A preparation process for a paper box used for food preservation and the food preservation paper box thereof.

Abstract

This invention discloses a preparation process for paper boxes used for food preservation and the resulting food preservation paper box, belonging to the field of packaging product technology. This invention constructs a dynamic covalent bond gradient interface and forms a strong anchoring-weak cohesive gradient structure by regulating the binding energy between fibers and functional layers, achieving a low fiber damage rate after multiple paper box cycles. A functional adaptation layer is simultaneously applied at the outlet of the paper machine's drying section, utilizing the water layer adsorbed on the fiber surface to achieve synergistic anchoring of interpenetrating network physical entanglement and chemical grafting. The core paper is micro-injected using hot press rollers, with molten chitosan-PEG graft material encapsulating softened PLA particles at 130°C, rapidly forming a mechanical interlocking structure within 2 seconds. Multi-scale synergistic slow release is achieved through spatial separation of modular slow-release tablets and electrostatically flocked citric acid. When humidity is triggered, water acts as a proton conductor at the interface, avoiding pre-reaction. Diatomaceous earth channels adsorb some NaClO2, forming a secondary release reservoir and extending the peak release time.

Description

Technical Field

[0001] This invention discloses a packaging product technology, and in particular relates to a preparation process for a paper box for food preservation and the food preservation paper box thereof. Background Technology

[0002] Fresh fruits and vegetables retain vigorous life activities after harvest, making them susceptible to microbial infection and spoilage, resulting in significant economic losses. Direct spraying of traditional chemical preservatives poses safety risks due to residues and has a short duration of action. Incorporating antibacterial agents into packaging materials to create antibacterial packaging has become a research hotspot in recent years. However, direct-contact antibacterial agents struggle to cover the irregular surfaces of fruits and vegetables, while non-contact volatile antibacterial agents (such as plant essential oils) often have strong odors that affect product flavor. Existing controlled-release packaging for preservation mostly uses films or labels, which suffer from complex processes, high costs, and reduced mechanical properties. Summary of the Invention

[0003] The purpose of this invention is to provide a preparation process for paper boxes used for food preservation and a paper box for food preservation, in order to solve the above-mentioned problems.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a preparation process for a paper box used for food preservation, comprising the following steps:

[0005] S1, face paper and core paper are prepared separately in the wet section of the paper machine;

[0006] The following components, by weight, comprise 70 parts softwood pulp and 30 parts OCC recycled pulp, mixed and beaten to 32 Schubert degrees, with 0.3-0.5 parts nanocellulose whiskers, 0.4-0.6 parts chitosan-PEG graft, 0.8 parts fluorocarbon sizing agent, and 0.2 parts boric acid-PVA dynamic gel added sequentially at the wet end.

[0007] The core pulp consists of 50 parts softwood pulp and 50 parts OCC recycled pulp mixed and beaten to 32 Schubert degrees, with 0.5 parts nanocellulose whiskers and 1.5 parts paraffin microcapsules added at the wet end.

[0008] S2, when the paperboard has a dryness of 75-80%, the functional adapter layer is applied online to the surface of the face paper using a doctor blade coater, with a wet coating amount of 6.0 g / m². 2 The functional adapter layer includes 2 parts epoxy-modified cationic starch, 0.4 parts silane coupling agent KH-560 and 1 part eutectic solvent DES;

[0009] S3, when the paperboard has a dryness of 75-80%, the functional adapter layer is applied online to the surface of the core paper using a curtain coating machine, with a wet coating amount of 7.5 g / m². 2 ;

[0010] S4. After infrared drying, air plasma treatment is performed on the surfaces of the face paper and core paper respectively, with a power of 200W and a time of 30s.

[0011] S5, the core paper is corrugated and laminated with the face paper using an adhesive. The lamination temperature is 180°C and the linear pressure is 60kN / m. The adhesive consists of 10 parts oxidized starch, 0.5 parts N,N'-methylenebisacrylamide, 2 parts carboxylated styrene-butadiene latex and 0.1 parts poly-N-isopropylacrylamide.

[0012] S6. After die-cutting, a reversible functional coating system of sodium alginate-NaClO2-diatomaceous earth mixture is formed inside the cardboard with a thickness of 0.08mm. Then, 0.5M CaCl2 solution is sprayed for cross-linking for 5 minutes to obtain the cardboard for the box.

[0013] Preferably, a polylactic acid (PLA) groove is formed in situ on the surface of the functional adaptation layer of the core paper using a hot press roller, and a NaClO2 slow-release sheet and an acid trigger sheet are configured, including the following steps:

[0014] K1, polylactic acid powder is pre-placed on the surface of the functional adaptation layer of the core paper, and hot-pressed by a hot press roller at a temperature of 130°C, a pressure of 2MPa and a time of 2s, so that the chitosan-polyethylene glycol graft in the functional adaptation layer melts to form a viscoelastic matrix, and at the same time induces the surface of the polylactic acid powder to soften. The two form a mechanical interlocking structure under pressure, and after cooling, a reversibly anchored polylactic acid PLA groove is generated in situ on the surface of the core paper.

[0015] K2, a sustained-release tablet, consists of 60% NaClO2, 30% diatomaceous earth, 5% magnesium stearate, and 5% PEG-4000, and is produced by dry compression.

[0016] K3, an acid-triggered tablet, consists of 85% citric acid, 10% microcrystalline cellulose, and 5% hydroxypropyl methylcellulose.

[0017] K4, the sustained-release tablet and the acid-triggered tablet are inserted into the polylactic acid (PLA) slot at a mass ratio of 3:4.

[0018] Preferably, in step S6, the reversible functional coating system includes:

[0019] The NaClO2 supported layer comprises the following components: 75 parts sodium alginate, 15 parts NaClO2, and 10 parts diatomaceous earth. The solids are mixed with deionized water to form a 3% solid content coating solution. A 0.5M calcium chloride solution is prepared as a crosslinking agent, with an amount of 5% of the volume of the mixed coating solution. The NaClO2 supported layer is then coated on the paperboard.

[0020] The acid-triggered layer was formed by electrostatically flocking 100 parts of citric acid micropowder onto a NaClO2 support layer, with a coating amount of 0.5 parts / 100cm².2 ;

[0021] The outer protective layer is made of a 30μm thick polyethylene film that is hot-pressed onto the acid trigger layer at 180°C.

[0022] A food preservation paper box, the paperboard is prepared by the above-mentioned preparation process, the paperboard of the paper box includes an outer protective layer, a face paper, a core paper, a functional adapter layer on the coated face paper and core paper, a citric acid micro powder flocking layer and a reversible functional coating system, and is equipped with a polylactic acid (PLA) slot formed in situ on the surface of the functional adapter layer by hot pressing interlocking, the PLA slot is equipped with a slow-release sheet and an acid trigger sheet.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] This invention constructs a dynamic covalent bond gradient interface and forms a strong anchoring-weak cohesive gradient structure by regulating the binding energy between fibers and functional layers, achieving low fiber damage rate after multiple paper box cycles. A functional adapter layer is simultaneously applied at the paper machine drying section outlet, utilizing the water layer adsorbed on the fiber surface to achieve synergistic anchoring of interpenetrating network physical entanglement and chemical grafting. The core paper is micro-injection molded using hot press rollers, where molten chitosan-PEG graft material encapsulates softened PLA particles at 130°C, rapidly forming a mechanically interlocked structure within 2 seconds. Multi-scale synergistic sustained release is achieved through spatial separation of modular sustained-release tablets and electrostatically flocked citric acid; when humidity is triggered, water acts as a proton conductor. Interfacial reactions are avoided by pre-reaction. Diatomaceous earth channels adsorb some NaClO2, forming a secondary release reservoir and prolonging the peak release time. NaClO2 is encapsulated by alginate calcium gel network, reducing the diffusion coefficient and achieving primary kinetic slow release. Consumable NaClO2 is made into slow-release tablets, which are physically isolated from the durable cardboard box body. The polylactic acid (PLA) slot insertion and extraction assembly enables on-demand adjustable loading to adapt to different fruit and vegetable respiration intensities. Furthermore, through differentiated formulation, the failure mechanisms of the face paper and core paper are staggered by 3-4 cycles. Targeted mechanical peeling → EDTA chelation → oligosaccharide penetration repair three-step process is used to achieve rapid regeneration and repair of minor damage. Attached Figure Description

[0025] Figure 1 A simplified cross-sectional diagram of the cardboard box for food storage.

[0026] Figure 2 A chart showing the dynamic changes in the decay rate (in %) as measured in the experiment;

[0027] Figure 3 A chart showing the changes in the fruit and vegetable firmness retention rate (in %) as measured in the experiment;

[0028] Figure 4 A graph showing the response thresholds for ClO2 release under different humidity levels;

[0029] Figure 5A graph showing the effect of temperature on release kinetics at 90% RH;

[0030] Figure 6 Chart showing the retention rate (in %) of mechanical properties of paper boxes after multiple cycles;

[0031] Figure 7 This is a graph showing the change (N / m) in the interfacial bonding strength of the paperboard under multiple cycles. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. In this description, it should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] A preparation process for a paper box used for food preservation includes the following steps:

[0034] S1, face paper and core paper are prepared separately in the wet section of the paper machine;

[0035] The following components, by weight, comprise 70 parts softwood pulp and 30 parts OCC recycled pulp, mixed and beaten to 32 Schubert degrees. OCC recycled pulp refers to recycled corrugated pulp from waste corrugated boxes, mainly composed of hardwood short fibers, accounting for 70%. In the wet end, 0.3-0.5 parts nanocellulose whiskers, 0.4-0.6 parts chitosan-PEG graft, 0.8 parts fluorocarbon sizing agent, and 0.2 parts boric acid-PVA dynamic gel are added sequentially.

[0036] The core pulp consists of 50 parts softwood pulp and 50 parts OCC recycled pulp mixed and beaten to 32 Schubert degrees, with 0.5 parts nanocellulose whiskers and 1.5 parts paraffin microcapsules added at the wet end.

[0037] Nanocellulose whiskers (CNF) exhibit a bridging effect, forming a three-dimensional hydrogen bond network between fibers. Their abundant surface hydroxyl groups anchor the cellulose fibers at multiple points. In the face paper, nanocellulose whiskers form anchoring nodes, while in the core paper, they form a continuous reinforcing phase. Paraffin microcapsules in the core paper have a phase change filling effect; they melt during the drying stage, capillarily penetrate into the micron-sized pores between fibers, and solidify upon cooling to form rigid support pillars, improving compression resilience. The fluorocarbon sizing agent in the face paper exhibits the directional arrangement of fluorocarbon chains, C8F... 17 - Self-assembled monolayer on fiber surface with CF3 groups facing outward to form a low surface energy barrier with a contact angle >120°; gradient pore structure, increased porosity of face paper, which is conducive to plasma penetration; increased stiffness of core paper after paraffin filling; fiber bonding mode changed from reversible hydrogen bonding to hydrogen bonding + CNF mechanical entanglement, which further enhanced bonding and reduced embrittlement rate.

[0038] S2, when the paperboard has a dryness of 75-80%, the functional adapter layer is applied online to the surface of the face paper using a doctor blade coater, with a wet coating amount of 6.0 g / m². 2 The functional adapter layer includes 2 parts of epoxy-modified cationic starch, 0.4 parts of silane coupling agent KH-560 and 1 part of eutectic solvent DES. DES is a eutectic mixture formed by mixing hydrogen bond donor HBD and hydrogen bond acceptor HBA in a certain proportion. Its melting point is significantly lower than the pure melting point of each component. The DES system here uses choline chloride-urea, and the molar ratio of choline chloride to urea is 1:2.

[0039] S3, when the paperboard has a dryness of 75-80%, the functional adapter layer is applied online to the surface of the core paper using a curtain coating machine, with a wet coating amount of 7.5 g / m². 2 ;

[0040] When the dryness is 75-80%, an adsorbed water layer exists on the fiber surface. The epoxy group -OCH2CH(O)CH2 of the epoxy-modified starch undergoes partial ring-opening etherification with the hydroxyl groups of the fiber, with a conversion rate of 35-40%, forming a graft copolymer. At the same time, the unreacted starch chains form physical entanglement with the fiber. KH-560 hydrolyzes to generate silanol group -Si-OH, which condenses with the hydroxyl groups of the fiber at one end, and the epoxy group at the other end forms a coordination pre-bonding with the carboxyl group of the subsequent coating sodium alginate.

[0041] The eutectic solvent DES has a plasticizing effect. DES breaks the hydrogen bonds between starch molecules, reduces the melt viscosity, and allows the coating to flow and spread under low pressure of 0.15MPa, avoiding high pressure compaction of fibers.

[0042] A gradient interface is constructed to form a gradient transition of fiber-ether bond-starch-hydrogen bond-calcium alginate, which improves stress transfer efficiency. During peeling, the DES plasticized layer is preferentially destroyed in the cohesive failure mode. Furthermore, since the epoxy group density on the face paper surface is greater than that on the core paper, the density of reversible anchor points can be controlled.

[0043] S4. After infrared drying, air plasma treatment is performed on the surfaces of the face paper and core paper respectively, with a power of 200W and a time of 30s; high-energy particles O2 are introduced into the air plasma through surface etching and functional groups. + N2 + e - Surface bombardment breaks CC / CH bonds and introduces oxygen-containing polar groups -COOH, -C=O, and -OH, increasing the surface energy of the fluorocarbon hydrophobic layer from 22mN / m to 40mN / m. Bombardment removes the weakly bonded layer on the surface, exposing the epoxy groups of the underlying starch layer. Plasma etching forms nano-pits on the surface with a depth of 50-100nm, increasing the mechanical bonding points with subsequent coatings. After plasma treatment, the interfacial shear strength between the calcium alginate gel and the adapter layer is improved, and the interfacial bonding energy is enhanced.

[0044] S5, the core paper is corrugated and laminated with the face paper using an adhesive. The lamination temperature is 180°C and the linear pressure is 60kN / m. The adhesive consists of 10 parts oxidized starch, 0.5 parts N,N'-methylenebisacrylamide, 2 parts carboxylated styrene-butadiene latex and 0.1 parts poly-N-isopropylacrylamide.

[0045] Thermally responsive phase transition: N,N'-methylenebisacrylamide in the adhesive undergoes a volume phase transition above 60°C, exposing hydrophobic groups and relaxing the starch-MBA crosslinking network. Upon cooling, hydrogen bonds are rebuilt, forming a physical crosslinking network. Methylenebisacrylamide (MBA) forms CNC bridge bonds with bond energies lower than cellulose glycosidic bonds. These bonds can undergo hydrolytic breakage under alkaline conditions (pH 8.5) with EDTA, but remain stable at room temperature. The cardboard box uses a UV-type corrugated top curvature radius of 0.8 mm. During hot pressing, the adhesive thickness at the corrugated top decreases from 20 μm to 12 μm, forming a stress concentration zone; the thickness at the corrugated waist remains constant, providing shear buffer.

[0046] Reversible interlayer bonding with higher interlayer bonding strength than functional adapter layer ensures that the functional layer is destroyed first during cyclic peeling without damaging the corrugated structure. Hot melt-cold solidification transition: when hot-pressed at 180°C, the adhesive melts and penetrates into the pores on the surface of the core paper, and forms an anchor after cooling. MBA crosslinks allow for breakage and recombination during recycling.

[0047] S6. After die-cutting, a reversible functional coating system of sodium alginate-NaClO2-diatomite mixture is formed in the cardboard with a thickness of 0.08mm. Then, 0.5M CaCl2 solution is sprayed for cross-linking for 5min to obtain the cardboard for the box.

[0048] Reversible functional coating systems include:

[0049] The NaClO2 supported layer comprises the following components: 75 parts sodium alginate, 15 parts NaClO2, and 10 parts diatomaceous earth. The solids are mixed with deionized water to form a 3% solid content coating solution. A 0.5M calcium chloride solution is prepared as a crosslinking agent, with an amount of 5% of the volume of the mixed coating solution. The NaClO2 supported layer is then coated on the paperboard.

[0050] The acid-triggered layer was formed by electrostatically flocking 100 parts of citric acid micropowder onto a NaClO2 support layer, with a coating amount of 0.5 parts / 100cm². 2 ;

[0051] The outer protective layer is made of a 30μm thick polyethylene film, which is hot-pressed onto the acid trigger layer at 180°C.

[0052] Ca 2+ The calcium alginate coordinates with the guluronic acid in sodium alginate, forming a three-dimensional network gel through ionic cross-linking and gelation. This network gel encapsulates the NaClO2 crystals and diatomaceous earth. The porous structure of the diatomaceous earth immobilizes some of the NaClO2 through capillary adsorption, reducing its diffusion coefficient and prolonging the release time, thus achieving a controlled-release effect. The carboxyl-COO group of calcium alginate... - The epoxy and silanol groups in the functional adapter layer form hydrogen bonds and coordination bonds, and the weak bonding interface is much lower than that of the covalent bonds, ensuring that EDTA chelates Ca. 2+ The gel peels off completely; the gel has a water content of >95%, and its swelling volume increases by 15% in a high humidity environment (RH>90%), the release channels expand, the ClO2 diffusion rate accelerates, and the gel shrinks and closes when the humidity decreases during drying.

[0053] A 20kV high voltage polarizes citric acid particles, causing them to be implanted perpendicularly to the surface of a semi-wet calcium alginate gel along the electric field lines, forming a micro-spiky structure with weak physical adsorption. The carboxyl groups of citric acid form hydrogen bonds with the hydroxyl groups of sodium alginate. The flocking density is 80 strands / mm. 2 At that time, the contact point spacing is approximately 110 μm, which is less than the 200 μm characteristic length of moisture diffusion, ensuring that H is triggered by humidity. + Rapid migration, triggered non-contactly, with citric acid and NaClO2 spatially separated, located in the flocked layer and gel layer respectively, avoiding pre-reaction; under high humidity, water acts as a proton conductor, allowing H... + With ClO2 - ClO2 is generated through an interfacial reaction; citric acid particles can be detached as a whole during vibration, resulting in high recovery rate and no chemical residue.

[0054] The process involves in-situ forming of polylactic acid (PLA) slots on the surface of the functional adaptation layer of the core paper using hot press rollers, and configuring NaClO2 slow-release sheets and acid trigger sheets, including the following steps:

[0055] K1, polylactic acid powder is pre-placed on the surface of the functional adaptation layer of the core paper, and hot-pressed by a hot press roller at a temperature of 130°C, a pressure of 2MPa and a time of 2s, so that the chitosan-polyethylene glycol graft in the functional adaptation layer melts to form a viscoelastic matrix, and at the same time induces the surface of the polylactic acid powder to soften. The two form a mechanical interlocking structure under pressure, and after cooling, a reversibly anchored polylactic acid PLA groove is generated in situ on the surface of the core paper.

[0056] Through hot-press micro-injection molding, chitosan-PEG graft melts at 130°C with a viscosity of 800 Pa·s, while PLA particles have a surface softening viscosity of 500 Pa·s. The two form a 20 μm thick interpenetrating blended region under 2 MPa. After cooling, radial compressive stress is generated due to the difference in thermal shrinkage coefficients, resulting in mechanical interlocking.

[0057] K2, a sustained-release tablet, consists of 60% NaClO2, 30% diatomaceous earth, 5% magnesium stearate, and 5% PEG-4000, and is produced by dry compression.

[0058] K3, an acid-triggered tablet, consists of 85% citric acid, 10% microcrystalline cellulose, and 5% hydroxypropyl methylcellulose.

[0059] K4, the sustained-release tablet and the acid-triggered tablet are inserted into the polylactic acid (PLA) slot at a mass ratio of 3:4;

[0060] like Figure 1 As shown, a food preservation paper box is prepared by the above-mentioned preparation process. The paper box includes an outer protective layer, a face paper, a core paper, a functional adapter layer on the coated face paper and core paper, a citric acid micro powder flocking layer and a reversible functional coating system, and is equipped with a polylactic acid (PLA) slot formed in situ on the surface of the functional adapter layer by hot pressing interlocking. The PLA slot is equipped with a slow-release sheet and an acid trigger sheet.

[0061] Modular assembly is possible, with the card slot and the slow-release tablet forming an interference fit, which is stable but does not damage the paper surface. The whole is reversible. When retired and recycled, the polylactic acid PLA card slot-functional adapter layer is peeled off as an integrated solid unit, with a low residue rate on the core paper surface, which can be directly coated again.

[0062] Each step is implemented through a gradient design of strong anchoring and weak bonding to achieve a loop:

[0063] Fiber (strong chemical bonds) → Functional adapter layer (moderate hydrogen bonds) → Gel layer (weak coordination bonds) → Module (mechanical interlocking) → During exfoliation, the failure path prioritizes cohesive failure.

[0064] When used as a food storage box for preserving fruits and vegetables, it relies on the CO2 and moisture generated by the post-harvest physiological activities of the fruits and vegetables as natural signal sources. The humidity threshold is when the relative humidity inside the box is >85%. Moisture is generated by the respiration and transpiration of the fruits and vegetables. Through the functional adaptation layer (porosity 38-48%), moisture permeates into the calcium alginate gel layer, where the gel swelling rate is 15-20%, releasing the expanded channels. Proton supply allows the permeated water to dissolve the electrostatically flocked citric acid micropowder (pH=3.5), generating H2O. + Simultaneously, CO2 and hydration produce carbonic acid, and the dual proton source reacts with the NaClO2 fixed in the gel:

[0065] 4H + +5ClO2 - →4ClO2↑+2H2O+Cl - ;

[0066] The response time is only 2-4 hours from the increase in humidity to the release of ClO2, achieving rapid inhibition of microorganisms;

[0067] The porous structure of diatomaceous earth adsorbs approximately 30% of NaClO2 through capillary action, slowing its diffusion rate and extending the release time from 7 days to 14 days. The ionic cross-linking network of calcium alginate gel also contributes to the release of NaClO2. - The diffusion coefficient is limited to 2.1 × 10⁻⁶. -8 cm 2 / s, conforming to first-order release kinetics, avoiding sudden concentration rise; citric acid micro powder and NaClO2 are located in the flocking layer and gel layer respectively, avoiding pre-reaction, and reacting only at the interface under humidity drive, thus improving utilization;

[0068] Studies indicate that the peak concentration of ClO2 is 1.8 mg / m³. 3 It can kill 99.9% of mold and yeast on the surface within 3 hours. Ethylene can remove ClO2. ClO2 oxidizes ethylene to produce ethylene oxide, which blocks the ripening signal of fruits and vegetables. It is expected to extend the shelf life of strawberries by 3-5 days and increase the strawberry firmness retention rate by 18%. ClO2 induces an increase in the closure rate of stomata on the surface of fruits and vegetables and a decrease in the transpiration rate, thereby reducing quality loss.

[0069] Modular adaptation enables the customization of fruit and vegetable preservation solutions, for example:

[0070] Strawberries: NaClO2 concentration 9g / L, 6 sustained-release tablets;

[0071] Strawberries have a high respiration rate and require strong sterilization.

[0072] Cherry tomatoes: NaClO2 concentration 6g / L, 4 sustained-release tablets

[0073] Cherry tomatoes have a low respiration rate, so preventing water loss is their primary concern.

[0074] Blueberries: Utilizes a microporous PE outer layer to maintain an internal RH level >95%.

[0075] Blueberries develop a bloom on their surface that helps preserve them, eliminating the need for additional slow-release tablets.

[0076] The functional layers of food storage boxes can be peeled off through a process that allows for the recycling and repair of the cardboard. This process employs mechanical peeling combined with vibration and airflow. It utilizes the weak physical adhesion of the flocked layer and the low adhesion of citric acid particles. A 60°C hot water spray softens and swells the calcium alginate gel, reducing the interfacial bonding strength. Then, 50Hz high-frequency vibration causes the citric acid micropowder to detach inertial motion. Finally, 0.3MPa compressed air is used to blow away the edges and corners, achieving precise peeling. Chemical dissociation is employed, involving the breaking of EDTA chelate-coordination bonds, targeting the Ca²⁺ ions in the calcium alginate gel. 2+ - Selective disruption of carboxyl coordination bonds, EDTA chelation, 0.1M EDTA with Ca 2+ A stable complex [Ca(EDTA)] is formed. 2- The driving force is strong; at the molecular level, the four carboxyl oxygen atoms of EDTA attack Ca. 2+ The oxygen atom of the sodium alginate G unit is replaced, and the gel network is depolymerized into single chains. The dissociation is completed within 10 minutes to avoid excessive swelling of the fiber by EDTA. The final result is 100% gel dissolution, NaClO2 residue <0.1ppm, which meets the food safety threshold, and fiber damage rate of only 3.2%. Then, the microcracks of the cardboard box are healed by fiber repair. The molecular-level penetration and hydrogen bond recombination of chitosan oligosaccharides are utilized. When the oligosaccharides penetrate, chitosan with a molecular weight <5000 can penetrate into the fiber microcracks and fill the pores. Under the catalysis of hydrogen bond recombination and citric acid, the hydroxyl groups of the fiber and the amino groups of chitosan form a new hydrogen bond network, repairing the broken hydrogen bonds. The final result is that the ring crush strength of the repaired fiber is restored to 90%, and the cycle life is extended by 3-4 times.

[0077] A controlled experiment was designed to verify the advantages of the food preservation box of this application in terms of preservation effect, cycle stability, and intelligent responsiveness. The experimental groups are shown in Table 1 below:

[0078] Table 1. Experimental Groups (Randomized Block Design, n=15)

[0079] ;

[0080] Storage conditions:

[0081] Temperature: 20±1°C;

[0082] Humidity: 90±5%RH;

[0083] Time: 0, 2, 4, 6, 8, 10 days;

[0084] The evaluation indicators and measurement methods are shown in Table 2 below:

[0085] Table 2. Evaluation Indicators and Measurement Methods

[0086] ;

[0087] The test results showed that the cardboard box had good preservation properties for strawberries. Figure 2-3 As shown, the decay rate of the MA-3 group was 34.3% lower than that of the HS group on day 6, and the performance decay was less than 8% after 10 cycles, proving that the preservation was excellent and the cycle was stable. The hardness decay rate of the MA-3 group was 42% slower than that of the CK group, and the decay was only 5.8% after 10 cycles, proving that the synergistic effect of ethylene removal and water retention was stable.

[0088] Cyclic performance degradation verification: After each preservation experiment, the complete regeneration process was executed: mechanical stripping → EDTA dissociation → fiber repair. Key monitoring points were after the 1st, 3rd, 5th, 7th, and 10th cycles. The monitoring indicators are as follows:

[0089] Mechanical properties: puncture strength, edge crush strength, compressive strength GB / T6543;

[0090] Interface performance: T-peel test of functional adaptation layer peel strength;

[0091] Chemical properties: XPS analysis was used to determine the hydroxyl group exposure rate and epoxy group residue rate of the fibers;

[0092] Pore ​​properties: BET determination of core paper porosity and Cobb 60 value;

[0093] The criteria for determining reversibility are as follows:

[0094] Compressive strength retention rate ≥85% after 1-5 cycles, downgrade standard 80-85%;

[0095] Compressive strength retention rate ≥80% after 6-10 cycles; if <80%, scrap.

[0096] If the cumulative freshness preservation performance declines by less than 20%, or by more than 20%, the product should be retired.

[0097] like Figure 4 and Figure 5 As shown, the critical humidity for response is 85%, which perfectly matches the microenvironment of fruit and vegetable respiration, avoiding ineffective release. The activation energy is 58.3 kJ / mol, indicating that the release process is jointly controlled by diffusion and chemical reaction, and the rate increases by 1.7 times for every 10°C increase in temperature.

[0098] Cyclic performance such as Figure 6 and 7 As shown, after 10 cycles, the strength retention rate is >80%, which meets the design expectations. The interfacial strength gradient remains stable, the peeling mode is always cohesive failure, and the fiber damage rate is <4%.

[0099] In summary, the food preservation box of this embodiment has high preservation performance, long cycle life, and intelligent response at a reasonable humidity threshold.

[0100] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0101] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A manufacturing process for a paper box used for food preservation, characterized in that, Includes the following steps: S1, face paper and core paper are prepared separately in the wet section of the paper machine; The following components, by weight, include 70 parts softwood pulp and 30 parts OCC recycled pulp mixed and beaten to 32°SR, with 0.3-0.5 parts nanocellulose whiskers, 0.4-0.6 parts chitosan-PEG graft, 0.8 parts fluorocarbon sizing agent and 0.2 parts boric acid-PVA dynamic gel added sequentially at the wet end; The core pulp consists of 50 parts softwood pulp and 50 parts OCC recycled pulp mixed and beaten to 32°SR, with 0.5 parts nanocellulose whiskers and 1.5 parts paraffin microcapsules added at the wet end. S2, when the paperboard has a dryness of 75-80%, the functional adaptation layer is applied online to the surface of the face paper using a doctor blade coater, with a wet coating amount of 6.0 g / m². 2 The functional adapter layer includes 2 parts epoxy-modified cationic starch, 0.4 parts silane coupling agent KH-560 and 1 part eutectic solvent DES; S3, when the paperboard has a dryness of 75-80%, the functional adapter layer is applied online to the surface of the core paper using a curtain coating machine, with a wet coating amount of 7.5 g / m². 2 ; S4. After infrared drying, air plasma treatment is performed on the surfaces of the face paper and core paper respectively, with a power of 200W and a time of 30s. S5, the core paper is corrugated and laminated with the face paper using an adhesive. The lamination temperature is 180°C and the linear pressure is 60kN / m. The adhesive consists of 10 parts oxidized starch, 0.5 parts N,N'-methylenebisacrylamide, 2 parts carboxylated styrene-butadiene latex and 0.1 parts poly-N-isopropylacrylamide. S6. After die-cutting, a reversible functional coating system of sodium alginate-NaClO2-diatomaceous earth mixture is formed inside the cardboard with a thickness of 0.08mm. Then, 0.5M CaCl2 solution is sprayed for cross-linking for 5 minutes to obtain the cardboard for the box.

2. The preparation process of a paper box for food preservation according to claim 1, characterized in that, PLA slots are formed in situ on the surface of the functional adaptation layer of the core paper using hot press rollers, and NaClO2 slow-release tablets and acid triggering tablets are configured, including the following steps: K1, polylactic acid powder is pre-placed on the surface of the functional adaptation layer of the core paper, and hot pressing is performed by hot press rollers at a temperature of 130°C, a pressure of 2MPa and a time of 2s, so that the chitosan-polyethylene glycol graft in the functional adaptation layer melts to form a viscoelastic matrix, and at the same time induces the surface of the polylactic acid powder to soften. The two form a mechanical interlocking structure under pressure, and after cooling, a reversible anchoring PLA groove is generated in situ on the surface of the core paper. K2, a sustained-release tablet, consists of 60% NaClO2, 30% diatomaceous earth, 5% magnesium stearate, and 5% PEG-4000, and is produced by dry compression. K3, an acid-triggered tablet, consists of 85% citric acid, 10% microcrystalline cellulose, and 5% hydroxypropyl methylcellulose. K4, the sustained-release tablet and the acid-triggered tablet are inserted into the PLA card slot at a mass ratio of 3:

4.

3. The preparation process of a paper box for food preservation according to claim 2, characterized in that, In step S6, the reversible functional coating system includes: The NaClO2 supported layer comprises the following components: 75 parts sodium alginate, 15 parts NaClO2, and 10 parts diatomaceous earth. The solids are mixed with deionized water to form a 3% solid content coating solution. A 0.5M calcium chloride solution is prepared as a crosslinking agent, with an amount of 5% of the volume of the mixed coating solution. The NaClO2 supported layer is then coated on the paperboard. The acid-triggered layer was formed by electrostatically flocking 100 parts of citric acid micropowder onto a NaClO2 support layer, with a coating amount of 0.5 parts / 100cm². 2 ; The outer protective layer is made of a 30μm thick polyethylene film, which is hot-pressed onto the acid trigger layer at 180°C.

4. A food storage box, characterized in that, The paperboard is prepared using any one of the preparation processes of claims 1-3. The paperboard of the carton includes a face paper, a core paper, a functional adaptation layer coated on the surface of the face paper and the core paper, and a reversible functional coating system. The reversible functional coating system includes a NaClO2 loading layer, a citric acid micropowder flocking layer, and an outer protective layer. It is also equipped with a PLA card slot formed in situ on the surface of the functional adaptation layer by hot pressing interlocking. The PLA card slot is equipped with a slow-release tablet and an acid triggering tablet.

Images