Pha-nanoscale rosin synergistic high-barrier water-based coating and preparation and application thereof

Abstract

The application discloses a PHA-nano-rosin synergistic high-barrier water-based coating and preparation and application thereof, and belongs to the technical field of bio-based polymer materials, interface modification and paper-based functional coating. According to the scheme, nano-rosin derivatives and modified sheet barrier fillers are synergistically introduced into a polyhydroxyalkanoate matrix, and a stable chemical bonding interlocking network is constructed between the organic phase and the inorganic phase by using an interface cross-linking coupling agent. The microscopic penetration and filling effect of the nano-rosin and the labyrinth effect of the high-aspect-ratio sheet filler are deeply synergized, and the paper-based material is endowed with the high-barrier effect of oil resistance, water resistance and water vapor. The composition has certain film forming flexibility and adhesion strength after curing, and the physical integrity of the barrier coating can be maintained under complex mechanical processing, indentation and severe folding conditions. The application has full water-based and excellent reslurry recycling performance, and meets the transformation needs in the field of food packaging.

Description

Technical Field

[0001] This invention belongs to the technical fields of bio-based polymer materials, interface modification and paper-based functional coatings, specifically involving PHA-nanorin synergistic high-barrier water-based coatings and their preparation and application. Background Technology

[0002] The demand for paper-based packaging materials to replace traditional plastic composites is growing. To meet the packaging requirements of food and daily chemical products, paper-based materials must possess excellent oil and water resistance, water vapor barrier properties, folding resistance, and long-lasting adhesion. Currently, the industry has developed various water-based barrier coating systems and their preparation processes, among which bio-based materials have attracted significant attention due to their environmentally friendly characteristics.

[0003] In the field of waterborne coatings for polyhydroxyalkanoates (PHAs), existing technologies have explored various aspects. For example, CN120757803A discloses a PHA dispersion emulsion, which aims to improve low-temperature film-forming properties and storage stability by limiting the polymer molecular weight and polydispersity index, and introducing film-forming aids such as 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and aliphatic polyisocyanate crosslinking agents. CN119777197A relates to a waterborne coating prepared by breaking down the cell walls of PHA fermentation broth and then combining it with emulsifiers, thickeners, etc. WO2020036843A1 discloses a biodegradable PHA waterborne dispersion system suitable for food contact substrates. To further improve barrier properties, CN117884325A proposes adding a hot-pressing process after coating to reduce the coating weight and improve density. In addition, CN120250392A attempted to compound PHA with polyvinyl alcohol (PVA) and prepare nanoscale paper-based barrier emulsions using a high-pressure homogenization process. CN120026524B constructed an aqueous emulsion blend system containing PHA, polybutylene adipate terephthalate (PBAT), and PVA. US11866606B2 introduced inorganic fillers and crosslinking components into a PHA dispersion to enhance water resistance.

[0004] In terms of functional modification and filler composites, the application of natural resins and inorganic materials is also quite common. CN119265999A discloses a heat-sealing coating composition comprising biomass materials, PHA emulsion, and rosin or epoxy vegetable oil, mainly relying on physical blending to prepare the slurry. CN111138718A utilizes a composite of rosin glycerol ester emulsion and nanocellulose to improve water and oil repellency. WO2024127356A1 uses rosin-based plant acids to modify PHA. Addressing the barrier mechanism of inorganic fillers, WO2009134538A1 extends the diffusion path by introducing layered inorganic fillers. CN115996838A employs a structure consisting of a water-based biodegradable polymer layer and a hydrophilic nanosheet dispersion layer. Regarding environmental assessment, CN120944505A discloses a fluorine-free bio-based paper protective coating and mentions using the European Paper Industry Federation laboratory evaluation method to assess recyclability.

[0005] Although the aforementioned existing technologies have made some progress in terms of film-forming properties, barrier properties, or heat-sealing properties, they still face many challenges in practical applications.

[0006] First, existing PHA waterborne coating systems mostly focus on improving film quality through film-forming aids. However, when dealing with high-strain conditions such as folding and indentation, the coating is prone to microcracks, forming penetration channels and resulting in a significant reduction in barrier performance.

[0007] Secondly, although rosin and its derivatives possess excellent hydrophobic and thickening properties, in aqueous systems, if introduced solely through conventional emulsification or coarse dispersion methods, phase separation or interfacial defects are highly likely to occur. Particularly at paper creases, these interfacial defects often lead to coating cracking or peeling, making the waterproof and oil-repellent properties unstable.

[0008] Furthermore, while layered inorganic fillers can theoretically improve barrier properties through the labyrinth effect, without effective surface modification and chemical bonding between the organic and inorganic phases, the fillers are prone to agglomeration and the formation of voids at the interface. Water molecules can often permeate along these interfacial voids, making it difficult to simultaneously achieve low water absorption, low water vapor transmission rate, and high folding endurance.

[0009] Furthermore, some existing technologies employ complex processes such as hot pressing and multi-layer lamination in pursuit of high barrier properties. This not only increases equipment investment and energy consumption but also hinders large-scale continuous production and may even increase the difficulty of re-pulping at the recycling end. Other solutions introduce non-bio-based functional components such as ethylene-acrylic acid compounds or use a high proportion of hydrophilic components, which to some extent increases raw material costs and may adversely affect the evaluation of paper-based material recycling.

[0010] In summary, developing a coating composition that enables stable nano-dispersion of the rosin phase, effective exfoliation and orientation of the lamellar inorganic filler in an aqueous system, and the construction of a robust interlocking structure between the organic and inorganic phases through interfacial crosslinking is of great significance for achieving high barrier properties, folding resistance, and industrial production of paper-based packaging materials. Summary of the Invention

[0011] The purpose of this invention is to overcome the shortcomings of the prior art and provide a PHA-nano rosin synergistic high-barrier water-based coating and its preparation and application.

[0012] To achieve the above objectives, the present invention provides the following technical solution:

[0013] This invention provides a PHA-nanorin synergistic high-barrier water-based coating, its preparation and application. Specifically, this invention provides a PHA-nanorin synergistic high-barrier water-based coating composition, which, based on the total dry solids of the coating composition, comprises the following components and their parts by weight: 45 to 90 parts of a polyhydroxyalkanoate (PHA) film-forming substance, such as 45, 50, 55, 60, 65, 67, 69, 71, 75, 80, 85, and 90 parts; and 3 to 35 parts of a nano-sized rosin derivative, such as 3, 5, 8, 10, 12, 15, 18, 20, 25, 30, and 35 parts. The mixture comprises: 5 to 15 parts of sheet-like barrier filler, such as 5, 6, 8, 10, 11.95, 12, 14, and 15 parts; 0.05 to 8 parts of interfacial crosslinking coupling agent, such as 0.05, 0.5, 1.0, 1.5, 2.0, 4.0, 6.0, and 8.0 parts; 0 to 20 parts of toughening and plasticizing agent, such as 0, 1.95, 2.5, 3.5, 5.0, 5.95, 10.0, 15.0, and 20.0 parts; and 0 to 10 parts of additives, such as 0, 0.05, 0.15, 0.75, 1.0, 3.0, 5.0, 8.5, and 10.0 parts. The nano-sized rosin derivative forms D in the aqueous phase. 50 The dispersed phase has a particle size of 50 nm to 300 nm, such as 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 200 nm, 250 nm, and 300 nm; the sheet-like barrier filler has an aspect ratio ≥20 and is surface-modified; the interfacial crosslinking coupling agent comprises one or more epoxy-functionalized silane coupling agents. The PHA film-forming substance exists in the form of an aqueous dispersion of polyhydroxyalkanoates, and the D0 of the PHA particles in the aqueous dispersion of the polyhydroxyalkanoates is... 50The particle size is ≤3μm, for example 0.1μm, 0.5μm, 0.8μm, 0.9μm, 1.0μm, 1.2μm, 2.0μm, 3.0μm; the pH value of the coating composition is 6.5 to 9.5, for example 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5; the coating composition is applied to at least one side of a paper-based substrate and dried, and then further thermosetting to form a barrier coating, the dry coating amount of the barrier coating is 3g / m² to 30g / m², for example 3g / m², 5g / m², 10g / m², 12g / m², 15g / m², 20g / m², 25g / m², 30g / m².

[0014] The PHA film-forming substance is selected from short-chain polyhydroxy fatty acid esters, medium- and long-chain polyhydroxy fatty acid esters, or copolymers between monomers forming short-chain and medium- and long-chain polyhydroxy fatty acid esters. The short-chain polyhydroxy fatty acid ester is selected from one or more combinations of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB); the medium- and long-chain polyhydroxy fatty acid ester is selected from one or more combinations of poly(3-hydroxyhexanoate), poly(3-hydroxyheptanoate), poly(3-hydroxyoctanoate), poly(3-hydroxynonanoate), poly(3-hydroxydecanoate), poly(3-hydroxyundecanoate), poly(3-hydroxydodecanate), poly(3-hydroxytetrate), and poly(3-hydroxytetradecanoate). The solid content of the aqueous dispersion of the polyhydroxy fatty acid ester is from 5 wt% to 70 wt%, for example, 5 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 45 wt%, 50 wt%, 60 wt%, and 70 wt%.

[0015] The nano-sized rosin derivative is a rosin-based material selected from one or more of the following: rosin acid or its salts or esters; hydrogenated rosin acid or its salts or esters; disproportionated rosin; polymerized rosin; rosin esters; hydrogenated rosin esters; maleated rosin and its esters; fumaric rosin and its esters; rosin-modified phenolic resin; rosin-modified terpene resin; rosin-based acrylate polymers; or rosin-based methacrylate polymers. The rosin ester comprises one or more of rosin glycerol ester, rosin pentaerythritol ester, and rosin trimethylpropane ester; the rosin-based acrylate polymer or rosin-based methacrylate polymer is obtained by copolymerizing rosin-based acrylate monomer or rosin-based methacrylate monomer with at least one vinyl monomer, wherein the vinyl monomer is selected from one or more of acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, styrene, vinyl acetate, and acrylonitrile; and the acid value of the nano-sized rosin derivative is from 0 mg KOH / g to 200 mg KOH / g, for example, 0 mg KOH / g, 6 mg KOH / g, 20 mg KOH / g, 50 mg KOH / g, 80 mg KOH / g, 100 mg KOH / g, 145 mg KOH / g, 180 mg KOH / g, and 200 mg KOH / g.

[0016] The layered barrier filler is selected from one or more combinations of layered silicates, layered double hydroxides, plated oxides, and plated boron nitrides. Among them, the layered silicates include one or more combinations of plated kaolin, montmorillonite, vermiculite, mica, and talc, and D... 50 The particle size is ≤5μm, for example, 0.5μm, 1.0μm, 1.5μm, 2.0μm, 2.5μm, 3.0μm, 4.0μm, 4.5μm, 5.0μm; the surface modification treatment of the sheet barrier filler is selected from one or a combination of the following: silane coupling agent treatment, titanate coupling treatment, zirconate coupling treatment, phosphate coupling treatment, aluminate coupling treatment, fatty acid hydrophobication treatment, wax hydrophobication treatment, cationic surfactant intercalation treatment, nonionic surfactant intercalation treatment, inorganic sol-gel coating treatment; wherein the silane coupling agent used in the silane coupling agent treatment includes the epoxy-functionalized silane coupling agent, and the epoxy-functionalized silane coupling agent is selected from one or more combinations of γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, and γ-glycidoxypropylmethyldimethoxysilane.

[0017] The interfacial crosslinking coupling agent further includes one or more crosslinking components selected from carbodiimides, oxazolines, polyfunctional epoxides, aminosilanes, polycarboxylic acids, acid anhydrides, or combinations thereof, and the total amount of the crosslinking components is included in the range of 0.05 parts to 8 parts of the interfacial crosslinking coupling agent. The toughening and plasticizing agent is a bio-based plasticizer selected from one or more combinations of citrate esters, succinate esters, fatty acid esters, and epoxidized vegetable oils. The additives include one or more of wetting and dispersing agents, emulsifiers, defoamers, leveling agents, thickeners, antisettling agents, preservatives, pH adjusters, and protective colloids; wherein the emulsifier or protective colloid is selected from one or more combinations of anionic surfactants, nonionic surfactants, amphoteric surfactants, and polyvinyl alcohol (PVA), and when the PVA is used as a protective colloid, the amount added, on a dry solids basis, is 1 wt% to 15 wt% of the mass of the nano-rosin derivative, for example, 1 wt%, 3 wt%, 5 wt%, 6.7 wt%, 10 wt%, 12 wt%, and 15 wt%.

[0018] The final solid content of the coating composition is 30wt% to 60wt%, for example, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%. After coating, the coating composition is dried at 60°C to 130°C, for example, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, and further heat-cured at 80°C to 160°C, for example, 80°C, 100°C, 120°C, 140°C, 160°C, for a curing time of 0.5min to 10min, for example, 0.5min, 1min, 2min, 5min, 8min, 10min. The resulting coating film has a weight gain of ≤15wt% after immersion in deionized water at 23°C for 24h, for example, 1wt%, 5wt%, 10wt%, 11wt%, 13wt%, 14wt%, 15wt%.

[0019] This invention also provides a method for preparing the PHA-nano rosin synergistic high-barrier waterborne coating composition, the preparation method comprising the following steps: Step 1 is surface modification and dispersion of the sheet barrier filler, dispersing the sheet barrier filler in an aqueous phase to form a slurry, adding a surface modifier for shear dispersion and completing surface modification to obtain a modified sheet filler slurry; Step 2 is rosin nanoforming, mixing rosin derivatives with an aqueous phase containing emulsifiers and / or protective colloids and pre-emulsifying, then preparing the volume median particle size D by high-pressure homogenization, microfluidization, ultrasonic emulsification, membrane emulsification or rotor-stator high-shear emulsification. 50The first step involves a rosin nanoemulsion with a wavelength of 50 nm to 300 nm. Step 3 is aqueous blending, in which the rosin nanoemulsion obtained in step 2 is added to a PHA aqueous dispersion and mixed. Then, the modified sheet filler slurry, interfacial crosslinking coupling agent, toughening and plasticizing agent, and additives obtained in step 1 are added to adjust the solid content and pH value to obtain a premixed coating composition. Step 4 is curing, in which the premixed coating composition obtained in step 3 is cured at 25°C to 60°C for 0.5 hours to 6 hours to obtain a coating composition.

[0020] In step 1, the surface modifier is selected from one or more combinations of silane coupling agents, titanate coupling agents, zirconate coupling agents, phosphate coupling agents, and aluminate coupling agents. The amount of the surface modifier is 0.1wt% to 8wt% of the mass of the sheet barrier filler, for example, 0.1wt%, 0.5wt%, 1.0wt%, 2.0wt%, 4.0wt%, 6.0wt%, or 8.0wt%. In step 2, the high-pressure homogenization pressure is 20MPa to 120MPa, for example, 20MPa, 40MPa, 60MPa, 80MPa, 100MPa, or 120MPa, and the homogenization times are 2 to 8 times, for example, 2 times, 3 times, 5 times, 6 times, or 8 times. In step 3, the rosin nanoemulsion is added to the PHA aqueous dispersion by dropwise or in stages, and the modified sheet filler slurry obtained in step 1 is added after the addition, and the interfacial crosslinking coupling agent is added last. Thus, the coating composition is obtained.

[0021] This invention also provides a paper-based barrier material prepared from the aforementioned PHA-nano rosin synergistic high-barrier water-based coating composition. The barrier coating is obtained by coating one or more sides of paper, paperboard, molded pulp substrate, or their composite paper-based materials with the aforementioned PHA-nano rosin synergistic high-barrier water-based coating composition and then drying and thermosetting it into a film. The paper-based barrier material, tested according to ISO 535:2023, has a 30-minute Cobb water absorption value ≤ 5 g / m², for example, 0.5 g / m², 1.0 g / m², 2.0 g / m², 3.0 g / m², 4.0 g / m², 4.2 g / m², or 5.0 g / m². According to TAPPI / ANSI T 559cm-22, its oil resistance Kit value is ≥ 11, for example, 11 or 12. According to ASTM... The E96 / E96M-24a exhibits a water vapor transmission rate ≤12g / (m²·d) at 23℃ and 50%RH, for example, 1g / (m²·d), 3g / (m²·d), 5g / (m²·d), 8g / (m²·d), 10g / (m²·d), and 12g / (m²·d). According to ISO 2409:2020, its cross-cut adhesion is grade 0 or 1. According to TAPPI / ANSI T 511 om-25, its mittance (MIT) is ≥250 folds, for example, 250, 300, 400, and 500 folds. Furthermore, after a 180-degree fold or crease, its Kit value at the crease is ≥11, and its total fluorine content, as determined by T / CNFIA 191—2024, is less than 5mg / kg.

[0022] The present invention also provides a packaging article made of the paper-based barrier material, wherein the packaging article is selected from one or more of food packaging paper, paper cups, paper bowls, paper lunch boxes, takeaway paper bags, molded pulp lunch boxes or trays, and the surface of the packaging article in contact with food or daily chemical products contains the paper-based barrier material.

[0023] Compared with the prior art, the use of this invention can achieve the following significant beneficial effects:

[0024] Excellent synergistic barrier properties. This invention uses nanotechnology to prepare rosin derivatives into nano-dispersed phases of 50nm to 300nm, enabling them to deeply penetrate and fill the micropores inside the substrate fiber network and coating. At the same time, it is combined with surface-modified lamellar barrier fillers with high aspect ratio to create a "maze effect". The synergistic effect of the two significantly extends the penetration path of water and oil molecules, thereby giving the paper-based material excellent oil-proof, water-proof and water vapor-blocking properties.

[0025] A robust interfacial interlocking structure. This invention utilizes an epoxy-functionalized silane coupling agent as an interfacial crosslinking component. One end of this component can react with the hydroxyl groups on the surface of the inorganic filler and the substrate, while the epoxy group at the other end can undergo ring-opening crosslinking with the end of the PHA molecular chain and the active groups in the rosin structure during thermosetting. This constructs a robust chemical bond network between the organic and inorganic phases, effectively solving the problems of weak interfacial bonding and easy phase separation in traditional physical blending systems, and significantly improving the adhesion and moisture resistance of the coating.

[0026] Excellent machinability. Thanks to the inherent properties of the PHA matrix and the appropriate introduction of toughening and plasticizing agents, combined with the reinforcing effect of nanoparticles, the coating composition exhibits excellent flexibility and folding resistance after curing. Even after undergoing severe mechanical deformations such as knurling, creasing, and 180-degree folding during high-speed paper cup forming, the coating surface remains smooth and crack-free, and the barrier properties at the folds do not diminish, fully meeting the processing requirements of industrial packaging products.

[0027] Wide applicability to various substrates and processes. The coating composition prepared by this invention is not only suitable for smooth paper, but also exhibits excellent film-forming properties and leak-proof effects on rough, porous molding pulp (such as sugarcane pulp lunch boxes); at the same time, the composition has a wide curing process window (80°C to 160°C), which can adapt to the drying conditions of different production lines, and maintains stable barrier performance at different coating amounts (3g / m² to 30g / m²).

[0028] Outstanding environmental and safety characteristics. The coating composition of this invention is an all-water-based system; the total fluoride content of the paper-based barrier material obtained by coating and curing with it is less than 5 mg / kg as determined by T / CNFIA 191—2024, which meets the technical requirements for low fluoride of paper-based materials for food contact; and the coating components are mainly derived from bio-based or natural materials, which are easy to separate from paper fibers during the pulping process after disposal, and have excellent repulping and recycling performance, which meets the requirements of circular economy and sustainable development. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the microscopic cross-sectional structure of the paper-based barrier material described in this invention.

[0030] In the figure, 1-paper-based substrate; 2-polyhydroxyalkanoate film-forming substance; 3-sheet barrier filler; 4-nanosized rosin derivative; 5-interfacial crosslinking coupling agent construct a stable chemical bond interlocking network between the organic and inorganic phases. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention. Unless otherwise stated, the raw materials used in this embodiment are commercially available industrial products or can be prepared by conventional methods. Unless otherwise specified, performance testing methods are performed according to the standards described in the invention summary section.

[0032] Figure 1 The cross-sectional structure of the paper-based barrier material of the present invention is schematically shown. The surface of the paper-based substrate 1 is covered with a barrier coating with polyhydroxyalkanoate film-forming substance 2 as the continuous phase. The sheet barrier filler 3 is dispersed in the coating and oriented along the plane of the coating. The nano-sized rosin derivative 4 is dispersed in the continuous phase and the gaps between the fillers. The interfacial crosslinking coupling agent helps to form an interfacial bonding structure 5 between the organic phase and the inorganic phase.

[0033] Main reagents and raw materials

[0034] The main reagents and raw materials used in the embodiments and comparative examples of this invention are shown in Table 1.

[0035] Table 1. Information on Main Reagents and Raw Materials:

[0036]

[0037] Main analytical and testing instruments

[0038] The main analytical instruments used in the embodiments and comparative examples of this invention are shown in Table 2.

[0039] Table 2: Information on Main Analytical and Testing Instruments

[0040]

[0041] Main test standards

[0042] (1) Cobb water absorption value: The Cobb value was tested for 30 minutes according to ISO 535:2023.

[0043] (2) Oil resistance Kit value: Refer to TAPPI T 559 cm-22.

[0044] (3) Water vapor transmission rate: Refer to ASTM E96 / E96M-24a, adopt the dry cup method (Desiccant Method, Procedure A), and the test environment is 23℃ and 50%RH.

[0045] (4) Adhesion: Refer to ISO 2409:2020.

[0046] (5) Flexural endurance: Refer to TAPPI / ANSI T 511 om-25.

[0047] (6) Particle size: Refer to ISO 13320:2020. Nano-rosin emulsions and PHA dispersions were tested using deionized water as the dispersion medium. Laminated fillers were tested after dispersion in deionized water with 0.1 wt% sodium hexametaphosphate. All results are expressed as the volume median particle size D. 50 express.

[0048] (7) Total Fluorine Content: The total fluorine content in food contact paper, paperboard and paper products was determined using online combustion-ion chromatography (CLC) according to T / CNFIA 191—2024. The test subject was coated and cured paper-based barrier material, with uncoated white cardboard as a blank control. The sample was cut into small fragments, mixed thoroughly, and 50 mg (accurate to 0.1 mg) was accurately weighed and placed in a clean quartz sample boat for testing. The result was expressed as fluorine. Method validation was performed based on the test conditions used in this application. The method detection limit was 0.5 mg / kg, and the method quantitation limit was 2 mg / kg. Samples with a concentration less than 5 mg / kg were recorded as "<5 mg / kg".

[0049] (8) Total sieve residue of repulping: The sample preparation, wet dissociation, 5 mm coarse sieve and 0.15 mm fine sieve steps in Paper and Board – Recyclability Laboratory Test Method – Part I: Recycling mill with Conventional process, Version 3, February 2025 were followed, and the total sieve residue TSR was calculated as CR + 0.9FR, where CR is the sieve residue of the 5 mm coarse sieve and FR is the sieve residue of the 0.15 mm slit sieve.

[0050] The coated paper sample was cut into 3cm×3cm (±0.5cm) fragments, and a sample equivalent to 50.0±1.0g of oven-dried sample was calculated and weighed. The sample was added to a laboratory wet dissociation machine, and tap water at 45±1℃ was added. The dissociated total pulp was first coarsely sieved for 5 minutes using a Somerville sieve at a water flow rate of 8.6±0.2L / min to obtain the 5mm mesh coarse sieve residue CR. Then, a portion equivalent to 20g of oven-dried pulp was taken from the coarse sieve and finely sieved for 20 minutes using a 0.15mm slotted sieve under the same water flow rate to obtain the 0.15mm slotted fine sieve residue FR. The coarse and fine sieve residues were dried to constant weight at 105±2℃, and the total sieve residue of the repulping was calculated according to TSR=CR+0.9FR.

[0051] Preparation of Examples and Comparative Examples:

[0052] The formulation composition of Examples 1-16.

[0053] The formulation composition (by dry solids mass) of the PHA-nano rosin synergistic high-barrier waterborne coating compositions of Examples 1-16 is detailed in Table 3.

[0054] Table 3. Formulation composition of Examples 1-16 (by dry solids mass):

[0055]

[0056] Polyhydroxy fatty acid ester dispersion type: Example 4 used P34HB dispersion; Example 8 used PHBH dispersion; Example 9 used PHB dispersion; and the remaining examples all used PHBV dispersion.

[0057] Nano-sized rosin derivatives: Example 10 uses polymerized rosin; the other examples all use hydrogenated rosin glycerol esters.

[0058] Inorganic filler types: Montmorillonite was used in Example 3; talc was used in Example 11; and flaky kaolin was used in the remaining examples.

[0059] Interfacial crosslinking coupling agent type: Example 12 uses γ-glycidoxypropyltriethoxysilane (epoxysilane B); Example 16 uses a combination of γ-glycidoxypropyltrimethoxysilane (epoxysilane A) and a water-dispersible polycarbodiimide crosslinking agent, wherein the mass parts of epoxysilane A and the water-dispersible polycarbodiimide crosslinking agent are 1.00 parts and 0.50 parts, respectively; the remaining examples all use γ-glycidoxypropyltrimethoxysilane (epoxysilane A).

[0060] Additional crosslinking component type: Example 16 uses a water-dispersible polycarbodiimide crosslinking agent; no additional crosslinking components were introduced in the other examples.

[0061] Plasticizer type: Tributyl acetylacetate was used in all examples.

[0062] In the table, both polyvinyl alcohol and AEO-9 are calculated based on the dry solids mass added to the final composition; when polyvinyl alcohol is used as a protective colloid in step 2, its amount is calculated as 6.7 wt% of the mass of the nano-rosin derivative; when AEO-9 is used as an emulsifier in step 2, its amount is calculated as 5.0 wt% of the mass of the nano-rosin derivative; the 0.05 parts of polyvinyl alcohol in Example 6 are auxiliary additives added after step 3; the "interfacial crosslinking coupling agent" in Table 3 is listed as a total amount, and the 1.50 parts of interfacial crosslinking coupling agent in Example 16 is the total amount of epoxy silane A and water-dispersible polycarbodiimide crosslinking agent.

[0063] The formulation composition of Comparative Examples 1-11.

[0064] The formulation composition (by dry solids mass) of the PHA-nano rosin synergistic high-barrier waterborne coating compositions of Comparative Examples 1-11 is detailed in Table 4.

[0065] Table 4. Composition of Comparative Examples 1-11 (by dry solids mass):

[0066]

[0067] Polyhydroxyalkanoate dispersion: Comparative Example 10 used a non-homogeneous crude PHBV dispersion (D 50 =10.0 μm); the other comparative examples all used the same PHBV dispersion as in Example 1.

[0068] Rosin derivatives: Comparative Example 2 used crude emulsion of unnanosized hydrogenated rosin glycerol esters (D 50 =1.5μm); the other comparative examples all used the same nano-hydrogenated rosin glycerol ester as in Example 1.

[0069] Inorganic fillers: Comparative Example 4 used heavy calcium carbonate (non-laminated); the other comparative examples all used flaky kaolin.

[0070] Plasticizer: Tributyl acetylacetate was used in all comparative examples.

[0071] The above examples and comparative examples were prepared using the following general methods (unless otherwise specified):

[0072] Step 1: Filler modification: The sheet filler is dispersed in deionized water to prepare a slurry with a solid content of 20 wt%, and a silane coupling agent is added for surface modification. The silane coupling agent is an epoxy-functionalized silane coupling agent (epoxy silane A and / or epoxy silane B). In step (1), the amount of silane coupling agent used for filler surface modification is fixed at 0.5 wt% of the sheet filler mass (based on dry solids) (except for Comparative Example 3). The modified sheet filler slurry is obtained by shearing at 10,000 rpm for 20 min using a rotor-stator high shear disperser. The "interfacial crosslinking coupling agent" listed in Tables 3 and 4 is the total amount of coupling agent used in this formulation. Except for the 0.5 wt% × filler mass part used in step (1), the rest is added in the blending stage of step (3).

[0073] Step 2: Rosin Nanoforming: When using hydrogenated rosin glycerol ester, heat it to 90℃ to completely melt it, and preheat the aqueous phase to 80℃; when using polymerized rosin, heat it to 160℃ to completely melt it, and preheat the aqueous phase to 95℃; add a protective colloid or emulsifier to the aqueous phase, wherein the protective colloid is polyvinyl alcohol, and the amount added is 6.7wt% (based on dry solids) of the rosin derivative, or the emulsifier is fatty alcohol polyoxyethylene ether (AEO-9), and the amount added is 5.0wt% (based on dry solids) of the rosin derivative; add the molten rosin to the aqueous phase at the corresponding preheated temperature, and pre-emulsify it for 5 minutes at 12000 rpm using a rotor-stator emulsifier to obtain a crude emulsion; then homogenize it five times under high pressure at 800 bar (80 MPa) to obtain a rosin nanoemulsion; wherein, the rosin nanoemulsion D prepared using hydrogenated rosin glycerol ester is... 50 The rosin nanoemulsion D, with a wavelength of 120 nm, was prepared using polymerized rosin. 50 For 150nm (Comparative Example 2, mechanical stirring only, D) 50 (1.5μm).

[0074] Step 3: Blending: Add the rosin nanoemulsion to the polyhydroxy fatty acid ester dispersion dropwise under stirring at 300 rpm for 10 min; after the dropwise addition is completed, continue stirring for 10 min, and then add the modified filler slurry, the remaining coupling agent, plasticizer and additives other than those in step (1) in sequence; when it is necessary to introduce crosslinking components, add the water-dispersible polycarbodiimide crosslinking agent or oxazoline crosslinking agent in the last stage and stir thoroughly for 10 min, and the amount of the agent and the amount of epoxy-functionalized silane coupling agent are combined and included in the range of 0.05 to 8 parts of the interfacial crosslinking coupling agent; use deionized water to adjust the solid content to 45 wt%; use 10 wt% sodium hydroxide solution to adjust the pH to 8.0 dropwise (Comparative Example 11 uses 1 mol / L hydrochloric acid solution to adjust the pH to 4.0 dropwise). In Example 16, 0.50 parts (based on dry solids) of water-dispersible polycarbodiimide crosslinking agent were added in the final stage of step 3, and combined with epoxy-functionalized silane coupling agent to be included in the total amount of 1.50 parts of interfacial crosslinking coupling agent; in Example 16, 0.05 parts of epoxy silane A were used for filler surface modification in step 1, and 0.95 parts of epoxy silane A were added in step 3.

[0075] Step 4: Mature: Mature at 40℃ for 2 hours.

[0076] Application examples

[0077] Application Example 1: Performance evaluation under standard coating process.

[0078] This application example aims to evaluate the film-forming and barrier properties of the coating compositions prepared in each embodiment and comparative example under standard coating and curing conditions. Industrial-grade white cardboard with a basis weight of 300 g / m² was used as the substrate and equilibrated in a constant temperature and humidity chamber (23°C, 50% RH) for 24 hours before coating. During the experiment, a K303 laboratory coater was used to fix the white cardboard to be coated on a vacuum adsorption platform with a flatness deviation of less than 10 μm. Three samples were prepared independently for each formulation. Based on the solid content and rheological properties of each composition, an RK4 filament doctor blade was selected, and the coating speed was set to 4 m / min. The actual dry coating amount was determined using a weighing method: the substrate mass m0 before coating was recorded. After drying at 90℃ for 3 minutes and curing at 120℃ for 2 minutes, followed by equilibration at 23℃ and 50%RH for 24 hours, the mass m1 was measured. The actual dry coating amount was calculated as (m1-m0) / coating area. By fine-tuning the wire rod type or coating speed, the actual dry coating amount was controlled to be 12.0 g / m² ± 0.5 g / m². After coating, the wet-coated sample was immediately transferred flat to a precision forced-air drying oven. The temperature was set to 90℃, and the damper opening of the DZF-6050 precision forced-air drying oven was fixed at 50% of the value displayed on the control panel. Drying was carried out for 3 minutes to remove most of the moisture. Subsequently, the sample was quickly transferred to a curing oven preheated to 120℃ and heat-treated at 120℃ for 2 minutes to induce physical entanglement and chemical cross-linking between components. After curing, the samples were suspended in a standard constant temperature and humidity environment (temperature 23℃±1℃, relative humidity 50%±2%) for 24 hours for equilibration. After equilibration, oil resistance (Kit grade), water absorption (Cobb value), water vapor transmission rate (WVTR), adhesion, and folding endurance were tested. For Cobb value, WVTR, and MIT folding endurance, three parallel samples were taken each, and the arithmetic mean was reported. For Kit value, cross-cut adhesion, Kit value after 180-degree fold, and Kit value after indentation, three parallel samples were taken each, and the median was reported. The Kit value after 180-degree fold was tested as follows: the sample was folded 180 degrees with the coated side facing outwards, and a 2kg steel roller was used to press it back and forth once at a speed of 50mm / s along the fold line. After unfolding, the Kit test was performed along the fold line, and the median of the three parallel samples was taken as the Kit value after 180-degree fold.The Kit value after indentation was tested as follows: The sample was cut into 100mm×150mm specimens, with the uncoated side facing up, and placed on a laboratory indentation apparatus with an indentation knife / indentation groove mold. An indentation knife with a blade width of 0.71mm and an indentation groove with a groove width of 1.40mm were used to press a straight indentation with a length of 80mm along the 100mm direction in the middle of the sample. The indentation load was 200N, the loading speed was 50mm / s, the pressure was held for 1s, and the indentation was performed once. After indentation, the sample was left to stand for 10min at 23℃ and 50%RH, and then the sample was flipped over. The Kit test was performed on the coated surface at the corresponding indentation line, and the median of 3 parallel samples was taken as the Kit value after indentation.

[0079] The test results for each sample are detailed in Table 5.

[0080] Table 5. Test results of coating performance for each formulation under standard process:

[0081]

[0082] Note: The reason for the "-" in the table is as follows: Comparative Example 5 is defined as "coating amount controlled at 2g / m²", and Comparative Example 6 is defined as "no 120℃ heat curing". However, this application example is set with standard process conditions (dry coating amount of 12g / m² and heat curing at 120℃). The preset conditions of these two comparative examples conflict with the test conditions of this example, and therefore are not applicable to the collection of data in this table.

[0083] Analysis: Table 5 shows that, under standard coating and curing processes, all performance indicators of Examples 1 to 16 met the expected design goals. The Kit oil repellency value of all examples remained stable at 11 to 12, the Cobb value was controlled at 5.0 g / m² or below, and the water vapor transmission rate (WVTR) was no higher than 12 g / (m²·d), indicating that a dense hydrophobic barrier network was successfully constructed through formulation optimization. The newly added indentation Kit value test showed that all examples maintained a level of 11 to 12 after linear indentation in the laboratory, consistent with the Kit value after 180-degree folding. This indicates that the formed barrier layer can withstand not only in-plane bending but also the interfacial tensile and compressive coupling effects caused by localized concentrated linear pressure. In particular, Example 16, by further introducing 0.50 parts of a water-dispersible polycarbodiimide crosslinking agent on the basis of the epoxy-based silane coupling agent, achieved a Cobb value of 4.0 g / m², a WVTR of 11 g / (m²·d), and Kit values ​​after 180-degree folding and indentation were both grade 12, indicating that the carbodiimide-based additional crosslinking component can further enhance the interfacial stability and water resistance within the system of this invention. Especially, the samples using P34HB (Example 4) and PHBH (Example 8) as film-forming matrices exhibited significantly higher folding endurance than the samples using the PHBV matrix, which is attributed to the flexible segments provided by the comonomers. Example 15 introduced a higher proportion of plasticizer, achieving a folding endurance of 500 times while maintaining good barrier properties, demonstrating excellent flexibility.

[0084] In contrast, the comparative data reveal the necessity of each key component in the system. Comparative Example 1 (pure PHBV), while forming a film, had a WVTR as high as 120 g / m²·d, failing to meet the high barrier requirements, and its Kit value after indentation was only level 9. Comparative Example 2, due to rosin particle size not reaching the nanoscale, had poor film density, with Kit values ​​of only level 2 and 3 after 180-degree folding and indentation, respectively. Comparative Example 3, lacking filler modification and coupling agent, suffered interface defects resulting in significantly worse WVTR and Cobb values ​​than the examples, and its Kit value after indentation was only level 8. The excessive rosin content in Comparative Example 8 led to an extremely brittle coating with only 40 folds, a Kit value of level 3 after 180-degree folding, and a Kit value of level 4 after indentation. Comparative Example 9, with excessive filler, resulted in an excessively high critical pigment volume concentration, causing coating cracking, poor adhesion, and a Kit value of only level 3 after indentation. Comparative Example 10, due to excessively large film-forming resin particle size, could not form a continuous film layer. Comparative Example 11 was prepared under acidic conditions, resulting in compromised emulsion stability and a comprehensive decline in performance.

[0085] Application Example 2: The effect of coating amount on barrier performance.

[0086] This application example aims to verify the performance and film stability of the coating composition under different dry coating amounts. All examples and comparative examples were selected as subjects to investigate their adaptability at extremely low coating amounts (3 g / m²) and higher coating amounts (30 g / m²). The coating process achieved the target coating amount by using a precision wire rod and adjusting the coating solids content and coating speed: for the 3 g / m² condition, an RK0 rod was used, the coating solids content was adjusted to 35 wt%, and the coating speed was set to 8 m / min; for the 30 g / m² condition, an RK8 rod was used, the coating solids content was adjusted to 55 wt%, and the coating speed was set to 2 m / min; except for Comparative Example 11, the pH of all other coatings was adjusted to 8.0 in both conditions; Comparative Example 11 maintained the pH of 4.0 obtained in step 3 to preserve the acidity variable. For ultra-thin coatings of 3 g / m², excellent leveling properties are required to avoid ink breaks and pinholes. For thick coatings of 30 g / m², a stepped temperature increase method (60℃ for 2 minutes + 90℃ for 3 minutes) is used during the drying stage to prevent internal blistering caused by excessively rapid surface skinning. The coatings are then cured uniformly at 120℃ for 2 minutes. Testing focuses on the most sensitive properties: oil resistance (Kit), water resistance (Cobb), and water vapor transmission rate (WVTR).

[0087] Table 6. Performance test results under different coating amounts:

[0088]

[0089] Note: The reasons for the "-" in the table are as follows: Comparative Example 5 is defined as "2g / m² coating", and cannot be used in the comparative tests of 3g / m² and 30g / m²; Comparative Example 6 is defined as "no heat curing", but this application example uses 120℃ heat curing to exclude curing process variables, so Comparative Example 6 is not applicable. The observation and judgment criteria for surface microcracks are as follows: After the sample is equilibrated in an environment of 23℃ and 50%RH for 24 hours, the coating surface and edge area are observed using a 10× magnifying glass; when the number of cracks is not less than 3 in a 100mm×100mm observation area and the length of any crack is not less than 1.0mm, it is judged as "surface microcracks". Comparative Example 9 meets the above judgment criteria when coated with 30g / m², so its barrier data is for reference only.

[0090] Analysis: Table 6 clearly demonstrates the nonlinear effect of coating thickness on barrier performance. For embodiments (1-16) of the present invention, even with an extremely thin coating of 3 g / m², thanks to the penetration and filling of nano-rosin and the parallel orientation of the lamellar filler, a Kit value ≥ 11 and a Cobb value ≤ 5.0 g / m² can still be maintained, proving its excellent pore-sealing ability. When the coating amount is increased to 30 g / m², the WVTR of all embodiments further decreases to 5-7 g / m²·d, and no peeling due to internal stress occurs, which is attributed to the chemical bonding force provided by the interfacial coupling agent. The newly added Example 16 exhibits Kit value grade 12 / Cobb value 4.7g / m² / WVTR 11g / (m²·d) and Kit value grade 12 / Cobb value 3.4g / m² / WVTR 6g / (m²·d) at 3g / m² and 30g / m², respectively, indicating that introducing 0.50 parts of water-dispersible polycarbodiimide crosslinking agent within the scope of this invention does not compromise the wide coating weight adaptability.

[0091] In contrast, at 3 g / m², Comparative Examples 1 (pure PHBV) and 10 (coarse PHA) almost completely failed to form a continuous film, resulting in a WVTR > 150. Comparative Example 2 (coarse rosin), due to its larger particle size than the film thickness, caused surface defects during thin coating, resulting in a Kit value of only 6. At a thick coating of 30 g / m², although most comparative examples showed improved barrier properties, this was accompanied by negative effects: Comparative Example 1 exhibited decreased adhesion (peeling); Comparative Examples 8 (high rosin) and 9 (high filler) showed extreme brittleness under thick coating, and although the WVTR reading decreased, they were prone to breakage with slight carelessness, rendering them impractical. The experimental results clearly demonstrate that only within a reasonable formulation range can robust performance be maintained across a wide coating weight window.

[0092] Application Example 3: Adaptability verification for different substrates.

[0093] This application example aims to evaluate the adaptability of the coating composition to substrates with different surface roughness and oil absorption. In addition to the smooth white cardboard used in Application Example 1, this experiment introduced a sugarcane pulp molded paper lunchbox as the substrate. To facilitate quantitative control of the coating amount, a 100mm × 100mm flat sample was cut from the bottom of the lunchbox as the test substrate, and the geometric area of ​​this cut sample, 0.0100m², was used as the coating area. The dry coating amount was uniformly controlled at 20g / m². The specific method was as follows: the mass m0 of the cut sample before coating was weighed, dried at 90℃ for 3 minutes and cured at 120℃ for 2 minutes to complete film formation, and then equilibrated at 23℃ and 50%RH for 24 hours. The mass m1 was then weighed, and the dry coating amount was calculated as (m1-m0) / 0.0100m². The amount of adhesive applied to the next sample was adjusted accordingly until the dry coating amount reached 20g / m². The coating method was manual scraping: a stainless steel wire rod was used to scrape the coating once at a uniform speed in the same direction to complete the spread. Then dry at 90°C for 3 minutes and cure at 120°C for 2 minutes.

[0094] The leak-proof test conditions are as follows: Place the coated, cut sample between the mouth of a 70mm inner diameter heat-resistant glass cup and the pressure ring, seal it with a 3mm diameter silicone rubber O-ring, and secure it with a stainless steel clamp, with the coated side facing the liquid inside the cup; add 100mL of 95℃ deionized water to the cup and maintain for 30 minutes, or add 100mL of 80℃ soybean oil and maintain for 30 minutes; test three parallel samples for each liquid and each formulation. Place the outside of the cup mouth tightly against clean absorbent paper with a basis weight of 80g / m², and weigh the initial mass m of the absorbent paper. A With mass m after 30 minutes B , with (m B -m A This serves as the basis for determining leakage.

[0095] The leakage prevention criteria are as follows: Place the sample on clean absorbent paper and observe and weigh the change in the mass of the absorbent paper; if the increase in the mass of the absorbent paper is ≤0.2g after 30 minutes and there are no visible wet marks on the outer surface of the sample, it is judged as "no leakage"; if the increase in the mass of the absorbent paper is 0.2g to 1.0g and only local watermarks / oilmarks appear on the outer surface, it is judged as "minor leakage"; if the increase in the mass of the absorbent paper is 1.0g to 5.0g or continuous penetration marks appear on the outer surface, it is judged as "leakage"; if liquid drips, obvious flow, or the increase in the mass of the absorbent paper is >5.0g, it is judged as "serious leakage".

[0096] Table 7. Test results of coating performance on molded pulp substrate:

[0097]

[0098] Note: The reasons for the "-" in the table are as follows: Comparative Example 5 is defined as 2g / m² coating, which cannot form a film at all on the rough surface of molding pulp (it will be absorbed into the substrate), making the test meaningless. Comparative Example 6 is defined as no heat curing. If it does not cure on a highly absorbent substrate like molding pulp, the coating will swell and peel off upon contact with water, making it impossible to conduct an effective seepage prevention test.

[0099] Analysis: Due to its loose fiber structure and large capillary pore size, molded pulp material places extremely high demands on the film-forming properties and sealing capabilities of coatings. As shown in Table 7, all examples (1-16) exhibited excellent adaptability to the molded pulp substrate, achieving "no leakage" with hot water and hot oil, with a surface Cobb value controlled below 5.0 g / m². This is attributed to the ability of nano-sized rosin particles to penetrate and fill the micropores deep within the fibers, while the modified lamellar filler constructs a dense "labyrinthine" barrier layer on the surface; the synergistic effect of both effectively blocks the penetration pathways. The newly added example 16 also achieved no leakage in 95°C hot water for 30 minutes and 80°C hot oil for 30 minutes on the molded pulp substrate, with a surface Cobb value of 4.4 g / m² and a cross-cut adhesion rating of 0, indicating that the carbodiimide-based additional cross-linking components do not weaken the adaptability to the rough pulp substrate.

[0100] In contrast, Comparative Examples 1 (pure PHBV) and 10 (coarse PHA) lacked an effective filling mechanism, leading to easy emulsion penetration and loss, resulting in discontinuous surface film formation and severe leakage. Comparative Examples 2 (coarse rosin) and 4 (non-lamellar filler) failed to form a dense packing, resulting in low barrier efficiency and leakage. Comparative Example 3, due to its unmodified filler, exhibited poor interfacial bonding with the organic phase, easily generating microcracks during drying shrinkage, leading to microleakage. Although Comparative Examples 8 and 9 achieved leak-proof properties thanks to their high hydrophobic component content, adhesion tests showed grades 1-2, indicating weak adhesion between the coating and the substrate, making them prone to detachment in practical use (such as stacked lunch boxes). The experimental results confirm that the coating composition of the present invention has broad substrate applicability.

[0101] Application Example 4: Verification of curing process boundaries.

[0102] This application example aims to verify the performance stability of the coating composition under different drying and curing temperature conditions, particularly examining the effects of low-temperature curing and high-temperature curing on the degree of crosslinking and final performance. The experiments cover all examples and some comparative examples (except Comparative Example 6). Two typical curing process conditions were set: Group A (low-temperature group): drying at 60℃ for 5 minutes + curing at 80℃ for 10 minutes; Group B (high-temperature group): drying at 130℃ for 1 minute + curing at 160℃ for 0.5 minutes. The coating amount was uniformly controlled at 12 g / m². The main test indicators were the Cobb value and the weight gain rate of the coating film after immersion in deionized water at 23℃ for 24 hours (measuring crosslinking density), while also observing changes in the substrate appearance. The coating film preparation method is as follows: the coating composition was uniformly coated onto a polytetrafluoroethylene (PTFE) plate using a 200 μm film scraper to form a wet film. After film formation was completed according to the drying and curing process corresponding to this application example, the film was cooled to room temperature, and the dry film was peeled off from the PTFE plate and cut into 50 mm × 50 mm samples; three parallel samples were taken under each condition. After drying the sample under vacuum at 50℃ for 2 hours, place it in an environment of 23℃ and 50%RH for 2 hours to equilibrate, and weigh the initial mass m0. After completely immersing the sample in deionized water at 23℃ for 24 hours, take it out and gently touch the surface with a lint-free paper for 10 seconds without applying pressure to remove the surface free water, and weigh the mass m1 immediately. The mass gain rate is calculated as (m1-m0) / m0×100%.

[0103] Table 8. Performance test results under different curing processes:

[0104]

[0105] Note: The reasons for the "-" marks in the table are as follows: Comparative Example 5 is defined as 2 g / m², the coating is too thin, the error in the water immersion test is extremely large, and it does not fall within the scope of process verification. Comparative Example 6 is defined as "heatless curing", which does not meet the experimental design requirements for curing temperature variables in this application example, so it is not included in the data in this table.

[0106] Analysis: The data in Table 8 strongly demonstrate that the coating composition of the present invention has a wide curing process window. Under the low-temperature group (80°C), the water immersion weight gain of all examples was controlled below 15% (13.5%-14.9%), and the Cobb value was ≤5.0 g / m². This indicates that even under relatively mild heat treatment, the epoxy silane coupling agent in the formulation can still be effectively activated, initiating the interfacial crosslinking reaction between biopolyester, rosin, and inorganic filler to form a water-resistant network. Under the high-temperature group (160°C), the crosslinking reaction was more thorough, and the water immersion weight gain of the examples was further reduced to 10.2%-11.9%, showing excellent water resistance, and the substrate paper did not show obvious discoloration or embrittlement. The newly added Example 16 showed a water immersion weight gain of 14.0% and 10.9% in the low-temperature group and the high-temperature group, respectively, corresponding to Cobb values ​​of 4.7 g / m² and 3.5 g / m², respectively. This indicates that after introducing 0.50 parts of water-dispersible polycarbodiimide crosslinking agent within the scope of this invention, the coating can still be effectively cured in the range of 80°C to 160°C.

[0107] In contrast, the comparative examples, Comparative Example 1 (pure PHBV), showed a significantly higher weight gain rate in water immersion than the examples (28%-35%), regardless of whether the temperature was low or high. This indicates that the single polymer film lacking a crosslinking mechanism has poor water resistance. Comparative Example 11 (low pH) still showed a high weight gain rate of 32% even at 160°C, indicating that the acidic environment inhibited the coupling reaction or led to polymer thermal degradation. Comparative Example 7 (excess coupling agent) showed incomplete reaction at low temperatures (20% weight gain), and although the degree of crosslinking increased at high temperatures (15% weight gain), it offered no advantage over the examples and, as previously mentioned, caused the coating to become brittle. The experimental results confirm that the present invention can achieve effective curing within the temperature range of 80°C to 160°C.

[0108] Application Example 5: Environmental friendliness and recyclability evaluation.

[0109] This application focuses on the environmental properties and recyclability of the coating material after disposal. The experiment covers all examples and comparative examples. First, according to T / CNFIA 191—2024, the total fluorine content in the coated and cured paper-based barrier materials prepared separately according to the corresponding formulations of each example and comparative example was determined by online combustion-ion chromatography; at the same time, uncoated white cardboard was used as a blank substrate for simultaneous testing. The sample was cut into small fragments, mixed well, and 50 mg (accurate to 0.1 mg) was accurately weighed and placed in a clean quartz sample boat for testing. The result was expressed as fluorine. The method was validated based on the test conditions adopted in this application. The method detection limit was 0.5 mg / kg, and the method quantitation limit was 2 mg / kg. When the sample test result was less than 5 mg / kg, it was recorded as "<5 mg / kg". Second, the repulping performance of the coated paper sample was evaluated according to Cepi Recyclability Laboratory Test Method, Version 3 (February 2025) Part I. The total repulping residue was determined according to the method of the aforementioned main test standard (8). The lower the total screen residue of repulping, the easier it is for the coating to separate or break down from the paper fibers during the recycling process, and the better the recyclability.

[0110] The evaluation criteria are as follows: ≤4.5% repulping screen residue is rated as “Excellent”; 4.5% < repulping screen residue ≤10.0% is rated as “Good”; >10.0% repulping screen residue is rated as “Poor (Difficult to recover)”.

[0111] The test results are detailed in Table 9.

[0112] Table 9. Environmental protection and recycling performance test results:

[0113]

[0114] Note: Total fluoride content was determined according to T / CNFIA 191—2024. Method validation was performed based on the testing conditions used in this application; the method detection limit was 0.5 mg / kg, and the method quantitation limit was 2 mg / kg. "<5" in the table indicates that the total fluoride content of the sample is less than 5 mg / kg. Although Comparative Examples 5 and 6 are not applicable in other tests, they still have reference value in environmental analysis.

[0115] Analysis: Test results show that, according to T / CNFIA 191—2024, the total fluorine content of the paper-based barrier materials in all examples and comparative examples is less than 5 mg / kg. This indicates that the system does not introduce fluorine-containing components that could cause the total fluorine content of the finished paper-based material to exceed 5 mg / kg, meeting the technical requirements for low-fluorine treatment of paper-based materials for food contact. Regarding repulping performance, the sieve residue of Examples 1-16 is between 2.8% and 4.1%, far below the recyclable standard line (<10%) typically set by the paper industry, and is rated as "excellent." This indicates that the coating of the present invention can be broken into sufficiently fine particles or undergo partial biodegradation during standard pulping hydraulic disintegration, without clogging the screen or forming adhesive substances that contaminate the pulp, thus achieving efficient closed-loop recycling of the paper-based material. The newly added Example 16 has a repulping sieve residue of 3.6%, indicating that even after introducing 0.50 parts of water-dispersible polycarbodiimide crosslinking agent, excellent repulping recycling performance is still maintained.

[0116] It is worth noting that Comparative Example 8 had a high residue of 15.2%, which was rated as "poor". This is because the rosin content in this formulation was too high (45 parts), resulting in a coating with extremely strong hydrophobicity and thermal tackiness. It was difficult to disperse in warm water and easily aggregated into large adhesive residues on the screen, which would seriously affect the quality of the recycled pulp and the operation of the paper machine. Comparative Example 10, due to the use of coarse-grained PHA, had uneven film formation and large particles, resulting in a high residue (8.5%). Comparative Examples 3 and 4 had slightly higher residues than the examples due to poor bonding between the filler and the matrix. Therefore, this invention, through reasonable formulation design, ensures high barrier properties while also taking into account excellent end-of-life recycling performance.

[0117] Application Example 6: Paper Cup Molding and Application Tests.

[0118] This application example aims to verify the mechanical adaptability of coated paper in actual packaging product processing and the performance of the finished product. Coated paper samples prepared separately under the corresponding conditions of each embodiment and comparative example were processed into 250mL paper cups using an LBZ-LA type paper cup forming machine. Ten paper cups were formed continuously for each formulation. If any defects unrelated to the coating formulation occurred, such as equipment feeding failure, cup wall non-overlap, missing cup bottom sheet, incomplete ultrasonic weld closure, or obvious mechanical damage, the cups were judged as mechanically defective and discarded. Five of the remaining qualified paper cups were randomly selected for hot water and hot oil leak-proof testing, and another three were selected for Kit value testing at the forming point and sensory evaluation of the knurled area. The processing included ultrasonic welding of the cup wall, cup bottom punching, 300℃ hot-press sealing, and rim rolling; the cup bottom hot-press sealing temperature was 300℃, the hot-press residence time was 0.30s, and the hot-press pressure was 0.40MPa. After molding, the paper cups undergo sensory evaluation (especially the knurled areas) and a leak-proof test: 200mL of 95℃ deionized water or 200mL of 80℃ soybean oil is added to the paper cup, which is then placed on clean absorbent paper with a basis weight of 80g / m² and kept for 30 minutes. After 30 minutes, the mass increment Δm of the absorbent paper is measured and judged in conjunction with visible marks on the outer surface of the cup. The judgment criteria are as follows: when Δm≤0.2g and there are no visible wet marks on the outer surface of the cup, it is judged as "no leakage"; when 0.2g<Δm≤1.0g and only local watermarks / oilmarks appear on the outer surface of the cup, it is judged as "minor leakage"; when 1.0g<Δm≤5.0g or continuous penetration marks appear on the outer surface of the cup, it is judged as "leakage"; when Δm>5.0g or liquid dripping or obvious flow occurs, it is judged as "serious leakage". Kit value testing at the molding area was performed by sampling the knurled area: a 50mm×50mm sample was cut along the densely knurled area at the bottom of the cup, and the Kit test was conducted according to TAPPI / ANSI T 559cm-22 and the results were recorded.

[0119] The sensory evaluation criteria for the knurled area are as follows: Observe the knurled area and the sealing area at the bottom of the cup using a 10× magnifying glass, and lightly touch it with your fingers; if there are no visible cracks, whitening, peeling, and no visible particle protrusions on the surface, it is judged as "smooth and crack-free"; if the total number of visible cracks is ≤2 and the length of a single crack is <2mm and does not penetrate the coating, it is judged as "micro-cracks in the knurled area"; if the total number of cracks is ≥3 or the length of a single crack is ≥2mm or there is local peeling / peeling, it is judged as "cracks"; if the crack penetrates and there is obvious cracking or visible exposure of the base paper, it is judged as "severe cracking"; if ≥10 particles / protrusions with a diameter ≥0.1mm are visible under 10× magnification and the surface is smooth to the touch... If the surface has a noticeable coarse texture, it is additionally recorded as "textured surface"; if the area of ​​continuous uneven / holey areas on the 10× lower surface is ≥50%, it is additionally recorded as "rough surface"; if there is peeling with a local coating detachment area ≥5mm² at the knurled area or the bottom seal, it is additionally recorded as "peeling"; if the surface has a noticeable matte finish and the specular reflection is significantly reduced compared to Example 1, it is additionally recorded as "dull surface"; if an irreversible indentation occurs when the bottom of the cup is pressed after the paper cup has cooled to 23°C (pressing area 10mm×10mm, loading mass 1kg, held for 10s) or the coating at the bottom seal softens and sticks, it is additionally recorded as "soft bottom".

[0120] Table 10. Test results of paper cup application performance:

[0121]

[0122] Note: The reason for the "-" in the table is as follows: The coating of Comparative Example 5 is too thin (2g / m²), and it is easily damaged or burned through during the heat sealing process at 300℃, making it impossible to form qualified paper cups for testing.

[0123] Analysis: The knurling process at the bottom of the paper cup during the forming process is a significant test of the coating's toughness, adhesion, and heat resistance. Table 10 shows that the paper cups prepared in all examples (1-16) maintained a smooth, crack-free coating at the knurled area, and no leakage occurred in subsequent hot water and hot oil tests. The Kit value at the forming point remained at a high level of 11-12. This fully demonstrates that the coating composition of the present invention possesses excellent heat resistance, resistance to mechanical deformation, and durable barrier properties. The newly added Example 16 also maintained a smooth, crack-free surface at the knurled area of ​​the paper cup and exhibited no leakage in both 95°C hot water and 80°C hot oil tests, with a Kit value of 12 at the forming point, indicating that the carbodiimide-based additional crosslinking components do not weaken the actual adaptability of the paper cup forming process. In particular, Examples 4 (P34HB), 8 (PHBH), and 15 (high plasticizer) demonstrated exceptional robustness in the face of severe deformation, fully meeting the processing requirements of high-speed paper cup machines.

[0124] Conversely, the paper cup in Comparative Example 8 exhibited severe cracking at the knurling area, resulting in complete failure in both hot water and hot oil tests, with the Kit value dropping to level 3. This further confirms that excessive rosin content increases coating brittleness, making it unable to withstand mechanical tension. Comparative Example 9 (high filler) also cracked due to excessive coating rigidity. Comparative Example 3, due to unmodified filler and weak interfacial bonding, developed micro-cracks under the combined effects of hot pressing and folding. Comparative Examples 1 and 10, due to poor film-forming quality, failed to provide effective barrier properties. Comparative Example 6, due to lack of heat curing and poor heat resistance, experienced coating softening and adhesion under 300°C hot pressing, leading to bottom leakage. The experimental results demonstrate that the coating material of this invention fully meets the performance requirements for industrial paper cup production and use.

[0125] Experimental Results and Analysis:

[0126] Synergistic effect analysis of key components in PHA-nano rosin synergistic high-barrier water-resistant coating composition formulation:

[0127] By comparing the performance data of Examples 1-16 with those of Comparative Examples 1-11, this invention successfully constructed a PHA-based waterborne coating system that combines excellent barrier properties, barrier retention after 180-degree folding, barrier retention after indentation, and mechanical properties.

[0128] The reinforcing effect of nano-sized rosin derivatives: Comparing Example 1 (containing nano-sized rosin) with Comparative Example 1 (pure PHBV) and Comparative Example 2 (coarse rosin), the data shows that the introduction of nano-sized rosin significantly improves the density of the coating. Although Comparative Example 1 forms a film, its water vapor transmission rate (WVTR) is as high as 120 g / m²·d, which cannot meet the barrier requirements; while in Comparative Example 2, the rosin particle size is large (1.5 μm), resulting in film formation defects, and the oil resistance (Kit value) is only level 8. Examples 1-16 all used D 50 The nano-rosin, ranging from 50 nm to 300 nm, can effectively fill the voids between the PHA matrix and the lamellar filler, reducing the WVTR to 12 g / (m²·d) or below, while maintaining the Kit value at the 11-12 level. This verifies the crucial role of nano-size effects in hydrophobic modification and micropore sealing.

[0129] The "maze effect" of layered barrier fillers: A comparison of Examples 3 and 11 with Comparative Example 4 shows that the layered structure (montmorillonite, talc) is crucial for barrier performance. Comparative Example 4, using non-layered heavy calcium carbonate, exhibited a significantly higher WVTR (75 g / m²·d) than Example 1, which used layered kaolin (12 g / m²·d). This indicates that the high aspect ratio layered filler forms an effective "maze path" in the coating, significantly extending the water molecule penetration path. Furthermore, the data for Comparative Example 3 (filler unmodified) were inferior to those for Example 1, demonstrating that surface modification with silane coupling agents effectively improved the compatibility of the inorganic-organic interface and reduced the generation of interfacial microcracks.

[0130] Stability of interfacial crosslinking and chemical bonding: A comparison of Examples 12, 14, and 16 with Comparative Example 7 reveals the sensitivity of crosslinking agent type and dosage. Examples 12 and 14 respectively verified different epoxy-functionalized silane coupling agents and their dosage windows; Example 16 further introduced 0.50 parts of a water-dispersible polycarbodiimide crosslinking agent on the basis of the epoxy-functionalized silane coupling agent, and the total amount of the polycarbodiimide crosslinking agent and the epoxy-functionalized silane coupling agent was combined into 1.50 parts of interfacial crosslinking coupling agent. The Cobb value of Example 16 was 4.0 g / m², the WVTR was 11 g / (m²·d), the Kit value after 180-degree folding and the Kit value after indentation were both level 12, and the water immersion weight gain rates of the low-temperature group and the high-temperature group were 14.0% and 10.9%, respectively, indicating that the introduction of carbodiimide-based additional crosslinking components within the scope of this invention can further enhance the water resistance and interfacial stability of the coating. The excessive use of coupling agent in Comparative Example 7 resulted in excessive crosslinking density of the coating, increased brittleness (only 80 folds withstand), and no further improvement in barrier properties, verifying the necessity of controlling the total amount of interfacial crosslinking coupling agent within a reasonable range.

[0131] Coating process adaptability and film formation mechanism analysis:

[0132] Wide coating weight window: Table 6 shows that the coating of this invention maintains Kit ≥ 11 and Cobb ≤ 5.0 g / m² even at extremely low coating weights (3 g / m²). This is due to the tight packing of nano-rosin and lamellar filler, which forms a continuous barrier layer even under thin coatings. In contrast, Comparative Examples 1 and 10 (coarse PHA) failed to cover the substrate fibers when coated thinly, resulting in complete performance failure. Under thick coating conditions (30 g / m²), no cracking or peeling was observed in the examples, while Comparative Example 8 (high rosin) experienced brittle cracking due to excessive internal stress, indicating that the formulation of this invention has excellent rheological properties and stress release capabilities.

[0133] Curing temperature tolerance: Table 8 shows that the coating of this invention achieves satisfactory water resistance (weight gain from water immersion <15%) under low-temperature curing conditions of 80℃, indicating that the catalytic crosslinking system has high reactivity; while under high-temperature curing at 160℃, the crosslinking network is further improved (weight gain <12%), and the substrate remains undamaged. This wide temperature range curing characteristic allows it to adapt to industrial production lines with different machine speeds and oven configurations.

[0134] Substrate universality and practical application performance analysis

[0135] Coverage on rough substrates: In the molding pulp (sugarcane pulp lunchbox) tests in Table 7, Examples 1-15 all achieved "no leakage" with hot water and hot oil, with surface Cobb values ​​controlled below 5.0 g / m². This is attributed to the penetration and anchoring effect of the nanoemulsion on the porous fiber surface and the directional arrangement of the sheet filler on the surface. In contrast, Comparative Examples 1 and 10, due to large emulsion particle size or lack of filler, resulted in severe leakage and could not be applied to molding products. Coverage on rough substrates: In the molding pulp (sugarcane pulp lunchbox) tests in Table 7, Examples 1-16 all achieved "no leakage" with hot water and hot oil, with surface Cobb values ​​controlled below 5.0 g / m². This is attributed to the penetration and anchoring effect of the nanoemulsion on the porous fiber surface and the directional arrangement of the sheet filler on the surface. In contrast, Comparative Examples 1 and 10, due to large emulsion particle size or lack of filler, resulted in severe leakage and could not be applied to molding products.

[0136] Machinability (folding endurance, indentation, and forming): 180-degree folding tests, indentation tests, and paper cup forming tests (Tables 5 and 10) of the flat samples jointly verified the coating's toughness and local stress resistance. Examples 1 to 16 maintained Kit values ​​of 11 to 12 after 180-degree folding and after indentation, indicating that the microporous filling of the nano-rosin, the path extension of the lamellar filler, and interfacial coupling jointly suppressed crack propagation at the fold lines and indentation lines. In Example 16, after introducing 0.50 parts of a water-dispersible polycarbodiimide crosslinking agent, the Kit values ​​after 180-degree folding and after indentation remained at 12, and the knurled area of ​​the paper cup showed "smoothness and no cracks," indicating that the carbodiimide-based additional crosslinking components do not impair the machinability of the system in this invention. Examples 4 (P34HB) and 8 (PHBH), thanks to the flexible segments provided by the comonomer, exhibited excellent "smoothness and crack-free" properties at both planar folding / crimping and paper cup knurling, and maintained a Kit value of 11 to 12 after molding. In contrast, Comparative Examples 8 (high rosin) and 9 (high filler) showed Kit values ​​of only 4 and 3 respectively after planar indentation testing, and experienced severe brittle fracture at the knurling, leading to final product failure. This demonstrates that the present invention successfully solves the common "brittleness" problem of bio-based coatings by introducing toughening and plasticizing agents and controlling the proportion of rigid components.

[0137] Environmental and sustainability assessment

[0138] Total Fluorine Control and Recyclability: Table 9 confirms that the total fluorine content of the paper-based barrier materials in all examples, measured according to T / CNFIA191—2024, is less than 5 mg / kg, meeting the low-fluorine control target set in this application. More importantly, the repulping screen residue of Examples 1-16 is between 2.8% and 4.1% (excellent grade), far below the industry standard of 10%. This indicates that the coating is easily broken down and separated during the recycling and pulping process, and will not form adhesive residues that interfere with the papermaking process, solving the pain point of traditional coated paper (such as PE coated paper) being difficult to recycle.

[0139] In summary, this invention successfully prepared a high-performance PHA waterborne coating through the synergistic effects of microscopic filling with nano-sized rosin derivatives, labyrinthine barrier properties of layered inorganic fillers, and interfacial chemical cross-linking. This coating not only overcomes the technical bottlenecks of poor water resistance and brittleness in bio-based materials, but also achieves robust performance under different substrates (paper, molding pulp) and processing conditions, and possesses excellent environmental recyclability, providing an ideal solution for paper-based food packaging.

[0140] Those skilled in the art should understand that the above embodiments are merely exemplary and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the technical solutions of the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A PHA-nanorin synergistic high-barrier water-based coating composition, characterized in that: The coating composition, based on total dry solids, comprises the following components and their parts by weight: 45 to 90 parts of a polyhydroxyalkanoate film-forming substance; 3 to 35 parts of a nano-sized rosin derivative; 5 to 15 parts of a lamellar barrier filler; 0.05 to 8 parts of an interfacial crosslinking coupling agent; 0 to 20 parts of a toughening and plasticizing agent; and 0 to 10 parts of an additive; wherein the nano-sized rosin derivative forms a median particle size D in an aqueous phase. 50 The dispersed phase is 50 nm to 300 nm; the aspect ratio of the sheet barrier filler is ≥20 and it has undergone surface modification treatment; the interfacial crosslinking coupling agent contains one or more epoxy-functionalized silane coupling agents; The polyhydroxyalkanoate film-forming substance exists in the form of an aqueous dispersion of polyhydroxyalkanoate, wherein the median particle size D of the polyhydroxyalkanoate particles in the aqueous dispersion is... 50 ≤3μm; the pH value of the coating composition is 6.5 to 9.5; the coating composition is applied to at least one side of the paper-based substrate and dried, and then further thermosetting to form a barrier coating, wherein the dry coating amount of the barrier coating is 3g / m² to 30g / m².

2. The coating composition according to claim 1, characterized in that: The polyhydroxyalkanoate film-forming substance is selected from short-chain polyhydroxyalkanoate, medium- and long-chain polyhydroxyalkanoate, or copolymers between monomers forming short-chain and medium- and long-chain polyhydroxyalkanoate; wherein, the short-chain polyhydroxyalkanoate is selected from one or more combinations of poly-3-hydroxybutyrate, poly-3-hydroxybutyrate-co-3-hydroxyvalerate, and poly-3-hydroxybutyrate-co-4-hydroxybutyrate; the medium- and long-chain polyhydroxyalkanoate is selected from one or more combinations of poly-3-hydroxyhexanoate, poly-3-hydroxyheptanoate, poly-3-hydroxyoctanoate, poly-3-hydroxynonanoate, poly-3-hydroxydecanoate, poly-3-hydroxyundecanoate, poly-3-hydroxydodecanate, poly-3-hydroxytetrate, and poly-3-hydroxytetradecanoate; the solid content of the aqueous dispersion of the polyhydroxyalkanoate is from 5 wt% to 70 wt%.

3. The coating composition according to claim 1, characterized in that: The nano-sized rosin derivative is a rosin-based material selected from one or more of the following: rosin acid or its salts and esters; hydrogenated rosin acid or its salts and esters; disproportionated rosin; polymerized rosin; rosin esters; hydrogenated rosin esters; maleated rosin and its esters; fumaric rosin and its esters; rosin-modified phenolic resin; rosin-modified terpene resin; rosin-based acrylate polymers; or rosin-based methacrylate polymers; wherein the rosin esters include one or two of the following: rosin glycerol esters, rosin pentaerythritol esters, and rosin trimethylpropane esters. The above combination; the rosin-based acrylate polymer or rosin-based methacrylate polymer is obtained by copolymerizing rosin-based acrylate monomer or rosin-based methacrylate monomer with at least one vinyl monomer, wherein the vinyl monomer is selected from one or more combinations of acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, styrene, vinyl acetate, and acrylonitrile; and the acid value of the nano-sized rosin derivative is from 0 mg KOH / g to 200 mg KOH / g.

4. The coating composition according to claim 1, characterized in that: The layered barrier filler is selected from one or more combinations of layered silicates, layered double hydroxides, plate-like oxides, and plate-like boron nitrides; wherein the layered silicates include one or more combinations of plate-like kaolin, montmorillonite, vermiculite, mica, and talc, and the median volumetric particle size D is [missing information]. 50 ≤5μm; the surface modification treatment of the sheet barrier filler is selected from one or a combination of the following: silane coupling agent treatment, titanate coupling treatment, zirconate coupling treatment, phosphate coupling treatment, aluminate coupling treatment, fatty acid hydrophobication treatment, wax hydrophobication treatment, cationic surfactant intercalation treatment, nonionic surfactant intercalation treatment, inorganic sol-gel coating treatment; wherein the silane coupling agent used in the silane coupling agent treatment includes the epoxy-functionalized silane coupling agent, and the epoxy-functionalized silane coupling agent is selected from one or more combinations of γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, and γ-glycidoxypropylmethyldimethoxysilane.

5. The coating composition according to claim 1, characterized in that: The interfacial crosslinking coupling agent further includes one or more crosslinking components selected from carbodiimides, oxazolines, polyfunctional epoxides, aminosilanes, polycarboxylic acids, acid anhydrides, or combinations thereof, and the total amount of the crosslinking components is included in the range of 0.05 to 8 parts of the interfacial crosslinking coupling agent; the toughening and plasticizing agent is a bio-based plasticizer selected from one or more combinations of citrate esters, succinate esters, fatty acid esters, and epoxidized vegetable oils; the additives include one or more of wetting and dispersing agents, emulsifiers, defoamers, leveling agents, thickeners, antisettling agents, preservatives, pH adjusters, and protective colloids; wherein the emulsifier or protective colloid is selected from one or more combinations of anionic surfactants, nonionic surfactants, amphoteric surfactants, and polyvinyl alcohol, and when the polyvinyl alcohol is used as a protective colloid, the amount added on a dry solids basis is 1 wt% to 15 wt% of the mass of the nano-sized rosin derivative.

6. The coating composition according to claim 1, characterized in that: The final solid content of the coating composition is 30wt% to 60wt%; the coating film obtained by drying the coating composition at 60°C to 130°C after coating and further heat curing at 80°C to 160°C for 0.5min to 10min, and then immersing it in deionized water at 23°C for 24h, has a weight gain of ≤15wt%.

7. A method for preparing the PHA-nanorosin synergistic high-barrier water-based coating composition according to claim 1, characterized in that, The preparation method includes the following steps: Step 1 is surface modification and dispersion of sheet barrier filler, dispersing sheet barrier filler in aqueous phase to form slurry, adding surface modifier for shear dispersion and completing surface modification to obtain modified sheet filler slurry; Step 2 involves rosin nano-sizing. Rosin derivatives are mixed with an aqueous phase containing emulsifiers and / or protective colloids and pre-emulsified. The resulting material is then prepared by high-pressure homogenization, microfluidization, ultrasonic emulsification, membrane emulsification, or rotor-stator high-shear emulsification to obtain a volume median particle size D. 50 Rosin nanoemulsions ranging from 50nm to 300nm; Step 3 is aqueous blending. The rosin nanoemulsion obtained in step 2 is added to the aqueous dispersion of polyhydroxy fatty acid ester and mixed. Then, the modified sheet filler slurry, interfacial crosslinking coupling agent, toughening and plasticizing agent and additives obtained in step 1 are added. The solid content and pH value are adjusted to obtain the premixed coating composition. Step 4 is curing, in which the premixed coating composition obtained in step 3 is cured at 25°C to 60°C for 0.5 hours to 6 hours to obtain the coating composition.

8. The method according to claim 7, characterized in that: In step 1, the surface modifier is selected from one or more combinations of silane coupling agents, titanate coupling agents, zirconate coupling agents, phosphate coupling agents, and aluminate coupling agents. The amount of the surface modifier is 0.1 wt% to 8 wt% of the mass of the sheet barrier filler. In step 2, the high-pressure homogenization pressure is 20 MPa to 120 MPa, and the homogenization is performed 2 to 8 times. In step 3, the rosin nanoemulsion is added to the polyhydroxyalkanoate aqueous dispersion by dropwise or segmented addition, and the modified sheet filler slurry obtained in step 1 is added after the addition, and the interfacial crosslinking coupling agent is added last. Thus, the coating composition is obtained.

9. The paper-based barrier material prepared by the PHA-nanorhoin synergistic high-barrier water-based coating composition according to claim 1, characterized in that: A barrier coating is obtained by coating one or more sides of paper, paperboard, molded pulp substrate, or their composite paper-based materials with the PHA-nano rosin synergistic high-barrier water-based coating composition and drying and thermosetting it into a film. The paper-based barrier material, according to ISO 535:2023, has a 30-minute Cobb water absorption value ≤ 5 g / m², according to TAPPI / ANSI T 559cm-22, an oil resistance Kit value ≥ 11, according to ASTM E96 / E96M-24a, a water vapor transmission rate ≤ 12 g / (m²·d) at 23°C and 50%RH, and according to ISO 2409:2020, a cross-cut adhesion grade of 0 or 1. The om-25 test MIT has a folding endurance of ≥250 times, and its Kit value at the crease after 180-degree folding or crease is ≥11, and the total fluorine content determined according to T / CNFIA191—2024 is less than 5mg / kg.

10. The packaging article prepared from the paper-based barrier material according to claim 9, characterized in that: The packaging article is selected from one or more of food packaging paper, paper cups, paper bowls, paper lunch boxes, takeaway paper bags, molded pulp lunch boxes or trays, and its surface in contact with food or daily chemical products contains the paper-based barrier material.

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