Method for producing a PHA-coated fibrous substrate with first and second PHA aqueous coating compositions, and fibrous substrate coated by the method

Abstract

The present invention provides a method for producing a PHA (polyhydroxyalkanoate) coated fibrous substrate, comprising the steps of: a) providing a fibrous substrate having a first major surface and a second major surface; b) applying a foamed first aqueous coating composition comprising a first PHA and a foaming agent onto the first major surface and drying the foamed first aqueous coating composition to form a first PHA layer; and 3 The present invention relates to a method for producing a fiber-based substrate, the method comprising the steps of: c) forming a first PHA layer, the first PHA layer being a foam having a foam density of 1 / 2; and b) applying a second aqueous coating composition comprising a second PHA onto the first PHA layer and drying the second aqueous coating composition to form a second PHA layer. The present invention further relates to a PHA-coated fiber-based substrate and a packaging container comprising the PHA-coated fiber-based substrate.

Description

[Technical Field]

[0001] The present disclosure relates to a method for preparing coated fiber-based substrates, particularly polyhydroxyalkanoate (PHA) coated paper or paperboard for use as packaging materials. [Background technology]

[0002] Coating paper and paperboard with plastics is often used to combine the mechanical properties of paper or paperboard with the barrier and sealing properties of plastic films. Paper or paperboard with even a relatively small amount of suitable plastic material can provide the properties necessary to make the paper or paperboard suitable for many demanding applications, such as liquid or food packaging boards. In liquid or food packaging boards, extrusion-coated polyolefin coatings are often used as liquid barrier layers, heat-sealing layers, and adhesives. However, recycling such polymer-coated boards is difficult because it is difficult to separate the polymer from the fibers.

[0003] Attempts have been made in the prior art to replace extrusion-coated polyolefin coatings with more environmentally friendly and / or more recyclable solutions, but to date have not met with real success. In many cases, some, but not all, of the properties of extrusion-coated polyolefin coatings are achieved by alternative solutions.

[0004] Dispersion barrier coatings for paper and paperboard are an interesting alternative to extrusion coating for improving the repulpability and recyclability of barrier-coated fiber-based substrates. Dispersion coatings are particularly beneficial because they can be performed while the paper or board machine is running. Many dispersions or emulsions, such as styrene / acrylate or styrene / butadiene emulsions, however, are neither biodegradable nor compostable.

[0005] On the other hand, polyhydroxyalkanoate (PHA)-based dispersion coating barriers are both compostable and biodegradable. The challenge with PHA dispersions is to find a suitable particle size distribution and composition that allows for good coater runnability, good coating coverage (holdout), especially at low coat weights, and good barrier performance. Another challenge is to efficiently cure or film-form the wet coating, especially to avoid the potential negative effects of additives such as surfactants on barrier performance. Coating coverage and subsequent barrier performance are highly dependent on substrate roughness and coat weight, while high coat weights have a negative impact on recyclability, drying efficiency, and cost.

[0006] Many of the aforementioned problems can be avoided by applying PHAs using melt extrusion coating. Unfortunately, however, extrusion coating of PHAs is not feasible on a full-scale paper or board machine while it is running. Furthermore, extrusion coating typically requires a relatively high coat weight, and extrusion-coated grades are more difficult to repulp than dispersion-coated grades.

[0007] Therefore, there remains a need for improved solutions to replace traditional plastic coatings, particularly 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 in paper or paperboard-based packaging materials that facilitate repulping and recycling of post-consumer packaging materials compared to packaging laminates that use traditional plastic films. Summary of the Invention

[0008] It is an object of the present disclosure to provide an alternative to plastic films that are typically used as barrier layers to provide liquid barrier properties to paper or paperboard based packaging materials, such as liquid or food packaging boards.

[0009] It is a further object of the present disclosure to provide a liquid barrier layer for paper or paperboard based packaging materials, such as liquid or food packaging boards, that is based on renewable raw materials.

[0010] It is a further object of the present disclosure to provide a liquid barrier layer for paper or paperboard based packaging materials, such as liquid or food packaging boards, that facilitates repulping of the packaging material compared to packaging laminates that use conventional plastic films.

[0011] It is a further object of the present disclosure to provide an improved method for coating a fibrous substrate with a PHA coating, particularly a method that can be carried out while a full-scale paper or board machine is in operation.

[0012] The above objectives, as well as other objectives which will be realized by those skilled in the art in light of the present disclosure, are accomplished by various aspects of the present disclosure.

[0013] The present invention is based on the realization that the problems associated with dispersion coating of PHA dispersions onto fibrous substrates, particularly fibrous substrates having relatively high surface roughness, can be overcome by applying the PHA in a two-step coating process, the first step involving applying a foamed aqueous coating composition comprising the PHA to the substrate. DETAILED DESCRIPTION OF THE INVENTION

[0014] According to a first aspect described herein, there is provided a method for producing a PHA (polyhydroxyalkanoate) coated fiber-based substrate, comprising: a) providing a fibrous substrate having a first major surface and a second major surface; b) forming a first PHA layer by applying a foamed first aqueous coating composition comprising a first PHA and a foaming agent onto the first major surface and drying the foamed first aqueous coating composition, wherein the foamed first aqueous coating composition is 0.75 g / cm 3 forming a first PHA layer, the first PHA layer being a foam having a foam density of: c) applying a second aqueous coating composition comprising a second PHA onto the first PHA layer and drying the second aqueous coating composition to form a second PHA layer; A method for producing a fiber-based substrate is provided, comprising:

[0015] The method of the present invention can be carried out on a full-scale paper or board machine in operation.

[0016] The two-layer PHA coating structure provides a more efficient barrier and reduces the risk of pinholes.

[0017] The composition of each layer can be tailored to achieve desired properties. For example, a first aqueous coating composition can be formulated with a PHA that optimizes foam formation, adhesion, and / or repulpability. A second aqueous coating composition can instead be formulated with a different PHA, preferably a hydrophobic PHA, that optimizes liquid barrier surface properties, such as hydrophobicity. Foaming a second dispersion containing a hydrophobic PHA using a surfactant is undesirable because it can result in reduced water repellency in the resulting dispersion-coated surface.

[0018] Dispersion-coated substrates can be repulped and recycled, preferably in accordance with PTS standards. Two-layer PHA coating structures, with a blowing agent in the first PHA layer, provide easier release of the coating layers, since wetting of the layers, and also wetting of the fibrous substrate, is enhanced by the blowing agent, typically in the form of a surfactant.

[0019] A fibrous substrate (also referred to herein as "substrate") is a sheet or web of material preferably formed primarily from wood pulp or other fibrous material. The fibrous substrate is preferably paper or paperboard.

[0020] Generally, paper refers to a sheet or roll of material made from wood pulp or other fibrous substances containing cellulose fibers, and is used, for example, for writing, drawing, or printing thereon, or as a packaging material. Depending on the end-use requirements, paper can be either bleached or unbleached and can be produced in a variety of thicknesses.

[0021] Generally, paperboard refers to strong, thick paper or cardboard containing cellulose fibers and is used, for example, as flat substrates, trays, boxes, and / or other types of packaging. Depending on the end-use requirements, paperboard can be either bleached or unbleached and can be produced in a variety of thicknesses.

[0022] In some embodiments, the fiber-based substrate includes two or more cellulose-based plies. Each of the cellulose-based plies can have a specific 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), broken, and / or mixtures thereof. The different plies can have different basis weights and / or thicknesses and may contain different amounts of additives, such as internal sizing agents.

[0023] As an example, a fibrous substrate can be constructed with a top ply of bleached or unbleached kraft pulp, a middle ply of bleached or unbleached kraft pulp and CTMP blend, and a bottom ply of bleached or unbleached kraft pulp, with the mid ply having a greater thickness and / or lower density than both the top and bottom plies, respectively.

[0024] A preferred fiber-based substrate is a paper or paperboard in which at least one of the plies has a high content of unbleached fibers, such as at least 50% by weight, thus forming a rough surface but with good mechanical performance and a natural appearance.

[0025] In some embodiments, the basis weight of the fibrous substrate is from 20 to 800 g / m 2 In some embodiments, the fiber-based substrate is at least 100 g / m 2 In some embodiments, the fibrous substrate has a basis weight of at least 150 g / m 2 , 200g / m 2 , 250g / m 2 , 300g / m 2 , 350g / m 2 , or 400 g / m 2 The grammage of the fibrous substrate is preferably 1000 g / m 2 , 800g / m 2 , or 600 g / m 2 Unless otherwise specified, basis weight is measured according to ISO standard 536.

[0026] The fibrous substrate may be surface sized or impregnated. In some embodiments, the fibrous 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 thereof. The starch derivative may be slightly modified, e.g., oxidized or cationized starch. The cellulose derivative may be, e.g., sodium carboxymethylcellulose having a degree of substitution greater than 0.4, e.g., in the range of 0.5 to 1.5. The PVOH may be fully or partially hydrolyzed. The surface sizing or impregnation may facilitate release of the PHA coating structure from the fibrous substrate during repulping.

[0027] In some embodiments, the surface sizing composition has a basis weight of 0.2 to 10 g / m per side on a dry weight basis.2 , preferably 0.4 to 8 g / m 2 , more preferably 0.8 to 5 g / m 2 is.

[0028] The fibrous substrate itself, prior to being coated with a PHA, can have a relatively high permeability to liquids such as water, oil and grease, water vapor, and gases such as oxygen, air, and carbon dioxide. In some embodiments, the fibrous substrate has a permeability of at least 200 g / m2 as measured at 50% relative humidity and 23°C according to ASTM standard F1249-20. 2 In some embodiments, the fibrous substrate has a water vapor transmission rate (WVTR) of 100 g / m 2 / 24 hours, as measured according to ISO standard 535. 2 less than 80 g / m 2 Less than 60g / m 2 Less than or equal to 40 g / m 2 have a Cobb60 value of less than

[0029] The methods of the present invention are particularly useful for coating fibrous substrates having relatively high surface roughness. In some embodiments, the first major surface of the fibrous substrate has a PPS surface smoothness at 1.0 MPa, measured according to ISO 8791-4:2007, in the range of 1 to 20 μm, preferably in the range of 1.5 to 10 μm, and more preferably in the range of 2 to 8 μm.

[0030] The first PHA layer is formed by applying a foamed first aqueous coating composition comprising a first PHA and a foaming agent onto the first major surface and drying the foamed first aqueous coating composition, the foamed first aqueous coating composition having a foaming density of 0.75 g / cm 3 less than 0.6 g / cm 3 or less than 0.5g / cm 3 The foam has the following foam density:

[0031] The term foam, as used herein, refers to a liquid containing dispersed air or gas bubbles. Typically, the volume of the gas is much greater than the volume of the liquid, with a thin film separating the pores. Three requirements must be met for a foam to form. Mechanical work is required to increase the contact area between the gas and the liquid. This occurs by agitation, dispersing a large amount of gas into the liquid, or by injecting gas into the liquid. The second requirement is that a bubble-forming agent, typically an amphiphilic substance, surfactant, or surface-active component, must be present to reduce surface tension. Finally, the foam must form faster than it can break.

[0032] Foams can be open-cell or closed-cell in nature. In open-cell foams, the gas regions are connected by pores, while closed-cell foams have enclosed cells. The cells are usually irregular in arrangement and vary in size. The cells present the smallest surface area and form a honeycomb shape or tessellation.

[0033] Foam coatings are advantageous because they provide coatings with a higher solids content than non-foam coatings. The low water content of foam coatings also reduces problems with rewetting of fibrous substrates.

[0034] The foamed first aqueous coating composition can be prepared by mixing a foaming agent with a PHA dispersion and then shearing or mixing the mixture into a foam, for example, using a high shear mixer or whisk.

[0035] The inventors have found that certain hydrophobic PHAs form hydrophobic coatings but are difficult to form stable foams from. Therefore, the foamed first aqueous coating composition contains a first PHA, thereby enabling the preparation of a stable foam. The inventors have found that the first PHA should preferably be a PHA copolymer, i.e., a PHA in which two or more different types of monomers are linked in the same PHA polymer chain. Such PHA copolymers are well known to those skilled in the art.

[0036] The inventors have further determined that, on the one hand, PHAs suitable for the foamed first aqueous coating composition are characterized by forming films having a relatively low water contact angle and a relatively high melting point, and, on the other hand, PHAs suitable for the second aqueous coating composition are characterized by forming films having a relatively high water contact angle and a relatively low melting point. The second PHA therefore has distinctly different characteristics compared to the first PHA.

[0037] In some embodiments, the first PHA is a PHA copolymer.

[0038] The type of PHA copolymer suitable for use in the first aqueous coating composition can be characterized by its melting point. In a preferred embodiment, the first PHA has a melting point in the range of 100-170°C, preferably in the range of 120-160°C.

[0039] 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 mixtures thereof. Those skilled in the art will appreciate that the PHA copolymers suitable for use in the first aqueous coating composition are not limited to those listed herein.

[0040] The first PHA is preferably the major ingredient of the foamed first aqueous coating composition based on the dry weight of the composition. In some embodiments, the foamed first aqueous coating composition comprises the first PHA in an amount of 70 to 99.9 wt %, preferably 90 to 99.9 wt %, based on the total dry weight of the foamed first aqueous coating composition.

[0041] Foaming agents are compounds that can form and / or stabilize foams in aqueous compositions. Foaming agents are typically amphiphilic, i.e., chemical compounds that possess both hydrophilic and hydrophobic (lipophilic) properties. Foaming agents reduce the work required to create a foam by reducing the surface tension of the liquid and increase the colloidal stability of the foam by inhibiting bubble coalescence.

[0042] The blowing agent for the solid composite material may be any blowing agent suitable for facilitating the formation of a foam in the aqueous PHA dispersion and stabilizing the formed foam. In other words, the blowing agent should be capable of forming a stable foam in the aqueous PHA dispersion. As used herein, "stable foam" means that the foam of the foamed first aqueous coating composition is sufficiently stable to remain in foam form at least until the foamed first aqueous coating composition is applied onto a first major surface.

[0043] The foaming agent is typically a surfactant such as SDS, or a surface-active polymer, or a combination thereof. In some embodiments, the foaming agent is a non-polymeric or polymeric surfactant, or a combination thereof. The surfactant may be anionic, nonionic, or zwitterionic.

[0044] In some embodiments, the foaming agent is a non-polymeric surfactant, preferably sodium dodecyl sulfate (SDS).

[0045] The polymeric foaming agent is preferably an amphiphilic polymer, i.e., a polymer that possesses both hydrophilic and hydrophobic (oleophilic) properties. In some embodiments, the foaming agent is water-soluble. The polymeric foaming agent may be, for example, a water-soluble polymer having a hydrophobic portion, such as a hydrophilic polymer backbone with hydrophobic side chains, or a block copolymer containing hydrophilic and hydrophobic segments.

[0046] In some embodiments, the foaming agent is selected from the group consisting of optionally hydrophobically modified polysaccharides, proteins, polyvinyl alcohol, polyvinyl acetate, and mixtures thereof. The optional hydrophobic modifications typically include one or more hydrophobic groups, such as alkyl groups, covalently bonded to the foaming agent.

[0047] In some embodiments, the blowing agent is an optionally hydrophobically modified polysaccharide selected from the group consisting of optionally hydrophobically modified cellulose, starch, hemicellulose, and mixtures thereof.

[0048] In some embodiments, the polymeric blowing agent is an optionally hydrophobically modified polysaccharide selected from the group consisting of optionally hydrophobically modified cellulose acetate (CA), ethyl (hydroxyethyl) cellulose (EHEC), methyl cellulose (MC), ethyl cellulose (EC), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), sodium carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose (HPMC), sulfoethyl cellulose, starch, and mixtures thereof.

[0049] In some embodiments, the polymeric blowing agent is selected from the group consisting of ethyl (hydroxyethyl) cellulose, hydrophobically modified ethyl (hydroxyethyl) cellulose (HM-EHEC), hydroxyethyl cellulose, hydrophobically modified hydroxyethyl cellulose (HM-HEC), methyl cellulose (MC), hydrophobically modified methyl cellulose (HM-MC), hydrophobically modified carboxymethyl cellulose (HM-CMC), and hydrophobically modified starch (HM-starch). Examples of useful hydrophobically modified starch derivatives include, but are not limited to, dialdehyde starch, hydroxypropylated starch, octenyl succinic anhydride (OSA) starch, and dodecyl succinic anhydride (DDSA) starch.

[0050] In some embodiments, the polymeric blowing agent is optionally hydrophobically modified methylcellulose.

[0051] In some embodiments, the polymeric blowing agent is a hydrophobically modified polyvinyl alcohol (PVOH), such as ethylene-modified PVOH. In some embodiments, the polymeric blowing agent is a polyvinyl alcohol containing at least 2% acetate groups, more preferably at least 10% acetate groups, and even more preferably at least 15% acetate groups.

[0052] In some embodiments, the foamed first aqueous coating composition comprises a foaming agent in an amount of 0.1 to 10 wt %, based on the total dry weight of the foamed first aqueous coating composition.

[0053] In some embodiments, the foamed first aqueous coating composition comprises SDS in an amount of 0.1 to 2 wt %, based on the total dry weight of the foamed first aqueous coating composition.

[0054] In some embodiments, the foamed first aqueous coating composition further comprises a polymeric additive, preferably selected from the group consisting of carboxymethyl cellulose (CMC), microfibrillated cellulose (MFC), and starch, in an amount of 0.1 to 20 wt %, based on the total dry weight of the foamed first aqueous coating composition.

[0055] The foamed first aqueous coating composition was 0.75 g / cm 3 In some embodiments, the foamed first aqueous coating composition is a foam having a foam density of 0.6 g / cm 3 less than 0.5 g / cm 3 The foam density is as follows:

[0056] In some embodiments, the foamed first aqueous coating composition has a viscosity in the range of 50 to 3500 mPas, measured using a Brookfield viscometer at a rotational speed of 100 rpm.

[0057] The first PHA layer is preferably formed by a liquid film coating process, i.e., in the form of a foamed aqueous dispersion of the first PHA that is spread in a thin, uniform layer onto the substrate upon application and then dried.

[0058] In some embodiments, the foamed first aqueous coating composition is applied by a non-contact application method. In some embodiments, the foamed first aqueous coating composition is applied by an application method selected from the group consisting of roller coating, thermal spray coating, curtain coating, knife coating, slot coating, dip coating, gravure roll coating, reverse direct gravure coating, rod coating, soft-tip knife coating, short dwell coating, and soft-tip rod coating, and combinations thereof. The foamed first aqueous coating composition can be applied directly to the fiber-based substrate or indirectly, for example, via a transfer roll or belt.

[0059] To minimize the risk of pinholes in the first PHA layer, the foamed first aqueous coating composition can be applied in at least two distinct coating steps with drying the coated film between steps.

[0060] In some embodiments, drying comprises subjecting the foamed first aqueous coating composition to heating. In some embodiments, drying comprises subjecting the foamed 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 foamed first aqueous coating composition is then subjected to at least one additional drying step, which can be, for example, a hot air drying step or a contact drying step using a heated belt or a heated cylinder.

[0061] In some embodiments, the foamed first aqueous coating composition is dried, causing the foam to collapse, meaning that the resulting first PHA layer preferably has a structure that is free or substantially free of air and other gas bubbles.

[0062] In some embodiments, the first PHA layer has a density of 0.3 to 8 g / m 2 in the range of 0.5 to 5 g / m 2 It has a basis weight in the range of

[0063] The formed first PHA layer is preferably characterized by a relatively low water contact angle and a relatively high melting point.

[0064] In some embodiments, the first PHA layer has a water contact angle measured after 3 seconds according to ASTM D7490-13 of less than 80 degrees, preferably less than 70 degrees. In some embodiments, the first PHA layer has a water contact angle measured after 3 seconds according to ASTM D7490-13 in the range of 30 to 80 degrees, preferably in the range of 30 to 70 degrees.

[0065] In some embodiments, the first PHA layer has a melting point, measured according to ASTM E794-06(2018), greater than 100° C., preferably greater than 110° C. In some embodiments, the second PHA layer has a melting point, measured according to ASTM E794-06(2018), in the range of 100-170° C., preferably in the range of 110-170° C.

[0066] The second PHA layer is formed by applying a second aqueous coating composition containing a second PHA onto the first PHA layer and drying the second aqueous coating composition. The second PHA layer is formed on top of the dried first PHA layer to prevent absorption of the second aqueous coating composition into the fiber-based substrate and to cover any pinholes that may be present in the first PHA layer.

[0067] In some embodiments, the second PHA is a PHA homopolymer, i.e., a PHA in which the polymer chain ID is formed from a single type of monomer. The second PHA is preferably a PHA homopolymer having a side chain length in the range of 2 to 14 carbon atoms, more preferably a PHA homopolymer having a side chain length in the range of 5 to 14 carbon atoms.

[0068] In some embodiments, the second PHA has a melting point in the range of 50-100°C, preferably in the range of 70-100°C.

[0069] In some embodiments, the second PHA is selected from the group consisting of poly(3-hydroxyoctanoate) (PHO), poly(3-hydroxydecanoate) (PHD), poly(3-hydroxyhexanoate) (PHH), and poly(3-hydroxyvalerate) (PHV), or mixtures thereof, preferably selected from the group consisting of PHO, PHD, and PHH, or mixtures thereof.

[0070] The second PHA is preferably the major ingredient of the second aqueous coating composition based on the dry weight of the composition. In some embodiments, the second aqueous coating composition comprises the second PHA in an amount of 70 to 99.9 wt %, preferably 90 to 99.9 wt %, based on the total dry weight of the second aqueous coating composition.

[0071] In some embodiments, the second aqueous coating composition does not include added foaming agents, such as non-polymeric or polymeric surfactants.

[0072] In some embodiments, the second aqueous coating composition is degassed. Thus, in some embodiments, the second aqueous coating composition is preferably free or substantially free of air and other gas bubbles.

[0073] In some embodiments, the second aqueous coating composition has a coating density of 0.9 g / cm 3 or more, preferably 0.95 g / cm 3More preferably, 0.98 g / cm 3 It has a density of more than 10 ...

[0074] The second PHA layer is preferably formed by a liquid film coating process, ie, in the form of an aqueous dispersion of the second PHA that is spread in a thin, uniform layer onto the substrate upon application and then dried.

[0075] In some embodiments, the second aqueous coating composition is applied by a non-contact application method, hi some embodiments, the second aqueous coating composition is applied by an application method selected from the group consisting of roller coating, thermal spray coating, curtain coating, knife coating, slot coating, dip coating, gravure roll coating, reverse direct gravure coating, rod coating, soft-tip knife coating, short dwell, and soft-tip rod coating, and combinations thereof.

[0076] To minimize the risk of pinholes in the second PHA layer, the second aqueous coating composition can be applied in at least two separate coating steps with drying the coated film between steps.

[0077] In some embodiments, drying comprises subjecting the second aqueous coating composition to heating. In some embodiments, 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, for example, a hot air drying step or a contact drying step using a heated belt or a heated cylinder.

[0078] In some embodiments, the second PHA layer has a density of 2 to 30 g / m 2 in the range of 5 to 20 g / m 2It has a basis weight in the range of

[0079] The formed second PHA layer is preferably characterized by a relatively high water contact angle and a relatively low melting point.

[0080] In some embodiments, the second PHA layer has a water contact angle greater than 90 degrees, preferably greater than 100 degrees, measured after 3 seconds according to ASTM D7490-13. In some embodiments, the second PHA layer has a water contact angle in the range of 100-140 degrees, preferably in the range of 105-125 degrees, measured after 3 seconds according to ASTM D7490-13.

[0081] In some embodiments, the second PHA layer has a melting point, measured according to ASTM E794-06(2018), below 100° C., preferably above 90° C. In some embodiments, the second PHA layer has a melting point, measured according to ASTM E794-06(2018), in the range of 40-100° C., preferably in the range of 50-90° C.

[0082] In some embodiments, the first or second aqueous coating composition further comprises a pigment in an amount of 0.1 to 20 wt %, based on the total dry weight of the aqueous coating composition. The pigment may comprise inorganic particles of oxides, such as talcum, silicates, or phyllosilicates, carbonates, alkaline earth metal carbonates and ammonium carbonates, or transition metal oxides and other metal oxides. The pigment may also comprise nano-sized pigments, such as nanoclays and nanoparticles of layered silicate minerals selected from the group including montmorillonite, bentonite, kaolinite, hectorite, and halloysite.

[0083] In some embodiments, the second major surface is uncoated.

[0084] In some embodiments, the second major surface is coated with a two-layer PHA coating structure as described herein with reference to the first major surface. The two-layer PHA coating structures of the first and second major surfaces can have the same or different compositions. In other words, the coating composition of each layer can be independently selected. In some embodiments, the second major surface is only coated with a foamed aqueous coating composition.

[0085] In some embodiments, the method comprises: d) applying a foamed third aqueous coating composition comprising a third PHA and a foaming agent onto the second major surface and drying the foamed third aqueous coating composition to form a third PHA layer, wherein the foamed third aqueous coating composition is 0.75 g / cm 3 and forming a third PHA layer, the third PHA layer being a foam having a foam density of:

[0086] The process for forming the third PHA layer, the third aqueous coating composition and its components, and the properties of the formed third layer may be further defined as described herein with reference to the process for forming the first PHA layer.

[0087] In some embodiments, the method comprises: e) applying a fourth aqueous coating composition comprising a fourth PHA onto the third PHA layer and drying the fourth aqueous coating composition to form a fourth PHA layer.

[0088] The process for forming the fourth PHA layer, the fourth aqueous coating composition and its components, and the properties of the formed fourth layer may be further defined as described herein with reference to the process for forming the second PHA layer.

[0089] The method according to the first aspect described herein provides for the preparation of an improved PHA coated fiber-based substrate. According to the second aspect described herein, a fibrous substrate having a first major surface and a second major surface; a first PHA layer on the first major surface, the first PHA layer comprising a first PHA and a blowing agent; a second PHA layer comprising a second PHA on the first PHA layer; A PHA (polyhydroxyalkanoate) coated fiber-based substrate is provided, comprising:

[0090] The PHA-coated fiber-based substrate according to the second embodiment described herein, and its components including the first PHA layer, the first PHA and the blowing agent, may be further defined as described with reference to the first embodiment.

[0091] In some embodiments, the PHA-coated fiber-based substrate has a coating density of 10 g / m2 as measured at 50% relative humidity and 23° C. according to ASTM standard F1249-20. 2 / 24 hours or less, preferably 5g / m 2 / Has a water vapor transmission rate (WVTR) of less than 24 hours.

[0092] In some embodiments, the PHA-coated fibrous substrate has a coating density of 15 g / m2 as measured according to ISO standard 535. 2 less than 10 g / m 2 have a Cobb 600 value of less than

[0093] In some embodiments, the PHA coated fiber-based substrate has a grease resistance of at least 0.5 hours, preferably at least 1 hour, as measured according to ASTM standard F119-82.

[0094] The coated fiber-based substrate provides an alternative to traditional packaging materials that use polyolefin layers, which can be easier to repulp and recycle. In some embodiments, the coated fiber-based substrate has a failure rate according to PTS RH 021 / 97 of less than 30%, preferably less than 20%, and more preferably less than 10%.

[0095] According to a third aspect described herein, there is provided a packaging container comprising a PHA-coated fiber-based substrate according to the second aspect. The PHA-coated fiber-based substrate is well suited for trays, plates, bowls, cups, and lids, as well as other liquid or food packaging materials. The PHA-coated fiber-based substrate is particularly well suited for trays, plates, and bowls formed by thermoforming, deep drawing, or press molding.

[0096] The two-layer PHA-coated structure of the PHA-coated fiber-based substrate of the present invention has been found to be useful as a liquid barrier for use on the interior surface of food and liquid packaging containers, such that in some embodiments, the first major surface of the PHA-coated layer forms the interior surface of the container.

[0097] The two-layer PHA-coated structure of the PHA-coated fiber-based substrate of the present invention has also been found to be useful as a moisture / liquid barrier for use on the exterior surface of food and liquid packaging containers, such that in some embodiments, the first major PHA-coated surface forms the exterior surface of the container.

[0098] Generally, although products, polymers, materials, layers, and processes are described as "comprising" various components or steps, these products, polymers, materials, layers, and processes may also "consist essentially of" or "consist of" those various components and steps.

[0099] While the present invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for those elements 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 not to be understood that the invention is limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but the invention is intended to include all embodiments falling within the scope of the appended claims.

Claims

1. 1. A method for producing a PHA (polyhydroxyalkanoate) coated fiber-based substrate, comprising: a) providing a fibrous substrate having a first major surface and a second major surface; b) forming a first PHA layer by applying a foamed first aqueous coating composition comprising a first PHA and a foaming agent onto the first major surface and drying the foamed first aqueous coating composition, wherein the foamed first aqueous coating composition has a foaming rate of 0.75 g / cm ３ forming a first PHA layer, the first PHA layer being a foam having a foam density of: c) applying a second aqueous coating composition comprising a second PHA onto the first PHA layer and drying the second aqueous coating composition to form a second PHA layer. A method for producing a fiber-based substrate, comprising:

2. The method of claim 1 , wherein the first PHA is a PHA copolymer.

3. 3. The method of claim 1 or 2, wherein the first PHA has a melting point in the range of 100 to 170°C, preferably in the range of 120 to 160°C.

4. 4. The method of any one of claims 1 to 3, 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 mixtures thereof.

5. 5. The method of any one of claims 1 to 4, wherein the foamed first aqueous coating composition comprises the first PHA in an amount of 70 to 99.9 wt%, preferably 90 to 99.9 wt%, based on the total dry weight of the foamed first aqueous coating composition.

6. 6. The method of any one of claims 1 to 5, wherein the blowing agent is a non-polymeric or polymeric surfactant.

7. 7. The method of any one of claims 1 to 6, wherein the foaming agent is a non-polymeric surfactant, preferably sodium dodecyl sulfate (SDS).

8. 7. The method according to any one of claims 1 to 6, wherein the blowing agent is an amphiphilic polymer, preferably selected from the group consisting of optionally hydrophobically modified polysaccharides, proteins, polyvinyl alcohol (PVOH), and partially hydrolyzed polyvinyl acetate (PVOH / Ac), and mixtures thereof.

9. 9. The method of any one of claims 1 to 8, wherein the foamed first aqueous coating composition comprises a foaming agent in an amount of 0.1 to 10 wt%, based on the total dry weight of the foamed first aqueous coating composition.

10. 10. The method of any one of claims 1 to 9, wherein the foamed first aqueous coating composition further comprises a polymeric additive, preferably selected from the group consisting of carboxymethyl cellulose (CMC), microfibrillated cellulose (MFC), and starch, in an amount of 0.1 to 10 wt%, based on the total dry weight of the foamed first aqueous coating composition.

11. The foamed first aqueous coating composition has a foaming density of 0.6 g / cm ３ Preferably 0.5 g / cm or less ３ 11. The method of claim 1, having a foam density of:

12. 12. The method of any one of claims 1 to 11, wherein the foamed first aqueous coating composition has a viscosity in the range of 50 to 3500 mPas, measured using a Brookfield viscometer at a rotational speed of 100 rpm.

13. 13. The method of any one of claims 1 to 12, wherein the foamed first aqueous coating composition is applied by a non-contact application method.

14. 14. The method of any one of claims 1 to 13, wherein drying comprises subjecting the foamed first aqueous coating composition to heating.

15. 15. The method of claim 1, wherein the foamed first aqueous coating composition is dried, thereby causing the foam to collapse.

16. The first PHA layer is 0.3 to 8 g / m ２ in the range of 0.5 to 5 g / m ２ 16. The method of claim 1, wherein the sieve has a basis weight in the range of

17. 17. The method of any one of claims 1 to 16, wherein the first PHA layer has a water contact angle of less than 80 degrees, preferably less than 70 degrees, measured after 3 seconds according to ASTM D7490-13.

18. 18. The method of any one of claims 1 to 17, wherein the first PHA layer has a melting point above 100°C, preferably above 110°C, measured according to ASTM E794-06(2018).

19. 19. The method of any one of claims 1 to 18, wherein the second PHA is a PHA homopolymer, preferably a PHA homopolymer having a side chain length in the range of 2 to 14 carbon atoms, more preferably a PHA homopolymer having a side chain length in the range of 5 to 14 carbon atoms.

20. a fibrous substrate having a first major surface and a second major surface; a first PHA layer on the first major surface, the first PHA layer comprising a first PHA and a blowing agent; a second PHA layer on the first PHA layer, the second PHA layer comprising a second PHA; A PHA (polyhydroxyalkanoate) coated fiber-based substrate comprising:

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