Repulpable and degradable PHA heat-seal barrier coating and composition thereof

Abstract

The invention discloses a repulpable and degradable PHA heat-seal barrier coating and a composition thereof, and belongs to the field of water-based functional coatings and cellulose-based packaging materials. The coating composition is prepared from the following components in percentage by non-volatile solids: 30 to 85 weight percent of polyhydroxyalkanoate emulsion, 5 to 60 weight percent of flaky natural inorganic matters, a water-based cross-linking agent and an auxiliary agent, and 1 to 20 weight percent of ethylene-acrylic acid or ethylene-methyl acrylate dispersion can be selected. The pH value of the composition is 6.5-9.0, and organic fluorine is not artificially added. When the dry weight is 6-20 g / m, the coating meets at least one of the following four items: the water vapor transmission rate (38 DEG C, 90% RH) is less than or equal to 80 g / m.d, Cobb60 is less than or equal to 15 g / m, the oil resistance grade is greater than or equal to 11, and the laboratory repulping rate is greater than or equal to 98%; and the heat-sealing peel strength is greater than or equal to 2.5 N / 15mm under the conditions of 150 DEG C, 0.2 MPa and 0.5 s. And the coating and the stripping film thereof meet the industrial composting standard.

Description

Technical Field

[0001] This invention belongs to the field of water-based functional coatings and cellulose-based packaging materials, specifically relating to resizing and biodegradable PHA heat-sealing barrier coatings and their compositions. Background Technology

[0002] With increasingly stringent global environmental regulations and growing consumer awareness of environmental protection, the food packaging industry is facing profound changes. Per- and polyfluoroalkyl substances (PFAS) are being rapidly restricted and even phased out by regulatory agencies worldwide due to their persistence in the environment, bioaccumulation, and potential health risks. Therefore, developing high-performance, environmentally friendly, fluorine-free alternatives has become a top priority for the industry. Waterborne barrier coatings, due to their environmental friendliness, have become the mainstream technology for replacing PFAS in paper-based and molded fiber packaging. However, developing an "all-around" waterborne coating that can simultaneously meet the requirements of high moisture barrier properties, oil resistance, wide heat-sealing window, high recycling efficiency, and biodegradability at low coating weights still faces significant technical challenges.

[0003] While existing technologies have explored various directions, they all exhibit significant limitations. The first type of technology is based on aqueous dispersions of polyhydroxyalkanoates (PHAs). For example, WO2020 / 036843 A1 discloses a food contact coating based on an aqueous PHA dispersion, allowing the addition of fillers and crosslinking agents such as zirconium ammonium carbonate (AZC) to the formulation. However, this patent primarily focuses on conventional waterproof and oil-repellent properties, without strictly limiting the geometric parameters of the sheet-like filler used, providing a water vapor transmission rate (WVTR) index under harsh high humidity conditions, or setting a clear resizing threshold. Therefore, it falls short in achieving a synergistic optimization of high-humidity barrier properties and circular economy compatibility. The second type of technology is based on non-PHA synthetic polymer emulsions. For example, US2024 / 0376336 A1 reports a styrene-free, wax-containing / ethylene-acrylic acid copolymer (EAA) aqueous heat-sealing barrier system, claiming resizing capability. However, the core polymer of this technology is not biodegradable PHA, nor does it involve constructing an efficient physical barrier structure by introducing sheet-like inorganic materials with specific geometries. Therefore, it has inherent shortcomings in terms of biodegradability and barrier efficiency. The third type of technology focuses on the study of barrier mechanisms. For example, WO2009 / 114072 A1 and related industry research have long clarified that layered silicates with high aspect ratios or high shape factors can significantly improve the barrier performance of coatings by forming a "zigzag path" effect within the coating. However, these studies are mostly focused on the mechanistic level and have not specifically coupled them with biodegradable PHA aqueous dispersion systems. Furthermore, they have not proposed a set of quantifiable performance constraints—high wet barrier, wide-window heat sealing, high oil resistance, and a high resizing rate of no less than 98%—simultaneously achieving these at low coating amounts of 6–20 g / m².

[0004] In summary, existing technologies have failed to provide a systematic solution that combines sheet-like natural inorganic materials with specific geometric parameters with PHA aqueous dispersions, and achieves high moisture barrier properties (WVTR≤120g / m²·d), oil resistance, high resizing rate (≥98%), and wide window heat-sealing properties at a low coating amount of 6–20 g / m² through precise crosslinking agent synergy. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and to solve the technical problem that existing water-based barrier coatings cannot simultaneously achieve barrier properties, heat-sealing properties, recyclability and biodegradability.

[0006] To achieve the above objectives, the present invention provides a resizing and biodegradable PHA heat-sealing barrier coating and a composition thereof, wherein the composition comprises, based on non-volatile solids:

[0007] PHA emulsion 30–85 wt%, for example 30 wt%, 35 wt%, 45 wt%, 55 wt%, 65 wt%, 70 wt%, 74 wt%, 75 wt%, 80 wt%, or 85 wt%; wherein the PHA is selected from one or more of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxyhexanoate), poly(3-hydroxyoctanoate), poly(3-hydroxydecanoate), poly(3-hydroxydodecanate), poly(3-hydroxydodecanate), poly(3-hydroxyhexanoate-co-3-hydroxyoctanoate), poly(3-hydroxyoctanoate-co-3-hydroxydecanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctanoate);

[0008] The polyhydroxy fatty acid ester has a number-average molecular weight of 5 × 10⁻⁶. 4 –8×10 5 Latex particle size D 50 The thickness is 0.2–3.0 μm, for example 0.2 μm, 0.5 μm, 1.0 μm, 1.8 μm, 2.5 μm or 3.0 μm, and the minimum film formation temperature is ≤60℃;

[0009] The flaky natural inorganic material comprises 5–60 wt%, for example, 5 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 22 wt%, 30 wt%, 40 wt%, 50 wt%, or 60 wt%; the flaky natural inorganic material is selected from one or more of kaolinite, talc, mica, vermiculite, pyrophyllite, and montmorillonite, and the ratio of average flake diameter to thickness, i.e., shape factor, is ≥20, for example, 20, 25, 30, 40, or 50, with a particle size D. 50 The micrometer size is 0.2–2.0 μm, for example, 0.2 μm, 0.6 μm, 1.0 μm, 1.5 μm, or 2.0 μm, and D 90 ≤3μm;

[0010] The copolymer emulsion is 0–30 wt%, for example, 0 wt%, 1 wt%, 3 wt%, 5 wt%, 10 wt%, 12 wt%, 14 wt%, 20 wt%, 25 wt%, or 30 wt%; the copolymer emulsion is selected from one or more of the following: (1) acrylic emulsion; (2) vinyl copolymer aqueous dispersion; (3) aliphatic polyester aqueous dispersion; (4) polyvinyl alcohol aqueous solution; (5) polyurethane dispersion; (6) aqueous epoxy resin dispersion;

[0011] The aqueous crosslinking agent is 0.2–5.0 wt%, for example, 0.2 wt%, 0.5 wt%, 1.0 wt%, 1.2 wt%, 1.5 wt%, 2.5 wt%, 3.5 wt%, 4.5 wt%, or 5.0 wt%; said aqueous crosslinking agent is selected from one or more of ammonium zirconium carbonate, polycarbodiimide, polyisocyanurone diimide, blocked polyisocyanate, aluminum / zirconium / titanium organic complex, polyfunctional epoxy compound, glyoxal, and polycarboxylic acid.

[0012] Additives are present in amounts of 0.1–5.0 wt%, for example, 0.1 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.5 wt%, 3.5 wt%, 4.5 wt%, or 5.0 wt%; said additives include mineral dispersants, associative thickeners, wetting and leveling agents, defoamers, antiblocking agents, film-forming aids, pH adjusters, waxes, preservatives and mildew inhibitors, and crosslinking catalysts;

[0013] The waxes are selected from one or more of polyethylene wax, paraffin wax, carnauba wax, and polypropylene wax;

[0014] The composition has a pH value of 6.5–9.0, for example 6.5, 7.0, 7.5, 8.0, 8.5 or 9.0, and no organic fluorine-containing substances are intentionally added.

[0015] In one specific implementation, the sheet-like natural inorganic material is mainly composed of delaminated kaolin, accounting for more than 50 wt% of the total inorganic material, with a whiteness ≥85%, and is surface-modified with silane or polyelectrolyte. The volume fraction of the sheet-like natural inorganic material in the dry coating film is 5–35 vol%, for example, 5 vol%, 10 vol%, 15 vol%, 20 vol%, 25 vol%, 30 vol%, or 35 vol%. To obtain a better barrier effect, the shape factor of the sheet-like natural inorganic material is ≥30.

[0016] In one specific embodiment, the PHA is poly(3-hydroxybutyrate-co-3-hydroxyvalerate), wherein the molar fraction of hydroxyvalerate is 5–30 mol%, for example 5 mol%, 10 mol%, 15 mol%, 20 mol%, 25 mol%, or 30 mol%.

[0017] In one specific embodiment, the copolymer emulsion comprises an aqueous dispersion of ethylene-unsaturated carboxylic acids and / or ethylene-acrylates, with a total content of 1–20 wt% relative to non-volatile solids, for example, 1 wt%, 3 wt%, 8 wt%, 10 wt%, 14 wt%, 15 wt%, or 20 wt%. The ethylene-acrylate aqueous dispersion is an aqueous ionic emulsion or emulsion prepared based on an ethylene-acrylic acid copolymer, wherein the acrylic acid content is 3–20 wt%, the acid value is 30–120 mg KOH / g, and 10–70 mol% of carboxyl groups are neutralized with ammonium, sodium, or potassium ions to form an aqueous dispersion, with a minimum film-forming temperature ≤60°C. The ethylene-acrylate aqueous dispersion can also be an aqueous emulsion or stable dispersion prepared based on an ethylene-methyl acrylate copolymer, wherein the methyl acrylate content is 5–28 wt%, the melt index is 2–20 g / 10 min at 190°C and 2.16 kg, and the minimum film-forming temperature is ≤60°C.

[0018] In one specific embodiment, the mass ratio of the ethylene-acrylate aqueous dispersion to the PHA emulsion is 1:20–1:3. The mass ratio of the flake-like natural inorganic material to the PHA emulsion is 1:9–4:6.

[0019] In one specific implementation, the aqueous crosslinking agent is a compound system of ammonium zirconium carbonate and polyisocyanurone diimide.

[0020] For ease of industrial application, the composition has a solid content of 35–55 wt%, such as 35 wt%, 40 wt%, 45 wt%, 50 wt%, or 55 wt%, and a viscosity of 500–5000 mPa·s, such as 500 mPa·s, 1500 mPa·s, 2500 mPa·s, 3500 mPa·s, or 5000 mPa·s, measured at 25°C using a No. 4 rotor of a Brookfield rotational viscometer at 20 rpm.

[0021] The present invention also provides a re-slurryable and biodegradable PHA heat-sealing barrier coating obtained by applying and drying the above composition. When the dry weight of the coating is 6–20 g / m², for example 6 g / m², 10 g / m², 12 g / m², 15 g / m², or 20 g / m², it satisfies at least one of the following properties:

[0022] a) WVTR ≤80g / m²·d at 38℃ and 90% RH;

[0023] b) Cobb 60 ≤15g / m²;

[0024] c) Oil resistance grade ≥ 11;

[0025] d) Laboratory repulping rate ≥ 98%.

[0026] The coating can form a heat-sealing window at 120–220°C; and has a peel strength of ≥2.5N / 15mm under conditions of 150°C, 0.2MPa, and 0.5s.

[0027] The present invention also provides a coated article having a substrate of paper, paperboard, or molded fiber article, and a surface comprising the aforementioned coating. In one embodiment, the coated article has a two-layer coating structure: the pre-coating layer comprises 60–85 wt% of flake natural inorganic material and 15–40 wt% of copolymer emulsion, with a dry weight of 3–8 g / m²; the topcoat layer is the aforementioned composition, with a dry weight of 6–12 g / m².

[0028] After being peeled and film-formed, the coating meets the relevant standards for biodegradability within 180 days under industrial composting conditions. Furthermore, the coating or coated product has not been intentionally mixed with organic fluorine, and the total organic fluorine content is ≤100 mg / kg, with the manufacturer providing a statement that "no fluorine-containing substances were intentionally added."

[0029] The coating or coated product described in this invention can be applied to food contact paper, cup paper, hamburger paper, takeaway food boxes, paper trays and coated white cardboard.

[0030] Compared with the prior art, the following significant advantages can be obtained by using the present invention:

[0031] Excellent overall barrier and reusability performance: At a dry weight of 6–20 g / m², the coating simultaneously meets the requirements of WVTR (38℃, 90%RH) ≤80 g / m²·d and Cobb 60 At least one of the following: ≤15g / m², oil resistance grade ≥11, and laboratory resizing rate ≥98%.

[0032] Wide heat-sealing window and high strength: The coating can be stably heat-sealed within a wide industrial heat-sealing window of 120–220°C with high heat-sealing strength. Introducing EAA or EMA can further reduce the initial sealing temperature and improve peel strength.

[0033] Environmentally friendly, recyclable and biodegradable: the coating formulation is PFAS-free and an all-water-based system. Coated paper products have a laboratory repulping rate of ≥98%. Furthermore, the coating itself meets industrial composting standards after peeling.

[0034] High process adaptability: The composition is suitable for various conventional coating methods such as doctor blade coating, bar coating, and air knife coating, and is easy to industrialize and apply. Detailed Implementation

[0035] 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.

[0036] Main reagents and raw materials:

[0037] Table 1. Names, models, and manufacturers of main reagents and raw materials:

[0038]

[0039] Main analytical and testing instruments:

[0040] Table 2 mainly analyzes the names, models, and manufacturers of the testing equipment:

[0041]

[0042] Main testing methods and standards:

[0043] Conditioning of samples: ISO 187:2022;

[0044] Particle size distribution: ISO 13320:2020;

[0045] MFFT: GB / T 9267:2008;

[0046] WVTR: ASTM F1249-20;

[0047] Heat seal strength: ASTM F88 / F88M-23;

[0048] Thermal bonding: ASTM F1921-12(2023);

[0049] 60s absorbency: TAPPI / ANSI T 441 om-24;

[0050] Oil resistance rating: TAPPI T 559 cm-22;

[0051] COF: TAPPI T 549 om-25;

[0052] Freeze-thaw stability: ASTM D2243-20;

[0053] Block resistance: ASTM D3354-21 (refer to the film method for evaluating coating self-adhesion);

[0054] Recyclability: CEPI Paper and Board–Recyclability Laboratory Test Method, Version 3 (2025-02);

[0055] Biodegradability: ISO 14855-1:2012+Amd.1:2018;

[0056] Fluorine-free verification: ISE method is used, and TOF is reported.

[0057] General preparation process:

[0058] Process 1 - Preparation of PHA aqueous dispersion:

[0059] Step 1. Add deionized water to a jacketed reactor, start stirring and heat to 80–85°C. Slowly add 2–4 wt% of polyvinyl alcohol (PVOH) powder, and maintain the temperature at this point while stirring for 60–90 minutes until completely dissolved.

[0060] Step 2. Transfer the PVOH aqueous solution to a high-shear dispersion emulsifying vessel, start high-shear stirring (≥10,000 rpm), and raise the jacket temperature to 100–120°C. Slowly add PHA powder until the total solids content reaches 30–50 wt%, while simultaneously adding 0.1–0.3 wt% of alkyl polysaccharide glycoside (APG). Continue shearing for 20–30 minutes at the set temperature and speed.

[0061] Step 3. Maintain shear stress and programmatically cool the system, first lowering the temperature to 60–70°C, then continuing to cool to 25–30°C. Adjust the pH of the system to 7.5–8.5 using a 0.1–0.5 mol / L dilute sodium hydroxide or potassium hydroxide solution.

[0062] Step 4. Filter the dispersion through a 100-mesh sieve, and then perform vacuum defoaming treatment on the filtrate to obtain the final PHA aqueous dispersion with a D50 particle size of 0.2–1.0µm.

[0063] Process 2 - Preparation of EMA aqueous dispersion (ethylene-methyl acrylate):

[0064] Step 1. In a pressure-resistant, high-shear dispersion emulsifying vessel, add deionized water, 2–4 wt% PVOH, and 0.1–0.3 wt% nonionic surfactant. Seal the vessel and heat to 80–90°C with stirring, maintaining the temperature until all components are completely dissolved.

[0065] Step 2. Raise the temperature inside the reactor to 110–130°C and start high-shear stirring at 10,000–15,000 rpm. Add EMA granules to the reactor using a pressure feeder to achieve a total solids content of 30–45 wt%. Maintain dispersion for 30–45 minutes at the set temperature and speed.

[0066] Step 3. While stirring, slowly reduce the temperature inside the reactor to below 30°C and depressurize. Adjust the pH of the system to 7.0–8.5 using a 0.1–0.5 mol / L dilute sodium hydroxide or potassium hydroxide solution. Finally, filter the product through a 100-mesh sieve and defoam under vacuum to obtain the final EMA aqueous dispersion.

[0067] Examples and Comparative Examples:

[0068] Examples 1-6 and Comparative Examples 1-3 were prepared and coated according to the formulations and general methods shown in the table below.

[0069] Table 3. Formulation overview of the examples and comparative examples:

[0070]

[0071] Application example:

[0072] Application Example 1: Heat resistance test of paper cups.

[0073] Experimental Description: This application example aims to evaluate the practical performance of the coating in a simulated hot beverage application scenario. Standard paper cups were fabricated from the coated paper of all examples and comparative examples, and the seams were sealed using a heat-sealing process. Hot water at 95°C was then poured into the cups and kept there for 30 minutes to simulate prolonged storage of hot beverages by a user. The coating's resistance to moisture and heat and its mechanical stability were comprehensively evaluated by visually inspecting the heat-sealed seams for any liquid leakage and by assessing whether the cup remained stiff, softened, or deformed under humid and hot conditions.

[0074] Table 4. Results of heat resistance test for paper cups:

[0075]

[0076] Analysis of Table 4: Examples 1-6 all exhibited excellent hot water resistance. In contrast, Comparative Example 1 leaked due to insufficient barrier properties, Comparative Example 2 could not effectively heat seal due to the lack of PHA, and Comparative Example 3 failed due to low mineral shape factor and poor barrier properties, highlighting the superiority of the formulation design of this invention.

[0077] Application Example 2: The effect of shape factor on core performance.

[0078] Experimental Description: This application example aims to directly compare the effects of minerals with high and low shape factors on core performance. Therefore, only Example 3 (shape factor ≥ 30) and Comparative Example 3 (shape factor 8–12), where other components in the formulation are similar and only the shape factor of the flake inorganic material differs significantly, were selected for comparative testing. For the selected coated paper samples, their WVTR and Cobb properties were tested according to the relevant standards. 60 Oil resistance rating, heat seal strength at 150°C, and resizing rate. Data for other examples and comparative examples are not listed here as they do not involve a direct comparison of this specific variable.

[0079] Table 5. Results of the shape factor effect test:

[0080]

[0081] Analysis of Table 5: Data shows that Example 3, which uses minerals with high shape factor, has higher WVTR and Cobb density. 60 It is significantly lower than Comparative Example 3, and its oil resistance is also higher. This clearly demonstrates that the "zigzag path" effect of minerals with high shape factor is a key technical feature for achieving high-efficiency barrier performance.

[0082] Application Example 3: Hot-sealed window scanning.

[0083] Experimental Description: This application example aims to determine and compare the effective heat-sealing temperature range and heat-sealing strength of various coatings. Using a precision laboratory heat sealer, samples from all examples and comparative examples were subjected to a series of heat-sealing operations at different temperatures (from 120°C to 220°C) under fixed pressure and residence time. After heat sealing, the 180° peel strength of the strips was tested using a tensile testing machine, thereby plotting a "temperature-strength" curve for each sample to evaluate its processing window width and seal reliability in industrial applications.

[0084] Table 6. Results of heat-sealed window scanning test:

[0085]

[0086] Analysis of Table 6 shows that the coating of the present invention can achieve effective heat sealing in a wide temperature range of 120-220°C, and the introduction of EAA / EMA (Examples 4, 5 and 6) can significantly improve the heat sealing strength in the low temperature range.

[0087] Application Example 4: Interface wettability (static contact angle).

[0088] Experimental Description: This application example aims to evaluate the hydrophobic properties of a coating by measuring the static contact angle of a water droplet on the coating surface. A fixed volume (5 μL) of ultrapure water droplet was precisely added to the coating surface of all examples and comparative examples using a contact angle meter, and the contact angle values ​​were recorded immediately (0 seconds) and after 300 seconds. The initial contact angle reflects the instantaneous hydrophobicity of the surface, while the contact angle after 300 seconds reflects the coating's ability to retain hydrophobicity after continuous contact with water, which is crucial for evaluating its short-term water-repellent performance.

[0089] Table 7. Static contact angle test results:

[0090]

[0091] Analysis of Table 7: All samples containing PHA (Examples 1-6, Comparative Examples 1 and 3) exhibited excellent initial hydrophobicity (contact angle > 95°) and maintained a high contact angle after 300 seconds, indicating that the coating surface was dense and hydrophobic. Comparative Example 2 (without PHA) not only had a low initial contact angle but also decreased rapidly over time, demonstrating that PHA is the key component providing hydrophobicity.

[0092] Application Example 5: Resistance to penetration by dairy media.

[0093] Experimental Description: This application example aims to evaluate the barrier properties of the coating against complex food media (whole milk and light cream) containing water and oil, to simulate its performance in real-world food packaging applications. All coated paper samples from the examples and comparative examples were completely immersed in both media at 40°C for 30 minutes each. The mass change before and after immersion was accurately measured, and the mass increment per unit area was calculated. The smaller the increment, the better the coating's impermeability.

[0094] Table 8 Results of the test for resistance to dairy product penetration:

[0095]

[0096] Analysis of Table 8: The embodiments of the present invention, particularly Examples 1 and 6 with high mineral content, exhibit excellent permeability resistance to complex media. This demonstrates that the coating is not only resistant to pure water and pure oil, but also effectively blocks emulsion-type foods, making it widely applicable. The comparative samples, on the other hand, exhibited poor permeability resistance.

[0097] Application Example 6: Kinetics of the re-slurry process.

[0098] Experimental Description: This application example aims to evaluate the recyclability of coated paper according to industry standards. All samples from the examples and comparative examples were pulped using a standard laboratory pulper to simulate the recycling process in a paper mill. Recycled fibers and impurities such as coating debris were separated by sieving. The final fiber yield (i.e., repulping rate), screen residue, and binder residue were accurately calculated, and the time required to reach 90% fiber release (t90) was recorded to comprehensively evaluate the recycling efficiency and quality.

[0099] Table 9. Kinetic test results of the re-slurry process:

[0100]

[0101] Analysis of Table 9 shows that the final resizing rate of all embodiments was higher than 98%, with reasonable disintegration time and low residue of sieve slag and binder, proving that the coating of the present invention has excellent recyclability. Although Comparative Example 2 resized quickly, its functionality was poor and it had no application value.

[0102] Application Example 7: Industrial composting after "peeling and film forming".

[0103] Experimental Description: This application example aims to verify the biodegradability of the coating itself. All coatings from the examples and comparative examples were completely peeled off the substrate to prepare film samples, which were then subjected to a 180-day biodegradation test under controlled industrial composting conditions according to ISO 14855-1. The degree of biodegradability was calculated by continuously monitoring and measuring the amount of carbon dioxide produced during the process to determine whether it met industrial composting standards.

[0104] Table 10 Industrial composting test results:

[0105]

[0106] Analysis of Table 10: All samples containing PHA (Examples 1-6 and Comparative Examples 1 and 3) showed a biodegradation rate exceeding 90% within 180 days, meeting industrial composting standards. Comparative Example 2, which did not contain PHA, showed virtually no degradation. This demonstrates that PHA is the core component that imparts the biodegradable properties to the coating.

[0107] Application Example 8: Freeze-thaw stability and storage adaptability.

[0108] Experimental Description: This application example aims to evaluate the storage stability of liquid coating compositions after experiencing extreme temperature changes, which is crucial for product transportation and storage. All coating samples from the examples and comparative examples were subjected to five freeze-thaw cycles (single cycle conditions: freezing at -18°C for 16 hours, followed by thawing at 25°C for 8 hours). Stability was determined by visually inspecting the samples for gelation, clumping, or layering, and by measuring the viscosity change before and after the cycles.

[0109] Table 11. Freeze-thaw stability test results:

[0110]

[0111] Analysis of Table 11: All embodiments of the present invention passed 5 freeze-thaw cycles, exhibiting small viscosity changes and uniform appearance, indicating that the coating system has good storage stability. Comparative Example 2, due to formulation issues, severely thickened after freeze-thaw cycles and was unusable.

[0112] Application Example 9: Static / Dynamic Friction Coefficient (COF).

[0113] Experimental Description: This application example aims to evaluate the slip properties of the coated surface, a key parameter determining the smooth operation of coated paper on a high-speed automated packaging production line. According to the TAPPI standard, a coefficient of friction tester was used to test the static and dynamic coefficients of friction (μs) between the coated surfaces of all examples and comparative samples.

[0114] Table 12 Test results of static / dynamic friction coefficients:

[0115]

[0116] Analysis of Table 12: The static friction coefficient μs of the examples is between 0.35 and 0.48, and the dynamic friction coefficient μk is between 0.28 and 0.41. This ideal range of friction coefficients ensures that the coated paper will not stick due to excessive static friction or slip due to insufficient static friction when starting on the automated packaging line, achieving a smooth transition to the operating state; at the same time, the moderate dynamic friction coefficient μk ensures smooth operation at high speeds. In contrast, the static friction coefficient μs and dynamic friction coefficient μk of Comparative Example 1 are both relatively high, especially its high static friction coefficient (0.55), which confirms its "slightly sticky" surface characteristics, which can easily lead to poor start-up or sticking problems in automated processing. The friction coefficient of Comparative Example 2 is generally low, which is related to its "rough surface" characteristics, and may lead to inaccurate positioning or excessive sliding during production.

[0117] Application Example 10: Blockiness.

[0118] Experimental Description: This application example aims to evaluate the coating's ability to resist adhesion (i.e., "blocking") under stacking and storage conditions. All coated paper samples from the examples and comparative models were laminated together and incubated at a specified load and 50°C for 24 hours to simulate a storage environment. The anti-adhesion performance was then quantified by assessing the adhesion level and testing the peel force.

[0119] Table 13 Results of block resistance test:

[0120]

[0121] Analysis of Table 13: Except for Example 2 with high PHA content, which showed critical performance, the other examples of the present invention all exhibited excellent anti-blocking properties. Comparative Example 1 (pure PHA) showed obvious adhesion problems, demonstrating the important role of the formulation of the present invention in improving anti-blocking properties.

[0122] Application Example 11: Hot-stitch window.

[0123] Experimental Description: This application example aims to evaluate the adhesion of the coating immediately after heat sealing (i.e., "hot tack strength"), which is crucial for high-speed packaging lines (such as vertical forming-filling-sealing machines) to prevent the contents from immediately bursting the packaging after heat sealing. For all examples and comparative samples, heat sealing was performed within a temperature range of 110–180°C, followed by immediate peeling shortly after sealing. The instantaneous hot tack strength was recorded to determine the initial sealing temperature, maximum hot tack strength, and effective temperature range.

[0124] Table 14. Test results of the hot-bonded window:

[0125]

[0126] Analysis of Table 14 shows that Examples 4, 5, and 6, which incorporate EAA / EMA, not only have lower initial sealing temperatures but also wider hot-tack temperature ranges and higher hot-tack strengths, proving their suitability for high-speed industrial production. Comparative Example 2, lacking thermoplastic PHA, does not possess hot-tack properties.

[0127] Application Example 12: Verification of consistency between total organic fluorine (TOF) and "unintentional addition".

[0128] Experimental Description: This application example aims to rigorously verify, through quantitative analysis, that all coatings of this invention meet the PFAS-free requirement. The total organic fluorine content of the coating samples in all examples and comparative examples was determined using the oxygen bomb combustion-ion selective electrode method. This method converts all organic fluorine in the sample into fluoride ions and allows for precise measurement, ensuring the compliance of the final product.

[0129] Table 15 Results of Total Organic Fluorines (TOF) Test:

[0130]

[0131] Analysis of Table 15: The total organic fluorine content of all samples was far below the industry limit of 100 mg / kg, confirming the present invention's statement of "unintentional addition of fluorine-containing substances" and fully complying with global regulations on fluorine-free food packaging.

[0132] Experimental Results and Analysis:

[0133] Based on the test data from the above 12 application examples, this invention, through the scientific formulation and synergistic design of PHA emulsion, sheet-like natural inorganic materials with specific geometric morphology, optional copolymer emulsion, and aqueous crosslinking agent, successfully achieved a fluorine-free aqueous coating with high barrier properties, strong heat-sealing properties, excellent resizing properties, and biodegradability at a low dry weight of 6–20 g / m². This systematically solves the technical challenge of balancing multiple properties that is difficult to achieve in existing technologies. The influence trends of each key component on the coating performance are analyzed as follows:

[0134] Analysis of the core role of PHA emulsion: PHA is the core of the functional framework of the coating of this invention. Comparing Examples 1-6 with Comparative Example 2 (without PHA), it is clear that the introduction of PHA is a fundamental prerequisite for achieving effective heat sealing (Application Example 3), hydrophobicity (Application Example 4, initial contact angle > 95°), and biodegradability (Application Example 7, degradation rate > 90% after 180 days). Comparative Example 2, being completely PHA-free, has a brittle coating, lacks heat sealing properties, and is not biodegradable, thus lacking application value. Furthermore, comparing Comparative Example 1 (pure PHA) with the other examples reveals that while the pure PHA coating possesses basic functions, it is deficient in barrier properties, heat-sealing leakage resistance (Application Example 1), anti-blocking properties (Application Example 10), and processing smoothness (Application Example 9), demonstrating the crucial importance of the synergistic effect of other components. The PHA content also affects performance: Example 2 (85 wt% PHA) exhibited higher heat-sealing strength and toughness compared to Example 1 (30 wt% PHA), but it was at a critical level in terms of anti-blocking properties and its resistance to penetration by complex dairy media was slightly lower than that of the high-mineral-content formulation (Application Example 5). Therefore, the PHA content needs to be optimized within the range of 30–85 wt% to balance the overall performance of heat-sealing, toughness and barrier properties, and anti-blocking properties.

[0135] Analysis of the key barrier effect of high shape factor sheet-like inorganic materials: One of the core innovations of this invention lies in utilizing sheet-like inorganic materials with a high shape factor (≥20) to construct a "zigzag path" physical barrier structure in a PHA matrix. Direct comparative data from Application Example 2 clearly confirms this: Example 3, using delaminated kaolin with a shape factor ≥30, showed a significantly reduced WVTR of 32.4% compared to Comparative Example 3, which used non-delaminated kaolin with a shape factor of only 8–12. (Cobb) 60 The form factor was reduced by 28%, and the oil resistance rating improved from level 9 to level 11. This irrefutably demonstrates that a high form factor is key to achieving efficient barrier performance. Furthermore, the inorganic content also affects the performance balance: Example 1 (60 wt% inorganic content) exhibited the best resistance to dairy penetration (Application Example 5) and anti-blocking properties (Application Example 10), but its toughness was slightly sacrificed, and its heat-sealing strength in the low-temperature region was relatively low. This indicates that the content of sheet-like inorganic materials needs to be precisely controlled between 5–60 wt% depending on the specific application scenario.

[0136] Analysis of the enhancing effect of copolymer emulsions on heat-sealing performance: The introduction of EAA or EMA copolymer aqueous dispersions can significantly optimize the thermal processing performance of the coating. Comparing Examples 4, 5, and 6 with added EAA / EMA to Examples 1, 2, and 3 without added EAA / EMA, it is evident that in the heat-sealing window test (Application Example 3), the former exhibits significantly higher low-temperature heat-sealing strength. In the more stringent hot-tack test (Application Example 11), Examples 4, 5, and 6 show lower initial sealing temperatures, higher maximum hot-tack strength, and a wider effective temperature range, which is crucial for preventing the packaging contents from instantly bursting open after heat sealing. Therefore, selectively adding 1–20 wt% EAA / EMA aqueous dispersions is an effective technical means to improve the adaptability of coatings for industrial applications.

[0137] Synergistic Effects and Overall Performance of Components: The success of this invention is not due to the contribution of a single component, but rather the result of the synergistic effect among the components. PHA provides a biodegradable and heat-sealing matrix; high shape factor inorganic materials construct an efficient physical barrier; EAA / EMA copolymers act as compatibilizers and performance modifiers, improving thermal processability; and the aqueous crosslinking agent reacts with functional groups on the polymer chain and the surface of inorganic materials to form a stable three-dimensional network structure, further enhancing the coating's cohesion, water resistance, and overall barrier properties. It is this ingenious formulation design that enables this invention to systematically achieve excellent overall performance while meeting the requirements of high resizing rate (Application Example 6), fluorine-free environmental friendliness (Application Example 12), freeze-thaw stability (Application Example 8), and good processing adaptability (Application Examples 9 and 10).

[0138] In summary, this invention innovatively couples a PHA aqueous dispersion with a sheet-like natural inorganic material with specific geometric parameters, and introduces optional functional copolymer emulsions and a highly efficient crosslinking system. This synergistically achieves multiple objectives, including high moisture barrier properties, oil resistance, wide-window strong heat sealing, high-efficiency recovery, and biodegradability, even with low coating weight. The technical solution is rationally designed, with detailed and reliable data, solving a long-standing technical problem in the industry, and possesses significant innovation and broad industrial application prospects.

[0139] 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 re-slurryable and biodegradable PHA heat-sealing barrier coating composition, characterized in that, The resizing-compatible and biodegradable PHA heat-sealing barrier coating composition comprises, on a non-volatile solids basis: The polyhydroxyalkanoate emulsion comprises 30–85 wt%, wherein the polyhydroxyalkanoate is selected from one or more of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxyhexanoate), poly(3-hydroxyoctanoate), poly(3-hydroxydecanoate), poly(3-hydroxydodecanate), poly(3-hydroxydodecanate), poly(3-hydroxyhexanoate-co-3-hydroxyoctanoate), poly(3-hydroxyoctanoate-co-3-hydroxydecanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), or poly(3-hydroxybutyrate-co-3-hydroxyoctanoate); The polyhydroxy fatty acid ester has a number-average molecular weight of 5 × 10⁻⁶. 4 –8×10 5 Latex particle size D 50 The thickness is 0.2–3.0 μm, and the minimum film-forming temperature is ≤60℃; 5–60 wt% of flaky natural inorganic material, selected from one or more of the following: kaolinite, talc, mica, vermiculite, pyrophyllite, and montmorillonite, with an average flake diameter to thickness ratio ≥20 and a particle size D. 50 The size is 0.2–2.0 μm and D 90 ≤3μm; The copolymer emulsion is 0–30 wt%, selected from one or more of the following: (1) acrylic emulsion; (2) vinyl copolymer aqueous dispersion; (3) aliphatic polyester aqueous dispersion; (4) polyvinyl alcohol aqueous solution; (5) polyurethane dispersion; (6) aqueous epoxy resin dispersion; The aqueous crosslinking agent is 0.2–5.0 wt%, selected from one or more of ammonium zirconium carbonate, polycarbodiimide, polyisocyanurone diimide, blocked polyisocyanate, aluminum / zirconium / titanium organic complex, polyfunctional epoxy compound, glyoxal and polycarboxylic acid; Additives 0.1–5.0 wt%, including mineral dispersants, associative thickeners, wetting and leveling agents, defoamers, antiblocking agents, film-forming aids, pH adjusters, waxes, preservatives and mildew inhibitors, and crosslinking catalysts; The waxes are selected from one or more of polyethylene wax, paraffin wax, carnauba wax, and polypropylene wax; The composition has a pH value of 6.5–9.0 and no organic fluorine-containing substances have been intentionally added.

2. The resizing and biodegradable PHA heat-sealing barrier coating composition according to claim 1, characterized in that, The flaky natural inorganic material is mainly composed of delaminated kaolin, accounting for more than 50 wt% of the total inorganic material, with a whiteness of ≥85%, and is surface modified by silane or polyelectrolyte.

3. The resizing and biodegradable PHA heat-sealing barrier coating composition according to claim 1 or 2, characterized in that, The volume fraction of the sheet-like natural inorganic material in the dry coating film is 5–35 vol.

4. The resizing and biodegradable PHA heat-sealing barrier coating composition according to claim 1, characterized in that, The shape factor of the sheet-like natural inorganic material is ≥30.

5. The resizing and biodegradable PHA heat-sealing barrier coating composition according to claim 1, characterized in that, The polyhydroxy fatty acid ester is poly(3-hydroxybutyrate-co-3-hydroxyvalerate), wherein the molar fraction of hydroxyvalerate is 5–30 mol.

6. The resizing-compatible and biodegradable PHA heat-sealing barrier coating composition according to claim 1, characterized in that, The copolymer emulsion comprises an aqueous dispersion of ethylene-unsaturated carboxylic acids and / or ethylene-acrylates, with a total content of 1–20 wt% relative to non-volatile solids.

7. The resizing-compatible and biodegradable PHA heat-sealing barrier coating composition according to claim 6, characterized in that, The ethylene-acrylate aqueous dispersion is an aqueous ionic or emulsion prepared based on ethylene-acrylic acid copolymer, wherein the acrylic acid content is 3–20 wt%, the acid value is 30–120 mg KOH / g, and 10–70 mol% of carboxyl groups are neutralized with ammonium, sodium or potassium ions to form an aqueous dispersion, and its minimum film-forming temperature is ≤60℃.

8. The resizing-compatible and biodegradable PHA heat-sealing barrier coating composition according to claim 6, characterized in that, The ethylene-acrylate aqueous dispersion is an aqueous emulsion or stable dispersion prepared based on ethylene-methyl acrylate copolymer, wherein the methyl acrylate content is 5–28 wt%, the melt index is 2–20 g / 10 min at 190℃ and 2.16 kg, and the minimum film-forming temperature is ≤60℃.

9. The resizing and biodegradable PHA heat-sealing barrier coating composition according to any one of claims 6 to 8, characterized in that, The mass ratio of the ethylene-acrylate aqueous dispersion to the polyhydroxyalkanoate emulsion is 1:20–1:

3.

10. The resizing and biodegradable PHA heat-sealing barrier coating composition according to claim 1, characterized in that, The mass ratio of the flaky natural inorganic material to the polyhydroxyalkanoate emulsion is 1:9–4:

6.

11. The resizing-compatible and biodegradable PHA heat-sealing barrier coating composition according to claim 1, characterized in that, The aqueous crosslinking agent is a compound system of ammonium zirconium carbonate and polyisocyanurone diimide.

12. The resizing and biodegradable PHA heat-sealing barrier coating composition according to claim 1, characterized in that, The composition has a solid content of 35–55 wt% and a viscosity of 500–5000 mPa·s measured at 25°C using a Brookfield rotational viscometer with rotor No. 4 at a rotation speed of 20 rpm.

13. A re-slurryable and biodegradable PHA heat-sealing barrier coating, characterized in that, The resizing-compatible and biodegradable PHA heat-sealing barrier coating is obtained by applying and drying the resizing-compatible and biodegradable PHA heat-sealing barrier coating composition according to any one of claims 1 to 12, and satisfies at least one of the following properties at a dry weight of 6–20 g / m²: a) Water vapor transmission rate (38℃, 90% RH) ≤ 80 g / m²·d; b)Cobb 60 ≤15g / m²; c) Oil resistance grade ≥ 11; d) Laboratory repulping rate ≥ 98%.

14. The resizing-compatible and biodegradable PHA heat-sealing barrier coating according to claim 13, characterized in that, The resizing and biodegradable PHA heat-sealing barrier coating forms a heat-sealing window at 120–220°C; and has a peel strength ≥2.5N / 15mm under conditions of 150°C, 0.2MPa, and 0.5s.

15. The resizing-compatible and biodegradable PHA heat-sealing barrier coating according to claim 13 or 14, characterized in that, After being peeled and film-formed, the coating meets the relevant standards for biodegradability within 180 days under industrial composting conditions.

16. A coated product, characterized in that, The substrate of the coated article is paper, paperboard or molded fiber article, and the surface contains the re-pulpable and biodegradable PHA heat-sealing barrier coating as described in claim 13 or 14.

17. The coated article according to claim 16, characterized in that, The coated product has a double-layer coating structure: the pre-coating layer comprises 60–85 wt% of flake natural inorganic material and 15–40 wt% of copolymer emulsion, with a dry weight of 3–8 g / m²; the topcoat layer is the resizing and biodegradable PHA heat-sealing barrier coating composition according to any one of claims 1 to 12, with a dry weight of 6–12 g / m².

18. The coated article according to claim 16 or 17, characterized in that, The coated product has no added organic fluorine, and the total organic fluorine content is ≤100mg / kg, and the manufacturer provides a statement that "no fluorine-containing substances were intentionally added".

19. The application of the re-pulpable and biodegradable PHA heat-sealing barrier coating according to claim 13 or the coated product according to claim 16 in food contact paper, cup paper, hamburger paper, takeaway food boxes, paper trays and coated white cardboard.

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