqueous dispersion on the support layer (2), the aqueous dispersion having solids content from 40 to 70 wt.%, thereby forming a barrier coating layer (3), the barrier coating layer (3) having a coat weight of 2 to 10 g / m2and comprising mineral fillers from 50 wt.% to 70 wt.% of a total dry weight of the barrier coating layer (3), and binding agents from 30 wt.% to 50 wt.% of the total dry weight of the barrier coating layer (3), wherein a first binding agent is a polyvinyl alcohol, and an amount of the first binding agent is from 15 to 30 wt.%, preferably from 17 wt.% to 25 wt.%, of the total dry weight of the barrier coating layer, and a total amount of the second binding agent is from 10 to 20 wt.% of the total dry weight of the barrier coating layer, wherein the second binding agent is selected from styrene-acrylate copolymers, acrylate-vinyl acetate copolymers, styrene-butadiene copolymers, and their mixtures.

2. A heat sealable packaging material (1 ) comprising a support layer (2) comprising a paper (2a) having a first side and a second side, the paper comprising cellulose-containing natural fibres, and a barrier coating layer (3) on the support layer, the barrier coating layer having a coat weight of 2 to 10 g / m2and comprisingmineral fillers from 50 wt.% to 70 wt.% of a total dry weight of the barrier coating layer (3), and binding agents from 30 wt.% to 50 wt.% of a total dry weight of the barrier coating layer (3), wherein the binding agents comprise a first binding agent and a second binding agent, wherein the first binding agent is a polyvinyl alcohol, and an amount of the first binding agent is from 15 wt.% to 30 wt.%, preferably from 17 wt.% to 25 wt.%, of a total dry weight of the barrier coating layer, and a total amount of the second binding agent is from 10 to 20 wt.% of a total dry weight of the barrier coating layer, wherein the second binding agent is selected from styrene-acrylate copolymers, acrylate-vinyl acetate copolymers, styrene-butadiene copolymers, and their mixtures.

3. The method according to claim 1 or the heat sealable packaging material according to claim 2, wherein the support layer (2) further comprises a first precoating layer (2b1 ), a grammage of the first precoating layer (2b1 ) being in a range between 1 g / m2and 10 g / m2, wherein- preferably, the first precoating layer (2b1 ) is on the first side of the paper, and the barrier coating layer (3) is on the first precoating layer (2b 1 ), and- optionally, the first precoating layer comprises polyvinyl alcohol, preferably equal to or more than 50 wt.%, determined from dry weight of binder(s) of the first precoating layer.

4. The method or the heat sealable packaging material according to any of the preceding claims, wherein the support layer (2) further comprises a second precoating layer (2b2), a grammage of the second precoating layer (2b2) being in a range between 1 g / m2and 10 g / m2, wherein- optionally, the second precoating layer comprises starch, preferably equal to or more than 80 wt.%, more preferably equal to or more than 90 wt.%, determined from dry weight of the second precoating layer, and- preferably, the second precoating layer is on the second side of the paper.

5. The method or the heat sealable packaging material according to any of the preceding claims, wherein a ratio of the first binding agent to the second binding agent is in a range from 0.75 to 3.

6. The method or the heat sealable packaging material according to any of the preceding claims, wherein the second binding agent comprises or consists of the styrene-butadiene copolymer.

7. The method or the heat sealable packaging material according to any of the preceding claims, wherein the second binding agent comprises or consists of the acrylate-vinyl acetate copolymer.

8. The method or the heat sealable packaging material according to any of the preceding claims, wherein the second binding agent comprises or consists of the styrene-butadiene copolymers.

9. The method or the heat sealable packaging material according to any of the preceding claims, wherein the barrier coating layer comprises equal to or more than 30 wt.% of kaolin.

10. The method or the heat sealable packaging material according to any of the preceding claims, wherein the heat sealable packaging material (1 ) has a mineral oil barrier, determined as heptane vapour transmission rate, of less than 10 g / m*day.11 . The method or the heat sealable packaging material according to any of the preceding claims, wherein the heat sealable packaging material (1 ) has a water vapour barrier value of less than 10 g / m2*day, determined at 23°C and 50% RH according to standard ISO 2528.

12. The method or the heat sealable packaging material according to any of the preceding claims, wherein the heat sealable packaging material (1 ) has a KIT value of at least 12, determined according to standard T559 cm-12.

13. The method or the heat sealable packaging material according to any of the preceding claims, wherein the heat sealable packaging material (1 ) is heat sealable at 160°C, determined by using 1 .0 s dwell time at 0.6 bar sealing pressure, and - the heat sealable packaging material does not exhibit adhesion at 80°C.

14. A package comprising the heat sealable packaging material (1) according to any of the preceding claims 2 to 13.

15. A use of the heat sealable packaging material (1 ) according to any of the preceding claims 2 to 13 in a package.

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