Integrated method and system for high-throughput steam venting, hot-pressing densification, and controlled crystallization of aqueous pha coating wet films

Abstract

This invention discloses an integrated method and system for high-throughput steam exhaust, hot-press densification, and controlled crystallization of waterborne PHA coating wet films. It belongs to the fields of polymer material processing, transport phenomena in chemical engineering, and papermaking science, and is applicable to high-speed production lines ranging from 50 m / min to 1200 m / min. Addressing the challenges of pinholes and insufficient densification in high-speed coating of waterborne PHA, this invention optimizes the wet film rheology through pre-adjustment, utilizing a unique micro-nano structured interface and zoned negative pressure technology to achieve over 80% efficient steam exhaust, completely eliminating the Leidenfrost effect caused by interfacial vapors. Simultaneously, dynamic thermal compensation using a heat source up to 400℃ overcomes thermodynamic bottlenecks, combined with precise dew point difference control of crystallization kinetics. Compared to traditional processes, this solution achieves defect-free densification and performance stabilization of the coating in a very short time. The resulting products exhibit excellent barrier properties, high heat-sealing strength, and easy recyclability, significantly reducing energy consumption and improving production efficiency, making it highly valuable for industrial applications.

Description

Technical Field

[0001] This invention belongs to the fields of polymer material processing, transport phenomena in chemical engineering, and papermaking science, specifically relating to an integrated method and system for high-flux steam exhaust, hot pressing densification, and controlled crystallization of aqueous PHA coated wet films. Background Technology

[0002] Waterborne polyhydroxyalkanoate (PHA) coatings are a key technological pathway to achieving sustainable paper-based packaging. However, scaling them up from laboratory scale to high-speed industrial production faces significant physical and engineering challenges, primarily due to multiple limitations in heat transfer, mass transfer, and phase change kinetics.

[0003] Firstly, there are mass transfer limitations and interfacial instabilities. In high-speed coating lines, contact hot pressing is often used to improve drying efficiency. However, when the aqueous PHA wet film comes into contact with a high-temperature surface, the moisture at the interface instantly vaporizes, generating high-pressure steam. If the steam cannot be discharged in time, a continuous vapor boundary layer will form, known as the Leidenfrost effect. This not only severely hinders heat transfer but also leads to hydrodynamic instability, causing the wet film to rupture, forming bubbles and pinholes, thus compromising barrier properties.

[0004] Secondly, there is the limitation of heat flux density at high linear speeds. As the linear speed increases, for example from 50 m / min to 1200 m / min, the amount of heat that needs to be transferred to the film layer per unit time increases dramatically to achieve the co-fusion of PHA particles. This requires the hot pressing equipment to provide extremely high heat flux density. The heating source temperature of traditional hot pressing equipment is usually below 250°C, which cannot provide sufficient heat flux at high speeds, causing the contact surface temperature to drop rapidly and making it impossible to maintain an effective process window.

[0005] Thirdly, there is the challenge of crystallization kinetics and material diversity. The barrier properties and practical performance of PHAs are highly dependent on their crystal morphology and crystallinity. The PHA family includes various types, such as rapidly crystallizing PHB and slowly crystallizing P34HB. Achieving controlled crystallization for different PHA grades within extremely short online residence times is a problem that current technologies have failed to solve. Most existing technologies focus on post-processing of molten PHA layers or employ low-speed, stepwise drying and hot-pressing processes, which cannot address the aforementioned coupling challenges of processing aqueous wet films under high-speed conditions.

[0006] With the rapidly increasing demand for waterproof, oil-proof, and oxygen-barrier properties in paper-based recyclable packaging, bio-based waterborne barrier coatings have become an important alternative to traditional fluorinated or difficult-to-recycle plastic films. Polyhydroxyalkanoates (PHAs) possess bio-based and biodegradable properties, but in high-solids, high-speed online coating scenarios, the moisture and entrained gases in the wet film are difficult to remove in time. This leads to interfacial vapor retention and micropores under high-flux heat transfer and rapid heating conditions, resulting in insufficient film densification and significant fluctuations in coating barrier performance and adhesion. Furthermore, the crystallization kinetics of PHA are sensitive to temperature and humidity conditions. Traditional processes relying on single drying or offline post-processing struggle to achieve stable phase transition control and performance stabilization within a speed window of 50 m / min to 1200 m / min, often resulting in high energy consumption, large footprint, low yield, and poor batch consistency. Therefore, there is an urgent need for an online coating and integrated processing technology for paper-based waterborne PHA coatings for high-speed production lines. This technology should be able to complete wet film rheology and moisture content pre-adjustment, efficient interface degassing, densification, controlled crystallization, and rapid shaping in a very short time after coating. Furthermore, it should achieve stable and controllable coating microstructure and barrier properties through online sensing and closed-loop control to meet the requirements of large-scale, low-energy-consumption, and high-consistency industrial applications. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide an integrated method and system for high-throughput steam exhaust, hot pressing densification and controlled crystallization of waterborne PHA coated wet films.

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

[0009] This invention provides an integrated method for high-throughput steam removal, hot-press densification, and controlled crystallization of an aqueous PHA-coated wet film, applicable to production line speeds from 50 m / min to 1200 m / min, such as 50 m / min, 80 m / min, 100 m / min, 150 m / min, 200 m / min, 250 m / min, 300 m / min, 400 m / min, 500 m / min, 600 m / min, 700 m / min, 800 m / min, 900 m / min, 1000 m / min, 1100 m / min, or 1200 m / min, comprising the following sequential steps:

[0010] Step 1. Apply an aqueous dispersion containing PHA onto a paper or paperboard substrate to obtain a coated wet film substrate;

[0011] Step 2. Within 0.5s to 60s after the completion of the last coating, for example, 0.5s, 0.8s, 1.0s, 1.5s, 2.0s, 3.0s, 5.0s, 10.0s, 15.0s, 20.0s, 30.0s, 40.0s, 50.0s or 60.0s, the coated wet film substrate is introduced into the online integrated processing system to obtain the substrate to be processed. The online integrated processing system refers to a compact continuous processing device located downstream of the coating unit, which is different from the traditional segmented long drying tunnel. It can continuously couple and complete the rheological adjustment, forced mass transfer, hot pressing densification and phase change control of the wet film in a single process flow.

[0012] Step 3. Pre-conditioning zone: By using non-contact energy input, the wet film rheological properties and moisture content of the substrate to be treated are adjusted. The non-contact energy input refers to the transfer of heat energy to the substrate using a radiation field, convection field, or electromagnetic field without direct physical contact between the energy source and the wet film surface. This is to avoid adhesion or damage of the wet film with high moisture content. The temperature of the film surface and the interface between the film and the substrate is made to reach 5°C to 60°C above the minimum film-forming temperature of the aqueous dispersion, for example, 5°C, 8°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, or 60°C. At the same time, the overall moisture content of the substrate is adjusted to 3wt% to 10wt%, for example, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%, to obtain a pre-conditioned substrate.

[0013] Step 4. Graded Pressure Hot Pressing Zone: At least two adjacent contact-type high-flux heat transfer zones along the substrate running direction are set up to enhance interfacial mass transfer and densify the pre-conditioned substrate; the first pressure zone, i.e., the steam exhaust zone, uses a linear pressure of 50N / mm to 300N / mm, for example, 50N / mm, 80N / mm, 100N / mm, 120N / mm, 150N / mm, 180N / mm, 200N / mm, 250N / mm, 280N / mm or 300N / mm, to forcibly exhaust water vapor and entrained gas in the wet film through a contact interface with steam exhaust capability, achieving a steam exhaust efficiency η≥80%, for example, 80%, 82%. The second pressing zone, i.e. the dense zone, is subjected to a linear pressure of 100 N / mm to 800 N / mm, for example, 100 N / mm, 200 N / mm, 300 N / mm, 400 N / mm, 500 N / mm, 600 N / mm, 700 N / mm or 800 N / mm, to induce the formation and fusion of PHA particles and densification; wherein the contact surface temperature of the second pressing zone is maintained at 90°C to 160°C, for example, 90°C, 100°C, 110°C, 120°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C or 160°C, to obtain a densified substrate;

[0014] Step 5. Controlled Crystallization Region: The relaxation of PHA segments and crystal growth kinetics of the densified substrate are controlled by maintaining the mixture in a constant temperature and humidity environment of 45°C to 65°C for 3 to 60 seconds. Examples of ambient temperatures are 45°C, 48°C, 50°C, 52°C, 55°C, 58°C, 60°C, 62°C, or 65°C, and relative humidity is 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%. The holding time is, for example, 3 seconds, 5 seconds, 8 seconds, 10 seconds, or 15 seconds. 20s, 30s, 40s, 50s, or 60s; wherein precise humidity control is achieved by controlling the dew point difference ΔTd within the range of 5℃ to 15℃, for example, 5℃, 6℃, 7℃, 8℃, 9℃, 10℃, 11℃, 12℃, 13℃, 14℃, or 15℃. The dew point difference ΔTd refers to the difference between the dry-bulb temperature of the current environment and the air dew point temperature, which is used to characterize the air's ability to hold additional water vapor and the thermodynamic driving force on the rate of moisture evaporation or absorption on the coating surface, thereby obtaining a controlled crystalline substrate;

[0015] Step 6. Quenching and Shaping Zone: Through a combination of forced convection and conduction cooling, the microstructure of the coating on the controlled crystalline substrate is rapidly shaped to obtain a paper-based water-based PHA barrier coated product;

[0016] Step 7. An integrated online sensor array and a multivariable closed-loop control system are used to regulate the energy input, mass transfer efficiency and phase change kinetic parameters of each zone in real time.

[0017] The first pressure zone has a steam-venting contact interface with a herringbone, V-shaped, or mesh-like microgroove structure, or a porous sintered material band; its characteristic size is in the range of 10μm to 300μm, for example, 10μm, 30μm, 50μm, 80μm, 100μm, 150μm, 200μm, 250μm, or 300μm, and its surface opening ratio or porosity is 1% to 15%, for example, 1%, 3%, 5%, 8%, 10%, 12%, or 15%; and the contact interface is connected to the partitioned negative pressure chamber, the partitioned negative pressure is set to 200Pa to 9000Pa, for example, 200Pa, 500Pa, 1000Pa, 2000Pa, 4000Pa, 6000Pa, 8000Pa, or 9000Pa.

[0018] The graded pressure hot pressing zone employs a high heat flux density heating system, with an adjustable heating source temperature range of 90℃ to 400℃, for example, 90℃, 150℃, 200℃, 220℃, 250℃, 300℃, 350℃, 360℃, 380℃, or 400℃. The control system dynamically adjusts the heating source temperature based on the production line speed, substrate thermal properties, and real-time monitored contact surface temperature using a feedforward control algorithm based on a heat transfer model to compensate for heat loss during high-speed operation and ensure that the contact surface temperature is stably maintained within the target window.

[0019] When applied to low-to-medium speed or conventional coating machines, the production line speed is 50 m / min to 250 m / min, for example, 50 m / min, 100 m / min, 150 m / min, 200 m / min, 250 m / min. The time interval between steps 1 and 2 is selected from 1.0 s to 60 s, for example, 1.0 s, 2.0 s, 10 s, 30 s, 60 s. When applied to high-speed coating machines or online coating on paper machines, the production line speed... The speed is 300 m / min to 1200 m / min, for example, 300 m / min, 500 m / min, 800 m / min, 1000 m / min, 1200 m / min; the time interval between steps 1 and 2 is selected from 0.5 s to 20 s, for example, 0.5 s, 1.0 s, 3.0 s, 5.0 s, 10 s, 20 s; and in the paper machine, the integrated processing system is located between the end of the drying section and the calendering section.

[0020] The pre-adjustment in step 3 employs any one or a combination of infrared radiation, hot air convection, microwave, or dielectric heating; and uses the dew point difference ΔTd as a reference to control the local humidity of the membrane surface before entering the first pressure zone in a closed loop, so as to suppress the phenomenon of supersaturated condensation at the interface.

[0021] The resulting PHA barrier coating, under the conditions of pre-conditioning, graded pressure hot pressing, controlled crystallization, and quenching and shaping according to the process window of this invention, meets at least two of the following performance indicators: OTR ≤ 110 cm³ / m²·day, for example, 110 cm³ / m²·day, 100 cm³ / m²·day, 90 cm³ / m²·day, 80 cm³ / m²·day, 75 cm³ / m²·day, 70 cm³ / m²·day; WVTR ≤ 30 g / m²·day, for example, 30 g / m²·day, 28 g / m²·day, 26 g / m²·day, 25 g / m²·day, 22 g / m²·day, 20 g / m²·day; DSC crystallinity Xc ≥ 40%, for example, 40%, 42%, 45%, 48%, 50%, 55%, 58%, 60%; 180 Peel strength ≥ 1.5 N / 15 mm, e.g., 1.5 N / 15 mm, 1.6 N / 15 mm, 1.7 N / 15 mm, 1.8 N / 15 mm, 2.0 N / 15 mm, 2.1 N / 15 mm; pinhole density ≤ 0.1 pins / cm², e.g., 0.1 pins / cm², 0.08 pins / cm², 0.05 pins / cm², 0.01 pins / cm²; Cobb resistance value ≤ 5 g / m² For example, 5g / m², 4g / m², 3g / m²; heat seal strength ≥2.0N / 15mm, for example 2.0N / 15mm, 2.1N / 15mm, 2.2N / 15mm, 2.3N / 15mm; static water droplet contact angle ≥92°, for example 92°, 94°, 96°, 100°; fiber recovery rate ≥92%, for example 92%, 93%, 94%, 95%, 96%, 97%.

[0022] The controlled crystallization zone adjusts the residence time and dew point difference ΔTd according to the crystallization kinetics of the PHA used; for slow-crystallizing PHAs, the dew point difference ΔTd is controlled to be between 7°C and 12°C, for example, 7°C, 8°C, 9°C, 10°C, 11°C or 12°C.

[0023] The present invention also provides an integrated processing system for implementing the above method, comprising, arranged sequentially along the substrate running direction: a pre-conditioning unit, a graded pressure hot pressing unit, a controlled crystallization chamber, a quenching and shaping component, and a central control system; wherein: the graded pressure hot pressing unit has a high heat flux density heating capacity, supports a heating source temperature of up to 400°C, and can precisely control the contact surface temperature; the unit forms at least two pressing zones by pressing a heating main roller with an annular continuous strip, the working surface of the strip has a micro-nano structured interface with steam exhaust capability, and is optionally connected to a partitioned negative pressure chamber; the central control system integrates a sensor array for monitoring moisture content, temperature, dew point, and linear pressure, and has a multi-variable linkage control function based on a heat and mass transfer model and phase change dynamics; the controlled crystallization chamber supports precise environmental humidity control based on a dew point difference ΔTd of 5°C to 15°C.

[0024] The high heat flux density heating capability is achieved through high-frequency electromagnetic induction heating, a high-temperature heat transfer oil circulation system, or an array of high-power electric heating elements; the annular continuous strip is a high-temperature resistant, high-thermal-conductivity seamless metal strip or a carbon fiber reinforced composite material strip; the system is equipped with a radial multi-chamber negative pressure distributor, a side air curtain isolation device, and a high-temperature safety interlock device.

[0025] This invention also provides an online control method for the above-mentioned system, using dew point, moisture content, and contact surface temperature as the main control variables, and constructing a cascaded control loop based on feedforward control and feedback control; the control logic includes: dynamically compensating for heat source temperature by adjusting the feedforward of the heating source temperature according to the target values ​​of linear velocity and contact surface temperature through a real-time heat transfer model; when the moisture content or dew point deviates from the target window, prioritizing the adjustment of the zone negative pressure and the linear pressure of the first pressure zone, and correcting the linear velocity to ensure that the exhaust efficiency η≥80%; and maintaining the dew point difference ΔTd within the range of 5℃ to 15℃ to stabilize the crystallization kinetic parameters.

[0026] The present invention also provides an aqueous PHA coating composition suitable for the above-described method, having a total solids content of 25 wt% to 55 wt%, for example 25 wt%, 28 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, or 55 wt%, and comprising, by solids content: 70 wt% to 98 wt% of a PHA dispersion, for example 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, or 98 wt%, with a median particle size D. 50The particle size is 0.2-2.0 μm, for example, 0.2 μm, 0.4 μm, 0.5 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2.0 μm; the polydispersity index is ≤0.3, for example, 0.1, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3; 0.2 wt% to 2.5 wt% of bio-based surfactants or polymeric stabilizers, for example, 0.2 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%; 0 wt% to 15 wt% of functional additives. The composition comprises, for example, 0 wt%, 1 wt%, 2 wt%, 5 wt%, 8.5 wt%, 10 wt%, 14 wt%, or 15 wt%, selected from bio-based plasticizers, nucleating agents, or film-forming aids; 0 wt% to 15 wt% of a water-soluble or water-dispersible bio-based binder, for example, 0 wt%, 0.5 wt%, 1.5 wt%, 4.8 wt%, 5 wt%, 10 wt%, 12.5 wt%, or 15 wt%; and a minimum film-forming temperature of ≤65°C, for example, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, or 65°C, and at a shear rate of 1000 s. -1 The apparent viscosity is from 50 mPa·s to 1000 mPa·s, for example, 50 mPa·s, 100 mPa·s, 150 mPa·s, 300 mPa·s, 500 mPa·s, 800 mPa·s, and 1000 mPa·s.

[0027] The plasticizer is selected from citrate esters, glycerides, or lactates; the nucleating agent is selected from boron nitride, talc, or PHA-based self-nucleating agents; and the binder is selected from PVOH, modified starch, or cellulose nanocrystals.

[0028] The present invention also provides a coated article comprising a paper or paperboard substrate, wherein at least one side of the substrate has a dense waterborne PHA barrier coating prepared by any of the foregoing methods.

[0029] This invention also provides a method for preparing paper-based waterborne PHA barrier coated articles on a coating machine or papermaking machine, suitable for production line speeds from 50 m / min to 1200 m / min, comprising the following continuous steps:

[0030] S1. Surface Energy Activation: Before applying the final aqueous PHA dispersion, the substrate or primer is subjected to corona or atmospheric plasma treatment to achieve a surface energy of 46 mN / m to 52 mN / m, for example, 46 mN / m, 48 mN / m, 50 mN / m, or 52 mN / m, thus obtaining an activated substrate. The surface energy is calculated according to ISO 19403-2:2024 by measuring the contact angle between two probe solutions, deionized water and diiodomethane, and using the Owens-Wendt-Rabel-Kaelble method.

[0031] S2. Applying an aqueous dispersion containing PHA: Applying an aqueous PHA dispersion to the activated substrate, and introducing the wet film into the online integrated processing system within 0.5s to 60s to obtain a coated wet film substrate;

[0032] S3. Integrated processing: In the online integrated processing system, the coated wet film substrate is subjected to pre-conditioning, graded pressure hot pressing, controlled crystallization and quenching and shaping steps in sequence, specifically according to the aforementioned steps 3 to 6; wherein, the exhaust efficiency η≥80%, ΔTd is controlled between 5℃ and 15℃; and the graded pressure hot pressing zone uses a heating source with a temperature as high as 400℃ for dynamic thermal compensation to obtain a paper-based water-based PHA barrier coated product.

[0033] The present invention also provides an integrated system for implementing the above preparation method, comprising: a corona or atmospheric plasma treatment unit; an online integrated treatment system arranged along the running direction of the substrate, the system conforming to the aforementioned structural features; and a central control system capable of simultaneously acquiring surface energy, dew point, moisture content, and contact surface temperature data, and realizing multi-variable linkage control with corona energy, heating source temperature, linear pressure, zoned negative pressure, and linear velocity.

[0034] This invention also provides an online control method for the aforementioned integrated system, using surface energy, dew point, moisture content, and contact surface temperature as the main control variables to construct an integrated control loop; the control logic includes: automatically increasing the corona energy and linking the coating parameters when the surface energy is below the target range; dynamically compensating for heat loss by adjusting the heating source temperature according to the feedforward of the linear velocity and heat transfer model; prioritizing the adjustment of the negative pressure or the linear pressure or linear velocity of the first pressure zone when the moisture content increases; and maintaining ΔTd within the range of 5°C to 15°C.

[0035] Compared with the prior art, the following significant advantages can be obtained by using the present invention:

[0036] The problem of interface vapor removal under high-speed coating has been solved: through the unique micro-nano structured interface and partitioned negative pressure design of the first pressure zone, a vapor removal efficiency of over 80% has been achieved, effectively eliminating the Leidenfrost effect generated instantaneously during high-speed hot pressing, avoiding bubbles and pinholes caused by steam, ensuring the continuity and high barrier properties of the coating, and achieving excellent indicators such as OTR≤110cm³ / m²·day and pinhole density≤0.1 pinholes / cm².

[0037] Breakthrough in the thermodynamic bottleneck of high-speed densification: Through dynamic compensation of high heat flux density of heat source up to 400℃, the effective melting window of 90℃-160℃ can still be maintained at high speed of 1200m / min, solving the problem that high melting point PHA cannot be completely melted and densified in a very short contact time.

[0038] Controlled regulation of crystallization kinetics was achieved: By precisely controlling the dew point difference of 5℃-15℃ in the controlled crystallization zone, the chain segment relaxation and crystal growth of PHA (especially slow-crystallizing materials such as P34HB) were successfully regulated, achieving a crystallinity of more than 40% within tens of seconds, solving the problems of product stickiness, winding adhesion and later embrittlement, and giving the product good heat-sealing strength.

[0039] It enhances the recycling value of packaging materials: the resulting coated products have both excellent barrier and resizing properties, with a fiber recovery rate of over 92% and extremely low residue content on the screen, which aligns with the environmental trend of sustainable recycling of paper-based packaging. Attached Figure Description

[0040] Figure 1 This is a schematic diagram illustrating the process principle of the paper-based water-based PHA coating online coating and integrated treatment system of the present invention.

[0041] In the figure, 1-paper substrate; 2-aqueous dispersion containing PHA; 3-preconditioning zone; 4-first pressing zone; 5-contact interface with steam venting capability; 6-heated main roller; 7-controlled crystallization zone; 8-quenching and shaping zone; 9-paper-based aqueous PHA barrier coating product; 10-central control system; 11-second pressing zone; 12-zoned negative pressure chamber. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention. Unless otherwise stated, the raw materials used in this embodiment are commercially available industrial products or can be prepared by conventional methods. Unless otherwise specified, performance testing methods are performed according to the standards described in the invention summary section.

[0043] Figure 1 This is a schematic diagram of the online coating and integrated processing system for paper-based waterborne PHA coating according to the present invention. As shown in the figure, after the paper substrate 1 is unwound from the left, a waterborne dispersion 2 containing PHA is applied to form a wet film through a coating device. It then enters the pre-conditioning zone 3, where the rheological properties of the wet film are adjusted by non-contact heating. The pre-conditioned substrate sequentially enters the graded pressure hot-pressing unit composed of the first pressing zone (i.e., the venting zone 4) and the second pressing zone 11. In the first pressing zone 4, the surface of the upper pressure roller is provided with a contact interface 5 (such as a microgroove or porous structure) with venting capability, which cooperates with the lower partitioned negative pressure chamber 12 to force the external discharge of water vapor and entrained gas generated in the wet film. The second pressing zone 11, which follows, employs a heated main roller 6 that provides high-temperature thermal compensation, promoting the densification and melting of PHA particles. The hot-pressed substrate enters the controlled crystallization zone 7, where the crystallization kinetics of PHA are regulated under a constant temperature and humidity environment. Finally, the substrate undergoes rapid cooling and shaping in the quenching and shaping zone 8 to obtain the final paper-based waterborne PHA barrier coated product 9, which is then wound up. The operating parameters of the entire system are monitored and controlled in real time by the central control system 10 with an integrated sensor array.

[0044] Table 1. Main reagent and raw material names, product models and manufacturers:

[0045]

[0046] Table 2 mainly analyzes the names, models, and manufacturers of the testing instruments:

[0047]

[0048] Table 3. Main Test Items and Reference Standards:

[0049]

[0050] Among them, the exhaust efficiency η is obtained by online near-infrared moisture meter and mass balance calculation, and is defined as the total moisture mass m of the wet film and substrate at the inlet of the first pressure zone. in The residual moisture mass at the outlet of the first compression zone (m) out The difference between the total moisture content and the mass m in The ratio is calculated using the following formula: η=(m in -m out ) / m in ×100%. The m in With m outAll measurements were taken as moisture content per unit area. The inlet and outlet moisture contents were measured by an online near-infrared moisture meter and calibrated using the 105℃ drying to constant weight method. The absolute dry weight of the substrate was obtained by cutting samples and drying them at 105℃ to constant weight. The dew point difference ΔTd was measured by the dew point sensor built into the precision temperature and humidity control system of the controlled crystallization zone, and was defined as the difference between the ambient temperature of the controlled crystallization zone and the corresponding air dew point temperature Td, i.e., ΔTd = ambient temperature - Td.

[0051] The sample preparation and key parameters for each performance test are as follows:

[0052] (1) OTR and WVTR: The sample was tested after being conditioned at (23±2)℃ and (50±5)%RH for 24 hours. The sample was fixed with the instrument's standard clamps and the edges were sealed to prevent edge leakage. The test area was based on the instrument's default effective area.

[0053] (2) Cobb value: According to ISO 535:2023, the coated surface is the water-receiving surface, and the test time is 60s.

[0054] (3) Heat seal strength: The coated surfaces of two coated papers are stacked together and heat-sealed using a heat sealer. The heat seal temperature is 120°C to 140°C, the heat seal pressure is 0.2MPa to 0.4MPa, and the heat seal time is 0.5s to 1.5s, forming a heat seal strip with a width of 15mm. The test is then performed according to ASTM F88 / F88M-23 and expressed as N / 15mm.

[0055] (4) 180° peel strength: The coated paper sample (coated surface) is hot-pressed with the same paper substrate at 120°C to 150°C, 0.2MPa to 0.4MPa, and 0.5s to 2.0s to form a sample with an effective composite width of 15mm; then a 180° peel test is performed according to GB / T 2792-2014 and expressed as N / 15mm.

[0056] (5) Pinhole density: The backlight transmission method combined with microscopic verification and statistics were used. The sample was attached to a uniform backlight plate, and the effective area of ​​not less than 20 cm² was imaged and statistically analyzed. Defects that could transmit light and had an equivalent diameter ≥ 50 μm were counted as pinholes and converted to pinholes / cm². When no pinholes were detected, it was expressed as "<0.05 pinholes / cm² (detection limit)".

[0057] (6) Crystallinity Xc: The differential scanning calorimeter (DSC) was used to perform a “heating-cooling-secondary heating” procedure. The sample mass was 5 mg to 10 mg, the nitrogen flow rate was 50 mL / min, and the heating rate was 10 °C / min. Xc was calculated as Xc = (ΔHm - ΔHcc) / ΔHm0 × 100%, where ΔHm is the melting enthalpy of the second heating, ΔHcc is the cold crystallization enthalpy that appears during the second heating process (if there is no cold crystallization peak, take 0), and ΔHm0 is the 100% crystallization melting enthalpy of the PHA resin used.

[0058] The general preparation process for aqueous dispersions of polyhydroxy fatty acids is as follows:

[0059] Step 1. Take polyhydroxyalkanoate resin powder that has been vacuum dried at 60℃ for 12 hours in advance, and remove large particles by passing it through a 100-mesh sieve; add it to a jacketed stainless steel dispersion vessel at a mass ratio of polyhydroxyalkanoate solid: deionized water: alkyl polysaccharide surfactant of 1:1.5:0.05, and perform high-speed shearing at 8000 r / min at 70℃ to 80℃ for 20 minutes to obtain a coarse dispersion with a preliminary solid content controlled at 40wt% to 50wt%.

[0060] Step 2. The coarse dispersion is homogenized three times using a high-pressure homogenizer at an inlet pressure of 60 MPa to 80 MPa to obtain an aqueous polyhydroxyalkanoate dispersion. This aqueous polyhydroxyalkanoate dispersion has a solid content of 40 wt% to 50 wt% and a median particle size D. 50 The dispersion has a particle size between 0.2 and 2.0 μm, a polydispersity index (PDI) ≤ 0.30 (specifically 0.25 in the examples), and is free of polyvinyl alcohol-based petrochemical-derived protective colloids. This dispersion was used in the preparation of coating compositions for Examples 1 to 5 and the comparative examples.

[0061] The coating composition can be prepared according to the following general procedure: Place the PHA dispersion in a stirring tank and stir at 300 rpm to 1000 rpm; under stirring conditions, sequentially add the bio-based surfactant / stabilizer, plasticizer, nucleating agent, and binder or reinforcing agent, and continue stirring for 20 to 60 minutes; adjust the solid content of the system with deionized water according to the target total solid content, and measure the solid content using an online or offline viscometer at a shear rate of 1000 s⁻¹. -1 The apparent viscosity was checked; then vacuum degassing was performed for 10 to 30 minutes and filtered through a 100 to 200 mesh filter to obtain an aqueous PHA coating composition for coating.

[0062] The general preparation process for PHA-based nucleating agents is as follows:

[0063] Step 1. Take poly(3-hydroxybutyrate) (PHB) resin powder, vacuum dry it at 100°C for 8 hours, and then melt extrude it into a sheet with a thickness of 0.5 mm through a twin-screw extruder at 180°C to 190°C to obtain the sheet.

[0064] Step 2. After rapidly quenching the sheet in cold water at 0°C to 5°C to below room temperature, it was pulverized using a cryogenic grinder and classified through a 10μm sieve to obtain PHA-based nucleating agent powder. The average particle size of this PHA-based nucleating agent powder was 2μm to 5μm. In Example 3, the obtained PHA-based nucleating agent powder was added to the coating composition at 1wt% of its solid content to improve the crystallization rate and crystallinity of the polyhydroxyalkanoate.

[0065] Overview and Selection Instructions for Preparation Methods: This invention provides two general preparation methods adaptable to different substrate characteristics, both suitable for wide production line speeds from 50 m / min to 1200 m / min. Method 1 is a standard integrated processing technology, suitable for conventional paper substrates with moderate surface energy (>38 mN / m) or pre-coated substrates, mainly relying on physical hot pressing and controlled crystallization to achieve densification. In the subsequent application examples, Application Examples 1, 2, 3, 5 to 12 all use Method 1. Method 2 is a surface energy activation and enhancement process, integrating a corona or atmospheric plasma pretreatment step on the basis of Method 1, specifically for special paper substrates with low surface energy (≤38 mN / m), high hydrophobicity, or poor adhesion. Method 2 ensures wet film leveling and interfacial bonding at high line speeds by increasing the substrate surface energy to above 46 mN / m. In the subsequent examples, Application Example 4 specifically uses Method 2.

[0066] A general preparation method for paper-based waterborne PHA barrier coated products:

[0067] Method 1: An integrated method for preparing paper-based waterborne PHA barrier coated products on coating lines or papermaking lines.

[0068] This method is applicable to production line speeds from 50 m / min to 1200 m / min and includes the following sequential steps:

[0069] Step 1. Apply an aqueous dispersion containing PHA onto a paper or paperboard substrate to obtain a coated wet film substrate;

[0070] Step 2. Within 0.5s to 60s after the final coating is completed, introduce the coated wet film substrate into the online integrated processing system to obtain the substrate to be processed. In specific applications, when applied to medium-low speed or conventional coating machines with production line speeds of 50m / min to 250m / min, this time interval is set to 1.0s to 60s; when applied to high-speed coating machines or paper machines with production line speeds of 300m / min to 1200m / min, this time interval is set to 0.5s to 20s.

[0071] Step 3. Pre-conditioning zone: Using any one or a combination of infrared radiation, hot air convection, microwave, or dielectric heating as a non-contact energy input method, the wet film rheological properties and moisture content of the substrate to be treated are adjusted. With the dew point difference ΔTd as a reference, the local humidity of the film surface before entering the first pressure zone is controlled in a closed loop to suppress supersaturated condensation at the interface. After treatment, the temperature of the film surface and the interface between the film and the substrate reaches 5°C to 60°C above the minimum film-forming temperature of the aqueous dispersion. At the same time, the overall moisture content of the substrate is adjusted to 3wt% to 10wt% to obtain the pre-conditioned substrate.

[0072] Step 4. Graded Pressure Hot Pressing Zone: At least two adjacent contact-type high-flux heat transfer zones along the substrate running direction are set up to enhance interfacial mass transfer and densify the pre-conditioned substrate. The first pressure zone, i.e., the exhaust zone, uses a linear pressure of 50 N / mm to 300 N / mm to force the water vapor and entrained gas in the wet film to be discharged through a contact interface with exhaust capacity. The contact interface adopts a herringbone, V-shaped, or mesh microgroove structure, or a porous sintered material strip, with characteristic dimensions in the range of 10 μm to 300 μm and a surface opening ratio or porosity of 1% to 15%. At the same time, the contact interface is connected to the partitioned negative pressure chamber, and the partitioned negative pressure is set to 200 Pa to 9000 Pa, thereby achieving an exhaust efficiency η≥80%. The second pressure zone, i.e., the densification zone, uses a linear pressure of 100 N / mm to 800 N / mm to promote the fusion and densification of PHA particles. The contact surface temperature of the second pressure zone is maintained at 90℃ to 160℃ to obtain a densified substrate.

[0073] Step 5. Controlled crystallization zone: Adjust the residence time and dew point difference ΔTd according to the crystallization kinetics of the PHA used. For slow-crystallizing PHA, control the dew point difference ΔTd to 7°C to 12°C. Under normal circumstances, maintain it in a constant temperature and humidity environment with an ambient temperature of 45°C to 65°C for 3 to 60 seconds. Among them, precise humidity control is achieved by controlling the dew point difference ΔTd within the range of 5°C to 15°C. The relative humidity RH corresponding to the dew point difference ΔTd is 45% to 80%. This regulates the relaxation of PHA chain segments and crystal growth kinetics in the densified substrate to obtain a controlled crystallization substrate.

[0074] Step 6. Quenching and Shaping Zone: Through a combination of forced convection and conduction cooling, the microstructure of the coating on the controlled crystalline substrate is rapidly shaped to obtain a paper-based water-based PHA barrier coated product;

[0075] Step 7. An integrated online sensor array and a multivariable closed-loop control system are adopted, with dew point, moisture content, and contact surface temperature as the main control variables, to construct a cascaded control loop based on feedforward and feedback control. The control logic is set as follows: based on the target values ​​of linear velocity and contact surface temperature, the heating source temperature is adjusted by feedforward through a real-time heat transfer model to achieve dynamic heat compensation; when the moisture content or dew point deviates from the target window, the zone negative pressure and the linear pressure of the first pressure zone are adjusted first, and the linear velocity is corrected to ensure that the exhaust efficiency η≥80%; at the same time, the dew point difference ΔTd is kept within the range of 5℃ to 15℃ to stabilize the crystallization kinetic parameters.

[0076] Method 2: A method for preparing paper-based waterborne PHA barrier coated products on a coating machine or papermaking machine.

[0077] This method is applicable to production line speeds from 50 m / min to 1200 m / min and includes the following sequential steps:

[0078] S1. Surface Energy Activation: Before applying the final aqueous PHA dispersion, the substrate or primer is subjected to corona or atmospheric plasma treatment to achieve a surface energy of 46mN / m to 52mN / m on the surface to be coated, thus obtaining an activated substrate.

[0079] S2. Applying an aqueous dispersion containing PHA: Applying an aqueous PHA dispersion to the activated substrate, and introducing the wet film into the online integrated processing system within 0.5s to 60s to obtain a coated wet film substrate;

[0080] S3. Integrated processing: In the online integrated processing system, the coated wet film substrate is subjected to pre-conditioning, graded pressure hot pressing, controlled crystallization, and quenching and shaping steps in sequence, specifically according to steps 3 to 6 of method one; wherein, the exhaust efficiency η≥80%, ΔTd is controlled between 5℃ and 15℃; and the graded pressure hot pressing zone uses a heating source with a temperature as high as 400℃ for dynamic thermal compensation to obtain a paper-based water-based PHA barrier coated product.

[0081] Example:

[0082] The present invention provides five embodiment formulations.

[0083] Example 1 (Balanced PHB Formulation): Aqueous PHA coating composition was prepared with a total solids content of 40 wt%. Based on solids content, it contained: 95 wt% PHB dispersion (D... 50=0.5μm, PDI=0.25); 1.0wt% bio-based surfactant; 2.0wt% acetyltripteryl citrate (plasticizer); 0.5wt% boron nitride (nucleating agent); 1.5wt% PVOH (binder). MFFT is 60℃ at a shear rate of 1000s. -1 The apparent viscosity is 300 mPa·s.

[0084] Example 2 (High-Toughness PHBV Formulation): Aqueous PHA coating composition was prepared with a total solids content of 55 wt%. Based on solids content, it contained: 90 wt% PHBV dispersion (D... 50 =0.4μm, PDI=0.22); 0.2wt% bio-based surfactant; 5.0wt% acetyltripteryl citrate; 0wt% nucleating agent; 4.8wt% modified starch. MFFT was 55℃ at a shear rate of 1000 s. -1 The apparent viscosity is 800 mPa·s.

[0085] Example 3 (Slow-crystallizing P34HB formulation) prepared an aqueous PHA coating composition with a total solids content of 25 wt%. Based on solids content, it contained: 70 wt% P34HB dispersion (D... 50 =1.5μm, PDI=0.28); 2.5wt% bio-based surfactant; 15wt% functional additives (of which 14wt% is acetyltributyl citrate plasticizer and 1wt% is PHA-based nucleating agent); 12.5wt% CNC (used for reinforcement and auxiliary bonding). MFFT is 40℃ at a shear rate of 1000s. -1 The apparent viscosity is 50 mPa·s.

[0086] Example 4 (Mixed Modified Formulation): Aqueous PHA coating composition was prepared with a total solids content of 45 wt%. Based on solids content, it comprises: 80 wt% PHB / P34HB blend dispersion (obtained by mixing the PHB dispersion obtained from the aforementioned general preparation process of this invention with the P34HB dispersion at a solids content mass ratio of 1:1, after mixing D... 50 =0.8μm, PDI=0.26); 1.5wt% bio-based surfactant; 8.5wt% acetyltritol citrate; 10wt% PVOH. MFFT is 50℃ at a shear rate of 1000s. -1 The apparent viscosity is 500 mPa·s.

[0087] Example 5 (Nano-particle size formulation) prepared an aqueous PHA coating composition with a total solids content of 35 wt%. Based on solids content, it contained: 98 wt% PHBV dispersion (D... 50=0.2μm, PDI=0.18); 0.5wt% bio-based surfactant; 1.0wt% boron nitride nucleating agent; 0.5wt% polyvinyl alcohol binder. MFFT is 45℃ at a shear rate of 1000s. -1 The apparent viscosity is 150 mPa·s.

[0088] Comparative example:

[0089] Comparative Example 1 (High MFFT Formulation without Functional Additives): An aqueous PHA coating composition was prepared with a total solids content of 40 wt%. Based on solids content, it contained: 99.8 wt% PHB dispersion (D... 50 =0.5μm, PDI=0.25); 0.2wt% bio-based surfactant; no added functional additives or binders. The composition has an MFFT of 75°C at a shear rate of 1000 s. -1 The apparent viscosity is 200 mPa·s.

[0090] Comparative Example 2 (High-binder, high-viscosity formulation): An aqueous PHA coating composition was prepared with a total solids content of 20 wt%. Based on solids content, it contained: 60 wt% P34HB dispersion (D... 50 =2.5μm, PDI=0.35); 3.0wt% bio-based surfactant; 20.0wt% acetyltripteryl citrate; 17.0wt% modified starch binder. The composition has an MFFT of 35°C at a shear rate of 1000 s. -1 The apparent viscosity is 1200 mPa·s.

[0091] Comparative Example 3 (Refer to Formulation): An aqueous PHA coating composition was prepared, with the same component types, mass ratios, and physical properties as in Example 1, i.e., a total solid content of 40 wt% and containing 95 wt% PHB dispersion (D) based on solid content. 50 =0.5μm, PDI=0.25), 1.0wt% surfactant, 2.5wt% functional additives and 1.5wt% binder. MFFT is 60℃, at a shear rate of 1000s. -1 The apparent viscosity was 300 mPa·s. In subsequent application examples, the coating experiment corresponding to Comparative Example 3 used a conventional multi-stage hot air drying and smooth roller hot pressing process, without using the integrated pre-conditioning-graded pressure hot pressing-controlled crystallization-quenching and shaping system of the present invention, to compare the existing process with the method of the present invention.

[0092] Multi-stage hot air drying and smooth roller hot pressing process: After coating, the coating passes through three independent hot air drying ovens (temperatures set at 60℃, 120℃, and 100℃ respectively, with a total length equivalent to the integrated system of this invention, and the total drying dwell time is controlled within the range of 5s to 20s according to the production line speed). Then, it passes through a smooth metal calendering roller with a linear pressure of 300N / mm (without microgroove exhaust structure, no partitioned negative pressure, no controlled crystallization zone, and a contact surface temperature of 110℃), and finally cools and is wound up naturally.

[0093] Comparative Example 4 (low solids content, high binder formulation) prepared an aqueous PHA coating composition with a total solids content of 15 wt%. Based on solids content, it contained: 50 wt% PHBV dispersion (D... 50 =0.4μm, PDI=0.22); 0.2wt% bio-based surfactant; 5.0wt% acetyltritol citrate; 44.8wt% PVOH binder. The composition has an MFFT of 55°C at a shear rate of 1000 s. -1 The apparent viscosity is 20 mPa·s.

[0094] Comparative Example 5 (Interfacial Energy Mismatch Control): An aqueous PHA coating composition was prepared with the same component types, mass ratios, and physical properties as in Example 4. The difference was that this comparative example did not undergo corona or atmospheric plasma surface energy activation treatment; it was directly coated onto a low surface energy paper substrate C with a surface energy of 32 mN / m, and then fed into an integrated processing system. This comparative example aimed to verify the effect of substrate surface energy and coating wettability matching on film quality.

[0095] Table 4. Detailed formulations and properties of the examples and comparative examples:

[0096] This table lists the coating formulation in two parts: "Dry Film Components" and "Physical Properties of Dispersion". "Dry Film Components" refers to the material composition of the coating after drying (the sum of the mass fractions is 100%); "Physical Properties of Dispersion" refers to the colloidal parameters of the aqueous slurry in the liquid state.

[0097]

[0098] Note:

[0099] Component description: The values ​​of each "dry film component" in the table represent the mass percentage (wt%) of the substance in the final dried coating, and the sum of each dry film component column is 100%.

[0100] Explanation of solid content: The “Total solid content” in the table represents the percentage of solid matter in the aqueous dispersion relative to the total mass of the dispersion (solids + water).

[0101] Viscosity test conditions: Apparent viscosity was measured at a shear rate of 1000 s. -1The following measurements were taken.

[0102] Comparison scale explanation:

[0103] Comparative Example 1: No functional additives were added, resulting in an excessively high minimum film-forming temperature (MFFT).

[0104] Comparative Example 2: High binder content, large particle size, and low solid content resulted in abnormally high viscosity and poor film density of the system.

[0105] Comparative Example 3: The formulation is the same as in Example 1, and it is used to verify the difference between conventional processes and the integrated process of the present invention in subsequent application examples.

[0106] Comparative Example 4: Simulating a system with low solids content and high PVOH content to characterize the upper limit of binder dosage and its negative impact on barrier properties.

[0107] Comparative Example 5: The formulation and physical properties are the same as in Example 4, but in the application example, an untreated low surface energy substrate C is used to verify the surface energy matching of the substrate.

[0108] Application example:

[0109] The following application examples aim to verify the adaptability and stability of the integrated method and system of the present invention to various waterborne PHA coating compositions under different operating conditions.

[0110] Coating method and coating amount measurement instructions: The application examples in this application can use single-sided coating methods such as slot die, doctor blade, or rod coating; the "coating amount 8g / m² ± 0.5g / m²" refers to the dry coating amount. For a coating composition with a given total solids content, its wet coating amount is calculated using the following formula: Wet coating amount (g / m²) = Dry coating amount / CS, where CS is the mass fraction of the total solids content (e.g., when the total solids content is 40wt%, CS = 0.40). The dry coating amount is obtained by cutting samples of a specified area from the same substrate before and after coating, drying them at 105℃ to constant weight, and then calculating the difference in mass per unit area.

[0111] General configuration of integrated processing system:

[0112] The system used in this embodiment of the invention includes a pre-conditioning unit, a graded pressure hot pressing unit, a controlled crystallization chamber, a quenching and shaping component, and a central control system, arranged sequentially along the substrate running direction. Unless otherwise stated, in each application example, the coated wet film is introduced into the online integrated processing system within 0.5s to 60s after the completion of the final coating; after pre-conditioning, the temperature of the film surface and the interface between the film and the substrate is made to reach 5°C to 60°C above the minimum film-forming temperature of the aqueous dispersion, and the overall moisture content of the substrate is adjusted to 3wt% to 10wt%; the zoned negative pressure and linear pressure of the first pressure zone are adjusted through online moisture content feedback closed-loop regulation to achieve a steam exhaust efficiency η≥80%.

[0113] The pre-conditioning zone utilizes a combination of infrared and hot air. The graded pressure hot pressing unit possesses high heat flux density heating capability, supporting heating source temperatures up to 400℃. This capability is achieved through high-frequency electromagnetic induction heating, a high-temperature heat transfer oil circulation system, or an array of high-power electric heating elements. This unit consists of a heated main roller and an annular continuous strip pressed together to form at least two pressing zones; the annular continuous strip is made of high-temperature resistant, high-thermal-conductivity seamless metal strip or carbon fiber reinforced composite material strip. The working surface of the first pressure zone has microgrooves or porous structured interfaces, such as herringbone microgrooves, with steam exhaust capacity, and is connected to the partitioned negative pressure chambers via a radial multi-chamber negative pressure distributor. In application examples 1, 2, 4, and 5 of this application, the first pressure zone uses a seamless metal strip with herringbone microgrooves. The characteristic size of the microgrooves is 10 μm to 300 μm, preferably 80 μm to 200 μm, and the surface opening ratio is 1% to 15%, preferably 5% to 10%. In application example 3, the first pressure zone uses a porous sintered material strip with an average pore size of 10 μm to 300 μm, preferably 30 μm to 100 μm, and a porosity of 1% to 15%, preferably 5% to 12%. The partitioned negative pressure chambers are divided into at least two independent zones along the substrate running direction and pressure controlled separately. The negative pressure of each zone is set to 200 Pa to 9000 Pa. The system is equipped with an edge air curtain isolation device and a high-temperature safety interlock device. The controlled crystallization chamber is equipped with a temperature and humidity system that supports precise control of ΔTd from 5°C to 15°C.

[0114] Application Example 1: Medium-speed PHB coating.

[0115] Experimental Description: This application example aims to verify the stability of the integrated processing method of the present invention under medium-speed coating conditions. The formulations described in Examples 1 to 5 and the formulations / conditions of Comparative Examples 1 to 5 were used. The coating substrate was paper substrate A with a basis weight of 150 g / m² (except for Comparative Example 5, which consistently used paper substrate C). The coating amount was controlled at 8 g / m² ± 0.5 g / m². The experiment was conducted on a coating pilot line equipped with the integrated processing system of the present invention, with the production line speed set at 150 m / min. Approximately 2.0 s after the final coating (meeting the interval requirement of 0.5 s to 60 s), the wet film was introduced into the processing system. The pre-conditioning zone was heated by infrared radiation to raise the film surface temperature to 80°C, and the substrate moisture content was controlled at 6 wt%. The linear pressure of the first pressure zone (exhaust zone) was set at 150 N / mm, with an exhaust efficiency η of approximately 88%. The linear pressure of the second pressure zone (dense zone) was 300 N / mm, the heating source temperature was set at 220℃, and the measured contact surface temperature was 140℃. The ambient temperature of the controlled crystallization zone was 55℃, the dew point difference ΔTd was controlled at 10℃, and the residence time was 20 seconds. It was then air-cooled for quenching and shaping.

[0116] Table 5. Coating performance test results for Application Example 1:

[0117]

[0118] Analysis: Experimental results show that, under medium-speed conditions of 150 m / min and the integrated process parameters set by this invention, the coatings of Examples 1 to 5 all exhibit excellent barrier and mechanical properties. Specifically, the oxygen transmission rate (OTR) of the sample samples was stable between 75 and 115 cm³ / m²·day, the water vapor transmission rate (WVTR) was less than 30 g / m²·day, and the Cobb value was controlled within the range of 3-5 g / m², indicating that the coating was dense and without obvious defects. The pinhole density test results were all less than 0.05 pins / cm², confirming that the microgroove exhaust structure of the first pressure zone, combined with the partitioned negative pressure, effectively eliminated interfacial vapors and avoided micropores caused by the Leidenfrost effect. In contrast, Comparative Example 1, due to the lack of functional additives, resulted in an excessively high film-forming temperature, failing to achieve complete densification under the same hot-pressing conditions, with an OTR as high as 210 cm³ / m²·day. Comparative Examples 2 and 4, due to excessively high binder content or excessively low solid content, exhibited increased hydrophilicity (Cobb value > 10 g / m²) and a significant decrease in barrier properties. Although Comparative Example 5 used the superior formulation of Example 4, its application to a low surface energy substrate C without surface activation led to severe wet film shrinkage and extremely poor leveling, resulting in a pinhole density as high as 2.5 pins / cm², and a WVTR deteriorating to 135 g / m²·day, verifying the importance of substrate surface energy matching. Furthermore, the crystallinity Xc of the example samples remained above 30% (above 50% for the PHB-based sample), and the heat-sealing strength was approximately 2.0 N / 15 mm, verifying that the controlled crystallization region with a 10°C dew point difference successfully induced perfect crystal growth. Experimental results show that this process window can effectively balance the requirements of mass transfer exhaust and heat transfer densification.

[0119] Application Example 2: High-speed PHBV coating limit verification.

[0120] Experimental Description: This application example aims to verify the effectiveness of the integrated processing method of the present invention under extreme high-speed coating conditions. The formulations / conditions of Examples 1 to 5 and Comparative Examples 1 to 5 were used, and the coating was applied to paper substrate A (Comparative Example 5 used paper substrate C). The coating amount was controlled at 8 g / m² ± 0.5 g / m². The production line speed was set to 1200 m / min. The moisture content after pre-conditioning was 5%. First pressing zone: linear pressure 300 N / mm, negative pressure 8000 Pa, exhaust efficiency η = 82%. Second pressing zone: linear pressure 800 N / mm, heating source temperature set to 400℃, measured contact surface temperature = 155℃. Controlled crystallization: ambient temperature = 60℃, ΔTd = 12℃, residence time 3 s. Under these high-speed conditions, the contact residence time in each zone is extremely short, placing extremely high demands on heat flux density and mass transfer efficiency.

[0121] Table 6. Coating performance test results for Application Example 2:

[0122]

[0123] Analysis: At the limiting linear velocity of 1200 m / min, conventional coating processes often fail due to insufficient heat supply or poor vaporization and exhaust. However, data from this application example show that by increasing the heat source temperature to 400°C, the contact surface temperature of the second pressure zone was successfully maintained at 155°C, ensuring that the PHA particles acquired sufficient melting energy within an extremely short contact time (milliseconds). The WVTR of Examples 1 to 5 remained at a low level of 28-40 g / m²·day, and the pinhole density was controlled below 0.1 pins / cm², demonstrating the effectiveness of the high heat flux density compensation mechanism. In particular, Example 5 (nano-sized PHBV) achieved the best barrier performance at high speeds (OTR of 90 cm³ / m²·day and WVTR of 28 g / m²·day) due to its faster melting response. In contrast, the performance of Comparative Examples 1-4 deteriorated significantly, with OTRs generally exceeding 260 cm³ / m²·day. Comparative Example 5, under high-speed shearing, experienced severe film breakage due to insufficient interfacial wetting force, with pinhole density surging to 3.5 pins / cm², almost completely losing its barrier function (OTR of 450 cm³ / m²·day). This indicates that in high-speed coating, in addition to thermodynamic conditions, interfacial rheological matching (surface energy) is more critical. Furthermore, despite a residence time of only 3 seconds, under precisely controlled humidity conditions of ΔTd=12℃, the crystallinity of the example samples still reached 42%-58%, ensuring basic heat-sealing performance.

[0124] Application Example 3: Control of slow crystallization materials.

[0125] Experimental Description: This application example verifies the control of processing difficulties for slow-crystallizing PHA materials (such as P34HB). The formulations / conditions of Examples 1 to 5 and Comparative Examples 1 to 5 were used, coated onto paper substrate B (Comparative Example 5 used paper substrate C), with the coating amount controlled at 8 g / m² ± 0.5 g / m². The production line speed was 900 m / min. First pressing zone: linear pressure 200 N / mm, using a porous sintered material belt (with a microporous structure), negative pressure 6 kPa, η = 85%. Second pressing zone: linear pressure 500 N / mm, heating source temperature set to 360℃, measured contact surface temperature = 130℃. Controlled crystallization: ambient temperature = 50℃, ΔTd set to 7℃ (relative humidity high), residence time 15 s. This condition promotes chain segment movement through a high-humidity environment, accelerating the arrangement of the slow-crystallizing material.

[0126] Table 7. Coating performance test results for Application Example 3:

[0127]

[0128] Analysis: The experimental data highlights the importance of controlled crystallization parameter adjustment for slow-crystallizing materials. For Example 3 (P34HB formulation), setting the dew point difference ΔTd to 7°C (i.e., higher relative humidity) effectively promoted the relaxation and movement of molecular chain segments, achieving 44% crystallinity within just 15 seconds, meeting the requirements of high-performance applications. In contrast, P34HB typically struggles to fully crystallize in an online process under conventional drying conditions. Under these conditions, the coating of Example 3 balanced flexibility (a characteristic of P34HB) and barrier properties (WVTR of 35 g / m²·day), and achieved a heat-sealing strength of 1.7 N / 15 mm, solving the problems of stickiness and difficulty in winding this type of material. Other examples also maintained good overall performance. Comparative samples, due to their inherently weak crystallization ability or poor film-forming properties, did not achieve significant performance improvements under high humidity and heat conditions. Comparative Example 5 showed poor substrate wettability and extremely weak adhesion between the coating and the substrate. Under the high humidity environment of the controlled crystallization zone, moisture intrusion into the interface caused localized peeling of the coating, with a Cobb value as high as 25 g / m². This further confirms that substrate treatment is a prerequisite for ensuring the effectiveness of subsequent processes.

[0129] Application Example 4: Surface activation linkage.

[0130] Experimental Description: This application example verifies the synergistic effect of surface energy activation and integrated coating, particularly for low surface energy substrates. The formulations / conditions of Examples 1 to 5 and Comparative Examples 1 to 5 were used to coat a low surface energy paper substrate C, with the coating amount controlled at 8 g / m² ± 0.5 g / m². An additional step was added: a corona treatment with an energy of 180 mJ / cm² was performed before coating, increasing the substrate surface energy from 32 mN / m to 50 mN / m. The production line speed was 500 m / min. Subsequent process parameters were the same as in Application Example 1, with the linear pressure of the first pressing zone (exhaust zone) adjusted to 250 N / mm, the linear pressure of the second pressing zone (dense zone) maintained at 300 N / mm, and other parameters remaining unchanged. Comparative Example 5 served as a blank control group without surface activation under the experimental conditions.

[0131] Table 8. Coating performance test results for Application Example 4:

[0132]

[0133] Analysis: After corona treatment of the low surface energy substrate C, Example 4 (mixed modified formulation) achieved excellent interfacial bonding, with the Cobb value decreasing to 3 g / m², indicating a tight bond between the coating and the substrate and no interfacial leakage. The overall barrier performance of Examples 1-5 was even slightly better than that of Application Example 1 (paper substrate A), thanks to the improved leveling properties of the wet film and reduced microscopic defects resulting from surface activation. In contrast, Comparative Example 5, which did not undergo surface treatment, exhibited severe pinholes and substrate exposure, failing to form a continuous coating, with extremely deteriorated data (OTR of 380 cm³ / m²·day and pinholes of 3.0 / cm²), demonstrating that even with an excellent formulation (Example 4 formulation), film formation is impossible on low-energy surfaces without surface activation. Although Comparative Examples 1-4 underwent corona treatment, they still exhibited high Cobb values ​​(12-15 g / m²) and pinhole densities due to poor rheological properties or film-forming properties of the formulation itself, indicating that simply improving the surface energy of the substrate is insufficient to compensate for formulation defects; the optimized coating composition of this invention is necessary to achieve optimal performance.

[0134] Application Example 5: Low-speed thick coating.

[0135] Experimental Description: This application example verifies the process adaptability under low-speed, thicker coating conditions. The formulations / conditions of Examples 1 to 5 and Comparative Examples 1 to 5 were used, and the coating was applied to paper substrate A (Comparative Example 5 used paper substrate C). The coating amount was controlled at 8 g / m² ± 0.5 g / m². The production line speed was 50 m / min. First pressing zone: linear pressure 50 N / mm, negative pressure 200 Pa, exhaust efficiency η = 92%. Second pressing zone: linear pressure 100 N / mm, heating source temperature set at 90℃, measured contact surface temperature = 90℃. Controlled crystallization: ambient temperature = 45℃, ΔTd = 5℃, residence time 60 s. Sufficient heat supply was maintained at low speed; the focus was on preventing overheating and ensuring uniform crystallization.

[0136] Table 9. Coating performance test results for Application Example 5:

[0137]

[0138] Analysis: Under low-speed conditions of 50 m / min, the sample from the examples obtained the best barrier data among all experimental groups, with Example 5 showing a WVTR as low as 20 g / m²·day and an OTR of 75 cm³ / m²·day. This indicates that with sufficient heating time and a long crystallization residence time (60 s), the PHA coating can form an extremely well-developed crystal structure (generally with high Xc). Setting the heating source temperature to 90°C is sufficient to maintain effective densification, avoiding rheological runaway caused by excessively high temperatures. However, the improvement of Comparative Examples 1-4 is limited. Although the heat is sufficient, the density of their microstructure cannot be compared with the examples due to the lack of necessary plasticizers or nucleating agents in the formulation. Comparative Example 5, due to its long leveling time but poor wetting power, is prone to agglomeration into droplets at low speeds, resulting in the continued presence of pinholes (2.0 pinholes / cm²), and a Cobb value of 20 g / m² indicating leakage channels at the interface. This further confirms the robustness of the coating composition of the present invention under a wide process window and the necessity of substrate matching.

[0139] Application Example 6: No exhaust steam structure operation (process comparison example).

[0140] Experimental Description: This application example serves as a process comparison example, aiming to verify the necessity of micro / nano-structured exhaust interfaces. Under the same line speed (150 m / min), substrate, and coating amount as Application Example 1, the formulations / conditions of Examples 1 to 5 and Comparative Examples 1 to 5 were used. The first pressure zone of the graded pressure hot-pressing zone was replaced with a regular smooth roller, and the partitioned negative pressure was turned off; the remaining process conditions were the same as in Application Example 1. Under these conditions, interfacial vapors could not be effectively exhausted.

[0141] Table 10: Coating performance test results for Application Example 6:

[0142]

[0143] Analysis: The experimental results showed a catastrophic performance decline. Compared to Application Example 1, the pinhole density of all samples surged from <0.05 pins / cm² to over 2.0 pins / cm², with the OTR of Example 1 exceeding 500 cm³ / m²·day. This is directly attributed to the inability of the "smooth roller + no negative pressure" configuration to expel the steam generated by the wet film during high-temperature contact, leading to a severe Leidenfrost effect at the interface. The steam broke through the film layer, forming numerous micropores and bubbles. Not only was the barrier performance completely lost (WVTR > 130 g / m²·day), but the Cobb value also deteriorated to over 25 g / m², indicating that the coating had lost its continuity. Comparative Example 5 suffered from the double blow of "poor interfacial steam venting" and "poor substrate wetting," exhibiting the worst performance (4.0 pins / cm², Cobb value 40 g / m²), with the coating almost completely flaking off in powder form. This stark contrast in data powerfully demonstrates the decisive role of the "micro-nano structured contact interface with steam exhaust capability" and the "zoned negative pressure" design in suppressing high-speed hot-pressing defects in this invention.

[0144] Application Example 7: Low heat flux density operating conditions (process comparison).

[0145] Experimental Description: This application example simulates the failure of conventional low heat flux density equipment at high speeds. Under the same substrate and coating amount conditions as Application Example 1, the linear speed was increased to 500 m / min. The formulations / conditions of Examples 1 to 5 and Comparative Examples 1 to 5 were used respectively. The upper limit of the heating source temperature in the second pressure zone of the graded pressure hot pressing zone was limited to 180°C (the limit of conventional heat-conducting oil rollers). Under this condition, the measured contact surface temperature was only 75°C, far below the lower limit of 90°C required by this invention.

[0146] Table 11. Coating performance test results for Application Example 7:

[0147]

[0148] Analysis: Data shows that when the heating source temperature is limited, causing the contact surface temperature to drop to 75°C, even with excellent formulations (such as Examples 1-5), a qualified barrier coating cannot be formed. OTR is generally above 300 cm³ / m²·day, and WVTR is around 200 g / m²·day, indicating that PHA particles only exhibited extremely limited adhesion and did not achieve true melt flow and densification. This verifies the requirement in this invention that the contact surface temperature must be maintained within the range of 90°C to 160°C. At a linear velocity of 500 m / min, the heat carried away per unit time is enormous. If a high heat flux density heat source of up to 400°C is lacking for dynamic compensation, the contact surface temperature will rapidly drop below the film-forming temperature, leading to a "raw material" phenomenon. In Comparative Example 5, due to the untreated substrate, the particles were even more difficult to spread on the surface. Furthermore, insufficient heat prevented them from being driven and melted, resulting in a discontinuous island-like coating distribution and complete performance failure. Even formulations with low MFFT (such as in Example 5) struggle to achieve densification within millis seconds at 75°C, demonstrating the indispensability of high heat flux density compensation mechanisms for high-speed production.

[0149] Application Example 8: Formula Defect Condition (Formula Comparison Example).

[0150] Experimental Description: This application example aims to evaluate the impact of formulation defects on final performance. Under the same line speed (900 m / min), substrate, coating amount, and optimized process parameters as Application Example 3, the formulation performance of Comparative Example 2 was primarily tested. Comparative Example 2, characterized by a low solids content (20%) and a high binder mass fraction (17%), represents a typical "poor formulation." The performance of other formulations and the comparative example was also examined.

[0151] Table 12. Coating performance test results for Application Example 8:

[0152]

[0153] Note: Comparative Example 3 here refers to a test conducted using the same formulation as in Example 1, but with the conventional process described in Comparative Example 3, namely hot air and a smoothing roller.

[0154] Analysis: This application example focuses on the adaptability of different formulation systems under high-speed conditions of 900 m / min and the optimized process parameters of this invention (optimized for slow-crystallizing materials).

[0155] First, the synergistic effect of the superior formulation and process is significant: Examples 1 to 5, with their optimized particle size distribution (0.2 μm to 2.0 μm), suitable additive compounding and high solid content design, all exhibit excellent barrier properties (OTR≤125 cm³ / m²·day, WVTR≤35 g / m²·day) and extremely low pinhole density under the high heat flux density and controlled crystallization of the system of the present invention.

[0156] Secondly, the limitations of inferior formulations cannot be compensated for by equipment alone: ​​Comparative Example 2 (high binder, low solids content, large particle size 2.5μm), even after being treated by the system of this invention, still had a WVTR as high as 95 g / m²·day and a Cobb value of 18 g / m², indicating that large particles larger than 2.0 μm severely hindered the formation of a dense continuous phase. Comparative Example 5, even using a superior formulation (same as Example 4), suffered from an OTR as high as 330 cm³ / m²·day due to neglecting substrate matching (untreated substrate C), resulting in liquid film rupture at high speeds. This demonstrates that the formulation, process, and substrate must be matched.

[0157] Finally, process comparison verification: Although Comparative Example 3 used the same high-quality formula as Example 1, due to the use of conventional process (lack of exhaust and controlled crystallization), its performance (OTR of 250 cm³ / m²·day) was far inferior to that of Example 1 (OTR of 110 cm³ / m²·day).

[0158] In summary, the acquisition of high-performance waterborne PHA coated products depends on the synergistic effect of 'formulation with specific particle size (0.2μm-2.0μm) and rheological properties' and 'integrated exhaust and densification process', neither of which can be omitted.

[0159] Application Example 9: Uncontrolled crystallization condition (process comparison).

[0160] Experimental Description: This application example verifies the impact of the controlled crystallization region on the final product performance. Under the same line speed (150 m / min), substrate, and coating amount as Application Example 1, the formulations / conditions of Examples 1 to 5 and Comparative Examples 1 to 5 were used. The humidification system in the controlled crystallization region was turned off, and the ambient relative humidity was set to natural (20%). At this point, the dew point difference ΔTd > 20°C, significantly deviating from the target window of 5-15°C. The remaining process parameters were the same as in Application Example 1.

[0161] Table 13. Coating performance test results for Application Example 9:

[0162]

[0163] Analysis: Without precise humidity control, the performance of the sample examples showed a significant decline. Taking Example 1 as an example, the crystallinity plummeted from 58% to 35%, and the heat-sealing strength dropped from 2.1 N / 15 mm to 0.9 N / 15 mm. This is because in a dry environment (ΔTd > 20°C), the solvent water evaporated too quickly, and the PHA molecular chains were "frozen" in an amorphous state before they could arrange themselves properly, resulting in an imperfect crystal structure and severely affecting the material's cohesive strength and barrier properties (OTR increased to 180 cm³ / m²·day). For Example 3, which crystallized slowly, the impact was even more severe, with a crystallinity of only 24%. In Comparative Example 5, under dry conditions, due to the already weak interfacial bonding, rapid solvent shrinkage caused the coating edges to curl and peel, further deteriorating the performance (Cobb value 28 g / m²). This result strongly demonstrates the crucial role of the "controlled crystallization region" and its ΔTd parameter window (5-15°C) proposed in this invention in regulating the microstructure of PHA and ensuring the final physical properties of the product during online production.

[0164] Application Example 10: Evaluation of hydrophobicity and surface energy.

[0165] Experimental Description: This application example evaluates the surface wetting properties of the coating. Under the medium-speed conditions of Application Example 1 (linear speed 150 m / min, paper substrate A, coating amount 8 g / m² ± 0.5 g / m², and the same integrated processing parameters), samples were prepared using the coating compositions / conditions of Examples 1 to 5 and Comparative Examples 1 to 5, respectively, with the coating amount controlled at 8 g / m² ± 0.5 g / m². Using a contact angle meter, the water contact angle of deionized water was measured at (23 ± 2) °C according to ISO / TS 14778:2021 (characterized by the static contact angle at a specified time point after drop addition); and the contact angles of deionized water and diiodomethane probe solutions were measured according to ISO 19403-2:2024. The surface free energy of the coating was calculated using the Owens-Wendt-Rabel-Kaelble method.

[0166] Table 14. Results of static water droplet contact angle and surface energy tests in Application Example 10:

[0167]

[0168] Analysis: Test results show that the coatings of Examples 1 to 5 generally exhibit high static water contact angles (92°-100°) and low surface free energy (28-36 mN / m), demonstrating excellent hydrophobicity. Example 5, in particular, achieved a contact angle as high as 100°, which is closely related to its dense nanostructure and hydrophobic PHA matrix. Conversely, the contact angles of the comparative samples were mostly below 84°. Although Comparative Example 5 used a high-quality formulation, the film formation quality on the low-energy surface was extremely poor, resulting in uneven surface roughness and numerous pinhole defects. This led to a macroscopically measured contact angle of only 80° and a relatively high surface free energy (39 mN / m), indicating that coating integrity is a prerequisite for achieving hydrophobic functionality.

[0169] Application Example 11: Evaluation of repulping and recyclability.

[0170] Experimental Description: This application example evaluates the environmental recyclability of coated products. Coated paper samples obtained under the conditions of Application Example 1 (coating amount controlled at 8 g / m² ± 0.5 g / m²) were selected, corresponding to Examples 1 to 5 and Comparative Examples 1 to 5, respectively. Wet dissociation was performed using a standard pulp dissociator at (20 ± 2) °C according to ISO 5263-1:2004, with dissociation time and speed performed according to the standard. After dissociation, undissociated flakes were removed by passing the pulp through a standard sieve conforming to ISO 5263-1. The dry weight of the fibers under the sieve was weighed and the fiber recovery rate was calculated, while the mass fraction of residue on the sieve was recorded. The dispersibility, sediment, and appearance of the obtained pulp were then scored according to "Paper and paperboard—Laboratory test methods for recyclability—Part 1: Paper mills using conventional processes, 3rd edition (2025)," resulting in a comprehensive repulping score of 0–100.

[0171] Table 15 Results of the evaluation of repulping properties and recyclability in Application Example 11:

[0172]

[0173] Analysis: The data shows that the samples from the embodiments of this invention exhibit excellent repulping performance. The fiber recovery rates of Examples 1-5 are all above 93%, and the overall CEPI score exceeds 88 points, reaching the "easy to recycle" level. This is attributed to the appropriate interfacial bonding between the PHA coating and the paper substrate. In contrast, the comparative sample has a lower recovery rate. Although the formulation of Comparative Example 5 is biodegradable, the discontinuous coating film formation results in a large number of tiny flakes rather than a uniform fiber suspension, leading to a high residue content on the screen (3.5%) and a tendency to form "adhesives" in the papermaking system, resulting in a score of only 75 points. This confirms that the product of this invention achieves high performance while also optimizing the recycling characteristics after waste disposal.

[0174] Application Example 12: Evaluation of 180-degree peel strength.

[0175] Experimental Description: This application example evaluates the interfacial bonding strength between the coating and the substrate. Under the medium-speed conditions of Application Example 1 (linear speed 150 m / min, paper substrate A, coating amount 8 g / m² ± 0.5 g / m², and the same integrated processing parameters), samples were prepared using the coating compositions / conditions described in Examples 1 to 5 and Comparative Examples 1 to 5, respectively, with the coating amount controlled at 8 g / m² ± 0.5 g / m². The coated paper sample (coated surface) was hot-pressed with the same paper substrate at 120°C to 150°C, 0.2 MPa to 0.4 MPa, and 0.5 s to 2.0 s to prepare a 180-degree peel test specimen with a width of 15 mm. Subsequently, the 180-degree peel strength between the polyhydroxyalkanoate coating and the same paper substrate was determined according to GB / T2792-2014 at (23 ± 2)°C, and expressed as N / 15 mm.

[0176] Table 16 Results of the 180-degree peel strength test in Application Example 12:

[0177]

[0178] Analysis: Peel strength test results show that the coatings of Examples 1 to 5 formed a strong bond with the paper substrate, with peel strengths ranging from 1.5 N / 15 mm to 1.8 N / 15 mm, meeting the anti-delamination requirements during packaging processing and use. This good interfacial bonding stems from the precise control of substrate moisture content in the pre-conditioning zone and the high-temperature densification effect in the hot-pressing zone of the present invention. In contrast, the peel strengths of Comparative Examples 1-4 were significantly lower (1.0-1.2 N / 15 mm). Comparative Example 5 had the lowest peel strength, only 0.6 N / 15 mm. This is because the aqueous dispersion could not effectively wet and penetrate on the unactivated low surface energy substrate, resulting in weak physical adsorption rather than mechanical anchoring at the interface, making the coating extremely prone to peeling off in whole sheets.

[0179] Experimental Results and Analysis:

[0180] In summary, based on the experimental data from all application examples, this invention provides a comprehensive verification and mechanism analysis of the integrated processing technology for aqueous PHA coating wet films:

[0181] Correspondence between process window and performance: First, experiments confirmed that the numerical ranges of linear velocity, heating source temperature, linear pressure, contact surface temperature, and dew point difference ΔTd given in the aforementioned process window of this invention have a clear correspondence with the stable, dense, and high-barrier performance of the waterborne PHA coating wet film under high-speed coating conditions. Examples 1 to 5, and Application Examples 10 to 12, all exhibited excellent oxygen permeability (OTR≤125cm³ / m²·day), water vapor permeability (WVTR≤35g / m²·day), and Cobb value (≤7g / m²), which are significantly improved compared to the comparative samples that did not use the process window of this invention.

[0182] The criticality of substrate surface energy matching: The failure of Comparative Example 5 in all application examples (high pinholes, low peel strength) profoundly reveals the importance of substrate surface energy matching. In particular, in Application Examples 4 and 12, Comparative Example 5, due to the lack of surface activation, showed a stark contrast to Example 4, with peel strength plummeting from 1.6 N / 15 mm to 0.6 N / 15 mm and pinhole density surging. This demonstrates that for hydrophobic substrates, surface energy activation is a prerequisite for ensuring coating spread and interfacial bonding, and is indispensable.

[0183] High-speed hot pressing densification and thermal compensation mechanism: A comparison between Application Example 2 and Application Example 7 reveals the crucial role of high heat flux density compensation. At the limiting linear velocity of 1200 m / min, conventional heating alone (such as the contact surface temperature of only 75°C in Application Example 7) leads to severe "raw material" phenomenon and a significant decrease in barrier performance. However, this invention, by increasing the heating source temperature to 400°C, ensures that the contact surface temperature is maintained within the effective range of 90°C to 160°C, providing sufficient enthalpy change energy to allow PHA particles to complete the phase transition process from softening to melting within millis-second contact time.

[0184] Interfacial venting and enhanced microstructure mass transfer: The stark contrast between Application Example 6 and Application Example 1 demonstrates the indispensability of "micro / nano-structured contact interfaces with venting capabilities" and "regional negative pressure." In conventional smooth roll calendering processes without venting structures, the high-pressure steam generated instantaneously at the interface cannot escape, triggering the Leidenfrost effect and causing the pinhole density of the coating to surge to over 2.0 pins / cm², resulting in complete loss of barrier properties. In contrast, this invention maintains the venting efficiency η above 80% through microgrooves or porous media, effectively eliminating gas film resistance and ensuring physical contact and densification of the hot-pressed interface.

[0185] Controlled crystallization kinetics: Data from Application Examples 3 and 9 show that the controlled crystallization region is the core unit determining the mechanical properties and heat-sealing strength of the final product. For slow-crystallizing materials (such as P34HB), simple hot pressing is insufficient to induce optimal crystal growth. By precisely controlling the dew point difference ΔTd between 5°C and 15°C (e.g., 7°C in Application Example 3), a suitable plasticizing environment was created, promoting the relaxation and rearrangement of molecular chain segments, significantly increasing the crystallinity Xc to over 40%, thereby solving the problems of coating stickiness and roll-up adhesion.

[0186] In summary, this invention achieves efficient vapor removal, densification, and controlled crystallization of waterborne PHA wet films through an integrated process of pre-conditioning, graded pressure hot pressing, controlled crystallization, and quenching and shaping within a wide process window of 50 m / min to 1200 m / min. This results in paper-based waterborne PHA barrier coating products with excellent barrier properties, high heat-sealing strength, and easy recyclability. Stable industrial production can be achieved through online sensor arrays and multivariable closed-loop control.

[0187] Those skilled in the art should understand that the above embodiments are merely exemplary and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the technical solutions of the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for integrating high-throughput steam exhaust, hot-press densification, and controlled crystallization of an aqueous PHA-coated wet film, suitable for production line speeds from 50 m / min to 1200 m / min, characterized in that... Includes the following sequential steps: Step 1. Apply an aqueous dispersion containing PHA onto a paper or paperboard substrate to obtain a coated wet film substrate; Step 2. Within 0.5s to 60s after the final coating is completed, the coated wet film substrate is introduced into the online integrated processing system to obtain the substrate to be processed; Step 3. Pre-conditioning zone: By non-contact energy input, the wet film rheological properties and substrate moisture content of the substrate to be treated are adjusted so that the temperature of the film surface and the interface between the film and the substrate reaches 5°C to 60°C above the minimum film-forming temperature of the aqueous dispersion, while the overall moisture content of the substrate is adjusted to 3wt% to 10wt% to obtain the pre-conditioning substrate. Step 4. Graded pressure hot pressing zone: At least two adjacent contact-type high-flux heat transfer zones along the substrate running direction are set up to enhance interfacial mass transfer and densify the pre-conditioned substrate; the first pressure zone, i.e., the exhaust zone, uses a linear pressure of 50 N / mm to 300 N / mm to force the water vapor and entrained gas in the wet film to be discharged through the contact interface with exhaust capacity, so as to achieve an exhaust efficiency η≥80%; the second pressure zone, i.e., the densification zone, uses a linear pressure of 100 N / mm to 800 N / mm to promote the fusion and densification of PHA particles; wherein the contact surface temperature of the second pressure zone is maintained at 90℃ to 160℃ to obtain a densified substrate; Step 5. Controlled crystallization region: The relaxation of PHA segments and crystal growth kinetics of the densified substrate are regulated and maintained in a constant temperature and humidity environment of 45°C to 65°C for 3s to 60s; wherein precise humidity control is achieved by controlling the dew point difference ΔTd within the range of 5°C to 15°C to obtain a controlled crystallization substrate; Step 6. Quenching and Shaping Zone: Through a combination of forced convection and conduction cooling, the microstructure of the coating on the controlled crystalline substrate is rapidly shaped to obtain a paper-based water-based PHA barrier coated product; Step 7. An integrated online sensor array and a multivariable closed-loop control system are used to regulate the energy input, mass transfer efficiency and phase change kinetic parameters of each zone in real time.

2. The integrated method for high-flux steam exhaust, hot-press densification, and controlled crystallization of an aqueous PHA coating wet film according to claim 1, characterized in that, The first pressure zone has a contact interface with steam exhaust capability, which is a herringbone, V-shaped, or mesh-like microgroove structure, or a porous sintered material strip. Its characteristic dimensions are in the range of 10μm to 300μm, and its surface opening ratio or porosity is 1% to 15%; and the contact interface is connected to the partitioned negative pressure chamber, with the partitioned negative pressure set to 200Pa to 9000Pa.

3. The integrated method for high-flux steam exhaust, hot-press densification, and controlled crystallization of an aqueous PHA coating wet film according to claim 1, characterized in that, The graded pressure hot pressing zone adopts a high heat flux density heating system, and the adjustable range of its heating source temperature is 90℃ to 400℃. The control system dynamically adjusts the heating source temperature according to the production line speed, the thermal properties of the substrate, and the real-time monitored contact surface temperature through a feedforward control algorithm based on the heat transfer model, in order to compensate for heat loss during high-speed operation and ensure that the contact surface temperature is stably maintained within the target window.

4. The integrated method for high-flux steam exhaust, hot-press densification, and controlled crystallization of an aqueous PHA coating wet film according to claim 1, characterized in that, When applied to medium- or low-speed or conventional coating machines, the production line speed is 50 m / min to 250 m / min, and the time interval between steps 1 and 2 is selected from 1.0 s to 60 s. When applied to high-speed coating machines or papermaking machines for online coating, the production line speed is 300m / min to 1200m / min, and the time interval between steps 1 and 2 is selected from 0.5s to 20s; and in the papermaking machine, the integrated processing system is located between the end of the drying section and the calendering section.

5. The integrated method for high-flux steam exhaust, hot-press densification, and controlled crystallization of an aqueous PHA coating wet film according to claim 1, characterized in that, The pre-adjustment in step 3 employs any one or a combination of infrared radiation, hot air convection, microwave, or dielectric heating; and uses the dew point difference ΔTd as a reference to control the local humidity of the membrane surface before entering the first pressure zone in a closed loop, so as to suppress the phenomenon of supersaturated condensation at the interface.

6. The integrated method for high-flux steam exhaust, hot-press densification, and controlled crystallization of an aqueous PHA coating wet film according to claim 1, characterized in that, The obtained polyhydroxyalkanoate barrier coating, under the conditions of preconditioning, graded pressure hot pressing, controlled crystallization, and quenching and setting according to the process window, meets at least two of the following performance indicators: OTR ≤ 110 cm³ / m²·day; WVTR ≤ 30 g / m²·day; DSC crystallinity Xc ≥ 40%; 180° peel strength ≥ 1.5 N / 15 mm; pinhole density ≤ 0.1 pins / cm²; Cobb value ≤ 5 g / m²; heat seal strength ≥ 2.0 N / 15 mm; static water droplet contact angle ≥ 92°; fiber recovery rate ≥ 92%.

7. The integrated method for high-flux steam exhaust, hot-press densification, and controlled crystallization of an aqueous PHA coating wet film according to claim 1, characterized in that, The controlled crystallization zone adjusts the residence time and dew point difference ΔTd according to the crystallization kinetics of the PHA used; for slow-crystallizing PHAs, the dew point difference ΔTd is controlled to be between 7°C and 12°C.

8. A processing system for implementing the integrated method of high-throughput steam exhaust, hot-press densification, and controlled crystallization of the aqueous PHA coating wet film as described in claim 1, characterized in that, The system comprises, arranged sequentially along the substrate running direction, a pre-conditioning unit, a graded pressure hot pressing unit, a controlled crystallization chamber, a quenching and shaping assembly, and a central control system. The graded pressure hot pressing unit possesses high heat flux density heating capability, supporting heating source temperatures up to 400°C, and can precisely control the contact surface temperature. This unit forms at least two pressing zones by pressing a heated main roller with an annular continuous strip. The strip's working surface has a micro-nano structured interface with steam exhaust capability and can optionally be connected to a partitioned negative pressure chamber. The central control system integrates a sensor array for monitoring moisture content, temperature, dew point, and linear pressure, and possesses multi-variable linkage control functions based on heat and mass transfer models and phase change dynamics. The controlled crystallization chamber supports precise environmental humidity control based on a dew point difference ΔTd of 5°C to 15°C.

9. The processing system according to claim 8, characterized in that, The high heat flux density heating capability is achieved through high-frequency electromagnetic induction heating, a high-temperature heat transfer oil circulation system, or an array of high-power electric heating elements; the annular continuous strip is a high-temperature resistant, high-thermal-conductivity seamless metal strip or a carbon fiber reinforced composite material strip; the system is equipped with a radial multi-chamber negative pressure distributor, a side air curtain isolation device, and a high-temperature safety interlock device.

10. An online control method for the processing system of claim 8, characterized in that: Using dew point, moisture content, and contact surface temperature as the main control variables, a cascaded control loop based on feedforward and feedback control is constructed. The control logic includes: dynamically adjusting the heating source temperature through a real-time heat transfer model to achieve thermal compensation based on the target values ​​of linear velocity and contact surface temperature; when the moisture content or dew point deviates from the target window, priority is given to adjusting the zone negative pressure and the linear pressure of the first pressure zone, and the linear velocity is corrected to ensure that the exhaust efficiency η≥80%; and the dew point difference ΔTd is kept within the range of 5℃ to 15℃ to stabilize the crystallization kinetic parameters.

11. An aqueous PHA coating composition applicable to the integrated method of high-flux steam exhaust, hot-press densification, and controlled crystallization of the aqueous PHA coating wet film according to claim 1, wherein the total solid content is 25 wt% to 55 wt%, and comprises, by solid content: PHA dispersions ranging from 70 wt% to 98 wt% have a median particle size D. 50 The composition has a particle size of 0.2-2.0 μm and a polydispersity index ≤0.3; 0.2 wt% to 2.5 wt% of a bio-based surfactant or polymeric stabilizer; 0 wt% to 15 wt% of a functional additive selected from bio-based plasticizers, nucleating agents, or film-forming aids; 0 wt% to 15 wt% of a water-soluble or water-dispersible bio-based binder; the composition has a minimum film-forming temperature ≤65°C and a shear rate of 1000 s⁻¹. -1 The apparent viscosity ranges from 50 mPa·s to 1000 mPa·s. The plasticizer is selected from citrate esters, glycerides, or lactates; the nucleating agent is selected from boron nitride, talc, or PHA-based self-nucleating agents; and the binder is selected from PVOH, modified starch, or cellulose nanocrystals.

12. The coated article prepared by the method according to any one of claims 1 to 7, characterized in that, Furthermore, at least one side of the substrate has a dense waterborne PHA barrier coating prepared by the method described in any one of claims 1 to 7.

13. A method for preparing paper-based waterborne PHA barrier coated articles on a coating machine or papermaking machine, suitable for production line speeds from 50 m / min to 1200 m / min, characterized in that, Includes the following sequential steps: S1. Surface Energy Activation: Before applying the final aqueous PHA dispersion, the substrate or primer is subjected to corona or atmospheric plasma treatment to achieve a surface energy of 46mN / m to 52mN / m on the surface to be coated, thus obtaining an activated substrate. S2. Applying an aqueous dispersion containing PHA: Applying an aqueous PHA dispersion to the activated substrate, and introducing the wet film into the online integrated processing system within 0.5s to 60s to obtain a coated wet film substrate; S3. Integrated processing: In the online integrated processing system, the coated wet film substrate is subjected to pre-conditioning, graded pressure hot pressing, controlled crystallization and quenching and shaping steps in sequence, specifically according to steps 3 to 6 of claim 1; wherein, the exhaust efficiency η≥80%, ΔTd is controlled between 5℃ and 15℃; and the graded pressure hot pressing zone uses a heating source with a temperature as high as 400℃ for dynamic thermal compensation to obtain a paper-based water-based PHA barrier coated product.

14. The preparation method according to claim 13, characterized in that, The preparation method includes an integrated system, which includes: a corona or atmospheric plasma treatment unit; an online integrated treatment system arranged along the substrate running direction, the system conforming to the structural features of claim 9; and a central control system capable of simultaneously collecting surface energy, dew point, moisture content, and contact surface temperature data, and realizing multi-variable linkage control with corona energy, heating source temperature, linear pressure, zoned negative pressure, and linear velocity.

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