Method for producing dispersion-coated paperboard having at least two layers of PHA with different crystallinity, and coated paperboard

Abstract

A dispersion-coated paperboard (1) for food packaging applications, the 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 comprises a PHA dispersion-coated first layer (3) coated on at least one side (2a, 2b) of the paperboard substrate (2), and a PHA dispersion-coated second layer (4) coated on at least one of the first layers (3), wherein the crystallinity of the second layer (4) is higher than the crystallinity of the first layer (3).

Description

[Technical Field]

[0001] The present invention relates to a dispersion coated paperboard for food packaging applications, the coated paperboard comprising a paper or paperboard substrate having a first side and a second side.

[0002] The present invention also relates to a method for making dispersion coated paperboard for food packaging.

[0003] Background technology / issues Paperboard for food packaging applications is often dispersion or extrusion coated or laminated with a plastic film to impart barrier properties to the paperboard. Unfortunately, many of the polymers are not sustainable and / or compostable, making them less attractive, especially for domestic or industrial recycling and composting.

[0004] Many dispersion barriers (e.g., based on styrene / acrylate, styrene / butadiene, polyvinylidene chloride (PVDC), or similar emulsions) have been used as dispersion coatings for paper and paperboard. These emulsions are designed with physical properties that ensure good film formation when applied offline or in-line in the production of paper or paperboard. Low or reduced film formation or melting temperatures (Tm) increase the risk of white spot buildup on the paper machine (due to broken paper), while also increasing the tendency for blocking and self-adhesion.

[0005] PHAs are thermoplastic, bio-based polymers synthesized by bacterial fermentation. They can be used in packaging applications and have been shown to degrade in all kinds of environments, especially those rich in bacteria, such as compost.

[0006] It is known to coat paperboard for food packaging with a PHA coating.

[0007] A drawback of these PHA dispersion coated paperboards is that they lack thermoformability and good barrier properties, especially after being formed into 3D shapes.

[0008] Paperboard coated with PHA dispersions is more susceptible to cracking and other problems due to the lower coating weight, the different coverage rates on the board, and the different solidification and setting of the dispersion. Also, lower Tm PHA grades tend to be more prone to blocking during thermoforming.

[0009] Thus, the following properties: Improved WVTR and good water resistance (pinhole-free, low COBB 600) High oil resistance: KIT>6 Suitable for thermoformed or disposable items that require heat sealing a dispersion coated multilayer barrier having · Home and industrial compostable rigid paperboard laminates, ·Methods for producing coatings in-line, off-line, or in a conversion line To achieve this, new features of PHAs need to be combined to solve the problem.

[0010] Problem to be solved by the invention It is an object of the present invention to provide a coated paperboard that has good barrier properties and is recyclable and reusable.

[0011] Another object is to provide a coated paperboard that has improved recyclability, particularly pre-consumer and post-consumer recyclability.

[0012] Yet another object is to provide a coated paperboard which overcomes or at least reduces the above problems.

[0013] Summary of the Invention According to the present invention, the coated paperboard comprises: a PHA dispersion coated first layer coated on at least one side of a paperboard substrate; and A PHA dispersion-coated second layer coated on at least one of the first layers. wherein the crystallinity of the second layer is higher than the crystallinity of the first layer.

[0014] The present invention further discloses a method for making a dispersion coated paperboard for food packaging, 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 paperboard with a PHA dispersion to form a first layer; and dispersion coating at least one of the first layers from a PHA dispersion to form a second layer; wherein the second dispersion coated layer has a higher crystallinity than the first dispersion coated layer.

[0015] A major advantage of the present invention is that the two-layer structure, in which the outer layer has a higher crystallinity than the inner layer, provides good thermoformability and good barrier properties, especially after forming into 3D shapes. The two-layer structure according to the present invention maintains its barrier properties even after 3D forming operations. Conventional barrier coatings often run the risk of defects when exposed to high temperatures, for example, during thermoforming, deep drawing, or heat sealing operations. For example, during thermoforming or deep drawing, the temperature of the male and / or female molds exceeds 80°C, for example, between 120 and 300°C. The present invention shows that these problems are solved by the claimed invention.

[0016] definition Polyhydroxyalkanoate (PHA) In the context of this patent application, PHA or polyhydroxyalkanoate refers to a family of biopolyesters with diverse structures synthesized by a wide range of natural and genetically modified bacteria, as well as by a wide range of genetically modified plant crops. PHA can be synthesized by 30% of soil-dwelling bacteria in a wide range of environmental conditions and media. Bacteria produce PHA by fermenting sugars or lipids for the purpose of storing carbon and energy. Examples of bacterial strains capable of producing PHA include Alcaligenes eutrophus, Alcaligenes latus, Azotobacter, Aeromonas, Comamonas, Pseudomonads, and other genetically modified organisms, such as Pseudomonas, Ralstonia, and Escherichia coli. PHAs are typically formed by enzymatic polymerization of one or more monomer units within living bacterial or plant cells. Over 100 different monomers have been identified and incorporated into PHA polymers (e.g., 3-hydroxybutanoic acid and 3-hydroxypentanoic acid). PHAs can be classified as homopolymers (e.g., the well-known polyhydroxybutyrate (PHB)) or copolymers (e.g., poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)). These are further classified according to the size of the carbon chain: short-chain length (SCL), medium-chain length (MCL), or long-chain length (LCL) PHAs. Because they constitute a broad family of biodegradable polymers, PHAs exhibit highly versatile properties that can benefit many different industrial applications, including cosmetics, biomedicine, and packaging, to name a few. [Brief explanation of the drawings]

[0017] [Figure 1]1 shows a first embodiment in which one side of a paper or paperboard substrate is coated with a first dispersion-coated layer and a second dispersion-coated layer, the second layer having a higher degree of crystallinity than the first layer. [Figure 2] 1 shows a second embodiment in which both sides of a paper or paperboard substrate are coated with a first dispersion and one of the first layers is coated with a second dispersion-coated layer, the second layer having a higher degree of crystallinity than the first layer. [Figure 3] 1 shows a third embodiment in which both sides of a paper or paperboard substrate are coated with a first dispersion-coated layer, and each of the first layers is coated with a second dispersion-coated layer, the second layer having a higher degree of crystallinity than the first layer.

[0018] The invention will now be further explained with reference to Figures 1 to 3. It should be noted that Figures 1 to 3 are schematic and are not to scale. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention relates to a dispersion coated paperboard 1 for food packaging applications. The coated paperboard comprises a paper or paperboard substrate 2 having a first side 2a and a second side 2b.

[0020] Those skilled in the art will recognize that there are many different types of substrate 2, but preferred substrate 2 contains less than 30 wt. % high-yield fiber, preferably 0-20 wt. % and most preferably 1-15 wt. % high-yield fiber, as this provides better compostability for the final product. High-yield fiber is pulp with a Kappa number greater than 70, preferably greater than 75, and most preferably greater than 80. Those skilled in the art will recognize that lower Kappa numbers are possible, for example, if the pulp is oxygen delignified and unbleached.

[0021] Preferred substrates 2 are multi-ply paper or paper boards such as SBS, FBB, LPB, kraftliner, and multi-ply wrapping paper. Sides 2a, 2b of the substrate to be coated are preferably unbleached for reasons of cost, stiffness, and compostability.

[0022] The dispersion-coated paperboard 1 further comprises a PHA dispersion-coated first layer 3 coated on at least one side 2a, 2b of the paperboard substrate 2. Figure 1 shows a first embodiment in which only the first side 2a of the substrate 2 is coated with the first layer 3, while the second side 2b is uncoated. Figures 2 and 3 disclose second and third embodiments in which both sides 2a, 2b of the substrate are coated with the first layer 3.

[0023] The PHA of the dispersion-coated first layer 3 is preferably a medium-chain-length polyhydroxyalkanoic acid (mcl-PHA). Mcl-PHAs, like PHBH, exhibit better properties (e.g., film-forming properties when applied by dispersion coating). Also, short-chain-length PHAs (scl-PHAs) are difficult to obtain suitable dispersions from and require higher temperatures to dry / cure (to properly melt the polymer and form a continuous film), making them more difficult to process.

[0024] Those skilled in the art will recognize that many mcl-PHAs in the first layer 3 can be 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 mixtures thereof. The mcl-PHA in the first layer 3 is preferably PHBH. Alternatively, exceptionally, some short-chain-length polyhydroxyalkanoates (scl-PHAs) can also be used, such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV, which has a high V content (V content >5%).

[0025] 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 been shown to provide better adhesion to the substrate 2 and better withstand interfacial stresses when formed into 3D packaging.

[0026] The melting 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 of the first layer 3 should not be too high, as adhesion may be affected and delamination may occur after conversion into packaging. PHAs with low crystallinity typically have a lower Tm than PHAs with high crystallinity, and therefore are below 145°C. However, the Tm should not be too low, as they may become sticky and therefore unsuitable for hot filling, for example.

[0027] The first layer 3 is preferably applied in an amount of 7 to 20 gsm, more preferably in an amount of 8 to 15 gsm.

[0028] Finally, the paperboard 1 further comprises a PHA dispersion coated second layer 4 coated on at least one of the first layers 3. Figure 1 shows a first embodiment in which the first layer 3 is coated with the second layer 4. Figure 2 discloses a second embodiment in which one of the two first layers 3 is coated with the second layer 4. Figure 3 shows a third embodiment in which both first layers 3 are coated with the second layer 4.

[0029] The PHA of the dispersion coated second layer 4 is preferably a medium chain length polyhydroxyalkanoate (mcl-PHA).

[0030] Mcl-PHAs, such as PHBH, have shown better properties (e.g., film-forming properties when applied by dispersion coating). Also, it is not easy to obtain a suitable dispersion from short-chain PHAs (scl-PHAs), and they require higher temperatures to dry / cure (to properly melt the polymer and form a continuous film), making them more difficult to process.

[0031] Those skilled in the art will recognize that many mcl-PHAs in the second layer 4 can be 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 mixtures thereof. Alternatively, in exceptional cases, some scl-PHAs can be used, such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV, which has a high V content (V content >5%).

[0032] 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).

[0033] 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 for the second layer 4 to have such a high melt temperature so as not to cause problems in thermoforming or 3D forming. This also results in better heat resistance and a lower risk of deposits or hot tack.

[0034] The second layer 4 is preferably applied in an amount of 3 to 20 gsm, more preferably in an amount of 5 to 15 gsm.

[0035] According to the present invention, the crystallinity of the dispersion-coated second layer 4 is higher than the crystallinity of the first layer 3. The crystallinity of the second layer 4 is preferably at least 10% higher than that of the first layer 3, and more preferably 20% higher than that of the first layer.

[0036] The dispersion coating formulation for the first and second layers 3, 4 includes a PHA and additives such as: 0-30 wt% (based on the amount of PHA) of fillers (e.g. clay, calcium carbonate, talc, kaolinite, montmorillonite, bentonite, silica, chitin, titanium dioxide, nanoclay, nanocellulose, or mixtures thereof), 0-5 wt% of dispersants and / or humectants, such as glycerol, sorbitol, mannitol, xylitol, ethylene glycol, fatty acids, monosaccharides, urea, hemicellulose, etc. 0-30 wt% of rheology modifiers and / or water retention agents (e.g., PVOH, PVOH / Ac, EVOH, PVAc, cellulose derivatives, polysaccharides, proteins, alginates, or their various derivatives and / or mixtures thereof) 0-30 wt% of nucleating agents, such as talc, mica, boron nitride, crystalline nanocellulose, sodium benzoate, calcium carbonate, silica, ionomers, clay, diacetals, titanium dioxide, dibenzylidene sorbitol, benzophenone, benzoic acid diacetals, lithium benzoate, sodium benzoate, potassium benzoate, thymine, sodium organophosphates) 0-5 wt. % wetting agents and / or antifoaming 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, saponin stearates, polyether siloxanes, silicones, stearates, glycols, vegetable oils).

[0037] The total amount of additives in the first layer 3 and the second layer 4, as described above, is less than 30 wt% in each layer, preferably less than 25 wt%, and most preferably less than 20 wt%.

[0038] The PHA content in each layer, ie, the first layer 3 and the second layer 4, is at least 70 wt% PHA.

[0039] The solids content of the PHA in the dispersion (ie the dispersions of the first and second layers 3, 4) is >20 wt%, preferably >35 wt%, most preferably 45-60 wt%.

[0040] The dispersion coating layer can be applied using roller coating, spray coating, curtain, blade coating, slot coating, dip 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.

[0041] It has surprisingly been found that the dispersion coated paperboard of the present invention comprising a dispersion coated first layer 3 and a dispersion coated second layer 4, where the second layer has a higher crystallinity than the first layer 3, provides good thermoformability and good barrier properties, especially after being formed into 3D shapes.

[0042] The combined crystallinity of the first layer 3 and second layer 4 of the paperboard is greater than 45%, preferably greater than 50%, according to ASTM E794-06(2018).

[0043] Both melting temperature (Tm) and crystallinity are determined according to ASTM E794-06(2018) and measured by differential scanning calorimetry (DSC).

[0044] The number of pinholes in the coated paperboard of the present invention is 10 pinholes / m according to the standard EN13676:2001. 2 Less than 5 pinholes / m 2 is less than.

[0045] Experimental and test results Dispersion barrier coatings were prepared on a base substrate using two coatings with different PHA grades.

[0046] The first grade (PHA1) was PHBH prepared in dry form and contained 20 wt% stabilizer to provide a stable dispersion when mixed with water. The melting point of the PHA was 130°C, and the mean particle size D50 of the PHA dispersion was 1.8 μm.

[0047] The second PHA grade (PHA2) was also PHBH but was supplied as a wet dispersion. The melting point was 145° C. and the mean particle size (D50) of the PHA dispersion was 2.9 μm.

[0048] 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).

[0049] The PHA samples were applied to paperboard using a rod coater and then allowed to dry to ensure film formation. The base substrate was Natura RFA CLC / F 260 mN, 270 gsm paperboard grade.

[0050] The first PHA1 coating and the second PHA2 coating had approximately the same coat weight (about 10 gsm), for a total of about 20 gsm.

[0051] DSC (Differential Scanning Calorimetry) tests were performed by sweeping the temperature from -20°C to +200°C at a rate of 10 min / °C. The coatings were removed from the paper substrate before analysis and tested in a heat-cool-heat-cool-heat mode. From the calorimetric curves, the crystallinity and melting behavior were determined.

[0052] Experiment 1: Comparison (double coating with PHA1) A paperboard substrate was double coated with PHA1 (with drying in between). Although the dispersion double coated sample had improved water vapor barrier properties, the heat sealability of this grade was poor. Further DSC analysis of the sample showed that melting of the sample began at very high temperatures, confirming that the coating had poor heat seal properties at low temperatures (150°C), pressures (500 N), and short dwell times (2 seconds).

[0053] Experiment 2: Comparison (pre-coating and top-coating with PHA2) In this case, a PHA grade with a relatively high degree of crystallinity (PHA2) was double coated onto cardboard as described above. This grade and the resulting coating exhibited pinholes and poor quality, making it unsuitable as a WVTR barrier.

[0054] Experiment 3: Double coating with PHA1 as pre-coating and PHA2 as top coating In this case, PHA1 (relatively low crystallinity) was used for the pre-coating and PHA2 (relatively high crystallinity) was used for the top-coating, which resulted in very good heat-sealing properties, no pinholes, and a very good water vapor barrier.

[0055] Experiment 4: Double coating with PHA2 as pre-coating and PHA1 as top coating In this case, PHA2 (relatively high crystallinity) was used for the pre-coating and PHA1 (relatively low crystallinity) was used for the top-coating, which provided good heat-sealing properties and was pinhole-free, but the water vapor barrier was not sufficient, especially when determining the WVTR in tropical conditions.

[0056] Experiment 5: Double coating with a 50-50 blend of PHA grades for both the pre-coating and top-coating Both the pre-coating and top coating were made with a 50-50 blend of the two PHAs, and in this case the WVTR properties were good, but at the same level as in Example 3. This sample also had a very high level of crystallinity.

[0057] TIFF2025542391000002.tif233170

[0058] Although the present invention has been described above with reference to several specific embodiments, those skilled in the art will recognize that other embodiments and variations are possible within the scope of the following claims.

Claims

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

1. A dispersion coated paperboard comprising:

2. 10. The dispersion coated paperboard of claim 1, wherein the PHA dispersion is a medium chain length polyhydroxyalkanoate (mcl-PHA).

3. 3. The dispersion-coated paperboard of claim 1 or 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) (PHDHHDD), or mixtures thereof.

4. 10. The dispersion coated paperboard of claim 1, wherein the PHA is short chain length, high V content (scl-PHA) poly(3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV.

5. 5. The dispersion coated paperboard according to any one of claims 1 to 4, wherein the crystallinity in the second layer (4) is at least 10% higher than in the first layer (3), preferably 20% higher than in the first layer (3).

6. 6. The dispersion-coated paperboard according to any one of claims 1 to 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. 7. The dispersion-coated paperboard according to any one of the preceding claims, wherein the crystallinity of the dispersion-coated first layer (3) is 10-45%, preferably 10-30%, according to ASTM E794-06(2018).

8. 8. The dispersion-coated paperboard according to any one of the preceding claims, wherein the crystallinity of the dispersion-coated second layer (4) is 30-70%, preferably 30-50%, according to ASTM E794-06(2018).

9. 9. The dispersion-coated paperboard of any one of claims 1 to 8, wherein the melting temperature of the first dispersion-coated layer is between 100°C and 140°C, while the melting temperature of the second dispersion-coated layer is between 120°C and 160°C, according to ASTM E794-06(2018).

10. The number of pinholes is 10 pinholes / m according to the standard EN13676:2001 ２ Less than 5 pinholes / m ２ 10. The dispersion-coated paperboard of any one of claims 1 to 9, wherein the viscosity is less than 100 MPa.

11. 11. The dispersion coated paperboard according to any one of the preceding claims, wherein the first layer (3) is applied in an amount of 7 to 20 gsm, preferably in an amount of 8 to 15 gsm, and the second layer (4) is applied in an amount of 3 to 20 gsm, preferably in an amount of 5 to 15 gsm.

12. 12. The dispersion coated paperboard of any one of claims 1 to 11, wherein the paper or paperboard substrate (2) comprises less than 30 wt% of high yield fibers, preferably 0-20 wt%, most preferably 1-15 wt%.

13. 13. The dispersion coated paperboard of any one of the preceding claims, wherein the high yield fiber is pulp with a Kappa number above 70, preferably above 75, and most preferably above 80.

14. A method for making a dispersion coated paperboard (1) for food packaging, comprising the following steps: - 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 paperboard with a PHA dispersion to form a first layer (3); and dispersion coating at least one of the first layers (3) from a PHA dispersion to form a second layer (4); wherein the crystallinity of the second dispersion coated layer (4) is higher than that of the first dispersion coated layer (3).

15. The method of claim 14, wherein the PHA dispersion is a medium chain length polyhydroxyalkanoate (mcl-PHA).

16. 16. The method of claim 14 or 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-hydroxyoctanoate-co-3-hydroxydodecanoate) (PHDHHDD), or a mixture thereof.

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