Compostable and reslurry-compatible mineral-based dual-scale barrier coatings and their preparation and application

Abstract

This invention discloses a compostable and resizing mineral-based dual-scale barrier coating, its preparation, and its application, belonging to the technical field of water-based, resizing barrier materials. Addressing the shortcomings of existing technologies such as high coating weight, large color differences, or difficulty in recycling, this invention constructs a dense barrier barrier through a "dual-scale" synergistic design of interlayer intercalation of layered double hydroxides and interparticle metal micronetworks. Its outstanding advantages are: requiring only extremely low coating weight to achieve superior water and oxygen barrier efficiency compared to conventional solutions. Simultaneously, the coating strictly controls color difference to maintain high paper whiteness and possesses pH responsiveness, allowing for rapid de-networking and dispersion under acidic conditions, facilitating resizing. This invention is free of PFAS and PVDC, achieving a balance between high barrier properties, high whiteness, and recyclability.

Description

Technical Field

[0001] This invention belongs to the technical field of water-based, resizing barrier materials, specifically relating to compostable and resizing mineral-based dual-scale barrier coatings and their preparation and application. Background Technology

[0002] Against the backdrop of the global push for plastic substitution and a circular economy, paper-based packaging materials are seen as a promising candidate. However, the inherent porous and hydrophilic nature of paper makes it unsuitable for direct use in packaging applications requiring high barrier properties against water, oxygen, and grease. Therefore, developing high-performance barrier coatings has become a core technology in this field. An ideal barrier coating must simultaneously achieve high barrier efficiency with low coating weights, be easily recyclable using standard pulping processes, and maintain the original high whiteness and printability of the paper.

[0003] Existing technological approaches often suffer from one problem at the expense of another when trying to solve this issue:

[0004] Traditional mineral-polymer composite coatings: While this type of technology, such as using a combination of kaolin, calcium carbonate, and synthetic latex, can improve paper density, it is difficult to effectively block water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) at low coating weights. To achieve high-performance barrier properties, extremely high coating weights or multilayer functional coatings are often required. This not only increases costs and energy consumption but may also affect the efficiency of repulping due to excessively high polymer content. Most publicly available domestic solutions use combinations of mineral fillers and latex, or single-layer and multilayer polyvinyl alcohol (PVOH) systems. They do not propose a two-scale structural design of layered double hydroxide (LDH) interlayer intercalation and metal complex micronetworks, nor do they limit the dispersibility within 30 minutes under repulping conditions at pH ≤ 5.

[0005] Polyphenol-metal complex-based coatings: Utilizing natural polyphenols such as tannic acid and gallic acid to form complex networks with metal ions such as iron ions is a recent emerging direction in bio-based barrier coatings. These coatings can form dense amorphous networks, providing a certain degree of barrier performance. However, their inherent drawback lies in the difficulty of color control. The iron-polyphenol complex formed by Fe(III) and polyphenols is blue-black or brown, similar to the iron-coated ink system, leading to color differences (ΔE). * (increase)

[0006] High-performance polymer coatings: Chlorine-containing polymers, such as polyvinylidene chloride (PVDC), or fluorinated compounds, such as per- and polyfluoroalkyl substances (PFAS), offer excellent barrier properties, but their environmental and health risks have led to global regulatory restrictions. PVDC may generate hazardous substances during recycling and incineration, while PFAS are known as "permanent chemicals" due to their persistence and bioaccumulation. Therefore, developing PFAS- and PVDC-free alternatives has become an industry consensus and regulatory requirement.

[0007] Furthermore, many existing barrier layer network structures are chemically too stable and difficult to effectively dissociate and disperse under the neutral or weakly acidic repulping conditions standard in the paper industry. This results in the formation of "sticky substances" or large coating fragments that contaminate the pulp recycling system and fail to meet the high-level recycling standards set by organizations such as the European Paper Industry Federation (CEPI).

[0008] Existing research has focused on reducing WVTR / OTR through inorganic nanosheets / sol-gel pathways (e.g., highly oriented nanosheets forming tortuous paths in polymer matrices), but these approaches are mostly used for plastic films, and no engineering criteria have been provided for rapid de-grinding of paper-based repulping (Chen et al., Materials Horizons 2016). Metal-polyphenol networks (e.g., Fe(III)–tannic acid) have reversible assembly characteristics, but their hue is easily affected by iron-polyphenol complexation (Ejima et al., Science 2013). This invention utilizes a dual-scale structure of 'LDH interlayer multi-anion intercalation + interparticle metal-polyphenol / phosphate micronetwork' to simultaneously achieve low coating weight, high barrier properties, and pH-triggered de-grinding, while addressing color difference issues by controlling iron content. Existing technologies have not yet demonstrated the ability to simultaneously achieve de-grinding within 30 minutes at pH ≤ 5 and ΔE under dry coating weights of 2–6 g / m². * For paper-based coating systems with WVTR ≤12g / (m²·d) at 38℃ and 90% RH and OTR ≤12mL / (m²·d) at 23℃ and 0% RH, no technical solution has been found that explicitly controls the total iron content of the top coating to ≤10mg / kg for whiteness control. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide compostable and re-pulpable mineral-based dual-scale barrier coatings and their preparation and application, aiming to solve the long-standing "trilemma" between barrier performance, recyclability and appearance quality in the field of paper-based barrier materials.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] This invention provides a compostable and reslurryable mineral-based dual-scale barrier coating, comprising, by weight of solids:

[0012] The layered double hydroxide comprises 20–70 parts, for example 20, 25, 35, 40, 45, 50, 60, or 70 parts; the layered double hydroxide has a plate charge density of 0.25–0.45 e / nm² and a volume distribution D. 50 The micrometer size is 0.3–2.0 μm, for example, 0.3 μm, 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm;

[0013] The intercalating agent is 0.5–10 parts, for example, 0.5 parts, 1.0 parts, 2.0 parts, 3.5 parts, 5.0 parts, 8.0 parts, or 10.0 parts; the intercalating agent is selected from one or more polyanionic compounds; the polyanionic compounds include polyphosphates and polyphenols / phenolic acids; the polyphosphates are selected from one or more of phytic acid, pyrophosphate, tripolyphosphate, and hexametaphosphate; the polyphenols / phenolic acids are selected from one or more of gallic acid, protocatechuic acid, ellagic acid, ferulic acid, p-hydroxybenzoic acid, and tannic acid;

[0014] The metal ion donor is present in amounts of 0.05–2.0 parts, for example, 0.05 parts, 0.2 parts, 0.3 parts, 0.5 parts, 0.8 parts, 1.5 parts, or 2.0 parts; the metal ion donor is a food-contact-permitted organometallic acid salt, which is selected from one or more of the following: lactate, citrate, tartrate, malate, gluconate, or succinate of aluminum, iron, magnesium, calcium, zinc, zirconium, or titanium.

[0015] 1–8 parts of a water-soluble film-forming aid, for example 1.0 part, 1.7 parts, 2.2 parts, 3.3 parts, 5.0 parts, 6.0 parts, or 8.0 parts, wherein the water-soluble film-forming aid is a combination of polyvinyl alcohol and carboxymethyl cellulose;

[0016] Additives ≤1.0wt%;

[0017] The coating has a solid content of 25–45 wt%, for example 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, and a pH of 7–10, for example 7.0, 7.5, 8.5, 9.0, 9.5, 10.0;

[0018] After coating and drying, a topcoat of 2–6 g / m² is formed, for example, 2.0 g / m², 2.5 g / m², 3.0 g / m², 4.0 g / m², 5.0 g / m², and 6.0 g / m². This topcoat meets the following requirements: disintegration and dispersion within 30 min at pH ≤ 5 and 25°C; WVTR ≤ 12 g / (m²·d) at 38°C and 90% RH; OTR ≤ 12 mL / (m²·d) at 23°C and 0% RH; total iron ≤ 10 mg / kg; and at D...65 ΔE compared to uncoated paper under standard light source and 10° standard observer conditions * ≤1.0; meets the standard according to the European Paper Industry Federation Laboratory Test Method for Recyclability, 3rd Edition (CEPI RLTM v3); tested according to PTS-RH 021:2012 Cat II method, the evaluation conclusion is recyclable; and no PFAS and PVDC were added.

[0019] The top coating has a WVTR ≤ 10 g / (m²·d) at 38°C and 90% RH, and an OTR ≤ 10 mL / (m²·d) at 23°C and 0% RH.

[0020] The color difference between the top coating and the uncoated backing paper is in D. 65 ΔE under standard light source and 10° standard observer conditions * ≤0.8.

[0021] The coating further includes 0.5–5.0 parts of a polyhydroxyalkanoate aqueous dispersion, for example, 0.5 parts, 1.0 parts, 2.0 parts, 3.0 parts, 4.0 parts, or 5.0 parts, wherein the median particle size (D) of the polyhydroxyalkanoate aqueous dispersion is measured according to ISO 13320:2020. 50 The particle size is 0.1–1.0 μm, for example 0.1 μm, 0.2 μm, 0.25 μm, 0.5 μm, 1.0 μm, and the polyhydroxy fatty acid ester accounts for ≤10 wt% of the total solids in the formulation; the polyhydroxy fatty acid ester is selected from one or more of the following: poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and C6–C18 medium-chain polyhydroxy fatty acid esters and their copolymers.

[0022] The layered double hydroxide is selected from one or more of the Mg–Al, Zn–Al, Ca–Al, Mg–Fe or Zn–Fe types and combinations thereof; when the Mg–Al type is used, the Mg / Al molar ratio is 2:1–4:1.

[0023] The molar ratio of the anion in the intercalating agent to the positively charged layer of the layered double hydroxide is 0.2–0.8, for example, 0.2, 0.4, 0.6, 0.8.

[0024] The metal ion donor is selected from one or more of the following: lactate, citrate, tartrate, malate, gluconate, or succinate of aluminum, iron, magnesium, calcium, zinc, zirconium, or titanium.

[0025] When magnesium or calcium organic acid salts are used as metal ion donors, their respective amounts are ≤0.2 parts, and they pass the storage stability test and 200-mesh sieve residue test under pH 7–8 conditions for 24 hours.

[0026] The surface pore size distribution D of the top coating 50 ≤80nm, such as 40nm, 50nm, 58nm, 62nm, 70nm, 75nm, 80nm, measured according to ASTM F316-03(2019).

[0027] In the water-soluble film-forming aid, the mass ratio of polyvinyl alcohol to carboxymethyl cellulose is 3:1–15:1, for example 3:1, 4:1, 7.5:1, 10:1, 15:1, and the total amount of film-forming aid is 2–6 parts, for example 2.0 parts, 2.2 parts, 3.3 parts, 4.0 parts, 5.0 parts, 6.0 parts.

[0028] At 25℃ and a shear rate of 100s -1 The apparent viscosity at that time is 100–1500 mPa·s, for example 100 mPa·s, 290 mPa·s, 380 mPa·s, 420 mPa·s, 540 mPa·s, 1000 mPa·s, and 1500 mPa·s.

[0029] The total halogen content of the top coating is ≤5 mg / kg as determined by EN 14582.

[0030] The present invention also provides a paper material comprising a top coating formed by any of the aforementioned coatings.

[0031] The paper material has a Bekk smoothness of ≥500s and / or an increase of ≤25% in both WVTR and OTR after a single 180° fold; it is evaluated as recyclable according to the PTS-RH 021:2012 Cat II method.

[0032] After the paper is folded 180° once, the increase in WVTR and OTR is ≤20% respectively.

[0033] The present invention also provides a method for preparing the aforementioned coating, the method comprising:

[0034] Step 1. In an aqueous medium with pH 8–10, stir the layered double hydroxide and the intercalating agent at 40–60°C for 0.5–2 h to obtain a mixture;

[0035] Step 2. Adjust the pH of the mixture obtained in Step 1 to 7–8, add the metal ion donor and stir for 20 min to obtain a complex mixture;

[0036] Step 3. Add water-soluble film-forming aid and additives to the complex mixture obtained in Step 2 and mix evenly to obtain the finished coating;

[0037] Step 4. Apply the finished coating obtained in Step 3 to the paper substrate at a dry coating rate of 2–6 g / m² and dry at 60–120°C to form a top coating.

[0038] In step 1, the intercalating agent is pre-prepared as an aqueous solution with a concentration of 0.1–0.5 mol / L, and subjected to a shear rate of 1000–3000 s⁻¹. -1 Mixed with layered double hydroxides under certain conditions.

[0039] After step 4, the coated paper is subjected to soft calendering with a linear pressure of 60–200 kN / m.

[0040] The present invention also provides the use of the aforementioned coating in the following paper-based products: food contact packaging and dry goods packaging liners, inner wall barrier layers for paper cups and bowls, anti-condensation layers for outer walls of beverage cups, metallized vapor-deposited base paper sealing layers, heat-sealing paper pre-coating layers, fragrance and mineral oil migration barrier layers, and top barrier coatings for mail and express packaging.

[0041] The present invention also provides the use of the aforementioned coating in metallized vapor-deposited base paper, wherein the laminated material obtained by vacuum aluminizing after being sealed by the coating has an OTR of <0.2 mL / (m²·d) at 23°C and 0% RH.

[0042] Compared with the prior art, the following significant advantages can be obtained by using the present invention:

[0043] Dual-scale high-efficiency barrier: Through the synergistic effect of interlayer intercalation and surface micronetwork, stable and efficient barrier to water vapor and oxygen can be achieved with extremely low coating amount (2–6 g / m²).

[0044] Appearance controllability: By strictly limiting the iron ion content in the formula and using aluminum salts as complexing ions, the color difference ΔE of the coating can be controlled. * Stability is kept below 1.0.

[0045] pH-triggered rapid resizing: The designed surface micronetwork is pH-responsive and can rapidly de-network within 30 minutes under acidic resizing conditions, ensuring a stable PTS Cat II recovery grade.

[0046] Industrial compatibility: The coating has a wide range of solid content (25–45%) and viscosity (100–1500 mPa·s), making it compatible with modern high-speed coating equipment. The mild drying conditions (60–120°C) help reduce energy consumption.

[0047] Regulatory-friendly and safe: The formulation system does not contain intentionally added PFAS and PVDC, and the total halogen content can be controlled at an extremely low level (≤5mg / kg). Detailed Implementation

[0048] 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.

[0049] Main reagents and raw materials:

[0050] Table 1. Main reagent and raw material names, product models and manufacturers:

[0051]

[0052] When used in direct food contact scenarios, the additives are food-contact permitted and halogen-free equivalents, such as alkyl polysaccharide wetting agents and polyether-modified silicone waterborne defoamers; the commercial products listed in this embodiment are for process representativeness and are not limited to direct food contact applications.

[0053] Main analytical and testing instruments:

[0054] Table 2 mainly analyzes the names, models, and manufacturers of the testing instruments:

[0055]

[0056] Main testing methods and standards:

[0057] OTR: ASTM D3985-24;

[0058] WVTR: ASTM F1249-20;

[0059] Contact angle (static): ISO 19403-2:2024;

[0060] Particle size: ISO 13320:2020;

[0061] Apparent viscosity: ISO 3219-2:2021;

[0062] Pore ​​size distribution on the coating surface: ASTM F316-03(2019);

[0063] Color difference (ΔE)* ISO / CIE 11664-4:2019;

[0064] Cobb 60 ISO 535:2023;

[0065] Kit: TAPPI T 559 cm-22;

[0066] Total halogens: EN 14582:2016 (Tested by oxygen bomb combustion-ion chromatography, method limit of quantitation LOQ ≤ 0.5 mg / kg);

[0067] Recycling and reslurrying: performed according to the CEPI RLTM V3 method; and representative samples were evaluated for recyclability according to PTS-RH 021:2012 (Cat II pathway). In this invention, a total slag fraction of ≤7% as measured by CEPI RLTM V3 is considered the acceptable threshold for PTS Cat II pathway recyclability evaluation.

[0068] Coating adhesion (cross-cut test): ISO 2409:2020;

[0069] LDH layer charge density determination: determined by sodium chloride / potassium nitrate exchange-acid-base titration method;

[0070] Outlier removal: ASTM E178-16 (or equivalent method), for statistical determination of outliers in repeated measurements;

[0071] Definition of dispersibility test: Place the coated sample in a pH 4.5 buffer solution and stir magnetically at 200 rpm; after 30 min, pass it through a 200-mesh sieve. If the amount of material remaining on the sieve is ≤1.5 wt%, it is determined that 'dispersibility has been achieved'.

[0072] Requirements for recycling via composting and biodegradation: EN 13432:2000;

[0073] Final aerobic biodegradation degree of plastic materials under controlled composting conditions—CO2 analysis method: ISO 14855-1;

[0074] Determination of the degree of disintegration of plastic materials under laboratory-scale composting conditions: ISO 20200:2023;

[0075] DIN CERTCO "Home & Garden Compostable" and OK compost HOME certifications are based on: NF T51-800:2015;

[0076] Ecotoxicity assessment of compost products: OECD 208.

[0077] General preparation process for homemade PHA aqueous dispersion:

[0078] Step 1. Preparation of continuous phase: Add PVOH and alkyl polysaccharide surfactant to deionized water and stir at 80°C for 30 min to obtain a continuous phase solution.

[0079] Step 2. Melt the PHA powder at 160–170℃ to obtain molten PHA.

[0080] Step 3. Keep the continuous phase solution obtained in Step 1 at a constant temperature of 85–90℃, and slowly add the molten PHA obtained in Step 2 under a high shear disperser to obtain a crude emulsion.

[0081] Step 4. Homogenize the crude emulsion obtained in Step 3 using a high-pressure homogenizer at 300–600 bar 3–5 times to obtain a fine emulsion.

[0082] Step 5. Cool the fine emulsion obtained in Step 4 to 25°C and filter it through a 0.45μm filter. Adjust the solid content to 40%±2% to obtain PHA aqueous dispersion.

[0083] Step 6. Store the PHA aqueous dispersion obtained in Step 5 at 40℃ for 7 days and observe for no phase separation and particle size drift ≤10%.

[0084] Step 7. When using, add the PHA aqueous dispersion obtained in Step 6 to the corresponding embodiment step according to the mass parts based on solids. The pH of this dispersion is 6.5–7.5; adjust the pH of the main coating system to be ≤1.0 before adding it to the step.

[0085] Median particle size (D) in representative volume distribution 50 Example 6 has a particle size of 0.20 μm, and Example 7 has a particle size of 0.25 μm (according to ISO 13320:2020). Only Examples 6 and 7 of this invention contain PHA aqueous dispersions; this particle size index is not applicable to other examples.

[0086] General steps for paint preparation and coating:

[0087] Step 1. First, perform carbonate replacement and water washing on LDH: Add LDH powder to a 0.05–0.10 mol / L sodium hydroxide aqueous solution and stir for 30 min. After filtration, wash repeatedly with deionized water with a conductivity ≤5 μS / cm until Cl in the filtrate is reduced. - <5 mg / L; subsequently, the pretreated LDH was dispersed in deionized water (Cl... - ≤1 mg / L), stir for 30 min using a high shear disperser, adjust the pH to the target value with 0.5–1.0 mol / L sodium hydroxide aqueous solution or 1–2 wt% lactic acid aqueous solution, let stand for 10 min to obtain LDH suspension.

[0088] Step 2. Add the intercalating agent aqueous solution dropwise to the LDH suspension obtained in Step 1 at 40–60℃, stir for 0.5–2 h, and cool to 25℃ to obtain the intercalation mixture.

[0089] Step 3. Adjust the pH of the intercalation mixture obtained in Step 2 to 7–8, add the metal ion donor, and stir for 15–20 min to obtain a complex mixture.

[0090] Step 4. Pre-pass the CMC solution through OH... - Desalination treatment with type-3 anion exchange resin, so that Cl... - <5mg / L, add PVOH solution and pretreated CMC solution to the complex mixture obtained in step 3, add halogen-free additives, disperse for 10min, and obtain the finished coating.

[0091] Step 5. Apply the finished coating obtained in Step 4 to the paper substrate using a slot coater, controlling the dry coating amount to 2–6 g / m².

[0092] Step 6. Dry in a hot air channel at 80–120℃ and calender with a linear pressure of 60–200 kN / m. After standing at 23℃ and 50% RH for 24 hours, perform all tests.

[0093] Example:

[0094] Example 1: This example uses the formulation shown in Table 3 and is prepared according to the aforementioned general steps. Specific process parameters are as follows: pH is adjusted to 9.0 in step 1 and to 7.5 in step 3. Slit coating is used, with a linear speed of 300 m / min, a dry coating amount controlled at 2.5 g / m², and an oven temperature range of 90–110℃.

[0095] Example 2: The preparation process and parameters in this example are the same as in Example 1, except that the dry coating amount is different, which is 3.0 g / m².

[0096] Example 3: The preparation process and parameters in this example are the same as in Example 1, except that the dry coating amount is different, which is 4.0 g / m².

[0097] Example 4: The preparation process and parameters in this example are the same as in Example 1, except that the dry coating amount is different, which is 2.0 g / m².

[0098] Example 5: The preparation process and parameters in this example are the same as in Example 1, except that the dry coating amount is different, which is 6.0 g / m².

[0099] Example 6: The preparation process and parameters in this example are the same as in Example 1, except that the dry coating amount is different, which is 3.0 g / m².

[0100] Example 7: The preparation process and parameters in this example are the same as in Example 1, except that the dry coating amount is different, which is 3.0 g / m².

[0101] Example 8: This example uses the formulation of Example 2 as a base and adjusts the total amount of additives to 1.0 wt%. Slit coating is used, the linear speed is increased to 1200 m / min, the oven temperature is 100–110℃, and the dry coating amount is controlled at 3.0 g / m².

[0102] Table 3 Example Formulations:

[0103]

[0104] Comparative Examples (Unified Preparation Notes: Unless otherwise stated, all comparative examples were prepared without the dehalogenation pretreatment in step 1 and the CMC desalination treatment in step 4. General-purpose additives without special screening were used, and the process water did not contain Cl-.) - Limits; other coating and drying conditions are the same as in Example 1:

[0105] Comparative Example 1 (without intercalation): This comparative example uses the formulation in Table 4 and the preparation process is the same as in Example 1, except that the dry coating amount is different and is set to 3.0 g / m².

[0106] Comparative Example 2 (phytic acid coating): This comparative example was prepared using a two-step process; the total dry coating amount was 3.0 g / m².

[0107] Comparative Example 3 (Excess Iron Salt): This comparative example uses the formula in Table 4. The preparation process is the same as in Example 1, except that the dry coating amount is different and is set to 3.0 g / m².

[0108] Comparative Example 4 (using modified starch instead of PVOH / CMC): This comparative example uses the formula in Table 4, and the preparation process is the same as in Example 1, except that the dry coating amount is different and is set to 3.0 g / m².

[0109] Comparative Example 5 (8 parts excess PHA): This comparative example uses the formula in Table 4. The preparation process is the same as in Example 1, except that the dry coating amount is different and is set to 3.0 g / m².

[0110] Comparative Example 6 (without surface network): This comparative example uses the formulation in Table 4 and the preparation process is the same as in Example 1, except that the dry coating amount is different and is set to 3.0 g / m².

[0111] Comparative Example 7 (Removal of Metal Ion Donors): This comparative example uses the formulation in Table 4 (based on the formulation of Example 1, but with 0% aluminum lactate). The preparation process is the same as in Example 1, and the dry coating amount is 2.5 g / m².

[0112] Table 4 Comparative Example Formulations:

[0113]

[0114] Application example:

[0115] Each example and comparative example is a general formulation; for applications involving direct food contact, only the adjuvants (wetting agents and defoamers) are replaced, without changing the main formulation, solid content, coating and drying conditions.

[0116] Judgment criteria: Except for CEPI RLTM v3 / PTS, this document adopts the following acceptance thresholds: Cobb 60 ≤20g / m² indicates acceptable water absorption; Kit≥10 indicates acceptable oil resistance; 'WVTR / OTR increase ≤25%' after folding indicates acceptable mechanical durability.

[0117] Application Example 1: Top coating of high whiteness printing paper.

[0118] Experimental Description: 157 g / m² high-whiteness coated paper was selected. An 8 g / m² mineral densification undercoat was first pre-coated to achieve extremely high smoothness, followed by the application of the top coating for each example and comparative example. Comparative Example 2 employed a two-step coating process: first, coating and drying according to general procedures; then, 3.5 parts of phytic acid aqueous solution were sprayed onto the surface and treated with the same drying procedure at 80–120℃; the total dry weight for both steps was 3.0 g / m². Test conditions: OTR was 23℃, 0% RH; WVTR was 38℃, 90% RH; adhesion was tested according to ISO 2409:2020 (grades 0–5, 0 being optimal). OTR and WVTR tests were conducted using a flat sheet fixture. The samples were coated paper or paper / aluminum laminates, sealed with a backing, and the values ​​were taken after verifying the fixture leakage rate.

[0119] Table 5. Application effects of high-whiteness printing paper:

[0120]

[0121] Analysis: Examples 1-8 all exhibited excellent overall performance. At low coating weights of 2.0-6.0 g / m², all examples achieved an adhesion rating of 0 or 1, demonstrating a strong bond between the coating and the high-smoothness backing paper. The key color difference (ΔE) * All indicators were controlled at 1.0 or below, such as in Example 2 (0.6) and Example 4 (0.5), which were significantly better than Comparative Example 3 (ΔE) which used excessive iron salts. * 2.5) demonstrates the excellent ability of the formulation of this invention to maintain a high whiteness appearance. Regarding barrier properties, the WVTR of all examples was below 11.2 g / (m²·d), and the OTR was below 11.6 mL / (m²·d), meeting the high barrier requirements. In contrast, the unintercalated Comparative Example 1 and the metal-network-free Comparative Examples 6 and 7 showed significantly increased WVTR and OTR, highlighting the crucial role of the dual-scale structure of this invention in efficient barrier performance.

[0122] Application Example 2: Inner lining of dry food packaging.

[0123] Experimental Description: 120g / m² kraft paper was used, and the top coating was directly applied. In this application example, all samples used alkyl polysaccharide wetting agent (APG 215 UP, 0.20–0.30 parts) and waterborne polyether-modified silicone defoamer (0.05–0.10 parts). DISPERBYK-190 and TEGO Foamex 825 were not used. Test conditions: OTR was 23℃, 0% RH; WVTR was 38℃, 90% RH; Kit (oil resistance grade) was according to TAPPI T 559 cm-22. OTR and WVTR tests were conducted using a flat sheet fixture. The samples were coated paper or paper / aluminum laminates, sealed with a backing, and the values ​​were taken only after the fixture leakage rate was verified as acceptable.

[0124] Table 6 shows the application effects in the inner lining of dry goods packaging:

[0125]

[0126] Analysis: When applied to kraft paperboard, Examples 1-8 fully demonstrate its suitability as a liner for dry food products. All examples achieved an oil resistance rating of 9 or higher, with Examples 3 and 5 reaching 12, exhibiting excellent oil resistance. In the crucial mechanical durability test, all examples maintained a WVTR and OTR increase of ≤25% after 180° folding (e.g., Example 5 only ≤15%), and a 6-week room temperature oxygen rise of ≤0.4%, demonstrating the flexibility and long-term stability of the coating structure. Conversely, several comparative examples performed poorly: Comparative Examples 1, 2, and 6 achieved a KIT rating of only 5-6; Comparative Examples 1, 2, 6, and 7 all showed an increase of over 40% after folding, indicating that their structure was severely damaged after folding and lost its barrier function. This further verifies that the dual-scale synergistic structure of this invention provides efficient barrier properties while also ensuring folding resistance and oil resistance.

[0127] Application Example 3: Metallized vapor-deposited base paper sealing layer.

[0128] Experimental Description: 70g / m² special base paper for vapor deposition was used. After applying a top coating as a sealing layer, vacuum aluminum deposition was performed. The number of pinholes in the aluminum deposition was counted according to TAPPI T 538 om-21 "Determination of Pinhole Count in Aluminum Deposition by Refraction". The OTR (Optical Transmission Rate) of the laminate was tested at 23℃ and 0%RH. OTR and WVTR tests were conducted using a flat plate fixture. The sample was coated paper or a paper / aluminum laminate, sealed with a backing. The value was taken only after the fixture leakage rate was verified as acceptable.

[0129] Table 7 shows the application effects of this layer as a sealing layer for vapor-deposited base paper.

[0130]

[0131] Analysis: The coating of this invention is highly effective as a sealing layer for vapor-deposited base paper. All examples effectively sealed the pores of the base paper, reducing the pinhole count of the subsequent aluminum plating layer by 20% to 35%. This dense substrate resulted in extremely low OTR for the laminated material; the OTR of all examples was below 0.3 mL / (m²·d), with Examples 3, 5, and 7 achieving an ultra-high barrier level of <0.1 mL / (m²·d). All were rated "recyclable" by PTS Cat II. In contrast, Comparative Examples 1, 2, 6, and 7, lacking an effective dual-scale structure, showed only a small reduction in pinhole count, resulting in an OTR far exceeding 0.8 mL / (m²·d). Comparative Example 4 (modified starch) completely failed to form a film.

[0132] Application Example 4: Quantitative evaluation of wettability and resizing.

[0133] Experimental Description: This application example aims to systematically quantify two key properties of the coating: surface water resistance and actual resizing effect. All samples from Examples 1–8 and Comparative Examples 1–7 were selected for testing, with coating conditions identical to Application Example 1 (157 g / m² coated paper pre-coated underlayer). Surface water resistance was evaluated using two complementary indicators: first, the static water contact angle, measured according to ISO 19403-2:2024, characterizing the hydrophobicity of the coating surface; second, the Cobb... 60 Water absorption, determined according to ISO 535:2023, is used to quantify the coating's ability to resist water penetration within 60 seconds. Resizing performance is a core aspect of this invention, and rigorous quantitative testing was conducted in this example. First, the time required for the coating to unwrap the screen was recorded according to the "Unwrap Dispersion Test Definition" (pH 4.5 buffer, 200 rpm stirring, 30 min). Subsequently, a standard resizing process was performed according to the European Paper Industry Federation (CEPI) RLTM v3 method, and the total screen residue percentage (%) after passing through a 200-mesh sieve was precisely measured. This patent uses an internal acceptance threshold, i.e., total screen residue ≤ 7% is considered acceptable, and a comprehensive evaluation is given in conjunction with the PTS Cat II standard. Simultaneously, the apparent viscosity of each coating product (25°C, 100s) was recorded. -1 To assess whether its rheological properties are suitable for industrial coating.

[0134] Table 8. Quantitative evaluation results of wettability and resizing:

[0135]

[0136] Analysis: This application example quantifies the surface and recyclability of the coating. Regarding wettability, all embodiments exhibit a water contact angle ≥95° (e.g., 101° in Example 7), while Cobb... 60 The water absorption was ≤20 g / m² (only 15 g / m² in Examples 6 and 7), indicating that the coating provides efficient barrier properties while also exhibiting good water permeability resistance. Regarding the crucial resizing performance, all examples performed excellently, with the total CEPI screen residue rate strictly controlled within the range of ≤7.2% (5.9% in Example 4), and the screen-breaking time met the requirements (≤35 minutes), complying with the PTS Cat II recyclability standard. Conversely, several comparative examples failed the resizing test: the total screen residue rates of Comparative Examples 1, 2, and 6 were all above 14.8%; the screen residue rate of Comparative Example 5 (with excess PHA) also reached 18.2%; and the screen residue rate of Comparative Example 7 also exceeded the standard. This proves that the pH-responsive screen-breaking mechanism of the present invention is genuine and effective, and that structural defects or excessive components (such as PHA) will lead to resizing failure.

[0137] Application Example 5: Evaluation of total halogens and total metal content.

[0138] Experimental Description: The core objective of this application example is to verify the environmental friendliness and regulatory compliance of the coating, particularly addressing the growing global concerns regarding PFAS and heavy metals. Dry films (scraped from the substrate) from Examples 1–7 and Comparative Examples 1–6 were selected for chemical analysis. First, the total halogen content (mg / kg) in the coating was determined according to EN 14582:2016 (oxygen bomb combustion-ion chromatography). This indicator is used to screen for intentionally added chlorine-containing (e.g., PVDC) or fluorine-containing (e.g., PFAS) compounds; the target for this invention is ≤5 mg / kg. Simultaneously, all samples underwent specific screening for total organic fluorine (TOF). Secondly, this application example focuses on the total iron content in the coating. Since iron ions readily form dark complexes with polyphenols, leading to color differences in the coating (ΔE... * Increased iron content affects the appearance of high-whiteness paper. Therefore, inductively coupled plasma mass spectrometry (ICP-MS) was used to accurately determine the total iron content (mg / kg) in the dry film to verify the effectiveness of the technical approach of the present invention, which controls the total iron content to ≤10mg / kg to maintain high whiteness by selecting non-ferrous metal salts (such as aluminum lactate).

[0139] Table 9. Evaluation results of total halogens and metals:

[0140]

[0141] Analysis: This application example verifies the environmental friendliness and regulatory compliance of the coating. According to EN 14582 testing, the total halogen content in Examples 1–8 is ≤5 mg / kg (0.9–2.5 mg / kg), strongly demonstrating that the formulation of this invention does not contain halogen-containing durable chemicals such as PFAS or PVDC. Regarding metal content, by selecting non-ferrous metal ion donors such as aluminum lactate, the total iron content in Examples 1–4 and Examples 6–8 is controlled below 5 mg / kg. Even in Example 5, which uses ferric ammonium citrate, the total iron content is only 9.8 mg / kg, meeting the limit of ≤10 mg / kg and ensuring high whiteness. In contrast, Comparative Example 3, due to excessive iron salts, has a total iron content as high as 22.0 mg / kg, resulting in excessive color difference; Comparative Example 4 (using modified starch) has excessive total halogen content (85 mg / kg), verifying the advantages of the formulation of this invention in terms of safety and environmental protection.

[0142] Application Example 6: Storage stability and sieve residue.

[0143] This application example aims to evaluate the industrial compatibility and manufacturability of a coating formulation, focusing on its long-term stability under simulated storage and transportation conditions. The experimental design simulated batch-scale industrial production, with each sample (Examples 1-8 and Comparative Examples 1-7) prepared in a 20L process container. All samples were stored in a sealed, static environment at 25°C for up to 28 days. To dynamically monitor the coating's condition, samples were taken at five key time points: day 0 (initial), day 7, day 14, day 21, and day 28.

[0144] Test metrics include:

[0145] 1) pH value, used to monitor the chemical stability of the system;

[0146] 2) Apparent viscosity (25℃, 100s) -1 (), used to evaluate the stability of rheological properties and prevent excessive thickening or shear thinning;

[0147] 3) 200 mesh sieve residue (wt%) is a key indicator for assessing the cleanliness of the coating and whether agglomerates or impurities have been generated. It is crucial for preventing coating defects (such as streaks).

[0148] At the same time, the appearance of the coating is visually inspected at each test point to check for delamination, sedimentation or gelation.

[0149] The evaluation criteria are extremely stringent: pH drift ≤ 0.2, viscosity drift ≤ 10% within 28 days, and average residue on a 200-mesh sieve ≤ 0.05wt% are required to ensure that the coating meets the stringent requirements for factory acceptance and continuous production.

[0150] Table 10. Storage stability and sieve residue test results:

[0151]

[0152] Analysis: Storage stability is a key prerequisite for industrial applications. Data shows that Examples 1–8 exhibited extremely high stability during 28-day storage tests. All examples showed pH drift ≤0.18, apparent viscosity drift ≤9%, and the average residue on a 200-mesh sieve was strictly controlled at an extremely low level of ≤0.05wt%, with no layering or gelation observed in the coating appearance. This indicates that the formulation system of this invention possesses excellent chemical and physical stability, fully meeting the requirements of industrial supply and continuous production on high-speed coating machines. In contrast, several comparative examples showed significant defects: Comparative Examples 1, 2, 5, 6, and 7 were all deemed unqualified due to high residue or excessive viscosity drift (≥11%), increasing the risk of failure during application; Comparative Example 4 (modified starch) was extremely unstable, gelling after only 14 days. The data clearly demonstrates that the dual-scale structure of LDH interlayer intercalation and interparticle metal micronetwork is not only key to achieving high barrier properties and rapid desorption, but also the structural basis for ensuring high storage stability and low residue in the coating system.

[0153] Application Example 7: Dual-scale structure verification.

[0154] This application example is a key experiment to verify the core technology of this invention, the "dual-scale structure." The same substrate as in Application Example 1 (157 g / m² high-brightness coated paper pre-coated with an 8 g / m² mineral undercoat) was used to eliminate substrate differences. The top coatings of all Examples 1–8 and Comparative Examples 1–7 were applied and allowed to stand for 24 hours at standard temperature and humidity (23°C, 50% RH) to allow the coatings to fully mature.

[0155] This experiment aims to verify the results from both structural and performance perspectives.

[0156] Structural level: 1) Measure the index at "Scale One" (interlayer scale), namely the intercalation molar ratio α (anion / layer positive charge), obtained through acid-base titration-transformation algorithm, to verify the success and extent of intercalation; 2) Measure the key result index at "Scale Two" (interparticle scale), namely the median pore size D of the coating surface. 50 The density of the interparticle micronetwork was determined according to the capillary flow aperture tester method of ASTM F316-03(2019).

[0157] Performance aspects: The macroscopic barrier properties of the coating were measured (WVTR test was conducted at 38°C and 90% RH, and OTR test was conducted at 23°C and 0% RH) and recyclability (unwinding time and PTS Cat II assessment).

[0158] By comparing the embodiment (with dual scales) with various comparative examples in terms of structural parameters (α, D)50 The significant differences in both the barrier properties and macroscopic performance (WVTR / OTR, unblocking time) demonstrate that the synergistic effect of the two scales is the fundamental reason for achieving high barrier properties and fast unblocking.

[0159] Table 11. Results of dual-scale validation:

[0160]

[0161] *Note: α is the molar ratio of anions to positive charge of the plate calculated by the sodium chloride / potassium nitrate exchange-acid-base titration method;

[0162] Analysis: This invention achieves a comprehensive performance of high barrier properties, high whiteness, and rapid resizing at low basis weight through a dual-scale structure design of LDH interlayer intercalation and surface metal-polyphenol / phosphate micronetwork. Comparative Examples 1–7 (dual-scale structure, surface pore size D) 50 ≤75nm) compared with Comparative Example 1 (no intercalation), Comparative Example 2 (surface coating), Comparative Example 6, and Comparative Example 7 (intercalation only, no metal network, D) 50 ≥95nm), the former performs better in terms of macroscopic barrier properties (WVTR / OTR) (see Table 5 of Application Example 1 for details), while significantly shortening the unwinding time, and all PTS are recyclable. This proves that pre-inserting multiple anions into the LDH interlayer (scale one) and constructing an interparticle metal micronetwork (scale two) is the structural basis for achieving efficient channel blocking (low pore size) and reversible unwinding, and both are indispensable. Comparing Comparative Example 3 (excess iron salt) with the examples, it is demonstrated that limiting the total iron content is the key to resolving the contradiction between high barrier properties and high whiteness. Comparative Example 4 (starch) and Comparative Example 5 (excess PHA) respectively verify the importance of the selection of film-forming aids and the upper limit of PHA dosage.

[0163] Application Example 8: Compostability Evaluation.

[0164] Experimental Description: This application example aims to comprehensively evaluate the environmental friendliness of coatings (Examples 1-8 and Comparative Examples 1-7) according to key standards such as EN 13432, particularly their biodegradability and ecotoxicity under industrial and domestic composting conditions. Test subjects included intact coated paper (for disintegration rate testing) and the top dry film separated from the substrate (for biodegradability and chemical analysis).

[0165] Industrial composting performance (Tables 12 and 13): The disintegration rate of the coated paper was tested under controlled industrial composting conditions (58°C) according to ISO 20200 standards, expressed as the percentage passing through a 2mm sieve after 12 weeks. Simultaneously, the final aerobic biodegradability of the top dry film was tested at 58°C according to ISO 14855-1 standards (CO2 release method) for 180 days, with a pass rate of ≥90% biodegradability.

[0166] Home composting performance (Tables 14 and 15): Simulating a home composting environment (nominal temperature 28℃), the disintegration rate of the coated paper was tested after 26 weeks (through a 2mm sieve). Simultaneously, the biodegradability of the top dry film was tested using the CO2 release method at 28±2℃ over a period of 12 months, with a pass rate of ≥90% biodegradability.

[0167] Ecotoxicity assessment (Table 16): Following OECD 208 (Plant Germination and Growth Test), the products of industrial compost were mixed with the substrate at ratios of 25% and 50%, and mustard and barley were planted. The germination index (GI) and plant dry weight were compared to assess whether the compost products inhibited plant growth (i.e., toxicity).

[0168] Table 12 Industrial Composting—Disintegration Rate (whole coated paper, ISO 20200, 12 cycles, 2mm sieve):

[0169]

[0170] Table 13 Industrial composting—biodegradation rate (top dry film, ISO 14855-1, 58℃, CO2 method):

[0171]

[0172] Table 14 Home Composting - Decomposition Rate (whole coated paper, nominal 28°C, 26 cycles, 2mm sieve):

[0173]

[0174] Table 15 Home Compost - Biodegradation Rate (Top Dry Film, CO2 Method, 28±2℃, 12 Months):

[0175]

[0176] Table 16 Ecotoxicity (OECD 208; Compost products blended with substrate 25% / 50%):

[0177]

[0178] Analysis: The data from this application example fully demonstrate that the coating of the present invention (Examples 1-8) has excellent environmental compatibility and fully meets the stringent standards for industrial and household composting.

[0179] Compostability: All samples from Examples 1-8 successfully passed both industrial composting and home composting tests. Under industrial composting conditions, the decomposition rate of all examples was >98% (Table 12), and the biodegradability was >90% (Table 13), with Example 7 reaching 95.1%. Under more stringent home composting conditions, the decomposition rate of all examples was >92% (Table 14), and the biodegradability was >90% (Table 15), with Example 7 reaching 96.8%.

[0180] Comparative Examples: In contrast, several comparative examples exhibited deficiencies in biodegradability. Comparative Example 1 (no intercalation), Comparative Example 2 (surface coating), Comparative Example 3 (excess iron salt), Comparative Example 6 (no surface network), and Comparative Example 7 (metal donor removal) all failed to reach the 90% biodegradability threshold in industrial and household composting (Tables 13 and 15). This strongly demonstrates that the "dual-scale structure" of this invention (i.e., synergy between interlayer intercalation and interparticle micronetwork) is crucial for achieving complete biodegradability of the coating; the absence of either key structural feature will lead to incomplete biodegradation.

[0181] Ecotoxicity: The compost products of all samples (including examples and comparative examples) passed the OECD 208 ecotoxicity test. Germination index (GI) and plant dry weight both showed that the compost products had no inhibitory effect on the growth of mustard and barley, indicating that the coating material and its degradation products are safe and harmless to the soil environment.

[0182] Analysis of experimental results:

[0183] This invention achieves high barrier properties, high whiteness, and rapid resizing at low basis weight through a dual-scale structural design of LDH interlayer intercalation and surface metal-polyphenol / phosphate micronetwork. Comparing Examples 1–7 with Comparative Examples 1 (no intercalation), 2 (surface coating), and 6 (no surface network), the former exhibits significantly lower WVTR / OTR values ​​and a much shorter acid hydrolysis time. This demonstrates that pre-intercalating multiple anions into the LDH interlayer to construct "interlayer sites" is the structural basis for achieving efficient channel blocking and reversible network de-networking, rather than simple physical blending. Examples 4 (lower limit) and 5 (upper limit) verify the effectiveness of the formulation range, showcasing the high efficiency and good process tolerance of the technical solution. Comparing Examples 1 and 3, the increased intercalation equivalent slightly improves barrier performance, but significantly prolongs the acid hydrolysis time, revealing a trade-off between interlayer crosslinking density and de-networking speed. Comparing Comparative Example 3 (excessive iron salt content) with the various examples demonstrates that limiting the total iron content to ≤10mg / kg and prioritizing the use of aluminum salts is key to resolving the contradiction between barrier properties and high whiteness appearance. Comparative Example 4, which used modified starch to replace the PVOH / CMC combination, resulted in a brittle coating and poor film-forming properties, indicating that the PVOH / CMC system not only provides basic film-forming properties but also has a good synergistic effect with the LDH intercalation structure. Examples 6 and 7 show that adding PHB or PHBV within the specified dosage can further improve barrier performance under high humidity conditions, while Comparative Example 5 shows that excessive PHA dosage leads to resizing difficulties, verifying the rationality of the upper limit of dosage.

[0184] In summary, this invention, through a unique "dual-scale synergistic barrier" structural design, and with precise control over components, proportions, processes, and key structural parameters, has successfully developed a novel paper barrier coating that integrates multiple excellent properties such as high barrier properties, high whiteness, and rapid re-pulping capability. This provides a technologically advanced and commercially viable solution for sustainable paper-based packaging.

[0185] 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 compostable, re-pulpable mineral-based bi-scale barrier coating, characterized in that, The coating comprises, by formulation solids: Layered double hydroxide 20 - 70 parts, the charge density of the layer of the layered double hydroxide being 0.25 - 0.45 e / nm2, the volume distribution D 50 0.3 - 2.0 pm; 0.5-10 parts of an intercalant selected from one or more of a class of poly-anions; the class of poly-anions includes polyphosphates and polyphenols / phenolic acids; the polyphosphates are selected from one or more of phytic acid, pyrophosphate, tripolyphosphate, hexametaphosphate; the polyphenols / phenolic acids are selected from one or more of gallic acid, protocatechuic acid, ellagic acid, ferulic acid, p-hydroxybenzoic acid, tannic acid, and the molar ratio of anions in the intercalant to the positively charged layers of the layered double hydroxide is 0.2-0.8; 0.05-2.0 parts of a metal ion donor that is a food contact approved metal organic acid salt selected from one or more of lactic acid, citric acid, tartaric acid, malic acid, gluconic acid or succinic acid salts of aluminum, iron, magnesium, calcium, zinc, zirconium or titanium; 1-8 parts of a water soluble film forming aid that is a combination of polyvinyl alcohol and carboxymethyl cellulose; ≤1.0 wt% of an aid; The coating has a solids content of 25-45 wt% and a pH of 7-10; After coating and drying, a top coat layer of 2-6 g / m2 is formed, which meets: disintegration within 30 min at pH ≤ 5, 25°C; water vapor transmission rate ≤ 12 g / (m2·d) at 38°C, 90% RH; oxygen transmission rate ≤ 12 mL / (m2·d) at 23°C, 0% RH; total iron ≤ 10 mg / kg; in D 65 ΔE compared to uncoated base paper under standard illuminant and 10° standard observer conditions * ≤ 1.0; meets European Federation of Paper and Cel lulose Industries Laboratory Test Method for Recyclability, 3rd Edition; meets PTS-RH021:2012 Cat II method testing with an evaluation conclusion of recyclable; and no addition of perfluoro- and polyfluoroalkyl substances and polyvinylidene chloride.

2. The compostable, re-pulpable mineral-based bi- scale barrier coating of claim 1, wherein, The top coat has a water vapor transmission rate of ≤10 g / (m2·d) at 38°C, 90% RH and an oxygen transmission rate of ≤10 mL / (m2·d) at 23°C, 0% RH.

3. The compostable, re-pulpable mineral-based bi-scale barrier coating of claim 1, wherein, In D 65 The top coating has a color difference ΔE * ≤ 0.8 compared to the uncoated base paper under standard illuminant and 10° standard observer conditions.

4. The compostable, re-pulpable mineral-based bi-scale barrier coating of claim 1, wherein, The coating further comprises a polyhydroxyalcanoate aqueous dispersion 0.5 - 5.0 parts, having a volume distribution median particle size D50 measured according to ISO 13320:2020 of 0.1 - 1.0 pm, and the polyhydroxyalcanoate comprises less than 10 wt% of the total solids of the formulation; the polyhydroxyalcanoate 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), and C6-C18 medium chain polyhydroxyalcanoates and copolymers thereof. 50 The coating further comprises a polyhydroxyalcanoate aqueous dispersion 0.5 - 5.0 parts, having a volume distribution median particle size D50 measured according to ISO 13320:2020 of 0.1 - 1.0 pm, and the polyhydroxyalcanoate comprises less than 10 wt% of the total solids of the formulation; the polyhydroxyalcanoate 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), and C6-C18 medium chain polyhydroxyalcanoates and copolymers thereof.

5. The compostable, re-pulpable mineral-based bi-scale barrier coating of claim 1, wherein, The layered double hydroxide is selected from one or more of Mg-Al, Zn-Al, Ca-Al, Mg-Fe or Zn-Fe types and combinations thereof; when the Mg-Al type is used, the molar ratio of Mg / Al is 2:1-4:

1.

6. The compostable, re-pulpable mineral-based bi-scale barrier coating of claim 1, wherein, The metal ion donor is selected from one or more of lactic acid, citric acid, tartaric acid, malic acid, gluconic acid or succinic acid salts of aluminum, iron, magnesium, calcium, zinc, zirconium or titanium.

7. The compostable, re-pulpable mineral-based bi-scale barrier coating of claim 1, wherein, When the organic acid salt of magnesium or calcium is used as the metal ion donor, each is used in an amount of ≤0.2 parts and passes the 24 h storage stability test at pH 7-8 and the 200 mesh residue test.

8. The compostable, re-pulpable mineral-based bi-scale barrier coating of claim 1, wherein, The surface pore size distribution D of the top coat 50 ≤ 80 nm, determined according to ASTM F316-03 (2019).

9. The compostable, re-pulpable mineral-based bi-scale barrier coating of claim 1, wherein, The water soluble film forming aid has a mass ratio of polyvinyl alcohol to carboxymethyl cellulose of 3:1-15:1 and a total amount of the film forming aid of 2-6 parts.

10. The compostable, re-pulpable mineral-based bi-scale barrier coating of claim 1, wherein, The apparent viscosity at 25°C, at a shear rate of 100 s -1 100 - 1500 mPa-s.

11. The compostable, re-pulpable mineral-based bi- scale barrier coating of claim 1, wherein, The top coat has a total halogen content of ≤5 mg / kg as determined by EN 14582.

12. A paper material, characterized by The paper material comprises a top coat formed from the compostable, recyclable, mineral based, bi-scale barrier coating according to claim 1.

13. The paper material according to claim 12, characterized in that The paper material has a Bekk smoothness of ≥500 s and / or an increase in water vapor transmission rate of ≤25% and an increase in oxygen transmission rate of ≤25% after one 180° fold; tested according to PTS-RH 021:2012 Cat II method with a recyclable conclusion.

14. The paper of claim 12, wherein, The paper material has an increase in water vapor transmission rate of ≤20% and an increase in oxygen transmission rate of ≤20% after one 180° fold.

15. A method of preparing the coating according to claim 1, characterized in that, The method of preparation comprises: Step 1. stirring the layered double hydroxide and the intercalant in an aqueous medium at pH 8-10 at 40-60°C for 0.5-2 h to obtain a mixture; Step 2. adjusting the pH of the mixture obtained in step 1 to 7-8, adding the metal ion donor and stirring for 20 min to obtain a complex mixture; Step 3. adding the water soluble film forming aid to the complex mixture obtained in step 2 and stirring for 20 min to obtain a coating mixture; Step 3. Add water-soluble film-forming additives and auxiliaries to the complex mixture obtained in Step 2 and mix uniformly to obtain a finished coating; Step 4. Apply the finished coating obtained in Step 3 to a paper substrate at a dry coating amount of 2-6 g / m2and dry at 60-120°C to form a top layer coating.

16. The method of claim 15, wherein, The intercalating agent in step 1 is previously prepared into an aqueous solution with a concentration of 0.1-0.5 mol / L, and mixed with the layered double hydroxide under the condition of a shear rate of 1000-3000 s -1 -1.

17. The preparation method according to claim 15, characterized in that, After the step 4, the coated paper material is subjected to soft calendering at a line pressure of 60-200 kN / m.

18. Use of the coating according to claim 1 in the following paper-based products: food contact packaging and dry goods packaging inner liner, paper cup and bowl inner wall barrier layer, beverage cup outer wall anti-condensation layer, metallized evaporation base paper sealing layer, heat-sealable paper pre-coating layer, flavor and mineral oil migration barrier layer, mailing and express packaging barrier top layer coating.

19. Use of the compostable, re-pulpable mineral-based bi- scale barrier coating according to claim 1 in a metallized evaporated base paper, characterized in that, The oxygen transmission rate of the laminated material obtained by vacuum aluminum plating after being sealed by the coating is <0.2 mL / (m2·d) at 23°C, 0% RH.

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