Polyhydroxyalkanoate coating method

Abstract

The present invention relates to a method for manufacturing a PHA (polyhydroxyalkanoate) coated fiber-based substrate, said method comprising the steps: a) providing a fiber-based substrate having a first main surface and a second 5 main surface and having a moisture content in the range of 4-10 wt%; b) forming a first PHA layer by applying a first aqueous coating composition comprising a first PHA having a melting point in the range of 120-180 °C on the first main surface and drying the first aqueous coating composition at a first drying temperature in the range of 90-130 °C and at least 20 °C below the melting point 10 of the first PHA.

Description

[0001] POLYHYDROXYALKANOATE COATING METHOD

[0002] Technical field

[0003] The present disclosure relates to methods for preparing coated fiber-based substrates, specifically polyhydroxyalkanoate (PHA) coated paper or paperboard, for use as packaging materials.

[0004] Coating of paper and paperboard with plastics is often used to combine the mechanical properties of the paper or paperboard with the barrier and sealing properties of a plastic film. Paper or paperboard provided with even a relatively small amount of a suitable plastic material can provide the properties needed to make the paper or paperboard suitable for many demanding applications, for example as liquid or food packaging board. In liquid or food packaging board, extrusion coated polyolefin coatings are frequently used as liquid barrier layers, heat sealing layers and adhesives. However, the recycling of such polymer coated board is difficult since it is difficult to separate the polymers from the fibers.

[0005] In the prior art, attempts have been made to replace extrusion coated polyolefin coatings with more environmentally friendly and / or easier to recycle solutions, but so far with no real success. In many cases some, but not all, of the properties of the extrusion coated polyolefin coatings are achieved by the alternative solutions.

[0006] Dispersion barrier coatings for paper and paperboard is an interesting alternative to extrusion coating for improving repulpability and recyclability of barrier coated fiber-based substrates. Dispersion coating is especially useful as it can be implemented on-line in paper or paperboard machines. Many dispersions or emulsions such as styrene / acrylate or styrene / butadiene emulsions are, however, not biodegradable or compostable.

[0007] Dispersion coating barriers based on polyhydroxyalkanoates (PHA), on the other hand, are both compostable and biodegradable. The challenge with PHA dispersions is to find suitable particle size distributions and compositions, which enable good coater runnability, good coating coverage (hold-out) especially at low coat weights, and good barrier performance. Another challenge is to efficiently cure or film-form the wet coating, particularly avoiding the potential negative effects of co-additives, for example surfactants, on barrier performance. Coating coverage, and subsequent barrier performance, is very dependent on substrate roughness and coat weight, whereas higher coat weights have a negative impact on recyclability, drying efficiency, and cost.

[0008] Usually, the dispersions need to be dried at conditions wherein the board surface temperature exceeds 120 °C. At such high temperatures, the board starts to lose its moisture and thereby also its mechanical properties. The dispersion also becomes sticky under these conditions, which can cause adhesion at the rewinding station and might also cause blocking in the rewinded roll.

[0009] Many of the aforementioned problems can be avoided by applying the PHA using melt extrusion coating. However, extrusion coating of PHA is unfortunately not implementable on-line on full scale paper or paperboard machines. Also, extrusion coating usually requires relatively high coat weights, and extrusion coated grades are more difficult to re-pulp than dispersion coated grades.

[0010] Thus, there remains a need for improved solutions to replace conventional plastic coatings, especially polyolefin coatings, in paper and paperboard based packaging materials, while maintaining acceptable liquid, water vapor, and oxygen barrier properties. At the same time, there is a need for liquid barrier layers for paper or paperboard based packaging materials that facilitate repulping and recycling of the used packaging materials as compared to packaging laminates using conventional plastic films.

[0011] Description of the invention

[0012] It is an object of the present disclosure to provide an alternative to the plastic films commonly used as barrier layers for providing liquid barrier properties in paper or paperboard based packaging materials, such as liquid or food packaging board. It is a further object of the present disclosure to provide a liquid barrier layer for a paper or paperboard based packaging material, such as a liquid or food packaging board, which is based on renewable raw materials.

[0013] It is a further object of the present disclosure to provide a liquid barrier layer for a paper or paperboard based packaging material, such as a liquid or food packaging board, which facilitates re-pulping of the packaging material as compared to packaging laminates using conventional plastic films.

[0014] It is a further object of the present disclosure to provide an improved method for coating a fiber-based substrate with a PHA coating, which solves or ameliorates at least some of the problems associated with prior art PHA coating methods.

[0015] The above-mentioned objects, as well as other objects as will be realized by the skilled person in the light of the present disclosure, are achieved by the various aspects of the present disclosure.

[0016] According to a first aspect illustrated herein, there is provided a method for manufacturing a PHA (polyhydroxyalkanoate) coated fiber-based substrate, said method comprising the steps: a) providing a fiber-based substrate having a first main surface and a second main surface and having a moisture content in the range of 4-10 wt%; b) forming a first PHA layer by applying a first aqueous coating composition comprising a first PHA having a melting point in the range of 120-180 °C on the first main surface and drying the first aqueous coating composition at a first drying temperature in the range of 90-130 °C and at least 20 °C below the melting point of the first PHA.

[0017] The inventive method may be implemented on-line in full scale paper or paperboard machines. The fiber-based substrate (also referred to herein as “the substrate”) is preferably a sheet or web of material mainly formed from pulp of wood or other fibrous substances. The fiber-based substrate is preferably paper or paperboard.

[0018] Paper generally refers to a material manufactured in sheets or rolls from the pulp of wood or other fibrous substances comprising cellulose fibers, used for e.g. writing, drawing, or printing on, or as packaging material. Paper can either be bleached or unbleached and produced in a variety of thicknesses, depending on the end-use requirements.

[0019] Paperboard generally refers to strong, thick paper or cardboard comprising cellulose fibers used for example as flat substrates, trays, boxes and / or other types of packaging. Paperboard can either be bleached or unbleached and produced in a variety of thicknesses, depending on the end-use requirements.

[0020] In some embodiments, the fiber-based substrate is comprised of two or more cellulose-based plies. Each of the cellulose-based plies can have a certain composition of pulp fibers, such as bleached and / or unbleached Kraft pulp, sulfite pulp, dissolving pulp, thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), high-temperature CTMP (HT-CTMP), broke, and / or mixtures thereof. The different plies can have different grammages and / or thicknesses and may contain different amounts of additives, such as internal sizing agents.

[0021] As an example, the fiber-based substrate can be built up of one top-ply consisting of bleached or unbleached Kraft pulp, a mid-ply consisting of a mixture of bleached or unbleached Kraft pulp and CTMP, and a bottom-ply consisting of bleached or unbleached Kraft pulp, wherein the mid-ply has a higher thickness and / or lower density than both the top and bottom plies, respectively.

[0022] A preferred fiber-based substrate is a paper or paperboard having high content of unbleached fibers, such as at least 50 wt% in at least one of the plies, thus forming rough surface but with good mechanical performance and a natural look. In some embodiments, the basis weight of the fiber-based substrate is in the range of 20-800 g / m2. In some embodiments, the fiber-based substrate has a grammage of at least 100 g / m2. In some embodiments, the fiber-based substrate has a grammage of at least 150 g / m2, 200 g / m2, 250 g / m2, 300 g / m2, 350 g / m2, or 400 g / m2. The grammage of the fiber-based substrate is preferably below 1000 g / m2, 800 g / m2, or 600 g / m2. Unless otherwise stated, the grammage is determined according to the standard ISO 536.

[0023] The fiber-based substrate may also be surface sized or impregnated. In some embodiments, the fiber-based substrate is surface sized or impregnated on one or both sides with a surface sizing composition, preferably comprising a starch derivative, a cellulose derivative, or polyvinyl alcohol (PVOH) or a combination of thereof. The starch derivative may for example be a slightly modified, such as oxidized or cationized, starch. The cellulose derivative may for example be a sodium carboxymethyl cellulose with a degree of substitution higher than 0.4 such as in the range of 0.5-1.5. The PVOH may be fully or partly hydrolyzed. The surface sizing or impregnation may facilitate the release of the PHA coating structure from the fiber-based substrate during repulping.

[0024] In some embodiments, the grammage of the surface sizing composition is 0.2-10 g / m2, preferably 0.4-8 g / m2, and more preferably 0.8-5 g / m2per side, based on dry weight.

[0025] The fiber-based substrate provided in a) has a moisture content in the range of 4- 10 wt%. The term moisture content as used herein refers to the amount of water contained in the fiber-based substrate expressed as a percentage of the fiberbased substrate's total weight.

[0026] The fiber-based substrate itself, before PHA coating, may have a relatively high permeability for liquids, such as water, oil and grease, water vapor and gases, such as oxygen, air and carbon dioxide. In some embodiments, the fiber-based substrate has a water vapor transmission rate (WVTR), measured according to the standard ASTM F1249 - 20 at 50% relative humidity and 23 °C, of at least 200 g / m2 / 24h. In some embodiments, the fiber-based substrate has a Cobb60 value as measured according to the standard ISO 535 of less than 100 g / m2, preferably less than 80 g / m2, less than 60 g / m2, or less than 40 g / m2.

[0027] The first aqueous coating composition comprises a first PHA having a melting point in the range of 120-180 °C. The first aqueous coating composition is preferably a dispersion coating composition comprising the first PHA dispersed in a liquid solvent. The liquid solvent may be water, an organic solvent, or a combination of water and an organic solvent. In preferred embodiments, the liquid solvent is water. A challenge with PHA dispersions is to find suitable particle size distribution. The particle size of the PHA in the first aqueous coating composition is preferably in the range of from 0.5 to 5 pm. Particle sizes exceeding 10 pm may cause clustering issues.

[0028] In addition to the first PHA, the first aqueous coating composition preferably also comprises at least one plasticizer, wherein said plasticizer is preferably an alcohol, preferably a low molecular weight polyol, and at least one rheology modifier, preferably a water soluble polymer.

[0029] In some embodiments, the first PHA has a melting point in the range of 130-170 °C preferably in the range of 140-160 °C.

[0030] The inventors have found that the first PHA should preferably be a PHA copolymer, i.e. a PHA wherein two or more different types of monomers are linked in the same PHA polymer chain. Such PHA co-polymers are well known to the skilled person.

[0031] In some embodiments, the first PHA is a PHA co-polymer, preferably a medium chain length PHA having 6-14 carbon atoms per monomer unit.

[0032] In some embodiments, the first PHA is selected from the group consisting of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co- 3-hydroxyhexanoate) (PHBH), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxyoctanoate-co-3-hydroxyhexanoate) (PHOHH), poly(3- hydroxyoctanoate-co-3-hydroxydecanoate) (PHOHD), and poly(3- hydroxyoctanoate-co-3-hydroxydodecanoate) (PHDHDD), or a mixture thereof.

[0033] The skilled person understands that the PHA co-polymers suitable for use in the first aqueous coating composition are not limited to those listed here.

[0034] The first PHA is preferably the main ingredient of the first aqueous coating composition based on dry weight of the composition. In some embodiments, the first aqueous coating composition comprises the first PHA in an amount of 60-99.9 wt%, preferably in an amount of 70-99.9 wt%, and more preferably in an amount of 90-99.9 wt%, based on the total dry weight of the first aqueous coating composition.

[0035] In some embodiments, the first aqueous coating composition further comprises a plasticizer in an amount of 0.1-20 wt%, preferably in an amount of 1-15 wt%, and more preferably in an amount of 1-10 wt%, based on the total dry weight of the first aqueous coating composition. The plasticizer may for example be an alcohol, preferably a low molecular weight polyol, and more preferably a low molecular weight polyol selected from the group consisting of sorbitol, maltitol, xylitol, mannitol, and glycerol, a polyethylene glycol, or acetyltributylcitrate.

[0036] In some embodiments, the plasticizer is an alcohol, preferably a low molecular weight polyol, preferably a sugar alcohol selected from the group consisting of sorbitol, maltitol, xylitol, mannitol, and glycerol, and combinations thereof, in an amount of 0.1-20 wt%, preferably in an amount of 1-15 wt%, and more preferably in an amount of 1-10 wt%, based on the total dry weight of the first aqueous coating composition. In some embodiments, the plasticizer is sorbitol. Without wishing to be bound to any specific scientific theory, it is believed that the plasticizer may also act as a dispersing agent which facilitates film formation of the aqueous coating composition at temperatures well below the melting temperature of the first PHA.

[0037] In some embodiments, the first aqueous coating composition further comprises a rheology modifier, preferably a water soluble polymer selected from the group consisting of polysaccharides, polysaccharide derivatives, polypeptides, polypeptide derivatives, and combinations thereof, in an amount of 0.1-5 wt% based on the total dry weight of the first aqueous coating composition. In some embodiments, the rheology modifier is a water soluble polysaccharide. In some embodiments, the rheology modifier is selected from the group consisting of carboxymethyl cellulose, hydroxyethyl cellulose, guar gum, xanthan gum, starch, sodium alginate, tamarind seed gum, locust bean gum, pectin, pullulan and combinations thereof. In some embodiments, the rheology modifier is xanthan gum.

[0038] In some embodiments, the first aqueous coating composition has a viscosity in the range of 500 to 1000 cP, as measured using spindle 4 at 100 rpm on a Brookfield RW viscometer at 23 °C and a total dry content in the range 45-55 wt%. Viscosity values below 300 cP may lead to issues with clustering.

[0039] In some embodiments, the first aqueous coating composition comprises both: i) a plasticizer, preferably an alcohol, preferably a low molecular weight polyol, preferably a sugar alcohol selected from the group consisting of sorbitol, maltitol, xylitol, mannitol, and glycerol, and combinations thereof, in an amount of 0.1-20 wt%, preferably in an amount of 1-15 wt%, and more preferably in an amount of 1- 10 wt%, based on the total dry weight of the first aqueous coating composition, and ii) a rheology modifier, preferably a water soluble polymer selected from the group consisting of polysaccharides, polysaccharide derivatives, polypeptides, polypeptide derivatives, and combinations thereof, in an amount of 0.1-5 wt% based on the total dry weight of the first aqueous coating composition.

[0040] The combination of the plasticizer and the rheology modifier has been found particularly useful for facilitating film formation of the aqueous coating composition at temperatures well below the melting temperature of the first PHA.

[0041] In some embodiments, the first aqueous coating composition further comprises a mineral filler, preferably selected from the group consisting of clay, talcum, CaCOs, TiC>2, AI2O3, SiC>2, bentonite, fibers, phyllosilicates, and combinations thereof, in an amount of 0.1-30 wt%, preferably in an amount of 0.1-25 wt%, and more preferably in an amount of 0.1-20 wt%, based on the total dry weight of the first aqueous coating composition. In some embodiments, the first aqueous coating composition comprises talcum in an amount of 0.1-30 wt%, preferably in an amount of 0.1-25 wt%, and more preferably in an amount of 0.1-20 wt%, based on the total dry weight of the first aqueous coating composition.

[0042] In some embodiments, the first aqueous coating composition further comprises a co-binder, preferably a latex co-binder, preferably styrene acrylic (SA) latex or styrene-butadiene (SB) latex, or a combination thereof, in an amount of 0.1-10 wt%, preferably in an amount of 0.1-5 wt%, and more preferably in an amount of 1-5 wt%, based on the total dry weight of the first aqueous coating composition. In some embodiments, the first aqueous coating composition comprises SA latex in an amount of 0.1-10 wt%, preferably in an amount of 0.1-5 wt%, and more preferably in an amount of 1-5 wt%, based on the total dry weight of the first aqueous coating composition.

[0043] In some embodiments, the first aqueous coating composition has a total dry content in the range of 30-70 wt%, preferably in the range of 35-65 wt%, and more preferably in the range of 40-60 wt%. In some preferred embodiments, the first aqueous coating composition has a total dry content in the range of 45-55 wt%.

[0044] In some embodiments, the first PHA layer has a grammage in the range of 0.3-10 g / m2, preferably in the range of 0.3-8 g / m2, and more preferably in the range of 0.5-5 g / m2.

[0045] The first PHA layer is formed by applying the first aqueous coating composition comprising the first PHA on the first main surface and drying the first aqueous coating composition at a first drying temperature in the range of 90-130 °C and at least 20 °C below the melting point of the first PHA.

[0046] In some embodiments, the first drying temperature is in the range of 95-125 °C, preferably in the range of 100-120 °C. In some embodiments, the drying temperature is at least 30 °C below the melting point of the first PHA, preferably at least 40 °C below the melting point of the first PHA, and more preferably at least 50 °C below the melting point of the first PHA.

[0047] The first PHA layer is preferably formed by means of a liquid film coating process, i.e. in the form of an aqueous dispersion of the first PHA which, on application, is spread out to a thin, uniform layer on the substrate and thereafter dried.

[0048] In some embodiments, the first aqueous coating composition is applied by a noncontact application method. In some embodiments, the first aqueous coating composition is applied by an application method selected from the group consisting of roller coating, spray coating, curtain, blade coating, slot coating, immersion coating, gravure roll coating, reverse direct gravure coating, rod coating, soft-tip blade coating, short dwell, and soft-tip rod coating, and combinations thereof. The first aqueous coating composition may be applied directly onto the fiber-based substrate or indirectly, for example via a transfer roll or belt.

[0049] In some embodiments, the drying comprises subjecting the first aqueous coating composition to heating. In some embodiments, the drying comprises subjecting the first aqueous coating composition to at least one non-contact drying step, such as infrared radiation, electron beam radiation, ultraviolet radiation, microwave radiation, hot air or a combination thereof. Optionally, the first aqueous coating composition is then subjected to at least one additional drying step, which can be a hot air drying step or a contact drying step, e.g. using a heated belt or heated cylinders.

[0050] In some embodiments, the inventive method further comprises the step: c) forming a second PHA layer by applying a second aqueous coating composition comprising a second PHA having a melting point in the range of 120- 180 °C on the first PHA layer and drying the second aqueous coating composition at a second drying temperature in the range of 90-130 °C and at least 20 °C below the melting point of the second PHA. The second PHA layer is formed by applying a second aqueous coating composition comprising a second PHA on the first PHA layer and drying the second aqueous coating composition. Forming the second PHA layer on top of the dried first PHA layer prevents absorption of the second aqueous coating composition into the fiber-based substrate and serves to cover pinholes possibly present in the first PHA layer.

[0051] A 2-layer PHA coating structure allows for more efficient barrier and reduced risks of pinholes. The composition of each layer can be tailored to achieve desired properties.

[0052] The second aqueous coating composition comprises a second PHA having a melting point in the range of 120-180 °C. The second aqueous coating composition is preferably a dispersion coating composition comprising the second PHA dispersed in a liquid solvent. The liquid solvent may be water, an organic solvent, or a combination of water and an organic solvent. In preferred embodiments, the liquid solvent is water. A challenge with PHA dispersions is to find suitable particle size distribution. The particle size of the PHA in the second aqueous coating composition is preferably in the range of from 0.5 to 5 pm. Particle sizes exceeding 10 pm may cause clustering issues.

[0053] In some embodiments, the second PHA has a melting point in the range of 130- 170 °C preferably in the range of 140-160 °C.

[0054] In some embodiments, the second PHA layer has a grammage in the range of 2- 30 g / m2, preferably in the range of 5-20 g / m2.

[0055] The inventors have found that the second PHA should preferably be a PHA copolymer, i.e. a PHA wherein two or more different types of monomers are linked in the same PHA polymer chain. Such PHA co-polymers are well known to the skilled person. In some embodiments, the second PHA is a PHA co-polymer, preferably a medium chain length PHA having 6-14 carbon atoms per monomer unit.

[0056] In some embodiments, the second PHA is selected from the group consisting of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co- 3-hydroxyhexanoate) (PHBH), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxyoctanoate-co-3-hydroxyhexanoate) (PHOHH), poly(3- hydroxyoctanoate-co-3-hydroxydecanoate) (PHOHD), and poly(3- hydroxyoctanoate-co-3-hydroxydodecanoate) (PHDHDD), or a mixture thereof. The skilled person understands that the PHA co-polymers suitable for use in the second aqueous coating composition are not limited to those listed here.

[0057] The second PHA is preferably the main ingredient of the second aqueous coating composition based on dry weight of the composition. In some embodiments, the second aqueous coating composition comprises the second PHA in an amount of 60-99.9 wt%, preferably in an amount of 70-99.9 wt%, and more preferably in an amount of 90-99.9 wt%, based on the total dry weight of the second aqueous coating composition.

[0058] In some embodiments, the second aqueous coating composition further comprises a plasticizer in an amount of 0.1-20 wt%, preferably in an amount of 1-15 wt%, and more preferably in an amount of 1-10 wt%, based on the total dry weight of the second aqueous coating composition. The plasticizer may for example be an alcohol, preferably a low molecular weight polyol, and more preferably a low molecular weight polyol selected from the group consisting of sorbitol, maltitol, xylitol, mannitol, and glycerol, a polyethylene glycol, or acetyltributylcitrate.

[0059] In some embodiments, the plasticizer is an alcohol, preferably a low molecular weight polyol, preferably a sugar alcohol selected from the group consisting of sorbitol, maltitol, xylitol, mannitol, and glycerol, and combinations thereof, in an amount of 0.1-20 wt%, preferably in an amount of 1-15 wt%, and more preferably in an amount of 1-10 wt%, based on the total dry weight of the second aqueous coating composition. In some embodiments, the plasticizer is sorbitol. Without wishing to be bound to any specific scientific theory, it is believed that the plasticizer may also act as a dispersing agent which facilitates film formation of the aqueous coating composition at temperatures well below the melting temperature of the second PHA.

[0060] In some embodiments, the second aqueous coating composition further comprises a rheology modifier, preferably a water soluble polymer selected from the group consisting of polysaccharides, polysaccharide derivatives, polypeptides, polypeptide derivatives, and combinations thereof, in an amount of 0.1-5 wt% based on the total dry weight of the second aqueous coating composition. In some embodiments, the rheology modifier is a water soluble polysaccharide. In some embodiments, the rheology modifier is selected from the group consisting of carboxymethyl cellulose, hydroxyethyl cellulose, guar gum, xanthan gum, starch, sodium alginate, tamarind seed gum, locust bean gum, pectin, pullulan and combinations thereof. In some embodiments, the rheology modifier is xanthan gum.

[0061] In some embodiments, the second aqueous coating composition has a viscosity in the range of 500 to 1000 cP, as measured using spindle 4 at 100 rpm on a Brookfield RW viscometer at 23 °C and a total dry content in the range 45-55 wt%. Viscosity values below 300 cP may lead to issues with clustering.

[0062] In some embodiments, the second aqueous coating composition comprises both: i) a plasticizer, preferably an alcohol, preferably a low molecular weight polyol, preferably a sugar alcohol selected from the group consisting of sorbitol, maltitol, xylitol, mannitol, and glycerol, and combinations thereof, in an amount of 0.1-20 wt%, preferably in an amount of 1-15 wt%, and more preferably in an amount of 1- 10 wt%, based on the total dry weight of the second aqueous coating composition, and ii) a rheology modifier, preferably a water soluble polymer selected from the group consisting of polysaccharides, polysaccharide derivatives, polypeptides, polypeptide derivatives, and combinations thereof, in an amount of 0.1-5 wt% based on the total dry weight of the second aqueous coating composition. The combination of the plasticizer and the rheology modifier has been found particularly useful for facilitating film formation of the aqueous coating composition at temperatures well below the melting temperature of the second PHA.

[0063] In some embodiments, the second aqueous coating composition further comprises a mineral filler, preferably selected from the group consisting of clay, talcum, CaCOs, TiC>2, AI2O3, SiC>2, bentonite, fibers, phyllosilicates, and combinations thereof, in an amount of 0.1-30 wt%, preferably in an amount of 0.1-25 wt%, and more preferably in an amount of 0.1-20 wt%, based on the total dry weight of the second aqueous coating composition. In some embodiments, the second aqueous coating composition comprises talcum in an amount of 0.1-30 wt%, preferably in an amount of 0.1-25 wt%, and more preferably in an amount of 0.1-20 wt%, based on the total dry weight of the second aqueous coating composition.

[0064] In some embodiments, the second aqueous coating composition further comprises a co-binder, preferably a latex co-binder, preferably styrene acrylic (SA) latex or styrene-butadiene (SB) latex, or a combination thereof, in an amount of 0.1-10 wt%, preferably in an amount of 0.1-5 wt%, and more preferably in an amount of 1-5 wt%, based on the total dry weight of the second aqueous coating composition. In some embodiments, the second aqueous coating composition comprises SA latex in an amount of 0.1-10 wt%, preferably in an amount of 0.1-5 wt%, and more preferably in an amount of 1-5 wt%, based on the total dry weight of the second aqueous coating composition.

[0065] In some embodiments, the second aqueous coating composition has a total dry content in the range of 30-70 wt%, preferably in the range of 35-65 wt%, and more preferably in the range of 40-60 wt%. In some preferred embodiments, the second aqueous coating composition has a total dry content in the range of 45-55 wt%.

[0066] In some embodiments, the second PHA layer has a grammage in the range of 0.3- 8 g / m2, preferably in the range of 0.5-5 g / m2.

[0067] The second PHA layer is formed by applying the second aqueous coating composition comprising the second PHA on the first PHA layer and drying the second aqueous coating composition at a second drying temperature in the range of 90-130 °C and at least 20 °C below the melting point of the second PHA.

[0068] In some embodiments, the second drying temperature is in the range of 95-125 °C, preferably in the range of 100-120 °C.

[0069] In some embodiments, the drying temperature is at least 30 °C below the melting point of the second PHA, preferably at least 40 °C below the melting point of the second PHA, and more preferably at least 50 °C below the melting point of the second PHA.

[0070] The second PHA layer is preferably formed by means of a liquid film coating process, i.e. in the form of an aqueous dispersion of the second PHA which, on application, is spread out to a thin, uniform layer on the substrate and thereafter dried.

[0071] In some embodiments, the second aqueous coating composition is applied by a non-contact application method. In some embodiments, the second aqueous coating composition is applied by an application method selected from the group consisting of roller coating, spray coating, curtain, blade coating, slot coating, immersion coating, gravure roll coating, reverse direct gravure coating, rod coating, soft-tip blade coating, short dwell, and soft-tip rod coating, and combinations thereof. The second aqueous coating composition may be applied directly onto the fiber-based substrate or indirectly, for example via a transfer roll or belt.

[0072] In some embodiments, the drying comprises subjecting the second aqueous coating composition to heating. In some embodiments, the drying comprises subjecting the second aqueous coating composition to at least one non-contact drying step, such as infrared radiation, electron beam radiation, ultraviolet radiation, microwave radiation, hot air or a combination thereof. Optionally, the second aqueous coating composition is then subjected to at least one additional drying step, which can be a hot air drying step or a contact drying step, e.g. using a heated belt or heated cylinders. In some embodiments, the second drying temperature is at least 10 °C lower than the first drying temperature, preferably at least 20 °C lower the first drying temperature, and more preferably at least 30 °C lower the first drying temperature.

[0073] In some embodiments, the inventive method further comprises subjecting the first PHA layer to an adhesion promotion treatment before forming the second PHA layer, wherein said adhesion promotion treatment is selected from the group consisting of corona treatment, plasma treatment, and flame treatment, or a combination thereof.

[0074] In some embodiments, the first or second aqueous coating composition further comprises a pigment in an amount of 0.1-20 wt% based on the total dry weight of the aqueous coating composition. The pigment may for example comprise inorganic particles of talcum, silicates or phyllosilicates, carbonates, alkaline earth metal carbonates and ammonium carbonate, or oxides, such as transition metal oxides and other metal oxides. The pigment may also comprise nano-size pigments such as nanoclays and nanoparticles of layered mineral silicates, for instance selected from the group comprising montmorillonite, bentonite, kaolinite, hectorite and hallyosite.

[0075] In some embodiments, the first PHA layer and the second PHA layer have a combined a grammage in the range of 10-30 g / m2, preferably in the range of 10-25 g / m2.

[0076] In some embodiments, the fiber-based substrate is a paper or a paperboard.

[0077] In some embodiments, the fiber-based substrate has a grammage in the range of 150-350 g / m2.

[0078] In some embodiments, the obtained PHA coated fiber-based substrate has a moisture content in the range of 3-9 wt%, preferably in the range of 4-8 wt%. In some embodiments, the PHA coated first main surface of the obtained PHA coated fiber-based substrate has a PPS surface smoothness at 1.0 MPa in the range of 2-8 pm, as determined according to ISO 8791-4:2007.

[0079] In some embodiments, the second main surface is uncoated.

[0080] In some embodiments the second main surface is coated with one or more PHA coating layers as described herein with reference to the first main surface. The PHA coating layers on the first and second main surfaces may have identical or different composition. In other words, the coating composition for each layer and each of the main surfaces may be selected independently.

[0081] In some embodiments, the obtained PHA coated fiber-based substrate has a water vapor transmission rate (WVTR), measured according to the standard ASTM F1249 - 20 at 50% relative humidity and 23 °C, of less than 20 g / m2 / 24h, preferably less than 10 g / m2 / 24h.

[0082] In some embodiments, the obtained PHA coated fiber-based substrate has a Cobb 600s value as measured according to the standard ISO 535 of less than 15 g / m2, preferably less than 10 g / m2.

[0083] In some embodiments, the obtained PHA coated fiber-based substrate has a grease resistance as measured according to the standard ASTM F119-82 of at least 0.5 h, preferably at least 1 h.

[0084] The obtained coated fiber-based substrate provides an alternative to conventional packaging materials using polyolefin layers, which can more readily be repulped and recycled. The obtained dispersion coated substrate is preferably repulpable and reusable according to the PTS standard. In some embodiments, the obtained coated fiber-based substrate has a reject rate according to PTS RH 021 / 97 of less than 30 %, preferably less than 20 %, more preferably less than 10 %.

[0085] The obtained PHA coated fiber-based substrate is well suited for trays, plates, bowls, cups, and lids, but also for other liquid or food packaging materials. The PHA coated fiber-based substrate is especially well suited for trays, plates and bowls formed by thermoforming, deep drawing or press-forming.

[0086] The PHA coating structure of embodiments of the inventive PHA coated fiberbased substrate has been found useful as a liquid barrier for use on the inside surface of food and liquid packaging containers. Thus, in some embodiments, the PHA coated first main surface forms an inside surface of the container.

[0087] The PHA coating structure of embodiments of the inventive PHA coated fiberbased substrate has also been found useful as a moisture / liquid barrier for use on the outside surface of food and liquid packaging containers. Thus, in some embodiments, the PHA coated first main surface forms an outside surface of the container.

[0088] In some embodiments, the PHA coating structure is provided on both of the main surfaces of the fiber-based substrate. Thus, in some embodiments the second main surface is also coated with one or more PHA coating layers as described herein with reference to the first main surface. The PHA coating layers on the first and second main surfaces may have identical or different composition. In other words, the coating composition for each layer and each of the main surfaces may be selected independently.

[0089] Unless stated otherwise, all particle sizes herein refer to volumetric median particle size (D50). The particle size may be determined by a laser diffraction method using a Mastersizer S according to ISO 13320:2009.

[0090] Generally, while the products, polymers, materials, layers and processes are described in terms of “comprising” various components or steps, the products, polymers, materials, layers and processes can also “consist essentially of” or “consist of” the various components and steps.

[0091] While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes can be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention is not to be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

[0092] EXAMPLES

[0093] PHA coating methods and drying conditions

[0094] In Examples 1-4 board reels were dispersion coated with two layers in pilot scale with short dwell application and metered with a non-rotating rod with a polymer tip. The machine speed was 200 m / min for all trial examples. The dispersion coated boards were dried with IR and two sided air dryers. In one of the comparisons corona treatment was used on the first layer before applying the second layer.

[0095] Example 5 was performed on a full-scale offline coater with two coating layers in one pass.

[0096] The same specific grade of medium chain length (mcl) PHA with a melting temperature (Tm) of 140 °C was used for all examples.

[0097] Example 1 - Impact of corona treatment

[0098] A dispersion was prepared containing 93.5 wt% PHA, 6 wt% sorbitol (PLASTILYS®, Roquette) as a plasticizer, and 0.5 wt% xanthan gum (KELTROL® V, CP Kelco) as a rheology modifier. It was dispersion coated in two layers on a 195 gsm Cupforma Natura board.

[0099] Sample PH402 was dried at higher temperatures than samples PH403 and PH404. The corona treated sample, PH404, got barrier levels which were equivalent to a sample which needed 10 °C higher drying temperature in the second layer, PH404.

[0100] Sample PH403, with the same drying conditions as PH404, but without corona treatment got clearly higher Cobb 600 s values.

[0101] The lower drying temperature gave higher moisture content which is beneficial in converting. The term moisture content as used herein refers to the amount of water contained in the fiber-based substrate expressed as a percentage of the fiber-based substrate's total weight. The other mechanical properties were not affected or slightly better when using lower temperature.

[0102] Example 2 - Too low web temperature gives a good moisture content within the board but the barrier properties are lost.

[0103] A dispersion was prepared containing 64 wt% PHA, 11 wt% sorbitol (PLASTILYS®, Roquette) as a plasticizer, 0.3 wt% xanthan gum (KELTROL® V, CP Kelco) as a rheology modifier, 21 wt% talcum as pigment, and 3.7 wt% styrene acrylic (SA) latex. It was dispersion coated in two layers on the backside of Tambrite HS 200 gsm.

[0104] The coated dispersion needed a higher web temperature got develop a barrier, here seen as KIT. The higher moisture level in PH232 performed slightly better with mechanical properties. When raising the temperature in the first coating layer with 20 °C, PH228, the barrier properties were significantly increased compared to PH232.

[0105] Example 3 - Too high web temperature gives too low moisture content within the board but also destroys the barrier due to too hard drying.

[0106] A dispersion was prepared containing 84.8 wt% PHA, 14.8 wt% sorbitol (PLASTILYS®, Roguette) as a plasticizer, and 0.4 wt% xanthan gum (KELTROL® V, CP Kelco) as a rheology modifier. It was dispersion coated in two layers on the backside of a 233 gsm New Natura board.

[0107] The higher web temperature for PH 104 caused a very low moisture content and weakened both the barrier and board properties compared to the moderate web temperatures for PH111. Theoretically the higher web temperature would be better for melting and film forming the barrier layer.

[0108] Example 4 - Too low coat weight weakens the barrier even if the web temperatures are on good levels. A dispersion was prepared containing 76.6 wt% PHA, 13.4 wt% sorbitol (PLASTILYS®, Roquette) as a plasticizer, 0.4 wt% xanthan gum (KELTROL® V, CP Kelco) as a rheology modifier, and 9.6 wt% talcum as pigment. It was dispersion coated in two layers on the backside of a 233 gsm New Natura board. The web temperature for PH205 indicates that the barrier and mechanical values should be on a good level but since the coat weight is too low there is not enough material to form as good barrier level seen as KIT as in PH 119. Example 5 - Full-scale coating

[0109] A dispersion was prepared containing 94.5 wt% PHA, 5 wt% sorbitol (PLASTILYS®, Roquette) as a plasticizer, and 0.5 wt% xanthan gum (KELTROL® V, CP Kelco) as a rheology modifier. Coating was performed on a full-scale offline coater with two coating layers in one pass on a 195 gsm Cupforma Natura board.

[0110] The data shows that upscaling is possible while still retaining good barrier properties. The data further shows that a high moisture content can be retained, even at relatively high surface temperatures in a full-scale setting.

Claims

CLAIMS1 . A method for manufacturing a PHA (polyhydroxyalkanoate) coated fiberbased substrate, said method comprising the steps: a) providing a fiber-based substrate having a first main surface and a second main surface and having a moisture content in the range of 4-10 wt%; b) forming a first PHA layer by applying a first aqueous coating composition comprising a first PHA having a melting point in the range of 120-180 °C on the first main surface and drying the first aqueous coating composition at a first drying temperature in the range of 90-130 °C and at least 20 °C below the melting point of the first PHA.

2. The method according to any one of the preceding claims, wherein the particle size of the first PHA in the first aqueous coating composition is in the range of from 0.5 to 5 pm.

3. The method according to claim 1 , wherein the first PHA has a melting point in the range of 130-170 °C preferably in the range of 140-160 °C.

4. The method according to any one of the preceding claims, wherein the first PHA is a PHA co-polymer, preferably a medium chain length PHA having 6-14 carbon atoms per monomer unit.

5. The method according to any one of the preceding claims, wherein the first PHA is selected from the group consisting of poly(3-hydroxybutyrate-co-3- hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3- hydroxyoctanoate-co-3-hydroxyhexanoate) (PHOHH), poly(3-hydroxyoctanoate- co-3-hydroxydecanoate) (PHOHD), and poly(3-hydroxyoctanoate-co-3- hydroxydodecanoate) (PHDHDD), or a mixture thereof.

6. The method according to any one of the preceding claims, wherein the first aqueous coating composition comprises the first PHA in an amount of 60-99.9 wt%, preferably in an amount of 70-99.9 wt%, and more preferably in an amount of 90-99.9 wt%, based on the total dry weight of the first aqueous coating composition.

7. The method according to any one of the preceding claims, wherein the first aqueous coating composition further comprises a plasticizer, wherein said plasticizer is preferably an alcohol, preferably a low molecular weight polyol, preferably a sugar alcohol selected from the group consisting of sorbitol, maltitol, xylitol, mannitol, and glycerol, and combinations thereof, in an amount of 0.1-20 wt%, preferably in an amount of 1-15 wt%, and more preferably in an amount of 1- 10 wt%, based on the total dry weight of the first aqueous coating composition.

8. The method according to any one of the preceding claims, wherein the first aqueous coating composition further comprises a rheology modifier, preferably a water soluble polymer selected from the group consisting of polysaccharides, polysaccharide derivatives, polypeptides, polypeptide derivatives, and combinations thereof, in an amount of 0.1-5 wt% based on the total dry weight of the first aqueous coating composition.

9. The method according to any one of the preceding claims, wherein the first aqueous coating composition further comprises a mineral filler, preferably selected from the group consisting of clay, talcum, CaCOs, TiC>2, AI2O3, SiC>2, bentonite, fibers, phyllosilicates, and combinations thereof, in an amount of 0.1-30 wt% based on the total dry weight of the first aqueous coating composition.

10. The method according to any one of the preceding claims, wherein the first aqueous coating composition has a viscosity in the range of 500 to 1000 cP, as measured using spindle 4 at 100 rpm on a Brookfield RW viscometer at 23 °C and a total dry content in the range 45-55 wt%.

11. The method according to any one of the preceding claims, wherein the first PHA layer has a grammage in the range of 0.3-10 g / m2, preferably in the range of 0.3-8 g / m2, and more preferably in the range of 0.5-5 g / m2.

12. The method according to any one of the preceding claims, wherein the first drying temperature is in the range of 95-125 °C, preferably in the range of 100-120 °C.

13. The method according to any one of the preceding claims, wherein the drying temperature is at least 30 °C below the melting point of the first PHA, preferably at least 40 °C below the melting point of the first PHA, and more preferably at least 50 °C below the melting point of the first PHA.

14. The method according to any one of the preceding claims, said method further comprising the step: c) forming a second PHA layer by applying a second aqueous coating composition comprising a second PHA having a melting point in the range of 120- 180 °C on the first PHA layer and drying the second aqueous coating composition at a second drying temperature in the range of 90-130 °C and at least 20 °C below the melting point of the second PHA.

15. The method according to claim 14, wherein the particle size of the second PHA in the second aqueous coating composition is in the range of from 0.5 to 5 pm.

16. The method according to any one of claims 14-15, wherein the second PHA has a melting point in the range of 130-170 °C preferably in the range of 140-160 °C.

17. The method according to any one of claims 14-16, wherein the second PHA is a PHA co-polymer, preferably a medium chain length PHA having 6-14 carbon atoms per monomer unit.

18. The method according to any one of claims 14-17, wherein the second PHA is selected from the group consisting of poly(3-hydroxybutyrate-co-3- hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3- hydroxyoctanoate-co-3-hydroxyhexanoate) (PHOHH), poly(3-hydroxyoctanoate- co-3-hydroxydecanoate) (PHOHD), and poly(3-hydroxyoctanoate-co-3- hydroxydodecanoate) (PHDHDD), or a mixture thereof.

19. The method according to any one of claims 14-18, wherein the second aqueous coating composition comprises the second PHA in an amount of 60-99.9 wt%, preferably in an amount of 70-99.9 wt%, and more preferably in an amount of 90-99.9 wt%, based on the total dry weight of the second aqueous coating composition.

20. The method according to any one of claims 14-19, wherein the second aqueous coating composition further comprises a plasticizer, wherein said plasticizer is preferably an alcohol, preferably a low molecular weight polyol, preferably a sugar alcohol selected from the group consisting of sorbitol, maltitol, xylitol, mannitol, and glycerol, and combinations thereof, in an amount of 0.1-20 wt%, preferably in an amount of 1-15 wt%, and more preferably in an amount of 1- 10 wt%, based on the total dry weight of the second aqueous coating composition.

21. The method according to any one of claims 14-20, wherein the second aqueous coating composition further comprises a rheology modifier, preferably a water soluble polymer selected from the group consisting of polysaccharides, polysaccharide derivatives, polypeptides, polypeptide derivatives, and combinations thereof, in an amount of 0.1-5 wt% based on the total dry weight of the second aqueous coating composition.

22. The method according to any one of claims 14-21 , wherein the second aqueous coating composition further comprises a mineral filler, preferably selected from the group consisting of clay, talcum, CaCOs, TiC>2, AI2O3, SiC>2, bentonite, fibers, phyllosilicates, and combinations thereof, in an amount of 0.1-30 wt% based on the total dry weight of the second aqueous coating composition.

23. The method according to any one of claims 14-22, wherein the second aqueous coating composition has a viscosity in the range of 500 to 1000 cP, as measured using spindle 4 at 100 rpm on a Brookfield RW viscometer at 23 °C and a total dry content in the range 45-55 wt%.

24. The method according to any one of claims 14-23, wherein the second PHA layer has a grammage in the range of 2-30 g / m2, preferably in the range of 5-20 g / m2.

25. The method according to any one of claims 14-24, wherein the second drying temperature is in the range of 95-125 °C, preferably in the range of 100-120 °C.

26. The method according to any one of claims 14-25, wherein the second drying temperature is at least 30 °C below the melting point of the second PHA, preferably at least 40 °C below the melting point of the second PHA, and more preferably at least 50 °C below the melting point of the second PHA.

27. The method according to any one of claims 14-26, wherein the second drying temperature is at least 10 °C lower than the first drying temperature, preferably at least 20 °C lower the first drying temperature, and more preferably at least 30 °C lower the first drying temperature.

28. The method according to any one of claims 14-27, said method further comprising subjecting the first PHA layer to an adhesion promotion treatment before forming the second PHA layer, wherein said adhesion promotion treatment is selected from the group consisting of corona treatment, plasma treatment, and flame treatment, or a combination thereof.

29. The method according to any one of the preceding claims, wherein the first PHA layer and the second PHA layer have a combined a grammage in the range of 10-30 g / m2, preferably in the range of 10-25 g / m2.

30. The method according to any one of the preceding claims, wherein the fiberbased substrate is a paper or a paperboard.

31. The method according to any one of the preceding claims, wherein the fiberbased substrate has a grammage in the range of 150-350 g / m2.

32. The method according to any one of the preceding claims, wherein the obtained PHA coated fiber-based substrate has a moisture content in the range of 3-9 wt%, preferably in the range of 4-8 wt%.

33. The method according to any one of the preceding claims, wherein the PHA coated first main surface of the obtained PHA coated fiber-based substrate has a PPS surface smoothness at 1.0 MPa in the range of 1-20 pm, preferably in the range of 1.5-10 pm, and more preferably in the range of 2-8 pm, as determined according to ISO 8791-4:2007.

34. The method according to any one of the preceding claims, wherein the obtained PHA coated fiber-based substrate has a water vapor transmission rate (WVTR), measured according to the standard ASTM F1249 - 20 at 50% relative humidity and 23 °C, of less than 20 g / m2 / 24h, preferably less than 10 g / m2 / 24h.

35. The method according to any one of the preceding claims, wherein the obtained PHA coated fiber-based substrate has a Cobb 600s value as measured according to the standard ISO 535 of less than 15 g / m2, preferably less than 10 g / m2.

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