PHA water-based water-resistant coated pulp molded seedling pot containing inorganic fillers and blended polymers and its preparation method

Abstract

This invention discloses a PHA water-based water-blocking coated pulp molded seedling pot containing inorganic fillers and blended polymers, and its preparation method, belonging to the technical fields of seedling containers, pulp molding, and water-based water-blocking coatings. This invention uses polyhydroxyalkanoates combined with sheet-like inorganic fillers to construct a dense water-based barrier layer and innovatively designs a sidewall drainage channel connecting to the bottom. Through a differentiated coating structure, this invention breaks the deadlock between moisture softening during the seedling stage and limited root penetration after transplanting, achieving a precise balance between excellent wet strength and free root growth. This solution eliminates fluorine-containing additives, ensuring the product's biodegradability throughout its entire life cycle.

Description

Technical Field

[0001] This invention belongs to the technical field of seedling containers, pulp molding and water-based water-blocking coatings, specifically relating to PHA water-based water-blocking coated pulp molding seedling pots containing inorganic fillers and blended polymers and their preparation methods. Background Technology

[0002] Pulp molding seedling pots, made primarily of renewable fibers, offer advantages such as potted transplanting, resource-based disposal, and reduced plastic waste pressure. However, under conditions of spraying, bottom irrigation, or high-frequency watering, the capillary conduction and swelling of the fiber network can lead to a decrease in wet strength, making it prone to sidewall collapse, pot rim cracking, pulp shedding, and breakage during handling.

[0003] To improve water resistance, existing solutions often employ full-coverage high-barrier coatings or strong densification treatments. While these solutions can improve short-term water resistance, they may create a root-blocking interface after transplanting, restricting root penetration and slowing down the disintegration of the container in soil or compost environments. Furthermore, solvent-based coatings pose volatile organic compound (VOC) emissions and safety risks, making them unsuitable for greenhouse seedling cultivation.

[0004] Among existing publicly available technologies, one type of solution targets paper-based barrier coatings. For example, CN120026524B discloses a method of combining polyhydroxyalkanoates (PHA) with polybutylene adipate terephthalate (PBAT) and polyvinyl alcohol (PVA, also known as PVOH) to form an aqueous emulsion for paper-based barrier applications. Another disclosed technology involves preparing a biodegradable polymer aqueous dispersion by melt blending and dispersing in an aqueous polyvinyl alcohol solution, such as WO2017151595A1. Other published documents and patents focus on the preparation and application of PHA aqueous dispersions or emulsions themselves. For example, CN101538400A discloses an aqueous latex containing polyhydroxyalkanoates, its preparation method, and its application; CN112867766A discloses a biodegradable coating based on an aqueous PHA dispersion. There are also publicly available patent records of technologies disclosed by Dubaicheng New Materials Technology (Shanghai) Co., Ltd., including PHA / PVA nano-scale paper-based barrier emulsion, PHA heat-sealing barrier coating, PHA nano-aqueous suspension, and pure bio-based PHA aqueous dispersion.

[0005] The aforementioned solutions primarily target objectives such as packaging barrier or coating dispersion stability, or employ a continuous high-barrier full-coverage approach. However, in seedling scenarios, issues may arise such as restricted root penetration due to continuous full-coverage coating, and insufficient wet structural stability caused by reducing coating amount. Furthermore, with increasing concern about persistent environmental pollutants, traditional fluorinated waterproofing agents or additives that may introduce fluorine pollution are restricted in seedling containers. There is a need to develop solutions that are free of perfluorinated and polyfluoroalkyl substances (PFAS) and allow for the extraction of organic fluorine (EOF) with controllable risks. Therefore, a water-based, scalable paper-based seedling container technology is required that balances wet stability during the seedling stage with controllable disintegration during transplanting or composting, and that allows for designable windows in coating formulation parameters and structured flow-guiding coating. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a PHA water-based water-resistant coated pulp molded seedling pot containing inorganic fillers and blended polymers, and a method for preparing the same.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a pulp molded seedling tray, comprising: a container body, which is a three-dimensional fiber-based structure molded from pulp, the container body having side walls, a bottom, and a rim; a drainage hole, a through hole disposed at the bottom; and a polyhydroxyalkanoate (PHA) water-based water-blocking coating disposed on the surface of the container body and covering the outer surface of the side walls, the PHA water-based water-blocking coating comprising a water-blocking surface coating, the water-blocking surface coating being formed by coating with an aqueous coating composition comprising PHA, flake-like inorganic fillers, and a second polymer, followed by drying to form a film, and having a water-blocking surface coating adjacent to and having a water-blocking surface coating on the differentiated coating area. In the outer surface region of the sidewall with a continuous PHA water-based water-blocking coating, the dry film coating weight per unit area of ​​the water-blocking surface coating is 30 to 120 g / m², for example, 30 g / m², 35 g / m², 45 g / m², 50 g / m², 60 g / m², 90 g / m², 100 g / m², 110 g / m², or 120 g / m²; a differentiated coating region is provided on the sidewall, the differentiated coating region having one or a combination of the following characteristics relative to the adjacent outer surface region of the sidewall with a continuous PHA water-based water-blocking coating: lower coating coverage; per unit area The dry film coating coverage is lower; the apparent coating thickness is lower; the coating continuity is interrupted; wherein, the differentiated coating area includes a strip-shaped flow channel area that extends continuously from the basin opening to the bottom after being spread on the outer surface of the sidewall, and the area of ​​the strip-shaped flow channel area after being spread on the outer surface of the sidewall accounts for 1% to 30% of the total area of ​​the outer surface of the sidewall, for example, 1%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 25% or 30%; the strip-shaped flow channel area is adjacent to and has the continuous PHA water-based water-blocking coating on the outer surface area of ​​the sidewall. The ratio of the dry film coating amount per unit area is ≤0.80, for example, 0.20, 0.30, 0.40, 0.45, 0.50, 0.55, 0.60, 0.75 or 0.80, or the ratio of the apparent thickness of the strip-shaped flow channel area to the coating of the adjacent sidewall outer surface area having the continuous PHA water-based water-blocking coating is ≤0.80, for example, 0.20, 0.30, 0.40, 0.45, 0.50, 0.55, 0.60, 0.75 or 0.80; the strip-shaped flow channel area is connected to the bottom outer surface area around the outer edge of the drain hole.

[0009] The PHA is selected from one or a combination of the following: short-chain polyhydroxy fatty acid esters; medium- and long-chain polyhydroxy fatty acid esters; copolymer polyhydroxy fatty acid esters containing short-chain monomer units and medium- and long-chain monomer units; or blends, copolymers, or modifiers of any two or more of the above PHAs; the short-chain polyhydroxy fatty acid ester is selected from one or more of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB); the medium- and long-chain polyhydroxy fatty acid ester is selected from one or more of poly(3-hydroxyhexanoate), poly(3-hydroxyheptanoate), poly(3-hydroxyoctanoate), poly(3-hydroxynonanoate), poly(3-hydroxydecanoate), poly(3-hydroxyundecanoate), poly(3-hydroxydodecanate), poly(3-hydroxytridecanate), and poly(3-hydroxytetradecanoate).

[0010] The sheet-like inorganic filler is selected from one or more of the following categories: layered silicate fillers, carbonate fillers, sulfate fillers, silicate or aluminosilicate fillers, oxide or hydroxide fillers; the layered silicate fillers include talc, kaolin, mica, montmorillonite fillers, vermiculite, sepiolite, or attapulgite; the carbonate fillers include calcium carbonate or magnesium carbonate; the sulfate fillers include barium sulfate or calcium sulfate; the silicate or aluminosilicate fillers include diatomaceous earth, wollastonite, zeolite, or aluminum silicate; the oxide or hydroxide fillers include silicon dioxide, titanium dioxide, zinc oxide, aluminum oxide, aluminum hydroxide, or magnesium hydroxide; the median particle size D of the sheet-like inorganic filler is... 50 The micrometer size is from 0.01 to 15 μm, for example 0.01 μm, 0.05 μm, 0.1 μm, 0.5 μm, 1.0 μm, 2.0 μm, 5.0 μm, 10.0 μm or 15.0 μm, and the mass ratio of the micrometer size to the dry PHA solid is from 0.80:1 to 2.00:1, for example 0.80:1, 0.90:1, 1.00:1, 1.10:1, 1.20:1, 1.50:1, 1.80:1 or 2.00:1.

[0011] The aqueous coating composition comprises a second polymer, which is a biodegradable polymer selected from one or more of polylactic acid (PLA), polybutylene succinate (PBS), polycaprolactone (PCL), polyglycolic acid (PGA), or thermoplastic starch (TPS); the mass ratio of the second polymer to the dry solids of the PHA is from 0.02:1 to 1.50:1, for example, 0.02:1, 0.10:1, 0.40:1, 0.50:1, 0.60:1, 0.80:1, 1.00:1, 1.20:1, or 1.50:1.

[0012] The extractable organic fluoride content in the seedling pot was tested according to the test method T / CNFIA 189-2024 and the result was not detected. The detection limit of the test method is ≤5mg / kg. Among them, not detected is determined by the extractable organic fluoride test result being less than the detection limit of the test method.

[0013] The aqueous coating composition comprises a dispersing and stabilizing component and an additive; the dispersing and stabilizing component is one or more of anionic, nonionic, or amphoteric surfactants; the additive is selected from one or more of toughening agents, wax emulsions, hydrophobic additives, rheology modifiers, wetting agents, defoamers, film-forming aids, crosslinking agents, adhesion promoters, bactericides and preservatives, pH adjusters, or freeze-thaw stabilizers.

[0014] The PHA water-based water-blocking coating is a multi-layer coating structure, including a sealing bottom coating disposed on the surface of the container body and a water-blocking top coating disposed outside the sealing bottom coating. The water-blocking top coating is a coating containing PHA, sheet-like inorganic filler and a second polymer. The sealing bottom coating is formed by a water-based bio-based film-forming material or a biodegradable film-forming material. The dry film coating weight per unit area of ​​the sealing bottom coating is 5 to 30 g / m², for example, 5 g / m², 10 g / m², 15 g / m², 20 g / m², 25 g / m² or 30 g / m².

[0015] The PHA water-based water-blocking coating is a gradient coating and meets the following conditions: the dry film coating per unit area in the basin opening region 0–15 mm from the basin opening edge is greater than the dry film coating per unit area in the middle area of ​​the side wall 15–60 mm from the basin opening edge.

[0016] The width of the strip-shaped flow guiding channel area after unfolding on the outer surface of the sidewall is 1 to 15 mm, for example, 1 mm, 1.5 mm, 2 mm, 3 mm, 5 mm, 8 mm, 10 mm, 12 mm or 15 mm, and when there are two or more strip-shaped flow guiding channel areas, the edge spacing between two adjacent strip-shaped flow guiding channel areas is 3 to 50 mm, for example, 3 mm, 6 mm, 8 mm, 11 mm, 12 mm, 19 mm, 25 mm, 30 mm, 40 mm or 50 mm; the strip-shaped flow guiding channel Differentiated units are provided within the area. The differentiated units are one or a combination of the following: lattice-shaped, mesh-shaped, microporous, annular, or spiral. The equivalent circle diameter corresponding to the projected area of ​​the lattice-shaped differentiated unit after unfolding on the outer surface of the sidewall is 0.5 to 8 mm, for example, 0.5 mm, 0.8 mm, 1.0 mm, 2.0 mm, 3.0 mm, 5.0 mm, or 8.0 mm, and the lattice spacing is 1 to 30 mm, for example, 1 mm, 3 mm, 8 mm, 15 mm, 20 mm, or 30 mm.

[0017] The ratio of the dry film coating amount per unit area of ​​the differentiated coating area to that of the adjacent sidewall outer surface area with continuous PHA water-based water-blocking coating is ≤0.60, for example, 0.20, 0.30, 0.40, 0.55, or 0.60; or the ratio of the apparent coating thickness of the differentiated coating area to that of the adjacent sidewall outer surface area with continuous PHA water-based water-blocking coating is ≤0.60, for example, 0.20, 0.30, 0.40, 0.45, 0.50, or 0.60; and the bottom outer surface area around the outer edge of the drain hole is an uncoated area, or the ratio of the dry film coating amount per unit area of ​​the bottom outer surface area around the outer edge of the drain hole to that of the adjacent sidewall outer surface area with continuous PHA water-based water-blocking coating is ≤0.60, or the continuity of the PHA water-based water-blocking coating is interrupted at the edge of the drain hole.

[0018] The base fiber raw material of the container body includes one or more of wood pulp, bamboo pulp, herbaceous plant fiber pulp or regenerated fiber pulp, wherein the herbaceous plant fiber pulp includes bagasse pulp, straw pulp, reed pulp or hemp pulp; the regenerated fiber pulp includes waste paper pulp, wherein the waste paper pulp includes newspaper-based regenerated fiber pulp; and the container body further contains lignin or lignin derivatives, the amount of which is added is from 0.1wt% to 30wt% based on oven-dry fiber, for example 0.1wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt% or 30wt%.

[0019] Cobb on the side wall of the seedling pot 60 ≤15g / m²; the ratio of the wet compressive strength of the seedling pot after soaking in deionized water for 24 hours to the dry compressive strength of the same batch is ≥80%; and the anti-softening time is ≥120 hours; the static water contact angle of the outer surface of the side wall of the seedling pot is ≥110°; the dry cross-cutting grade of the outer surface of the seedling pot is 0, and the wet cross-cutting grade is 0 after soaking in deionized water for 24 hours; the abrasion weight loss of the outer surface of the seedling pot is ≤5mg.

[0020] The present invention also provides a method for preparing the above-mentioned pulp molding seedling pot, comprising the following steps:

[0021] Step 1. Pulp preparation: Mix the fiber raw material with deionized water and dissociate it using a high-speed shear disperser for 20 minutes to obtain a pulp suspension.

[0022] Step 2. Wet molding: Inject the pulp suspension obtained in Step 1 into the molding mold, turn on the vacuum pump to form a wet blank.

[0023] Step 3. Dehydration and drying: After pressing and dehydrating the wet blank obtained in step 2, place it in a forced-air drying oven to dry and obtain a preformed blank.

[0024] Step 4. Hot pressing and shaping: The preform obtained in step 3 is placed in a hot press for hot pressing and shaping to obtain a container body with side walls, bottom and rim.

[0025] Step 5. Conditioning: Place the container body obtained in Step 4 in a constant temperature and humidity chamber to condition the moisture content to 1wt%–15wt%, for example, 1wt%, 5wt%, 10wt%, 12wt% or 15wt%. The moisture content is expressed as a mass fraction and determined according to GB / T 462-2023 to obtain the container body to be coated.

[0026] Step 6. Preparation of composition: The PHA aqueous dispersion, the sheet-like inorganic filler, and the second polymer are added to a high-speed shear disperser and dispersed at 20–60°C to obtain an aqueous coating composition, wherein the second polymer is a biodegradable polymer selected from one or more of polylactic acid (PLA), polybutylene succinate (PBS), polycaprolactone (PCL), polyglycolic acid (PGA), or thermoplastic starch (TPS);

[0027] Step 7. Coating: The aqueous coating composition obtained in step 6 is coated onto the outer surface of the container body to be coated obtained in step 5 to form a wet coating and obtain a coated part.

[0028] Step 8. Forming a Differentiated Area: During the coating process in Step 7, a masking or differential deposition method is used to form a strip-shaped flow channel area that extends continuously from the rim to the bottom of the coated part after the sidewall of the part is expanded on the outer surface of the sidewall, thus creating a differentiated coating area and obtaining a differentiated coated part.

[0029] Step 9. Film Formation and Punching: After drying the differentiated coating obtained in Step 8 into a film, a punch is used to punch holes at the bottom to form drainage holes, and the bottom outer surface area around the outer edge of the drainage holes is connected to the strip-shaped flow channel area to obtain a pulp molded seedling pot; wherein, due to the punching and cutting process, the continuity of the polyhydroxyalkanoate water-based water-blocking coating at the edge of the drainage hole is interrupted, forming an exposed fiber substrate interface;

[0030] Alternatively, during the coating process in step 7, a pre-defined area for the bottom drainage hole can be reserved to avoid coating. After the differentiated coating obtained in step 8 is dried into a film, a punch is used to punch holes in the pre-defined area for the drainage hole to form drainage holes. The bottom outer surface area around the outer edge of the drainage hole is connected to the strip-shaped flow channel area to obtain a pulp molded seedling pot.

[0031] Compared with the prior art, the following significant advantages can be obtained by using the present invention:

[0032] Balancing water resistance and root penetration: This invention provides a growth breakthrough for plant roots while ensuring the water resistance performance of the main body of the seedling pot by setting a differentiated coating area (strip-shaped flow channel) with a specific proportion and connectivity on the side wall, thus balancing the water resistance stability during the seedling period and the root penetration ability after transplanting.

[0033] Significantly improves wet strength: The water-blocking coating constructed with PHA and sheet-like inorganic fillers significantly improves the resistance to wet softening and wet strength of pulp molded seedling pots through the physical barrier of the fillers and the film-forming properties of PHA, preventing collapse during the seedling process.

[0034] Fluorine-free, environmentally friendly and safe: This invention strictly controls the fluorine content in the dispersed and stable components to ensure that extractable organic fluorine (EOF) in the final product is undetectable, meeting green and environmental protection requirements and avoiding the risk of PFAS pollution;

[0035] Fully biodegradable: All materials used in this invention are bio-based or biodegradable, which can be completely degraded after transplanting, without causing pollution to the soil environment, thus achieving the sustainability of agricultural production. Attached Figure Description

[0036] Figure 1 This is a partial cross-sectional view of the pulp molding seedling tray described in this invention.

[0037] In the diagram, 1-Pulp molded seedling pot; 2-Container body (referring to the fiber-based three-dimensional structure substrate molded from pulp); 3-Sealing bottom coating (the bottom coating located on the outer surface of the container body and inside the water-blocking top coating); 4-Drainage hole; 5-Water-blocking top coating (part of the polyhydroxyalkanoate water-based water-blocking coating, located in most areas of the outer wall); 6-Strip-shaped flow channel area; 7-Pot opening. Detailed Implementation

[0038] 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.

[0039] Figure 1A partial cross-sectional view of a pulp molding seedling pot 1 according to an embodiment of the present invention is shown. The seedling pot is made of a container body 2 with a three-dimensional structure based on a fiber base. It has a pot opening 7 at the top and a through drainage hole 4 at the bottom. A coating structure is provided on the surface of the container body 2, wherein a sealing bottom coating 3 is formed on the outer surface, and a polyhydroxyalkanoate water-resistant coating is formed on the outside of the sealing bottom coating 3. The outer surface coating includes a water-resistant surface coating 5 with high barrier properties distributed in most areas of the sidewall, and a strip-shaped flow channel area 6 that extends continuously from the pot opening 7 to the bottom on the sidewall and communicates with the area around the outer edge of the drainage hole 4. This area is a differentiated coating area with different coating characteristics.

[0040] Main reagents and raw materials:

[0041] Table 1. Names, product models / specifications, and manufacturers / sources of the main raw materials used in the examples and comparative examples:

[0042]

[0043] Main analytical and testing instruments:

[0044] Table 2 mainly analyzes the names, models, and manufacturers / sources of the testing instruments:

[0045]

[0046] Main testing standards and methods:

[0047] Water absorption test: Refer to standard GB / T 1540-2002 "Determination of water absorption of paper and paperboard - Koebner method".

[0048] Freeness test: Refer to standard GB / T 3332-2004 "Determination of pulp freeness (Schober-Regler method)".

[0049] Moisture content test: Refer to standard GB / T 462-2023 "Determination of moisture content of analytical samples of paper, paperboard and pulp".

[0050] Cross-cut adhesion test of coating: Refer to standard GB / T 9286-2021 "Cross-cut test of paints and varnishes".

[0051] Coating abrasion resistance: Refer to standard GB / T 1768-2006 "Determination of abrasion resistance of paints and varnishes - Rotary rubber grinding wheel method".

[0052] Stacking / compression loading method: Refer to standard GB / T 4857.4-2008 "Basic tests for transport packages - Part 4: Compression and stacking tests performed using a compression testing machine".

[0053] Contact angle test: Refer to ISO 19403-2:2024 "Coatings and varnishes — wettability — part 2: determination of surface free energy of solids by measuring contact angle".

[0054] Extractable organic fluorine (EOF) test: Refer to the group standard T / CNFIA 189-2024 "Determination of extractable organic fluorine content in food contact paper, paperboard and paper products - online combustion-ion chromatography", and the detection limit is controlled at ≤5mg / kg.

[0055] Total fluorine content test of dispersed stable components: Refer to group standard T / CNFIA 191-2024 "Determination of total fluorine content in food contact paper, paperboard and paper products by online combustion-ion chromatography", and the detection limit is controlled at ≤5mg / kg.

[0056] Parameter definition and measurement method:

[0057] (1) Dry film coating amount per unit area: Δm / A is calculated by dividing the mass increment Δm after coating and drying to constant weight by the unfolded area A of the coated area, and the unit is g / m².

[0058] Wherein, A of the outer surface of the sidewall is the unfolded area of ​​the outer surface of the sidewall after being cut along the generatrix and flattened, or the unfolded area of ​​the outer surface of the sidewall calculated according to the geometric dimensions of the mold; A of the outer surface of the bottom is the area of ​​the outer surface of the bottom.

[0059] When there are differentiated coating areas on the outer surface of the sidewall, they are defined as follows:

[0060] a) Dry film coating amount per unit area of ​​adjacent continuous coating zones: G_continuous = Δm_continuous / A_continuous;

[0061] b) Dry film coating amount per unit area in the strip-shaped flow channel area: G flow = Δm flow / A flow;

[0062] Among them, A-continuous and A-guided are the areas of the corresponding regions after unfolding on the outer surface of the sidewall, which can be obtained by calculating the design size of the masking template or by calculating the image binarization segmentation.

[0063] The amount of dry film coating per unit area of ​​the adjacent and continuously coated outer surface regions of the sidewalls is characterized by G continuity.

[0064] (2) Coating coverage: defined as the coverage of the flow channel area and the coverage of the adjacent continuous coating area, respectively.

[0065] a) Coverage of the flow channel area: The coverage of the flow channel area is defined as the proportion of the projected area of ​​the coating actually formed in the flow channel area to the total projected area of ​​the flow channel area, that is: Coverage of the flow channel area = Projected area of ​​the coated area in the flow channel area / Total projected area of ​​the flow channel area.

[0066] When a masking template is used, if the masking template is a "through-coating open-hole template", that is, the open-hole area can be coated and the non-open-hole area is masked, the projected area of ​​the coated area in the guide channel area is calculated according to the projected area of ​​the open-hole.

[0067] If the masking template is a "masking dot matrix template", that is, the dot matrix masking sheet is an area that cannot be coated, then the projected area of ​​the coated area in the flow channel area is calculated as (total projected area of ​​the flow channel area - projected area of ​​the masking dot matrix).

[0068] When using differential deposition instead of masking the template, the area ratio of the coated region can be calculated using the post-photograph binarization segmentation method.

[0069] b) Coverage of adjacent continuous coating areas:

[0070] When the continuous coating area is fully covered by spraying, the coverage rate is calculated as 100%.

[0071] When there are localized areas of uncoated areas in a continuously coated area, the calculation is performed using the binarization segmentation method described above.

[0072] (3) Apparent thickness of coating: The cross section of the coating after drying is measured using a cross-sectional scanning electron microscope (SEM) or an optical microscope. At least 10 different locations are selected on each sample to measure the thickness and the average value is taken as the apparent thickness t, in μm. When it is necessary to calculate the apparent thickness ratio, the flow channel area and the adjacent continuous coating area are measured in the same way and the ratio is taken.

[0073] (4) Coating continuity: The leakage judgment method is adopted. At least 3 height rings are selected on the outer surface of the side wall. Each ring is 10 mm high. A water solution containing 0.9 wt% sodium chloride is added to each ring at a rate of 1 mL / min along the circumference. The total amount of water added is 30 mL. After the addition is completed, the solution is maintained for 30 min. The presence of a through leakage point on the inner surface is recorded. If a through leakage point is found, it is judged as "interruption exists". Otherwise, it is judged as "continuous".

[0074] (5) Weak coating ratio: Prepare additional flat plates, for example, 100mm×100mm, on the same batch of pulp molding substrate. Place them side by side with the seedling pots in the same spraying batch. Use the same masking template and the same spraying parameters to form "guide channel area" and "adjacent continuous coating area" respectively. Cut samples that are completely located in the corresponding area from the guide channel area and the adjacent continuous coating area respectively. After unfolding, the width of the sample is 70% of the width of the guide channel area (rounded to 0.1mm), and the length is fixed at 100mm. The sample area A is the actual unfolded length × width measured by a digital caliper. Weigh the sample before and after coating and measure the mass difference Δm. Calculate the dry film coating amount G per unit area according to (1).

[0075] (6) pH of dispersion: The aqueous dispersion sample was directly measured using a pH meter at 25±1℃. The pH meter was calibrated at three points using pH 4.01, 7.00 and 10.01 buffer solutions, and the stable readings were recorded as pH.

[0076] (7) Apparent viscosity of dispersion: The apparent viscosity of aqueous dispersion was measured at 25±0.5℃ using a rotational viscometer. Example measurement conditions were Brookfield DV2T viscometer, LV-3 rotor, 60 rpm. The reading was recorded after it stabilized. The unit is mPa·s.

[0077] The weak coating ratio is defined as Gguide channel area / Gadjacent continuous coating area. When the apparent thickness ratio is used, the apparent thickness t is measured according to (3) and then tguide channel area / tadjacent continuous coating area is taken.

[0078] General preparation process for self-made materials and equipment:

[0079] General preparation process of newspaper-based recycled fiber pulp:

[0080] Step 1. Cut waste newsprint into 1cm×1cm pieces and soak them in deionized water at a mass ratio of 1:20 for 12 hours.

[0081] Step 2. Add the soaking material obtained in Step 1 to a high-speed shear disperser and dissociate it at 3000 rpm for 20 minutes to obtain regenerated fiber slurry.

[0082] Step 3. The regenerated fiber pulp obtained in Step 2 is sieved using a 0.5mm sieve. The pulp that passes through the sieve is collected and adjusted to a concentration of 2wt% to obtain newspaper-based regenerated fiber pulp.

[0083] General preparation process of second polymer and thermoplastic starch micro powder:

[0084] Step 1. Polylactic acid resin, polybutylene succinate resin, polycaprolactone resin, polyglycolic acid resin and thermoplastic starch resin are freeze-ground separately to obtain polylactic acid micro powder, polybutylene succinate micro powder, polycaprolactone micro powder, polyglycolic acid micro powder and thermoplastic starch micro powder respectively.

[0085] Step 2. Add the desired micro powder obtained in Step 1 to the polyhydroxyalkanoate aqueous emulsion and disperse it for 10 min at 10000 rpm using a high-speed shear disperser to obtain a mixed dispersion.

[0086] Construction process of self-made equipment and tooling:

[0087] Vacuum forming mold: 6061 aluminum alloy is selected as the main material of the mold. The shape of the seedling pot shade model cavity is sculpted by a computer numerical control (CNC) machining center. The design dimensions are: inner diameter of the pot opening 80mm, pot depth 90mm, and draft angle of the side wall 3°. 1.5mm diameter suction holes are evenly drilled on the inner surface of the mold, with a hole spacing of 5mm. Subsequently, a layer of 60-mesh stainless steel wire mesh is hot-pressed onto the inner surface of the mold as a filter to prevent fiber loss and impart surface texture to the product.

[0088] Shielding template: 0.5mm thick 304 stainless steel sheet is selected to ensure corrosion resistance and easy cleaning. The guide channel shapes, such as strip, dot matrix, and grid, designed according to various embodiments, are precisely cut on the sheet using a laser cutter. For suspended structures such as dot matrix shielding sheets, thin metal wires are used to connect and fix them to the main frame. The cut flat template is then heat-bent and shaped on a mold with the same curvature as the side wall of the seedling pot, or the stainless steel template is shaped using a roller pressing method to ensure a tight fit to the outer surface of the seedling pot.

[0089] Horizontal support: The frame is made of acrylic sheet. The upper layer is a support plate with 70mm diameter holes to support the edge of the seedling pot, ensuring that the bottom of the pot is suspended. The lower layer is a water tray support. Ensure that the drainage holes at the bottom of the seedling pot are fully exposed and unobstructed after placement.

[0090] Slotted screen: A 300mm×300mm square frame is made by welding stainless steel strips. Stainless steel wedge wires are arranged in parallel at the bottom. The wire gap is adjusted to 0.50mm and then fixed and locked. It is used for slurry screening and impurity removal.

[0091] Example:

[0092] Unless otherwise specified, the following embodiments use the same vacuum forming mold to prepare seedling pots with a diameter of 80 mm and a height of 90 mm. During pulp preparation, the solid content of the pulp suspension is controlled to be 2.0 wt% based on the oven-dry fiber count, and a high-speed shear disperser is used at 10,000 rpm for 20 minutes for dissociation. During wet forming, the vacuum pump is used to draw the forming vacuum at a gauge pressure of -80 kPa for 30 seconds. The wet preform pressing and dewatering pressure is 0.40 MPa, and the pressing time is 60 seconds. After dewatering, the preform is dried at 80°C until the moisture content is 10 wt%, as determined by GB / T 462-2023. Hot pressing and shaping parameters are as described in each embodiment. Humidification is carried out at 25°C and 60% relative humidity, and the moisture content is measured according to GB / T 462-2023 until the values ​​specified in each embodiment are reached. When coating is done by spraying, the spraying distance is 150mm, the spray gun speed is 200mm / s, and the overlap rate between adjacent spray guns is 50%. Multiple reciprocating sprays are used until the dry film coating amount per unit area specified in each embodiment is achieved. After spraying, the coating is dried at 60°C to constant weight. Constant weight is determined by: under the same drying conditions, a mass change rate ≤ 0.1% between two adjacent weighings within a 30-minute interval. Unless otherwise specified, there are four bottom drainage holes with a diameter of 6.0mm, centered on the same circumference and spaced at 90° equidistant intervals.

[0093] Example 1:

[0094] Step 1. Add softwood pulp and bamboo pulp to deionized water at a mass ratio of 7:3, and dissociate them using a high-speed shear disperser for 20 minutes to obtain a pulp suspension.

[0095] Step 2. Inject the pulp suspension obtained in Step 1 into the molding die, turn on the vacuum pump to form the wet blank.

[0096] Step 3. After pressing and dehydrating the wet blank obtained in Step 2, place it in a forced-air drying oven to dry it until the moisture content is 10wt%, thus obtaining a preformed blank.

[0097] Step 4. Place the preform obtained in Step 3 into a hot press and heat-press it at 110℃, 0.1MPa, and 120s to obtain the container body.

[0098] Step 5. Place the container body obtained in Step 4 in a constant temperature and humidity chamber to adjust the humidity so that the water content is 10wt%, and obtain the container body to be coated.

[0099] Step 6. Sealing Primer: Apply PHB water-based emulsion (D) 50=0.5μm, pH=7.2, viscosity=120mPa·s) diluted to a solid content of 15wt%, applied to the outer surface of the container body to be coated using a spraying device and dried at 50℃ to constant weight. The dry film coating amount per unit area of ​​the sealing primer was controlled to be 10g / m², and the sealing primer was obtained.

[0100] Step 7. Preparation of the topcoat composition: At 30°C, according to the dry solids mass ratio of PHB: talc: polylactic acid: wax emulsion solids: polycarbodiimide crosslinking agent solids = 1:0.80:0.02:0.05:0.02, mix the PHB aqueous emulsion and talc flakes D... 50 =5μm, polylactic acid micro powder (D 50 =30μm), wax emulsion and water-based polycarbodiimide crosslinking agent were added to a high-speed shear disperser and dispersed at 10000 rpm for 10 min to obtain a water-based coating composition.

[0101] Step 8. Coating: The aqueous coating composition obtained in step 7 is applied to the outer surface of the sealing primer obtained in step 6 using a spraying device to form a wet coating and obtain a coated part.

[0102] Step 9. Forming Differentiated Areas: During the coating process in Step 8, a strip masking template is used to form 13 parallel and continuous strip-shaped flow channels on the outer surface of the sidewall. The strip width is 1mm, the distance between adjacent strip edges is 19mm, and the area of ​​the differentiated coating area accounts for 5%. Among them, 4 strip-shaped flow channels are aligned with the center line of the 4 drainage holes at the bottom along the generatrix of the sidewall, so that the 4 strip-shaped flow channels extend continuously from the rim to the bottom and cover the periphery of the corresponding drainage hole punching position. By controlling the opening ratio of the masking template and the spray gun speed, the weak coating ratio between the flow channel area and the adjacent continuous coating area is 0.80, resulting in a differentiated coated part.

[0103] Step 10. Drying and film formation: Place the differentiated coated part obtained in step 9 into a forced-air drying oven to dry and form a film. Control the dry film coating amount per unit area of ​​the top coating to be 30g / m² to obtain the film-formed part.

[0104] Step 11. Film Formation and Punching: Using a punch, punch four drainage holes with a diameter of 6.0 mm at the bottom of the film-forming part obtained in Step 10. The drainage holes are distributed at equal intervals of 90°, and the periphery of the drainage holes is connected to the strip-shaped flow channel area to obtain a seedling pot with drainage holes.

[0105] Example 2: The preparation process is the same as in Example 1, except that:

[0106] In step 1, the pulp is a mixture of bleached softwood pulp, unbleached bamboo pulp board and newspaper-based recycled fiber pulp (freezing degree 38°SR) in a mass ratio of 5:3:2, and alkali lignin is added at 10 wt% based on oven-dry fiber. The freezing degree of the mixed pulp is 38°SR.

[0107] The hot pressing conditions in step 4 are 180℃, 5.0MPa, and 30s.

[0108] The topcoat composition formulation in step 7 is as follows: at 40°C, the dry solids mass ratio is PHBV: kaolin: polybutylene succinate: wax emulsion solids: polycarbodiimide crosslinking agent solids = 1:1.00:0.50:0.03:0.02, wherein the PHBV aqueous dispersion (D... 50 =0.6μm, pH=7.4, viscosity=150mPa·s), polybutylene succinate micro powder (D 50 =25μm). The above components were added to a high-speed shear disperser and dispersed at 10000 rpm for 10 min to obtain an aqueous coating composition.

[0109] In step 9, a strip-shaped masking template is used and a dot matrix masking sheet is superimposed. After unfolding on the outer surface of the sidewall, 19 parallel strip-shaped flow guiding channels are formed, extending continuously along the height direction. The strip width is 2mm, the distance between adjacent strip edges is 11mm, and the area of ​​the flow guiding channel area accounts for 15%. The channel contains dot matrix differentiated units with an equivalent diameter of 2.0mm and a dot matrix spacing of 8.0mm. The ratio of the apparent thickness of the coating in the flow guiding channel area to that in the adjacent continuous coating area is controlled to be 0.50. Four of the strip-shaped flow guiding channels are aligned with the center line direction of the four drainage holes at the bottom along the generatrix direction of the sidewall, so that the strip-shaped flow guiding channels are connected to the bottom outer surface area around the outer edge of the drainage holes. In step 10, the topcoat application amount is 60g / m².

[0110] Example 3: The preparation process is the same as in Example 1, except that:

[0111] In step 1, the pulp is newspaper-based recycled fiber pulp (freezing degree 42°SR).

[0112] In step 4, the hot-pressing conditions are 220℃, 8.0MPa, and 10s. In step 6, the sealing primer uses PHBH aqueous dispersion (D... 50 =0.4μm, pH=7.5, viscosity=100mPa·s).

[0113] The topcoat composition formulation in step 7 is as follows: at 50°C, the dry solids mass ratio is PHBH: fumed silica: polycaprolactone: wax emulsion solids: polycarbodiimide crosslinking agent solids = 1:0.80:1.00:0.05:0.02, with polycaprolactone micro powder (D... 50=28μm). The above components were added to a high-speed shear disperser and dispersed at 10000 rpm for 10 min to obtain an aqueous coating composition.

[0114] In step 9, a strip masking template is used and a mesh masking sheet is superimposed. After unfolding on the outer surface of the side wall, 10 parallel strip-shaped flow guiding channels are formed, which extend continuously along the height direction. The strip width is 5.0 mm, the distance between the edges of adjacent strips is 20 mm, and the area of ​​the flow guiding channel area accounts for 20%. The channel contains mesh-shaped differentiated units with a mesh hole side length of 3.0 mm and a mesh rib width of 0.5 mm. The weak coating ratio is controlled to be 0.30, and 4 of the strip-shaped flow guiding channels are aligned with the center line direction of the 4 bottom drainage holes along the generatrix direction of the side wall, so that the strip-shaped flow guiding channels are connected to the bottom outer surface area around the outer edge of the drainage holes.

[0115] In step 10, the topcoat application rate is 90 g / m².

[0116] Example 4: The preparation process is the same as in Example 1, except that:

[0117] In step 1, the pulp is a mixture of bleached softwood pulp and alkali lignin at a mass ratio of 9:1 (freezing degree 45°SR).

[0118] The hot pressing conditions in step 4 are 250℃, 9.0MPa, and 5s.

[0119] The topcoat composition formulation in step 7 is as follows: at 60°C, the dry solids mass ratio is P34HB: heavy calcium carbonate: thermoplastic starch: wax emulsion solids: polycarbodiimide crosslinking agent solids = 1:1.50:1.50:0.05:0.03, wherein the P34HB aqueous dispersion (D 50 =0.7μm, pH=7.3, viscosity=130mPa·s), thermoplastic starch micro powder (D 50 =35μm). The above components were added to a high-speed shear disperser and dispersed at 10000 rpm for 10 min to obtain an aqueous coating composition.

[0120] In step 9, a strip masking template is used and a microporous masking sheet is superimposed. After unfolding on the outer surface of the sidewall, a strip-shaped flow channel area extending continuously along the height direction is formed. The strip width is 2.5 mm, and the area of ​​the flow channel area accounts for 1%. The channel contains microporous differentiated units with a micropore diameter of 0.8 mm and a center-to-center distance of 3.0 mm. The ratio of the apparent thickness of the coating in the flow channel area to that in the adjacent continuous coating area is controlled to be 0.20, and the strip-shaped flow channel area is aligned with the center line of one of the drainage holes and extends to the bottom, so that the strip-shaped flow channel area is connected to the bottom outer surface area around the outer edge of the drainage hole.

[0121] In step 10, the topcoat application rate is 60 g / m².

[0122] Example 5: The preparation process is the same as in Example 1, except that:

[0123] In step 1, the pulp is a mixture of unbleached bamboo pulp board and alkali lignin at a mass ratio of 7:3 (beating degree 35°SR).

[0124] The hot pressing conditions in step 4 are 260℃, 10.0MPa, and 0.5s.

[0125] The topcoat composition formulation in step 7 is as follows: at 20°C, the dry solids mass ratio of PHBV: mica powder: polyglycolic acid = 1:2.00:1.50, wherein the PHBV aqueous dispersion (D 50 =0.6μm, pH=7.4, viscosity=150mPa·s), polyglycolic acid micro powder (D 50 =22μm). The above components were added to a high-speed shear disperser and dispersed at 10000 rpm for 10 min to obtain an aqueous coating composition.

[0126] In step 9, a strip masking template is unfolded on the outer surface of the sidewall to form 15 parallel strip-shaped flow guide channels that extend continuously along the height direction. The strip width is 5.0 mm, the distance between adjacent strip edges is 12 mm, and the area of ​​the flow guide channel area accounts for 30%. A transverse non-penetrating masking sheet with a length of 3.0 mm is set every 20 mm along the height direction on the strip masking template, so that each strip-shaped flow guide channel area forms a periodic coating continuity interruption structure along the height direction. By controlling the opening ratio of the masking template and the spray gun speed, the weak coating ratio between the flow guide channel area and the adjacent continuous coating area is 0.75. Four of the strip-shaped flow guide channels extend to the bottom along the generatrix direction of the sidewall, aligned with the center line direction of the four bottom drainage holes, so that the strip-shaped flow guide channel area is connected to the bottom outer surface area around the outer edge of the four bottom drainage holes.

[0127] In step 10, a gradient coating is formed, with a dry film coating amount of 120 g / m² per unit area in the basin mouth area 0–15 mm from the edge of the basin mouth, and a dry film coating amount of 90 g / m² per unit area in the middle area of ​​the side wall 15–60 mm from the edge of the basin mouth.

[0128] Example 6: The preparation process is the same as in Example 1, except that:

[0129] In step 1, the pulp is bagasse pulp board (beating degree 40°SR).

[0130] The hot pressing conditions in step 4 are 150℃, 2.0MPa, and 60s.

[0131] The topcoat composition formulation in step 7 is as follows: at 35°C, the dry solids mass ratio is PHBV:barium sulfate (D) 50=1.0μm): Polycaprolactone micron powder (D 50 =28μm): Wax emulsion solid: Polycarbodiimide crosslinking agent solid = 1:1.20:0.80:0.04:0.02, wherein the PHBV aqueous dispersion (D 50 =0.6μm, pH=7.4, viscosity=150mPa·s). The above components were added to a high-speed shear disperser and dispersed at 10000rpm for 10min to obtain an aqueous coating composition.

[0132] In step 9, a spiral shielding template is used to form a spiral strip-shaped flow channel area that extends continuously from the rim to the bottom after being unfolded on the outer surface of the side wall. The area of ​​the flow channel area accounts for 10%. The bandwidth of the spiral strip-shaped flow channel area is 3.0 mm and the spiral pitch is 12 mm. The weak coating ratio is controlled to be 0.60, and the spiral strip-shaped flow channel area is connected to the bottom outer surface area around the outer edge of the drain hole.

[0133] In step 10, the topcoat application rate is 50 g / m².

[0134] Example 7: The preparation process is the same as in Example 1, except that:

[0135] In step 1, the slurry is reed pulp board (beating degree 38°SR).

[0136] The hot pressing conditions in step 4 are 160℃, 3.0MPa, and 45s.

[0137] The topcoat composition formulation in step 7 is as follows: at 30°C, the dry solids mass ratio is PHB:titanium dioxide (D) 50 =0.30μm): Polybutylene succinate micro powder (D 50 =25μm): Wax emulsion solid: Polycarbodiimide crosslinking agent solid = 1:0.90:0.60:0.03:0.02, wherein the PHB aqueous dispersion (D 50 =0.5μm, pH=7.2, viscosity=120mPa·s). The above components were added to a high-speed shear disperser and dispersed at 10000rpm for 10min to obtain an aqueous coating composition.

[0138] In step 9, a strip masking template is used and a ring-shaped masking sheet is superimposed. After unfolding on the outer surface of the side wall, 10 parallel strip-shaped flow guiding channels are formed, which extend continuously along the height direction. The strip width is 2.0 mm, the distance between adjacent strip edges is 23 mm, and the area of ​​the flow guiding channel area accounts for 8%. A ring-shaped differentiation unit is set in the strip-shaped flow guiding channel area. The ring width of the ring-shaped differentiation unit after unfolding is 1.5 mm, and the distance between adjacent ring edges is 6.0 mm. The ratio of the apparent thickness of the coating of the flow guiding channel area to that of the adjacent continuous coating area is controlled to be 0.40, and 4 of the strip-shaped flow guiding channels are aligned with the center line direction of the 4 bottom drainage holes and extend to the bottom, so that the strip-shaped flow guiding channel area is connected to the bottom outer surface area around the outer edge of the 4 bottom drainage holes.

[0139] In step 10, the topcoat application rate is 45 g / m².

[0140] Example 8: The preparation process is the same as in Example 1, except that:

[0141] The topcoat composition formulation in step 7 is as follows: at 30°C, the dry solids mass ratio is PHBH: wollastonite (D) 50 =5.0μm): Polylactic acid micropowder (D 50 =30μm)=1:1.10:0.40, of which the PHBH aqueous dispersion (D 50 =0.4μm, pH=7.5, viscosity=100mPa·s). The above components were added to a high-speed shear disperser and dispersed at 10000rpm for 10min to obtain an aqueous coating composition.

[0142] In step 9, after the strip masking template is unfolded on the outer surface of the side wall, 15 parallel strip-shaped flow guiding channels are formed and continuously extend along the height direction. The strip width is 2.0 mm, the distance between the edges of adjacent strips is 15 mm, and the area of ​​the flow guiding channel area accounts for 12%. The weak coating ratio is controlled to be 0.55, and 4 of the strip-shaped flow guiding channels are aligned with the center line direction of the 4 bottom drainage holes and extend to the bottom, so that the strip-shaped flow guiding channels are connected to the bottom outer surface area around the outer edge of the 4 bottom drainage holes.

[0143] In step 10, the dry film coating amount per unit area of ​​the topcoat is 35 g / m².

[0144] Example 9: The preparation process is the same as in Example 1, except that:

[0145] In steps 6 and 7, the alkyl glycoside surfactant used in the preparation of the PHB aqueous dispersion was replaced with the nonionic surfactant fatty alcohol polyoxyethylene ether (Lutensol AO 9, BASF). The resulting PHB aqueous dispersion (D) 50=0.5μm, pH=7.3, viscosity=110mPa·s).

[0146] The topcoat composition formulation in step 7 is as follows: at 30°C, the dry solids mass ratio is PHB: talc (flakes, D) 50 =5μm): Polylactic acid micro powder (D 50 =30μm): Wax emulsion solid: Polycarbodiimide crosslinking agent solid = 1:0.80:0.02:0.05:0.02. The above PHB aqueous dispersion (surfactant is Lutensol AO 9, parameters are the same as above), talc, polylactic acid micro powder, wax emulsion and aqueous polycarbodiimide crosslinking agent are added to a high-speed shear disperser and dispersed at 10000 rpm for 10 min to obtain an aqueous coating composition.

[0147] In step 9, after the strip masking template is unfolded on the outer surface of the side wall, nine parallel strip-shaped flow guiding channels are formed, which extend continuously along the height direction. The strip width is 5.0 mm, the distance between the edges of adjacent strips is 23 mm, and the area of ​​the flow guiding channel area accounts for 18%. The ratio of the apparent thickness of the coating of the flow guiding channel area to that of the adjacent continuous coating area is controlled to be 0.45, and four of the strip-shaped flow guiding channels are aligned with the center line of the four bottom drainage holes and extend to the bottom, so that the strip-shaped flow guiding channel area is connected to the bottom outer surface area around the outer edge of the four bottom drainage holes.

[0148] In step 10, the topcoat application rate is 60 g / m².

[0149] Comparative example:

[0150] Comparative Example 1: The preparation process is the same as in Example 1, except that the coating and subsequent related steps are omitted, and after the moisture conditioning in step 5, the holes are directly punched to obtain an uncoated seedling pot (substrate beating degree 40°SR).

[0151] Comparative Example 2: The preparation process is the same as in Example 1, except that: in step 7, the topcoat composition does not contain flake inorganic fillers, polylactic acid, wax emulsion, or crosslinking agents, and is a pure PHB aqueous dispersion (D). 50 =0.5μm, pH=7.2, viscosity=120mPa·s); The PHB aqueous dispersion was added to a high-speed shear disperser at 30℃ and dispersed at 10000rpm for 10min to obtain an aqueous coating composition. In step 9, no masking template was used for full-coverage spraying, with no differentiated coating area (the area of ​​the guide channel region was 0%). In step 10, the topcoat application rate was 60g / m².

[0152] Comparative Example 3: The preparation process is the same as in Example 2, except that: in step 7, no wax emulsion or crosslinking agent is added to the topcoat composition. The formulation is as follows: at 40°C, the dry solids mass ratio is PHBV: kaolin: polybutylene succinate = 1:1.00:0.50, wherein the PHBV aqueous dispersion (D 50 =0.6μm, pH=7.4, viscosity=150mPa·s), polybutylene succinate micro powder (D 50 =25μm); PHBV aqueous dispersion, kaolin, and polybutylene succinate micro powder were added to a high-speed shear disperser and dispersed at 10000 rpm for 10 min to obtain an aqueous coating composition. In step 9, no masking template was used for full-coverage spraying, resulting in no differentiated coating areas. In step 10, the topcoat application rate was 60 g / m².

[0153] Comparative Example 4: The preparation process is the same as Comparative Example 3, except that: in step 7, no wax emulsion or crosslinking agent is added to the topcoat composition. The formulation is as follows: at 40°C, the dry solids mass ratio is PHBV: kaolin: polybutylene succinate = 1:1.00:0.50, wherein the PHBV aqueous dispersion (D 50 =0.6μm, pH=7.4, viscosity=150mPa·s), polybutylene succinate micro powder (D 50 =25μm); PHBV aqueous dispersion, kaolin, and polybutylene succinate micro powder were added to a high-speed shear disperser and dispersed at 10000 rpm for 10 min to obtain an aqueous coating composition. In step 9, 11 parallel and continuously extending strip-shaped guide channels were formed using a strip masking template. The strip width was 8.0 mm, the distance between adjacent strip edges was 15 mm, and the area of ​​the guide channel area accounted for 35%. By controlling the opening ratio of the masking template and the spray gun speed, the ratio of the apparent thickness of the coating in the guide channel area to that in the adjacent continuous coating area was made 0.50. Four of the strip-shaped guide channels were aligned with the center line of the four bottom drainage holes and extended to the bottom, so that the guide channel area was connected to the bottom outer surface area around the outer edge of the bottom drainage holes. In step 10, the topcoat application rate was 60 g / m².

[0154] Comparative Example 5: The preparation process is the same as in Example 2, except that the topcoat composition formulation in step 7 is as follows: at 40°C, the dry solids mass ratio is PHBV: kaolin: polybutylene succinate: wax emulsion solids: polycarbodiimide crosslinking agent solids = 1:1.00:0.50:0.03:0.02, wherein the PHBV aqueous dispersion (D... 50 =0.6μm, pH=7.4, viscosity=150mPa·s), polybutylene succinate micro powder (D 50=25μm); The above components were added to a high-speed shear disperser and dispersed at 10000rpm for 10min to obtain an aqueous coating composition. In step 9, a strip masking template was used and a dot matrix masking sheet was superimposed. After unfolding on the outer surface of the side wall, 19 parallel and continuously extending strip-shaped flow channel areas were formed. The strip width was 2mm, the distance between the edges of adjacent strips was 11mm, and the area of ​​the flow channel area accounted for 15%; the channel contained dot matrix differentiated units with an equivalent diameter of 2.0mm and a dot matrix spacing of 8.0mm; by controlling the opening ratio of the masking template and the spray gun speed, the ratio of the apparent thickness of the coating of the flow channel area to that of the adjacent continuous coating area was 0.50; however, when the strip-shaped flow channel area extended from the rim to the bottom, it terminated 10mm above the outer edge of the bottom (along the height direction of the side wall), so that the strip-shaped flow channel area was not connected to the bottom outer surface area around the outer edge of the drain hole. In step 10, the topcoat application rate is 60 g / m².

[0155] Comparative Example 6: The preparation process is the same as in Example 2, except that the topcoat composition formulation in step 7 is as follows: at 40°C, the dry solids mass ratio is PHBV: kaolin: polybutylene succinate: wax emulsion solids: polycarbodiimide crosslinking agent solids = 1:1.00:0.50:0.03:0.02, wherein the PHBV aqueous dispersion (D... 50 =0.6μm, pH=7.4, viscosity=150mPa·s), polybutylene succinate micro powder (D 50 =25μm); The above components were added to a high-speed shear disperser and dispersed at 10000 rpm for 10 min to obtain an aqueous coating composition. In step 9, a strip masking template is used and a dot matrix masking sheet is superimposed. After unfolding on the outer surface of the side wall, 19 parallel strip-shaped flow guiding channels are formed, which extend continuously along the height direction. The strip width is 2mm, the distance between the edges of adjacent strips is 11mm, and the area of ​​the flow guiding channel area accounts for 15%. The channel contains dot matrix differentiated units with an equivalent diameter of 2.0mm and a dot matrix spacing of 8.0mm. By increasing the through-coating opening rate of the masking template and adjusting the number of spraying cycles, the dry film coating amount per unit area of ​​the flow guiding channel area is 54g / m², and the dry film coating amount per unit area of ​​the adjacent continuous coating area is 60g / m², so that the weak coating ratio between the flow guiding channel area and the adjacent continuous coating area is 0.90. Four of the strip-shaped flow guiding channels extend to the bottom along the generatrix direction of the side wall, aligned with the center line direction of the four drainage holes at the bottom, so that the strip-shaped flow guiding channel area is connected to the bottom outer surface area around the outer edge of the drainage holes. In step 10, the topcoat application rate is 60 g / m².

[0156] Comparative Example 7: The preparation process is the same as in Example 2, except that the topcoat composition formulation in step 7 is as follows: at 40°C, the dry solids mass ratio is PHBV: kaolin: polybutylene succinate: wax emulsion solids: polycarbodiimide crosslinking agent solids = 1:1.00:0.50:0.03:0.02, wherein the PHBV aqueous dispersion (D... 50 =0.6μm, pH=7.4, viscosity=150mPa·s), polybutylene succinate micro powder (D 50 =25μm); The above components were added to a high-speed shear disperser and dispersed at 10000 rpm for 10 min to obtain an aqueous coating composition. In step 9, a strip masking template was used and a dot matrix masking sheet was superimposed to form 19 parallel and continuously extending strip-shaped flow channel areas on the outer surface of the sidewall. The strip width was 2 mm, the distance between adjacent strip edges was 11 mm, and the area of ​​the flow channel area accounted for 15%; the channel contained dot matrix differentiated units with an equivalent diameter of 2.0 mm and a dot matrix spacing of 8.0 mm; the ratio of the apparent thickness of the coating of the flow channel area to that of the adjacent continuous coating area was controlled to be 0.50, and 4 of the strip-shaped flow channel areas were aligned with the center line of the 4 drainage holes at the bottom along the generatrix direction of the sidewall to the bottom, so that the strip-shaped flow channel areas were connected to the bottom outer surface area around the outer edge of the drainage holes. In step 10, the dry film coating amount per unit area of ​​the topcoat was controlled to be 20 g / m².

[0157] Comparative Example 8: The preparation process is the same as in Example 5, except that in step 7, the formulation of the topcoat composition is adjusted to be prepared at 20°C according to the dry solids mass ratio of PHBV:mica powder (flakes, D). 50 =15μm): Polyglycolic acid micro powder (D 50 =22μm)=1:2.30:1.50, of which the PHBV aqueous dispersion (D 50 =0.6μm, pH=7.4, viscosity=150mPa·s); PHBV aqueous dispersion, mica powder and polyglycolic acid micro powder were added to a high-speed shear disperser and dispersed at 10000rpm for 10min to obtain an aqueous coating composition.

[0158] Comparative Example 9: The preparation process is the same as in Example 4, except that: in step 7, no wax emulsion and crosslinking agent are added to the topcoat composition, and the formula is adjusted to be prepared at 60°C with a dry solids mass ratio of P34HB: heavy calcium carbonate (D 50 =10μm): Thermoplastic starch micropowder (D 50 =35μm)=1:1.50:1.80, of which the P34HB aqueous dispersion (D 50=0.7μm, pH=7.3, viscosity=130mPa·s); P34HB aqueous dispersion, heavy calcium carbonate and thermoplastic starch micro powder were added to a high-speed shear disperser and dispersed at 10000rpm for 10min to obtain an aqueous coating composition.

[0159] Comparative Example 10: The preparation process is the same as in Example 2, except that in step 6, when preparing the PHBV aqueous dispersion, the alkyl glycoside surfactant (APG) is replaced with the fluorinated surfactant Zonyl FSN-100 (Chemours). The amount of fluorinated surfactant added is 3.0 wt% based on PHBV dry solids. The remaining freeze-milling, pre-dispersion, and high-pressure homogenization conditions are the same as the general preparation process for polyhydroxyalkanoate aqueous dispersions, resulting in a fluorinated PHBV aqueous dispersion (D). 50 =0.3μm, pH=7.0, viscosity=80mPa·s). The formulation of the topcoat composition in step 7 is as follows: at 40℃, the dry solids mass ratio is PHBV: kaolin: polybutylene succinate: wax emulsion solids: polycarbodiimide crosslinking agent solids = 1:1.00:0.50:0.03:0.02, wherein the polybutylene succinate micro powder (D 50 =25μm); The above-mentioned fluorinated PHBV aqueous dispersion, kaolin, polybutylene succinate micro powder, wax emulsion and aqueous polycarbodiimide crosslinking agent were added to a high-speed shear disperser and dispersed at 10000 rpm for 10 min to obtain an aqueous coating composition. The topcoat coating amount in step 10 was 60 g / m².

[0160] Comparative Example 11: The preparation process is the same as in Example 2, except that spherical silica (spherical, D) is used in step 7. 50 =1.0μm) to replace flaky kaolin. The topcoat composition formulation in step 7 is as follows: at 40°C, the dry solids mass ratio is PHBV: spherical silica: polybutylene succinate: wax emulsion solids: polycarbodiimide crosslinking agent solids = 1:1.00:0.50:0.03:0.02, wherein the PHBV aqueous dispersion (D... 50 =0.6μm, pH=7.4, viscosity=150mPa·s), polybutylene succinate micro powder (D 50 =25μm); The above components were added to a high-speed shear disperser and dispersed at 10000 rpm for 10 min to obtain an aqueous coating composition. The topcoat coating amount in step 10 was 60 g / m².

[0161] Comparative Example 12: The preparation process is the same as in Example 2, except that the formulation of the topcoat composition in step 7 is adjusted to: at 40°C, the dry solids mass ratio of PHBV: kaolin: polybutylene succinate: wax emulsion solids: polycarbodiimide crosslinking agent solids = 1:0.50:0.50:0.03:0.02, wherein the PHBV aqueous dispersion (D... 50 =0.6μm, pH=7.4, viscosity=150mPa·s), polybutylene succinate micro powder (D 50 =25μm); The above components were added to a high-speed shear disperser and dispersed at 10000 rpm for 10 min to obtain an aqueous coating composition. In step 9, a strip masking template was used and a dot matrix masking sheet was superimposed to form 19 parallel and continuously extending strip-shaped flow guiding channels on the outer surface of the sidewall. The strip width was 2 mm, the distance between adjacent strip edges was 11 mm, and the area of ​​the flow guiding channel area accounted for 15%; the channel contained dot matrix differentiated units with an equivalent diameter of 2.0 mm and a dot matrix spacing of 8.0 mm; the ratio of the apparent thickness of the coating of the flow guiding channel area to that of the adjacent continuous coating area was controlled to be 0.50, and 4 of the strip-shaped flow guiding channels were aligned with the center line direction of the 4 drainage holes at the bottom along the generatrix direction of the sidewall, so that the strip-shaped flow guiding channel area was connected to the bottom outer surface area around the outer edge of the drainage holes. In step 10, the topcoat coating amount was 60 g / m².

[0162] Comparative Example 13: The preparation process is the same as in Example 2, except that in step 9, a narrow strip masking template is used. After being unfolded on the outer surface of the sidewall, a strip-shaped guide channel area extending continuously along the height direction is formed. The strip width is 1.0 mm, and the area of ​​the guide channel area accounts for 0.5%. By controlling the opening ratio of the masking template and the spray gun speed, the ratio of the apparent thickness of the coating in the guide channel area to that in the adjacent continuous coating area is 0.20. The strip-shaped guide channel area extends to the bottom along the generatrix direction of the sidewall, aligned with the center line of one of the drainage holes, so that the strip-shaped guide channel area is connected to the bottom outer surface area around the outer edge of the drainage hole. In step 10, the topcoat application amount is 60 g / m².

[0163] Application example:

[0164] Application Example 1: Water resistance and wet strength test of seedling trays.

[0165] This application example aims to verify the effects of different coating formulations, filler types, substrate types, and flow channel designs on the stability of seedling trays under simulated high-humidity seedling environments. Seedling trays prepared in Examples 1 to 9 and Comparative Examples 1 to 13 were selected as test samples.

[0166] The testing method is as follows: First, the samples are conditioned by placing all the seedling pots to be tested in a constant temperature and humidity environment of 23±1℃ and 50±2% for 24 hours.

[0167] Cobb 60s test: conducted according to GB / T 1540-2002 standard. To meet the sampling size requirement of 125mm diameter samples, pulp molded flat plates (150mm×150mm) were prepared simultaneously with the seedling pots under the same batch, substrate formulation, and spraying parameters. The same masking template and spray gun parameters as the corresponding seedling pots were used to ensure that the area ratio of the strip-shaped flow channel region and the weak coating ratio / thickness ratio on the surface of the flat plate were consistent with the outer surface of the seedling pot sidewall. The flat plates were then cut into 125mm diameter circular samples, ensuring that the area ratio of the flow channel region within the circular sample coverage area was consistent with the corresponding embodiment (allowable error ±0.5 percentage points). During testing, 100mL of deionized water was added to a metal cylinder, and after contacting the sample coating surface for 60 seconds, the water was poured out. Excess water was absorbed with absorbent paper, and the mass difference before and after water absorption was measured to calculate the water absorption per unit area. Five parallel samples were tested for each formulation, and the average value was taken.

[0168] Wet compressive strength retention rate test: Referring to GB / T 4857.4-2008 standard, the vertical compressive strength of the dry samples in the same batch was first tested. Then, the seedling pots to be tested were completely immersed in deionized water at 25℃ for 24 hours. After removal, the surface free water was gently wiped with absorbent paper, and the pots were immediately placed between the upper and lower pressure plates of an electronic universal testing machine. Vertical pressure was applied at a speed of 12.5 mm / min, and the maximum load before the seedling pot collapsed was recorded. The retention rate was calculated using the formula: (maximum wet load / maximum dry load) × 100%. Five samples were tested in each group.

[0169] Anti-softening time test: Simulating actual watering conditions, the seedling pots were placed horizontally on a special perforated support to ensure the bottom drainage holes were fully exposed and unobstructed. 200mL of deionized water was poured into the pots at once. Timing began after the continuous water flow from the bottom drainage holes ceased, and the pots were placed in an environment of 25℃ and 60% relative humidity. The pot diameter was measured every 2 hours using a digital caliper (average of two perpendicular diameters was taken). The time elapsed when the measured diameter decreased by 5% compared to the initial dry state was recorded as the anti-softening time. Five samples were tested in each group.

[0170] Table 3. Results of water resistance and wet strength tests on seedling trays (n=5, average value):

[0171]

[0172] Analysis: The test data in Table 3 show that the coating formulation and microstructure play a decisive role in the water resistance of the seedling pots. Examples 1 to 9 successfully constructed a dense "maze effect" water-blocking layer by introducing sheet-like inorganic fillers (where sheet-like fillers such as talc, kaolin, and mica are more conducive to forming a maze effect; barium sulfate, titanium dioxide, and other inorganic fillers can also be used to achieve filling and barrier reinforcement) and controlling the ratio of filler to polyhydroxyalkanoates. Even when using herbal fibers (Example 6) or different shaped drainage channels (spiral, ring-shaped), the compressive strength retention rate was controlled below 15 g / m², the wet compressive strength retention rate remained above 80%, and the softening resistance time exceeded 120 hours, meeting the usage requirements of the seedling cycle. In contrast, Comparative Example 11 used non-sheet-shaped spherical filler. Because it could not form an effective layered barrier structure, the water molecule path was shortened, leading to a surge in the Cobb value to 45.0 g / m², and a wet compressive strength retention rate of only 40%, demonstrating the crucial role of the sheet-like filler morphology. In Comparative Example 12, the filler ratio was too low (below 0.8:1), resulting in high dry film shrinkage stress and a lack of rigid support, reducing the wet compressive strength retention rate to 60%. In Comparative Example 7, the coating amount was below 30 g / m², failing to form a continuous and dense film layer, leading to water resistance failure. In Comparative Example 4, the excessively large proportion of the flow channel area (over 30%) compromised the overall structural mechanical integrity, resulting in a wet compressive strength retention rate of only 45%. It is noteworthy that while Comparative Example 13 exhibited excellent water resistance due to its small flow channel area (0.5%), subsequent experiments confirmed that it severely affected root penetration. Therefore, considering only a single water resistance indicator is insufficient; a balance must be found between water resistance and root penetration.

[0173] Application Example 2: Simulation test of root penetration ability and degradation performance.

[0174] This application focuses on examining the biological performance of seedling pots after transplanting, specifically root penetration ability and degradation rate in a compost environment. These are core indicators for evaluating whether seedling pots possess the value of "transplanting without removing the pot." Samples from Examples 1 to 9 and Comparative Examples 1 to 13 were selected for testing.

[0175] The testing process is as follows:

[0176] Root penetration test: In a greenhouse environment (25℃, 60% RH, 12h / 12h photoperiod), soybean seeds (Zhonghuang 13) were sown in seedling pots filled with Potground H compost substrate at a depth of 20mm. Watering was done via automatic sprinkler system twice daily (09:00 and 17:00), spraying each seedling pot with 50mL of deionized water each time to keep the substrate moist but without continuous water accumulation at the bottom of the pot. After 30 days of seedling growth, the seedling pots, along with the substrate, were transplanted into 180mm diameter and 170mm high flowerpots. Potground H was continued as the substrate, and the same watering schedule was maintained for another 20 days. After this period, the substrate was carefully washed away, and the sidewalls of the seedling pots were observed. After cutting and flattening the sidewalls along the generatrix, they were divided into 6 equal segments along the height direction and 6 equal segments along the circumference, forming 36 equal-area observation units of 6×6. The number of units with roots penetrating through was counted, and the penetration rate was calculated as (number of penetrating units / total number of units × 100%). Ten samples were counted in each group.

[0177] Compost weight loss test: Seedling pots were buried in standardized compost substrate with a moisture content adjusted to 50 wt%, and the ambient temperature was controlled at 25℃. The top of the seedling pots was 50 mm below the soil surface, and water was added every 3 days to maintain humidity. After 60 days of burial, the samples were removed, and the surface soil and microbial film were gently rinsed with warm water. The samples were then dried in a 60℃ oven until constant weight. The percentage of mass loss before and after burial was calculated. Five samples were tested in each group.

[0178] Table 4. Results of root penetration and degradation tests:

[0179]

[0180] Analysis: The experimental data clearly reveal the guiding effect of the differentiated coating area on plant root behavior. The root penetration rates of Examples 1 to 9 were all between 80% and 97%, and the 60-day weight loss rates were between 72 wt% and 90 wt%, indicating that the designed flow channels (whether strips, spirals, rings, or grids) can effectively serve as root breakthrough points and starting points for microbial erosion. In particular, Example 5, employing a continuous interruption design, achieved a penetration rate as high as 97%, demonstrating the effectiveness of artificially creating coating weaknesses in overcoming biodegradation bottlenecks. In contrast, Comparative Example 3 (full coverage) showed a root penetration rate of only 25%, with roots coiling inside the container, severely inhibiting post-transplant growth. Comparative Example 13, by compressing the flow channel area ratio to 0.5% (below the 1% lower limit), made it difficult for roots to find a breakthrough point, resulting in a sharp drop in penetration rate to 35%, proving the scientific validity of the lower limit setting for the area ratio in this invention. Although Comparative Example 5 features a strip-shaped flow channel area, this area is not connected to the bottom outer surface region around the drainage hole. This makes it difficult for roots to migrate from near the bottom drainage hole to the side wall flow channel area and form an effective penetration opening, resulting in a root penetration rate of only 55%. This verifies the necessity of the aforementioned connectivity structure design. Comparative Example 6 has a weak coating ratio of 0.90 (higher than 0.80), indicating insufficient coating difference, and roots still struggle to penetrate (40%). While Comparative Examples 11 and 12 have higher penetration rates, this comes at the cost of sacrificing wet strength (see Application Example 1), rendering them impractical.

[0181] Application Example 3: Testing of hydrophobicity, abrasion resistance and adhesion stability of coating surface.

[0182] This application example aims to evaluate the physical durability of the coating during production, transportation, and use. Tests covered surface hydrophobicity, coating-substrate adhesion, and abrasion resistance. Test samples were Examples 1 to 9 and Comparative Examples 1 to 13.

[0183] The testing method shall be performed in accordance with the following standards:

[0184] Static water contact angle test: Following ISO 19403-2:2024, a contact angle measuring instrument was used. 5.0 μL of deionized water was dropped onto a smooth coating surface. After the droplet stabilized for 5 seconds, the average contact angle of the left and right sides was read. For each sample, five different points were selected in adjacent continuous coating areas (non-strip channel areas) for testing, and the average value was taken as the static water contact angle of that sample.

[0185] Cross-cut adhesion test: According to GB / T 9286-2021 standard, the test area is selected as the adjacent continuous coating area on the outer surface of the sidewall (avoiding the strip-shaped guide channel area and the hole edge area). Using a cross-cut tester (Elcometer 107) with a cut distance of 1mm, six cuts are made in each of two mutually perpendicular directions in the same area to form a grid; then, cross-cut test tape (3M 610) is applied, and a rubber roller is used to press it back and forth twice with constant force. After standing for 90 seconds, the tape is peeled off at a uniform speed of 0.5–1.0 seconds at a 60° angle; the grade is determined according to GB / T 9286-2021. For wet cross-cut grade test, the sample is soaked in deionized water for 24 hours, then taken out, and the surface free water is gently wiped with absorbent paper. The cross-cut test and determination are completed within 2 minutes.

[0186] Wear resistance test: According to GB / T 1768-2006 standard, 100mm×100mm samples were prepared from adjacent continuous coating areas on the outer surface of the sidewall. An abrasion testing machine (Taber 5135) and a CS-10 grinding wheel were used, with a wheel speed of 60 r / min. Each grinding wheel was loaded with 500g (total load 1000g), and the cycle count was 1000 times. Before and after the test, the samples were equilibrated at 23±1℃ and 50±2%RH for 24 hours, and their mass was measured using an analytical balance. The wear loss was defined as the difference in mass before and after the test, expressed in mg.

[0187] Table 5. Test results of coating surface properties (n=5, average value):

[0188]

[0189] Note: Comparative Example 1 is an uncoated sample and is not applicable to this test.

[0190] Analysis: Test results show that reasonable filler introduction and formulation design significantly improve the physical and mechanical properties of the coating. The abrasion weight loss of Examples 1 to 9 was controlled between 4-6 mg, and the dry and wet cross-cut adhesion grades were all grade 0 (or grade 1 for the edge of Example 8), demonstrating excellent abrasion resistance and adhesion. This is attributed to the parallel arrangement structure formed by the lamellar filler in the coating, which effectively shares the external friction force and forms a stable network structure in conjunction with the cross-linking agent. Comparative Example 2 (no filler) and Comparative Example 12 (insufficient filler) showed abrasion weight losses as high as 30 mg and 35 mg, respectively, and poor wet adhesion (grades 2-3), indicating that the lack of inorganic filler reinforcement resulted in a softer pure polymer film that easily swelled and peeled after water absorption. Although Comparative Example 8 had a high contact angle, the excessively high filler ratio (exceeding 2.0:1) prevented the resin from completely coating the filler, resulting in a "powdering" phenomenon on the surface and an increased abrasion weight loss of 12 mg. Comparative Example 11 used spherical fillers, which could not form a dense reinforcing layer like sheet fillers and were prone to detachment during friction, resulting in a wear weight loss of 25 mg. These data fully demonstrate the critical influence of the type, morphology, and addition ratio of inorganic fillers on the durability of the coating.

[0191] Application Example 4: Wet-dry cycle stability and dimensional retention test.

[0192] This application example simulates the repeated "watering-drying" cycle during seedling cultivation to examine the dimensional stability and structural integrity of seedling pots after experiencing multiple cycles of expansion and contraction due to humidity and heat. Test samples include Examples 1 to 9 and Comparative Examples 1 to 13.

[0193] The experimental procedure was as follows: Each seedling pot sample was numbered, and 20 mL of deionized water was evenly sprayed onto its outer surface using a spray bottle to fully wet it. After draining naturally for 10 minutes, it was placed in a 25℃, 60% RH environment to dry for 24 hours, which constituted one complete wet-dry cycle. After 10 consecutive cycles, the pot diameter and height were measured using a digital caliper, and the retention rate relative to the initial dimensions was calculated. Subsequently, according to GB / T 4857.4-2008 standard, the samples that had undergone 10 cycles were immersed in water again for 24 hours to test their wet compressive strength, and the retention rate relative to the initial dry strength was calculated. Five samples were tested in each group.

[0194] Table 6. Results of wet-dry cycle stability test (10 cycles, n=5, average value):

[0195]

[0196] Analysis: Wet-dry cycle testing further verified the long-term reliability of the coating of the present invention. After 10 rigorous wet-dry cycles, Examples 1 to 9 all maintained a dimensional retention rate of over 97%, and the wet compressive strength retention rate remained between 70% and 80% after the cycles. This indicates that the coating not only has excellent water resistance, but also, due to the addition of appropriate amounts of toughening and crosslinking agents, can adapt to the slight deformation of the substrate during moisture absorption without cracking or peeling. Comparative Example 1 (uncoated) showed severe deformation after cycling, with almost complete loss of strength. Comparative Example 4, due to its excessively large pore area, resulted in excessive water absorption by the substrate, leading to structural collapse and a strength retention rate of only 30%. Comparative Examples 8 (excess filler) and 11 (spherical filler) experienced gradual softening of the substrate due to stress concentration or barrier failure during cycling, resulting in strength retention rates decreasing to 55% and 40%, respectively. Comparative Example 9, due to the excessive amount of the second polymer, increased the hydrophilicity of the system, causing the coating to swell after cycling and significantly reducing its strength. These results highlight the importance of balancing the proportions of fillers, polymers, and additives in formulation design.

[0197] Application Example 5: Drainage hole patency and anti-clogging performance test.

[0198] This application example aims to verify whether the coating process affects the drainage function of the bottom of the seedling pot, ensuring that water accumulation and root rot will not occur due to coating dripping or buildup in actual use. The test samples are Examples 1 to 9 and Comparative Examples 1 to 13.

[0199] The experimental method is as follows: After balancing the humidity, place the seedling pots horizontally on a dedicated perforated support, with a measuring cylinder placed below. Measure 200mL of deionized water using a measuring cup and pour it into the center of the pot within 5 seconds, with the pouring spout 50mm above the top edge of the pot. Use a stopwatch to record the time required from the start of pouring until the continuous water flow from the bottom drain hole ends (switching to a dripping state and remaining dripping for 10 seconds). This time is recorded as the drainage completion time. Simultaneously, visually inspect all four bottom drain holes and use a digital caliper to measure the effective diameter of each drain hole in two mutually perpendicular directions. Take the average of the two measurements as the effective diameter of the hole. If a drain hole is completely covered by the coating film or its effective diameter is less than 80% of the original designed diameter of 6.0mm (i.e., less than 4.8mm), the hole is considered "blocked or significantly reduced." The blockage rate is calculated as (number of blocked or significantly reduced holes / 4) × 100%. Five samples are tested in each group.

[0200] Table 7 Drainage performance test results (n=5, average value):

[0201]

[0202] Analysis: Test results show that the drainage completion time for all examples (1-9) was between 10-13 seconds, and the drainage hole blockage rate was 0%. This is attributed to the "post-punching coating" or "coating avoidance" process used in this invention, as well as the reasonable use of rheology modifiers in the coating formulation, which ensured that the coating did not drip on the vertical surface or accumulate at the edge of the hole. Comparative Examples 2 and 3 used full-coverage spraying without coating avoidance treatment, causing some coating to accumulate at the bottom drainage hole under gravity, resulting in a 20-30% blockage rate and significantly prolonging the drainage time. Comparative Example 12 (insufficient filler) had a high polymer content, resulting in severe shrinkage during drying, which easily led to "edge curling" or "stringing" at the edge of the hole, resulting in 15% blockage. Comparative Example 9 had excessive second polymer added, resulting in excessive coating viscosity and poor leveling properties, which also increased the risk of blockage. Ensuring unobstructed drainage holes is a basic requirement for the functionality of seedling trays, and the process and formulation of this invention effectively avoid this common defect.

[0203] Application Example 6: Validation of the absence of extractable organic fluorine (EOF).

[0204] This application example aims to verify the environmental safety of the product of the present invention, in particular to confirm whether it contains per- or polyfluoroalkyl substances (PFAS) that are harmful to the environment and human health. The tests cover all examples (Examples 1 to 9) and all comparative examples (Comparative Examples 1 to 13).

[0205] The test was conducted according to the group standard T / CNFIA 189-2024, "Determination of Extractable Organic Fluorine Content in Food Contact Paper, Paperboard and Paper Products - Online Combustion-Ion Chromatography". The specific procedure was as follows: Samples from the side wall of a seedling tray were cut into pieces smaller than 5mm × 5mm. 5.00g of sample was accurately weighed and placed in an extraction flask. 100mL of anhydrous ethanol was added, and the sample was extracted at 200rpm for 60min on a 25℃ constant-temperature shaker. The extract was transferred and concentrated to near dryness using a nitrogen blowdown concentrator at 40℃. 1.00mL of anhydrous ethanol was added to redissolve the extract, and the mixture was thoroughly mixed. The redissolved solution was filtered through a 0.45μm PES needle filter. 100μL of the filtered redissolved solution was injected into the combustion furnace. After combustion, the fluoride ions were converted and detected by the ion chromatography system. A standard curve was established using a fluoride ion standard solution, and blank correction was performed. The method detection limit (LOD) was controlled at 5mg / kg.

[0206] Table 8. Results of tests on extractable organic fluorine:

[0207]

[0208] Analysis: As can be seen from the test results in Table 8, the extractable organic fluorine (EOF) content in all embodiments (1-9) of the present invention is less than 5 mg / kg (not detected). This is attributed to the fact that the coating formulation system of the present invention is entirely based on bio-based polymers (PHA, PLA, etc.) and natural inorganic mineral fillers, without introducing any fluorinated additives or fluorinated surfactants.

[0209] For the comparative examples, except for Comparative Example 10, the other comparative examples (1-9 and 11-13), although having defects in physical structure or formulation ratio (such as insufficient coating amount, excessive filler, or unreasonable structural design), also showed no fluorine in the chemical safety test because their basic raw material components were also fluorine-free. However, Comparative Example 10 added a fluorinated surfactant when preparing the PHA aqueous dispersion in order to pursue hydrophobic effect, resulting in an EOF value of 35 mg / kg, which was judged as "detectable". This indicates that although fluorinated additives can improve hydrophobicity, they bring clear environmental risks. This invention replaces chemical fluorinated modification with physical structural design (inorganic filler maze effect), successfully avoiding the risk of PFAS pollution while ensuring performance, and meeting the environmental protection requirements of green agricultural materials.

[0210] Application Example 7: Quantitative verification of key structural parameters in the strip-shaped flow channel area.

[0211] This application example aims to verify the actual preparation parameters of the "differentiated coating region" in each embodiment and comparative example through quantitative means, and to determine whether they conform to the structural range defined by the present invention. The test samples cover Examples 1 to 9 and Comparative Examples 1 to 13.

[0212] Test method:

[0213] Area percentage determination: The sidewall of the seedling pot was cut along the generatrix and flattened, and images were acquired using a high-resolution scanner. Image processing software (such as ImageJ) was used to identify and calculate the pixel area of ​​the coated area and the differential area (such as uncoated or weakly coated areas), and the percentage of the differential area to the total area of ​​the sidewall was calculated.

[0214] Weak coating ratio / thickness ratio determination: On the flat control sample prepared in the same batch, cut out sample pieces (area 2cm²) located in the "continuous coating area" and "guide channel area", accurately weigh the mass difference before and after coating, calculate the coating amount per unit area, and calculate the ratio of the two (weak coating ratio); or measure the cross-sectional thickness by scanning electron microscope (SEM) and calculate the ratio (thickness ratio).

[0215] Connectivity determination: Visual inspection combined with drip tracing to confirm whether the side wall drainage channel physically extends to the periphery of the bottom drain hole and is connected to it.

[0216] Conformity assessment criteria: According to the design requirements of this invention, if a sample meets all three of the following conditions, it is deemed "compliant"; otherwise, it is deemed "non-compliant" or a specific defect is pointed out:

[0217] 1. Area ratio: The area ratio of the flow channel area on the outer surface of the side wall should be between 1% and 30%.

[0218] 2. Degree of differentiation: The ratio of the dry film coating amount per unit area (weak coating ratio) or the ratio of the thickness (thickness ratio) between the flow channel area and the adjacent continuous coating area must be ≤0.80.

[0219] 3. Connectivity: The flow channel area must be connected to the area surrounding the outer edge of the bottom drain hole.

[0220] Table 9. Verification results of structural parameters:

[0221]

[0222] Note: "Compliant" for Comparative Examples 7-12 only indicates that their macroscopic structural parameters (area, ratio, connectivity) fall within the structural design range, and does not mean that they meet all the limiting conditions of this invention; for example, the dry film coating amount per unit area of ​​the topcoat of Comparative Example 7 is 20 g / m², which is lower than the 30 g / m² lower limit described in this invention, and therefore does not fall within the scope of this invention. Due to formulation or microscopic material defects (as described in Table 3), the overall performance of the above samples also did not meet the requirements. Inapplicable items are marked with "-".

[0223] Analysis: The verification results of the structural parameters clearly define the effective boundaries of the technical solution of this invention. All structural parameters of Examples 1 to 9 strictly fall within the judgment criteria range: the area ratio is controlled between 1-30%, the weak coating ratio or thickness ratio is ≤0.80, and effective communication with the bottom is achieved in all cases. This precise structural control is the physical basis for achieving the dual functions of "water blocking and entropy preservation during seedling stage" and "root penetration after transplanting".

[0224] In contrast, the structural deviations in the comparative examples directly led to performance failure. Comparative Examples 2 and 3, lacking flow channels (0% area), resulted in a closed barrier formed by the coating, preventing root penetration (refer to data from Application Example 2). While Comparative Example 4 was interconnected and differentiated, its excessively large flow channel area (35%) compromised the overall wet strength of the pot, severely reducing its wet compressive strength. Conversely, Comparative Example 13, with its insufficient channel area (0.5%), failed to provide adequate entry points for root growth.

[0225] Of particular note are Comparative Examples 5 and 6. While Comparative Example 5 possesses a suitable area-to-thickness ratio, its strip-shaped flow channel area is not connected to the bottom outer surface area around the drainage hole. This makes it difficult for roots to grow along the path near the bottom drainage hole and enter the sidewall flow channel area, demonstrating the necessity of the connectivity design. Comparative Example 6 has a weak coating ratio of 0.90, indicating that the coating in the flow channel area is still too thick, failing to create sufficient strength difference, making it difficult for roots to penetrate. This further confirms the scientific validity and criticality of the differentiation ratio (≤0.80) setting in this invention. For Comparative Examples 7-12, although their macroscopic shielding structural parameters mostly conform to the design (all using the shielding template of the embodiments), due to defects in coating amount, filler type, or environmentally friendly formulation, they still cannot obtain satisfactory overall product performance.

[0226] Experimental Results and Analysis:

[0227] Based on the test data from Application Examples 1 to 7 (Tables 3 to 9), the comprehensive performance of the PHA-coated pulp molded seedling pot with a flow channel provided by the present invention and its preparation method are analyzed as follows:

[0228] Analysis of the synergistic improvement of water-blocking performance and wet strength:

[0229] As can be seen from the data in Tables 3 to 9, the seedling pots prepared by this invention exhibit significant advantages in terms of water resistance and wet strength.

[0230] Cobb value and softening resistance: The Cobb value (60s) of the sample examples was controlled below 15.0 g / m², and the softening resistance time exceeded 120 hours. Compared with the uncoated Comparative Example 1 (Cobb value 100 g / m², softening resistance only 0.5 hours), the performance improvement is significant. This indicates that the dense coating formed by PHA and sheet-like inorganic fillers (such as talc, kaolin, mica, etc.) effectively blocks the penetration of moisture into the fiber substrate.

[0231] The key role of filler morphology: Compared with Comparative Example 11, which uses spherical filler, the Comparative Example 11 has a high Cobb value of 45.0 g / m² and a wet compressive strength retention rate of only 40%. This confirms that the "sheet-like inorganic filler" emphasized in this invention significantly extends the diffusion path of water molecules by forming a parallel "maze effect" in the coating, and is a key factor in achieving high barrier properties.

[0232] Integrity of the coating structure: The failures of Comparative Example 7 (coating amount of only 20 g / m²) and Comparative Example 12 (filler ratio too low) indicate that forming a continuous coating with a certain rigidity and thickness is crucial for maintaining the structural integrity of the seedling pot under wet conditions.

[0233] Analysis of the regulatory effect of flow channel structure on root penetration and degradation:

[0234] The core innovation of this invention lies in the introduction of a "differentiated coating area (strip-shaped flow channel)" to solve the problem of "root obstruction" in traditional water-blocking coatings.

[0235] Root penetration efficiency: The root penetration rates of Examples 1-9 were all above 80%, with the highest reaching 97% (Example 5). In contrast, the root penetration rates of Comparative Examples 2 and 3 with full-coverage coatings were only 25%-30%, severely inhibiting root growth. This indicates that the flow channel successfully became a "window" for root penetration.

[0236] The necessity of connectivity: Although Comparative Example 5 had a flow channel, it was not connected to the bottom drainage hole, resulting in a root penetration rate of only 55%. This confirms that the "connectivity" design (described in this invention) plays a decisive role in guiding the root system to grow from the bottom to the sidewall and find a breakthrough point.

[0237] Balancing Area Ratio: Comparative Example 13 reduced the area ratio of the drainage channel to 0.5%, resulting in a root penetration rate of 35%; while Comparative Example 4 increased the area ratio to 35%, achieving a high penetration rate but severely sacrificing wet compressive strength (retention rate of only 45%). The data from these examples demonstrate that controlling the area ratio between 1% and 30% achieves the optimal balance between water blocking and root penetration.

[0238] Surface properties and environmental safety analysis:

[0239] Abrasion resistance and adhesion: The cross-cut adhesion grades of the sample samples in both dry and wet conditions were all grade 0 (or occasionally grade 1), with abrasion weight loss as low as 4-6 mg, which is better than the unfilled comparative example 2 (abrasion loss of 30 mg). This indicates that the addition of inorganic fillers not only improves the barrier properties but also enhances the mechanical abrasion resistance of the coating.

[0240] Fluorine-free and environmentally friendly characteristics: In all examples and comparative examples without added fluorine-containing additives, the content of extractable organic fluorine (EOF) was not detected (<5 mg / kg). Only in comparative example 10, due to the addition of a fluorinated surfactant, was EOF detected (35 mg / kg). This invention achieves excellent hydrophobic effects (contact angle >110°) without relying on fluorinated chemicals through physical structural design, which is in line with the development trend of green agriculture.

[0241] Trend analysis of the impact of changes in the content of key components on experimental results:

[0242] The influence trend of dry film coating amount per unit area (30g / m² to 120g / m²) on water-resistant surface coating:

[0243] As the coating amount increased from 30 g / m² (Examples 1 and 8) to 120 g / m² (pot rim area in Example 5), the anti-softening time and wet compressive strength retention rate of the seedling pots showed an upward trend. For example, the anti-softening times of Example 2 (60 g / m²) and Example 3 (90 g / m²), with higher coating amounts, reached 155 h and 130 h, respectively, which were better than Example 8 (35 g / m², 122 h), with a lower coating amount. However, when the coating amount was below the critical value of 30 g / m² (such as 20 g / m² in Comparative Example 7), the water-blocking performance dropped sharply (anti-softening time was only 60 h), failing to meet the usage requirements. Therefore, 30-120 g / m² is the effective range for ensuring performance, and appropriately increasing the coating amount within this range is beneficial for improving water resistance and durability.

[0244] The influence trend of the area ratio of the strip-shaped diversion channel zone (1% to 30%):

[0245] This parameter exhibits a typical "inverted U-shaped" or "trade-off" trend. As the area percentage increases from 1% (Example 4) to 30% (Example 5), the root penetration rate shows a significant upward trend (from 80% to 97%), which is beneficial for transplant survival. However, at the same time, the retention rate of wet compressive strength shows a slow downward trend. When the area percentage exceeds the upper limit of 30% (e.g., 35% in Comparative Example 4), the retention rate of wet compressive strength drops sharply to 45%, compromising the structural stability of the container; when the area percentage is below the lower limit of 1% (e.g., 0.5% in Comparative Example 13), the root penetration rate drops sharply to 35%, losing its root-promoting function. Therefore, the range of 1%-30% precisely defines the balance window between structural stability and biological function.

[0246] The influence trend of the mass ratio of inorganic filler to PHA (0.80:1 to 2.00:1):

[0247] As the filler ratio increases within the range of 0.80:1 to 2.00:1, the rigidity, abrasion resistance, and water-blocking path tortuosity of the coating increase. Good overall performance was achieved at different ratios in the examples. However, when the filler ratio was below 0.80:1 (Comparative Example 12), polymer shrinkage led to stress concentration and a decrease in wet strength; when the filler ratio was above 2.00:1 (Comparative Example 8), the resin matrix in the coating was insufficient to completely encapsulate the filler, resulting in surface "powdering," increased abrasion weight loss (12 mg), and a decreasing trend in adhesion. This indicates that 0.80:1 to 2.00:1 is the optimal ratio range for maintaining a dense microstructure and stable mechanical properties in the coating.

[0248] In summary, this invention has successfully prepared pulp molded seedling pots that combine excellent wet stability, good root penetration ability, and environmental friendliness by precisely controlling the coating formulation (PHA / flaky filler ratio), coating structure (coating amount), and differentiated functional areas (proportion and connectivity of flow channels). This solves the problem of balancing water resistance and root penetration in existing technologies.

[0249] Those skilled in the art should understand that the above embodiments are merely exemplary and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the technical solutions of the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A PHA water-based water-resistant coated pulp molded seedling pot containing inorganic fillers and blended polymers, characterized in that, The pulp molding seedling tray includes: The container body is a three-dimensional fiber-based structure molded from pulp, and the container body has side walls, a bottom, and a bowl opening; Drainage holes are provided in the through holes at the bottom. There are 4 drainage holes with a diameter of 6.0 mm. The centers of the holes are located on the same circumference and are distributed at equal 90° intervals. A water-based polyhydroxyalkanoate (PHA) water-blocking coating is disposed on the surface of the container body and covers the outer surface of the sidewall. The PHA water-blocking coating has a multi-layer coating structure, including a sealing bottom coating disposed on the surface of the container body and a water-blocking top coating disposed outside the sealing bottom coating. The water-blocking top coating contains at least PHA and sheet-like inorganic fillers, and further contains a second polymer. The sealing bottom coating is formed of a water-based biofilm-forming material or a biodegradable film-forming material. The dry film coating weight per unit area of ​​the sealing bottom coating is 5 to 30 g / m². The water-blocking surface coating is formed by coating an aqueous coating composition comprising polyhydroxyalkanoate, flake-like inorganic filler, and a second polymer, followed by drying to form a film. The second polymer is a biodegradable polymer selected from one or more of polylactic acid, polybutylene succinate, polycaprolactone, polyglycolic acid, or thermoplastic starch. The mass ratio of the second polymer to the dry solids of the polyhydroxyalkanoate is from 0.02:1 to 1.50:

1. A differentiated coating area is disposed on the sidewall, the differentiated coating area having one or a combination of the following characteristics relative to the adjacent outer surface region of the sidewall having a continuous polyhydroxyalkanoate aqueous water-blocking coating: Lower coating coverage; Lower dry film coating amount per unit area; The coating has a lower apparent thickness; The coating continuity is interrupted; In the outer surface region of the sidewall of the water-blocking surface coating adjacent to the differentiated coating area and having a continuous polyhydroxyalkanoate water-blocking coating, the dry film coating amount per unit area of ​​the water-blocking surface coating is 30 to 120 g / m². The differentiated coating area includes a strip-shaped flow channel area that extends continuously from the opening of the basin to the bottom after being spread on the outer surface of the sidewall. The area of ​​the strip-shaped flow channel area after being spread on the outer surface of the sidewall accounts for 1% to 30% of the total area of ​​the outer surface of the sidewall. The width of the strip-shaped flow channel area after unfolding on the outer surface of the side wall is 1 to 15 mm, and when there are two or more strip-shaped flow channel areas, the edge spacing between two adjacent strip-shaped flow channel areas is 3 to 50 mm. The four strip-shaped flow guiding channels are aligned with the center line of the four drainage holes at the bottom along the generatrix of the side wall, so that the four strip-shaped flow guiding channels extend continuously from the mouth of the basin to the bottom and cover the periphery of the corresponding drainage hole punching position. The sheet-like inorganic filler is selected from one or more of the following: talc, kaolin, mica, montmorillonite, vermiculite, sepiolite, attapulgite, diatomite, wollastonite, zeolite, aluminum silicate, calcium carbonate, magnesium carbonate, barium sulfate, calcium sulfate, silicon dioxide, titanium dioxide, zinc oxide, aluminum oxide, aluminum hydroxide, or magnesium hydroxide. The median particle size D of the sheet-like inorganic filler 50 The particle size is 0.01 to 15 μm, and the mass ratio of the solid to the polyhydroxyalkanoate is 0.80:1 to 2.00:

1. The ratio of the dry film coating amount per unit area of ​​the strip-shaped flow channel area to the adjacent sidewall outer surface area with the continuous polyhydroxyalkanoate water-resistant coating is ≤0.80, or the ratio of the apparent coating thickness of the strip-shaped flow channel area to the adjacent sidewall outer surface area with the continuous polyhydroxyalkanoate water-resistant coating is ≤0.

80. The strip-shaped flow channel area is connected to the bottom outer surface area around the outer edge of the drainage hole; Furthermore, the bottom outer surface area around the outer edge of the drain hole is an uncoated area, or the ratio of the dry film coating per unit area of ​​the bottom outer surface area around the outer edge of the drain hole to the dry film coating per unit area of ​​the adjacent sidewall outer surface area with the continuous polyhydroxyalkanoate water-resistant coating is ≤0.60, or the continuity of the polyhydroxyalkanoate water-resistant coating is interrupted at the edge of the drain hole. The Cobb60 content of the sidewall of the seedling pot is ≤15g / m². The ratio of the wet compressive strength of the seedling pots after soaking in deionized water for 24 hours to the dry compressive strength of the same batch is ≥80%. And the softening prevention time is ≥120h; The static water contact angle of adjacent continuous coating areas on the outer surface of the sidewall of the seedling pot is ≥110°; The dry grading level of the adjacent continuous coating area on the outer surface of the seedling pot is 0, and the wet grading level is 0 after soaking in deionized water for 24 hours. The abrasion weight loss of adjacent continuous coating areas on the outer surface of the seedling pot is ≤5mg.

2. The PHA water-based water-resistant coated pulp molded seedling pot containing inorganic fillers and blended polymers according to claim 1, characterized in that, The polyhydroxyalkanoate is selected from one or a combination of the following: short-chain polyhydroxyalkanoates; medium- and long-chain polyhydroxyalkanoates; copolymer polyhydroxyalkanoates containing short-chain monomer units and medium- and long-chain monomer units; or blends, copolymers, or modifiers of any two or more of the above polyhydroxyalkanoates. The short-chain polyhydroxy fatty acid ester is selected from one or more of poly3-hydroxybutyrate, poly3-hydroxybutyrate-co-3-hydroxyvalerate, and poly3-hydroxybutyrate-co-4-hydroxybutyrate. The medium- and long-chain polyhydroxy fatty acid esters are selected from one or more of poly(3-hydroxyhexanoate), poly(3-hydroxyheptanoate), poly(3-hydroxyoctanoate), poly(3-hydroxynonanoate), poly(3-hydroxydecanoate), poly(3-hydroxyundecanoate), poly(3-hydroxydodecanate), poly(3-hydroxytridecanate), and poly(3-hydroxytetradecanoate).

3. The PHA water-based water-resistant coated pulp molded seedling pot containing inorganic fillers and blended polymers according to claim 1, characterized in that, The extractable organic fluoride content in the seedling pot was tested according to the test method T / CNFIA 189-2024 and the result was not detected. The detection limit of the test method is ≤5mg / kg. Among them, not detected is determined by the extractable organic fluoride test result being less than the detection limit of the test method.

4. The PHA water-based water-resistant coated pulp molded seedling pot containing inorganic fillers and blended polymers according to claim 1, characterized in that, The aqueous coating composition comprises dispersing and stabilizing components and additives; The dispersing and stabilizing component is one or more of anionic, nonionic, or amphoteric surfactants; The additives are selected from one or more of the following: toughening agents, wax emulsions, hydrophobic additives, rheology modifiers, wetting agents, defoamers, film-forming aids, crosslinking agents, adhesion promoters, bactericides and preservatives, pH adjusters, or freeze-thaw stabilizers.

5. The PHA water-based water-resistant coated pulp molded seedling pot containing inorganic fillers and blended polymers according to claim 1, characterized in that, The polyhydroxyalkanoate water-resistant coating is a gradient coating and meets the following conditions: the dry film coating per unit area in the basin opening region 0–15 mm from the basin opening edge is greater than the dry film coating per unit area in the middle area of ​​the side wall 15–60 mm from the basin opening edge.

6. The PHA water-based water-resistant coated pulp molded seedling pot containing inorganic fillers and blended polymers according to claim 1, characterized in that, Differentiated units are provided within the strip-shaped flow channel area. The differentiated units are one or a combination of the following: dot matrix, mesh, microporous, annular, or spiral. The equivalent circle diameter corresponding to the projected area of ​​the dot matrix differentiated unit after unfolding on the outer surface of the sidewall is 0.5 to 8 mm, and the dot matrix spacing is 1 to 30 mm.

7. The PHA water-based water-resistant coated pulp molded seedling pot containing inorganic fillers and blended polymers according to claim 1, characterized in that, The base fiber material of the container body includes one or more of wood pulp, bamboo pulp, herbaceous plant fiber pulp or regenerated fiber pulp, wherein the herbaceous plant fiber pulp includes sugarcane bagasse pulp, straw pulp, reed pulp or hemp pulp. The recycled fiber pulp includes waste paper pulp, which includes newspaper-based recycled fiber pulp; and the container body further includes lignin or lignin derivatives, the amount of which is 0.1 wt% to 30 wt% based on oven-dry fiber.

8. A method for preparing a PHA water-based water-resistant coated pulp molded seedling pot containing inorganic fillers and blended polymers according to claim 1, characterized in that, The preparation method includes the following steps: Step 1. Pulp preparation: Mix the fiber raw material with deionized water and dissociate it using a high-speed shear disperser for 20 minutes to obtain a pulp suspension; Step 2. Wet forming: Inject the pulp suspension obtained in Step 1 into the forming mold, turn on the vacuum pump to form a wet blank; Step 3. Dehydration and drying: After pressing and dehydrating the wet blank obtained in step 2, place it in a forced-air drying oven to dry, and obtain a preformed blank; Step 4. Hot pressing and shaping: The preform obtained in step 3 is placed in a hot press for hot pressing and shaping to obtain a container body with side walls, bottom and rim. Step 5. Conditioning: Place the container body obtained in Step 4 in a constant temperature and humidity chamber to condition the moisture content to 1wt%–15wt%. The moisture content is expressed as a mass fraction and determined according to GB / T 462-2023 to obtain the container body to be coated. Step 6. Preparation of composition: The aqueous dispersion of polyhydroxy fatty acid ester, the sheet-like inorganic filler, and the second polymer are added to a high-speed shear disperser and dispersed at 20–60°C to obtain an aqueous coating composition, wherein the second polymer is a biodegradable polymer selected from one or more of polylactic acid, polybutylene succinate, polycaprolactone, polyglycolic acid, or thermoplastic starch. Step 7. Coating: The aqueous coating composition obtained in step 6 is coated onto the outer surface of the container body to be coated obtained in step 5 to form a wet coating and obtain a coated part; Step 8. Forming a differentiated area: During the coating process in Step 7, a masking or differentiated deposition method is used to form a strip-shaped flow channel area that extends continuously from the rim to the bottom of the coated part after the sidewall of the sidewall is expanded. This is the differentiated coating area, resulting in a differentiated coated part. Step 9. Film Formation and Punching: After drying the differentiated coating obtained in Step 8 into a film, a punch is used to punch holes at the bottom to form drainage holes, and the bottom outer surface area around the outer edge of the drainage holes is connected to the strip-shaped flow channel area to obtain a pulp molded seedling pot; wherein, due to the punching and cutting process, the continuity of the polyhydroxyalkanoate water-based water-blocking coating at the edge of the drainage hole is interrupted, forming an exposed fiber substrate interface; Alternatively, during the coating process in step 7, a pre-defined area for the bottom drainage hole can be reserved to avoid coating. After the differentiated coating obtained in step 8 is dried into a film, a punch is used to punch holes in the pre-defined area for the drainage hole to form drainage holes. The bottom outer surface area around the outer edge of the drainage hole is connected to the strip-shaped flow channel area to obtain a pulp molded seedling pot.

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