Reaction compatibilized acr-phacore-shell latexes and applications thereof

Abstract

The application discloses a reactive compatibilized ACR-PHA core-shell latex and application thereof, and belongs to the field of high polymer chemistry and material science. The latex comprises composite particles with a core-shell structure, and the interface between the ACR phase and the PHA phase is connected through a covalent bond, thus fundamentally solving the compatibility problem of physical blending. The Z-average particle size of the latex particles is 80-400 nm, the PDI is less than or equal to 0.30, and the minimum film formation temperature (MFFT) is between -10 and 12 DEG C. The coating prepared by the application has excellent high-humidity barrier stability (WVTR is less than or equal to 65 g / m2.d), low-temperature rapid heat sealing property, water resistance and oil resistance, and complete recyclability, and does not contain PFAS, and is an ideal alternative scheme of traditional PE coating film, and is suitable for fields such as food packaging paper and paper cups.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of polymer chemistry and material science, and specifically relates to a reactive compatibilized ACR-PHA core-shell emulsion and application thereof. BACKGROUND

[0002] With the increasing emphasis on sustainable development worldwide, "using paper to replace plastic" has become an important development trend in the packaging industry. In order to endow fiber-based materials such as paper and paperboard with necessary water, oxygen and oil resistance, it is usually necessary to apply a functional barrier coating on the surface thereof. Traditionally, polyethylene (PE) film is the main means to achieve this function, but it is difficult to recycle after being combined with paper fibers, which does not meet the requirements of circular economy.

[0003] Therefore, the development of biodegradable and recyclable water-based emulsion coatings has become a research hotspot. Polyhydroxyalkanoate (PHA) is a kind of aliphatic polyester synthesized by microorganisms, which has excellent biodegradability and good gas barrier property, and is one of the ideal materials to replace traditional plastics. However, PHA itself has high crystallinity, brittle and hard texture and high film-forming temperature, and it is difficult to directly form a continuous film in the form of a water-based dispersion at low temperature. Acrylate (ACR) polymer emulsion has the advantages of low film-forming temperature, good flexibility and strong adhesion, but its barrier property is relatively poor. In order to combine the advantages of both, the existing technology usually adopts the method of physically blending PHA dispersion and ACR emulsion. However, due to the large difference in polarity between PHA and ACR, they are thermodynamically incompatible, resulting in obvious interfacial defects in the blended coating. These defects not only weaken the mechanical strength of the coating, but also become a rapid penetration channel for water and oxygen molecules, resulting in unstable barrier property of the coating and unsatisfactory heat sealing performance.

[0004] The existing technical routes in the art can be mainly classified into the following categories, but all have obvious limitations:

[0005] The first category is PHA emulsion or water dispersion technology. For example, US5977250 A, CA 2239980 C and US6025028 A, etc. patents related to PHA emulsion / water dispersion for paper coating, which mainly contributes to solving the problem of water-based preparation and dispersion of high crystallinity PHA, and proposes that PHA emulsion can be used for paper treatment. However, these technologies are still single-phase PHA systems or simple physically stable dispersions in nature, and the core is to stabilize PHA itself, and they do not involve the complex problem of solving the problems of low-temperature film-forming, interfacial compatibility and high wet barrier stability by forming a "reactive compatibilized core-shell structure" with ACR polymer. Therefore, they cannot fundamentally overcome the inherent brittleness of pure PHA coating or the interfacial defects of physically blended systems.

[0006] The second category is reactive acrylic latex technology. For example, US 2016 / 0319169 A1 and US 8809447 B2 disclose the use of reactive monomers such as acetoacetoxyethyl methacrylate (AAEM), EP 489941 B1 discloses emulsions containing oxazoline, and WO 2016 / 060159 A1 discloses emulsions containing silane. These technologies provide a rich chemical "toolbox" that can be used to achieve self-crosslinking of the latex or adhesion to the substrate. However, none of these documents teach the application of the reaction chemistry described therein to construct covalent interfacial bridges between ACR and PHA, two incompatible polymers. Their application scenarios are not to solve the compatibility of ACR-PHA composite systems, nor are they specifically targeted at solving the high moisture barrier performance required for paper-based packaging.

[0007] The third category is particle morphology engineering technology. For example, US 7875654 B2, US 2019 / 0177458 A1, and US 12023641 systematically describe the preparation methods of Janus particles or raspberry-shaped particles. However, these morphology engineering technologies are mainly applied in the fields of paint self-organization or decoration, and their core purpose is not to construct functional barrier layers. They do not combine these complex morphologies with ACR-PHA reactive compatibilization systems to solve the unique challenges of high moisture barrier and recyclability in the field of food contact packaging.

[0008] In summary, the prior art has not disclosed a comprehensive solution that organically combines the above three types of technologies, i.e., effectively combining PHA and ACR through interfacial chemical bonds to construct composite particles with a clear core-shell structure, and thereby simultaneously achieving the goals of stable and excellent barrier performance under high humidity conditions, meeting the low-temperature rapid heat sealing requirements, and ensuring material recyclability within a single latex coating system. SUMMARY

[0009] The present application provides a reactive compatibilized ACR-PHA core-shell latex and its applications, aiming to solve the problem of poor compatibility, many interfacial defects, unstable coating barrier performance, high film forming temperature, and poor heat sealing performance when polyhydroxyalkanoate and acrylic polymers are physically blended in the prior art.

[0010] The present application adopts a synergistic strategy of interfacial chemistry (such as GMA) and particle morphology (such as core-shell); with a Z-average particle size of 80-400 nm, PDI ≤ 0.30 (ISO 22412:2025), and / or a volume distribution median diameter D 50 80-400 nm, D 90 / D 10particle dispersion window of < 3.5 (ISO 13320:2020) and residual anionic surfactant limited to < 0.10 wt% by MBAS (SM 5540C, 2023). After standardized coating / annealing, the coating has a water vapor transmission rate (WVTR) of < 65 g / m2d (ASTM F1249-20, 38°C, 90% RH) and an oxygen transmission rate (OTR) of < 120 cm3 / m2d (ASTM F1927-20, controlled humidity). In preferred embodiments, the coating can achieve a WVTR of < 50 g / m2d and an OTR of < 80 cm3 / m2d. In use, the present application covers wet-on-wet and back-coated COF and is evaluated for paper-based sensory by ISO 1230-1 / -2:2009, validated for migration by GB 31604 and EN 1186 system, completed AOF total amount screening by DIN 38409-59:2022 / EPA 1621:2024, and evaluated for repulping recycling by CEPI Recyclability Laboratory Testmethod, Version 3 (2025-02).

[0011] To achieve the above-mentioned purposes, the present application provides a reactive compatibilized acrylate-polyhydroxyalkanoate core-shell emulsion, which is an aqueous dispersion comprising composite particles, the composite particles have a core-shell structure, this structure design regularly distributes two polymers with different properties inside one particle, forming a clear core phase and shell phase; the core phase of the composite particles is polyhydroxyalkanoate, and the shell phase is acrylate polymer, or the core phase is acrylate polymer, and the shell phase is polyhydroxyalkanoate, for example, when the core phase is polyhydroxyalkanoate, the shell phase is acrylate polymer, and vice versa, this design takes advantage of the controllability of emulsion polymerization to build an ordered microstructure; the interface between the core phase and the shell phase contains a covalent chemical bond, which is the key to fundamentally solving the phase interface problem; the polyhydroxyalkanoate is selected from one or more of poly-3-hydroxybutyrate (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB), or medium-chain-length polyhydroxyalkanoate, which are currently common biodegradable polyester types in industry; the monomer component of the acrylate polymer comprises:

[0012] at least one main monomer selected from one or more of C1-C18 alkyl acrylate, C1-C18 alkyl methacrylate, cycloalkyl acrylate, cycloalkyl methacrylate, and aromatic vinyl monomer;

[0013] The monomer component of the acrylate-based polymer further comprises:

[0014] at least one other functional monomer selected from carboxyl-, hydroxyl- or amido-containing monomers; and / or

[0015] at least one crosslinking monomer which is a monomer containing at least two polymerizable double bonds.

[0016] and at least one reactive functional monomer capable of reacting with the functional groups of the polyhydroxyaliphatic ester to form a covalent chemical bond, the reactive functional monomer being selected from epoxy group-containing monomers;

[0017] The composite particles have a Z-average particle size (Z-average) of 80-400 nm, for example 80 nm, 90 nm, 100 nm, 120 nm, 145 nm, 151 nm, 153 nm, 155 nm, 157 nm, 162 nm, 165 nm, 180 nm, 185 nm, 200 nm, 210 nm, 250 nm, 300 nm, 350 nm or 400 nm, and a polydispersity index (PDI) of no more than 0.30, for example 0.08, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.18, 0.22, 0.26 or 0.30; and / or, a volume distribution median diameter D 50 of 80-400 nm, and a volume distribution D 90 / D 10 of no more than 3.5. Smaller particle sizes and narrower particle size distributions facilitate the formation of more compact coatings.

[0018] The latex has a minimum film formation temperature of -10 to 12 °C, for example -10 °C, -5 °C, 0 °C, 5 °C, 6 °C, 7 °C, 8 °C, 9 °C, 10 °C, 11 °C or 12 °C, ensuring that it can form a continuous and compact film at a lower baking temperature, thereby saving energy.

[0019] The covalent chemical bonds at the interface originate from the reaction products of a pair of reactions selected from the following: epoxy / -COOH, epoxy / -OH, through which efficient chemical reactions can form stable chemical links at the core-shell interface under mild emulsion polymerization conditions.

[0020] The grafting ratio (GR) of the shell phase to the core phase, or the grafting ratio (GR) of the core phase to the shell phase is 10% to 60%, for example 10%, 15%, 20%, 22%, 25%, 28%, 30%, 40%, 45%, 50%, 53%, 55%, 58% or 60%, and a suitable grafting ratio ensures the stability of the core-shell structure and the effective combination of the phase interface.

[0021] The acrylic ester polymer has an acid value of 3-60 mg KOH / g, such as 3 mg KOH / g, 5 mg KOH / g, 10 mg KOH / g, 15 mg KOH / g, 20 mg KOH / g, 30 mg KOH / g, 40 mg KOH / g, 50 mg KOH / g or 60 mg KOH / g, based on non-volatile solids, to ensure the stability of the emulsion and compatibility with other auxiliaries.

[0022] The acrylic ester polymer has a hydroxyl value of 0-50 mg KOH / g, such as 0 mg KOH / g, 5 mg KOH / g, 10 mg KOH / g, 15 mg KOH / g, 20 mg KOH / g, 25 mg KOH / g, 30 mg KOH / g, 40 mg KOH / g or 50 mg KOH / g, based on non-volatile solids, and the presence of hydroxyl groups can further improve the adhesion of the coating.

[0023] For the consideration of sustainability, the bio-based carbon content BCC of the latex is not less than 70% (preferably 72%-80%), and the latex does not contain artificially added perfluoro and polyfluoro alkyl substances PFAS.

[0024] To ensure the water resistance and stability of the coating, the residual anionic surfactant (MBAS, converted to LAS equivalent) in the latex is not more than 0.10 wt%, such as 0.01 wt%, 0.05 wt% or 0.10 wt%, based on non-volatile solids.

[0025] To ensure the safety of the product, the total residual monomer content in the latex is not more than 0.03 wt%, such as 0.01 wt%, 0.02 wt% or 0.03 wt%.

[0026] To ensure the commercial application value, the latex has a D 50 change rate of not more than 3% and a viscosity change rate of not more than 10% after being stored at 40°C for 12 weeks, showing excellent storage stability.

[0027] The present application also provides a coating method, which comprises applying the core-shell latex of any one of the preceding embodiments to a substrate. The substrate is selected from paper, paperboard, molded fiber, plastic film or non-woven fabric, and the application range is wide. The dry basis coating amount of the coating is 6-12 g / m², such as 6 g / m², 7 g / m², 8 g / m², 9 g / m², 10 g / m², 11 g / m² or 12 g / m².

[0028] The present invention also provides an article prepared by the above method. The article exhibits excellent comprehensive performance. When measured at 120°C, 0.30 MPa, and 1.0 s, the heat-sealing peel strength is not less than 1.8 N / 15 mm, for example, 1.8 N / 15 mm, 1.9 N / 15 mm, 2.0 N / 15 mm, or 2.1 N / 15 mm, and the heat-sealing initiation temperature, also known as the sealing temperature, is not higher than 110°C, for example, 110°C, 105°C, or 100°C.

[0029] The water vapor transmission rate (WVTR) of the product, measured at 38°C and 90% RH, is no higher than 65 g / m²·d, for example, 65 g / m²·d, 60 g / m²·d, 55 g / m²·d, 50 g / m²·d, 49 g / m²·d, 48 g / m²·d, 47 g / m²·d, 45 g / m²·d, or 44 g / m²·d, and at 23°C and 0% RH, it is also no higher than 65 g / m²·d. The oxygen permeability (OTR) measured under RH conditions should not exceed 120 cm³ / m²·d, for example, 120 cm³ / m²·d, 100 cm³ / m²·d, 95 cm³ / m²·d, 90 cm³ / m²·d, 80 cm³ / m²·d, 78 cm³ / m²·d, 75 cm³ / m²·d, 72 cm³ / m²·d, 70 cm³ / m²·d, or 68 cm³ / m²·d.

[0030] The product is Cobb 60 Not higher than 16g / m², such as 16g / m², 15g / m² or 14g / m², with a Kit value of not less than 10 for grease resistance and a resistance to methyl ethyl ketone (MEK) abrasion cycles of not less than 100.

[0031] Therefore, the articles described in this invention can be used for food packaging, personal care product packaging, medical device packaging, or as paper cups, paper bowls, food wrapping paper, and molded fiber products.

[0032] Compared with the prior art, the use of this invention can achieve the following significant beneficial effects:

[0033] Fundamentally solves the compatibility problem: By introducing covalent chemical bonds at the interface between ACR and PHA, the thermodynamic incompatibility problem during the physical blending of the two polymers is fundamentally solved, phase interface defects are eliminated, and the coating becomes more uniform and dense.

[0034] Excellent and stable barrier performance: By eliminating the "highway" of water and oxygen permeation through interface defects, the coating of this invention can still maintain extremely low water vapor and oxygen permeability even under harsh conditions of high temperature and high humidity, and its barrier stability far exceeds that of physical blending systems.

[0035] Superior low-temperature heat-sealing performance: The regular core-shell structure and flexible ACR shell phase (or core phase) give the coating a lower minimum film-forming temperature and heat-sealing initiation temperature, enabling rapid and robust heat sealing at lower temperatures, with an ideal "fiber pull-out" failure mode, meeting the needs of high-speed packaging production lines.

[0036] Fully recyclable and environmentally friendly: The coating can be easily separated from paper fibers under standard repulping conditions, with a high fiber recycling rate and no adhesion issues, achieving full recyclability of the material, meeting the requirements of the circular economy, and is an ideal green alternative to traditional PE coating. Detailed Implementation

[0037] 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.

[0038] Main reagents and raw materials:

[0039] Table 1. Names, models, and manufacturers of main reagents and raw materials:

[0040]

[0041] Main analytical and testing instruments:

[0042] Table 2 mainly analyzes the names, models, and manufacturers of the testing instruments and equipment:

[0043]

[0044] Main testing standards:

[0045] Table 3. Main Test Items and Standard Numbers:

[0046]

[0047] General preparation process:

[0048] Preparation of PHA aqueous dispersion:

[0049] Pre-wetting: Using deionized water as the medium, add 0.5–1.0 wt% of alkyl polysaccharide (APG) and stir at 25–30°C for 5 minutes.

[0050] Powder incorporation: Slowly add PHA powder at 10,000–12,000 rpm until the target solid content is 30–35 wt%, and continue shearing for 10 minutes.

[0051] High-pressure homogenization: Homogenize the pre-dispersed liquid 3–5 times at 600–800 bar, with an outlet temperature <50℃.

[0052] Stabilize the solution: If necessary, add 0.1 wt% hydroxyethyl cellulose and allow to stand to remove bubbles.

[0053] Quality control: Particle size D 50 PDI (ISO 22412:2025), zeta potential (ISO 13099-2:2025), and MBAS (SM5540C, equivalent to linear alkylbenzene sulfonate (LAS)) ≤0.20wt% as non-volatile solids.

[0054] Simulated vomit solution (homemade):

[0055] Formula: Sodium carboxymethyl cellulose 2.0 wt%, NaCl 0.9 wt%, pH adjusted to 2.0 with HCl, and the remainder is deionized water.

[0056] Steps: Dissolve with magnetic stirring at room temperature, adjust pH to 2.0±0.1, filter at 0.45μm and set aside.

[0057] Example:

[0058] MAH-PHA (core) / ACR (shell).

[0059] Example 1: Preparation of MAH-PHA: 100 parts of PHA powder (PHBV) and 5 parts of maleic anhydride (MAH) were fed into a twin-screw reactive extruder (temperature range 180–195℃, nitrogen protection), with 0.5 parts of dicumyl peroxide (DCP) as the initiator. The screw speed was 150 rpm, and the residence time was 3–5 min. The extrudate was cooled and granulated to obtain MAH-PHA powder. This entire process did not use organic solvents. 30 parts of MAH-PHBV were briefly swollen and dispersed in ethyl acetate (solvent / solid mass ratio ≤1:1, within 30 min). Emulsifier and water were added, and the mixture was homogenized using a high-pressure homogenizer to prepare a MAH-PHA micro-dispersion. The dispersion was transferred to a reactor and heated to 80℃. A monomer emulsion consisting of 60 parts of butyl acrylate (BA), 8 parts of methyl methacrylate (MMA), and 2 parts of glycidyl methacrylate (GMA), along with a potassium persulfate (KPS) initiator solution, was added dropwise. After the addition is complete, maintain the temperature, adjust the pH, and bring the volume to 45% solids. After the reaction, remove the solvent under reduced pressure (≤30 kPa) and at 50–60 °C and recycle to ensure that the residual ethyl acetate in the finished product is no more than 10 mg / kg (according to HS-GC-MS).

[0060] Example 2: Core phase preparation was the same as in Example 1. The shell phase monomer formulation was changed to: 55 parts BA, 5 parts MMA, and 10 parts GMA. The remaining process conditions were the same as in Example 1.

[0061] Example 3: The core phase preparation was the same as in Example 1, but the amount of MAH-PHBV was 50 parts. The shell phase monomer formulation was changed to: 45 parts BA, 3 parts MMA, and 2 parts GMA to achieve a 50:50 core-shell-solid ratio. The remaining process conditions were the same as in Example 1.

[0062] Example 4: The route is the same as in Example 2, using a type A process, but the core phase uses a PHB homopolymer. 30 parts of maleic anhydride-grafted modified PHB (MAH-PHB) were prepared into an aqueous dispersion as the core phase according to the method in Example 1. The shell phase monomer formulation is the same as in Example 2: 55 parts BA, 5 parts MMA, and 10 parts GMA. The remaining process conditions are the same as in Example 1.

[0063] Comparative example:

[0064] Comparative Example 1 (non-reactive monomer): The formulation is the same as in Example 1, but the GMA in the shell phase monomer is replaced by an equal amount of MMA.

[0065] Comparative Example 2 (pure ACR): emulsion polymerization was carried out directly without the addition of MAH-PHA core.

[0066] Comparative Example 3 (physical blending): MAH-PHA dispersion and pure ACR emulsion were prepared separately and mechanically mixed at a solid content ratio of 30:70.

[0067] Comparative Example 4 (Mineral-filled polyolefin extrusion coating): Referring to US10420370B2, an HDPE-PE blend containing 40 wt% calcium carbonate was prepared and coated onto cardboard by extrusion.

[0068] Comparative Example 5 (SBR / Wax Blend Emulsion): A blend emulsion of styrene-butadiene rubber (SBR) and paraffin wax was prepared and coated.

[0069] Overview of formulations and structural characterization of examples and comparative examples

[0070] To systematically elucidate the core technology of this invention, Table 4 integrates the formulation design, process route, and core structural characterization data of each embodiment and comparative example. This section aims to clearly demonstrate, by directly correlating formulation variables with structural characterization results, that this invention successfully constructs a stable core-shell structure with the expected physicochemical properties through interfacial covalent bonding by introducing reactive monomers.

[0071] Experimental Description and Characterization Methods: All samples in Table 4 were prepared according to the methods described above. The core characterization methods used include:

[0072] Quantification of interfacial reactions: The conversion rate of GMA was determined by epoxy equivalence titration to quantitatively demonstrate the occurrence of interfacial chemical reactions.

[0073] Thermodynamic analysis: The crystallization enthalpy (ΔHc) of the PHA component was determined by differential scanning calorimetry (DSC) to assess the binding effect of interfacial bonding on the movement of PHA chain segments.

[0074] Dynamic mechanical analysis: The storage modulus (E') of the material at 25°C was determined by DMA to characterize the effect of interfacial interactions on the material's stiffness.

[0075] Colloidal stability analysis: The stability of core-shell particles is assessed by measuring the zeta potential of the emulsion. Some samples, due to their formulation or physical form, are not suitable for specific testing items and are indicated in the table.

[0076] Table 4 summarizes the formulation, process, and core structure characterization data of the examples and comparative examples:

[0077]

[0078] Analysis: Table 4 intuitively establishes the necessary connection between formulation design and material microstructure, providing decisive data support for the core innovation of this invention.

[0079] First, from a formulation design perspective, all examples introduced reactive functional group monomers (such as GMA) into the ACR or PHA phase, while Comparative Examples 1 and 3 lacked such a design. This key difference is directly reflected in the structural characterization data: all examples using GMA showed extremely high conversion rates (>88%), demonstrating the efficient occurrence of the expected interfacial chemical reactions; while Comparative Examples 1 and 3 showed almost no reaction. This chemically confirms the formation of covalent bonds.

[0080] Secondly, the formation of interfacial covalent bonds directly leads to the construction of a stable core-shell structure, which is verified by thermodynamic and dynamic mechanical data. Compared with the phase-separated PHA in Comparative Examples 1 and 3, the enthalpy of crystallization (ΔHc) of PHA in all examples is significantly reduced, clearly indicating that the interfacial bonding effectively restrains the movement of PHA molecular chains and inhibits their crystallization. This is a typical characteristic of a successful core-shell structure and strong interfacial interaction. At the same time, the storage modulus (E') of all examples is significantly higher than that of Comparative Examples 1, 3, and 5, which serve as references, confirming that the strong interface formed by chemical bonding plays an effective role in stress transfer and reinforcement, improving the overall rigidity of the composite material.

[0081] Application Example 1: Overall performance comparison.

[0082] This application example aims to comprehensively evaluate the basic physicochemical properties of the coatings in the various embodiments and comparative examples. Each sample was coated on 150 g / m² cardstock with a dry coating basis weight of approximately 10 g / m². After drying at 120°C for 60 s, its particle size distribution, minimum film-forming temperature, grafting rate, heat-sealing initiation temperature, and critical barrier, water, oil, and solvent resistance properties were tested.

[0083] Table 5: Overall Performance Comparison

[0084]

[0085] Analysis: Table 5 shows that all examples formed latexes with narrow particle size distribution (PDI ≤ 0.18) and low MFFT (≤ 12°C), thanks to the regularity of the core-shell structure. Regarding key performance indicators, the WVTR and OTR of the examples were significantly better than those of Comparative Examples 1 and 3 (without chemical bonding) and Comparative Example 2 (with pure ACR), demonstrating the synergistic effect of the PHA barrier phase and the ACR film-forming phase. Notably, Example 4 (based on PHB) exhibited barrier performance comparable to or even slightly better than Example 2 (based on PHBV), attributed to the higher crystallinity and regularity of the PHB homopolymer, further enhancing the barrier effect. All examples demonstrated excellent resistance to water (Cobb), oil (Kit), and solvents (MEK), while Comparative Examples 1, 2, 3, and 5 showed significant deficiencies in these aspects.

[0086] Application Example 2: Heat sealing performance.

[0087] This application example aims to evaluate the heat-sealing performance of the coating, a key indicator in packaging applications. According to ASTM F88 / F88M-23 standards, the heat-sealing peel strength of the coating was tested at different temperatures under a pressure of 0.30 MPa and a heat-sealing time of 1 second, and the peeling patterns were observed to determine the reliability of the heat seal.

[0088] Table 6 Heat sealing performance:

[0089]

[0090] Analysis: The heat-sealing data in Table 6 shows that all examples achieved effective heat sealing at relatively low temperatures (100-110°C) and achieved excellent peel strength of over 1.8 N / 15 mm at 120°C. More importantly, the peeling mode was "fiber pull-out," meaning that the adhesion between the coating and the paper substrate, as well as the cohesive force of the coating itself, were greater than the interlayer strength of the paper, which is an ideal heat-sealing effect. Conversely, Comparative Examples 1 and 3, due to poor interfacial compatibility and weak coating cohesive force, experienced interfacial peeling at extremely low strength. Comparative Examples 4 and 5 required higher temperatures to initiate sealing and lacked sufficient strength, failing to meet the needs of high-speed packaging applications. For further demonstration of heat tack strength and short-term sealing temperature window, please refer to Application Examples 14 and 18, which will not be elaborated here.

[0091] Application Example 3: High Humidity Aging and Barrier Stability.

[0092] This application example aims to examine the barrier performance stability of the coating under harsh, high-humidity environments, a key indicator of material reliability. Coated samples were aged for 7 days at 38°C and 90% RH, and changes in water vapor transmission rate (WVTR) were compared. Simultaneously, according to ASTM F1927-20, the difference in oxygen transmission rate (OTR) under dry (0% RH) and wet (80% RH) conditions was tested to assess its sensitivity to humidity.

[0093] Table 7 High Humidity Aging and Barrier Stability:

[0094]

[0095] Analysis: The results in Table 7 are one of the core advantages of this invention. Under harsh high humidity (38°C, 90% RH) conditions, the WVTR growth rate of all examples was less than 20%, and the OTR growth rate was less than 45%, demonstrating excellent barrier stability. This is attributed to the elimination of interfacial defects through chemical bonding, which effectively prevents the aggregation and penetration of water molecules at the interface, thereby protecting the barrier performance of the PHA phase. In contrast, the barrier performance of Comparative Examples 1 and 3 deteriorated sharply under high humidity (growth rate > 60%), which is a fatal weakness of physically blended systems. Comparative Example 4 (polyolefin) showed stable WVTR, but its OTR was extremely poor. Comparative Example 5 (SBR / wax) also performed poorly under high humidity.

[0096] Application Example 4: Re-pulping compatibility.

[0097] This application example aims to evaluate the recyclability of coated paper, an important criterion for measuring its environmental friendliness. Following CEPI's latest laboratory recyclability testing method (Version 3.0, 2025-02), a repulping experiment was conducted on the coated samples. The final fiber recovery rate, coarse residue rate, and adhesion grade were measured to determine whether the coating could effectively separate from the paper fibers in a standard recycling process.

[0098] Table 8 Re-pulping Compatibility:

[0099]

[0100] Analysis: The recycling performance test results in Table 8 show that the coated paper of all embodiments of the present invention can be easily separated from paper fibers in a standard repulping process, with high fiber recovery rate, and the coarse residue rate and adhesion grade all meet industry standards, demonstrating excellent recyclability. This is comparable to the performance of pure ACR coating (Comparative Example 2). However, Comparative Example 3 (physical blend) produced more adhesion due to coating fragmentation caused by phase separation. Comparative Example 4 (extrusion coating) and Comparative Example 5 (SBR / wax) failed the test completely, causing serious screen clogging and adhesion problems, which do not meet the requirements of a circular economy.

[0101] Application Example 5: Wet-over-wet double layer + COF back coating / anti-curling verification.

[0102] This application example aims to verify the suitability of the latex of the present invention in complex coating processes, particularly its performance in the production of double-sided coated cup and bowl preforms. By applying a thin coating to the back of the paperboard, its ability to control the coefficient of friction (COF) and balance paper stress, preventing curling, was tested. This is crucial for subsequent printing, die-cutting, and automated cup / bowl manufacturing processes.

[0103] Table 9. Back Coating Friction Coefficient and Anti-curling Properties:

[0104]

[0105] Analysis: The results in Table 9 verify the applicability of the latex of this invention in complex coating processes. As a back coating, it provides a moderate static and dynamic coefficient of friction (μs / μk in the range of 0.3-0.5), which is crucial for the smooth transport of paper in subsequent printing, die-cutting, and cup / bowl making processes. Simultaneously, the presence of the back coating effectively balances the stress on both sides of the paper, significantly improving the curling problem commonly encountered after single-sided coating and ensuring smooth processing. Curling radii R ≥ 500 mm (coated side inwards) measured according to ISO 11556:2005 are all considered 'qualified'.

[0106] Application Example 6: High-temperature accelerated storage 40℃ / 12 weeks.

[0107] Experimental Description: This application example aims to evaluate the storage stability of the emulsion itself, a crucial prerequisite for assessing its commercial application value. Accelerated aging tests were conducted at 40°C for 12 weeks, monitoring the particle size (D) of the emulsion. 50 Changes in viscosity and other properties are used to predict shelf life and stability under normal conditions.

[0108] Table 10 Emulsion Storage Stability:

[0109]

[0110] Analysis: The accelerated aging test results in Table 10 demonstrate the excellent storage stability of the core-shell latex of this invention. After 12 weeks of storage at 40°C, the particle size and viscosity changes in all examples were within acceptable ranges. This is because the interfacial chemical bonds firmly anchor the core and shell phases together, effectively preventing particle aggregation or phase separation. In contrast, Comparative Example 1 (unbonded) and Comparative Example 5 (SBR / wax) showed poor stability, while Comparative Example 3 (physical blend) experienced severe stratification within a short period, rendering it completely unsuitable for commercial application.

[0111] Application Example 7: Performance Verification under Extreme Operating Conditions.

[0112] Experimental Description: This application example aims to evaluate the coating's performance under extreme usage scenarios, including simulated cold chain transportation (freeze-thaw cycles) and hot food filling (hot oil contact). These tests determine whether the coating can maintain its structural integrity and barrier function under drastic temperature changes and chemical contact.

[0113] Table 11 Extreme operating condition performance:

[0114]

[0115] Analysis: The results in Table 11 show that the coating of this invention can withstand extreme usage scenarios such as cold chain transportation (freeze-thaw cycles) and hot food filling (hot oil contact). Its stable core-shell structure and strong interfacial bonding endow the coating with excellent flexibility and thermal stability, and it will not crack or lose its barrier properties even under drastic temperature changes. The coatings of Comparative Examples 1, 2, 3, and 5 exhibit obvious defects under these conditions, such as cracking, swelling, or dissolution, which limits their application range.

[0116] Application Example 8: Food Contact Migration and Comprehensive Compliance Verification.

[0117] Experimental Description: This application example aims to verify the food contact safety of the material, which is a decisive factor in whether it can be used in food packaging. Comprehensive migration tests were conducted on the coating in accordance with the regulatory systems of China's GB and the European Union's EN, including total migration, migration of specific heavy metals, and screening for the highly concerning perfluorinated compounds (PFAS) and mineral oils (MOSH / MOAH).

[0118] Table 12 Food Contact Migration and Compliance:

[0119]

[0120] Analysis: The compliance test results in Table 12 show that the coatings of all embodiments of this invention meet the stringent regulatory requirements of Chinese GB and EU EN regarding food contact materials. Their total migration and heavy metal migration are far below the limits, and they do not contain harmful substances such as PFAS. The MOSH / MOAH migration risk is extremely low. This is due to the use of high-purity food-grade raw materials in the formulation, and the stable chemical structure effectively inhibits the migration of small molecules. In contrast, Comparative Example 4 (mineral-filled polyolefin) and Comparative Example 5 (SBR / wax) have a risk of exceeding MOSH / MOAH migration limits, raising concerns about their safety.

[0121] Application Example 9: Sensory evaluation.

[0122] Experimental Description: This application example aims to evaluate whether coating materials have an adverse effect on the flavor of food. In accordance with EN 1230-2:2009, a professional sensory evaluation team assessed any unusual odors or tastes that might migrate from the coated samples upon contact with hot water.

[0123] Table 13 Sensory Evaluation:

[0124]

[0125] Analysis: The sensory evaluation results in Table 13 show that the coatings of all embodiments of the present invention exhibited no off-odor or migration after contact with hot water, meeting the sensory requirements for food packaging. However, Comparative Examples 4 and 5 exhibited unpleasant plastic and wax / rubber odors, respectively, which would severely impact the flavor and consumer experience of the food.

[0126] Application Example 10: Outer packaging paper for disposable toothbrushes in hotels.

[0127] Experimental Description: This application example aims to evaluate the potential of this invention in the packaging of non-food personal care products that require high moisture resistance, abrasion resistance, and a good appearance. The overall performance of the coating is tested by simulating the humid and hot environment of a hotel bathroom and the friction that the packaging may experience during transportation and use.

[0128] Table 14 Packaging Performance of Personal Care Products:

[0129]

[0130] Analysis: The results in Table 14 show that, under simulated humid and hot conditions and frequent friction in hotel bathrooms, all samples from the embodiments of this invention maintained low WVTR and controlled OTR, with COF remaining stable within the ideal range of 0.35–0.45. The printability and abrasion resistance met the requirements of ASTM D5264, and there was no odor migration, fully satisfying the functional and sensory requirements of packaging materials for the humid environment of hotel bathrooms. In contrast, Comparative Examples 1, 3, and 5 failed to meet the abrasion resistance standards due to poor coating cohesion; Comparative Examples 4 and 5 exhibited significant odor problems.

[0131] Application Example 11: Outer liner paper for cosmetic trial packs.

[0132] Experimental Description: This application example aims to verify the applicability of the invention in the field of oil- and surfactant-resistant fast-moving consumer goods packaging. By simulating the production and use scenarios of cosmetic sample sachets, the coating's resistance to oily / solvent-based contents, heat-sealing strength, and print adhesion are tested.

[0133] Table 15 Packaging Performance of Fast-Moving Consumer Goods:

[0134]

[0135] Analysis: The results in Table 15 confirm that, under simulated oily / surfactant contents, all samples of the present invention maintained excellent oil resistance (Kit≥12) and solvent resistance (MEK≥100 times). The heat-sealing curves show that it can achieve high-strength adhesion at low temperatures, and has high printing firmness and no odor, fully meeting the stringent requirements of FMCG small bag liner paper.

[0136] Application Example 12: Microwave heating performance evaluation.

[0137] Experimental Description: To evaluate the suitability of the material of this invention for microwaveable food packaging, this application example designed a microwave heating test simulating a real-world usage scenario. The test protocol was based on EN 15284:2007 (methodological framework) and reviewed with reference to FPI, Rev.#1, 2013 / 2021. The test established the working conditions and criteria for disposable paper cups / bowls, focusing on the integrity of the coating, leak-proofness, and temperature uniformity for single use. A commercial microwave oven was used to heat the coated paper cups filled with water, and the temperature distribution was monitored using a thermal imager. Simultaneously, the physical changes in the coating and the cup body were visually inspected.

[0138] Table 16 Microwave Heating Performance Evaluation:

[0139]

[0140] Analysis: The results in Table 16 show that the coatings of all embodiments of the present invention maintain excellent structure and coating integrity after being subjected to high-power microwave heating, without leakage, deformation, or blistering. Thermal imaging analysis shows that the surface temperature distribution is uniform (ΔT < 5℃), and no dangerous local hot spots appear. The fundamental reason for this phenomenon is that the stable core-shell interface chemical bonding provides strong interfacial adhesion, effectively resisting the huge vapor pressure generated when water boils and vaporizes at the interface, thereby avoiding coating blistering and delamination. In contrast, the coatings of Comparative Examples 1 and 3 exhibited blistering and delamination due to weak interfacial bonding. The polyolefin system of Comparative Example 4 showed significant local hot spots (ΔT > 18℃), which may pose a safety risk.

[0141] Application Example 13: Suitability assessment of aircraft vomit bags.

[0142] Experimental Description: The core requirements for aircraft vomit bags are instantaneous and sustained liquid impermeability, sufficient mechanical strength, and reliable sealing. This application example uses quantitative burst strength testing (ASTM F1140 / F1140M-20) and highly sensitive dye penetration testing (ASTM F1929-23) to evaluate the performance of the sealing bag made of the material of this invention under internal liquid pressure, in order to determine whether it meets this high-requirement application scenario.

[0143] Table 17. Suitability Assessment of Aircraft Vomit Bags:

[0144]

[0145] Analysis: The quantitative results in Table 17 strongly demonstrate that the material of this invention is suitable for high-requirement liquid packaging applications such as aircraft vomit bags. All samples from the embodiments exhibited burst pressures exceeding 35 kPa, and the failure mode was tearing of the substrate itself, rather than seal or coating failure. This indicates that the strength of the heat-sealed joint exceeds the strength of the paper substrate itself, which is an extremely desirable result. Dye penetration testing further confirmed that the seals of the embodiments were completely sealed, with no micro-leakage channels. In contrast, Comparative Examples 1, 3, and 5 all exhibited burst pressures below 20 kPa, and the failure mode was seal cracking, indicating that their heat-sealing strength was insufficient to withstand liquid pressure.

[0146] Application Example 14: Hot tack properties (ASTM F1921 / F1921M-12(2023)).

[0147] Experimental Description: This application example aims to evaluate the "hot" adhesive strength of the coating after heat sealing and before cooling, i.e., hot tack performance. This metric is crucial for automated packaging processes such as high-speed vertical bag making, determining the immediate integrity of the seal after the packaging contents are filled.

[0148] Table 18 Results of Hot Adhesion Strength Test:

[0149]

[0150] Analysis: The data in Table 18 are highly consistent with the results in Table 6 (cold peel strength) and provide crucial process performance information. All examples exhibited effective hot tack strength at relatively low temperatures of 100–110°C, reaching or exceeding 1.9 N / 15 mm at 120°C, sufficient to withstand the weight of the contents and ensure stable operation of high-speed packaging lines. In contrast, Comparative Examples 1 and 3 showed severely insufficient cohesion in the hot state due to poor interfacial compatibility, resulting in almost no hot tack strength. This again demonstrates, from a process perspective, the decisive role of interfacial chemical bonding in achieving reliable heat sealing.

[0151] Application Example 15: Water droplet contact angle / wetting properties (TAPPI / ANSI T 458cm-24).

[0152] Experimental Description: This application example quantitatively evaluates the hydrophobicity and wettability of a coating by measuring the contact angle of a water droplet on the coating surface and its change over time. A high initial contact angle and a low angular attenuation rate generally indicate better instantaneous water-repellent performance and more stable barrier properties.

[0153] Table 19 Results of water droplet contact angle test:

[0154]

[0155] Analysis: The results in Table 19 clearly show that the coating surfaces of all examples exhibit excellent hydrophobicity (initial contact angle θ0 > 102°) and slow contact angle decay within 10 s. This indicates that water droplets are difficult to spread and penetrate on the coating surface, consistent with the excellent Cobb values ​​in Table 5. In contrast, Comparative Examples 1, 2, and 3 show stronger surface hydrophilicity and rapid water droplet spread, which is related to their incomplete interfacial structure and high residual surfactant content, contributing to the instability of their high-humidity barrier properties.

[0156] Application Example 16: Blocking Load (ASTM D3354-21).

[0157] Experimental Description: This application example aims to evaluate the tendency of coatings to stick together (i.e., "blocking") under pressure and temperature. Low blocking properties are crucial for the storage, transportation, and subsequent printing and processing of roll materials, preventing damage to the coating surface.

[0158] Table 20 Results of the adhesive load test:

[0159]

[0160] Analysis: The data in Table 20 show that the coatings in all embodiments exhibit extremely low resistance to adhesion (load < 50 g / 100 cm²), meaning that the coated paper rolls are less prone to sticking during storage and transportation. This is due to the complete core-shell structure and strong interfacial bonding, resulting in a stable surface phase. In contrast, Comparative Examples 1, 3, and 5 are highly susceptible to adhesion under temperature and pressure conditions due to phase separation or low molecular weight wax migration, with resistance loads far exceeding acceptable limits—an unacceptable defect in industrial production.

[0161] Application Example 17: Quantitative assessment of anti-curling (ISO 11556:2005).

[0162] Experimental Description: This application example aims to quantitatively evaluate the curling degree of paper after single-sided coating. Good anti-curling properties are crucial to ensuring the smooth operation of paper in subsequent processes such as printing and die-cutting.

[0163] Table 21 Results of anti-curling performance test:

[0164]

[0165] Analysis: The results in Table 21 show that the curl radius R of all examples is greater than or equal to 500 mm, which can be judged as "qualified against curling", indicating that the shrinkage stress of the coating and the paper substrate is well matched. In contrast, Comparative Examples 1, 2, 3 and 5 all showed obvious curling (R < 350 mm), while Comparative Example 4, which uses the extrusion coating process, showed the most severe curling, which is consistent with industrial production experience.

[0166] Application Example 18: Heat sealing process window mapping (ASTM F88 / F88M-23).

[0167] Experimental Description: This application example aims to plot the onset temperature curves for different heat-sealing times to map the material's actual "process window." A wider process window (i.e., maintaining a lower onset temperature at a shorter heat-sealing time) means higher production efficiency and greater tolerance to equipment fluctuations.

[0168] Table 22 Test results of heat sealing process window:

[0169]

[0170] Analysis: The data in Table 22 clearly demonstrate the significant advantages of the embodiments of the present invention in low-temperature rapid heat sealing. Even with an extremely short heat sealing time of 0.3 s, the initial sealing temperature of most embodiments remains around 110°C, far lower than all comparative examples. This proves that the material of the present invention has a wide processing window and can adapt to the requirements of high-speed automated packaging production lines. This result, together with the results of Application Example 14 (hot tack performance) and Application Example 2 (cold peel strength), forms a complete chain of evidence that corroborates each other.

[0171] Application Example 19: Bio-based carbon content (BCC, ASTM D6866-24a).

[0172] Experimental Description: The proportion of bio-based carbon in the non-volatile solids of the sample was determined according to ASTM D6866-24a radiocarbon dating (AMS mode). The non-volatile solids of the sample were dried at 105°C under normal pressure before sample preparation.

[0173] Table 23 Results of Bio-based Carbon Content (BCC) Test:

[0174]

[0175] Analysis: The data in Table 23 clearly show that the bio-based carbon content (BCC) in the non-volatile solids of all embodiments exceeds 70%, reaching a maximum of 77.3%. This strongly demonstrates that the technical route of this invention successfully and efficiently integrates the biomass-derived PHA component into the final material. In contrast, the BCC values ​​of all comparative examples are significantly lower, especially those of Comparative Example 4 (HDPE / PE) and Comparative Example 5 (SBR / wax), which are entirely based on petrochemical feedstocks, with BCC values ​​of 0.0% and 5.6%, respectively. This result highlights the significant advantages of this invention in achieving high bio-based content in materials, meeting the requirements of sustainable development and environmental protection.

[0176] Application Example 20: Residual anionic surfactant (MBAS, SM5540C, LAS equivalent).

[0177] Experimental instructions: Standard Methods 5540C (24th, 2023) MBAS method was used. The weight was converted to LAS equivalent and reported as the percentage of non-volatile solids by mass. Methylene blue and chloroform, among other reagents, were prepared according to the methodology.

[0178] Table 24 Residual Anionic Surfactant (MBAS) Test Results:

[0179]

[0180] Analysis: The results in Table 24 show that the residual anionic surfactant content in the latex of all examples, based on non-volatile solids, was controlled at an extremely low level of 0.04% to 0.09%, far lower than that of the comparative examples (0.18%–0.26%). This low residual surfactant content is crucial for the coating's water resistance and barrier stability under high humidity conditions, as it reduces hydrophilic substances in the coating, thereby decreasing the possibility of water molecule penetration. This result also indirectly confirms the high efficiency and cleanliness of the core-shell structure synthesis process of this invention, which is one of the key factors in achieving excellent and stable barrier performance.

[0181] Application Example 21: Total residual monomers (HS-GC-MS / LC-MS / MS, stoichiometric summation).

[0182] Experimental Description: Quantitative methods were established for common monomers (BA, MMA, GMA, etc.): Volatile / Semi-volatile: HSGCMS, internal standard method; Non-volatile / Polar: LCMS / MS, multiple reaction monitoring; Dry membrane extraction (methanol / toluene) was used, with a blank paper base as a control. The report is the percentage of non-volatile solids by mass (sum of the concentrations of each monomer).

[0183] Table 25 Results of Total Residual Monomer Tests:

[0184]

[0185] Analysis: The data in Table 25 confirm the high efficiency of the emulsion polymerization process of this invention. The total residual monomer content in all examples is no higher than 0.030 wt%, meeting the stringent safety standards for food contact materials. This indicates a very high monomer conversion rate, thanks to the well-ordered core-shell structure and optimized reaction conditions, effectively avoiding odor problems and migration risks that may arise from small molecule residues. In contrast, the residual monomer content in the comparative examples is generally higher (0.056%–0.083%), which is an unacceptable deficiency in commercial applications, especially in the food packaging field.

[0186] Experimental Results and Analysis:

[0187] This invention successfully solves the key pain points of existing technologies by constructing a reactive core-shell structure inside ACR-PHA composite particles.

[0188] In terms of emulsion performance, all examples (including systems based on PHBV and PHB) formed D 50The narrow particle distribution (PDI ≤ 0.18) in the 155-180 nm range and the ideal MFFT within the 8-12 °C window demonstrate the universality and controllability of this synthetic route. Example 4, based on PHB homopolymer, exhibits performance comparable to or even slightly superior in barrier properties compared to the copolymer-based examples. This fully illustrates that the core technology of this invention—interfacial chemical bonding—is a platform technology applicable to various types of PHB, greatly expanding its application potential.

[0189] In terms of coating performance, the initial sealing temperature of all embodiments did not exceed 110°C, and high peel strength (>1.8 N / 15 mm) was achieved within a wide temperature window of 100–130°C, with the ideal fiber pull-out mode of failure. This contrasts sharply with the interfacial peeling and low strength commonly observed in the comparative examples, highlighting the decisive role of interfacial chemical bonds in improving heat-sealing performance.

[0190] Regarding the critical barrier performance, the embodiments of the present invention exhibit extremely low WVTR growth rate (<20%) after high humidity aging, and OTR is minimally affected by humidity, demonstrating excellent performance stability. This is because the interfacial chemical bonds effectively eliminate the permeation channels of small molecules such as water and oxygen, protecting the integrity of the PHA barrier phase under high humidity conditions.

[0191] In terms of recycling performance, the embodiments of the present invention exhibit excellent resizing compatibility, meeting the requirements of the circular economy, while the extrusion coating and SBR / wax systems in the comparative examples do not meet the recycling standards at all.

[0192] Furthermore, the superiority of the material of this invention was fully verified in two demanding application examples. In microwave heating tests (Application Example 12), the coating of this invention, with its strong interfacial adhesion, successfully resisted water vapor pressure, avoiding delamination and blistering. Thermal imaging confirmed that it had no dangerous localized hot spots, demonstrating excellent safety. In the suitability evaluation of aircraft vomit bags (Application Example 13), quantitative burst pressure tests showed that the heat-sealing strength of the coating of this invention exceeded that of the paper substrate itself, capable of withstanding internal pressure exceeding 35 kPa. Dye penetration tests proved its absolute sealing reliability, meeting the liquid tightness requirements under extreme conditions.

[0193] In summary, by constructing a reactive core-shell structure, this invention successfully combines the high barrier properties of PHA with the excellent film-forming properties of ACR. Through interfacial chemical bonding, the compatibility problem is fundamentally overcome, resulting in a novel environmentally friendly barrier material with comprehensive performance (especially barrier stability, low-temperature heat sealing, recyclability, and reliability in extreme application scenarios) that far surpasses existing physical blending, extrusion coating, and SBR / wax technologies.

[0194] 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 reactive, compatible acrylate-polyhydroxyalkanoate core-shell latex, wherein the core-shell latex comprises an aqueous dispersion of composite particles, characterized in that: The composite particles have a core-shell structure; The core phase of the composite particles is a polyhydroxy fatty acid ester, and the shell phase is an acrylate polymer, or the core phase is an acrylate polymer, and the shell phase is a polyhydroxy fatty acid ester. The interface between the core phase and the shell phase contains covalent chemical bonds; The polyhydroxy fatty acid ester 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), or medium- and long-chain polyhydroxy fatty acid esters; The monomer component of the acrylate polymer comprises: At least one main monomer is selected from one or more of C1-C18 alkyl acrylates, C1-C18 alkyl methacrylates, cycloalkyl acrylates, cycloalkyl methacrylates, and aromatic vinyl monomers; And at least one reactive functional monomer capable of reacting with the functional groups of the polyhydroxy fatty acid ester to form a covalent chemical bond, wherein the reactive functional monomer is selected from monomers containing epoxy groups.

2. The core-shell latex according to claim 1, characterized in that, The composite particles have a Z-mean particle size of 80–400 nm and a polydispersity index not higher than 0.30; and / or, a median diameter D of the volume distribution as measured according to ISO 13320:2020. 50 The wavelength is 80–400 nm, and the volume distribution is D. 90 / D 10 No higher than 3.

5.

3. The core-shell latex according to claim 1 or 2, characterized in that, The minimum film-forming temperature of the latex, as determined according to ASTM D2354-10(2023), is -10–12°C.

4. The core-shell latex according to claim 1, characterized in that, The covalent chemical bonds at the interface originate from the reaction products selected from the following reaction pairs: epoxy group / -COOH, epoxy group / -OH.

5. The core-shell latex according to claim 1, characterized in that, The monomer component of the acrylate polymer further includes: At least one other functional monomer, selected from monomers containing carboxyl, hydroxyl, or amide groups; and / or At least one crosslinking monomer, which is a monomer containing at least two polymerizable double bonds.

6. The core-shell latex according to claim 1 or 4, characterized in that, The grafting rate of the shell phase to the nucleus phase, or the grafting rate of the nucleus phase to the shell phase, is 10% to 60%.

7. The core-shell latex according to claim 1, characterized in that, The acrylate polymers have an acid value of 3–60 mg KOH / g, based on non-volatile solids.

8. The core-shell latex according to claim 1, characterized in that, The acrylate polymers have a hydroxyl value of 0–50 mg KOH / g, based on non-volatile solids.

9. The core-shell latex according to claim 1, characterized in that, The non-volatile solids of the latex contain a bio-based carbon content (BCC) of not less than 70%, and do not contain artificially added per- and polyfluoroalkyl substances (PFAS).

10. The core-shell latex according to claim 1, characterized in that, The residual anionic surfactant content in the latex, measured by MBAS according to Standard Methods 5540C (2023) and converted to linear alkylbenzene sulfonate equivalents, is not higher than 0.10 wt% based on non-volatile solids.

11. The core-shell latex according to claim 1, characterized in that, The total residual monomer content in the latex is not higher than 0.03 wt%.

12. The core-shell latex according to claim 2, characterized in that, The latex was stored at 40°C for 12 weeks, and its D 50 The rate of change is not higher than 3%, and the rate of change in viscosity is not higher than 10%.

13. A coating method comprising applying the core-shell latex of any one of claims 1-12 onto a substrate.

14. The method according to claim 13, characterized in that, The substrate is selected from paper, paperboard, molded fiber, plastic film or non-woven fabric.

15. The method according to claim 14, characterized in that, The dry coating weight of the core-shell latex is 6–12 g / m².

16. An article prepared by the method according to any one of claims 13-15, characterized in that, The product is food packaging, personal care product packaging, medical device packaging, or as a paper cup, paper bowl, or molded fiber product.

17. The article of claim 16, characterized in that, The heat-sealing peel strength was measured at 120℃, 0.30MPa, and 1.0s, and the heat-sealing initiation temperature was not lower than 1.8N / 15mm, and the heat-sealing peel strength was not higher than 110℃.

18. The article of manufacture according to claim 16 or 17, characterized in that, The water vapor transmission rate (WVTR) measured at 38℃ and 90% RH is no higher than 65 g / m²·d, and the oxygen transmission rate (OTR) measured at 23℃ and 0% RH is no higher than 120 cm³ / m²·d.

19. The article of manufacture according to claim 16 or 17, characterized in that, Its Cobb 60 Not higher than 16g / m², grease resistance Kit value not lower than 10, and resistance to methyl ethyl ketone (MEK) abrasion cycles not lower than 100 times.

20. The article of claim 16, characterized in that, The product, in accordance with ASTM F1921 / F1921M-12(2023) standard, has a heat-tack strength of not less than 1.9 N / 15 mm after heat sealing for 0.1–0.2 s at 120 °C and 0.30 MPa.

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