Degradable pha / PU composite water-based barrier coating and coated paper product

Abstract

The application discloses degradable PHA / PU composite water-based barrier coating and coated paper products, and belongs to the field of biodegradable polymer coating. The coating composition contains a high proportion of polyhydroxyalkanoate as a barrier phase and a bio-based polyurethane as a toughening and heat-sealing phase. The key innovation is that by precisely controlling the ratio of the two phases and using bio-based cross-linking, the synergy of rigid barrier and flexible function is achieved, and the problem that the barrier property, heat-sealing property and flexibility of traditional single material are difficult to balance is solved at low coating amount. The application provides a full life cycle green packaging solution, which aims to replace polyethylene shower film and fluorine-containing coating, and has significant application value in the field of food packaging.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of biodegradable high molecular coating, and provides a degradable PHA / PU composite water-based barrier coating and a coated paper product. BACKGROUND

[0002] Currently, paper-based food packaging widely relies on polyethylene (PE) film or fluorine-containing chemical (PFAS) coating to obtain oil resistance, barrier and heat sealing performance, but PE film is difficult to repulp and is not biodegradable, PFAS is controversial in terms of persistence and health, and is restricted in many places. Water-based barrier coating has become a replacement direction due to low volatile organic compounds (VOC) and industrialization of coating.

[0003] In terms of bio-based barrier materials, polyhydroxyalkanoate (PHA) is concerned due to its excellent gas barrier and compostability. Prior art such as WO2020036843A1, CA2239980C, etc. proposes a water-based PHA dispersion coating, discloses the dispersion solid content and particle size window, and realizes biodegradable barrier on paper or paperboard substrates; CN115698427A uses poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) and an adhesive to improve coating defects; at the same time, the disclosed documents and patents also focus on improving dispersion stability and water resistance, such as US20220033158A1, WO2023049120A1, EP4239028A1. However, these prior arts have a core technical dilemma: most of the schemes are based on a single PHA phase or focus on the stability of the dispersion, and fail to effectively solve the inherent contradiction between high gas barrier, reliable low-temperature heat sealing and excellent repulping performance under the severe condition of thin coating, i.e. not higher than 10 g / m 2 , Especially, pure PHA coating has a very narrow heat sealing window due to its high crystallinity and brittleness, and the barrier performance will decrease sharply after bending, which cannot meet the actual needs of flexible packaging.

[0004] On the other hand, although water-based polyurethane (PU) has excellent flexibility and heat sealing property, its gas barrier performance, especially the barrier ability to water vapor, is usually poor, and it is difficult to be used independently as a high barrier material. In addition, many so-called "bio-based" schemes only focus on the source of the main resin, ignoring the source of the key auxiliary components such as crosslinking agent and plasticizer in the formula, resulting in that the bio-based carbon content of the whole coating cannot reach a really high proportion, which does not meet the concept of complete sustainable development.

[0005] Therefore, there is an urgent need in the art for a brand new technical solution that must be able to solve the "trilemma" of gas barrier, heat seal and flexibility simultaneously in a unified aqueous system through synergistic effect at extremely low coating amount, and to ensure that the entire solid system from the main material to the auxiliary agent is derived from renewable resources, thereby providing a truly full life cycle green closed-loop solution. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a degradable PHA / PU composite aqueous barrier coating and coated paper product, which solves the internal contradictions of particle size control, biological purity, long-term stability and process chemical compatibility by introducing a specific stabilization system and using an advanced preparation process.

[0007] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0008] The present application provides a composite aqueous barrier coating composition. The total amount of the composition is 100wt% based on non-volatile solids, comprising:

[0009] 60 to 90wt% of polyhydroxyalkanoate solids;

[0010] 8 to 30wt% of bio-based polyurethane solids;

[0011] 0.3 to 3.0wt% of bio-based crosslinking agent;

[0012] 0 to 20wt% of the sum of bio-based plasticizer, bio-based wax and bio-based auxiliary agent;

[0013] Wherein, the polyhydroxyalkanoate solids are provided in the form of a water dispersion with a Z-average particle size of not more than 3μm; the bio-based polyurethane solids have a bio-based carbon content of not less than 80%, and are composed of soft segments and hard segments, wherein the soft segments are selected from one or more of polycaprolactone, polybutylene succinate or polycarbonate diol, and have an acid value of not more than 2mg KOH / g;

[0014] When the bio-based crosslinking agent is an isocyanate crosslinking agent, the total equivalent ratio of isocyanate groups to hydroxyl and carboxyl groups is between 1.05 and 1.20, for example, it can be 1.05, 1.10, 1.15 or 1.20; when it is a non-isocyanate system, it contains bio-based epoxy compounds and bio-based polycarboxylic acids or anhydrides, and the equivalent ratio of epoxy groups to carboxyl groups is between 0.90 and 1.10, for example, it can be 0.90, 1.00 or 1.10; the overall bio-based carbon content of the non-volatile solids of the composition is not less than 94%.

[0015] Further, the PHA aqueous dispersion can have a solids content of 60 wt%, 65 wt%, 67 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 89 wt%, or 90 wt%. The bio-based polyurethane can have a solids content of 8 wt%, 10 wt%, 15 wt%, 18 wt%, 20 wt%, 25 wt%, or 30 wt%. The bio-based crosslinker can have a content of 0.3 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, or 3.0 wt%. The sum of the bio-based plasticizer, bio-based wax, and conventional additives can have a content of 0 wt%, 1 wt%, 4 wt%, 5 wt%, 8 wt%, 10 wt%, 15 wt%, or 20 wt%. The overall bio-based carbon content of the non-volatile solids of the composition can be no less than 94%, for example, 94.4%, 95.2%, 95.8%, 96.5%, 97.4%, or 97.5%.

[0016] In one embodiment, the PHA aqueous dispersion has a solids content of 35 to 55 wt%, further, it can be 35%, 40%, 45%, 50%, or 55%; and the bio-based polyurethane is composed of soft segments and hard segments, wherein the hard segments of the bio-based polyurethane are composed of the reaction residues of aliphatic diisocyanate and small molecule chain extender; the aliphatic diisocyanate is selected from one or more of pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), or isophorone diisocyanate (IPDI); the chain extender is selected from one or more of 1,3-propanediol, 1,4-butanediol, isosorbide; the soft segment is selected from one or more of polycaprolactone, polybutylene succinate, or polycarbonate diol, which has an acid value no higher than 2 mg KOH / g. The PHA is one or more of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB), or PHBH.

[0017] In yet another embodiment, the composite aqueous barrier coating composition has a viscosity of 500 to 1500 mPa-s at 25°C, and a pH of 6.5 to 7.5.

[0018] In another aspect of the present application, a paper product is provided. The product has a coating on its surface formed from the aforementioned composition, and the dry coating amount is 6 to 10 g / m 2 , for example, it can be 6 g / m 2 , 7 g / m 2 , 8 g / m 2 , 8.5 g / m 2 , 9 g / m 2 , or 10 g / m2 .

[0019] In conjunction with the accompanying Figure 1 , the coated paper product of the present invention exhibits a particular cross-sectional microstructure. The structure shown in the figure is composed of a paper substrate 1 as the carrier, and a composite barrier coating 4 coated on the surface of the paper substrate. The composite barrier coating 4 itself is composed of two main phases: the PHA barrier phase 2 as the main barrier phase, which forms the barrier region in the coating; and the PU toughening and heat sealing phase 3 as the toughening and heat sealing phase, which surrounds or fills around the polyhydroxyalkanoate phase to form the matrix. This unique dual-phase synergistic structure is the key to achieving comprehensive performance of the present invention.

[0020] Further, the coated paper product has an oxygen transmission rate (OTR) of no more than 12 cm 3 / (m 2 · day) at 23°C and 0% relative humidity, for example, it can be 12 cm 3 / (m 2 · day), 10 cm 3 / (m 2 · day), 9 cm 3 / (m 2 · day), 8 cm 3 / (m 2 · day) or 7 cm 3 / (m 2 · day).

[0021] Further, the coated paper product has a water vapor transmission rate (WVTR) of no more than 80 g / (m 2 · day) at 38°C and 90% relative humidity, for example, it can be 78 g / (m 2 · day), 68 g / (m 2 · day), 65 g / (m 2 · day), 60 g / (m 2 · day), 58 g / (m 2 · day) or 52 g / (m 2 · day).

[0022] Further, the coated paper product has a heat seal strength of no less than 9.0 N / 15 mm, for example, it can be no less than 9.2 N / 15 mm, 9.8 N / 15 mm, 10.2 N / 15 mm, 10.8 N / 15 mm, 11.8 N / 15 mm or 12.8 N / 15 mm, under the conditions of 140 to 160°C, 0.6 to 0.8 seconds, 0.3 MPa, according to the standard test of ASTM F88 / F88M-23.

[0023] In still another aspect of the present application, a method for preparing the above-mentioned composite water-based barrier coating composition is provided. The method comprises the following steps:

[0024] Step 1. Under stirring, the PHA water dispersion, the bio-based polyurethane water dispersion and the bio-based auxiliary agent are sequentially mixed uniformly, and the pH value of the system is adjusted to 6.8 to 7.2;

[0025] Step 2. The crosslinking agent is pre-emulsified separately before use, and then added to the mixture of Step 1, and the equivalent ratio is controlled as described above, and stirred uniformly to obtain the coating composition.

[0026] The present application also relates to the use of the above-mentioned composite water-based barrier coating composition or coated paper products, which can be particularly used for preparing food contact resistant, barrier and low-temperature heat-seal packaging materials, aiming to replace polyethylene film or fluorine-containing coating.

[0027] Compared with the prior art, the following remarkable beneficial effects can be obtained by using the present application:

[0028] Innovative synergistic effect mechanism: the present application creatively designs a two-phase synergistic system, in which the high crystallinity PHA serves as the main barrier phase to provide excellent gas barrier performance, and the flexible bio-based PU serves as the toughening phase and heat-seal phase to effectively overcome the fundamental defects of pure PHA coating, such as brittleness and narrow heat-seal window. By accurately controlling the ratio of the two and the formation of the crosslinking network, the advantages of rigid barrier segments and flexible functional segments are complemented at the molecular level, producing a "1+1>2" synergistic effect.

[0029] Excellent comprehensive performance under thin coating: based on the above-mentioned synergistic mechanism, the present application successfully realizes high barrier property (OTR≤12, WVTR≤80), excellent low-temperature heat-seal property (≥9.0 N / 15 mm) and outstanding flexibility (barrier retention rate after bending >90%) under an extremely low dry coating amount of 6 to 10 g / m 2 , solving the technical problem that the prior art cannot balance these mutually restrictive performance indicators under thin coating.

[0030] Completely green and sustainable solution: the present application not only limits to the main resin, but also implements the bio-based concept to the entire solid formulation system including the crosslinking agent and the plasticizer, ensuring that the overall bio-based carbon content of the non-volatile substances is not less than 94%, reaching the industry-leading level. Combined with its complete biodegradability, excellent repulping performance and fluorine-free formulation, the present application provides a truly green packaging solution from raw material source to waste disposal throughout the whole life cycle. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 : a schematic diagram of the cross-sectional microstructure of the coating layer of the present application on a paper or paperboard substrate.

[0032] In the figure, 1, paper base; 2, PHA barrier phase; 3, PU toughening and heat sealing phase; 4, composite barrier coating. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with specific examples. It should be understood that the specific examples described herein are only used to explain the present application and should not be used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application. Unless otherwise specified, the raw materials used in the present application are commercially available industrial products or can be prepared by conventional methods. The performance test methods are carried out according to the standards described in the summary of the invention, unless otherwise specified.

[0034] Main reagents and raw materials:

[0035] The main reagents and raw materials used in the present application are shown in Table 1 below.

[0036] Table 1 Name of main reagents and raw materials, product model and supplier:

[0037]

[0038] Main analysis and detection instruments:

[0039] pH meter: Mettler Toledo SevenCompact S210 (accuracy ±0.002 pH, or equivalent).

[0040] Analytical balance: Mettler Toledo ME204E (d=0.1 mg, or equivalent).

[0041] Air drying oven: Memmert UF110 / UF110plus (room temperature +10-300℃, or equivalent).

[0042] Constant temperature and humidity chamber / hot and humid shock: ESPEC SH-241 (can execute 85℃, 85% RH program) or equivalent equipment; Binder KMF 115 (10-70℃, 0-95% RH) is used for other humidity and aging tests under conditions lower than 70℃.

[0043] Viscometer: Brookfield RVT (Spindle #3, 60rpm, 25℃; periodically reviewed by standard silicone oil).

[0044] Particle size / potential analyzer: Malvern Zetasizer Nano ZS.

[0045] High speed disperser / homogenizer: T 25 digital ULTRA-TURRAX, IKA.

[0046] High pressure homogenizer: AH-100D, ATS Engineering.

[0047] Particle size and zeta potential analyzer: Zetasizer Nano ZS90, Malvern.

[0048] OTR tester: AMETEK MOCON OX-TRAN 2 / 22.

[0049] WVTR tester: AMETEK MOCON AQUATRAN 3 / 34.

[0050] Tensile tester: Instron 5967, for heat seal strength testing.

[0051] Hot press sealer: Labthink HST-H3.

[0052] Gelbo Flex flex fatigue tester: Testing Machines Inc. (TMI) Model 173.

[0053] Friction coefficient tester: Labthink MXD-02 or Thwing-Albert FP-2260.

[0054] Blockage tester: Labthink BLD-01 parallel plate blockage tester.

[0055] Paperboard / film thickness measurement: L&W Thickness Tester 51 or Mitutoyo 293 series digital micrometer (anvil / pressure set up according to ISO 534).

[0056] Scanning electron microscope (SEM): Hitachi SU3500.

[0057] TOC / COD testing: Shimadzu TOC-L.

[0058] Gas chromatograph: Agilent 7890B, or equivalent model such as Agilent 8890.

[0059] Combustion-ion chromatography system: Mitsubishi AQF-2100H coupled with Metrohm 930 Compact IC Flex.

[0060] Laboratory coater: RK Print K Control Coater K202.

[0061] Main test standards:

[0062] Non-volatile content: ISO 3251:2019.

[0063] Viscosity: Brookfield RV (Spindle #3, 60 rpm, 25°C).

[0064] Particle size (DLS): ISO 22412:2025; when Z-average particle size ≥ 1000 nm or close to the upper limit of the instrument range, use laser diffraction static light scattering ISO 13320:2020 to determine the volume distribution D 50 , as an equivalent criterion for Z-average particle size; if the relative deviation of DLS and static light scattering results is > 20%, use microscopic image analysis ISO 13322-1 (counting method) as the arbitration. The test report needs to indicate the method, temperature, medium refractive index and distribution type.

[0065] OTR: dry state according to ASTM D3985-24 (23°C, 0% RH); wet state or different humidity according to ASTM F1927-20.

[0066] WVTR: ASTM F1249-20 (38°C, 90% RH).

[0067] Heat seal strength: ASTM F88 / F88M-23 (180° peel, 200 mm / min).

[0068] Heat seal sample preparation and window: ASTM F2029-16(2021).

[0069] Flex fatigue pretreatment: ASTM F392 / F392M-23 (Gelbo Flex).

[0070] Bio-based carbon content: ASTM D6866-22.

[0071] Biodegradation rate: ASTM D5338-15(2021).

[0072] Disintegration rate: ISO 20200:2023.

[0073] Reslurry performance: CEPI Recyclability Laboratory Test Method (Version 3, 2025-02).

[0074] Total organic fluorine (TOF): EN 14582:2016.

[0075] Oil resistance (Kit): TAPPI T 559 cm-12(R2022).

[0076] Water absorption (Cobb): TAPPI T441 om-24.

[0077] Blocking tendency: ASTM D3354-21 (parallel plate method, adapted clamp and load according to coated paper sample).

[0078] Static / dynamic coefficient of friction (COF): ASTM D1894-24.

[0079] Sensory migration: DIN 10955:2024.

[0080] Paper basis weight and caliper: ISO 536:2019; ISO 534:2011.

[0081] Chemical equivalent calculations: acid value (ISO 2114:2000); hydroxyl value (ISO 4629-2:2016); NCO content (ASTM D2572).

[0082] Regulatory compliance (non-limiting): GB 4806.8-2022; GB 31604.1-2023; EN 1186 (series, current edition).

[0083] Quality control (non-limiting): VOC content (ISO 11890-2:2020, target < 50 g / L); Zeta potential (ISO 13099-2:2012, PHA dispersion target -30 ± 10 mV).

[0084] Examples and comparative examples:

[0085] General test condition notes: all OTR / WVTR / heat seal / COF / blocking data are reported as mean ± standard deviation, n > 5, unless otherwise noted; OTR sample area > 50 cm2, WVTR sample opening diameter 50 cm2 (or instrument default), clamping and sealing performed according to instrument instructions. Heat seal preparation according to ASTM F2029, heat seal strength according to ASTM F88 / F88M-23, tested at 140-160 °C, 0.7 s, 0.3 MPa; COF according to ASTM D1894-24, blocking according to ASTM D3354-21, Cobb according to TAPPI T441 om-24, SEM observation for post-bend crack morphology, repulping and stickies according to CEPI V3 (ISO 5263-1 pulping, Somerville screen and Rapid-Köthen sheet formation).

[0086] General method for preparing composite coating: In a reaction kettle equipped with mechanical stirring, deionized water was added according to the formulation amount, and stirring was started. PHA aqueous dispersion, bio-based PU aqueous dispersion, triethyl citrate, carnauba wax emulsion, wetting agent and defoaming agent were slowly added in turn. The pH value of the system was adjusted to 7.0 with ammonia water. In another container, the bio-based HDI crosslinking agent or bio-based epoxide / citric acid crosslinking system was pre-emulsified, and then slowly pumped into the main reaction kettle. Stirring was continued at room temperature for 30 minutes to obtain the final composite water-based barrier coating.

[0087] Bioten TM General preparation steps of PHA aqueous dispersion:

[0088] The PHA aqueous dispersion used in the embodiments of the present application is prepared by an environmentally friendly solvent-free high-energy homogenization method. The specific steps are as follows:

[0089] Step 1. Dissolve 0.5 g of PVA in 200 mL of deionized water and heat to 80°C as the water phase.

[0090] Step 2. Melt 10 g of PHA powder at 175°C.

[0091] Step 3. Slowly add the melted PHA prepared in step 2 to the hot water phase of step 1 in a high-shear homogenizer at a speed of 10,000 rpm, and continue shearing for 10 minutes to form a coarse emulsion.

[0092] Step 4. Immediately transfer the hot coarse emulsion to a high-pressure homogenizer preheated to 80°C, and cycle homogenization 5-8 times at a pressure of 80-100 MPa.

[0093] Step 5. Cool the homogenized emulsion to room temperature under stirring to obtain a stable PHA aqueous dispersion with a milky white appearance. The prepared dispersion has a solid content of 40-45 wt%, an average particle size D 50 controlled in the range of 0.5-2.0 pm.

[0094] General method for preparing coated paper products: The base paper with a basis weight of 80±2 g / m 2 , and a thickness of 110±5 pm was selected as the substrate. The prepared coating was uniformly applied to the surface of the base paper by blade coating using a laboratory coater. The coated paper was dried and cured in ovens at 70, 90 and 110°C, respectively, with a residence time of 2 minutes in each temperature zone. The dry coating weight was determined by the before-after weighing method (ISO 536) and the volatile content (ISO 3251) was deducted; the thickness was checked by a thickness gauge (ISO 534). The dried coated paper was aged at room temperature for 24 hours before performance testing.

[0095] Examples 1-6 and Comparative Examples 1-4 were prepared according to the general method described above, based on the formulations given in Table 2 (in mass parts of non-volatile solids), and coated on paper substrates for performance evaluation.

[0096] Table 2 Formulation of Examples and Comparative Examples (in mass parts):

[0097]

[0098] Results and analysis:

[0099] The coatings prepared from Examples and Comparative Examples were coated on paper substrates with a dry coating weight of 8.5±0.5 g / m 2 , and their performances were tested.

[0100] Basic performance and sustainability evaluation:

[0101] To comprehensively evaluate the basic physical performance, key barrier properties, and sustainability indicators of each coating formulation, and to verify whether they meet the core design goals of the present application, a series of comprehensive tests were conducted. These tests aimed to quantify the proportion of biobased origin of the product, the barrier ability to oxygen and water vapor, the macroscopic coating quality, and the final biodegradation characteristics.

[0102] Table 3 Results of basic performance and sustainability tests of Examples and Comparative Examples:

[0103]

[0104] Analysis: Table 3 data shows that all examples meet the technical indicators of not less than 94% overall biobased carbon content, not higher than 12 cm 3 / (m 2 ·day)OTR, not higher than 80 g / (m 2 ·day)WVTR, coating appearance is smooth, and biodegradation rate is high, fully meeting the expected goals of the present application. The formulations of comparative examples exceed the limited range of the present application, resulting in obvious short boards in performance: Comparative Example 1 (pure PHA) has too high WVTR and the coating is brittle; Comparative Example 2 (pure PU) has too high OTR; Comparative Example 3 (too low PHA content) has OTR exceeding the standard; Comparative Example 4 (too low PU content) also has a brittle coating.

[0105] Processing and application performance evaluation:

[0106] Heat sealing performance is the key to the sealing function of packaging materials, and is directly related to its potential for industrial application. This test aims to evaluate the heat sealing ability of the coating under specific temperature, time, and pressure, including the sealing initiation temperature, the optimal heat sealing range, and the final peel strength, to verify its effectiveness as a packaging sealing layer.

[0107] Table 4. Test results of heat sealing performance of examples and comparative examples (time: 0.7 s, pressure: 0.3 MPa):

[0108]

[0109] Note: Failure mode: A - adhesive failure, C - cohesive failure, S - substrate tear.

[0110] Analysis: Table 4 shows that all examples have a wide and suitable low-temperature heat sealing window, high heat sealing strength, and the failure mode is ideal substrate tear (S), indicating that the cohesive strength of the coating and the adhesion to the substrate are superior to its own strength. Comparative Example 1 has almost no heat sealing property; Comparative Example 4 has insufficient heat sealing strength and an undesirable failure mode, proving the key role of the PU component in the formula of the present application in achieving reliable heat sealing.

[0111] Oil resistance is a core requirement for food packaging materials, especially for applications that come into contact with oil-containing food. In this section, the Kit grade test is used to evaluate the ability of the coating to resist the penetration of a series of oil-containing reagents with different surface tensions, in order to quantify its oil resistance grade.

[0112] Table 5. Test results of oil resistance (Kit) of examples and comparative examples:

[0113]

[0114] Analysis: Table 5 shows that the Kit grade of all examples is not less than 8, reaching the high oil resistance standard, and can effectively replace fluorine-containing coatings. However, too high a content of PU (Comparative Examples 2 and 3) will significantly reduce the oil resistance, highlighting the necessity of high content of PHA in the formula of the present application for achieving oil resistance.

[0115] In order to achieve the recycling of packaging materials, their recyclability in the standard papermaking process is crucial. In this section, the repulping performance of coated paper products is evaluated according to the industry standard CEPI V3, focusing on indicators such as waste residue rate, stick contamination, and fiber recovery rate, to determine their friendliness to the recycling system.

[0116] Table 6. Test results of repulping performance (CEPI V3) of examples and comparative examples:

[0117]

[0118] Analysis: Table 6 proves that all examples have excellent repulping performance, with good performance in all indicators, high fiber recovery rate, and high paper appearance grade, meeting the requirements of circular economy. However, unreasonable ratios (especially too high a content of PU) result in a significant increase in waste residue, DCS index, and stick area, seriously affecting the quality of recycling, which inversely proves the superiority of the formula of the present application.

[0119] In view of the strict regulations on perfluoro and polyfluoroalkyl substances (PFAS) globally, it is a prerequisite for market entry to prove that the product is fluorine-free. This test measures the total organic fluorine (TOF) content accurately by combustion-ion chromatography to confirm that no fluorine-containing chemicals are artificially added in the product of the invention.

[0120] Table 7 Test results of total organic fluorine (TOF) content of examples and comparative examples:

[0121]

[0122] Analysis: The results of Table 7 consistently show that all the example and comparative example formulations of the invention do not artificially add fluorine-containing substances, meeting the requirements of environmental regulations.

[0123] Flexible packaging will experience repeated bending and folding during circulation and use, which can cause the barrier coating to crack and fail. This experiment uses a Gelbo Flex bending tester to simulate this physical stress, and by measuring the change in barrier performance before and after bending, to evaluate the flexibility and durability of the coating.

[0124] Table 8 Barrier retention rate after bending fatigue (Gelbo Flex, Level D, 100 times) of examples and comparative examples:

[0125]

[0126] Analysis: Table 8 shows that the barrier performance retention rate of the coating of the examples is very high after being subjected to bending, showing excellent flexibility and durability, and being able to adapt to the physical challenges in actual circulation. The pure PHA (Comparative Example 1) has almost completely lost its barrier properties due to its brittleness, and the retention rates of the other comparative examples are also significantly lower than those of the examples, again proving the key role of PU in the formulation for improving flexibility.

[0127] In roll-to-roll industrial production and storage, the blocking (i.e. sticking) between coatings is a serious problem that can cause material to be scrapped. This test evaluates the anti-blocking ability of the coating by pressing the coating face-to-face at a set temperature and pressure for a period of time, which is an important indicator of its processing stability.

[0128] Table 9 Test results of blocking tendency of examples and comparative examples (50°C, 24h, 1.0kg):

[0129]

[0130] Analysis: Table 9 proves that all the examples of the invention have no blocking tendency and are suitable for roll-to-roll processing and storage. High content of PU (Comparative Examples 2 and 3) will cause serious blocking problems, which is a technical defect that needs to be avoided by the invention.

[0131] The coefficient of friction (COF) of the coating surface is a key parameter that affects its smooth operation on high-speed automated packaging lines. Both too high or too low friction coefficients can lead to processing problems. This experiment aims to determine the static and dynamic coefficients of friction of the coating surface to evaluate its operability in actual production.

[0132] Table 10: Test results of friction coefficient (coating-coating) for examples and comparative examples:

[0133]

[0134] Analysis: The examples in Table 10 have moderate friction coefficients, which are beneficial for the smooth operation of automated packaging lines. Comparative Examples 2 and 3 have too high friction coefficients, which can easily lead to sticking; Comparative Examples 1 and 4 may be too slippery, which is not conducive to stacking.

[0135] The packaging material may come into contact with moisture during storage or use, so its water resistance is a basic requirement. This experiment uses the standard Cobb test method to evaluate its ability to resist liquid water penetration by measuring the amount of water absorbed by the coating per unit area within a specified time.

[0136] Table 11: Test results of water absorption (Cobb) for examples and comparative examples:

[0137]

[0138] Analysis: Table 11 shows that all examples have good water resistance, with Cobb 60 values less than 20 g / m 2 . Comparative Examples 2 and 3 with high PU content have poor water resistance, further supporting the rationality of the formulation of the present application.

[0139] As a food contact material, the coating itself cannot impart any off-flavor or off-odor to the food. This experiment evaluates the samples according to the DIN standard by a professional sensory evaluation team to ensure their sensory inertness when in contact with food, which is an important step in ensuring food safety and consumer acceptance.

[0140] Table 12: Test results of sensory migration (DIN 10955:2024) for examples and comparative examples:

[0141]

[0142] Analysis: All examples passed the sensory migration evaluation with an off-flavor score of 0, indicating that they are safe for food contact. The comparative examples also passed the sensory migration evaluation, indicating that this indicator is mainly related to the purity of the raw materials. High content of PU may cause a slight odor, but it is still within the acceptable range.

[0143] Industrial applicability verification experiment:

[0144] 1. Hot oil pollution scene penetration resistance.

[0145] In order to simulate the harsh scene of hot oil contact in actual applications such as take-out and baking, the experiment contacts the edible oil mixed with red dye with the coating at high temperature, and observes the penetration of the oil by visual observation, so as to more intuitively evaluate the heat oil resistance of the coating.

[0146] Table 13 Example and comparative example hot oil penetration performance test results (70℃, 30min):

[0147]

[0148] Analysis: Table 13 shows that all examples of the present application still maintain excellent penetration resistance in high temperature oily environment, which can meet the requirements of harsh food packaging. However, too high PU content (comparative examples 2 and 3) leads to a serious decline in heat oil resistance.

[0149] 2. Humid heat / condensation environment WVTR stability.

[0150] When the packaging material undergoes temperature changes (such as being taken out from refrigeration) or is in a high humidity environment, it may cause a decline in barrier properties due to condensation or moisture absorption. This experiment simulates the impact of high temperature and high humidity conditions to test the change of the WVTR of the coating, in order to verify its performance stability in harsh environments.

[0151] Table 14 Example and comparative example WVTR test results after humid heat treatment:

[0152]

[0153] Analysis: Table 14 shows that the coating of the present application can still maintain very high water vapor barrier performance under humid heat impact. Pure PHA (comparative example 1) will crack due to heat shock, and high PU content coating (comparative examples 2 and 3) will swell due to water absorption, resulting in a serious decline in barrier properties.

[0154] 3. Heat sealing pollution resistance.

[0155] On the actual packaging line, the sealing area may sometimes be unavoidably contaminated by the contents (such as oil droplets, water droplets). This experiment aims to evaluate the heat sealing ability of the coating in the presence of oil or water pollution on the sealing interface, which is an important indicator for measuring the process robustness and practical application reliability of the coating.

[0156] Table 15 Example and comparative example heat sealing pollution resistance performance test results:

[0157]

[0158] Analysis: Table 15 data shows that even in the presence of oil, water contamination, the inventive coating examples still achieve high strength heat sealing, with ideal failure mode, demonstrating excellent process adaptability. Comparative Examples 1, 2, 3 and 4, however, cannot form reliable seals under the contaminated conditions.

[0159] 4. Food contact migration (regulatory adaptation, exemplary).

[0160] Total migration is one of the final and most critical indicators for assessing the safety of food contact materials, which is directly related to the health of consumers. This test uses different types of food simulants to test the total amount of non-volatile substances migrated from the coating to the simulant under severe conditions, to verify whether it meets the regulatory limit requirements according to the Chinese national food safety standards.

[0161] Table 16 Total migration test results of examples and comparative examples (GB 4806.8-2022):

[0162]

[0163] Analysis: Table 16 is the total migration test result for the Chinese market. The experimental data shows that the total migration of all tested samples under the condition of simulating different types of food is far lower than the limit value of 10 mg / dm² specified in the national standard GB 4806.8-2022. All examples of the present invention show extremely low migration levels, proving their high safety as food contact materials.

[0164] 5. Coating resistance to folding cracking observation.

[0165] This experiment directly observes the surface morphology of the coating after bending fatigue test on a microscopic scale by scanning electron microscope (SEM). This is aimed at verifying the results of the barrier retention rate test (Table 8) from a mechanistic point of view, by quantifying the density of microcracks, and directly revealing the fundamental differences in flexibility of different formulations.

[0166] Table 17 Microscopic observation of coating after bending (100 cycles / Level D) of examples and comparative examples:

[0167]

[0168] Analysis: The microscopic observation results of Table 17 directly prove the excellent flexibility of the inventive formulations. The coating of the examples has almost no cracks or only a small amount of microcracks after repeated bending, which is highly consistent with the results of high barrier retention rate (Table 8). In contrast, the pure PHA coating (Comparative Example 1) cracks severely, and the coating with insufficient PU content (Comparative Example 4) also cracks significantly.

[0169] 6. Coating disintegration performance (ISO 20200).

[0170] Biodegradability (Table 3) focuses on the chemical transformation of the material under the action of microorganisms, while disintegration focuses on its physical disintegration ability in the composting environment. The disintegration test according to the ISO 20200 standard is a key step to prove that the material is "compostable", and this experiment aims to verify whether the coating can be sufficiently broken down within the specified time to meet the requirements of industrial composting.

[0171] Table 18 Disintegration performance test results of examples and comparative examples (ISO 20200:2023, 12 weeks):

[0172]

[0173] Analysis: Table 18 data shows that the residual mass of the coating part of all examples of the application is less than 10% after 12 weeks of industrial composting, and there is no visible debris, meeting the disintegration requirements of ISO 20200 standard. This is mutually verified with the ASTM D5338 biodegradation rate data (Table 3). Comparative examples 2 and 3 with too high PU content cannot be completely disintegrated, proving the superiority of the application formula in ensuring complete biodegradability.

[0174] 7. Quality control project verification.

[0175] To ensure the quality stability and batch consistency from raw materials to final products, key quality control (QC) projects need to be set. This section detects the volatile organic compounds (VOC) content of the coating and the Zeta potential of the system, the former is related to the compliance of environmental and safety regulations, and the latter directly reflects the storage stability of the water-based dispersion system.

[0176] Table 19 Test results of quality control projects of examples and comparative examples (ISO 11890-2:2020):

[0177]

[0178] Analysis: The test results in Table 19 show that the VOC content of the representative coating products meets the low volatility requirement. The Zeta potential of the key raw material PHA water dispersion is in the ideal stable interval. In the finished coating, the absolute value of the Zeta potential of all examples is high (greater than 35 mV), indicating that the system has excellent storage stability. The absolute value of the Zeta potential of comparative examples 2 and 3 is low, which may have the risk of flocculation under long-term storage, thereby ensuring the quality of the system of the application.

[0179] Comprehensive result analysis:

[0180] Analysis of the influence of key components on performance:

[0181] Ratio of PHA water dispersion solid (PHA) to bio-based polyurethane solid (PU): The core of the invention lies in the precise regulation of the ratio of hard and brittle barrier phase PHA to flexible toughening phase PU to achieve a balance of comprehensive performance. The design of the examples verifies the scope defined by the invention: PHA is 60 to 90 wt%, and PU is 8 to 30 wt%.

[0182] When the PHA content is at the high end of the range, such as Example 2 (PHA is 90%) and Example 5 (PHA is 89%), the coating exhibits the best oxygen barrier (OTR is 7 to 8) and oil resistance (Kit grade is 10), but the flexibility is slightly worse (the barrier retention rate after bending is about 90%, and the coating appearance is slightly brittle).

[0183] When the PHA content is at the low end of the range, such as Example 3 (PHA is 60%), the coating exhibits the best flexibility (the barrier retention rate after bending is 98%), the widest heat sealing window, and the highest heat sealing strength (12.8 N / 15 mm), but the gas barrier performance is at the critical value of the index (OTR is 12).

[0184] Example 1 (PHA is 75%) and Example 4 (PHA is 67%) demonstrate the ideal balance point of each performance.

[0185] Comparative Examples 1 to 4 clearly reveal the consequences of exceeding this range: pure PHA (Comparative Example 1) has no heat sealing and flexibility; too high PU content (Comparative Examples 2 and 3) severely sacrifices barrier, oil resistance, and resizability; and too low PU content (Comparative Example 4) cannot effectively toughen, resulting in insufficient heat sealing strength.

[0186] Bio-based crosslinking agent: The invention limits the crosslinking agent content to 0.3 to 3.0 wt%. Examples 1 to 5 use a bio-based HDI crosslinking agent, with a dosage of 0.5 to 2.0 wt%, and Example 6 uses a bio-based epoxy / carboxylic acid system, with a total dosage of 2.0 wt%. Comparison of data (such as Example 1 vs. Example 6) shows that different crosslinking paths and dosages within this range can all make the coating have excellent comprehensive performance, proving the universality of the technical solution of the invention. The formation of the crosslinking network is crucial for the cohesive strength, durability (bending fatigue), and adhesion of the coating.

[0187] Bio-based plasticizer and other additives such as wax: The total amount of additives is limited to 0-20wt% in the present application. The comparison between Example 2 (without plasticizer) and Example 5 (with 1% plasticizer) shows that the addition of plasticizer can effectively improve the flexibility of the high PHA content formula and eliminate the appearance of "slightly brittle". The addition of wax can regulate the surface energy and surface morphology, which is usually beneficial to reduce the risk of blocking and obtain a moderate COF; the directional effect on COF is related to the amount, type of wax and substrate roughness, which needs to be measured (see Table 10).

[0188] Sustainability and compliance analysis:

[0189] All examples achieve an overall bio-based carbon content of no less than 94% and have excellent biodegradation rate. The re-pulping performance test shows that the waste residue and stickies generated by the formula of the present application are much less than the comparative examples, the fiber recovery rate is high, and it is environmentally friendly. In addition, all samples pass the total organic fluorine test and sensory migration test, proving their safety in food contact applications.

[0190] Comprehensive evaluation of processing and application performance:

[0191] By introducing bending fatigue, blocking, friction coefficient and water absorption and other evaluations close to actual application, the industrial applicability of the present application is further verified. The sample of the example can still maintain high barrier property after being subjected to physical deformation, is not prone to sticking during storage and transportation, has a smooth surface suitable for automatic packaging line, and can effectively resist moisture penetration, fully demonstrating its reliability as a packaging material.

[0192] In summary, the present application successfully prepares a composite water-based barrier coating with high barrier property, excellent heat sealing property, complete biodegradability, high bio-based content and excellent processing and application performance by precisely controlling the ratio of high bio-based content PHA and PU, and combining bio-based crosslinking agent and additives, solving many shortcomings of the prior art.

[0193] Those skilled in the art should understand that the above examples are only exemplary and are not intended to limit the scope of the present application. Any modification, equivalent replacement, improvement, etc. of the technical solutions of the present application within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A composite water-based barrier coating composition, characterized in that, The total amount of non-volatile solids is 100 wt%, comprising: 60 to 90 wt% polyhydroxy fatty acid ester solids; 8 to 30 wt% bio-based polyurethane solids; 0.3 to 3.0 wt% of bio-based crosslinking agent; 0 to 20 wt% of bio-based plasticizers, bio-based waxes and conventional additives; The polyhydroxyalkanoate solid is provided in the form of an aqueous dispersion with a Z-average particle size of not more than 3 μm; the bio-based polyurethane solid has a bio-based carbon content of not less than 80% and is composed of soft segments and hard segments, wherein the soft segments are polycarbonate diols with an acid value of not more than 2 mg KOH / g; when the bio-based crosslinking agent is an isocyanate crosslinking agent, the total equivalent ratio of isocyanate groups to hydroxyl and carboxyl groups is between 1.05 and 1.20; when the bio-based crosslinking agent is a non-isocyanate system, it contains bio-based epoxy compounds and bio-based polycarboxylic acids or anhydrides, and the equivalent ratio of epoxy groups to carboxyl groups is between 0.90 and 1.10; the overall bio-based carbon content of the non-volatile solid in this composition is not less than 94%.

2. The composite water-based barrier coating composition according to claim 1, characterized in that, The polyhydroxy fatty acid ester is one or more of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), or poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

3. The composite water-based barrier coating composition according to claim 1, characterized in that, The solid content of the aqueous dispersion of the polyhydroxy fatty acid ester solid is 35 to 55 wt%.

4. The composite water-based barrier coating composition according to claim 1, characterized in that, The composition has a viscosity of 500 to 1500 mPa·s at 25°C and a pH of 6.5 to 7.

5.

5. A coated paper product, characterized in that, The coated paper product surface has a coating formed by the composition according to any one of claims 1 to 4, with a dry coating weight of 6 to 10 g / m². 2 .

6. The coated paper product according to claim 5, characterized in that, The oxygen permeability of the coated paper product is no higher than 12 cm under conditions of 23°C and 0% relative humidity. 3 / (m 2 ·day).

7. The coated paper product according to claim 5, characterized in that, The water vapor transmission rate of the coated paper product is no higher than 80 g / (m³) under conditions of 38°C and 90% relative humidity. 2 ·day).

8. The coated paper product according to claim 5, characterized in that, The coated paper product, when tested according to ASTM F88 / F88M-23 standards at 140 to 160°C, 0.6 to 0.8 seconds, and 0.3 MPa, has a heat-sealing strength of not less than 9.0 N / 15 mm.

9. A method for preparing a composite waterborne barrier coating composition according to any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1. Under stirring, the polyhydroxyalkanoate aqueous dispersion, the bio-based polyurethane aqueous dispersion, the bio-based plasticizer, the bio-based wax and conventional additives are mixed evenly in sequence, and the pH value of the system is adjusted to 6.8 to 7.

2. Step 2. Pre-emulsify the crosslinking agent separately before use, then add it to the mixture in Step 1, and control the amount according to the equivalent ratio in claim 1, and stir until uniform to obtain the coating composition.

10. Use of the composite waterborne barrier coating composition according to any one of claims 1 to 4 or the coated paper article according to any one of claims 5 to 8 in the preparation of oil-resistant, barrier, and low-temperature heat-sealing packaging materials for food contact, said use being intended to replace polyethylene lamination or fluorinated coating.

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