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EP4642979A1 - A method for the manufacturing of a dispersion coated paperboard with at least two layers of pha having different cristallinity and a coated paperboard - Google Patents

A method for the manufacturing of a dispersion coated paperboard with at least two layers of pha having different cristallinity and a coated paperboard

Info

Publication number
EP4642979A1
EP4642979A1 EP23911067.9A EP23911067A EP4642979A1 EP 4642979 A1 EP4642979 A1 EP 4642979A1 EP 23911067 A EP23911067 A EP 23911067A EP 4642979 A1 EP4642979 A1 EP 4642979A1
Authority
EP
European Patent Office
Prior art keywords
layer
dispersion
pha
coated
paperboard
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP23911067.9A
Other languages
German (de)
French (fr)
Inventor
Gisela CUNHA
Kaj Backfolk
Åsa NYFLÖTT
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Stora Enso Oyj
Original Assignee
Stora Enso Oyj
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Stora Enso Oyj filed Critical Stora Enso Oyj
Publication of EP4642979A1 publication Critical patent/EP4642979A1/en
Pending legal-status Critical Current

Links

Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H19/00—Coated paper; Coating material
    • D21H19/80—Paper comprising more than one coating
    • D21H19/82—Paper comprising more than one coating superposed
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B27/10—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of paper or cardboard
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B29/00—Layered products comprising a layer of paper or cardboard
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D167/00—Coating compositions based on polyesters obtained by reactions forming a carboxylic ester link in the main chain; Coating compositions based on derivatives of such polymers
    • C09D167/04—Polyesters derived from hydroxycarboxylic acids, e.g. lactones
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H19/00—Coated paper; Coating material
    • D21H19/10—Coatings without pigments
    • D21H19/14—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12
    • D21H19/20—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12 comprising macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H19/00—Coated paper; Coating material
    • D21H19/10—Coatings without pigments
    • D21H19/14—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12
    • D21H19/20—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12 comprising macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • D21H19/22—Polyalkenes, e.g. polystyrene
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H19/00—Coated paper; Coating material
    • D21H19/80—Paper comprising more than one coating
    • D21H19/84—Paper comprising more than one coating on both sides of the substrate
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
    • D21H27/30—Multi-ply
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H5/00—Special paper or cardboard not otherwise provided for
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/70—Other properties
    • B32B2307/724—Permeability to gases, adsorption
    • B32B2307/7242—Non-permeable
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/70—Other properties
    • B32B2307/726—Permeability to liquids, absorption
    • B32B2307/7265—Non-permeable
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D167/00—Coating compositions based on polyesters obtained by reactions forming a carboxylic ester link in the main chain; Coating compositions based on derivatives of such polymers

Definitions

  • the present invention relates to a dispersion coated paperboard for food packaging applications , which coated paperboard comprising a paper or paperboard substrate having a first side and a second side .
  • Paperboard for food packaging applications is often dispersion coated or extrusion coated or laminated with plastic films for providing barrier properties to the paperboard .
  • many of the polymers are not sustainable and/or compostable , which makes them less attractive especially in home or industrial recycling and composting .
  • dispersion barriers based on e . g . styrene/acrylates , styrene/butadiene , polyvinylidene chloride ( PVDC ) or similar emulsions , have been used as dispersion coatings for paper and paperboards .
  • These emulsions are designed with physical properties that ensures good film formation when applied of f-line or in-line in paper or paperboard manufacturing .
  • a low or reduced film forming temperature or melting temperature ( Tm) means on the other hand, a higher risk of white spot deposits on the paper machine (via broke ) , but also greater tendency to blocking and sel f -adhesion .
  • PHA is a thermoplastic bio-based polymer synthesi zed by bacterial fermentation .
  • PHA can be used in packaging application and is recogni zed for breaking down in all types of environments but especially in bacteria-rich environments like composts .
  • PHA dispersion coated paperboards lack thermoformability and good barrier properties , especially after forming into 3D shapes .
  • Dispersion coated paperboard with PHA is more sensitive to cracking etc . due to less coat weight and di f ferent coverage and dispersion consolidation and setting on the board . Also , lower Tm PHA grades have a greater tendency to blocking when thermoformed .
  • thermoforming or disposable items which requires heat sealing .
  • a rigid paperboard-laminate which is home and industrial compostable .
  • a method to manufacture said coating in-line , of fline or converting lines is a method to manufacture said coating in-line , of fline or converting lines .
  • An obj ect with the invention is to provide a coated paperboard with good barrier properties and which is recyclable and reusable .
  • Another obj ect is to provide a coated paperboard for which recyclability is improved, especially pre- and post-consumer recyclability .
  • Yet another obj ect is to provide a coated paperboard which solves , or at least reduces , the above-mentioned problems .
  • coated paperboard further comprising
  • the invention further discloses a method for making a dispersion coated paperboard for food packaging, wherein the method comprising the steps of :
  • the two-layer structure where the outer layer has a higher crystallinity than the inner layer, gives a good thermoformability and good barrier properties , especially after forming into 3D shapes .
  • the inventive two-layer structure provides that the barrier properties are maintained after 3D forming operation .
  • the male and/or female temperatures are above 80 ° C such as between 120 and 300 ° C .
  • the invention shows that the claimed invention solves these problems .
  • PHAs or polyhydroxyalkanoates shall in the context of the patent application refer to a biopolyester family that has a variety of structures and that are synthesized by a broad range of natural and genetically engineered bacteria and genetically engineered plant crops. PHAs can be synthesized in a wide range of environmental conditions and media by 30% of bacteria that live in soil. The bacteria produce PHAs by fermentation of sugar or lipids with the aim to store carbon and energy.
  • Examples of bacterial strains that can produce PHAs include Alcaligenes eutrophus, Alcaligenes latus, Azotobacter, Aeromonas, Comamonas, Pseudomonads, and other genetically engineered organisms, such as genetically engineered microbes like Pseudomonas, Ralstonia and Escherichia coll.
  • PHAs are formed by enzymatic polymerization of one or more monomer units inside living bacteria or plant cell. Over 100 different types of monomers have been identified and incorporated into the PHA polymers, including 3-hydroxybutanoic acid and 3-hydroxypentanoic acid.
  • PHAs can be classified into homopolymers, such as the well-known polyhydroxybutyrate (PHB) , or co-polymers like poly ( 3-hydroxybutyrate-co-3-hydroxyvalerate ) (PHBV) . Additionally, depending on the size of the carbon chain, they are further categorized into short chain length (SCL) , medium chain length (MCL) or long chain length (LCL) PHAs. Since they constitute a broad family of biodegradable polymers, PHAs display very versatile properties that can benefit many different industrial applications, including cosmetics, biomedicine and packaging, to name a few.
  • PHB polyhydroxybutyrate
  • PHBV 3-hydroxybutyrate-co-3-hydroxyvalerate
  • Figure 1 shows a first embodiment, where one side of a paper of a paperboard substrate is coated with a first dispersion coated layer and a second dispersion coated layer .
  • the second layer has a higher crystallinity than the first layer .
  • Figure 2 shows a second embodiment , where both sides of a paper of a paperboard substrate is coated with a first dispersion coated layer and where one of the first layers are coated with a second dispersion coated layer .
  • the second layer has a higher crystallinity than the first layer .
  • Figure 3 shows a third embodiment , where both sides of paper of a paperboard substrate is coated with a first dispersion coated layer and where each of the first layers are coated with a second dispersion coated layer .
  • the second layer has a higher crystallinity than the first layer .
  • the present invention concerns a dispersion coated paperboard 1 for food packaging applications .
  • the coated paperboard comprising a paper or paperboard substrate 2 , which substrate having a first side 2a and a second side 2b .
  • the skilled person reali zes that many di f ferent types of substrates 2 are possible , but a preferred substrate 2 comprising less than 30 wt% high yield fibers , preferably 0-20 wt% and most preferred 1- 15 wt% , since this gives a better compostability of the end product .
  • the high yield fiber is a pulp with KAPPA number above 70 , preferably above 75 and most preferred above 80 .
  • the skilled person reali zes that lower KAPPA number also are possible e . g . i f the pulp is oxygen deligni fied and unbleached .
  • a preferred substrate 2 is a multiply paper or paper board such as SBS , FBB, LPB, kraftliner and multiply packaging paper .
  • the side 2a, 2b of the substrate to be coated is preferably unbleached due to cost , sti f fness and compostability .
  • the dispersion coated paperboard 1 further comprising a PHA dispersion coated first layer 3 which is coated on at least one side 2a, 2b of the paperboard substrate 2 .
  • Figure 1 discloses a first embodiment where only the first side 2a of the substrate 2 is coated with the first layer 3 while the second side 2b is uncoated .
  • Figure 2 and figure 3 discloses second and third embodiment where both sides 2a, 2b of the substrate are coated with the first layer 3 .
  • the PHA of the dispersion coated first layer 3 is preferably a medium chain length po lyhydroxya lkanoate (mcl- PHA) , Mcl-PHA, like PHBH, has shown better properties , including film forming ability when applied through dispersion coating . Also , it is not easy to get a proper dispersion out of short chain length PHA ( scl- PHA) , and processability would be di f ficult since it would demand higher temperatures for drying/curing (properly melting the polymer to form a continuous film) .
  • mcl- PHA medium chain length po lyhydroxya lkanoate
  • mcl-PHA in the first layer 3 are possible selected from the group consisting of 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 mcl-PHA in the first layer 3 is PHBH .
  • some short chain length polyhydroxyalkanoate (scl-PHA) can also be used, such as poly ( 3-hydroxybutyrate-co-3-hydroxyvalerate ) PHBV with high V content (V content >5% ) .
  • the crystallinity of the first dispersion coated layer 3 is 10-45% , preferably 10-30% according to ASTM E794- 06 ( 2018 ) . This crystallinity range has shown better adhesion to the substrate 2 and tolerates better interfacial stresses when formed into 3D packages .
  • the melt temperature ( Tm) of the first dispersion coated layer 3 is preferably between 100 ° C and 145 ° C according to ASTM E794- 06 ( 2018 ) .
  • the Tm in the first layer 3 should not be too high since then adhesion is af fected and delamination might occur after converting into a package .
  • PHAs with lower crystallinity usually have lower Tm than those with higher crystallinity, so equal or lower than 145 ° C .
  • the Tm cannot be too low, because it would become sticky and would not be suitable for hot filling for example .
  • the first layer 3 is preferably applied in an amount of 7-20 gsm and more preferred 8- 15 gsm .
  • the paperboard 1 further comprising a PHA dispersion coated second layer 4 which is coated on at least one of the first layer 3 .
  • Figure 1 discloses a first embodiment where the first layer 3 is coated with the second layer 4 .
  • Figure 2 a discloses second embodiment where one of two first layers 3 is coated with the second layer 4 .
  • Figure 3 discloses a third embodiment where both the first layers 3 are coated with the second layer 4
  • the PHA of the dispersion coated second layer 4 is preferably a medium chain length polyhydroxyalkanoate (mcl-PHA) .
  • Mcl-PHA e . g . PHBH
  • has shown better properties including film forming ability when applied through dispersion coating .
  • it is not easy to get a proper dispersion out of short chain length PHA ( scl-PHA) and processability would be di f ficult since it would demand higher temperatures for drying/curing (properly melting the polymer to form a continuous film) .
  • mcl-PHA in the second layer 4 are possible selected from the group consisting of 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 mcl-PHA in the second layer 4 is PHBH .
  • scl-PHA poly ( 3-hydroxybutyrate-co-3- hydroxyvalerate) PHBV with high V content (V content
  • the crystallinity of the second dispersion coated layer 4 is 30-70%, preferably 30-50% according to ASTM E794-06 ( 2018 ) .
  • the melt temperature (TM) of the second dispersion coated layer 4 is between 120°C and 160°C according to ASTM E794-06 ( 2018 ) . It is beneficial that the second layer 4 has these high melting temperatures in order not to cause any problems in thermoforming or 3D forming. It also gives a better thermo-resistance, less risk for deposits or hot tack.
  • the second layer 4 is preferably applied in an amount of 3-20 gsm and more preferred 5-15 gsm.
  • the crystallinity of the dispersion coated second layer 4 is higher than the crystallinity of first layer 3.
  • the crystallinity in the second layer 4 is preferably at least 10% higher than the first layer 3, more preferred 20% higher than the first layer .
  • the dispersion coating formulations, for the first and second layers 3,4, contains PHA, and additives such as:
  • filler such as e.g., clays, calcium carbonate, talc, kaolinite, montmorillonite, bentonite, silica, chitin, titanium dioxide, nanoclay, nanocellulose, or mixtures thereof.
  • filler such as e.g., clays, calcium carbonate, talc, kaolinite, montmorillonite, bentonite, silica, chitin, titanium dioxide, nanoclay, nanocellulose, or mixtures thereof.
  • dispersing agents and/or humectants for example e.g., glycerol, sorbitol, mannitol, xylitol, ethylene glycol, fatty acids, monosaccharides, urea, hemicellulose, etc.
  • rheology modifier and/or water retention agents e.g. PVOH, PVOH/Ac, EVOH, PVAc, cellulose derivates, polysaccharides, protein, alginates, or various derivatives and/or mixtures thereof.
  • nucleating agents e.g. talc, mica, boron nitride, crystalline nanocellulose, sodium benzoate, calcium carbonate, silica, ionomers, clay, diacetal, titanium oxide, dibenzylidene sorbitol, benzophenone, diacetal benzoate, lithium benzoate, sodium benzoate, potassium benzoate, thymine, sodium organophosphate
  • nucleating agents e.g. talc, mica, boron nitride, crystalline nanocellulose, sodium benzoate, calcium carbonate, silica, ionomers, clay, diacetal, titanium oxide, dibenzylidene sorbitol, benzophenone, diacetal benzoate, lithium benzoate, sodium benzoate, potassium benzoate, thymine, sodium organophosphate
  • wetting and/or defoaming agents such as surfactants or surface active polymers e.g. polysorbates, aromatic polyethylene oxides, sorbitan derivatives, block copolymers of poly ( ethylene oxide) and poly (propylene oxide) , poly(glycol ethers) , alkyl sulfates, alkyl phosphates, stearates saponins, polyether siloxanes, silicones, stearates, glycols, vegetable oils) .
  • surfactants or surface active polymers e.g. polysorbates, aromatic polyethylene oxides, sorbitan derivatives, block copolymers of poly ( ethylene oxide) and poly (propylene oxide) , poly(glycol ethers) , alkyl sulfates, alkyl phosphates, stearates saponins, polyether siloxanes, silicones, stearates, glycols, vegetable oils) .
  • the total amount of additives, as listed above, in the first layer 3 and the second layer 4 are less than 30 wt%, preferably less than 25 wt% and most preferred less than 20 wt% in each layer.
  • the content of PHA in each layer is at least 70 wt% PHA.
  • the solid content of PHA in the dispersions , i . e . dispersion for the first and second layer 3 , 4 is >20 wt% , preferably >35 wt% and most preferred 45- 60 wt% .
  • the dispersion coating layers may be applied by the use 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 and/or combinations thereof .
  • Preferred coating methods are blade coating and rod coating .
  • the inventive dispersion coated paperboard with a dispersion coated first layer 3 and a dispersion coated second layer 4 , where the second layer has a higher degree of crystallinity than the first layer 3 gives a good thermoformability and good barrier properties , especially after forming into 3D shapes .
  • the total crystallinity of the first layer 3 and second layer 4 of the paperboard is higher than 45% , preferably higher than 50% according to ASTM E794 - 06 ( 2018 ) .
  • the melt temperature , Tm and the crystallinity are both determined with ASTM E794- 06 ( 2018 ) and measured with Di f ferential Scanning Calorimetry (DSC ) .
  • the number of pinholes in the inventive coated paperboard is less than 10 pinholes/m 2 , preferably less than 5 pinholes/m 2 according to standard EN13676 : 2001 .
  • the first grade, PHA1 was a PHBH provided in dry form and contained 20 wt% stabilization agent to get a stable dispersion when mixed in water.
  • the PHA had a melting point of 130 °C and mean particle size D50 of the PHA dispersion was 1.8 pm.
  • PHA1 was a PHBH type with a crystallinity below 30 % and PHA2 was a PHBH type with a crystallinity above 30 %, as determined according to ASTM E794-06 ( 2018 ) .
  • the PHA samples were applied on paperboard using a rod coater and then dried to ensure film formation.
  • the base substrate was a paperboard grade, Skypea RFA CLC/F 260 mN, 270 gsm.
  • the first PHA1 coating and the second PHA2 coating had approximately the same coat weight, about 10 gsm. Hence, in total about 20 gsm.
  • the DSC (Differential Scanning Calorimeter) tests were made by making temperature sweep from -20 °C to +200 °C at a speed of 10 min/ °C.
  • the coating was removed from the paper substrate before analysis and tested with the following mode: heating-cooling-heating-cooling-heating. From the calorimetric curves, the crystallinity and melting behavior was determined.
  • EXPERIMENT 1 - Comparative Double coating with PHA1 )
  • the paperboard substrate was double coated with PHA1 with interim drying .
  • the double dispersion coated sample shows improved water vapor barrier, whereas the heatsealability of this grade was poor .
  • Further DSC analysis of the samples shows that the melting of the sample starts at very high temperature , which confirms its poor heat-sealing properties at lower temperature ( 150 ° C ) , pressure ( 500 N) and short dwell times ( 2 s ) .
  • the PHA grade with higher crystallinity, PHA2 was double coated on board as described above .
  • This grade and the obtained coating gave pinholes and was of poor quality and was therefore not suitable as WVTR barrier .
  • the PHA2 (higher crystallinity) was used in the pre-coating and PHA1 ( lower crystallinity) in the top coating .
  • Both the pre and top coatings were made with a 50-50 blend of both PHAs .
  • the WVTR properties were good but on same level as in the example 3 . Crystallinity of this sample was on very high level .

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Wood Science & Technology (AREA)
  • Organic Chemistry (AREA)
  • Laminated Bodies (AREA)
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Abstract

A dispersion coated paperboard (1) for food packaging applications, which coated paperboard comprising a paper or paperboard substrate (2) having a first side (2a) and a second side (2b). The paper coated paperboard (1) further comprising a PHA dispersion coated first layer (3) which is coated on at least one side (2a, 2b) of the paperboard substrate (2); and a PHA dispersion coated second layer (4) which is coated on at least one of the first layer (3), wherein the crystallinity of the second layer (4) is higher than the crystallinity of first layer (3).

Description

A METHOD FOR THE MANUFACTURING OF A DISPERSION COATED PAPERBOARD WITH AT LEAST TWO LAYERS OF PHA HAVING DIFFERENT CRIS TALL INI TY AND A COATED PAPERBOARD
TECHNICAL FIELD
The present invention relates to a dispersion coated paperboard for food packaging applications , which coated paperboard comprising a paper or paperboard substrate having a first side and a second side .
The invention also relates to a method for making a dispersion coated paperboard for food packaging .
BACKGROUND - PROBLEM
Paperboard for food packaging applications is often dispersion coated or extrusion coated or laminated with plastic films for providing barrier properties to the paperboard . Unfortunately, many of the polymers are not sustainable and/or compostable , which makes them less attractive especially in home or industrial recycling and composting .
Many dispersion barriers based on e . g . styrene/acrylates , styrene/butadiene , polyvinylidene chloride ( PVDC ) or similar emulsions , have been used as dispersion coatings for paper and paperboards . These emulsions are designed with physical properties that ensures good film formation when applied of f-line or in-line in paper or paperboard manufacturing . A low or reduced film forming temperature or melting temperature ( Tm) , means on the other hand, a higher risk of white spot deposits on the paper machine (via broke ) , but also greater tendency to blocking and sel f -adhesion .
PHA is a thermoplastic bio-based polymer synthesi zed by bacterial fermentation . PHA can be used in packaging application and is recogni zed for breaking down in all types of environments but especially in bacteria-rich environments like composts .
It is known to coat paperboard for food packaging with PHA coatings .
A drawback with these PHA dispersion coated paperboards is that they lack thermoformability and good barrier properties , especially after forming into 3D shapes .
Dispersion coated paperboard with PHA is more sensitive to cracking etc . due to less coat weight and di f ferent coverage and dispersion consolidation and setting on the board . Also , lower Tm PHA grades have a greater tendency to blocking when thermoformed .
Hence , there is a need to solve the problem combining novel features of PHA for obtaining a dispersion coated multilayer barrier having
Improved WVTR and good water resistance (pinhole free , low COBB 600 )
High grease resistance : KIT >6
Suitable for thermoforming or disposable items which requires heat sealing . A rigid paperboard-laminate , which is home and industrial compostable .
A method to manufacture said coating in-line , of fline or converting lines .
OBJECT OF THE INVENTION
An obj ect with the invention is to provide a coated paperboard with good barrier properties and which is recyclable and reusable .
Another obj ect is to provide a coated paperboard for which recyclability is improved, especially pre- and post-consumer recyclability .
Yet another obj ect is to provide a coated paperboard which solves , or at least reduces , the above-mentioned problems .
SUMMARY OF THE INVENTION
In accordance with the invention the coated paperboard further comprising
- a PHA dispersion coated first layer which is coated on at least one side of the paperboard substrate ; and
- a PHA dispersion coated second layer which is coated on at least one of the first layer, wherein the crystallinity of the second layer is higher than the crystallinity of first layer . The invention further discloses a method for making a dispersion coated paperboard for food packaging, wherein the method comprising the steps of :
- providing a paper or paperboard substrate having a first side and a second side ;
- dispersion coating at least one side of the paper board with a PHA dispersion to form a first layer ; and
- dispersion coating at least one of the first layer with a PHA dispersion to form a second layer, wherein the crystallinity of the second dispersion coated layer is higher than the first dispersion coated layer .
A great benefit with the invention is that the two-layer structure , where the outer layer has a higher crystallinity than the inner layer, gives a good thermoformability and good barrier properties , especially after forming into 3D shapes . The inventive two-layer structure provides that the barrier properties are maintained after 3D forming operation . There is often a risk that normal barrier coatings get defects when subj ected to high temperatures such as in thermoforming, deep-drawing or heat-sealing operations . In e . g . thermoforming or deep drawing, the male and/or female temperatures are above 80 ° C such as between 120 and 300 ° C . The invention shows that the claimed invention solves these problems .
DEFINITIONS
Polyhydroxyalkanoate ( PHA)
PHAs or polyhydroxyalkanoates shall in the context of the patent application refer to a biopolyester family that has a variety of structures and that are synthesized by a broad range of natural and genetically engineered bacteria and genetically engineered plant crops. PHAs can be synthesized in a wide range of environmental conditions and media by 30% of bacteria that live in soil. The bacteria produce PHAs by fermentation of sugar or lipids with the aim to store carbon and energy. Examples of bacterial strains that can produce PHAs include Alcaligenes eutrophus, Alcaligenes latus, Azotobacter, Aeromonas, Comamonas, Pseudomonads, and other genetically engineered organisms, such as genetically engineered microbes like Pseudomonas, Ralstonia and Escherichia coll. In general, PHAs are formed by enzymatic polymerization of one or more monomer units inside living bacteria or plant cell. Over 100 different types of monomers have been identified and incorporated into the PHA polymers, including 3-hydroxybutanoic acid and 3-hydroxypentanoic acid. PHAs can be classified into homopolymers, such as the well-known polyhydroxybutyrate (PHB) , or co-polymers like poly ( 3-hydroxybutyrate-co-3-hydroxyvalerate ) (PHBV) . Additionally, depending on the size of the carbon chain, they are further categorized into short chain length (SCL) , medium chain length (MCL) or long chain length (LCL) PHAs. Since they constitute a broad family of biodegradable polymers, PHAs display very versatile properties that can benefit many different industrial applications, including cosmetics, biomedicine and packaging, to name a few.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 shows a first embodiment, where one side of a paper of a paperboard substrate is coated with a first dispersion coated layer and a second dispersion coated layer . The second layer has a higher crystallinity than the first layer .
Figure 2 shows a second embodiment , where both sides of a paper of a paperboard substrate is coated with a first dispersion coated layer and where one of the first layers are coated with a second dispersion coated layer . The second layer has a higher crystallinity than the first layer .
Figure 3 shows a third embodiment , where both sides of paper of a paperboard substrate is coated with a first dispersion coated layer and where each of the first layers are coated with a second dispersion coated layer . The second layer has a higher crystallinity than the first layer .
In the following, the invention will be described further with reference to Figures 1-3 . Note that the drawings in figures 1-3 are schematical and not to scale .
The present invention concerns a dispersion coated paperboard 1 for food packaging applications . The coated paperboard comprising a paper or paperboard substrate 2 , which substrate having a first side 2a and a second side 2b .
The skilled person reali zes that many di f ferent types of substrates 2 are possible , but a preferred substrate 2 comprising less than 30 wt% high yield fibers , preferably 0-20 wt% and most preferred 1- 15 wt% , since this gives a better compostability of the end product . The high yield fiber is a pulp with KAPPA number above 70 , preferably above 75 and most preferred above 80 . The skilled person reali zes that lower KAPPA number also are possible e . g . i f the pulp is oxygen deligni fied and unbleached .
A preferred substrate 2 is a multiply paper or paper board such as SBS , FBB, LPB, kraftliner and multiply packaging paper . The side 2a, 2b of the substrate to be coated is preferably unbleached due to cost , sti f fness and compostability .
The dispersion coated paperboard 1 further comprising a PHA dispersion coated first layer 3 which is coated on at least one side 2a, 2b of the paperboard substrate 2 . Figure 1 discloses a first embodiment where only the first side 2a of the substrate 2 is coated with the first layer 3 while the second side 2b is uncoated . Figure 2 and figure 3 discloses second and third embodiment where both sides 2a, 2b of the substrate are coated with the first layer 3 .
The PHA of the dispersion coated first layer 3 is preferably a medium chain length po lyhydroxya lkanoate (mcl- PHA) , Mcl-PHA, like PHBH, has shown better properties , including film forming ability when applied through dispersion coating . Also , it is not easy to get a proper dispersion out of short chain length PHA ( scl- PHA) , and processability would be di f ficult since it would demand higher temperatures for drying/curing (properly melting the polymer to form a continuous film) .
The skilled person reali zes that many mcl-PHA in the first layer 3 are possible selected from the group consisting of 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 . Preferably the mcl-PHA in the first layer 3 is PHBH . Alternatively and exceptionally, some short chain length polyhydroxyalkanoate ( scl-PHA) can also be used, such as poly ( 3-hydroxybutyrate-co-3-hydroxyvalerate ) PHBV with high V content (V content >5% ) .
In a preferred embodiment , the crystallinity of the first dispersion coated layer 3 is 10-45% , preferably 10-30% according to ASTM E794- 06 ( 2018 ) . This crystallinity range has shown better adhesion to the substrate 2 and tolerates better interfacial stresses when formed into 3D packages .
The melt temperature ( Tm) of the first dispersion coated layer 3 is preferably between 100 ° C and 145 ° C according to ASTM E794- 06 ( 2018 ) . The Tm in the first layer 3 should not be too high since then adhesion is af fected and delamination might occur after converting into a package . PHAs with lower crystallinity usually have lower Tm than those with higher crystallinity, so equal or lower than 145 ° C . However, the Tm cannot be too low, because it would become sticky and would not be suitable for hot filling for example .
The first layer 3 is preferably applied in an amount of 7-20 gsm and more preferred 8- 15 gsm . Finally, the paperboard 1 further comprising a PHA dispersion coated second layer 4 which is coated on at least one of the first layer 3 . Figure 1 discloses a first embodiment where the first layer 3 is coated with the second layer 4 . Figure 2 a discloses second embodiment where one of two first layers 3 is coated with the second layer 4 . Figure 3 discloses a third embodiment where both the first layers 3 are coated with the second layer 4
The PHA of the dispersion coated second layer 4 is preferably a medium chain length polyhydroxyalkanoate (mcl-PHA) .
Mcl-PHA, e . g . PHBH, has shown better properties , including film forming ability when applied through dispersion coating . Also , it is not easy to get a proper dispersion out of short chain length PHA ( scl-PHA) , and processability would be di f ficult since it would demand higher temperatures for drying/curing (properly melting the polymer to form a continuous film) .
The skilled person reali zes that many mcl-PHA in the second layer 4 are possible selected from the group consisting of 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 . Preferably the mcl-PHA in the second layer 4 is PHBH .
Alternatively and exceptionally, some scl-PHA can also be used, such as poly ( 3-hydroxybutyrate-co-3- hydroxyvalerate) PHBV with high V content (V content
>5%) .
In a preferred embodiment, the crystallinity of the second dispersion coated layer 4 is 30-70%, preferably 30-50% according to ASTM E794-06 ( 2018 ) .
The melt temperature (TM) of the second dispersion coated layer 4 is between 120°C and 160°C according to ASTM E794-06 ( 2018 ) . It is beneficial that the second layer 4 has these high melting temperatures in order not to cause any problems in thermoforming or 3D forming. It also gives a better thermo-resistance, less risk for deposits or hot tack.
The second layer 4 is preferably applied in an amount of 3-20 gsm and more preferred 5-15 gsm.
In accordance with the invention the crystallinity of the dispersion coated second layer 4 is higher than the crystallinity of first layer 3. The crystallinity in the second layer 4 is preferably at least 10% higher than the first layer 3, more preferred 20% higher than the first layer .
The dispersion coating formulations, for the first and second layers 3,4, contains PHA, and additives such as:
0-30 wt% (based on PHA amount) of filler such as e.g., clays, calcium carbonate, talc, kaolinite, montmorillonite, bentonite, silica, chitin, titanium dioxide, nanoclay, nanocellulose, or mixtures thereof. 0-5 wt% of dispersing agents and/or humectants, for example e.g., glycerol, sorbitol, mannitol, xylitol, ethylene glycol, fatty acids, monosaccharides, urea, hemicellulose, etc.
0-30 wt% of rheology modifier and/or water retention agents e.g. PVOH, PVOH/Ac, EVOH, PVAc, cellulose derivates, polysaccharides, protein, alginates, or various derivatives and/or mixtures thereof.
0-30 wt% of nucleating agents e.g. talc, mica, boron nitride, crystalline nanocellulose, sodium benzoate, calcium carbonate, silica, ionomers, clay, diacetal, titanium oxide, dibenzylidene sorbitol, benzophenone, diacetal benzoate, lithium benzoate, sodium benzoate, potassium benzoate, thymine, sodium organophosphate)
0-5 wt% of wetting and/or defoaming agents such as surfactants or surface active polymers e.g. polysorbates, aromatic polyethylene oxides, sorbitan derivatives, block copolymers of poly ( ethylene oxide) and poly (propylene oxide) , poly(glycol ethers) , alkyl sulfates, alkyl phosphates, stearates saponins, polyether siloxanes, silicones, stearates, glycols, vegetable oils) .
The total amount of additives, as listed above, in the first layer 3 and the second layer 4 are less than 30 wt%, preferably less than 25 wt% and most preferred less than 20 wt% in each layer.
The content of PHA in each layer, i.e. the first layer 3 and the second layer 4, is at least 70 wt% PHA. The solid content of PHA in the dispersions , i . e . dispersion for the first and second layer 3 , 4 is >20 wt% , preferably >35 wt% and most preferred 45- 60 wt% . The dispersion coating layers may be applied by the use 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 and/or combinations thereof . Preferred coating methods are blade coating and rod coating .
It has surprisingly been showed that the inventive dispersion coated paperboard, with a dispersion coated first layer 3 and a dispersion coated second layer 4 , where the second layer has a higher degree of crystallinity than the first layer 3 gives a good thermoformability and good barrier properties , especially after forming into 3D shapes .
The total crystallinity of the first layer 3 and second layer 4 of the paperboard is higher than 45% , preferably higher than 50% according to ASTM E794 - 06 ( 2018 ) .
The melt temperature , Tm and the crystallinity are both determined with ASTM E794- 06 ( 2018 ) and measured with Di f ferential Scanning Calorimetry (DSC ) .
The number of pinholes in the inventive coated paperboard is less than 10 pinholes/m2 , preferably less than 5 pinholes/m2 according to standard EN13676 : 2001 .
EXPERIMENTS AND TEST RESULTS Dispersion barrier coatings were made on base substrate using two different PHA grades of the coatings.
The first grade, PHA1, was a PHBH provided in dry form and contained 20 wt% stabilization agent to get a stable dispersion when mixed in water. The PHA had a melting point of 130 °C and mean particle size D50 of the PHA dispersion was 1.8 pm.
The second PHA grade, PHA2, was also a PHBH, but supplied as wet dispersion. The melting point was 145 °C and mean particle size (D50) of the PHA dispersion was 2.9 pm.
PHA1 was a PHBH type with a crystallinity below 30 % and PHA2 was a PHBH type with a crystallinity above 30 %, as determined according to ASTM E794-06 ( 2018 ) .
The PHA samples were applied on paperboard using a rod coater and then dried to ensure film formation. The base substrate was a paperboard grade, Natura RFA CLC/F 260 mN, 270 gsm.
The first PHA1 coating and the second PHA2 coating had approximately the same coat weight, about 10 gsm. Hence, in total about 20 gsm.
The DSC (Differential Scanning Calorimeter) tests were made by making temperature sweep from -20 °C to +200 °C at a speed of 10 min/ °C. The coating was removed from the paper substrate before analysis and tested with the following mode: heating-cooling-heating-cooling-heating. From the calorimetric curves, the crystallinity and melting behavior was determined. EXPERIMENT 1 - Comparative ( Double coating with PHA1 )
The paperboard substrate was double coated with PHA1 with interim drying . The double dispersion coated sample shows improved water vapor barrier, whereas the heatsealability of this grade was poor . Further DSC analysis of the samples shows that the melting of the sample starts at very high temperature , which confirms its poor heat-sealing properties at lower temperature ( 150 ° C ) , pressure ( 500 N) and short dwell times ( 2 s ) .
EXPERIMENT 2 - Comparative ( Pre-coating and top coating with PHA2 )
In this case , the PHA grade with higher crystallinity, PHA2 , was double coated on board as described above . This grade and the obtained coating gave pinholes and was of poor quality and was therefore not suitable as WVTR barrier .
EXPERIMENT 3 - Double coating with PHA1 in pre-coating and PHA2 in top coating
In this case , the PHA1 ( lower crystallinity) was used in the pre-coating and PHA2 (higher crystallinity) in the top coating . This gave very good heat-sealing properties as well as no pinholes and very good water vapor barrier .
EXPERIMENT 4 - Double coating with PHA2 in pre-coating and PHA1 in top coating
In this case , the PHA2 (higher crystallinity) was used in the pre-coating and PHA1 ( lower crystallinity) in the top coating . This gave good heat-sealing properties as well as no pinholes and but not satis fying water vapor barrier, especially when determining WVTR at tropical conditions .
EXPERIMENT 5 - Double coating with 50-50 blend of both PHA grades in pre and top coating
Both the pre and top coatings were made with a 50-50 blend of both PHAs . In this case , the WVTR properties were good but on same level as in the example 3 . Crystallinity of this sample was on very high level .
* Normalized against coat thickness
In the foregoing the invention has been described in some speci fic embodiments . However, a skilled person reali zes that other embodiments and variants are possible within the scope of the following claims .

Claims

C L A I M S
1. A dispersion coated paperboard (1) for food packaging applications, which coated paperboard comprising a paper or paperboard substrate (2) having a first side (2a) and a second side (2b) , characterized in that the coated paperboard (1) further comprising:
- a PHA dispersion coated first layer (3) which is coated on at least one side (2a, 2b) of the paperboard substrate ( 2 ) ; and
- a PHA dispersion coated second layer (4) which is coated on at least one of the first layer (3) , wherein the crystallinity of the second layer (4) is higher than the crystallinity of first layer (3) .
2. Dispersion coated paperboard according to claim 1, wherein the PHA dispersion is a medium chain length polyhydroxyalkanoate (mcl-PHA) .
3. Dispersion coated paperboard according to any of claims 1-2, wherein the PHA is selected from the group consisting of 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.
4. Dispersion coated paperboard according to claim 1, wherein the PHA is a short chain length (scl-PHA) poly (3- hydroxybutyrate-co-3-hydroxyvalerate ) PHBV with high V content .
5. Dispersion coated paperboard according to any of claims 1-4, wherein the crystallinity in the second layer (4) is at least 10% higher than the first layer (3) , preferably 20% higher than the first layer (3) .
6. Dispersion coated paperboard according to any of claims 1-5, wherein the total crystallinity of the first and second layers (3, 4) is higher than 45%, preferably higher than 50% according to ASTM E794-06 ( 2018 ) .
7. Dispersion coated paperboard according to any of claims 1-6, wherein the crystallinity of the dispersion coated first layer (3) is 10-45%, preferably 10-30% according to ASTM E794-06 ( 2018 ) .
8. Dispersion coated paperboard according to any of claims 1-7, wherein the crystallinity of the dispersion coated second layer (4) is 30-70%, preferably 30-50% according to ASTM E794-06 ( 2018 ) .
9. Dispersion coated paperboard according to any of claims 1-8, wherein the melt temperature of the first dispersion coated layer is between 100°C and 140°C, whereas the melt temperature of the second dispersion coated layer is between 120°C and 160°C according to ASTM E794-06 (2018) .
10. Dispersion coated paperboard according to any of claims 1-9, wherein the number of pinholes is less than 10 pinholes/m2, preferably less than 5 pinholes/m2 according to standard EN13676 : 2001.
11. Dispersion coated paperboard according to any of claims 1-10, wherein the first layer (3) is applied in an amount of 7-20 gsm, preferably 8-15 gsm and the second layer (4) is applied in an amount of 3-20 gsm, preferably 5-15 gsm.
12. Dispersion coated paperboard according to any of claims 1-11, wherein paper or paperboard substrate (2) comprises less than 30 wt% high yield fibers, preferably 0-20 wt% and most preferred 1-15 wt%.
13. Dispersion coated paperboard according to any of claims 1-12, wherein high yield fiber is a pulp with KAPPA number above 70, preferably above 75 and most preferred above 80.
14. Method for making a dispersion coated paperboard (1) for food packaging, wherein the method comprising the steps of:
- providing a paper or paperboard substrate (2) having a first side (2a) and a second side (2b) ;
- dispersion coating at least one side (2a, 2b) of the paper board with a PHA dispersion to form a first layer
( 3 ) ; and
- dispersion coating at least one of the first layer (3) with a PHA dispersion to form a second layer (4) , wherein the crystallinity of the second dispersion coated layer
(4) is higher than the first dispersion coated layer (3) .
15. Method according to claim 14, wherein the PHA dispersion is a medium chain length polyhydroxyalkanoate
(mcl-PHA) .
16. Method according to any of claims 14-15, wherein the PHA is selected from the group consisting of 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 -hydroxyoct anoate- co- 3 -hydroxydodecanoate )
(PHDHDD) , or a mixture thereof.
EP23911067.9A 2022-12-27 2023-12-18 A method for the manufacturing of a dispersion coated paperboard with at least two layers of pha having different cristallinity and a coated paperboard Pending EP4642979A1 (en)

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PCT/IB2023/062877 WO2024141850A1 (en) 2022-12-27 2023-12-18 A method for the manufacturing of a dispersion coated paperboard with at least two layers of pha having different cristallinity and a coated paperboard

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