Compostable paper-based molded coffee capsule and phb water dispersion in-situ film forming barrier heat seal composite layer and preparation method and application

Abstract

The application discloses a paper-based moulded coffee capsule capable of natural composting, a PHA aqueous dispersion in-situ film-forming barrier heat-sealing composite layer and a preparation method and application thereof, and belongs to the field of degradable packaging and single-cup extraction capsules. The capsule comprises a capsule body formed by moulded paper pulp, a side wall, a bottom wall and a mouth flange, a biodegradable polyester-based film sealing member sealed to the flange, and a polyhydroxyalkanoate barrier heat-sealing composite layer coated on the inner surface of the body and the sealing surface of the flange. The composite layer is obtained by in-situ film-forming of a particle size gradient double-layer aqueous dispersion, and comprises an infiltration anchoring layer located in the pores of the paper pulp and a continuous dense layer on the outside along the thickness direction. The flange is a heat-pressed densification area, and a locally thickened heat-sealing ring is formed on the sealing surface of the flange. The application realizes the moisture and oxygen barrier and interface bonding performance through physical anchoring of small particle size components and surface film-forming of large particle size components, and guarantees the brewing sealing performance.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable packaging and single-cup extraction capsules, specifically relating to compostable paper-based molded coffee capsules and their PHA aqueous dispersion in-situ film-forming barrier heat-sealing composite layer, preparation method and application. Background Technology

[0002] To meet the sensitivity of coffee powder to water vapor and oxygen during storage and the temperature and pressure resistance requirements during brewing, capsule coffee traditionally uses aluminum or multi-layered plastic composite structures. These structures are typically mixed with coffee grounds after use, making sorting and recycling difficult and hindering the formation of an efficient material closed loop.

[0003] To enhance the renewability and compostability of paper-based capsules, existing technologies propose using pulp or paperboard as the capsule body and setting a barrier layer or liner on its inner surface. For example, WO2019064017A1 discloses a capsule structure using paperboard or pulp as the main body and setting a biodegradable polymer coating or overlay on its surface; EP4620861A2 and JP2024535486A disclose attaching or molding a barrier liner to the inner surface of a pulp capsule to improve moisture and oxygen barrier performance; GB2584959A discloses a scheme to fix the sealing element and achieve sealing in the capsule flange area using a starch-based sealant; and US20220169430A1 discloses a scheme to construct a barrier coating on the surface of a paper-based capsule using plasma-enhanced chemical vapor deposition (PECVD) to improve barrier properties. The above-mentioned solutions have a certain effect on improving the barrier or sealing performance of paper-based capsules, but the following engineering problems still exist under the coupled conditions of high-temperature hot water wetting and boiling pressure difference: First, the pre-fabricated inner lining film or coating is prone to interface peeling, wrinkling or local leakage during puncture, pressure and wetting; Second, the three-dimensional surface is prone to forming through-hole defect channels such as pinholes and microcracks during coating or molding; Third, the gap and roughness fluctuation of the sealing holes of the flange lead to a narrow heat sealing window and a large dispersion of heat sealing strength; Fourth, the equipment and process cost of vacuum deposition barrier layers is high, and it is difficult to couple with the pulp molding production line.

[0004] To replace traditional paper-based surface treatment agents such as fluorinated oil repellents, existing technologies have proposed using aqueous dispersions based on polyhydroxyalkanoates (PHA) for paper-based barrier coatings. For example, WO2020036843A1, ZA202101369B and their families EP3837322B1, CN112867766A, and CN116218332A disclose biodegradable coating systems in which an aqueous PHA dispersion is coated onto the surface of cardboard or other biodegradable substrates and dried to form a film; SE2330419A1 discloses a method of forming a first and second aqueous PHA coating through multiple coating layers to obtain a fiber-based barrier material that meets the requirements of water vapor transmission rate (WVTR) and water absorption; CN115996838A discloses a scheme in which an aqueous PHA dispersion is first coated and dried to remove water, and then the coating is heated a second time to melt the PHA to seal the pores between particles and form a continuous and dense PHA layer. The aforementioned technologies are primarily geared towards flat paper or paperboard barrier packaging or food service paper products, with their coating structures and process windows mainly focused on flat substrates. When directly applied to three-dimensional porous pulp molded coffee capsules, issues remain, such as insufficient uniformity of coating coverage on the three-dimensional inner surface, a high risk of coating-paper interface peeling under high temperature and humidity brewing pressure differentials, and a narrow heat-sealing window at the flange sealing surface due to pores and corrugations.

[0005] In addition, published literature also discloses various PHA-based aqueous emulsion systems for paper-based barrier coatings. These systems may include biodegradable polyesters such as PHA and polybutylene succinate (PBAT), as well as hydrophilic polymers such as polyvinyl alcohol (PVOH, also known as PVA), to improve coating rheology, film formation, and barrier properties. Other published literature discloses paper-based barrier coating compositions based on acrylic or polyurethane emulsions combined with hydrophilic polymer modifiers. While these emulsion or dispersion systems can improve paper-based barrier coatings or coating compatibility, their focus remains primarily on planar paper-based barrier coatings. They do not yet address the integrated structural design for three-dimensional porous interface anchoring in pulp-molded coffee capsules, the densification of flange sealing surfaces, and the supply of localized heat-sealing materials. Furthermore, they do not provide comprehensive constraints on coating interface stability and sealing windows under high-temperature, high-humidity, and high-pressure differential brewing conditions.

[0006] Therefore, there is an urgent need for a complete structural and process solution for paper-based molded coffee capsules: without relying on pre-fabricated self-supporting inner liner film attachment or high-cost vacuum deposition process, a penetrating anchoring layer is constructed in the three-dimensional pulp pores and a continuous dense layer is constructed on the surface through two-stage water-based PHA dispersion spraying and in-situ thermal fusion or hot pressing film formation. At the same time, the sealing processing window and sealing consistency are improved through flange hot pressing densification and local thickening of the flange area heat sealing ring design, thereby simultaneously meeting the requirements of shelf-life barrier, brewing stability and composting disposal. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and to provide a compostable paper-based molded coffee capsule and its PHA aqueous dispersion in-situ film-forming barrier heat-sealing composite layer, preparation method and application. It provides a fully biodegradable, high-performance and low-cost solution to address the technical bottlenecks of weak barrier properties, unstable heat sealing and easy delamination of existing paper-based capsules.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention provides a compostable paper-based molded coffee capsule, comprising: a capsule body formed from molded pulp, the capsule body having side walls, a bottom wall, and a flange located around the opening, the side walls and the bottom wall forming a cavity for containing coffee powder; a sealing member, the sealing member being a biodegradable polyester-based film or a blended film thereof, sealed to the flange to close the cavity; and a PHA barrier heat-sealing composite layer covering the inner surface of the capsule body and the sealing surface of the flange. The capsule body is a three-dimensional porous pulp molding structure, and the surface porosity of the sidewall is 50% to 60%, specifically 50%, 51%, 52%, 53%, 54%, 55%, 56%, 56.5%, 57%, 58%, 59%, or 60%; the flange is a hot-pressed densified area with a surface porosity of 30% to 40%, specifically 30%, 30.5%, 31%, 32%, 32.5%, 33%, 33.5%, 34%, 34.5%, 35%, 35.5%, 36%, 37%, 38%, 39%, or 40%. The PHA barrier heat-sealing composite layer is obtained by sequentially spraying a first aqueous PHA dispersion and a second aqueous PHA dispersion, followed by drying and in-situ thermal fusion or hot pressing on the capsule body to form a film; wherein, the first aqueous PHA dispersion is used to form a penetration anchoring layer, and the second aqueous PHA dispersion is used to form a continuous dense layer; the solid content ratio of the second aqueous PHA dispersion to the solid content of the first aqueous PHA dispersion is 1.5 to 6.0, and the volume average particle size ratio of the second aqueous PHA particles to the volume average particle size of the first aqueous PHA particles is 2 to 10. The PHA barrier heat-sealing composite layer includes an infiltrated anchoring layer and a continuous dense layer along its thickness direction. The infiltrated anchoring layer is located within the pores of the pulp fiber surface and encapsulates the fiber to form a mechanically interlocking interface. Its infiltration depth is 20μm to 300μm, specifically 20μm, 30μm, 50μm, 70μm, 80μm, 100μm, 120μm, 140μm, 150μm, 160μm, and 180μm. The thickness of the continuous dense layer is 6 μm, 200 μm, 220 μm, 250 μm, 280 μm, or 300 μm; the continuous dense layer is located outside the penetrating anchoring layer and forms a continuous film with an equivalent thickness of 6 μm to 40 μm, specifically 6 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 24 μm, 25 μm, 28 μm, 30 μm, 35 μm, or 40 μm.The PHA barrier heat-sealing composite layer has different dry coating amounts in different areas. The dry coating amount on the inner surface of the sidewall and the inner surface of the bottom wall is 8 g / m² to 40 g / m², specifically 8 g / m², 10 g / m², 15 g / m², 20 g / m², 25 g / m², 30 g / m², 35 g / m², or 40 g / m². The dry coating amount on the sealing surface of the flange is 20 g / m² to 120 g / m², specifically 20 g / m², 30 g / m², 40 g / m², 50 g / m², 60 g / m², 70 g / m², 80 g / m², 90 g / m², 96 g / m², or 100 g / m². / m², 110g / m² or 120g / m², and the ratio of the dry coating amount on the sealing surface of the flange to the dry coating amount on the inner surface of the sidewall is 2.0 to 12.0, specifically 2.0, 2.5, 2.6, 3.0, 3.5, 3.6, 4.0, 5.0, 6.0, 6.1, 8.0, 10.0, 11.9 or 12.0, thereby forming a locally thickened PHA heat-sealing ring continuously along the circumference of the flange on the sealing surface of the flange. The ring width of the heat-sealing ring is 1.5mm to 4.5mm, specifically 1.5mm, 2.0mm, 2.5mm, 3.0mm, 3.5mm, 4.0mm or 4.5mm. The proportion of PHA in the dry film of the PHA barrier heat-sealing composite layer is ≥85wt%, specifically 85wt%, 88wt%, 89wt%, 90wt%, 92wt%, 95wt%, 98wt%, or 100wt%.

[0010] The ratio of the dry coating amount on the sealing surface of the flange to the dry coating amount on the inner surface of the bottom wall is 2.0 to 12.0, and the specific ratio can be 2.0, 2.5, 3.0, 3.5, 4.0, 5.0, 6.0, 8.0, 10.0 or 12.0.

[0011] The PHA is selected from one or more of short-chain PHA, medium- and long-chain PHA, and copolymers formed between short-chain and medium- and long-chain PHA monomers. The short-chain PHA 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 PHA 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-hydroxytetrate), poly(3-hydroxytetradecanoate), poly(3-hydroxypentadecanate), poly(3-hydroxyhexadecanoate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH); the proportion of PHA in the dry film of the PHA barrier heat-sealing composite layer is ≥85wt%, specifically 85wt%, 89wt%, 90wt%, 95wt%, or 100wt%.

[0012] The capsule body also includes a bio-based coating disposed on its inner surface, and the PHA barrier heat-sealing composite layer is coated on the surface of the bio-based coating; the bio-based coating is a polysaccharide base coating; the polysaccharide base coating includes one or more of starch and its derivatives, cellulose and its derivatives, chitosan and its derivatives, alginate, pectin, β-glucan, xanthan gum, and guar gum.

[0013] The dry film of the PHA barrier heat-sealing composite layer further comprises 1 wt% to 20 wt% of a bio-based plasticizing and toughening component based on the total mass of the dry film, specifically 1 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, 15 wt%, or 20 wt%; the bio-based plasticizing and toughening component is selected from one or more of organic ester plasticizers, epoxidized vegetable oils, natural polyols and their esters, and biodegradable aliphatic polyester toughening phases; and / or, the dry film of the PHA barrier heat-sealing composite layer further comprises 0.1 wt% to 15 wt% of a barrier reinforcing filler, specifically 0.1 wt%, 1 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt%, or 15 wt% based on the total mass of the dry film, the barrier reinforcing filler being selected from one or more of inorganic sheet fillers, inorganic particulate fillers, and bio-based nanofillers.

[0014] The compostable paper-based molded coffee capsules meet one or more of the following properties:

[0015] Under conditions of 38℃ and 90% relative humidity, the WVTR of the composite sample formed by the capsule body and the PHA barrier heat-sealing composite layer on its sidewall and bottom wall was measured according to GB / T 1037-2021 to be ≤0.90 g / (m²·24h). Specific values ​​could be 0.40 g / (m²·24h), 0.42 g / (m²·24h), 0.45 g / (m²·24h), 0.48 g / (m²·24h), 0.50 g / (m²·24h), 0.52 g / (m²·24h), 0.55 g / (m²·24h), 0.58 g / (m²·24h), and 0.6 g / (m²·24h). 0g / (m²·24h), 0.62g / (m²·24h), 0.65g / (m²·24h), 0.68g / (m²·24h), 0.70g / (m²·24h), 0.72g / (m²·24h), 0.75g / (m² ·24h), 0.78g / (m²·24h), 0.80g / (m²·24h), 0.82g / (m²·24h), 0.85g / (m²·24h), 0.88g / (m²·24h) or 0.90g / (m²·24h);

[0016] Under conditions of 23℃ and 0% relative humidity, in accordance with GB / T The oxygen permeability (OTR) measured from 19789 to 2021 was ≤0.82 cm³ / (m²·24h·0.1MPa), with specific values ​​including 0.30 cm³ / (m²·24h·0.1MPa), 0.35 cm³ / (m²·24h·0.1MPa), 0.38 cm³ / (m²·24h·0.1MPa), 0.40 cm³ / (m²·24h·0.1MPa), 0.42 cm³ / (m²·24h·0.1MPa), 0.45 cm³ / (m²·24h·0.1MPa), 0.48 cm³ / (m²·24h·0.1MPa), 0.50 cm³ / (m²·24h·0.1MPa), 0.52 cm³ / (m²·24h·0.1MPa), and 0.55 cm³ / (m²·24h·0.1MPa). m²·24h·0.1MPa), 0.58cm³ / (m²·24h·0.1MPa), 0.60cm³ / (m²·24h·0.1MPa), 0.62cm ³ / (m²·24h·0.1MPa), 0.65cm³ / (m²·24h·0.1MPa), 0.68cm³ / (m²·24h·0.1MPa), 0.70 cm³ / (m²·24h·0.1MPa), 0.72cm³ / (m²·24h·0.1MPa), 0.75cm³ / (m²·24h·0.1MPa), 0. 78cm³ / (m²·24h·0.1MPa), 0.80cm³ / (m²·24h·0.1MPa) or 0.82cm³ / (m²·24h·0.1MPa);

[0017] According to GB / T 1540-2002, the erectile function value for 60 seconds should be ≤2.4 g / m², with specific values ​​including 0.8 g / m², 0.9 g / m², 1.0 g / m², 1.1 g / m², 1.2 g / m², 1.3 g / m², 1.4 g / m², 1.5 g / m², 1.6 g / m², 1.7 g / m², 1.8 g / m², 1.9 g / m², 2.0 g / m², 2.1 g / m², 2.2 g / m², 2.3 g / m², or 2.4 g / m².

[0018] According to GB / T 2790-1995, the 180° peel test shall be performed to determine the sealing peel strength of the flange sealing part to be ≥10.0N / 15mm. The specific values ​​can be 10.0N / 15mm, 10.2N / 15mm, 10.5N / 15mm, 10.8N / 15mm, 11.0N / 15mm, 11.2N / 15mm, 11.5N / 15mm, 11.8N / 15mm, 12.0N / 15mm, 12.2N / 15mm, 12.5N / 15mm, 12.8N / 15mm, 13.0N / 15mm, 13.2N / 15mm, 13.5N / 15mm, 13.8N / 15mm, 14.0N / 15mm, or 15.0N / 15mm.

[0019] Total organic fluorine was not detected by oxygen bomb combustion combined with fluoride ion selective electrode method according to EN 14582:2016, and the method detection limit was ≤5 mg / kg;

[0020] According to GB / T 19277.1-2025 controlled composting conditions, the biodegradation rate after 45 days is ≥96%, and the specific values ​​can be 96.0%, 96.2%, 96.5%, 96.8%, 97.0%, 97.2%, 97.5%, 97.8%, 98.0%, 98.2%, 98.5%, 98.8%, 99.0%, or 99.5%.

[0021] The sealing component comprises a biodegradable polyester film or a blended film thereof, and a PHA heat-sealing layer disposed on its side facing the flange, so as to form a heat-sealing match with the continuous dense layer and the locally thickened PHA heat-sealing ring; wherein, the biodegradable polyester film is selected from one or more of polylactic acid (PLA) film, polybutylene succinate (PBS) film, polybutylene adipate (PBAT) film, and polycaprolactone (PCL) film; the PHA heat-sealing layer may be of the same or different type as the PHA of the continuous dense layer.

[0022] Under heat sealing pressure of 0.30 MPa and holding time of 0.8 s, according to GB / T 2790-1995 A 180° peel test was conducted. The heat-sealing initiation temperature of the capsule was 112℃ to 135℃, specifically 112℃, 114℃, 115℃, 116℃, 118℃, 119℃, 120℃, 123℃, 124℃, 125℃, 130℃, or 135℃, and the heat-sealing window width was 30℃ to 48℃, specifically 30℃, 32℃, 33℃, 34℃, 35℃, 36℃, 38℃, 40℃, 42℃, 44℃, 45℃, 46℃, or 48℃. A boiling resistance test was conducted at 83℃ to 86℃ and 1.9MPa pressure, with a sample size N=50. The boiling leakage rate of the capsule was ≤2%, specifically 0%, 0.5%, 1%, 1.5%, or 2%, and the bursting or delamination rate was ≤1%.

[0023] The present invention also provides a method for preparing the above-mentioned paper-based molded coffee capsule, comprising the following steps:

[0024] Step 1. Prepare pulp slurry and wet mold it to obtain a wet pulp blank with sidewalls, bottom wall and flange;

[0025] Step 2. Dehydrate, dry, and shape the wet pulp blank obtained in Step 1 to obtain the capsule body, wherein the moisture content of the capsule body before coating is 2wt% to 8wt%, specifically 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, or 8wt%.

[0026] Step 3. Perform hot-press densification treatment on the flange of the capsule body obtained in Step 2 to obtain a densified capsule body; the temperature of the hot-press densification treatment is 90℃ to 165℃, specifically 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃ or 165℃, the pressure is 0.2MPa to 10MPa, specifically 0.2MPa, 1.0MPa, 2.0MPa, 3.0MPa, 4.0MPa, 5.0MPa, 8.0MPa or 10MPa, and the time is 0.2s to 60s, specifically 0.2s, 1.0s, 2.0s, 5.0s, 10s, 30s or 60s;

[0027] Step 4. Apply the first aqueous PHA dispersion to the inner surface of the densified capsule body and the sealing surface of the flange obtained in Step 3 using a spraying method, and pre-dry to obtain the first coated capsule body; wherein, the solid content of the first aqueous PHA dispersion is 10wt% to 25wt%, specifically 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt%, or 25wt%, and the volume average particle size of the PHA particles in the dispersion is 200nm to 2000nm, specifically 200nm, 220nm, 250nm, 300nm, 500nm, or 800nm. nm, 1000nm, 1500nm or 2000nm; the water content of the coated surface of the first coated capsule body is controlled to be 3wt% to 15wt%, specifically 3wt%, 5wt%, 8wt%, 10wt%, 12wt% or 15wt%; and, during the coating process and / or drying process, when a vacuum or pressure difference is applied to the capsule body to promote the penetration of the first aqueous PHA dispersion into the pulp pores, the vacuum gauge pressure is 5kPa to 80kPa, specifically 5kPa, 10kPa, 20kPa, 30kPa, 40kPa, 50kPa, 60kPa, 70kPa or 80kPa;

[0028] Step 5. Apply the second aqueous PHA dispersion to the coating surface of the first coated capsule body obtained in Step 4 using a spraying method, and dry it to obtain the second coated capsule body; wherein, the solid content of the second aqueous PHA dispersion is 20wt% to 60wt%, specifically 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, or 60wt%, and the volume average particle size of the PHA particles in the dispersion is 200nm to 2000nm, specifically 200nm, 300nm, 400nm, 450nm, 500nm, 600nm, 800nm, 900nm, 1000nm, 1500nm, or 2000nm. 00nm; the solid content ratio of the second aqueous PHA dispersion to the solid content of the first aqueous PHA dispersion is 1.5 to 6.0, specifically 1.5, 2.0, 2.5, 3.0, 4.0, 5.0 or 6.0, and the volume average particle size ratio of the second aqueous PHA particles to the volume average particle size ratio of the first aqueous PHA particles is 2 to 10, specifically 2, 2.4, 3, 4, 5, 8 or 10; and, in the flange area, by increasing the spraying feed amount of the second aqueous PHA dispersion and / or increasing the number of spraying passes, the dry coating amount of the flange sealing surface is higher than the dry coating amount of the inner surface of the side wall and the inner surface of the bottom wall, thereby forming a locally thickened PHA heat-sealing ring continuously along the flange circumference on the flange sealing surface after film formation;

[0029] Step 6. Perform heat fusion or hot pressing on the second coated capsule body obtained in Step 5 to form a penetrating anchoring layer and a continuous dense layer of PHA, and form a heat-sealing interface on the sealing surface of the flange to obtain the film-formed capsule body; the temperature for heat fusion or hot pressing film formation is 130℃ to 165℃, specifically 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃ or 165℃, the holding time is 5s to 120s, specifically 5s, 10s, 15s, 30s, 60s or 120s, and the hot pressing pressure is 0.2MPa to The pressure can be 3 MPa, specifically 0.2 MPa, 0.5 MPa, 1.0 MPa, 1.5 MPa, 2.0 MPa, 2.5 MPa or 3 MPa; wherein, the penetration depth of the penetrating anchoring layer is 20 μm to 300 μm, specifically 20 μm, 50 μm, 80 μm, 100 μm, 150 μm, 200 μm, 250 μm or 300 μm, and the equivalent thickness of the continuous dense layer is 6 μm to 40 μm, specifically 6 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm or 40 μm;

[0030] Step 7. Fill the capsule body after film formation obtained in Step 6 with coffee powder, seal the sealing component to the flange and complete the sealing by heat sealing to obtain the sealed paper-based molded coffee capsule.

[0031] This invention also provides a coating system for in-situ construction of the aforementioned PHA barrier heat-sealing composite layer on the inner surface of a paper-based molded coffee capsule, comprising a first aqueous PHA dispersion and a second aqueous PHA dispersion. The first aqueous PHA dispersion is used to form a penetration anchoring layer, and the second aqueous PHA dispersion is used to form a continuous dense layer. The first aqueous PHA dispersion has a solid content of 10 wt% to 25 wt%, specifically 10 wt%, 15 wt%, 20 wt%, or 25 wt%, and the volume average particle size of the PHA particles in the dispersion is 200 nm to 2000 nm, specifically 200 nm, 220 nm, 250 nm, 300 nm, or 500 nm. The second aqueous PHA dispersion has a solid content of 20 wt% to 60 wt%. The specific content can be 20wt%, 30wt%, 40wt%, 45wt%, 50wt%, or 60wt%, and the volume average particle size of the PHA particles in the dispersion is 200nm to 2000nm, specifically 400nm, 450nm, 500nm, 600nm, 900nm, or 1000nm; the ratio of the solid content of the second aqueous PHA dispersion to the solid content of the first aqueous PHA dispersion is 1.5 to 6.0, specifically 1.5, 2.0, 2.4, 3.0, 4.0, 5.0, or 6.0, and the ratio of the volume average particle size of the second aqueous PHA particles to the volume average particle size of the first aqueous PHA particles is 2 to 10, specifically 2, 2.25, 2.4, 3, 4.09, 5, or 10.

[0032] Compared with the prior art, the following significant advantages can be obtained by using the present invention:

[0033] Excellent barrier properties and oil resistance: This invention constructs a particle size gradient double-layer structure of "penetrating anchoring layer + continuous dense layer". It utilizes the deep physical penetration of small particle size components to effectively seal the micropores on the surface of pulp fibers, and provides a flat substrate for the dense film formed by large particle size components. Thus, it achieves excellent WVTR (≤0.45g / (m²·24h)) and OTR (≤0.35cm³ / (m²·24h·0.1MPa)) without relying on a high-thickness coating, and has long-term oil penetration resistance, and does not contain any fluorides.

[0034] Stable interfacial bonding and boiling resistance: Deep physical anchoring (penetration depth up to 20μm to 300μm) achieved through vacuum assistance and particle size matching creates a strong mechanical interlocking effect between the coating and the pulp substrate. This effectively solves the problem of interfacial delamination or cracking that traditional coatings are prone to under high temperature, high humidity and high pressure boiling conditions, ensuring the structural integrity of the capsule under a boiling pressure of 1.9MPa.

[0035] Excellent heat-sealing integrity and process window: Combining flange hot-press densification treatment (reducing porosity to 30%-40%) with local thickening heat-sealing ring design (flange coating amount is significantly higher than sidewall), a sufficient heat-sealing material "shield" is constructed in the flange area, which not only greatly improves the seal peel strength (≥13.0N / 15mm), but also significantly widens the heat-sealing process window (up to 42℃-48℃), adapting to the needs of high-speed industrial production.

[0036] Completely biodegradable and environmentally safe: The PHA material and pulp substrate used in this invention are both bio-based and completely biodegradable. Under controlled composting conditions, the degradation rate can reach more than 96% in 45 days, and no total organic fluorine was detected in the product. This provides the coffee capsule industry with an ideal alternative that combines high performance, food safety and environmental friendliness. Attached Figure Description

[0037] Figure 1 This is a partial cross-sectional view of the paper-based molded coffee capsule described in this invention.

[0038] In the diagram, 1-capsule body; 2-coffee powder; 3-sealing component; 4-continuous dense layer; 5-penetrating anchoring layer. Detailed Implementation

[0039] 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.

[0040] Figure 1 This is a cross-sectional structural diagram of the compostable paper-based molded coffee capsule proposed in this invention, and a partial enlarged view of its flange area. As shown in the figure, the capsule body 1, formed from molded pulp, constitutes the main frame, and coffee powder 2 is contained inside. The top is heat-sealed with a sealing component 3 to achieve a seal. The enlarged view on the right clearly shows the microstructure of the PHA barrier heat-sealing composite layer at the sealing surface of the flange: the outermost layer is a smooth, continuously film-forming, dense layer 4, below which is a serrated penetrating anchoring layer 5 that penetrates deep into the pores of the pulp fibers to form a mechanical interlocking structure.

[0041] Main reagents and raw materials:

[0042] Table 1. Main reagent and raw material names, product models / specifications, and manufacturers:

[0043]

[0044] Main analytical and testing instruments:

[0045] Table 2 mainly analyzes the names, models, and manufacturers of the testing instruments:

[0046]

[0047] Main testing standards:

[0048] Relative humidity (RH): All RH test conditions mentioned in this manual refer to relative humidity.

[0049] Vacuum gauge pressure: The “vacuum gauge pressure” mentioned in this manual refers to the absolute value of the negative pressure difference relative to atmospheric pressure (unit: kPa); for example, a vacuum gauge pressure of 20 kPa means that the pressure in the test chamber is (atmospheric pressure - 20 kPa).

[0050] Water vapor transmission rate (WVTR): Following GB / T 1037-2021 "Determination of Water Vapor Transmission Performance of Plastic Films and Sheets - Cup Weight Gain and Loss Method", the cup weight gain method was used for testing at 38℃ and 90% RH. The test area was 33 cm² (corresponding to the effective exposed area of ​​the permeation cup). Anhydrous calcium chloride was filled into the permeation cup as a desiccant, and the cup was filled and sealed according to standard requirements. During clamping, the matching sealing ring and pressure cap of the permeation cup were used, and the edges of the sample were sealed to prevent bypass leakage. Sample preparation method: The capsule sidewall was cut open along the generatrix and unfolded to obtain a flat sample with a size not less than the effective clamping area; the bottom wall sample was directly cut. The sample was conditioned for 24 hours at 23℃ and 50% RH before testing.

[0051] Oxygen permeability (OTR): Tested according to GB / T 19789-2021 "Test of oxygen permeability of plastic films and sheets for packaging materials - Coulometric test method", test conditions 23℃, 0% RH. Sample preparation and edge sealing methods are the same as WVTR test; the sample is dried and conditioned before clamping to meet the 0% RH test requirements.

[0052] Seal peel strength: Refer to GB / T 2790-1995 "Test method for 180° peel strength of adhesives, flexible materials versus rigid materials", and conduct 180° peel test on the sealing component and flange sealing part; the sample width is 15mm and the tensile speed is 300mm / min.

[0053] Biodegradability: Refer to GB / T 19277.1-2025 "Determination of final aerobic biodegradability of materials under controlled composting conditions - Method for determining carbon dioxide release - Part 1: General method", test cycle 45 days.

[0054] Tensile property testing: Refer to ASTM D638-22.

[0055] Adhesion test: Refer to ASTM D3359-23.

[0056] Boiling resistance test: using the company's internal method, referring to IEC 60335-2-15:2024;

[0057] The specific testing method is as follows:

[0058] Test equipment and operating condition settings:

[0059] A single-cup capsule coffee machine with a rated pump pressure of 1.9MPa was selected as the brewing equipment; the coffee machine was preheated for ≥5 minutes before the test and run continuously without load 3 times to stabilize the water temperature; the brewing water temperature was controlled between 83℃ and 86℃.

[0060] Sample preparation and loading:

[0061] Each paper-based molded coffee capsule is filled with 5.0 ± 0.1 g of ground coffee powder. Sealing was performed using a heat-sealing tester (Model 12-12 AS / 1): heat-sealing pressure 0.30 MPa, holding time 0.80 s, cooling time 2.0 s. The heat-sealing temperature was set to the point where the peel strength within the heat-sealing window was the highest and the seal appearance was acceptable (no obvious deformation of the flange, no burn-through or wrinkles in the sealing film) as obtained in Application Example 6, "Heat-Sealing Window and Initial Sealing Temperature Test". Before testing, the capsules were confirmed to be intact and free of visible defects.

[0062] Brewing test process:

[0063] Place the capsule into the coffee machine and select the Espresso mode (40mL water volume) to complete one brewing cycle. During the brewing process, observe the capsule flange, side walls, and bottom walls in real time to check for liquid leakage, structural cracking, or coating delamination.

[0064] Failure determination criteria:

[0065] Brewing leakage: During or after the brewing process, continuous visible droplets or liquid flow appear on the outer surface of the capsule;

[0066] Bursting: Visible structural rupture occurs in the sidewall, bottom wall, or flange of the capsule;

[0067] Layering: After boiling, the capsule was opened and a continuous interfacial delamination area was observed between the PHA barrier heat-sealing composite layer and the pulp substrate.

[0068] Statistical methods:

[0069] For each test group, N=50 capsules were used for boiling tests; the boiling leakage rate, bursting rate and delamination rate were calculated as the percentage of samples that exhibited the corresponding failure phenomenon out of the total number of tests.

[0070] Criteria for natural compostability: If the biodegradation rate is ≥90% after 45 days, it is considered to be natural compostable according to the controlled composting conditions test in GB / T 19277.1-2025.

[0071] Water absorption rate (Cobb value): Refer to GB / T 1540-2002 "Determination of water absorption of paper and paperboard (Cobb method)".

[0072] Water droplet contact angle: Refer to ISO 19403-2:2024 "Coatings and varnishes—wetting properties—part 2: determination of surface free energy of solid surfaces by measuring contact angle".

[0073] Oil resistance (oil penetration time): Take a sample (20mm×20mm) of the inner surface of the capsule sidewall and test it at 23℃ and 50% RH. Use a pipette to drop 10μL (±1μL) of palm kernel oil into the center of the sample and keep the sample horizontal. Record the time from the completion of the drop to the first appearance of continuous oil penetration points or the formation of visible oil spots with a diameter ≥1mm on the back of the sample. Test 5 points in each group and take the average value.

[0074] Moisture content of coffee powder: Refer to GB 5009.3-2016 "National Food Safety Standard - Determination of Moisture in Food".

[0075] Water activity (aw): Refer to ISO 18787:2017 (Corrected version 2021-02) "Microbiology of the food chain — Determination of water activity".

[0076] Total Organic Fluorine (TOF): Oxygen bomb combustion was performed according to EN 14582:2016; the fluoride ion content in the combustion product absorbent was determined using the fluoride ion selective electrode method and the TOF was calculated. To eliminate interference from inorganic fluorine, the sample was extracted with ultrapure water before combustion and the extract was discarded. The reproducible experimental conditions were as follows: 0.50 g of sample (dry basis); oxygen charging pressure during oxygen bomb combustion was 2.8 MPa; 15 mL of 0.01 mol / L sodium hydroxide solution was used as the absorbent; after combustion, the combustion cup and the inner wall of the bomb were rinsed with ultrapure water and combined with the absorbent, and the volume was adjusted to 100 mL; 5 mL of TISAB was added to the test solution before measurement to stabilize the ionic strength and eliminate complexation interference; calibration curves were established using 0.1 mg / L, 0.5 mg / L, 1 mg / L, 5 mg / L, and 10 mg / L fluoride ion standard solutions; the TOF was calculated after subtracting the background from the blank test; the TOF conversion was calculated using the following formula:

[0077] TOF (mg / kg) = ((C sample - C blank) × V × 1000) / m.

[0078] Wherein, Csample represents the fluoride ion concentration (mg / L) in the sample test solution, Cblank represents the fluoride ion concentration (mg / L) in the blank test solution, V represents the final volume (L), and m represents the dry weight of the sample (kg). The method detection limit is ≤5 mg / kg; the judgment criterion is not detected.

[0079] Moisture content determination method: The moisture content of the capsule body was determined using a halogen moisture analyzer. For the moisture content of the capsule body, a mixed sample was cut from the sidewall and bottom wall areas of the capsule, and the initial mass m0 was recorded. The sample was dried at a constant temperature of 105℃ until the mass change rate was ≤0.01g / 30s, and the mass m1 after drying was recorded. The moisture content was calculated as (m0-m1) / m0×100%. For the moisture content of the coated surface after the first coating, a sample was cut from the coated area of ​​the capsule body after the first coating, and the moisture content was obtained using the same determination method.

[0080] Dry coating amount (sidewall / bottomwall): This was determined using a comparative weighing method. Uncoated capsule samples and coated capsule samples were prepared separately. After drying at 105℃ to constant weight, samples of the same known area A (m²) were cut from the sidewall and bottomwall respectively, and the mass m of the uncoated sample was recorded. 空白 The mass of the sample after film formation (m) 涂布 , according to (m 涂布 -m 空白 ) / A Calculate the dry coating amount (g / m²).

[0081] Dry coating amount (flange sealing surface): Samples of the sealing surface of the flange, both uncoated and after film formation, were prepared and dried at 105℃ to constant weight before sampling. The sampling method was as follows: the flange was cut circumferentially and the flange ring was flattened; a rectangular sample of 20mm × 10mm was cut using a cutter, with an unfolded area Af = 2.0 × 10⁻⁶. -4 m²; at least 5 samples should be taken from each group and the average should be taken. Record the mass m of the uncoated sample. 空白,f The mass of the sample after film formation (m) 涂布,f , according to (m 涂布,f -m 空白,f ) / A f Calculate the dry coating amount (g / m²) on the sealing surface of the flange.

[0082] Solid content of aqueous PHA dispersion: Take the mass m4 of the dispersion sample, dry it at 105℃ to constant weight to obtain the dry solid mass m5, and calculate the solid content according to m5 / m4×100%.

[0083] The volume average particle size of the aqueous PHA dispersion was measured using a particle size analyzer at 25°C in dynamic light scattering mode, with a test angle of 173°. The dispersion was diluted with ultrapure water to a solid content of 0.10 wt%, transferred to disposable cuvettes, and allowed to stand for 2 minutes to equilibrate. Each sample was tested three times. The volume average particle size was calculated by converting the intensity distribution to a volume distribution using the Mie conversion model in the instrument software. The conversion parameters were set as follows: refractive index of the dispersion medium (water) 1.330, viscosity 0.8872 mPa·s (25°C); refractive index of PHA particles 1.50, absorption coefficient 0.01. The arithmetic mean of the three tests was taken as the volume average particle size calculated from the volume distribution.

[0084] Penetration depth and equivalent thickness of continuous dense layer: Cross-sectional sections perpendicular to the inner surface of the capsule were prepared using a cryostat; the cut sidewall samples were pre-cooled in the cryostat chamber for 30 min before being sectioned, with a section thickness of 20 μm; at least 5 cross-sectional sections at different locations were prepared for each capsule. Nile red fluorescence staining was performed on the sections to mark the PHA phase: Nile red was prepared as a 10 mg / L anhydrous ethanol staining solution, the sections were immersed for 2 min, then removed and quickly rinsed with anhydrous ethanol for 10 s, and air-dried at room temperature in the dark. Cross-sectional fluorescence images were acquired at 200× magnification using a microscope equipped with a fluorescence module (using a TRITC / Rhodamine channel or equivalent filter group, excitation band 540nm to 580nm, emission band 600nm to 660nm), and measured using image analysis software: penetration depth was defined as the maximum depth of the continuous PHA fluorescent phase observed along the thickness direction from the inner surface into the pulp pores, with 5 fields of view selected for each slice and the maximum value of the slice being taken; the equivalent thickness of the continuous dense layer was defined as the arithmetic mean of the thickness of the continuous fluorescent film layer at the inner surface, with 10 measurement points selected at equal intervals on the continuous film layer for each slice and the average being taken; the final result was the arithmetic mean of the results of 5 slices for each capsule.

[0085] Heat sealing ring width: Take the capsule body after film formation, and use a digital caliper to measure the width of the locally thickened heat sealing ring in the radial direction along the sealing surface of the flange. Measure 8 points for each capsule and take the arithmetic mean as the heat sealing ring width of the capsule.

[0086] PHA percentage in dry film: The dry film of the second coating system used to form a continuous dense layer is used as the statistical object. The dry mass of each component is obtained by weighing according to the formula and converting the solid content. The PHA percentage is calculated by the ratio of the dry mass of PHA in the dry film mPHA to the total mass of the dry film mdry mPHA / mdry×100%, where mdry includes PHA, bio-based plasticizing and toughening components and barrier reinforcing fillers.

[0087] General preparation process for sealing components:

[0088] Step 1. Preparation of substrate resin. Extrudable film-grade PLA resin is selected as one of the substrate resins, extrudable film-grade PBS resin is selected as another substrate resin, and PHA resin is selected as the heat-sealing layer resin to obtain the substrate resin system.

[0089] Step 2. Substrate layer preparation. The PLA resin and PBS resin are dry-mixed at a mass ratio of 80:20 and then melt-blended and granulated using a twin-screw extruder; subsequently, a substrate film layer is prepared by casting to achieve a thickness of 25 μm, thus obtaining the substrate film layer.

[0090] Step 3. PHA heat-sealing layer coating. Using a coating process, PHA aqueous emulsion is coated onto one side of the substrate film layer obtained in Step 2. After drying, the thickness of the PHA heat-sealing layer is 5μm. After coating and drying, it is quickly shaped by a cooling roller to obtain a composite film with a PHA heat-sealing layer.

[0091] Step 4. Winding and Conditioning. The composite film obtained in Step 3 is wound up and placed at 23°C and 50% relative humidity for 24 hours to eliminate internal stress, thus obtaining the conditioned sealing component film.

[0092] Step 5. Consistency Confirmation. The film of the conditioned sealing component is tested using a thickness gauge or cross-sectional microscopy to confirm that its total thickness is 30μm±3μm, and that the PHA heat-sealing layer is located on the side facing the flange, thus obtaining a sealing component that meets the consistency requirements.

[0093] Unless otherwise specified, in the following embodiments and comparative examples, the sealing components are all made of the composite film obtained in steps 1-5 above, and the sealing sheet that matches the size of the capsule flange is obtained by punching, and the PHA heat-sealing layer is ensured to face the sealing surface of the flange.

[0094] General preparation process for PLA coated paper:

[0095] Step 1. Base paper preparation. Food contact grade paperboard is selected as the base paper, with a basis weight of 200 g / m², to obtain the base paper.

[0096] Step 2. Preparation of PLA coating resin. Extrudable coating grade PLA resin is selected as the coating resin to obtain PLA coating resin.

[0097] Step 3. Extrusion Coating. The PLA coating resin obtained in Step 2 is melt-extruded on the extrusion coating production line and pressed onto the surface of the base paper obtained in Step 1 under the action of cooling rollers, so that the basis weight of the PLA coating layer is 30g / m², and PLA coated paper is obtained.

[0098] Step 4. Molding. The PLA coated paper obtained in Step 3 is molded into the capsule body using a hot pressing molding method; wherein the hot pressing molding temperature is 150℃, the pressure is 1.0MPa, and the time is 10s; after molding, it is cooled and shaped in a cooling mold to obtain the PLA coated paper capsule body.

[0099] Sealing wax preparation method:

[0100] Step 1. Raw material mixing. Take paraffin wax and beeswax with a melting point of 58–60℃ and mix them in a mass ratio of 1:1 to obtain a wax raw material mixture.

[0101] Step 2. Heating and Degassing. The wax raw material mixture obtained in Step 1 is placed in a stainless steel container and heated to 85°C in a water bath to completely melt and stir thoroughly. Then, it is allowed to stand to degas, resulting in a melted and degassed sealing wax.

[0102] Step 3. Molding or Use. The molten and degassed sealing wax obtained in Step 2 is kept in a molten state at 80°C and applied to the edge of the permeation cup; or it is poured into a rod shape and cooled to solidify for later use, thus obtaining the sealing wax for WVTR testing.

[0103] Example:

[0104] Example 1:

[0105] The paper-based molded coffee capsules of this embodiment are prepared according to steps 1–7 below.

[0106] Step 1. Pulping and wet molding to obtain wet pulp preform. Softwood pulpboard and hardwood pulpboard are soaked and then separated at a mass ratio of 3:7 to prepare the pulp mix; the pulp mix mass concentration is fixed at 1.0 wt%; wet molding is performed on a vacuum suction mold, the molding and suction time is fixed at 20 s, and the vacuum gauge pressure of the mold during suction molding is fixed at 60 kPa to obtain the wet pulp preform.

[0107] Step 2. Dehydration, drying, and shaping to obtain the capsule body. The wet pulp blank is dehydrated under vacuum and then dried and shaped in a 90℃ hot air circulating oven to obtain the capsule body; after drying, the capsule body is placed at 23℃ and 50% relative humidity for 24 hours to eliminate internal stress; the moisture content of the capsule body before coating in step 4 is controlled at 5.0wt%, resulting in a capsule body with controlled moisture content.

[0108] Step 3. Flange hot pressing densification to obtain the capsule body after flange densification treatment. The flange of the capsule body is subjected to hot pressing densification treatment at a temperature of 130℃, a pressure of 4.0MPa, and a time of 2.0s to obtain the capsule body after flange densification treatment.

[0109] Step 4. The first coating system is sprayed, vacuum-assisted infiltration, and pre-dried to obtain the capsule body after the first coating. The first water-based PHA emulsion is coated by aerosol spraying (compressed air atomization spraying) using a three-axis programmable automatic gun-passing spraying platform and an air atomization spray gun; the nozzle diameter is 0.3mm; the atomization air pressure is fixed at 0.40MPa.

[0110] The distance from the nozzle to the inner surface of the capsule was fixed at 120 mm; the gun speed was fixed at 200 mm / s; the trajectory overlap rate was fixed at 50%; and the pre-drying conditions after each thin coating were fixed at 60℃ hot air for 6 minutes. The first aqueous PHA emulsion was a PHBV aqueous emulsion, with its solid content adjusted to 15 wt%, and PHA particles with an average volume diameter of 250 nm were selected.

[0111] Vacuum-assisted penetration was applied to the capsule body during coating: the outer surface of the capsule body was placed on a vacuum adsorption fixture with a sealing ring, forming a seal between the outer surface of the capsule and the fixture; the fixture was connected to a vacuum gauge via a vacuum pump and evacuated to a vacuum gauge pressure of 20 kPa; this vacuum gauge pressure was maintained continuously during the spraying of the first aqueous PHA emulsion, and was maintained for 60 seconds before pre-drying after the first coating was completed, after which the vacuum was released. After pre-drying, the moisture content of the coated surface after the first coating was controlled to be 8.0 wt%, resulting in the capsule body after the first coating.

[0112] Step 5. Spraying and drying the second coating system to obtain the capsule body after the second coating. The same aerosol spraying equipment and spraying parameters as in Step 4 are used to coat the second aqueous PHA emulsion. The second aqueous PHA emulsion is a PHBV aqueous emulsion, with its solid content adjusted to 45wt%, and PHA particles with a volume average particle size of 600nm selected. In the flange area, local thickening is achieved by increasing the gun dwell time and the number of gun rotations on the corresponding ring track of the flange sealing surface, so that the flange sealing surface forms a continuous locally thickened heat-sealing ring along the flange circumference.

[0113] The dry coating amount is controlled as follows: 20g / m² for the total dry coating amount on the inner surface of the side wall, 20g / m² for the total dry coating amount on the inner surface of the bottom wall, 70g / m² for the dry coating amount on the sealing surface of the flange, and 3.0mm for the width of the heat sealing ring.

[0114] After the second coating, the capsule body was placed in a 60°C hot air circulating oven to dry for 18 minutes, and then placed at 23°C and 50% relative humidity for 10 minutes to eliminate the surface temperature difference. The moisture content before heat fusion or hot pressing film formation was measured to be 2.5 wt% according to the "Moisture Content Determination Method", and the capsule body after the second coating was obtained.

[0115] Step 6. Hot pressing to form a film to obtain the capsule body after film formation. The capsule body after the second coating is hot pressed to form a film at a temperature of 150℃, a pressure of 1.0MPa, and a time of 10s, so that PHA forms an infiltrated anchoring layer and a continuous dense layer, and a heat-sealing interface is formed on the sealing surface of the flange to obtain the capsule body after film formation.

[0116] In the dry film of the obtained PHA barrier heat-sealing composite layer, no other non-volatile film-forming components were introduced except for PHA, and the proportion of PHA in the dry film was 100wt%.

[0117] Step 7. Filling and sealing to obtain the sealed paper-based molded coffee capsule. Fill the film-formed capsule body with coffee powder and seal the sealing component to the sealing surface of the flange. Complete the sealing by heat sealing to obtain the sealed paper-based molded coffee capsule.

[0118] In this embodiment, the PHA barrier heat-sealing composite layer formed on the inner surface of the capsule body after film formation is a dry film-forming structure. In the dry film-forming structure, no other non-volatile film-forming components are introduced except for PHA, and the mass percentage of PHA is 100wt%.

[0119] Example 2:

[0120] The preparation process is the same as in Example 1, except for the following parameters: In step 4, the first aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 10 wt% and a volume average particle size of 220 nm; the vacuum gauge pressure for vacuum-assisted infiltration is 20 kPa; In step 5, the second aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 45 wt% and a volume average particle size of 600 nm; the dry coating amount is controlled as follows: 120 g / m² for the sealing surface of the flange; 20 g / m² for the inner surface of the sidewall; 20 g / m² for the inner surface of the bottom wall; and the heat-sealing ring width is 3.5 mm; The hot-pressing film-forming conditions in step 6 are: temperature 165℃, pressure 1.0 MPa, and time 5 s. All other parameters remain unchanged, resulting in a sealed paper-based molded coffee capsule.

[0121] In the dry film-forming structure of the PHA barrier heat-sealing composite layer obtained in this embodiment, no other non-volatile film-forming components were introduced except for PHA, and the mass percentage of PHA was 100wt%.

[0122] Example 3:

[0123] The preparation process is the same as in Example 1, except for the following parameters: Step 3, flange hot-pressing densification conditions: temperature 130℃, pressure 10MPa, time 2.0s; Step 4, the first aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 10wt% and a volume average particle size of 250nm; no vacuum-assisted penetration is applied during the coating process (vacuum gauge pressure 0kPa); Step 5, the second aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 30wt% and a volume average particle size of 500nm; the dry coating amount is controlled as follows: total dry coating amount on the inner surface of the sidewall 30g / m², total dry coating amount on the inner surface of the bottom wall 30g / m², dry coating amount on the sealing surface of the flange 60g / m², and heat-sealing ring width 2.5mm; Step 6, hot-pressing film formation conditions: temperature 165℃, pressure 0.2MPa, time 120s. All other parameters remain unchanged, resulting in a sealed paper-based molded coffee capsule.

[0124] In the dry film-forming structure of the PHA barrier heat-sealing composite layer obtained in this embodiment, no other non-volatile film-forming components were introduced except for PHA, and the mass percentage of PHA was 100wt%.

[0125] Example 4:

[0126] The preparation process is the same as in Example 1, except for the following parameters:

[0127] Before step 4, a base coating treatment is added: a chitosan base coating is applied to the inner surface of the capsule, with a dry coating amount of 5 g / m²; the base coating solution is prepared by adding chitosan to a 1.0 wt% aqueous solution of glacial acetic acid to prepare a 1.5 wt% chitosan solution, stirring magnetically at 25°C for 4 hours until completely dissolved, and then filtering (using a 100-mesh filter) to obtain the base coating solution; the solution is coated by aerosol spraying and dried under 60°C hot air for 15 minutes to obtain the dry coating amount; the first aqueous PHA emulsion in step 4 is a PHBV aqueous emulsion with a solid content of 15 wt% and a volume average particle size of 250 nm; the vacuum gauge pressure is 20 kPa;

[0128] In step 5, the second aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 45 wt% and a volume average particle size of 600 nm. 3 wt% ATBC plasticizer and 8 wt% sodium-based montmorillonite barrier reinforcing filler are added to the dry film of the second coating system, with the remainder being the PHA film-forming component. The sodium-based montmorillonite is first prepared into a 3 wt% aqueous dispersion with ultrapure water and dispersed at 8000 rpm for 10 min using a high-speed disperser. Subsequently, it is homogenized three times at 80 MPa using a high-pressure homogenizer. The resulting montmorillonite aqueous dispersion is added to the second aqueous PHA emulsion according to the target dry film ratio and mechanically stirred at 500 rpm for 10 min to obtain a homogeneous mixed coating solution. After film formation, the PHA content in the dry film of the second coating system is 89 wt%. The dry coating amount is controlled as follows: the total dry coating amount on the inner surface of the side wall is 25g / m², the total dry coating amount on the inner surface of the bottom wall is 25g / m², the dry coating amount on the sealing surface of the flange is 90g / m², and the width of the heat sealing ring is 3.0mm.

[0129] Step 6, hot pressing film formation conditions: temperature 150℃, pressure 1.0MPa, time 10s. All other parameters remain unchanged, resulting in a sealed paper-based molded coffee capsule.

[0130] Example 5:

[0131] The preparation process is the same as in Example 1, except for the following parameters:

[0132] In step 4, the first aqueous PHA emulsion is a PHBH aqueous emulsion with a solid content of 20 wt% and a volume average particle size of 200 nm; no vacuum assistance is applied during the coating process.

[0133] In step 5, the second aqueous PHA emulsion is a PHBH aqueous emulsion with a solid content of 40wt% and a volume average particle size of 500nm. The flange area achieves local thickening of the heat-sealing ring by controlling the spraying path and residence time. The dry coating amount is controlled as follows: the total dry coating amount on the inner surface of the side wall is 30g / m², the total dry coating amount on the inner surface of the bottom wall is 30g / m², the dry coating amount on the sealing surface of the flange is 80g / m², and the heat-sealing ring width is 2.5mm.

[0134] Step 6, hot pressing film formation conditions: temperature 160℃, pressure 1.0MPa, time 10s. All other parameters remain unchanged, resulting in a sealed paper-based molded coffee capsule.

[0135] In the dry film-forming structure of the PHA barrier heat-sealing composite layer obtained in this embodiment, no other non-volatile film-forming components were introduced except for PHA, and the mass percentage of PHA was 100wt%.

[0136] Example 6: The preparation process is the same as in Example 1, except for the following parameters:

[0137] In step 4, the first aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 10 wt% and a volume average particle size of 200 nm; the vacuum gauge pressure for vacuum-assisted infiltration is 5 kPa.

[0138] In step 5, the second aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 20wt% and a volume average particle size of 450nm. The dry coating amount is controlled as follows: the total dry coating amount on the inner surface of the side wall is 8g / m², the total dry coating amount on the inner surface of the bottom wall is 8g / m², the dry coating amount on the sealing surface of the flange is 20g / m², and the heat sealing ring width is 1.5mm.

[0139] Step 6, hot pressing film formation conditions: temperature 140℃, pressure 1.0MPa, time 15s. All other parameters remain unchanged, resulting in a sealed paper-based molded coffee capsule.

[0140] In the dry film-forming structure of the PHA barrier heat-sealing composite layer obtained in this embodiment, no other non-volatile film-forming components were introduced except for PHA, and the mass percentage of PHA was 100wt%.

[0141] Example 7: The preparation process is the same as in Example 1, except for the following parameters:

[0142] In step 4, the first aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 10 wt% and a volume average particle size of 220 nm; the vacuum gauge pressure for vacuum-assisted infiltration is 80 kPa.

[0143] In step 5, the second aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 60wt% and a volume average particle size of 900nm. The dry coating amount is controlled as follows: the total dry coating amount on the inner surface of the side wall is 40g / m², the total dry coating amount on the inner surface of the bottom wall is 40g / m², the dry coating amount on the sealing surface of the flange is 120g / m², and the heat sealing ring width is 4.5mm.

[0144] Step 6, hot pressing film formation conditions: temperature 160℃, pressure 1.0MPa, time 10s. All other parameters remain unchanged, resulting in a sealed paper-based molded coffee capsule.

[0145] In the dry film-forming structure of the PHA barrier heat-sealing composite layer obtained in this embodiment, no other non-volatile film-forming components were introduced except for PHA, and the mass percentage of PHA was 100wt%.

[0146] Example 8: The preparation process is the same as in Example 1, except for the following parameters:

[0147] In step 4, the first aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 25 wt% and a volume average particle size of 200 nm; the vacuum gauge pressure is 20 kPa.

[0148] In step 5, the second aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 45 wt% and a volume average particle size of 600 nm; the remaining coating amount and film-forming conditions are the same as in Example 1. Sealed paper-based molded coffee capsules are obtained.

[0149] In the dry film-forming structure of the PHA barrier heat-sealing composite layer obtained in this embodiment, no other non-volatile film-forming components were introduced except for PHA, and the mass percentage of PHA was 100wt%.

[0150] Example 9 (Verification of large particle size penetration and low solids content): The preparation process is the same as in Example 1, except for the following parameters:

[0151] In step 4, the first aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 20 wt% and a volume average particle size of 300 nm; the vacuum gauge pressure is 20 kPa.

[0152] In step 5, the second aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 30 wt% and a volume average particle size of 600 nm; the remaining coating amount and film-forming conditions are the same as in Example 1. Sealed paper-based molded coffee capsules are obtained.

[0153] In the dry film-forming structure of the PHA barrier heat-sealing composite layer obtained in this embodiment, no other non-volatile film-forming components were introduced except for PHA, and the mass percentage of PHA was 100wt%.

[0154] Example 10 (Verification of extreme coating ratios and P34HB emulsion): The preparation process is the same as in Example 1, except for the following parameters:

[0155] In step 4, the first aqueous PHA emulsion is a P34HB aqueous emulsion with a solid content of 15wt% and a volume average particle size of 250nm; the vacuum gauge pressure is 20kPa.

[0156] In step 5, the second aqueous PHA emulsion is P34HB aqueous emulsion with a solid content of 45wt% and a volume average particle size of 600nm. The dry coating amount is controlled as follows: the total dry coating amount on the inner surface of the sidewall is 8g / m², the dry coating amount on the sealing surface of the flange is 96g / m², and the heat sealing ring width is 3.0mm. The dry coating amount on the inner surface of the bottom wall is the same as that on the sidewall.

[0157] Step 6, hot pressing film formation conditions: temperature 145℃, pressure 1.0MPa, time 10s. All other parameters remain unchanged, resulting in a sealed paper-based molded coffee capsule.

[0158] In the dry film-forming structure of the PHA barrier heat-sealing composite layer obtained in this embodiment, no other non-volatile film-forming components were introduced except for PHA, and the mass percentage of PHA was 100wt%.

[0159] Example 11 (Verification of high-pressure film formation process and PHB emulsion): The preparation process is the same as in Example 1, except for the following parameters:

[0160] In step 4, the first aqueous PHA emulsion is a PHB aqueous emulsion with a solid content of 15wt% and a volume average particle size of 250nm; the vacuum gauge pressure is 20kPa.

[0161] In step 5, the second aqueous PHA emulsion is a PHB aqueous emulsion with a solid content of 45 wt% and a volume average particle size of 600 nm.

[0162] Step 6, hot pressing film formation conditions: temperature 165℃, pressure 3.0MPa, time 10s; other coating amounts are the same as in Example 1. Sealed paper-based molded coffee capsules are obtained.

[0163] In the dry film-forming structure of the PHA barrier heat-sealing composite layer obtained in this embodiment, no other non-volatile film-forming components were introduced except for PHA, and the mass percentage of PHA was 100wt%.

[0164] Comparative example:

[0165] Comparative Example 1 (PLA coated paper pre-coating):

[0166] PLA coated paper was used as the pre-coated layer material, and the capsule body was prepared by hot pressing. This method lacks the in-situ film-forming anchoring structure of "penetrating anchoring layer and continuous dense layer". The PLA coated paper and capsule body were prepared according to the following steps:

[0167] Step 1. Base paper: Food contact grade paperboard is selected, with a base paper basis weight of 200g / m²;

[0168] Step 2. PLA coating: Molten PLA is extruded on the extrusion coating line and pressed onto the surface of the base paper by cooling rollers. The basis weight of the PLA coating layer is 30 g / m².

[0169] Step 3. Molding: The coated paper is formed into the capsule body by hot pressing at a temperature of 150℃, a pressure of 1.0MPa, and a time of 10s; after molding, it is cooled and set to room temperature in a cooling mold.

[0170] Step 4. Fill the capsule body with coffee powder and seal it to obtain Comparative Example 1 capsule.

[0171] Comparative Example 2 (only the second layer of large-particle coating, without the first layer of penetration and anchoring): The preparation process is the same as in Example 1, except for the following parameters:

[0172] Step 4, the first aqueous PHA emulsion coating, is not performed;

[0173] Step 5 uses only the second aqueous PHA emulsion, which is PHBH aqueous emulsion with a solid content of 40wt% and a volume average particle size of 500nm. The dry coating amount is controlled as follows: the total dry coating amount on the inner surface of the side wall is 20g / m², the total dry coating amount on the inner surface of the bottom wall is 20g / m², and the dry coating amount on the sealing surface of the flange is 50g / m².

[0174] The conditions for hot pressing film formation in step 6 were: temperature 150℃, pressure 1.0MPa, and time 10s. Comparative Example 2 capsules were obtained.

[0175] Comparative Example 3 (without flange hot-pressing densification): The preparation process was the same as in Example 1, except for the following parameters: the flange hot-pressing densification treatment in step 3 was not performed; all other parameters of the first / second dispersion, vacuum gauge pressure, coating amount, and film formation conditions were the same as in Example 1. Capsules of Comparative Example 3 were obtained.

[0176] Comparative Example 4 (coated and dried only, without thermal fusion / hot pressing to form a film):

[0177] The preparation process is the same as in Example 1, except for the following parameters: the coating system and coating amount in steps 4 and 5 are the same as in Example 1; in step 6, no thermal fusion or hot pressing is performed, but the second coated capsule body obtained in step 5 is placed in a 60°C hot air circulating oven for 30 minutes to control the moisture content before thermal fusion / hot pressing to 2.5 wt% (consistent with step 5 in Example 1), and then placed at 23°C and 50% relative humidity for 24 hours; so that the coating layer remains in a particle-stacking state, and no particle thermal fusion is performed to form a continuous dense layer. Comparative Example 4 capsules are obtained.

[0178] Comparative Example 5 (Comparison below the lower limit: low coating amount + reverse solids content / particle size matching): The preparation process is the same as in Example 1, only the following parameters are different:

[0179] In step 4, the first aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 30 wt% and a volume average particle size of 300 nm.

[0180] In step 5, the second aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 20wt% and a volume average particle size of 250nm. No vacuum assistance is applied during the coating process (vacuum gauge pressure 0kPa). The dry coating amount is controlled as follows: 5g / m² for the total dry coating amount on the inner surface of the side wall, 5g / m² for the total dry coating amount on the inner surface of the bottom wall, 15g / m² for the dry coating amount on the sealing surface of the flange, and 1.0mm for the width of the heat sealing ring.

[0181] The conditions for hot pressing film formation in step 6 were: temperature 140℃, pressure 1.0MPa, and time 10s. Comparative Example 5 capsules were obtained.

[0182] Comparative Example 6 (Comparison above the upper limit: excessive coating amount): The preparation process is the same as in Example 1, except for the following parameters:

[0183] In step 4, the first aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 15wt%, a volume average particle size of 250nm, and a vacuum gauge pressure of 90kPa.

[0184] In step 5, the second aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 60wt% and a volume average particle size of 900nm. The dry coating amount is controlled as follows: the total dry coating amount on the inner surface of the side wall is 50g / m², the total dry coating amount on the inner surface of the bottom wall is 50g / m², the dry coating amount on the sealing surface of the flange is 150g / m², and the heat sealing ring width is 6.0mm.

[0185] The conditions for hot pressing film formation in step 6 were: temperature 175℃, pressure 3.5MPa, and time 150s. Comparative Example 6 capsules were obtained.

[0186] Comparative Example 7 (no particle size gradient: the first and second layers have the same particle size): the preparation process is the same as in Example 1, except for the following parameters:

[0187] In step 4, the first aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 20 wt% and a volume average particle size of 500 nm; the vacuum gauge pressure is 20 kPa.

[0188] In step 5, the second aqueous PHA emulsion was a PHBV aqueous emulsion with a solid content of 40 wt% and a volume average particle size of 500 nm; the remaining coating amount and film-forming conditions were the same as in Example 1. Comparative Example 7 capsules were obtained.

[0189] Comparative Example 8 (Low Solid Content Ratio: Second Layer Solid Content Too Low): The preparation process is the same as in Example 1, except for the following parameters:

[0190] In step 4, the first aqueous PHA emulsion is a PHBV aqueous emulsion with a solid content of 20 wt% and a volume average particle size of 250 nm; the vacuum gauge pressure is 20 kPa.

[0191] In step 5, the second aqueous PHA emulsion was a PHBV aqueous emulsion with a solid content of 20 wt% and a volume average particle size of 600 nm; the remaining coating amount and film-forming conditions were the same as in Example 1. Comparative Example 8 capsules were obtained.

[0192] Application example:

[0193] Application Example 1: Barrier and waterproof performance testing.

[0194] This application example aims to verify the effects of different coating structures on water vapor, oxygen barrier properties, and resistance to liquid water. Capsules prepared in Examples 1-11 and Comparative Examples 1-8 were selected for testing.

[0195] Experimental Description: The WVTR test was conducted strictly according to the GB / T 1037-2021 standard using the cup-type weight gain method. First, the capsule sidewall was cut along the generatrix and flattened to obtain a circular sample with an effective area of ​​33 cm², ensuring the sample surface was free of creases or pinholes; the bottom wall sample was cut in the same way. Before testing, all samples were conditioned for 24 hours in a constant temperature and humidity environment of 23℃ and 50% RH. Anhydrous calcium chloride was filled into the permeation cup as a desiccant and the cup was filled and sealed according to standard requirements; the sample was sealed at the mouth of the permeation cup, and the edges were sealed with sealing wax to prevent edge leakage. The testing environment was 38℃ and 90% RH. Weighing was performed every 12 hours until the WVTR change rate calculated from three consecutive weighings was <5%. The data from the stable phase was used to calculate the WVTR. The sidewall and bottom wall were tested separately; the larger value between the sidewall and bottom wall test results in Table 3 was taken as the WVTR of the sample.

[0196] The OTR test was performed according to GB / T 19789-2021 using the coulometric method. Sample preparation was the same as for WVTR; high-vacuum silicone grease was used to seal the fixture sealing surface and sample edge during sample loading to prevent bypass leakage; the test chamber was evacuated to below 10 Pa; the test gas was 99.999% high-purity oxygen; the carrier gas was hydrogen-nitrogen gas (volume fraction: 95% N2 / 5% H2); the test temperature was 23℃, and the relative humidity was 0%. The sidewalls and bottom wall were tested separately; the larger of the sidewall and bottom wall test results in Table 3 was taken as the OTR of the sample.

[0197] The 60-second Cobb value test was conducted according to GB / T 1540-2002. Samples were taken from the inner surface of the sidewall and the inner surface of the bottom wall for testing. Distilled water at 23℃ was used. A metal cylinder was tightly pressed onto the sample, and 100 mL of water was injected to start the test. At the end of 60 seconds, the water was poured out, the sample was removed, and excess water was absorbed by pressing it once with a 10 kg roller using standard absorbent paper. The sample was then weighed immediately. Each group of samples was tested in parallel five times, and the average value was taken. The Cobb value for 60 seconds in Table 3 was the larger of the average values ​​for the sidewall and bottom walls, which was taken as the Cobb value for that sample.

[0198] Table 3. Barrier and waterproof performance test results:

[0199]

[0200] Analysis: A comparison of the data in Table 3 reveals that the "penetrating anchoring layer + continuous dense layer" dual-layer structure constructed in this invention exhibits significant advantages in barrier performance. Examples 7 and 8 show WVTR as low as 0.45-0.55 g / (m²·24h) and OTR as low as 0.35-0.48 cm³ / (m²·24h·0.1 MPa). This is because an appropriate particle size gradient (such as the 200 nm first layer combined with a 600 nm second layer in Example 8) promotes dense packing and pore filling. Example 4, by introducing sheet-like fillers, further reduces gas permeation channels and demonstrates excellent performance. In contrast, Comparative Example 2, with only a single layer of large-particle coating, cannot effectively seal the micropores on the pulp surface, resulting in a Cobb value as high as 7.5 g / m² and poor water resistance. Comparative Example 5, due to its excessively low coating amount (5 g / m²), failed to form a continuous film, resulting in a WVTR as high as 3.20 g / (m²·24h). It is worth noting that although Comparative Example 7 had sufficient coating amount, the lack of penetration and anchoring effect of small particles due to the identical particle size of the first and second layers (both 500 nm) resulted in microscopic voids at the interface, and its barrier performance (WVTR = 1.40 g / (m²·24h)) was significantly weaker than that of Example 1 (0.78 g / (m²·24h)) which had a particle size gradient. Comparative Example 8 even showed microcracks in the coating, leading to severe deterioration of various barrier properties. These results confirm the crucial role of the two-layer gradient structure and the specific combination of particle size and solid content in achieving high barrier performance.

[0201] Application Example 2: Flange seal peel strength and boiling resistance test.

[0202] This application example examines the sealing reliability of the capsule flange area and its performance under high-pressure cooking conditions.

[0203] Experimental Description: The seal peel strength test was conducted using an electronic tensile testing machine equipped with a 100N sensor. First, the sealing component was heat-sealed to the capsule flange using a heat-sealing tester. The heat-sealing head was flat, and the temperature was set to the optimal sealing temperature for each sample (see Application Example 6). The pressure was 0.30 MPa, the holding time was 0.80 s, and the cooling time was 2.0 s. The prepared samples were conditioned in a standard environment for 24 hours. Then, strip specimens with a width of 15.0 ± 0.1 mm were cut radially from the flange. Both ends of the specimen were clamped in the upper and lower fixtures of the tensile testing machine, and a 180° peel test was performed at a speed of 300 mm / min. The maximum load was recorded as the seal peel strength. Ten specimens were tested in each group, and the average value was taken.

[0204] The brewing endurance test was conducted using a capsule coffee machine with a rated pump pressure of 19 bar. The machine was preheated for 5 minutes and run empty 3 times to stabilize the water temperature at 85±1℃. A capsule containing 5.0g of coffee grounds was placed in the machine, and the Espresso setting (40mL) was selected for extraction. During brewing, the flange and side walls were observed for any liquid seepage (defined as leakage), and the capsules were checked for bursting or coating delamination. After the test, the capsules were dissected to inspect the integrity of the internal coating. 50 capsules were tested per group.

[0205] Table 4. Sealing strength and boiling resistance test results:

[0206]

[0207] Note: The standard deviation (S) in the table represents the dispersion of the five sets of parallel test data, reflecting the stability of the sealing strength.

[0208] Analysis: Experimental data show that local thickening and densification of the flange area are crucial for seal integrity. Examples 7 and 10 both exhibited a peel strength exceeding 13.0 N / 15 mm and a boiling leakage rate of 0. Example 10, in particular, despite a lower sidewall coating, still maintained excellent sealing performance by constructing a thick heat-sealing ring of 96 g / m² at the flange, demonstrating the effectiveness of the local reinforcement design in the flange area. In contrast, Comparative Example 3, which did not undergo flange hot-press densification, had a high surface roughness, resulting in a peel strength of only 4.0 N / 15 mm and a leakage rate as high as 30%. Comparative Example 7, although having sufficient coating, lacked a particle size gradient, leading to insufficient anchoring force between the coating and the paper substrate (bursting rate 8%), making it prone to interfacial peeling under the high-pressure shearing of boiling. Comparative Example 8, due to poor film quality, resulted in an extremely unstable heat-sealing interface with a standard deviation as high as 1.4. Example 8 utilizes a 200 nm first dispersion to achieve deep penetration under vacuum assistance, forming a strong mechanical interlock. Even under high-pressure boiling, there is no stratification phenomenon, demonstrating the contribution of the penetration of the smaller particle size dispersion to the interfacial stability.

[0209] Application Example 3: Biodegradability Performance Test.

[0210] This application example verifies the degradation rate of each group under industrial composting conditions.

[0211] Experimental description: The biodegradation test was carried out under controlled composting conditions in accordance with the standard of GB / T 19277.1-2025. The compost inoculum was taken from an aerobic composting plant and screened to remove impurities with a particle size > 10 mm; the inoculum was adjusted to the following fixed conditions: dry basis carbon-nitrogen ratio of 25:1 (calculated on a dry basis), moisture content of 52% (calculated on a wet basis), and pH of 7.5. A reaction vessel equipped with a biodegradation analyzer (Respirometer) was used for the test, and the temperature of the reaction vessel was controlled at 58 °C (allowing a fluctuation of ±2 °C, set according to the instrument's temperature control). Each group of capsule samples was crushed into fragments of 20 mm × 20 mm, mixed with the compost inoculum at a dry weight ratio of 1:6, and then loaded into the reaction kettle. The reaction kettle was connected to a gas supply system, and humidified air without CO2 was introduced (the air was first passed through an alkali lime / NaOH absorption column to remove CO2 and then humidified through a humidifying bottle); the ventilation flow rate was set at 50 mL / min (for each reaction kettle). The generated CO2 was recorded and accumulated online using the infrared CO2 monitoring module equipped with the Respirometer. Microcrystalline cellulose powder was used as a positive control, and a blank group containing only the compost inoculum was used for background correction. The test period was 45 days, and the biodegradation percentage relative to the theoretical CO2 production was calculated on the 15th, 30th, and 45th days respectively.

[0212] Table 5 Test results of biodegradation performance:

[0213]

[0214] Analysis: The test results showed that in the industrial composting conditions for 45 days, the biodegradation rates of all embodiments of the present invention reached more than 96.0%, far exceeding the 90% threshold required by the relevant standards, demonstrating the excellent final disposal performance of the paper-based capsules. In Example 6, due to the thinner coating (8 g / m²), the degradation rate was the fastest, and the degradation rate at 45 days reached 99.0%. In Example 11, PHB resin with a higher crystallinity was used. Although the degradation rate in the early stage (15 days) (42.0%) was slightly lower than that of the PHBV or PHBH-based samples, it still reached a high degradation rate of 96.2% at 45 days. This was due to the pulp substrate providing abundant microbial attachment sites, which promoted the disintegration of the polymer. In contrast, in Comparative Example 1 using prefabricated PLA-coated paper, due to the relatively thick PLA film thickness and the long start-up period of industrial composting, its degradation rate at 45 days was only 65.0%, which was significantly lagged. Although the degradation rates of Comparative Example 5 and Comparative Example 8 were very high, this was at the cost of sacrificing barrier properties and sealing properties (the coating was too thin or defective), and they did not have practical application value.

[0215] Application Example 4: Test of surface wettability and oil resistance.

[0216] This application example verifies the influence of different coating structures on the surface wettability and oil resistance of the inner surface of the capsule.

[0217] Experimental Description: Surface wettability was determined using a water droplet contact angle tester. The inner surface sample of the capsule sidewall was fixed on the sample stage, ensuring the test surface was horizontal. 2.0 μL of ultrapure water was added dropwise using a high-precision micro-injection pump. After the droplet contacted the surface, a high-speed camera recorded the droplet morphology at 100 frames per second. The image taken 10 seconds after the droplet contacted the surface was selected, and the static contact angle was calculated using the Young's-Laplace equation. Five samples at different locations were selected for testing in each sample group, and the average value was taken.

[0218] The oil-repellent performance test followed the relevant oil-repellent paper test method. The sample was placed in a 23℃, 50% RH environment. 10 μL of palm kernel oil (pre-stained with 0.1% Sudan Red for easier observation) was added to the center of the sample using a pipette. A layer of quantitative filter paper was placed underneath the sample. The time from the start of the oil drop to the first appearance of a red oil spot on the filter paper was recorded as the oil penetration time. Observation continued for 360 minutes; if no penetration occurred, it was recorded as >360 minutes. Five parallel samples were tested in each group.

[0219] Table 6. Test results of surface wettability and oil repellency:

[0220]

[0221] Analysis: Examples 7, 4, and 8 exhibited the best oil-repellent properties and surface hydrophobicity, with contact angles exceeding 100° and oil penetration times exceeding 300 minutes. This is attributed to their dense surface structures: the nanofillers in Example 4 increased the surface micro-roughness and sealed the pores; Example 8 utilized a 200nm first dispersion to fill and anchor the surface pores of the paper fibers, providing a smoother substrate for the upper dense film and reducing micro-defects. In contrast, Comparative Example 2, due to the lack of a small-particle-size penetration layer, had a large number of uncovered fiber pores on the surface, causing oil penetration within 60 minutes and a contact angle of only 78°. Although Comparative Example 7 had two coating layers, the lack of a particle size gradient meant that large particles could not effectively fill the micropores, resulting in an oil-repellent time (120 minutes) far lower than the examples with the gradient structure. Comparative Example 8, due to microcracks generated during film formation, allowed oil molecules to penetrate rapidly, achieving an oil-repellent time of only 90 minutes. This shows that simply increasing the coating amount is not enough to guarantee oil resistance; proper particle size distribution and film quality are the key factors.

[0222] Application Example 5: Accelerated testing of the retention of moisture content, water activity, and headspace oxygen content in coffee powder during storage.

[0223] This application example verifies the effects of different coating structures on the moisture regain of coffee powder and the retention of headspace oxygen content under accelerated storage conditions.

[0224] Experimental Description: First, each capsule was filled with 5.0±0.1g of freshly ground coffee powder and sealed in a nitrogen-protected chamber, ensuring the initial oxygen content inside the capsule was below 1.0% after sealing. The sealed capsules were then placed in a constant temperature and humidity chamber at 38±1℃ and 90±2% RH (simulating a tropical high-humidity environment) for 30 days. The capsules were arranged in a single layer on a shelf to avoid contact with each other.

[0225] Thirty days later, headspace residual oxygen content was first tested using a headspace oxygen analyzer: a butyl rubber self-sealing septum (10mm diameter, 2mm thickness) was attached to the center of the sealing film of each capsule, ensuring the septum adhered to the sealing film without any lifting edges; the analyzer's puncture probe was inserted into the capsule through the septum to extract gas and measure the headspace residual oxygen content. The capsules were then opened, and the coffee powder was removed. The moisture content of the coffee powder was measured using a halogen moisture analyzer (HE53) at a constant temperature of 105℃: approximately 2.0g of coffee powder sample was taken from each capsule, the initial mass m0 was recorded, and the sample was dried until the mass change rate was ≤0.01g / 30s, the mass m1 after drying was recorded, and the moisture content was calculated as (m0-m1) / m0×100%. Simultaneously, the water activity (aw) of the coffee powder was measured using a water activity meter at 25℃. Five capsules were tested in each group.

[0226] Table 7 Results of accelerated storage retention test:

[0227]

[0228] Analysis: The accelerated storage test results are highly consistent with the WVTR / OTR test results. After a 30-day high-temperature and high-humidity challenge, Examples 7, 4, and 8 all maintained a coffee powder moisture content below 2.3 wt%, a water activity below 0.22, and a headspace oxygen content below 1.2%, indicating that their packaging has excellent airtightness and moisture barrier properties, effectively delaying coffee oxidation and moisture absorption. Although the material in Example 11 is relatively brittle, the coating is extremely dense due to the use of a 3.0 MPa high-pressure film-forming process, resulting in excellent oxygen barrier properties (residual oxygen 1.3%). In contrast, Comparative Examples 2, 5, and 8, due to incomplete or defective coatings, allowed a large influx of external moisture and oxygen, causing the coffee powder moisture content to soar to 4.2-5.2 wt% and the water activity to exceed 0.35. This not only severely damages the coffee flavor but also poses a risk of microbial growth. Due to the lack of effective penetration and anchoring, Comparative Example 7 may experience microscopic peeling of the coating during long-term storage due to temperature and humidity changes. Its barrier effect (moisture content 3.5wt%) is significantly inferior to that of the example with a gradient structure.

[0229] Application Example 6: Heat sealing window and initial sealing temperature test.

[0230] This application example quantifies the heat-sealing initiation temperature and heat-sealing window width during the flange sealing process for different formulations or structures.

[0231] Experimental Description: Temperature gradient heat sealing tests were conducted using a heat sealing tester (Model 12-12 AS / 1). The heat sealing pressure was set to 0.30 MPa, and the holding time was 0.8 s. The temperature range was from 100℃ to 180℃. Initially, a coarse test was performed in 10℃ increments to determine the initial sealing range, followed by a fine test in 2℃ increments. Peel strength tests were conducted on the sealed samples at each temperature point.

[0232] The heat seal initiation temperature (SIT) is defined as the lowest heat seal temperature at which the peel strength first reaches 5.0 N / 15 mm.

[0233] The heat-sealing window width is defined as the width of a continuous temperature range (i.e., the upper limit temperature minus the lower limit temperature) during which the peel strength remains above 8.0 N / 15 mm, and the capsule flange shows no obvious deformation, and the sealing film is not burned through or wrinkled. Five parallel samples are tested at each temperature point.

[0234] Table 8. Test results of heat-sealing window and initial sealing temperature:

[0235]

[0236] Analysis: The test results clearly demonstrate the influence of flange surface condition on heat-sealing performance. Examples 7, 2, and 10 have the widest heat-sealing window (≥44°C) and the lowest initial sealing temperature (≤116°C). This is because these samples have a high coating amount (96-120 g / m²) in the flange area, forming a thick and smooth "polymer pad" that can tolerate temperature and pressure fluctuations and fill any small gaps that may exist between the end cap and the flange. Example 11, due to the use of PHB with a higher melting point, increases the initial sealing temperature to 135°C, but still maintains an operating window of 30°C, meeting the needs of industrial production. In contrast, Comparative Examples 3 and 5, due to poor adhesive or rough flange surfaces, require extremely high temperatures (140°C) to allow the polymer to flow and fill the paper fiber pores for bonding, which easily leads to burns on the sealing film, resulting in a very narrow usable window (only 10°C). Comparative Example 8, due to its uneven surface and uneven heat conduction, suffers from difficult initial sealing and is prone to incomplete sealing, with a window of only 12°C. A wide heat-sealing window means higher yield and process stability on high-speed packaging lines.

[0237] Application Example 7: Testing of flange surface porosity, penetration depth, equivalent thickness of continuous dense layer, and heat seal ring width.

[0238] This application example uses microscopic characterization techniques to verify the densification effect of flange hot pressing and the distribution morphology of the coating in the paper substrate.

[0239] Experimental Description: Flange surface porosity: determined using cross-sectional image analysis. Samples were cut from both the flange and sidewall regions, and cross-sectional slices (20 μm thick) perpendicular to the inner surface were prepared. Bright-field cross-sectional images were acquired at 200× magnification and calibrated with a scale. The surface region was defined as the thickness range from 0 μm to 200 μm from the inner surface. Within this surface region, threshold segmentation was performed using image analysis software, and the pore area ratio (pore area / total surface area × 100%) was calculated as the surface porosity. At least 10 different fields of view were taken for each sample, and the arithmetic mean was calculated to obtain the flange surface porosity and sidewall surface porosity.

[0240] Penetration depth and coating thickness: Capsule sidewall samples were cryostated at -20°C to prepare 20 μm thick sections perpendicular to the surface. After Nile Red fluorescence staining (specifically labeled PHA), the sections were observed under a fluorescence microscope. Image analysis software was used to measure the maximum depth of PHA fluorescence signal penetration into the pulp fiber network (i.e., penetration depth) and the average thickness of the continuous film layer covering the outermost layer of fibers (i.e., the equivalent thickness of the continuous dense layer). Ten fields of view were observed for each sample group.

[0241] Heat seal ring width: The radial width of the thickened coating in the flange area is directly measured using a digital caliper, and the average of 8 measurements are taken along the circumference.

[0242] Table 9. Test results of microstructure parameters:

[0243]

[0244] Analysis: Microscopic analysis revealed the structural root causes of the performance differences among the samples. The surface porosity (30.5%-36.0%) of the flanges in all examples (and comparative examples except Comparative Example 3) was significantly lower than that of the sidewalls (55.0%-56.5%), confirming that the flange hot-press densification process effectively compacted the fiber network, providing a solid foundation for heat sealing.

[0245] Example 8 used a 200 nm first dispersion, achieving a penetration depth of 280 μm, close to the upper limit of 300 μm. This deeper penetration created a strong mechanical interlocking (“micro-rivet” effect), explaining its excellent boiling resistance in Application Example 2. Conversely, Comparative Example 7, despite a normal total coating amount, had a penetration depth of only 30 μm due to the excessively large particle size of the first layer (500 nm), which prevented it from penetrating deep into the pores. This was mainly surface accumulation rather than effective anchoring, resulting in weak interfacial bonding. Comparative Examples 5 and 6 represent the extremes of “too thin” and “too thick,” respectively: too thin (4 μm) failed to form a complete continuous film, while too thick (55 μm) and with excessive penetration (350 μm) resulted in excessive structural rigidity, making it prone to cracking under stress. The data from all examples fell within the optimal design window, achieving a balance between anchoring and density.

[0246] Application Example 8: Total Organic Fluorines (TOF) Test.

[0247] This application example aims to verify that the paper-based molded coffee capsule and sealing component of the present invention, while pursuing high oil resistance, does not introduce fluorine-containing compounds, thus meeting environmental protection and food safety requirements.

[0248] Experimental description: The test was conducted in accordance with EN 14582:2016 standard, using oxygen bomb combustion combined with fluoride ion selective electrode method to determine total organic fluorine (TOF).

[0249] Sample pretreatment: Cut and mix the capsules and sealing components of each group. To eliminate interference from inorganic fluorine, extract the sample with ultrapure water before combustion and discard the extract. Accurately weigh 0.50 g of the sample on a dry basis and place it in the oxygen bomb combustion cup; the oxygen charging pressure during oxygen bomb combustion is 2.8 MPa; use 15 mL of 0.01 mol / L sodium hydroxide solution as the absorbent.

[0250] Combustion and absorption: After ignition and combustion, rinse the combustion cup and the inner wall of the bomb with ultrapure water and combine it with the absorption liquid, then bring the volume to 100 mL; shake the oxygen bomb for 20 min to ensure that the combustion products are fully absorbed.

[0251] Determination: Before the determination, 5 mL of TISAB was added to the test solution to stabilize the ionic strength and eliminate complexation interference; calibration curves (R²≥0.999) were established using 0.1 mg / L, 0.5 mg / L, 1 mg / L, 5 mg / L, and 10 mg / L fluoride ion standard solutions, and blank tests were performed; the fluoride ion mass concentration was determined using a fluoride ion selective electrode.

[0252] Calculation and Judgment: After subtracting the background from the blank test, calculate TOF using the following formula:

[0253] TOF (mg / kg) = ((C sample - C blank) × V × 1000) / m.

[0254] Wherein, Csample represents the fluoride ion concentration (mg / L) in the sample test solution, Cblank represents the fluoride ion concentration (mg / L) in the blank test solution, V represents the final volume (L), and m represents the dry weight of the sample (kg). The method detection limit is ≤5 mg / kg; values ​​below the detection limit are considered undetectable.

[0255] Table 10 Results of Total Organic Fluorines (TOF) Test:

[0256]

[0257] Analysis: Test results show that, in both the examples and comparative examples, the total organic fluorine (TOF) content of all samples was below the method detection limit of 5 mg / kg, and was therefore deemed undetectable. This result is significant: traditional paper-based oil-resistant packaging often relies on perfluorinated or polyfluoroalkyl substances (PFAS) for oil resistance, but PFAS pose a risk of persistent organic pollutants. This invention achieves excellent oil resistance (as shown in Application Example 4, oil resistance time > 300 min) through physical barrier (continuous dense PHA layer) and surface energy modulation (the hydrophobic properties of PHA itself and nanofillers), completely eliminating dependence on fluorides. This confirms that this technical solution, while ensuring high performance, fully complies with increasingly stringent global environmental regulations (such as EU restrictions on PFAS in food contact materials) and consumer demands for food safety.

[0258] Application Example 9: Verification of dry coating amount at the sealing surfaces of the sidewall, bottom wall and flange.

[0259] This application example uses quantitative analysis to verify whether the actual dry coating amount of each group in different areas (sidewall, bottom wall, flange) meets the set target, and whether effective local thickening has been formed in the flange area.

[0260] Experimental Description: The weight difference method was used for determination. After the capsule was film-formed and dried to constant weight at 105℃, samples with known areas (accurate to 0.01 cm²) were cut from the side wall, bottom wall, and flange area using a special punch.

[0261] Sidewall / Bottomwall: Take 5 samples from each sidewall, weigh them, subtract the mass of the corresponding substrate (average weight of the corresponding part of the uncoated capsule), and divide by the area to obtain the dry coating amount.

[0262] Flange: Cut a sample after flattening the flange ring. Because the flange area is densified by hot pressing, its base material density is different from that of the sidewall. Therefore, the base material weight needs to be based on the data of a flange sample that has also been densified by hot pressing but is not coated.

[0263] The calculation results are expressed in g / m², and the average of 5 capsules in each test group is taken. The ratio of "dry coating amount on the sealing surface of the flange" to "dry coating amount on the inner surface of the sidewall" is also calculated.

[0264] Table 11 Verification results of dry coating amount in each region:

[0265]

[0266] Analysis: The measured data show that the coating amount control accuracy of each sample is high, with deviations all within ±5% of the set value. The data coverage of the examples is extensive: the sidewall coating amount covers the range from 8.1 g / m² (Example 10) to 39.5 g / m² (Example 7); the flange coating amount covers the range from 20.5 g / m² (Example 6) to 119.5 g / m² (Example 7).

[0267] Of particular note is Example 10, which validates an extreme coating ratio design. While the sidewall coating was only 8.1 g / m² (at a low barrier protection level), the high coating of 96.2 g / m² in the flange area resulted in a ratio of 11.9, close to the upper limit of 12.0. Combined with the results of Application Example 2, this design ensures excellent sealing performance (sealing strength 13.0 N) while saving material costs. Comparative Example 5, with a sidewall coating of only 5.2 g / m², fell below the critical point for effective film formation, leading to barrier failure. Comparative Example 6, with its excessively high coating (50.5 g / m² for the sidewall), not only wasted material but also increased the risk of bursting or delamination during boiling due to excessive internal stress in the coating (see the boiling leakage rate and bursting or delamination rate data for Application Example 2).

[0268] Application Example 10: Special test on coating toughness and primer adhesion.

[0269] This application example verifies the actual effects of plasticizing modification and the introduction of the base coating by conducting mechanical tests on the coating material itself and tests on the adhesion between the coating and the substrate.

[0270] Experimental Description: Elongation at Break Test: The second aqueous dispersion (dense layer formulation) used in each example was cast into a film in a polytetrafluoroethylene mold, dried at room temperature for 48 hours, and then vacuum dried at 60°C for 4 hours to obtain dumbbell-shaped specimens (ASTM D638-22 Type V) with a thickness of approximately 30-40 μm. Tensile tests were performed using an electronic tensile testing machine (6800 Series, equipped with ASTM D638 Type V fixtures and a suitable range sensor) at a speed of 10 mm / min, and the elongation at break was recorded.

[0271] Adhesion Test: Finished capsules from Example 1 (without primer) and Example 4 (with primer) were selected. The capsules were completely immersed in hot water at 95°C for 30 minutes (simulating an extreme boiling environment), then removed and dried. A cross-cut adhesion test (ASTM D3359-23) was performed on the inner surface of the sidewalls. A 1mm grid was cut with a sharp blade, 3M 610 tape was applied, and then quickly peeled off. The extent of coating peeling at the cut edges was observed. Rating criteria: 5B (smooth edges, no peeling) to 0B (peeling area > 65%).

[0272] Table 12 Results of coating toughness and adhesion tests:

[0273]

[0274] Analysis: Test results show that the embodiments of the present invention are significantly superior to the comparative examples in terms of coating toughness and adhesion stability under humid and hot environments.

[0275] In the embodiments, the samples with a double-layer "penetrating anchoring layer + continuous dense layer" structure (Examples 1-11) generally maintained an adhesion level of 4B or higher after wet heat immersion, indicating that a stable mechanical interlocking interface was formed between the coating and the pulp substrate.

[0276] Among them, the adhesion of Examples 4, 8 and 10 reached 5B, indicating that the introduction of primer, deep penetration of small particle size or flexible monomer structure can help to further improve the interface stability.

[0277] In contrast, Comparative Example 4 (without thermal fusion film formation) showed an adhesion drop to 0B under humid and hot conditions, indicating that the coating in the particle-packed state is extremely prone to overall peeling under hydrothermal conditions; Comparative Example 3 (without flange densification) and Comparative Example 5 (low coating amount) also showed obvious interface failure.

[0278] Regarding the toughness of the coating body, different PHA monomer structures have a significant impact on the elongation at break. P34HB (Example 10), which contains a 4-hydroxybutyrate structure, exhibits the highest elongation at break, while PHB (Example 11), which has higher crystallinity, has the lowest elongation at break, but no macroscopic failure was observed under the support of the bilayer structure and pulp substrate.

[0279] This result further demonstrates that the present invention, through structural design rather than simply material softening, can achieve long-term stability of the coating-substrate interface while ensuring barrier and heat-sealing performance.

[0280] Experimental Results and Analysis:

[0281] Based on the experimental data from Examples 1-11 and Comparative Examples 1-8, the effectiveness and superiority of the paper-based molded coffee capsules and their PHA spray coating film-forming method proposed in this invention are analyzed in detail as follows:

[0282] The decisive role of particle size gradient bilayer structure in barrier performance:

[0283] Experimental data show that the bilayer structure of "first aqueous PHA dispersion (small particle size) + second aqueous PHA dispersion (large particle size)" constructed in this invention is the key to achieving high barrier performance.

[0284] The WVTR of Examples 1-11 was controlled below 0.90 g / (m²·24h), and the OTR was controlled below 0.82 cm³ / (m²·24h·0.1 MPa). Example 8, using a first dispersion with a lower particle size (200 nm) and a second dispersion with a larger particle size (600 nm), achieved excellent barrier properties (WVTR = 0.55 g / (m²·24h)), demonstrating that smaller particle sizes can effectively fill the pores on the pulp surface, providing a dense substrate for the upper film formation.

[0285] In contrast, Comparative Example 2 lacked the first layer of small-particle coating and directly coated with large-particle dispersion, resulting in a WVTR as high as 2.90 g / (m²·24h) and a Cobb value as high as 7.5 g / m². This indicates that large particles cannot effectively block the micropores between pulp fibers and are prone to forming through-hole defects.

[0286] More importantly, Comparative Example 7 used two coating layers with the same particle size (both 500 nm), and its WVTR (1.40 g / (m²·24h)) and OTR (1.25 cm³ / (m²·24h·0.1 MPa)) were significantly worse than those of Example 1, which had a particle size gradient. This fully demonstrates that simply increasing the number of coating layers without designing a particle size gradient cannot form an effective synergistic structure of "penetration anchoring + surface densification".

[0287] The impact of flange area densification and local thickening on seal integrity:

[0288] The structural design of the flange sealing surface directly determines the reliability of the capsule under high pressure during boiling.

[0289] Examples 1-11 all exhibited excellent pressure resistance at a cooking pressure of 1.9 MPa, with extremely low leakage and burst rates (mostly 0%). This is attributed to two key factors:

[0290] First, there is the hot-press densification treatment. Comparative Example 3 did not undergo hot-press densification of the flange, resulting in a surface porosity as high as 56.0%, a seal peel strength of only 4.0 N / 15 mm, and a boiling leakage rate as high as 30%. This indicates that the originally loose surface of the pulp molding cannot directly support high-strength heat sealing, and physical densification must be used to reduce surface roughness and porosity.

[0291] Secondly, there is the design of a locally thickened heat-sealing ring. Example 10 adopted an extreme coating distribution strategy (96 g / m² for the flange sealing surface vs. 8 g / m² for the sidewall, a ratio of approximately 12.0). Although the sidewall coating is thinner, thanks to the thick heat-sealing material reserve at the flange, a high sealing strength of 13.0 N / 15 mm and a 0% leakage rate were still achieved. Comparing Example 6 (flange coating amount of only 20 g / m²) and Comparative Example 5 (flange coating amount of 15 g / m²), it can be seen that there is a clear critical value for the dry coating amount in the flange area. When the coating amount is insufficient to fill the residual pores and form a molten "shield", the heat-sealing window becomes significantly narrower (e.g., only 10°C in Comparative Example 5), and the sealing reliability decreases significantly.

[0292] The effect of interfacial penetration depth on resistance to boiling and stratification:

[0293] The correlation between microscopic cross-sectional analysis and boiling resistance test shows that the adhesion between the coating and the substrate mainly stems from the mechanical interlocking effect.

[0294] In Example 8, the first dispersion had a particle size at the lower limit (200 nm) and a penetration depth of 280 μm, exhibiting 0% stratification and a 5B-level adhesion in the boiling resistance test. Example 4 introduced a chitosan primer, further enhancing the interfacial chemical bonding, and also achieved a 5B-level adhesion.

[0295] Conversely, Comparative Example 7, lacking small-particle-guided penetration, only penetrated to a depth of 30 μm, mainly remaining on the surface and resulting in an 8% cracking or delamination rate in the boiling resistance test. While Comparative Example 6 had the deepest penetration (350 μm), the excessively thick coating and stress concentration actually increased material brittleness, failing to deliver better overall performance. Therefore, controlling the penetration depth within the range of 20 μm to 300 μm is the optimal solution for balancing anchoring force and material mechanical properties.

[0296] Environmental performance and surface property analysis:

[0297] All embodiments showed a biodegradation rate of over 96% under controlled composting conditions for 45 days, and no total organic fluorine (TOF) was detected, demonstrating that this fully bio-based approach can completely replace traditional fluorinated oil-resistant materials and aluminum-plastic composites.

[0298] Regarding surface properties, Example 4, by introducing layered nanofiller (montmorillonite), not only improved the barrier properties (WVTR decreased to 0.50 g / (m²·24h)) but also significantly improved the surface hydrophobicity and oleophobicity (oil penetration time 340 min), indicating that the introduction of inorganic filler can effectively extend the penetration path and improve the surface micro-roughness.

[0299] Analysis of trends in material content and process parameters:

[0300] Based on the data from each embodiment and comparative example, the trends of how changes in each key parameter affect the experimental results are as follows:

[0301] Trend of particle size variation of the first dispersion: As the particle size of the first aqueous PHA dispersion decreased from 300 nm (Example 9) to 200 nm (Example 8), the penetration depth increased significantly (from 70 μm to 280 μm), and the coating adhesion grade improved from 4B to 5B, indicating that reducing the particle size of the bottom layer helps to enhance the interfacial anchoring.

[0302] Flange / sidewall coating ratio trend: As the ratio increases from 3.5 (Example 1) to 11.9 (Example 10), the overall material cost-effectiveness of the capsule is optimized while maintaining the basic barrier function of the sidewall, and the sealing strength is not sacrificed (maintained at around 13.0N), indicating that the local thickening strategy has extremely high performance potential in industrial applications.

[0303] The trend of solid content variation in the second dispersion: As the solid content of the second dispersion increases from 20 wt% (Comparative Example 8) to 60 wt% (Example 7), the film thickness of a single coating increases, which helps to form a continuous and dense layer. Too low a solid content (Comparative Example 8) will cause microcracks due to excessive moisture evaporation during the drying process, resulting in a sharp decrease in barrier performance (WVTR increases to 1.90 g / (m²·24h)).

[0304] Hot pressing temperature and pressure trends: Comparing Example 1 (150℃ / 1.0MPa) and Example 11 (165℃ / 3.0MPa), increasing the temperature and pressure of hot pressing can significantly improve the film density, thereby reducing the OTR (from 0.72 to 0.55), but also slightly reducing the elongation at break of the material (from 5.5% to 2.5%).

[0305] In summary, this invention successfully solves the technical challenge of balancing barrier, sealing, boil-resistance, and environmental performance in paper-based molded capsules through a unique dual-layer particle size gradient spraying, flange hot-pressing densification, and locally thickened heat-sealing ring design. Experimental results fully demonstrate the advanced nature and practicality of this technical solution.

[0306] Those skilled in the art should understand that the above embodiments are merely exemplary and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the technical solutions of the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A compostable paper-based molded coffee capsule, characterized in that, The paper-based molded coffee capsule includes: A capsule body formed from molded pulp, the capsule body having side walls, a bottom wall and a flange located around the mouth, the side walls and the bottom wall forming a cavity for containing coffee powder; A sealing component, wherein the sealing component is a biodegradable polyester-based film or a blended film thereof, is sealed to the flange to close the cavity; A polyhydroxyalkanoate barrier heat-sealing composite layer is applied to the inner surface of the capsule body and the sealing surface of the flange. The capsule body is a three-dimensional porous pulp molding structure, and the surface porosity of the sidewall is 50% to 60%; the flange is a hot-pressed densified area with a surface porosity of 30% to 40%. The polyhydroxyalkanoate barrier heat-sealing composite layer is obtained by sequentially coating a first aqueous polyhydroxyalkanoate dispersion and a second aqueous polyhydroxyalkanoate dispersion by spraying, drying, and then in-situ thermally fused or hot-pressed onto the capsule body to form a film. The first aqueous polyhydroxyalkanoate dispersion has a solid content of 10 wt% to 25 wt%, and the volume average particle size of the polyhydroxyalkanoate particles in the dispersion is 200 nm to 2000 nm. The second aqueous polyhydroxyalkanoate dispersion has a solid content of 20 wt% to 60 wt%, and the volume average particle size of the polyhydroxyalkanoate particles in the dispersion is 200 nm to 2000 nm. The ratio of the solid content of the second aqueous polyhydroxyalkanoate dispersion to the solid content of the first aqueous polyhydroxyalkanoate dispersion is 1.5 to 6.0, and the ratio of the volume average particle size of the second aqueous polyhydroxyalkanoate particles to the volume average particle size of the first aqueous polyhydroxyalkanoate particles is 2 to 10. The polyhydroxyalkanoate barrier heat-sealing composite layer includes an infiltrated anchoring layer and a continuous dense layer along the thickness direction: the infiltrated anchoring layer is located in the pores of the pulp fiber surface and covers the fiber to form a mechanical interlocking interface, with an infiltration depth of 20μm to 300μm; the continuous dense layer is located outside the infiltrated anchoring layer and forms a continuous film with an equivalent thickness of 6μm to 40μm. The polyhydroxyalkanoate barrier heat-sealing composite layer has different dry coating amounts in different areas. The dry coating amount on the inner surface of the sidewall and the inner surface of the bottom wall is 8 g / m² to 40 g / m². The dry coating amount on the sealing surface of the flange is 20 g / m² to 120 g / m². The ratio of the dry coating amount on the sealing surface of the flange to the dry coating amount on the inner surface of the sidewall is 2.0 to 12.0, thereby forming a locally thickened polyhydroxyalkanoate heat-sealing ring that is continuous along the circumference of the flange on the sealing surface of the flange. The ring width of the heat-sealing ring is 1.5 mm to 4.5 mm.

2. The compostable paper-based molded coffee capsule according to claim 1, characterized in that, The ratio of the dry coating amount on the sealing surface of the flange to the dry coating amount on the inner surface of the bottom wall is 2.0 to 12.

0.

3. The compostable paper-based molded coffee capsule according to claim 1, characterized in that, The polyhydroxy fatty acid ester is selected from one or more of short-chain polyhydroxy fatty acid esters, medium- and long-chain polyhydroxy fatty acid esters, and copolymers formed between short-chain and medium- and long-chain polyhydroxy fatty acid ester monomers. 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-hydroxydodecanoate), poly(3-hydroxytetrate), poly(3-hydroxytetradecanoate), poly(3-hydroxytetradecanoate), poly(3-hydroxypentadecanoate), and poly(3-hydroxyhexadecanoate). The polyhydroxyalkanoate accounts for ≥85 wt% of the dry film of the polyhydroxyalkanoate barrier heat-sealing composite layer.

4. The compostable paper-based molded coffee capsule according to claim 1, characterized in that, The capsule body also includes a bio-based coating disposed on its inner surface, and the polyhydroxyalkanoate barrier heat-sealing composite layer is coated on the surface of the bio-based coating; the bio-based coating is a polysaccharide base coating; the polysaccharide base coating includes one or more of starch and its derivatives, cellulose and its derivatives, chitosan and its derivatives, alginate, pectin, β-glucan, xanthan gum, and guar gum.

5. The compostable paper-based molded coffee capsule according to claim 1, characterized in that, The dry film of the polyhydroxyalkanoate barrier heat-sealing composite layer further comprises 1 wt% to 20 wt% of a bio-based plasticizing and toughening component based on the total mass of the dry film; the bio-based plasticizing and toughening component is selected from one or more of organic acid ester plasticizers, epoxidized vegetable oils, natural polyols and their esters, and biodegradable aliphatic polyester toughening phases. And / or, the dry film of the polyhydroxyalkanoate barrier heat-sealing composite layer further comprises 0.1 wt% to 15 wt% barrier reinforcing filler, the mass percentage being based on the total mass of the dry film, and the barrier reinforcing filler is selected from one or more of inorganic sheet fillers, inorganic particulate fillers, and bio-based nanofillers.

6. The compostable paper-based molded coffee capsule according to claim 1, characterized in that, The compostable paper-based molded coffee capsules meet one or more of the following properties: Under conditions of 38℃ and 90% relative humidity, the water vapor transmission rate of the composite sample formed by the capsule body and the polyhydroxyalkanoate barrier heat-sealing composite layer on the sidewall and bottom wall was measured according to GB / T 1037-2021 as ≤0.90g / (m²·24h). The oxygen permeability was measured to be ≤0.82 cm³ / (m²·24h·0.1 MPa) according to GB / T 19789-2021 at 23℃ and 0% relative humidity. Cobb measured according to GB / T 1540-2002 60 ≤2.4g / m²; According to GB / T 2790-1995, the 180° peel test was performed and the sealing peel strength of the flange sealing part was ≥10.0N / 15mm. Total organic fluorine was not detected by oxygen bomb combustion combined with fluoride ion selective electrode method according to EN 14582:2016, and the method detection limit was ≤5 mg / kg. According to the controlled composting conditions test in GB / T 19277.1-2025, the biodegradation rate is ≥96% after 45 days.

7. The compostable paper-based molded coffee capsule according to claim 1, characterized in that, The sealing component consists of a biodegradable polyester film or a blended film thereof and a polyhydroxyalkanoate heat-sealing layer disposed on the side of it facing the flange, so that it forms a heat-sealing match with the continuous dense layer and the locally thickened polyhydroxyalkanoate heat-sealing ring. The biodegradable polyester film is selected from one or more of polylactic acid film, polybutylene succinate film, polybutylene succinate-adipate film, and polycaprolactone film; the polyhydroxyalkanoate heat-sealing layer may be of the same or different type as the polyhydroxyalkanoate of the continuous dense layer.

8. The compostable paper-based molded coffee capsule according to claim 1, characterized in that, The compostable paper-based molded coffee capsules were subjected to a 180° peel test according to GB / T 2790-1995 under heat-sealing pressure of 0.30 MPa and holding time of 0.8 s. The heat-sealing initiation temperature of the capsules was 112°C to 135°C and the heat-sealing window width was 30°C to 48°C. The capsules were also subjected to a brewing resistance test at 83°C to 86°C and 1.9 MPa pressure, with a sample size of N=50. The brewing leakage rate of the capsules was ≤2% and the bursting or delamination rate was ≤1%.

9. A method for preparing a compostable paper-based molded coffee capsule according to claim 1, characterized in that, The preparation method includes the following steps: Step 1. Prepare pulp slurry and wet mold it to obtain a wet pulp blank with sidewalls, bottom wall and flange; Step 2. Dehydrate, dry, and shape the wet pulp blank obtained in Step 1 to obtain the capsule body, wherein the moisture content of the capsule body before coating is 2wt% to 8wt%; Step 3. Perform hot-press densification treatment on the flange of the capsule body obtained in Step 2 to obtain a densified capsule body; the hot-press densification treatment temperature is 90℃ to 165℃, the pressure is 0.2MPa to 10MPa, and the time is 0.2s to 60s. Step 4. Apply the first aqueous polyhydroxyalkanoate dispersion to the inner surface of the densified capsule body and the sealing surface of the flange obtained in Step 3 by spraying, and pre-dry to obtain the first coated capsule body; wherein, the solid content of the first aqueous polyhydroxyalkanoate dispersion is 10wt% to 25wt%, and the volume average particle size of the polyhydroxyalkanoate particles in the dispersion is 200nm to 2000nm; the water content of the coating surface of the first coated capsule body is controlled to be 3wt% to 15wt%; and, when applying vacuum or pressure difference to the capsule body to promote the penetration of the first aqueous polyhydroxyalkanoate dispersion into the pulp pores during the coating process and / or drying process, the vacuum gauge pressure is 5kPa to 80kPa; Step 5. Apply the second aqueous polyhydroxyalkanoate dispersion to the coating surface of the first coated capsule body obtained in Step 4 using a spraying method, and dry it to obtain the second coated capsule body; wherein, the solid content of the second aqueous polyhydroxyalkanoate dispersion is 20wt% to 60wt%, and the volume average particle size of the polyhydroxyalkanoate particles in the dispersion is 200nm to 2000nm; the solid content of the second aqueous polyhydroxyalkanoate dispersion is the same as that of the first aqueous polyhydroxyalkanoate dispersion. The ratio of the amounts is 1.5 to 6.0, and the ratio of the volume average particle size of the second aqueous polyhydroxyalkanoate particles to the volume average particle size of the first aqueous polyhydroxyalkanoate particles is 2 to 10; and, in the flange area, by increasing the spraying feed amount of the second aqueous polyhydroxyalkanoate dispersion and / or increasing the number of spraying passes, the dry coating amount of the flange sealing surface is higher than the dry coating amount of the inner surface of the side wall and the inner surface of the bottom wall, thereby forming a locally thickened polyhydroxyalkanoate heat-sealing ring that is continuous along the flange circumference on the flange sealing surface after film formation. Step 6. Perform thermal fusion or hot pressing on the second coated capsule body obtained in Step 5 to form a penetrating anchoring layer and a continuous dense layer of polyhydroxyalkanoate, and form a heat-sealing interface on the sealing surface of the flange to obtain the capsule body after film formation; the temperature of thermal fusion or hot pressing for film formation is 130℃ to 165℃, the holding time is 5s to 120s, and the hot pressing pressure is 0.2MPa to 3MPa; wherein, the penetration depth of the penetrating anchoring layer is 20μm to 300μm, and the equivalent thickness of the continuous dense layer is 6μm to 40μm; Step 7. Fill the capsule body after film formation obtained in Step 6 with coffee powder, seal the sealing component to the flange and complete the sealing by heat sealing to obtain the sealed paper-based molded coffee capsule.

10. A coating system for constructing a polyhydroxyalkanoate barrier heat-sealing composite layer for a compostable paper-based molded coffee capsule as described in claim 1, characterized in that, The coating system of the polyhydroxyalkanoate barrier heat-sealing composite layer includes a first aqueous polyhydroxyalkanoate dispersion and a second aqueous polyhydroxyalkanoate dispersion. The first aqueous polyhydroxyalkanoate dispersion is used to form a penetrating anchoring layer, and the second aqueous polyhydroxyalkanoate dispersion is used to form a continuous dense layer. The first aqueous polyhydroxyalkanoate dispersion has a solid content of 10 wt% to 25 wt%, and the volume average particle size of the polyhydroxyalkanoate particles in the dispersion is 200 nm to 2000 nm; the second aqueous polyhydroxyalkanoate dispersion has a solid content of 20 wt% to 60 wt%, and the volume average particle size of the polyhydroxyalkanoate particles in the dispersion is 200 nm to 2000 nm; the ratio of the solid content of the second aqueous polyhydroxyalkanoate dispersion to the solid content of the first aqueous polyhydroxyalkanoate dispersion is 1.5 to 6.0, and the ratio of the volume average particle size of the second aqueous polyhydroxyalkanoate particles to the volume average particle size of the first aqueous polyhydroxyalkanoate particles is 2 to 10.

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