Paper-based molded coffee capsule capable of being naturally composted, PHA water-based dispersion in-situ film forming barrier heat-sealing composite layer, preparation method and application of paper-based molded coffee capsule

Abstract

The invention discloses a paper-based molded coffee capsule capable of being naturally composted, a PHA aqueous dispersion in-situ film forming barrier heat-sealing composite layer, a preparation method and application thereof, and belongs to the field of degradable packaging and single-cup extraction capsules. The capsule body is formed by molding paper pulp and is provided with a side wall, a bottom wall and a mouth flange; the biodegradable polyester-based film sealing component is connected to the flange in a sealing manner; and the polyhydroxyalkanoate barrier heat-sealing composite layer covers 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 a permeation anchoring layer located in paper pulp pores and a continuous compact layer located on the outer side in the thickness direction. The flange is a hot-pressing densified area, and a local thickening heat sealing ring is formed on the sealing face of the flange. Through physical anchoring of the small-particle-size components and surface film forming of the large-particle-size components, the moisture and oxygen blocking and interface bonding performance is achieved, and the brewing sealing performance is guaranteed.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of degradable packaging and single-serve extraction capsules, in particular to a paper-based molded coffee capsule naturally compostable and its PHA aqueous dispersion in-situ film-forming barrier heat-seal composite layer and preparation method and application. BACKGROUND

[0002] Capsule coffee is traditionally made of aluminum or multi-layer plastic composite structure to meet the sensitivity of coffee powder to water vapor and oxygen during storage period and the requirement of temperature and pressure resistance during brewing process. Such structure is usually mixed with coffee grounds after use, which is difficult to separate and recycle, and it is difficult to form a high-efficiency material closed loop.

[0003] To improve the renewable and compostable properties of paper-based capsules, the prior art proposes to form a capsule body with paper pulp or paperboard, and to set a barrier layer or inner liner on the inner surface thereof. For example, WO2019064017A1 discloses a capsule structure with paperboard or paper pulp as the main body and a biodegradable polymer coating or cladding layer on the surface thereof; EP4620861A2 and JP2024535486A disclose attaching or forming an attached barrier inner liner on the inner surface of the paper pulp capsule to improve the moisture and oxygen barrier performance; GB2584959A discloses a scheme of using a starch-based sealant to fix and seal the closure piece in the flange area of the capsule; US20220169430A1 discloses a scheme of constructing a barrier coating on the surface of the paper-based capsule by plasma-enhanced chemical vapor deposition (PECVD) to improve the barrier performance. The above schemes have certain effect in improving the barrier or sealing performance of paper-based capsules, but still have the following engineering problems under the coupling condition of high-temperature hot water immersion and brewing pressure difference: first, the pre-made inner liner film or cladding layer is prone to interfacial peeling, wrinkling or local leakage during piercing, pressure and immersion; second, the three-dimensional surface is prone to form through defect channels such as pinholes and micro-cracks during coating or molding; third, the sealing surface aperture and roughness fluctuation of the flange leads to a narrow heat-seal window and a large heat-seal strength dispersion; fourth, the equipment and process cost of vacuum deposition type barrier layer is high, and it is difficult to couple with the paper pulp molding production line.

[0004] To replace traditional paper-based surface treatment agents such as fluorine-containing oil repellents, the prior art proposes water-based dispersions based on polyhydroxyalkanoates (PHA) for paper-based barrier coating. For example, WO2020036843A1, ZA202101369B and its EP3837322B1, CN112867766A, CN116218332A disclose a biodegradable coating system for coating a water-based PHA dispersion on the surface of paperboard or other biodegradable substrates and drying it into a film; SE2330419A1 discloses forming a first and second water-based PHA coating by multi-pass coating to obtain a fiber-based barrier material that meets the requirements of water vapor transmission rate (WVTR) and water absorption; CN115996838A discloses a scheme of first coating a water-based PHA dispersion and drying to remove water, and then heating the coating again to melt the PHA to seal the inter-particle pores and form a continuous and dense PHA layer. The above technical systems are mainly aimed at flat paper or paperboard barrier packaging or paper products for dining, and their coating structure and process window are mainly developed around flat substrates. When they are directly migrated to three-dimensional porous pulp molded coffee capsules, there are still problems such as insufficient uniformity of the coating on the inner surface of three dimensions, high risk of peeling of the coating and paper interface under high temperature and high humidity cooking pressure, and narrow heat sealing window of the sealing surface of the flange due to pores and corrugations.

[0005] In addition, the disclosed documents also disclose various PHA-based water-based emulsion systems for paper-based barrier, which components can include PHA, degradable polyester such as polybutylene succinate-terephthalate (PBAT), and hydrophilic polymers such as polyvinyl alcohol (PVOH, also known as PVA) to improve coating rheology, film formation and barrier; there are also disclosed paper-based barrier coating compositions using acrylic emulsion or polyurethane emulsion as the main component and combining with hydrophilic polymer modification components. The above emulsion or dispersion system can improve the barrier or coating adaptability of paper-based, but its focus is still mainly on flat paper-based barrier, and has not yet carried out integrated structural design for three-dimensional porous interface anchoring, flange sealing surface densification and local heat sealing material supply of pulp molded coffee capsules, nor has it proposed a complete set of constraints for the stability of the coating interface and the sealing window under high temperature and high humidity pressure conditions of cooking.

[0006] Therefore, there is an urgent need for a complete set of structure and process scheme for paper-based molded coffee capsules: without relying on pre-made self-supporting liner film attachment and high-cost vacuum deposition process, through two-stage water-based PHA dispersion spraying and in-situ thermal fusion or thermal pressure film formation, a penetration anchoring layer is constructed in the three-dimensional pulp pores and a continuous and dense layer is constructed on the surface, and the sealing processing window and sealing consistency are improved through flange thermal densification and local thickening of the flange area, so as to meet the requirements of shelf life barrier, cooking stability and compost disposal. SUMMARY

[0007] The present application aims at overcoming the deficiencies of the prior art, and provides a paper-based molded 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.

[0008] To achieve the above object, the present application provides the following technical solutions:

[0009] The application provides a compostable paper-based molded coffee capsule, comprising: a capsule body molded from molded paper pulp, the capsule body having a side wall, a bottom wall, and a flange located at the periphery of the mouth, the side wall and the bottom wall enclosing a cavity for containing coffee powder; a sealing member, which is a biodegradable polyester-based film or a blended film thereof, sealed to the flange to close the cavity; and a PHA barrier heat-seal 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 paper pulp molded structure, the surface porosity of the side wall being 50% to 60%, and the specific values can be 50%, 51%, 52%, 53%, 54%, 55%, 56%, 56.5%, 57%, 58%, 59%, or 60%; the flange is a hot-pressed densification area and its surface porosity is 30% to 40%, and the specific values can be 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-seal composite layer is obtained by sequentially coating the first and second aqueous PHA dispersions on the capsule body by spraying, drying, and in-situ hot fusion or hot pressing; wherein the first aqueous PHA dispersion is used to form an infiltration anchoring layer, and the second aqueous PHA dispersion is used to form a continuous dense layer; 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, and the ratio of the volume average particle size of the second aqueous PHA to the volume average particle size of the first aqueous PHA is 2 to 10. The PHA barrier heat-seal composite layer includes an infiltration anchoring layer and a continuous dense layer along the thickness direction: the infiltration anchoring layer is located in the surface porosity of the pulp fiber and covers the fiber to form a mechanical interlocking interface, the infiltration depth is 20 μm to 300 μm, and the specific values can be 20 μm, 30 μm, 50 μm, 70 μm, 80 μm, 100 μm, 120 μm, 140 μm, 150 μm, 160 μm, 180 μm, 200 μm, 220 μm, 250 μm, 280 μm, or 300 μm; the continuous dense layer is located outside the infiltration anchoring layer and forms a continuous film, and the equivalent thickness is 6 μm to 40 μm, and the specific values can be 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-seal composite layer has different dry coating amounts in different areas, the dry coating amount of the inner surface of the side wall and the inner surface of the bottom wall is 8 g / m2to 40 g / m2, and the specific value can be 8 g / m2, 10 g / m2, 15 g / m2, 20 g / m2, 25 g / m2, 30 g / m2, 35 g / m2or 40 g / m2; the dry coating amount of the sealing surface of the flange is 20 g / m2to 120 g / m2, and the specific value can be 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, 100 g / m2, 110 g / m2or 120 g / m2, and the ratio of the dry coating amount of the sealing surface of the flange to the dry coating amount of the inner surface of the side wall is 2.0 to 12.0, and the specific ratio can be 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-seal ring continuous in the circumferential direction of the flange on the sealing surface of the flange, the ring width of the heat-seal ring is 1.5 mm to 4.5 mm, and the specific width can be 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm or 4.5 mm. The PHA accounts for ≥85 wt% in the dry film of the PHA barrier heat-seal composite layer, and the specific value can be 85 wt%, 88 wt%, 89 wt%, 90 wt%, 92 wt%, 95 wt%, 98 wt% or 100 wt%.

[0010] The ratio of the dry coating amount of the sealing surface of the flange to the dry coating amount of 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 chain PHA, and copolymer formed between short chain PHA and medium 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), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB); the medium 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-hydroxydodecanoate), poly(3-hydroxytridecanoate), poly(3-hydroxytetradecanoate), poly(3-hydroxy-pentadecanoate), poly(3-hydroxyhexadecanoate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH); the PHA comprises ≥ 85 wt% of the dry film of the PHA barrier heat seal composite layer, specifically 85 wt%, 89 wt%, 90 wt%, 95 wt%, or 100 wt%.

[0012] The capsule body further comprises a bio-based primer coating disposed on the inner surface thereof, and the PHA barrier heat seal composite layer is disposed on the surface of the bio-based primer coating; the bio-based primer coating is a polysaccharide primer coating; the polysaccharide primer coating comprises one or more of starch and derivatives thereof, cellulose and derivatives thereof, chitosan and derivatives thereof, alginate, pectin, beta-glucan, xanthan gum, guar gum.

[0013] The dry film of the PHA barrier heat seal 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 acid ester plasticizers, epoxidized vegetable oil, natural polyols and esters thereof, and biodegradable aliphatic polyester toughening phase; and / or, the dry film of the PHA barrier heat seal composite layer further comprises 0.1 wt% to 15 wt% of a barrier-enhancing 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-enhancing filler is selected from one or more of inorganic sheet-like fillers, inorganic particulate fillers, and bio-based nanofillers.

[0014] The naturally compostable paper-based molded coffee capsule meets one or more of the following properties:

[0015] The WVTR of a composite sample formed by the side wall and the bottom wall of the capsule body and the PHA barrier heat-seal composite layer is less than or equal to 0.90 g / (m2·24h) at 38°C and 90% relative humidity according to GB / T 1037-2021, and the specific value can 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), 0.60 g / (m2·24h), 0.62 g / (m2·24h), 0.65 g / (m2·24h), 0.68 g / (m2·24h), 0.70 g / (m2·24h), 0.72 g / (m2·24h), 0.75 g / (m2·24h), 0.78 g / (m2·24h), 0.80 g / (m2·24h), 0.82 g / (m2·24h), 0.85 g / (m2·24h), 0.88 g / (m2·24h), or 0.90 g / (m2·24h);

[0016] The oxygen transmission rate (OTR) measured at 23°C and a relative humidity of 0% according to GB / T 19789-2021 is ≤0.82 cm³ / (m²·24h·0.1MPa), and the specific value can be 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), 0.55 cm³ / (m²·24h·0.1MPa), 0.58 cm³ / (m²·24h·0.1MPa), 0.60 cm³ / (m²·24h·0.1MPa), 0.62 cm³ / (m²·24h·0.1MPa), 0.65 cm³ / (m²·24h·0.1MPa), 0.68 cm³ / (m²·24h·0.1MPa), 0.70 cm³ / (m²·24h·0.1MPa), 0.72 cm³ / (m²·24h·0.1MPa), 0.75 cm³ / (m²·24h·0.1MPa), 0.78 cm³ / (m²·24h·0.1MPa), 0.80 cm³ / (m²·24h·0.1MPa), or 0.82 cm³ / (m²·24h·0.1MPa);

[0017] The 60-second Cobb value measured according to GB / T 1540-2002 is ≤2.4 g / m², and the specific value can be 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] The flange sealing part has a sealing peeling strength of ≥10.0 N / 15 mm, specifically 10.0 N / 15 mm, 10.2 N / 15 mm, 10.5 N / 15 mm, 10.8 N / 15 mm, 11.0 N / 15 mm, 11.2 N / 15 mm, 11.5 N / 15 mm, 11.8 N / 15 mm, 12.0 N / 15 mm, 12.2 N / 15 mm, 12.5 N / 15 mm, 12.8 N / 15 mm, 13.0 N / 15 mm, 13.2 N / 15 mm, 13.5 N / 15 mm, 13.8 N / 15 mm, 14.0 N / 15 mm or 15.0 N / 15 mm, measured by the 180° peeling test according to GB / T 2790-1995;

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

[0020] The 45-day biodegradation rate is ≥96%, specifically 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%, tested under the controlled composting conditions according to GB / T 19277.1-2025.

[0021] The sealing member is composed of a biodegradable polyester-based film or a blended film thereof and a PHA heat sealing layer arranged on the 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-based film is selected from one or more of polylactic acid (PLA) film, polybutylene succinate (PBS) film, polybutylene succinate-adipate (PBAT) film and polycaprolactone (PCL) film; the PHA heat sealing layer is the same as or different from the PHA type of the continuous dense layer.

[0022] The heat seal initiation temperature of the capsule is 112-135℃, and the specific temperature can be 112℃, 114℃, 115℃, 116℃, 118℃, 119℃, 120℃, 123℃, 124℃, 125℃, 130℃ or 135℃, and the heat seal window width is 30-48℃, and the specific width can be 30℃, 32℃, 33℃, 34℃, 35℃, 36℃, 38℃, 40℃, 42℃, 44℃, 45℃, 46℃ or 48℃; and the capsule has a boiling resistance of 83-86℃, 1.9MPa, a sample size N=50, a boiling leakage rate of ≤2%, and a burst or delamination rate of ≤1%.

[0023] The application also provides a preparation method of the paper-based molded coffee capsule, comprising the following steps:

[0024] Step 1. Preparing a paper pulp slurry and wet-molding to obtain a paper pulp wet blank having a side wall, a bottom wall and a flange;

[0025] Step 2. Dehydrating, drying and shaping the paper pulp wet blank obtained in step 1 to obtain a capsule body, wherein the water content of the capsule body before coating is 2-8wt%, and the specific value can be 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt% or 8wt%;

[0026] Step 3. Hot pressing and densifying the flange of the capsule body obtained in step 2 to obtain a densified capsule body; the hot pressing and densifying treatment has a temperature of 90-165℃, and the specific temperature can be 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃ or 165℃, a pressure of 0.2-10MPa, and the specific pressure can be 0.2MPa, 1.0MPa, 2.0MPa, 3.0MPa, 4.0MPa, 5.0MPa, 8.0MPa or 10MPa, and a time of 0.2-60s, and the specific time can be 0.2s, 1.0s, 2.0s, 5.0s, 10s, 30s or 60s;

[0027] Step 4. The first water-based PHA dispersion is sprayed on the inner surface of the densified capsule body and the sealing surface of the flange obtained in step 3, and pre-dried to obtain a first coated capsule body; wherein the solid content of the first water-based PHA dispersion is 10wt% to 25wt%, and the specific content can be 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, and the specific particle size can be 200nm, 220nm, 250nm, 300nm, 500nm, 800nm, 1000nm, 1500nm or 2000nm; the water content of the coated surface of the first coated capsule body is controlled to be 3wt% to 15wt%, and the specific value can be 3wt%, 5wt%, 8wt%, 10wt%, 12wt% or 15wt%; and during the coating process and / or the drying process, a vacuum or pressure difference is applied to the capsule body to promote the penetration of the first water-based PHA dispersion into the pores of the pulp, and the vacuum gauge pressure is 5kPa to 80kPa, and the specific value can be 5kPa, 10kPa, 20kPa, 30kPa, 40kPa, 50kPa, 60kPa, 70kPa or 80kPa;

[0028] Step 5. The second water-based PHA dispersion is sprayed on the coated surface of the first coated capsule body obtained in step 4, and dried to obtain a second coated capsule body; wherein the solid content of the second water-based PHA dispersion is 20wt% to 60wt%, and the specific content can be 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, and the specific particle size can be 200nm, 300nm, 400nm, 450nm, 500nm, 600nm, 800nm, 900nm, 1000nm, 1500nm or 2000nm; the ratio of the solid content of the second water-based PHA dispersion to the solid content of the first water-based PHA dispersion is 1.5 to 6.0, and the specific ratio can be 1.5, 2.0, 2.5, 3.0, 4.0, 5.0 or 6.0, and the ratio of the volume average particle size of the second water-based PHA particles to the volume average particle size of the first water-based PHA particles is 2 to 10, and the specific ratio can be 2, 2.4, 3, 4, 5, 8 or 10; and by increasing the spraying feed amount of the second water-based PHA dispersion and / or increasing the spraying passes in the flange area, the dry coating amount of the sealing surface of the flange is higher than that of the inner surface of the side wall and the inner surface of the bottom wall, so that a locally thickened PHA heat-sealing ring is formed on the sealing surface of the flange after film formation, which is continuous along the circumference of the flange;

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

[0030] Step 7. Coffee powder is filled into the film-formed capsule body obtained in step 6, a sealing member is sealed to the flange, and the sealing is completed by heat sealing, to obtain a sealed paper-based molded coffee capsule.

[0031] The application also provides a coating system for constructing the aforementioned PHA barrier heat-sealing composite layer in situ on the inner surface of a paper-based molded coffee capsule, comprising a first aqueous PHA dispersion for forming an infiltration anchoring layer and a second aqueous PHA dispersion for forming a continuous dense layer; wherein the solid content of the first aqueous PHA dispersion is 10 wt% to 25 wt%, and the volume average particle size of PHA particles in the dispersion is 200 nm to 2000 nm; the solid content of the second aqueous PHA dispersion is 20 wt% to 60 wt%, and the volume average particle size of PHA particles in the dispersion is 200 nm to 2000 nm; 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, 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.

[0032] Compared with the prior art, the following remarkable beneficial effects can be obtained by using the application:

[0033] Excellent barrier performance and oil resistance: By constructing the particle size gradient double-layer structure of "infiltration anchoring layer + continuous dense layer", the application utilizes the deep physical infiltration of small particle size components to effectively block the surface micropores of pulp fibers, and provides a flat base for the surface dense film formed by large particle size components, thereby realizing excellent WVTR (≤0.45 g / (m²·24h)) and OTR (≤0.35 cm³ / (m²·24h·0.1 MPa)) without relying on a high-thickness coating, and having long-term oil penetration resistance, and not containing any fluorides.

[0034] Stable interfacial bonding and resistance to boiling: Deep physical anchoring (infiltration depth of 20 μm to 300 μm) achieved by vacuum assistance and particle size matching forms a strong mechanical interlocking effect between the coating and the pulp substrate, effectively solving the problem of interfacial delamination or bursting of traditional coatings under high temperature and humidity and high pressure boiling conditions, and ensuring the structural integrity of the capsule under a boiling pressure of 1.9 MPa.

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

[0036] Complete biodegradability and environmental safety: the PHA material and pulp substrate used in the application are both derived from biological sources and are completely biodegradable, with a degradation rate of more than 96% in controlled composting conditions within 45 days, and no total organic fluorine detected, providing an ideal alternative for the coffee capsule industry with high performance, food safety and environmental friendly attributes. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a partial cross-sectional structure schematic diagram of the paper-based molded coffee capsule described in the application.

[0038] In the figure, 1 is the capsule body; 2 is coffee powder; 3 is a sealing member; 4 is a continuous dense layer; and 5 is a penetration anchoring layer. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be further described in detail below in combination with specific examples. It should be understood that the specific examples described herein are only used to explain the application and not to limit the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the protection scope of the application. Unless otherwise specified, the raw materials used in the examples are commercially available industrial products or can be prepared by conventional methods. Unless otherwise specified, the performance test methods are carried out according to the standards described in the summary of the invention.

[0040] Figure 1 is a cross-sectional structure schematic diagram of the naturally compostable paper-based molded coffee capsule proposed by the application and a partial enlarged view of the flange area thereof. As shown in the figure, the capsule is composed of a capsule body 1 formed by molded paper pulp, which contains coffee powder 2 in the inside, and a sealing member 3 connected by heat sealing at the top to achieve sealing. The enlarged view on the right clearly shows the microstructure of the PHA barrier heat seal composite layer at the sealing surface of the flange: the outermost layer is a smooth, continuous film-forming continuous dense layer 4, and below it is a sawtooth-shaped penetration anchoring layer 5 forming a mechanical interlocking structure into the pores of the pulp fibers.

[0041] Main reagents and raw materials:

[0042] Table 1 Name, product model / specification and manufacturer of main reagents and raw materials:

[0043]

[0044] Main analysis instrument:

[0045] Table 2 Name, model and manufacturer of main analysis instrument:

[0046]

[0047] Main test standard:

[0048] Relative humidity (RH): The test conditions involving RH in this specification refer to relative humidity.

[0049] Vacuum gauge pressure: The "vacuum gauge pressure" referred to in this specification refers to the absolute value (unit: kPa) of the negative pressure differential of the relative atmospheric pressure; for example, a vacuum gauge pressure of 20 kPa indicates that the test cavity pressure is (atmospheric pressure - 20 kPa).

[0050] Water vapor transmission rate (WVTR): Referring to GB / T 1037-2021 "Determination of water vapor transmission properties of plastic films and sheets - Cup method for weight gain and loss", the test is carried out by cup method for weight gain, and the test conditions are 38℃, 90% RH. The test area is 33cm² (corresponding to the effective exposed area of the used moisture permeable cup). The moisture permeable cup is filled with anhydrous calcium chloride as a drying agent and is sealed according to the standard requirements; when clamping, use the sealing ring and pressure cap matched with the moisture permeable cup, and seal the edge of the sample sheet to avoid bypassing the moisture. Sample preparation method: cut the capsule side wall along the generatrix direction and unfold it to obtain a flat sample sheet with a size not less than the effective area of the clamp; the bottom wall sample is directly cut. Before testing, adjust the humidity to 23℃, 50% RH for 24h.

[0051] Oxygen transmission rate (OTR): Referring to GB / T 19789-2021 "Packaging materials - Plastic films and sheets - Determination of oxygen transmission - Coulometric method", the test conditions are 23℃, 0% RH. The sample preparation and edge sealing method is the same as the WVTR test; before clamping, dry and adjust the humidity of the sample to meet the 0% RH test requirement.

[0052] Sealing and peeling strength: Referring to GB / T 2790-1995 "Adhesives - Test methods for 180° peel strength - Flexible materials to rigid materials", the 180° peeling test is carried out on the sealing member and the flange sealing part; the sample width is 15mm, and the tensile speed is 300mm / min.

[0053] Biodegradability: Referring to GB / T 19277.1-2025 "Determination of ultimate aerobic biodegradability of materials under controlled composting conditions - Method for determination of released carbon dioxide - Part 1: General method", the test period is 45d.

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

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

[0056] Boil-off resistance test: Refer to IEC 60335-2-15:2024.

[0057] Specific test methods are as follows:

[0058] Test equipment and working condition settings:

[0059] A single-serve capsule coffee machine with a rated pump pressure of 1.9 MPa was selected as the brewing equipment; the coffee machine was preheated for ≥5 min before testing and continuously run for 3 times under no load to stabilize the water temperature; the brewing water temperature was controlled at 83-86°C.

[0060] Sample preparation and loading:

[0061] Each paper-based molded coffee capsule was loaded with 5.0±0.1 g of ground coffee powder; the sealing was completed using a heat sealing tester (Model 12-12 AS / 1): heat sealing pressure 0.30 MPa, pressure holding time 0.80 s, cooling time 2.0 s; the heat sealing temperature was set at the temperature point at which the peel strength was the largest and the sealing appearance was qualified (no obvious deformation of the flange, no scorching or wrinkling of the sealing film) within the heat sealing window obtained by the sample in the “Heat sealing window and unsealing temperature test” of Example 6. Before testing, it was confirmed that the capsule had a complete appearance and no visible defects.

[0062] Brewing test process:

[0063] The capsule was placed in the coffee machine and the Espresso mode (40 mL water volume) was selected for a complete brewing cycle; during the brewing process, the capsule flange, side wall and bottom wall were observed in real time for liquid leakage, structural rupture or coating delamination.

[0064] Failure criteria:

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

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

[0067] Delamination: After brewing, the capsule was cut open and a continuous interfacial peeling area between the PHA barrier heat sealing composite layer and the paper pulp substrate was observed.

[0068] Statistical method:

[0069] Each test group takes N=50 capsules for brewing test; the leakage rate, bursting rate and delamination rate are respectively calculated as the percentage of the number of samples with corresponding failure phenomenon in the total number of tests.

[0070] Natural composting criterion: tested under controlled composting conditions according to GB / T 19277.1-2025, with a 45d biodegradation rate ≥90% to determine natural composting.

[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 "Paints and varnishes - Wetness - Part 2: Determination of surface free energy of solid surfaces by measurement of contact angle".

[0073] Oil resistance performance (oil penetration time): take a sample (20mm×20mm) of the inner surface of the capsule side wall, test under the condition of 23℃, 50% RH; use a pipette to drop 10μL (±1μL) of palm kernel oil at the center of the sample, keep the sample horizontal; record the time from the completion of dropping 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 for 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) "Food chain microbiology - Determination of water activity".

[0076] Total organic fluorine (TOF): oxygen bomb combustion according to EN 14582:2016; the combustion product absorption liquid is used to determine the fluoride ion content by fluoride ion selective electrode method and convert TOF. To exclude the interference of inorganic fluorine, the sample is extracted with ultrapure water before combustion and the extraction liquid is discarded. The reproducible experimental conditions are as follows: the sample is weighed 0.50g on a dry basis; the oxygen bomb combustion is charged with oxygen at a pressure of 2.8MPa; the absorption liquid is selected as 0.01mol / L sodium hydroxide solution 15mL; after combustion, the inner wall of the combustion cup and the bomb is washed with ultrapure water and combined with the absorption liquid, and the volume is made to 100mL; before measurement, 5mL of TISAB is added to the test liquid to stabilize the ion strength and eliminate complex interference; the calibration curve is established with 0.1mg / L, 0.5mg / L, 1mg / L, 5mg / L, 10mg / L fluoride ion standard solution; TOF is calculated after deducting the background of the blank test; the conversion of TOF is calculated according to the following formula:

[0077] TOF(mg / kg) = ((Csample-Cblank) x V x 1000) / m.

[0078] Wherein, Csample is the mass concentration of fluoride ion in the sample to be tested (mg / L), Cblank is the mass concentration of fluoride ion in the blank to be tested (mg / L), V is the constant volume (L), and m is the dry basis mass of the sample (kg). The detection limit of the method is ≤5 mg / kg; the determination standard is not detected.

[0079] Moisture content determination method: halogen moisture meter is used to determine the moisture content of the capsule body. For the moisture content of the capsule body, the mixed sample is cut from the side wall and bottom wall area, the initial mass m0 is recorded, and the sample is dried at 105°C constant temperature mode until the mass change rate is ≤0.01 g / 30 s, the mass after drying m1 is recorded, and the moisture content is calculated as (m0-m1) / m0x100%. For the moisture content of the coated surface after the first coating, the coated area of the capsule body after the first coating is cut into a sample, and the same determination method is used to obtain the moisture content.

[0080] Dry coating amount (side wall / bottom wall): using the control weighing method, uncoated capsule body samples and film-formed capsule body samples are prepared respectively; after drying at 105°C to constant weight, samples with the same known area A (m2) are cut from the side wall and the bottom wall, and the mass of the uncoated sample m 空白 and the mass of the film-formed sample m 涂布 are recorded, and the dry coating amount (g / m2) is calculated as (m 涂布 -m 空白 ) / A.

[0081] Dry coating amount (flange sealing surface): uncoated and film-formed flange sealing surface samples are prepared respectively, and the samples are taken after drying at 105°C to constant weight. The sampling method is: cut along the circumference of the flange and flatten the flange ring into a plane; use a cutting knife to cut a rectangular sample with a size of 20 mm x 10 mm, the unfolded area Af = 2.0 x 10 -4 m2; at least 5 samples are taken for each group and the average is taken. The mass of the uncoated sample m 空白,f and the mass of the film-formed sample m 涂布,f are recorded, and the dry coating amount (g / m2) of the flange sealing surface is calculated as (m 涂布,f -m 空白,f ) / A f .

[0082] Solid content of aqueous PHA dispersion: take the sample mass m4 of the dispersion, dry it at 105°C to constant weight to obtain the dry solid mass m5, and calculate the solid content as m5 / m4x100%.

[0083] Volume average particle size of aqueous PHA dispersion: tested by particle size analyzer at 25°C in dynamic light scattering mode, test angle 173°; dispersion diluted to 0.10wt% solid content with ultrapure water, transferred to a disposable cuvette and allowed to stand for 2min to equilibrate; each sample repeated 3 times. The volume average particle size is calculated by the Mie conversion model of the instrument software to convert the intensity distribution to the volume distribution, with the conversion parameters set as follows: refractive index of dispersion medium (water) 1.330, viscosity 0.8872 mPa·s (25°C); PHA particle refractive index 1.50, absorption coefficient 0.01. The volume average particle size calculated from the volume distribution is taken as the arithmetic mean of the 3 tests.

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

[0085] Heat-seal ring width: the capsule body after film formation was taken, a digital caliper was used to measure the width of the local thickened heat-seal ring in the radial direction along the sealing surface of the flange, 8 orientation points were measured for each capsule and the arithmetic mean was taken as the heat-seal ring width of the capsule.

[0086] PHA proportion in dry film: the dry film of the second coating system used to form the continuous dense layer was taken as the statistical object, the dry mass of each component was calculated according to the formulation and solid content conversion; the PHA proportion was calculated as the ratio of the dry mass of PHA mPHA to the total mass of dry film mdry mPHA / mdry x 100%, where mdry included PHA, bio-based plasticizing and toughening components, and barrier-enhancing fillers.

[0087] General preparation process of sealing member:

[0088] Step 1. Substrate resin preparation. Selecting an extrudable film grade PLA resin as one of the substrate resins, selecting an extrudable film grade PBS resin as the second substrate resin, and selecting a PHA resin as the heat seal layer resin to obtain a substrate resin system.

[0089] Step 2. Substrate layer preparation. Dry blending the PLA resin and PBS resin in a mass ratio of 80:20 and melt blending and granulating by a twin-screw extruder; then using a casting method to prepare a substrate film layer, so that the thickness of the substrate film layer is 25 μm to obtain a substrate film layer.

[0090] Step 3. PHA heat seal layer coating. Using a coating process, the PHA aqueous emulsion is coated on one side of the substrate film layer obtained in step 2, and after drying to form a film, the thickness of the PHA heat seal layer is 5 μm; after coating and drying, rapid shaping is performed by a cooling roller to obtain a composite film with a PHA heat seal layer.

[0091] Step 4. Rolling and humidity conditioning. The composite film obtained in step 3 is rolled and placed in a 23°C, 50% relative humidity environment for 24 hours to eliminate internal stress, obtaining a humidity-conditioned sealing component film.

[0092] Step 5. Consistency confirmation. The humidity-conditioned sealing component film is detected by a thickness gauge or cross-sectional microscopic measurement method to confirm that the total thickness is 30 μm ± 3 μm, and that the PHA heat seal layer is located on the side facing the flange, obtaining a sealing component that meets the consistency requirements.

[0093] In the following examples and comparative examples, unless otherwise specified, the sealing component is a composite film prepared by steps 1-5 described above, and a sealing piece matching the size of the capsule flange is obtained by punching, and the PHA heat seal layer is ensured to face the sealing surface of the flange.

[0094] General preparation process of PLA-coated paper:

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

[0096] Step 2. PLA coating resin preparation. Selecting an extrudable coating grade PLA resin as the coating resin to obtain a PLA coating resin.

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

[0098] Step 4. Forming. The PLA-laminated paper obtained in step 3 is formed into a capsule body by hot-pressing forming, wherein the hot-pressing forming temperature is 150°C, the pressure is 1.0 MPa, and the time is 10 s; the formed capsule body is cooled and shaped in a cooling mold to obtain a PLA-laminated paper capsule body.

[0099] Sealing wax preparation method:

[0100] Step 1. Raw material mixing. Paraffin wax with a melting point of 58-60°C and beeswax are mixed in a mass ratio of 1:1 to obtain a wax raw material mixture.

[0101] Step 2. Heating, melting, and degassing. The wax raw material mixture obtained in step 1 is placed in a stainless steel container and heated to 85°C under water bath conditions to completely melt and uniformly stir, and then it is left to stand and degas to obtain a molten and degassed sealing wax.

[0102] Step 3. Forming or use. The molten and degassed sealing wax obtained in step 2 is kept in a molten state at 80°C and used for smearing on the edge of a moisture-permeable cup; or it is poured into a rod shape and cooled and solidified for standby use to obtain a sealing wax for WVTR testing.

[0103] Example:

[0104] Example 1:

[0105] The paper-based molded coffee capsule of this example is prepared according to the following steps 1-7.

[0106] Step 1. Preparing pulp and wet molding to obtain a pulp wet blank. Pine pulp board and broadleaf pulp board are soaked and then disintegrated in a mass ratio of 3:7 to prepare a pulp slurry; the mass concentration of the pulp slurry is fixed at 1.0 wt%; wet molding is performed on a vacuum suction filter mold, the suction filter molding time is fixed at 20 s, and the mold suction vacuum gauge pressure is fixed at 60 kPa during suction filter molding to obtain a pulp wet blank.

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

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

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

[0110] The nozzle to capsule inner surface distance is fixed at 120 mm; the gun speed is fixed at 200 mm / s; the track overlap rate is fixed at 50%; the pre-drying condition after each thin coating is fixed at 60°C hot air for 6 min. The first water-based PHA emulsion is a PHBV water-based emulsion, the solid content of which is adjusted to 15 wt%, and the specification of PHA particles with a volume average particle size of 250 nm is selected.

[0111] Vacuum assisted infiltration is applied to the capsule body during coating: the outer surface of the capsule body is placed on a vacuum suction jig with a sealing ring, so that the outer surface of the capsule forms a seal with the jig; the jig is connected to a vacuum pump and a vacuum gauge and is evacuated to a vacuum gauge pressure of 20 kPa; the vacuum gauge pressure is continuously maintained during the spraying of the first water-based PHA emulsion, and the vacuum is released after 60 s of pre-drying after the first coating is completed. The water content of the coated surface after pre-drying is controlled to be 8.0 wt%, and the first coated capsule body is obtained.

[0112] Step 5. Second coating system spraying + drying to obtain the second coated capsule body. The second water-based PHA emulsion is coated by using the same air spray equipment and spraying parameters as in Step 4. The second water-based PHA emulsion is a PHBV water-based emulsion, the solid content of which is adjusted to 45 wt%, and the specification of PHA particles with a volume average particle size of 600 nm is selected. The flange area is locally thickened by increasing the gun dwell time and the number of gun circles on the corresponding ring track of the sealing surface of the flange, so that the sealing surface of the flange forms a locally thickened heat sealing ring which is continuous along the circumference of the flange.

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

[0114] After the second coating, the capsule body is placed in a 60°C hot air circulating oven for drying for 18 min, and then placed at 23°C and 50% relative humidity for 10 min to eliminate the surface temperature difference; the water content before heat fusion or heat pressing to form a film is measured by the "Water Content Determination Method" to be 2.5 wt%, and the second coated capsule body is obtained.

[0115] Step 6. Hot-pressing to form a film to obtain the film-formed capsule body. The second coated capsule body is subjected to hot-pressing to form a film, the hot-pressing temperature is 150°C, the pressure is 1.0 MPa, and the time is 10 s, so that the PHA penetrates into the anchor layer and the continuous dense layer and forms a heat-sealing interface on the sealing surface of the flange, thereby obtaining the film-formed capsule body.

[0116] The PHA accounts for 100 wt% in the dry film of the PHA barrier heat-sealing composite layer.

[0117] Step 7. Filling and sealing to obtain the sealed paper-based molded coffee capsule. The film-formed capsule body is filled with coffee powder, and the sealing member is sealed to the sealing surface of the flange, and the sealing is completed by heat sealing, thereby obtaining 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 film-formed capsule body is a dry film structure, and no other non-volatile film-forming components are introduced in the dry film structure except for the PHA, and the mass fraction of the PHA is 100 wt%.

[0119] Example 2:

[0120] The preparation process is the same as that in Example 1, except that the following parameters are different: 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 table pressure for vacuum-assisted penetration 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: the dry coating amount on the sealing surface of the flange is 120 g / m²; the dry coating amount on the inner surface of the side wall is 20 g / m²; the dry coating amount on the inner surface of the bottom wall is 20 g / m²; and the width of the heat-sealing ring is 3.5 mm; in Step 6, the hot-pressing to form a film is performed at a temperature of 165°C, a pressure of 1.0 MPa, and a time of 5 s. The remaining parameters are unchanged, thereby obtaining the sealed paper-based molded coffee capsule.

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

[0122] Example 3:

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

[0124] In the dry film structure of the PHA barrier heat sealing composite layer obtained in this example, no other non-volatile film forming components are introduced except PHA, and the mass fraction of PHA is 100wt%.

[0125] Example 4:

[0126] The preparation process is the same as that of Example 1, except that the following parameters are different:

[0127] A primer treatment is added before step 4: a chitosan primer layer is arranged on the inner surface of the capsule with a dry coating amount of 5g / m²; the primer solution is prepared as follows: chitosan is added to a 1.0wt% ice acetic acid aqueous solution to prepare a 1.5wt% chitosan solution, which is magnetically stirred at 25℃ for 4h until completely dissolved, and then filtered (100 mesh filter) to obtain the primer solution; the primer solution is coated by air spraying and dried at 60℃ with hot air for 15min to obtain the dry coating amount; the first aqueous PHA emulsion in step 4 is a PHBV aqueous emulsion with a solid content of 15wt% and a volume average particle size of 250nm; the vacuum gauge pressure is 20kPa;

[0128] The second aqueous PHA emulsion in Step 5 is a PHBV aqueous emulsion with a solid content of 45wt% and a volume average particle size of 600nm; 3wt% of ATBC plasticizer and 8wt% of sodium-based montmorillonite barrier-enhancing filler are added to the dry film of the second coating system, and the balance is the PHA film-forming component; the sodium-based montmorillonite is first prepared into a water dispersion with a mass fraction of 3wt% with ultrapure water, and then dispersed at 8000rpm for 10min under a high-speed disperser; then homogenized at 80MPa for 3 times under a high-pressure homogenizer; the obtained montmorillonite water dispersion is added to the second aqueous PHA emulsion according to the target dry film ratio, and mechanically stirred at 500rpm for 10min to obtain a uniform mixed coating liquid; the PHA proportion in the dry film after film formation of the second coating system is 89wt%. The dry coating amount is controlled as follows: the total dry coating amount of the inner surface of the side wall is 25g / m², the total dry coating amount of the inner surface of the bottom wall is 25g / m², the dry coating amount of the sealing surface of the flange is 90g / m², and the width of the heat-sealing ring is 3.0mm;

[0129] The hot-pressing film formation conditions in Step 6 are as follows: temperature 150℃, pressure 1.0MPa, and time 10s. The remaining parameters remain unchanged, and a paper-based molded coffee capsule with a sealed mouth is obtained.

[0130] Example 5:

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

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

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

[0134] The hot-pressing film formation conditions in Step 6 are as follows: temperature 160℃, pressure 1.0MPa, and time 10s. The remaining parameters remain unchanged, and a paper-based molded coffee capsule with a sealed mouth is obtained.

[0135] In the dry-state film formation structure of the PHA barrier heat-sealing composite layer obtained in this example, no other non-volatile film-forming components are introduced except for PHA, and the mass proportion of PHA is 100wt%.

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

[0137] The first aqueous PHA emulsion in Step 4 is a PHBV aqueous emulsion with a solid content of 10wt%, and a volume average particle size of 200nm; the vacuum assisted infiltration is at a vacuum gauge pressure of 5kPa;

[0138] The second aqueous PHA emulsion in Step 5 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 ring width of the heat sealing ring is 1.5mm;

[0139] The heat pressing film forming condition in Step 6 is: temperature 140℃, pressure 1.0MPa, and time 15s. The remaining parameters are unchanged, and a sealed paper-based molded coffee capsule is obtained.

[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 are introduced except PHA, and the mass proportion of PHA is 100wt%.

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

[0142] The first aqueous PHA emulsion in Step 4 is a PHBV aqueous emulsion with a solid content of 10wt%, and a volume average particle size of 220nm; the vacuum assisted infiltration is at a vacuum gauge pressure of 80kPa;

[0143] The second aqueous PHA emulsion in Step 5 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 ring width of the heat sealing ring is 4.5mm;

[0144] The heat pressing film forming condition in Step 6 is: temperature 160℃, pressure 1.0MPa, and time 10s. The remaining parameters are unchanged, and a sealed paper-based molded coffee capsule is obtained.

[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 are introduced except PHA, and the mass proportion of PHA is 100wt%.

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

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

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

[0149] In the dry film-forming structure of the PHA barrier heat-seal composite layer obtained in this example, no other non-volatile film-forming components are introduced in addition to PHA, and the mass proportion of PHA is 100wt%.

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

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

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

[0153] In the dry film-forming structure of the PHA barrier heat-seal composite layer obtained in this example, no other non-volatile film-forming components are introduced in addition to PHA, and the mass proportion of PHA is 100wt%.

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

[0155] The first aqueous PHA emulsion in Step 4 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] The second aqueous PHA emulsion in Step 5 is a 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 side wall is 8g / m², the dry coating amount on the sealing surface of the flange is 96g / m², and the heat-seal ring width is 3.0mm; the dry coating amount on the inner surface of the bottom wall is the same as that on the side wall.

[0157] The heat pressing film-forming conditions in Step 6 are as follows: temperature 145℃, pressure 1.0MPa, and time 10s. The rest of the parameters remain unchanged, and the paper-based molded coffee capsules after sealing are obtained.

[0158] In the dry film-forming structure of the PHA barrier heat-seal composite layer obtained in this example, no other non-volatile film-forming components are introduced in addition to PHA, and the mass proportion of PHA is 100wt%.

[0159] Example 11 (verify high pressure film forming process with PHB emulsion): preparation procedure same as Example 1, only the following parameters are different:

[0160] The first aqueous PHA emulsion in Step 4 is a PHB aqueous emulsion with solid content of 15wt%, volume average particle size of 250nm; vacuum gauge pressure of 20kPa;

[0161] The second aqueous PHA emulsion in Step 5 is a PHB aqueous emulsion with solid content of 45wt%, volume average particle size of 600nm;

[0162] The hot-press film forming conditions in Step 6 are: temperature 165℃, pressure 3.0MPa, time 10s; the rest of the coating amount is the same as Example 1. The sealed paper-based molded coffee capsule is obtained.

[0163] In the dry film forming structure of the PHA barrier heat sealing composite layer obtained in this example, no other non-volatile film forming components are introduced except PHA, and the mass fraction of PHA is 100wt%.

[0164] Comparative Example:

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

[0166] PLA laminated paper is used as the pre-coated laminated layer material, and the capsule body is prepared by hot-press forming, which does not have the in-situ film forming anchoring structure of "penetrating into the anchoring layer and continuous dense layer". The PLA laminated paper and the capsule body are prepared according to the following steps:

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

[0168] Step 2. PLA lamination: melt PLA is extruded on the extrusion lamination line and pressed onto the surface of the base paper on the cooling roller, and the PLA lamination layer has a basis weight of 30g / m²;

[0169] Step 3. Forming: the laminated paper is formed into a capsule body by hot-press forming, the hot-press temperature is 150℃, the pressure is 1.0MPa, and the time is 10s; after forming, it is cooled and shaped in a cooling mold to room temperature;

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

[0171] Comparative Example 2 (only the second layer is coated with large particle size, without the first layer penetrating into the anchoring layer): the preparation procedure is the same as Example 1, only the following parameters are different:

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

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

[0174] Step 6: heat-pressing film-forming conditions: temperature 150℃, pressure 1.0MPa, time 10s. The comparative example 2 capsule is obtained.

[0175] Comparative example 3 (no flange heat-pressing densification): preparation process same as example 1, only the following parameters are different: no flange heat-pressing densification treatment in step 3; the rest of the first / second dispersion parameters, vacuum gauge pressure, coating amount and film-forming conditions are the same as example 1. The comparative example 3 capsule is obtained.

[0176] Comparative example 4 (only drying after coating, no heat fusion / heat-pressing film-forming):

[0177] Preparation process same as example 1, only the following parameters are different: coating system and coating amount in step 4 and step 5 are the same as example 1; no heat fusion or heat-pressing film-forming in step 6, only the second coated capsule body obtained in step 5 is placed in a 60℃ hot air circulation oven for drying for 30min, so that the water content before heat fusion / heat-pressing film-forming is controlled to be 2.5wt% (consistent with step 5 of example 1), and then placed at 23℃, 50% relative humidity for 24h; the coating layer is kept in a particle accumulation state, and no particle heat fusion is performed to form a continuous dense layer. The comparative example 4 capsule is obtained.

[0178] Comparative example 5 (lower limit comparison: low coating amount + reverse solid content / particle size matching): preparation process same as example 1, only the following parameters are different:

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

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

[0181] Step 6: heat-pressing film-forming conditions: temperature 140℃, pressure 1.0MPa, time 10s. The comparative example 5 capsule is obtained.

[0182] Comparative example 6 (higher than the upper limit comparison: too high coating amount): preparation process same as example 1, only the following parameters are different:

[0183] 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 90 kPa;

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

[0185] The heat pressing film forming condition in step 6 is: temperature 175 ℃, pressure 3.5 MPa, and time 150 s. The capsule of Comparative Example 6 is obtained.

[0186] Comparative Example 7 (no particle size gradient: the particle sizes of the first layer and the second layer are the same): the preparation process is the same as that of Example 1, except that the following parameters are different:

[0187] The first aqueous PHA emulsion in step 4 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] The second aqueous PHA emulsion in step 5 is 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 condition are the same as those of Example 1. The capsule of Comparative Example 7 is obtained.

[0189] Comparative Example 8 (low solid content ratio: the solid content of the second layer is too low): the preparation process is the same as that of Example 1, except that the following parameters are different:

[0190] The first aqueous PHA emulsion in step 4 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] The second aqueous PHA emulsion in step 5 is 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 condition are the same as those of Example 1. The capsule of Comparative Example 8 is obtained.

[0192] Application Example:

[0193] Application Example 1: Barrier property and waterproof property test.

[0194] This application example aims to verify the influence of different coating structures on the resistance of water vapor, oxygen and liquid water. The capsules prepared in Examples 1-11 and Comparative Examples 1-8 are selected for testing.

[0195] Test notes: WVTR test was conducted by cupping gravimetric method strictly according to GB / T 1037-2021. First, the capsule side wall was cut along the generatrix and flattened, and a circular sample with an effective area of 33 cm2was cut, ensuring that the sample surface was free of creases or pinholes; the bottom wall sample was also cut. Before testing, all samples were conditioned at 23°C and 50% RH for 24 h in a constant temperature and humidity environment. The moisture permeable cup was filled with anhydrous calcium chloride as a moisture absorbent and was filled and sealed according to the standard requirements; the sample was sealed in the moisture permeable cup opening and the edge was sealed with sealing wax to prevent edge leakage. The test environment was 38°C and 90% RH, and the weight was measured every 12 h until the WVTR change rate calculated from 3 consecutive measurements was <5%, and the data in the stable stage was used to calculate the WVTR. The side wall and the bottom wall were tested respectively; the larger value of the side wall and the bottom wall test results in Table 3 was taken as the WVTR of the sample.

[0196] OTR test was conducted by Coulomb meter detection method according to GB / T 19789-2021. Sample preparation was the same as WVTR; high vacuum silicone grease was used to seal the sealing surface of the clamp and the edge of the sample to avoid bypass leakage; the test cavity was vacuumed to below 10 Pa; the test gas was 99.999% high-purity oxygen; the carrier gas was hydrogen-containing nitrogen (volume fraction: 95% N2 / 5% H2); the test temperature was 23°C and the relative humidity was 0%. The side wall and the bottom wall were tested respectively; the larger value of the side wall and the bottom wall test results in Table 3 was taken as the OTR of the sample.

[0197] 60s Cobb value test was conducted according to GB / T 1540-2002. The inner surface of the side wall and the inner surface of the bottom wall were tested respectively. The test water was 23°C distilled water, and a metal cylinder was tightly pressed on the sample, and 100 mL of water was injected. At the end of 60 s, the water was poured off, the sample was removed, and the excess water on the surface was absorbed with a standard water absorption paper with a 10 kg roller, and immediately weighed. Each group of samples was tested in parallel for 5 times to take the average value; the larger value of the average value of the side wall and the bottom wall in Table 3 was taken as the Cobb value of the 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 brew resistance test was performed using a capsule coffee machine with a nominal pump pressure of 19 bar. The machine was turned on and preheated for 5 minutes and run empty for 3 times to stabilize the water temperature to 85±1℃. A capsule filled with 5.0 g of coffee powder was placed into the machine and the Espresso setting (40 mL) was selected for extraction. During the brewing process, the flange and sidewall were observed for any liquid leakage (defined as a breach) and the capsule was inspected for any burst or coating delamination. After the test, the capsule was opened and the internal coating integrity was checked. 50 capsules were tested for each group.

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

[0206]

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

[0208] Analysis: The experimental data shows that the local thickening of the flange area and the densification treatment are crucial to the sealing integrity. The peel strength of both Example 7 and Example 10 exceeds 13.0 N / 15 mm, and the brew leakage rate is 0. In particular, Example 10, despite the lower coating amount on the sidewall, still guarantees excellent sealing performance by building a thick heat seal ring of 96 g / m2 at the flange, which proves that the local reinforcement design of the flange area is effective. In contrast, Comparative Example 3, which did not undergo flange hot-press densification, has a large surface roughness, resulting in a sealing strength of only 4.0 N / 15 mm and a leakage rate as high as 30%. Comparative Example 7 has sufficient coating amount, but lacks a particle size gradient, resulting in insufficient anchoring force between the coating and the paper base (burst rate 8%), which is prone to interfacial peeling under high pressure shear during brewing. Comparative Example 8 has poor film formation quality, resulting in an extremely unstable heat seal interface with a standard deviation of 1.4. Example 8 utilizes a first dispersion of 200 nm to achieve deeper penetration under vacuum assistance, forming a strong mechanical interlock, and there is no delamination even under high pressure brewing, which proves the contribution of smaller particle size dispersion to the stability of the interface.

[0209] Application Example 3: Biodegradation performance test.

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

[0211] Experimental instruction: Biodegradation test was conducted under controlled composting conditions according to GB / T 19277.1-2025 standard. The compost inoculum was taken from an aerobic composting plant, and impurities with particle size >10 mm were removed by screening; the inoculum was adjusted to the following fixed conditions: carbon-nitrogen ratio 25:1 (dry basis), moisture content 52% (wet basis), pH 7.5. The test was carried out using a reaction vessel equipped with a respirometer, and the temperature of the reaction vessel was controlled at 58°C (allowing a fluctuation of ±2°C according to the instrument temperature control setting). Each group of capsule samples was crushed into 20mm x 20mm fragments, and mixed with the compost inoculum at a dry weight ratio of 1:6 before being loaded into the reaction kettle. The reaction kettle was connected to the air supply system, and CO2-free humidified air was introduced (the air was first passed through an alkali lime / NaOH absorption column to remove CO2, and then humidified in a humidification bottle); the air flow was set at 50mL / min (for each reaction kettle). The generated CO2 was recorded and accumulated online using the infrared CO2 monitoring module equipped with the respirometer, with microcrystalline cellulose powder as the positive control, and the blank group containing only the compost inoculum as the background correction. The test period was 45 days, and the biodegradation percentage relative to the theoretical CO2 production was calculated at 15, 30, and 45 days.

[0212] Table 5 Biodegradation performance test results:

[0213]

[0214] Analysis: The test results show that all the examples of the present application have a biodegradation rate of more than 96.0% under industrial composting conditions for 45 days, far exceeding the 90% threshold required by the relevant standard, proving the excellent end-of-life disposal performance of the paper-based capsule. Example 6 has the fastest degradation rate due to the thin coating (8g / m²), with a 45-day degradation rate of 99.0%. Example 11 uses a PHB resin with high crystallinity, although the early-stage (15-day) degradation rate (42.0%) is slightly lower than that of PHBV or PHBH-based samples, it still reaches a high degradation rate of 96.2% at 45 days, which is due to the paper pulp substrate providing abundant microbial attachment sites, promoting the disintegration of the polymer. In contrast, Comparative Example 1, which uses a pre-made PLA film paper, has a 45-day degradation rate of only 65.0% due to the thick PLA film and the long start-up period of industrial composting, which is significantly lagging behind. Comparative Examples 5 and 8 have very high degradation rates, but this is at the expense of barrier properties and sealing performance (too thin or defective coating), which is not of practical value.

[0215] Application Example 4: Surface wettability and oil-proof performance test.

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

[0217] Experimental Note: Surface wettability was measured by water droplet contact angle tester. The inner surface of the capsule sidewall sample was fixed on the sample stage, ensuring the test surface was horizontal. 2.0 μL of ultrapure water was added using a high-precision microsyringe. After the droplet contacted the surface, a high-speed camera recorded the droplet morphology at a speed of 100 frames per second. The image at the 10thsecond after the droplet contacted the surface was selected, and the static contact angle was calculated by fitting the Young-Laplace equation. Five different positions of the sample were selected for testing, and the average value was taken.

[0218] Oil resistance was tested according to the relevant test method for oil-proof paper. The sample was placed in an environment of 23 °C and 50% RH. 10 μL of palm kernel oil (previously dyed with 0.1% Sudan red for easy observation) was added to the center of the sample using a pipette. A piece of quantitative filter paper was placed under the sample. The time from the start of oil droplet addition to the first appearance of red oil spots on the filter paper was recorded, which was the oil penetration time. Observation continued until 360 minutes, and if no penetration occurred, it was recorded as > 360 minutes. Five parallel samples were tested for each group.

[0219] Table 6: Surface wettability and oil resistance test results

[0220]

[0221] Analysis: Examples 7, 4, and 8 exhibited the best oil resistance and surface hydrophobicity, with contact angles exceeding 100° and oil penetration times exceeding 300 minutes. This was attributed to their dense surface structure: the nanofiller in Example 4 increased the micro-roughness of the surface and closed the pores; Example 8 used a 200 nm first dispersion to fill and anchor the surface layer of the paper fibers, providing a smoother substrate for the upper dense film and reducing micro-defects. In contrast, Comparative Example 2 lacked a small-particle-size infiltration layer, and there were many uncoated fiber pores on the surface, resulting in oil penetration within 60 minutes and a contact angle of only 78°. Although Comparative Example 7 had two layers of coating, it lacked a particle size gradient, and the large particles could not effectively fill the micro-pores, resulting in an oil resistance time (120 min) much lower than that of the examples with a gradient structure. Comparative Example 8 had micro-cracks generated during film formation, allowing oil molecules to quickly penetrate, with an oil resistance time of only 90 minutes. This shows that simply increasing the coating amount is not enough to ensure oil resistance; a reasonable particle size distribution and film quality are the key.

[0222] Application Example 5: Test of coffee powder moisture content, water activity, and headspace gas oxygen content retention under accelerated storage.

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

[0224] Experimental instruction: First, fill each group of capsules with 5.0 ± 0.1 g of fresh ground coffee powder, and seal in a nitrogen protection box, control the initial oxygen content in the capsule after sealing to be less than 1.0%. Place the sealed capsules in a constant temperature and humidity test chamber, set the conditions to be 38 ± 1 ℃, 90 ± 2% RH (simulate the hot and humid environment in the tropics), and store for 30 days. The capsules are placed on the shelf in a single layer to avoid mutual contact.

[0225] After 30 days, first use the headspace gas oxygen content analyzer to test the residual oxygen content in the headspace: attach a butyl rubber self-sealing gasket (diameter 10 mm, thickness 2 mm) to the center of the sealing film of each capsule, and ensure that the gasket is in contact with the sealing film without edge lifting; insert the analyzer puncture probe into the capsule through the gasket and extract the gas to determine the residual oxygen content in the headspace. Then open the capsule and take out the coffee powder. Use a halogen moisture meter (HE53) to measure the water content of the coffee powder at 105°C constant temperature mode: take about 2.0 g of coffee powder sample from each capsule, record the initial mass m0, dry to a mass change rate ≤0.01 g / 30 s, record the mass after drying m1, and calculate the water content as (m0-m1) / m0x100%. At the same time, use a water activity meter to measure the water activity (aw) of the coffee powder, and the test temperature is 25°C. Take 5 capsules from each group for testing.

[0226] Table 7: Accelerated storage retention test results:

[0227]

[0228] Analysis: The accelerated storage test results are highly consistent with the WVTR / OTR test results. After 30 days of high temperature and high humidity challenge, the water content of the coffee powder in Example 7, Example 4 and Example 8 is maintained below 2.3wt%, the water activity is below 0.22, and the headspace oxygen content is below 1.2%, which indicates that the packaging has excellent air tightness and moisture resistance, and can effectively delay coffee oxidation and moisture. Although Example 11 is brittle, it uses a high-pressure film-forming process of 3.0 MPa, and the coating is extremely dense, with excellent oxygen barrier effect (residual oxygen 1.3%). In contrast, Comparative Example 2, Comparative Example 5 and Comparative Example 8, due to incomplete or defective coating, a large amount of external moisture and oxygen enters, resulting in a sharp increase in the water content of the coffee powder to 4.2-5.2wt%, and the water activity exceeds 0.35, which not only seriously damages the flavor of the coffee, but also poses a risk of microbial growth. Comparative Example 7 lacks effective infiltration anchoring, and the coating may microscopically peel off due to changes in temperature and humidity during long-term storage, and its barrier effect (water content 3.5wt%) is significantly inferior to that of the gradient structure of the examples.

[0229] Application Example 6: Heat-sealing window and seal initiation temperature test.

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

[0231] Experimental instruction: Temperature gradient heat seal test was performed using a heat seal tester (Model 12-12 AS / 1). The heat seal pressure was set at 0.30 MPa with a dwell time of 0.8 s. The temperature range was from 100 °C to 180 °C. First, a coarse test was performed with a step size of 10 °C to determine the initiation range. Then, a fine test was performed with a step size of 2 °C. The peel strength of the sealed sample at each temperature point was tested.

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

[0233] The heat seal window width was defined as the width of the continuous temperature interval at which the peel strength remained above 8.0 N / 15 mm, and the capsule flange showed no obvious deformation, and the lid film showed no burning or wrinkling (i.e., the upper limit temperature minus the lower limit temperature). Five parallel samples were tested at each temperature point.

[0234] Table 8 Heat seal window and initiation temperature test results:

[0235]

[0236] Analysis: The test results clearly demonstrate the effect of the flange surface state on heat seal performance. Example 7, Example 2, and Example 10 have the widest heat seal window (≥ 44 °C) and the lowest initiation 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 flat “polymer cushion” that can tolerate fluctuations in temperature and pressure, and fill the small gaps that may exist between the lid and the flange. Example 11, due to the use of PHB with a higher melting point, the initiation temperature is increased to 135 °C, but still maintains a 30 °C operating window, meeting the needs of industrial production. In contrast, Comparative Example 3 and Comparative Example 5 require extremely high temperatures (140 °C) to flow and fill the paper fiber pores with polymer to achieve adhesion due to the lack of glue or roughness on the flange surface, which can easily cause the lid film to be burned, resulting in a very narrow usable window (only 10 °C). Comparative Example 8 has a rough surface, uneven heat conduction, making it difficult to initiate and prone to false sealing, with a window of only 12 °C. A wide heat seal window means higher yield and process stability on high-speed packaging lines.

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

[0238] This application example verifies the heat pressure densification effect of the flange and the distribution pattern of the coating in the paper base through microscopic characterization methods.

[0239] Experimental instruction: Flange surface porosity: measured by cross-section image analysis. Sample pieces were cut from both flange area and side wall area, and cross-section slices (slice thickness 20 pm) perpendicular to the inner surface were prepared. Bright field cross-section images were collected at 200x magnification and scale calibration was performed. Surface layer area was defined as the thickness range from 0 pm to 200 pm from the inner surface; threshold segmentation was performed in the surface layer area using image analysis software, and the porosity area ratio (porous area / surface layer total area x 100%) was calculated as the surface layer porosity. At least 10 different fields were calculated for each sample and the arithmetic mean was taken to obtain the flange surface porosity and side wall surface porosity.

[0240] Infiltration depth and coating thickness: Capsule side wall samples were prepared into 20 pm thick slices using a cryomicrotome at -20°C along the direction perpendicular to the surface. After Nile red fluorescence staining (specifically labeling PHA), the slices were observed under a fluorescence microscope. Image analysis software was used to measure the maximum depth of PHA fluorescence signal infiltrating the pulp fiber network (i.e. infiltration depth) and the average thickness of the continuous film layer covering the outermost layer of fibers (i.e. continuous dense layer equivalent thickness). 10 fields were observed for each group of samples.

[0241] Heat seal ring ring width: The radial width of the thickened coating in the flange area was directly measured using a digital caliper, and 8 points were measured along the circumference to take the average.

[0242] Table 9 Microstructure parameter test results:

[0243]

[0244] Analysis: Microscopic analysis revealed the structural root of the performance difference of each sample. The flange surface porosity of all examples (and comparative examples except for comparative example 3) (30.5%-36.0%) was significantly lower than that of the side wall (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 first dispersion of 200 nm, and the infiltration depth reached 280 pm, close to the upper limit of 300 pm. This deeper layer of penetration formed a strong mechanical interlocking ("micro rivet" effect), which explained its excellent resistance to boiling performance in application example 2. On the contrary, comparative example 7, although the total coating amount was normal, the first layer particle size was too large (500 nm), and it could not penetrate into the pores, with an infiltration depth of only 30 pm. This was mainly the accumulation of the surface layer 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 pm) cannot form a complete continuous film, and too thick (55 pm) and too deep (350 pm) infiltration result in too much structural rigidity, which is prone to cracking under stress. The data of the examples all fall within the designed optimal window, achieving a balance between anchoring and densification.

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

[0247] This application example aims to verify that the paper-based molded coffee capsules and closure components of the application do not introduce fluorine-containing compounds while pursuing high oil resistance performance, meeting environmental protection and food safety requirements.

[0248] Experimental Description: The test refers to the EN 14582:2016 standard, which uses oxygen bomb combustion combined with a fluoride ion selective electrode method to determine total organic fluorine (TOF).

[0249] Sample Pretreatment: Cut and mix the capsules and closure components of each group. To exclude inorganic fluorine interference, extract the sample with ultrapure water before combustion and discard the extract. Accurately weigh 0.50g of the sample on a dry basis, and place it in an oxygen bomb combustion cup. The oxygen pressure during oxygen bomb combustion is 2.8MPa. The absorption liquid is 15mL of 0.01mol / L sodium hydroxide solution.

[0250] Combustion and Absorption: After ignition and combustion, rinse the inner walls of the combustion cup and bomb with ultrapure water and combine with the absorption liquid, and dilute to 100mL. Shake the oxygen bomb for 20 minutes to ensure that the combustion products are fully absorbed.

[0251] Determination: Before measurement, add 5mL of TISAB to the test solution to stabilize the ion strength and eliminate complex interference. Use 0.1mg / L, 0.5mg / L, 1mg / L, 5mg / L, and 10mg / L fluoride ion standard solutions to establish a calibration curve (R²≥0.999), and perform a blank test. Use a fluoride ion selective electrode to determine the fluoride ion concentration.

[0252] Calculation and Determination: Calculate TOF according to the following formula after deducting the background from the blank test:

[0253] TOF(mg / kg)=((Csample-Cblank)×V×1000) / m.

[0254] Where Csample is the fluoride ion concentration in the sample test solution (mg / L), Cblank is the fluoride ion concentration in the blank test solution (mg / L), V is the constant volume (L), and m is the dry sample mass (kg). The method detection limit is ≤5mg / kg; below the detection limit is determined as not detected.

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

[0256]

[0257] Analysis: The test results show that the total organic fluorine (TOF) content of all samples is below the method detection limit of 5 mg / kg, regardless of examples or comparative examples, and is determined as not detected. This result is of great significance: traditional paper-based oil-proof packaging often relies on perfluoro or polyfluoro alkyl substances (PFAS) to achieve oil-proofing, but PFAS has the risk of persistent organic pollutants. The present application achieves excellent oil-proofing performance (as shown in application example 4, oil-proofing time > 300 min) through physical barrier (continuous dense PHA layer) and surface energy regulation (hydrophobic properties of PHA itself and nanofiller), completely eliminating the dependence on fluorides. This confirms that the technical solution completely meets the increasingly stringent global environmental regulations (such as the EU's restrictions on PFAS in food contact materials) and consumer demand for food safety while ensuring high performance.

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

[0259] This application example verifies whether the actual dry coating amount of each group in different areas (side wall, bottom wall, flange) meets the set target and whether the flange area forms an effective local thickening through quantitative analysis.

[0260] Experimental explanation: The weight difference method is used for determination. After film formation and drying at 105°C to constant weight, the capsules are cut into samples with a known area (accurate to 0.01 cm²) from the side wall, bottom wall and flange area using a special knife.

[0261] Side wall / bottom wall: Take 5 samples each, weigh them, subtract the mass of the corresponding substrate (the average gram weight of the corresponding part of the uncoated capsule), and divide by the area to get the dry coating amount.

[0262] Flange: The flange ring is flattened and cut into samples. Since the flange area is densified by hot pressing, its substrate density is different from that of the side wall, so the substrate weight deduction needs to use the same hot-pressed densified but uncoated flange sample data.

[0263] The calculation result is expressed in g / m², and 5 capsules are tested for each group to obtain the average value. The ratio of the "sealing surface dry coating amount of the flange" to the "inner surface dry coating amount of the side wall" is also calculated.

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

[0265]

[0266] Analysis: The measured data shows that the coating amount control precision of each sample is relatively high, and the deviation is within ±5% of the set value. The data of the examples covers a wide range: the side wall coating amount covers the interval of 8.1 g / m² (Example 10) to 39.5 g / m² (Example 7); the flange coating amount covers the interval of 20.5 g / m² (Example 6) to 119.5 g / m² (Example 7).

[0267] Particularly noteworthy is Example 10, which verifies an extreme coating amount ratio design. Although the side wall coating amount is only 8.1 g / m² (at a lower level of barrier protection), the flange area has a coating amount as high as 96.2 g / m², making the ratio reach 11.9, close to the upper limit of 12.0. Combined with the results of Application Example 2, this design not only saves material costs, but also ensures excellent sealing performance (sealing strength 13.0 N). The side wall coating amount of Comparative Example 5 is only 5.2 g / m², which is below the critical point of effective film formation, resulting in barrier failure. The coating amount of Comparative Example 6 is too high (side wall 50.5 g / m²), not only causing material waste, but also increasing the risk of bursting or delamination under brewing conditions due to excessive internal stress of the coating (see the brewing leakage rate and bursting or delamination rate data in Application Example 2).

[0268] Application Example 10: Coating toughness and primer adhesion special test.

[0269] This application example verifies the actual effect of plasticizing modification and the introduction of primer coating through mechanical testing of the coating material itself and the adhesion test between the coating and the substrate.

[0270] Experimental instructions: Elongation at break test: Take the second water-based dispersion used in each example (dense layer formula), cast a film in a polytetrafluoroethylene mold, dry at room temperature for 48 hours, and then vacuum dry at 60°C for 4 hours to obtain dumbbell-shaped samples (ASTM D638-22 Type V) with a thickness of about 30-40 μm. Use an electronic tensile testing machine (6800 Series, equipped with ASTM D638 Type V clamps and appropriate range sensors) to perform tensile testing at a speed of 10 mm / min, and record the elongation at break.

[0271] Adhesion test: Select the finished capsules of Example 1 (without primer) and Example 4 (with primer). Completely immerse the capsules in hot water at 95°C for 30 minutes (simulate extreme brewing environment), take out and dry. Perform crosshatch adhesion test (ASTM D3359-23) on the inner surface of the side wall. Cut a grid with a 1 mm spacing with a sharp blade, attach 3M 610 tape and quickly tear it off, and observe the coating peeling at the edge of the cut. Rating criteria: 5B (smooth edge, no peeling) to 0B (peeling area > 65%).

[0272] Table 12 Coating toughness and adhesion test results

[0273]

[0274] Analysis: The test results show that the coating toughness and adhesion stability of the application examples are significantly better than those of the comparative examples in the wet heat environment.

[0275] In the examples, the samples with a double-layer "infiltration anchor layer + continuous dense layer" structure (Examples 1-11) generally maintain an adhesion grade of 4B or higher after wet heat soaking, indicating that a stable mechanical interlocking interface is formed between the coating and the pulp substrate.

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

[0277] In contrast, Comparative Example 4 (without thermal fusion film formation) has an adhesion of 0B under wet heat conditions, indicating that the coating in a particle accumulation state is prone to overall peeling in a hydrothermal environment; Comparative Example 3 (without flange densification) and Comparative Example 5 (low coating amount) also show obvious interface failure.

[0278] In terms of coating toughness, different PHA monomer structures have a significant impact on elongation at break. P34HB containing 4-hydroxybutyrate structure (Example 10) shows the highest elongation at break, while PHB with higher crystallinity (Example 11) has the lowest elongation at break, but does not show macroscopic failure under the support of the double-layer structure and the pulp substrate.

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

[0280] Experimental results and analysis:

[0281] Based on the experimental data of Examples 1-11 and Comparative Examples 1-8, the effectiveness and superiority of the paper-based molded coffee capsule and the PHA spray film forming method proposed by the application are analyzed as follows:

[0282] The decisive role of the particle size gradient double-layer structure on barrier performance:

[0283] The experimental data show that the double-layer structure of "first aqueous PHA dispersion (small particle size) + second aqueous PHA dispersion (large particle size)" constructed by the application is the key to achieving high barrier performance.

[0284] The WVTR of Examples 1-11 are all controlled below 0.90 g / (m²·24h), and the OTR below 0.82 cm³ / (m²·24h·0.1MPa). Among them, Example 8 adopts the first dispersion with lower limit particle size (200 nm) and the second dispersion with larger particle size (600 nm), achieving excellent barrier effect (WVTR = 0.55 g / (m²·24h)), which confirms that smaller particle size particles can effectively fill the surface layer pores of the pulp, providing a dense substrate for the upper film formation.

[0285] On the contrary, Comparative Example 2 lacks the first layer of small particle size coating and directly coats the large particle size dispersion, resulting in a WVTR as high as 2.90 g / (m²·24h) and a Cobb value as high as 7.5 g / m², indicating that large particles cannot effectively block the fine pores between pulp fibers, and are prone to form through defects.

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

[0287] Effect of flange area densification and local thickening on sealing integrity:

[0288] The structure design of the sealing surface of the flange directly determines the reliability of the capsule under high pressure brewing.

[0289] Examples 1-11 all exhibit excellent pressure resistance under a brewing pressure of 1.9 MPa, with extremely low leakage rate and burst rate (mostly 0%). This is due to two key factors:

[0290] First, the hot-pressing densification process. Comparative Example 3 does not perform hot-pressing densification on the flange, resulting in a flange surface porosity as high as 56.0% and a sealing peel strength of only 4.0 N / 15 mm, and a brewing leakage rate as high as 30%. This shows that the originally loose surface of the pulp molding cannot directly support high-strength heat sealing, and must be physically densified to reduce surface roughness and porosity.

[0291] Secondly, the design of the local thickened heat-seal ring. Example 10 adopted an extreme coating weight distribution strategy (96 g / m2 on the sealing surface of the flange vs. 8 g / m2 on the sidewall, ratio ~ 12.0), and still achieved a high seal strength of 13.0 N / 15 mm and 0% leakage rate, thanks to the thick heat-seal material reserve at the flange. Compared with Comparative Example 6 (flange coating weight only 20 g / m2) and Comparative Example 5 (flange coating weight 15 g / m2), it can be seen that there is a clear critical value of the dry coating weight in the flange area. When the coating weight is not enough to fill the residual pores and form a molten "cushion", the heat-seal window narrows significantly (e.g. only 10°C in Comparative Example 5), and the sealing reliability decreases significantly.

[0292] Influence of interfacial penetration depth on the resistance to delamination under boiling:

[0293] Through the correlation of micro cross-section analysis and boiling resistance test, it can be seen that the adhesion between the coating and the substrate is mainly due to the mechanical interlocking effect.

[0294] The first dispersion particle size of Example 8 is at the lower limit (200 nm), and its penetration depth reaches 280 μm, showing 0% delamination rate and 5B level adhesion in the boiling resistance test. Example 4 introduces a chitosan primer, further enhancing the chemical bonding at the interface, also achieving a 5B level adhesion.

[0295] On the contrary, Comparative Example 7 lacks small particle size to guide penetration, with a penetration depth of only 30 μm, mainly staying on the surface and accumulating, resulting in an 8% burst or delamination rate in the boiling resistance test. Although Comparative Example 6 has the deepest penetration depth (350 μm), the coating is too thick and stress is concentrated, which increases the brittleness of the material, and does not bring better overall performance. Therefore, controlling the penetration depth in the range of 20 μm to 300 μm is the optimal solution to balance the anchoring force and the mechanical properties of the material.

[0296] Environmental performance and surface property analysis:

[0297] The biodegradation rate of all examples under controlled composting conditions for 45 days is more than 96%, and the total organic fluorine (TOF) is not detected, proving that this fully bio-based solution can completely replace traditional fluorine-containing oil-proof materials and aluminum plastic composite materials.

[0298] In terms of surface properties, Example 4 introduces a lamellar nano-filler (montmorillonite), which not only improves the barrier property (WVTR drops to 0.50 g / (m2·24h)), but also significantly improves the surface hydrophobic and oleophobic properties (oil penetration time 340 min), indicating that the introduction of inorganic fillers can effectively extend the penetration path and improve the surface micro-roughness.

[0299] Trend analysis of material content and process parameters:

[0300] Based on the data of each example and comparative example, the influence trend of the change of each key parameter on the experimental results is as follows:

[0301] The first dispersion particle size change trend: as the first aqueous PHA dispersion particle size decreases from 300 nm (Example 9) to 200 nm (Example 8), the penetration depth increases significantly (from 70 μm to 280 μm), and the coating adhesion grade is improved from 4B to 5B, indicating that reducing the particle size of the bottom layer helps to enhance the interface anchoring.

[0302] The flange / side wall coating amount ratio change trend: as the ratio increases from 3.5 (Example 1) to 11.9 (Example 10), the overall material cost efficiency of the capsule is optimized while maintaining the basic barrier function of the side wall, and the sealing strength is not sacrificed (maintained at about 13.0 N), indicating that the local thickening strategy has a high potential in industrial applications.

[0303] The second dispersion solid content change trend: as the second dispersion solid content 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 dense layer. Too low solid content (Comparative Example 8) will cause micro-cracks during the drying process due to excessive water evaporation, resulting in a sharp decrease in barrier performance (WVTR rises to 1.90 g / (m²·24h)).

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

[0305] In summary, the present application successfully solves the technical problem of balancing the barrier, sealing, boiling resistance and environmental protection performance of paper-based molded capsules by unique double-layer particle size gradient spraying, flange hot pressing densification and local thickening hot sealing ring design. The experimental results fully demonstrate the advancement and practicality of the technical scheme.

[0306] Those skilled in the art should understand that the above examples are only exemplary and are not intended to limit the scope of the present application. Any modification, equivalent replacement, improvement, etc. of the technical scheme of the present application within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A 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 preform 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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