Specialty paper for packaging and method for manufacturing the same

Abstract

The application discloses a special paper for packaging and a manufacturing method thereof, and the special paper comprises a needle-leaf wood pulp and broad-leaf wood pulp compound base paper and a three-layer gradient composite functional coating, and from inside to outside, the three-layer gradient composite functional coating comprises a wet heat densification modified bottom coating, a microcapsule fresh-keeping middle coating and a plant source nanocrystal densification protective surface coating. Through step-by-step coating and three-stage gradient drying forming, and in cooperation with steam wet heat coupling high-pressure densification treatment, the paper porosity is effectively reduced, and the structural densification is improved. The water vapor permeability of the special paper is significantly reduced compared with the prior art product, the fat penetration resistance time and the folding resistance are greatly improved, and the special paper has excellent barrier performance and mechanical strength.

Description

Technical Field

[0001] This invention belongs to the field of specialty paper manufacturing technology, and particularly relates to a specialty paper for packaging and its manufacturing method. Background Technology

[0002] Currently, with the rapid development of the logistics and packaging industry, higher requirements are being placed on the barrier properties of packaging materials. Traditional packaging materials often use aluminum foil or aluminized film to block water vapor, oxygen, and light to achieve moisture-proof, anti-oxidation, and preservation functions. However, the price of aluminum foil and other metal materials has risen sharply, and their supply is tight. Moreover, the production and recycling of metal materials consume a lot of energy, which not only increases packaging costs but also does not conform to the current green and environmentally friendly development trend of "replacing plastic with paper" and "replacing metal with paper".

[0003] In existing technologies, the industry has explored several alternatives to aluminum foil. One approach involves vacuum-depositing an aluminum layer onto polymer films (such as PET and PE) to reduce aluminum usage. However, this method still relies on metal resources, and the extremely thin coating is prone to pinholes after rubbing or folding, leading to a precipitous drop in barrier performance. Another approach uses multi-layer co-extruded composite plastics. While this achieves better barrier properties, its base material is derived from non-renewable petroleum resources, and most composite plastics are difficult to recycle, facing increasingly stringent plastic restrictions. None of these solutions fundamentally eliminate reliance on metal or petrochemical resources. Another technological approach involves the functional modification of paper. While paper itself is composed of natural plant fibers and possesses good biodegradability and renewability, its naturally porous structure and hydrophilicity render it devoid of any barrier capabilities. Traditional coated paper achieves waterproofing by coating a continuous polyethylene (PE) film onto its surface. However, coated paper has limited resistance to oil penetration, and the PE layer has weak adhesion to the paper fibers, making it prone to softening and separation at high temperatures. Furthermore, it lacks thermal insulation properties. In addition, simple surface coating cannot change the loose internal structure of the paper, allowing gases and liquids to still permeate through the capillary channels between the fibers.

[0004] For example, utility model patent document CN203668761U discloses a special paperboard for packaging, which includes: a first paperboard body, a second paperboard body, a mesh metal layer disposed between the upper surface of the first paperboard body and the lower surface of the second paperboard body, a first flame-retardant layer coated on the upper surface of the second paperboard body, and a third paperboard body disposed on the first flame-retardant layer. The third paperboard body is divided into a bottom layer paper and a top layer paper. Colored fibers are randomly dispersed in the top layer paper, and a plastic thread with an aluminum-plated layer or an aluminum-plated plastic thread with a holographic image is embedded at the interface between the bottom layer paper and the top layer paper. According to this utility model, the special paperboard for packaging has the characteristics of intuitive and easy identification of anti-counterfeiting features, and is also strong, not easily burned, and not easily damaged. However, this solution incorporates a mesh metal layer and aluminum-plated plastic wires, containing a large amount of non-recyclable metal components. This makes recycling and regeneration difficult, and its environmental compatibility is poor. Furthermore, it only focuses on structural strength, flame retardancy, and anti-counterfeiting performance, without incorporating antibacterial, antioxidant, or preservation functions. As a result, it cannot meet the long-term shelf-life requirements of food packaging. In addition, the metal-doped structure is not suitable for microwave heating scenarios, limiting its versatility. Summary of the Invention

[0005] To overcome the defects in the above-mentioned technologies, the present invention provides a special paper for packaging and a method for manufacturing the same. This special paper does not rely on metal materials and is prepared by multiple coatings of ordinary paper combined with a wet hot pressing densification process, and has high barrier properties, heat insulation and recyclability.

[0006] To achieve the above objectives, the technical solution adopted by this invention is as follows: a special paper for packaging, composed of virgin wood pulp base paper and a three-layer gradient composite functional coating; the three-layer gradient composite functional coating consists of, from the inside out, a moisture-heat densification modified base coating, a microcapsule preservation intermediate coating, and a plant-derived nanocrystalline dense protective top coating; the moisture-heat densification modified base coating is formulated from waterborne polyurethane, polyvinyl alcohol, hydrophobic nano-silica, and other additives, and is used for densification and reinforcement of the fiber matrix; the microcapsule preservation intermediate coating uses chitosan quaternary ammonium salt and sodium alginate as wall materials and natural plant preservatives as core materials to encapsulate slow-release microcapsules; the plant-derived nanocrystalline dense protective top coating is formed by in-situ crystallization of green tea extract, tannic acid, plant wax emulsion, and pectin to generate a nanocrystalline protective film; after steam moisture-heat coupled high-pressure densification treatment, the special paper has a fiber porosity ≤8% and a density of 0.95~1.15 g / cm³. 3 The average antibacterial rate is ≥99%.

[0007] Preferably, the base paper is made from a mixture of softwood pulp and hardwood pulp at a mass ratio of (3-5):5, with a basis weight of 90-110 g / m³. 2 The original porosity is 45%~50%.

[0008] Preferably, the wet-heat densification modified base coating comprises, by mass percentage: 45-55% waterborne polyurethane emulsion, 12-18% polyvinyl alcohol, 6-9% hydrophobic nano-silica, 0.8-1.2% coupling agent, 4-7% stearate, 3-4% polyether polyol, 0.2-0.4% polyether defoamer, 2-3% crosslinking agent, and the balance being deionized water.

[0009] Preferably, the aqueous polyurethane emulsion is Yoshida Chemical 1624 anionic aliphatic aqueous polyurethane emulsion.

[0010] Preferably, the polyvinyl alcohol is non-cellulose grade polyvinyl alcohol 24-88, provided by Anhui Wanwei High-Tech Materials Co., Ltd.; the hydrophobic nano silica is hydrophobic fumed silica AEROSIL R972; and the coupling agent is at least one of silane coupling agent KH550, silane coupling agent KH560, and silane coupling agent KH570.

[0011] Preferably, the stearate is glyceryl monostearate; the polyether polyol is polyether polyol DL2000; the polyether defoamer is SH-237; and the crosslinking agent is polycarbodiimide curing agent XR-201.

[0012] Preferably, the microcapsule preservation coating comprises, by mass percentage, 8-12 parts of food-grade chitosan quaternary ammonium salt, 6-10 parts of sodium alginate, 2-4 parts of rosemary extract, 1.5-3 parts of tea polyphenols, 1-2 parts of vitamin E, 2-3 parts of glycerin, and the remainder being deionized water.

[0013] Preferably, the food-grade chitosan quaternary ammonium salt has a degree of substitution of 90%-95% and a molecular weight of 150-250 kDa; the sodium alginate is food-grade sodium alginate, brand name MYF, specification 200-600 cps, provided by Qingdao Mingyue Seaweed Group; and the rosemary extract is provided by Hunan Denuo Health Industry Group Co., Ltd.

[0014] Preferably, the plant-derived nanocrystalline dense protective coating comprises, by mass percentage: 5-8% green tea extract, 3-5% tannins, 4-6% plant wax emulsion, 2-4% pectin, and the remainder is deionized water.

[0015] Preferably, the green tea extract is provided by Huzhou Rongkai Plant Extract Co., Ltd.; the plant wax emulsion is a carnauba wax emulsion with the brand name AQUACER 1541; and the pectin is GRINDSTED® PectinAMD 780.

[0016] Another object of the present invention is to provide a method for manufacturing the special paper for packaging, comprising the following steps: Step S1: Prepare the wet heat dense base coating liquid, the microcapsule preservation intermediate coating emulsion, and the plant-derived nanocrystal dense protective top coating liquid, respectively; Step S2: Plasma activation pretreatment of base paper; Step S3: Three-layer gradient stepwise precision coating; Step S4: Three-stage gradient drying and shaping; Step S5: Steam-heat coupled high-pressure densification treatment; Step S6: Set and cut at room temperature.

[0017] Preferably, the preparation method of the humid heat dense base coating adhesive in step S1 includes the following steps: after mixing the raw materials of the humid heat dense base coating evenly, filtering to obtain the humid heat dense base coating adhesive.

[0018] Preferably, the preparation method of the microcapsule preservation coating emulsion in step S1 includes the following steps: sodium alginate is added to deionized water and stirred at 58-62℃ for 0.8-1.2h to obtain a colloidal solution; glycerol is added to the above colloidal solution and stirred for 4-6min to mix; chitosan quaternary ammonium salt is added in 3 batches while stirring, with an interval of 3-5min between each batch, and after all materials are added, the mixture is stirred at a constant temperature for 13-18min; after cooling to 30-35℃, rosemary extract, tea polyphenols, and vitamin E are added in sequence, and the mixture is stirred for 8-12min; the resulting mixture is homogenized at 3000-4000r / min for 5-8min, and then allowed to stand at room temperature in a sealed container for 13-16min to defoam, thus obtaining the microcapsule preservation coating emulsion.

[0019] Preferably, the preparation method of the plant-derived nanocrystalline dense protective coating liquid in step S1 includes the following steps: green tea extract, tannic acid, and pectin are added sequentially to deionized water, stirred at a constant temperature of 43-47℃ for 28-32 min, then plant wax emulsion is added and stirred at low speed to homogenize, and allowed to stand for 0.8-1.2 h to prepare the plant-derived nanocrystalline dense protective coating liquid; the speed of the low-speed stirring homogenization is 200-250 r / min.

[0020] Preferably, the plasma activation pretreatment in step S2 is a normal pressure low temperature oxygen plasma activation pretreatment, with specific process parameters as follows: working gas source pressure 0.3~0.5MPa, gas flow rate 15~20L / min, processing power 11-13kW, discharge frequency 20~40kHz, and paper feed speed 11-13m / min.

[0021] Preferably, the three-layer gradient stepwise precision coating in step S3 specifically involves: first, applying a wet-heat dense primer, with a dry coating amount of 5.8-6.2 g / m³. 2 The substrate structure is pre-dried to solidify the interlayer bonding; then a microcapsule preservation intermediate coating emulsion is applied, with a dry coating amount of 3.8-4.2 g / m². 2 A stable microcapsule preservation intermediate coating is formed by uniformly coating the microcapsules; finally, a plant-derived nanocrystalline dense protective topcoat is applied, with a dry coating amount of 2.8-3.2 g / m². 2 A dense, non-porous plant-derived nanocrystalline protective coating was constructed; the total dry film thickness of the three-layer coating was 9-11 μm, and the coating speed was 11-13 m / min.

[0022] Preferably, the three-stage gradient drying temperatures in step S4 are 60~70℃, 80~90℃, and 100~110℃, respectively, and the corresponding drying times are 4~6min, 5~8min, and 1~3min, respectively. The final overall coating moisture content is controlled to ≤4%, which simultaneously protects the microcapsule structure and promotes the cross-linking of the bottom layer and the nanocrystallization of the surface layer.

[0023] Preferably, the process parameters for the densification treatment in step S5 are: constant steam temperature of 100℃, rolling pressure of 15~25MPa, and paper feed speed of 5~10m / min.

[0024] Due to the application of the above technical solution, the present invention has the following beneficial effects: (1) The special paper for packaging and its manufacturing method disclosed in this invention, through the hierarchical structure of virgin wood pulp base paper combined with a three-layer gradient composite functional coating, combined with a wet-heat coupled high-pressure densification molding process, breaks through the technical bottlenecks of traditional packaging paper coatings with weak bonding force, high porosity, and single protective and preservation properties, and achieves a dual upgrade of paper matrix structure and functional characteristics. By optimizing the wood pulp compounding ratio and base coating formula, combined with plasma activation pretreatment process, the bonding tightness between the coating and the paper fiber matrix is ​​improved. After special densification treatment, the paper fiber porosity is low, which solves the defects of traditional packaging paper such as loose pores, easy water permeability, easy air permeability, and insufficient structural strength, and improves the overall structural stability and physical barrier performance of packaging paper.

[0025] (2) The special paper for packaging disclosed in this invention and its manufacturing method are provided with a microcapsule preservation coating. The food-grade chitosan quaternary ammonium salt and sodium alginate are used as composite wall materials to encapsulate natural plant active preservation ingredients such as rosemary extract and tea polyphenols. This can achieve long-term slow release of preservation factors. Unlike traditional coatings, which have problems such as easy loss of preservation ingredients and short antibacterial effect, the special paper has a high average antibacterial rate and can effectively inhibit the growth of bacteria and microorganisms inside and outside the packaging. At the same time, there are no chemical residues, which meets the safety and hygiene requirements of high-end packaging such as food and fresh food, and greatly expands the application scenarios of the product.

[0026] (3) The special paper for packaging disclosed in this invention and its manufacturing method generate a nanocrystalline protective film through the in-situ crystallization reaction of green tea extract, tannic acid and pectin. Combined with the hydrophobic reinforcement effect of plant wax emulsion, a dense and non-porous protective surface layer can be formed without relying on chemical film-forming aids. This gives the packaging paper excellent water resistance, moisture resistance and abrasion resistance, effectively avoiding the problems of packaging paper deformation due to moisture, coating peeling and protective failure in humid environments. It is perfectly adapted to the use needs of complex circulation environments such as warehousing and transportation.

[0027] (4) The special paper for packaging disclosed in this invention and its manufacturing method adopt a three-layer gradient step-by-step precision coating combined with a three-stage gradient drying process, which can effectively control the coating amount and drying parameters of each layer. It can effectively protect the complete sustained-release structure of the microcapsules in the middle coating layer, and promote the cross-linking and curing of the bottom coating layer and the nano-crystallization of the top coating layer. It can achieve complementary functions and layer adaptation of the three coating layers. Compared with single-layer functional modified packaging paper, it takes into account multiple properties such as matrix reinforcement, long-term antibacterial preservation and surface dense protection. Moreover, the synergistic effect of each functional layer has no performance offset, the process is stable, the finished product qualification rate is high, and it can be mass-produced on a large scale. Detailed Implementation

[0028] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0029] Example 1

[0030] A specialty paper for packaging comprises virgin wood pulp base paper and a three-layer gradient composite functional coating. The three-layer gradient composite functional coating, from the inside out, consists of a moisture-heat densification modified base coating, a microcapsule preservation intermediate coating, and a plant-derived nanocrystalline dense protective top coating. The moisture-heat densification modified base coating is formulated from waterborne polyurethane, polyvinyl alcohol, hydrophobic nano-silica, and other additives, used for densifying and reinforcing the fiber matrix. The microcapsule preservation intermediate coating uses chitosan quaternary ammonium salt and sodium alginate as wall materials, and natural plant preservatives as core materials to encapsulate slow-release microcapsules. The plant-derived nanocrystalline dense protective top coating is formed by in-situ crystallization of green tea extract, tannic acid, plant wax emulsion, and pectin to create a nanocrystalline protective film. After steam moisture-heat coupled high-pressure densification treatment, the specialty paper has a fiber porosity ≤8% and a density of 0.95 g / cm³. 3 The average antibacterial rate is ≥99%.

[0031] The base paper is made from a blend of softwood pulp and hardwood pulp in a mass ratio of 3:5, with a basis weight of 90 g / m³. 2The original porosity is 45%. The wet-heat densification modified base coating, by mass percentage, comprises: 45% waterborne polyurethane emulsion, 12% polyvinyl alcohol, 6% hydrophobic nano-silica, 0.8% coupling agent, 4% stearate, 3% polyether polyol, 0.2% polyether defoamer, 2% crosslinking agent, and the balance being deionized water. The waterborne polyurethane emulsion is Yoshida Chemical 1624 anionic aliphatic waterborne polyurethane emulsion. The polyvinyl alcohol is non-fiber grade polyvinyl alcohol 24-88, provided by Anhui Wanwei High-Tech Materials Co., Ltd. The hydrophobic nano-silica is hydrophobic fumed silica AEROSIL R972. The coupling agent is silane coupling agent KH550. The stearate is glyceryl monostearate. The polyether polyol is polyether polyol DL2000. The polyether defoamer is SH-237. The crosslinking agent is polycarbodiimide curing agent XR-201.

[0032] The microcapsule preservation coating comprises, by weight percentage: 8 parts food-grade chitosan quaternary ammonium salt, 6 parts sodium alginate, 2 parts rosemary extract, 1.5 parts tea polyphenols, 1 part vitamin E, 2 parts glycerin, and the remainder being deionized water; the food-grade chitosan quaternary ammonium salt has a substitution degree of 90% and a molecular weight of 150 kDa; the sodium alginate is food-grade sodium alginate, brand name MYF, specification 200-600 cps, provided by Qingdao Mingyue Algae Group; the rosemary extract is provided by Hunan Denuo Health Industry Group Co., Ltd.; the plant-derived nanocrystalline dense protective coating comprises, by weight percentage: 5% green tea extract, 3% tannin, 4% plant wax emulsion, 2% pectin, and the remainder being deionized water; the green tea extract is provided by Huzhou Rongkai Plant Extract Co., Ltd.; the plant wax emulsion is a carnauba wax-based wax emulsion, brand name AQUACER. 1541; The pectin is graded GRINDSTED® Pectin AMD 780.

[0033] A method for manufacturing the special paper for packaging includes the following steps: Step S1: Prepare the wet heat dense base coating liquid, the microcapsule preservation intermediate coating emulsion, and the plant-derived nanocrystal dense protective top coating liquid, respectively; Step S2: Plasma activation pretreatment of base paper; Step S3: Three-layer gradient stepwise precision coating; Step S4: Three-stage gradient drying and shaping; Step S5: Steam-heat coupled high-pressure densification treatment; Step S6: Set and cut at room temperature.

[0034] The preparation method of the humid heat dense base coating solution in step S1 includes the following steps: after mixing the raw materials of the humid heat dense base coating solution evenly, the solution is filtered to obtain the humid heat dense base coating solution; the preparation method of the microcapsule preservation intermediate coating emulsion in step S1 includes the following steps: sodium alginate is added to deionized water and stirred at 58°C for 0.8 h to obtain a colloidal solution; glycerol is added to the above colloidal solution and stirred for 4 min to mix evenly; chitosan quaternary ammonium salt is added in 3 batches while stirring, with an interval of 3 min between each batch, and after all the materials are added, the mixture is stirred at a constant temperature for 13 min; after cooling to 30°C, rosemary extract, tea polyphenols, and vitamin E are added in sequence, and the mixture is stirred for 8 min; the resulting mixture is homogenized at 3000 r / min for 5 min, and then allowed to stand at room temperature in a sealed container for 13 min to degas, thus obtaining the microcapsule preservation coating emulsion.

[0035] The preparation method of the plant-derived nanocrystalline dense protective coating liquid in step S1 includes the following steps: green tea extract, tannic acid and pectin are added to deionized water in sequence, stirred at 43°C for 28 min, then plant wax emulsion is added and stirred at low speed to homogenize, and allowed to stand for 0.8 h to prepare the plant-derived nanocrystalline dense protective coating liquid; the speed of the low-speed stirring homogenization is 200 r / min.

[0036] The plasma activation pretreatment mentioned in step S2 is a normal pressure low temperature oxygen plasma activation pretreatment. The specific process parameters are: working gas source pressure 0.3MPa, gas flow rate 15L / min, processing power 11kW, discharge frequency 20kHz, and paper feed speed 11m / min.

[0037] Preferably, the three-layer gradient stepwise precision coating in step S3 specifically involves: first, applying a wet-heat dense primer, with a dry coating amount of 5.8 g / m². 2 Pre-drying fixes the substrate structure, establishing a solid foundation for interlayer bonding; then, a microcapsule preservation intermediate coating emulsion is applied, with a dry coating amount of 3.8 g / m². 2 A stable microcapsule preservation intermediate coating is formed by uniformly coating the microcapsules; finally, a plant-derived nanocrystalline dense protective topcoat is applied, with a dry coating amount of 2.8 g / m². 2 A dense, non-porous plant-derived nanocrystalline protective coating was constructed; the total dry film thickness of the three-layer coating was 9 μm, and the coating speed was 11 m / min.

[0038] The three-stage gradient drying temperatures in step S4 are 60℃, 80℃, and 100℃, respectively, with corresponding drying times of 4min, 5min, and 1min. The final overall coating moisture content is controlled to be ≤4%, simultaneously protecting the microcapsule structure and promoting the cross-linking of the underlying layer and the nanocrystallization of the surface layer. The densification process parameters in step S5 are: constant steam temperature of 100℃, rolling pressure of 15MPa, and paper feed speed of 5m / min.

[0039] Example 2

[0040] A specialty paper for packaging comprises virgin wood pulp base paper and a three-layer gradient composite functional coating. The three-layer gradient composite functional coating, from the inside out, consists of a moisture-heat densification modified base layer, a microcapsule preservation intermediate layer, and a plant-derived nanocrystalline dense protective top layer. The moisture-heat densification modified base layer is formulated with waterborne polyurethane, polyvinyl alcohol, hydrophobic nano-silica, and other additives, and is used for densification and reinforcement of the fiber matrix. The microcapsule preservation intermediate layer uses chitosan quaternary ammonium salt and sodium alginate as wall materials, and natural plant preservatives as core materials to encapsulate slow-release microcapsules. The plant-derived nanocrystalline dense protective top layer is formed by in-situ crystallization of green tea extract, tannic acid, plant wax emulsion, and pectin to create a nanocrystalline protective film. After steam moisture-heat coupled high-pressure densification treatment, the specialty paper has a fiber porosity ≤8% and a density of 1 g / cm³. 3 The average antibacterial rate is ≥99%.

[0041] The base paper is made from a blend of softwood pulp and hardwood pulp at a mass ratio of 3.5:5, with a basis weight of 95 g / m³. 2 The original porosity is 46%. The wet-heat densification modified base coating, by mass percentage, comprises: 47% waterborne polyurethane emulsion, 13% polyvinyl alcohol, 7% hydrophobic nano-silica, 0.9% coupling agent, 5% stearate, 3.2% polyether polyol, 0.25% polyether defoamer, 2.3% crosslinking agent, and the balance being deionized water. The waterborne polyurethane emulsion is Yoshida Chemical 1624 anionic aliphatic waterborne polyurethane emulsion. The polyvinyl alcohol is non-fiber grade polyvinyl alcohol 24-88, provided by Anhui Wanwei High-Tech Materials Co., Ltd. The hydrophobic nano-silica is hydrophobic fumed silica AEROSIL R972. The coupling agent is silane coupling agent KH560. The stearate is glyceryl monostearate. The polyether polyol is polyether polyol DL2000. The polyether defoamer is SH-237. The crosslinking agent is polycarbodiimide curing agent XR-201.

[0042] The microcapsule preservation coating comprises, by weight percentage: 9 parts food-grade chitosan quaternary ammonium salt, 7 parts sodium alginate, 2.5 parts rosemary extract, 2 parts tea polyphenols, 1.2 parts vitamin E, 2.3 parts glycerin, and the balance being deionized water; the food-grade chitosan quaternary ammonium salt has a substitution degree of 92% and a molecular weight of 180 kDa; the sodium alginate is food-grade sodium alginate, brand name MYF, specification 200-600 cps, provided by Qingdao Mingyue Algae Group; the rosemary extract is provided by Hunan Denuo Health Industry Group Co., Ltd.; the plant-derived nanocrystalline dense protective coating comprises, by weight percentage: 6% green tea extract, 3.5% tannin, 4.5% plant wax emulsion, 2.5% pectin, and the balance being deionized water; the green tea extract is provided by Huzhou Rongkai Plant Extract Co., Ltd.; the plant wax emulsion is a carnauba wax-based wax emulsion, brand name AQUACER. 1541; The pectin is graded GRINDSTED® Pectin AMD 780.

[0043] A method for manufacturing the special paper for packaging includes the following steps: Step S1: Prepare the wet heat dense base coating liquid, the microcapsule preservation intermediate coating emulsion, and the plant-derived nanocrystal dense protective top coating liquid, respectively; Step S2: Plasma activation pretreatment of base paper; Step S3: Three-layer gradient stepwise precision coating; Step S4: Three-stage gradient drying and shaping; Step S5: Steam-heat coupled high-pressure densification treatment; Step S6: Set and cut at room temperature.

[0044] The preparation method of the wet-heat dense base coating solution in step S1 includes the following steps: after mixing the raw materials of the wet-heat dense base coating solution evenly, the solution is filtered to obtain the wet-heat dense base coating solution; the preparation method of the microcapsule preservation intermediate coating emulsion in step S1 includes the following steps: sodium alginate is added to deionized water and stirred at 59°C for 0.9 h to obtain a colloidal solution; glycerol is added to the above colloidal solution and stirred for 4.5 min to mix evenly; chitosan quaternary ammonium salt is added in 3 batches while stirring, with an interval of 3.5 min between each batch, and after all materials are added, the mixture is stirred at a constant temperature for 14 min; after cooling to 32°C, rosemary extract, tea polyphenols, and vitamin E are added in sequence, and the mixture is stirred for 9 min; the resulting mixture is homogenized at 3300 r / min for 6 min, and then allowed to stand at room temperature in a sealed container for 14 min to degas, thus obtaining the microcapsule preservation coating emulsion.

[0045] The preparation method of the plant-derived nanocrystalline dense protective coating liquid in step S1 includes the following steps: green tea extract, tannic acid, and pectin are added sequentially to deionized water, stirred at 44℃ for 29 min, then plant wax emulsion is added and stirred at low speed for homogenization, and allowed to stand for 0.9 h to prepare the plant-derived nanocrystalline dense protective coating liquid; the speed of the low-speed stirring homogenization is 220 r / min; the plasma activation pretreatment in step S2 is a normal pressure low temperature oxygen plasma activation pretreatment, and the specific process parameters are: working gas source pressure 0.35 MPa, gas flow rate 16 L / min, processing power 11.5 kW, discharge frequency 25 kHz, and paper feed speed 11.5 m / min.

[0046] The three-layer gradient stepwise precision coating described in step S3 specifically involves: first, applying a wet-heat dense primer with a dry coating amount of 5.9 g / m². 2 Pre-drying fixes the substrate structure, establishing a solid foundation for interlayer bonding; then, a microcapsule preservation intermediate coating emulsion is applied, with a dry coating amount of 3.9 g / m². 2 A stable microcapsule preservation intermediate coating is formed by uniformly coating the microcapsules; finally, a plant-derived nanocrystalline dense protective topcoat is applied, with a dry coating amount of 2.9 g / m². 2 A dense, non-porous plant-derived nanocrystalline protective coating was constructed; the total dry film thickness of the three-layer coating was 9.5 μm, and the coating speed was 11.5 m / min; the three-stage gradient drying temperatures in step S4 were 63℃, 82℃, and 103℃, respectively, with corresponding drying times of 4.5 min, 6 min, and 1.5 min, respectively, and the final overall coating moisture content was controlled to ≤4%, simultaneously protecting the microcapsule structure and promoting the cross-linking of the bottom layer and the nanocrystallization of the surface layer; the densification process parameters in step S5 were: constant steam temperature of 100℃, rolling pressure of 17 MPa, and paper feed speed of 6 m / min.

[0047] Example 3

[0048] A specialty paper for packaging comprises virgin wood pulp base paper and a three-layer gradient composite functional coating. The three-layer gradient composite functional coating, from the inside out, consists of a moisture-heat densification modified base coating, a microcapsule preservation intermediate coating, and a plant-derived nanocrystalline dense protective top coating. The moisture-heat densification modified base coating is formulated with waterborne polyurethane, polyvinyl alcohol, hydrophobic nano-silica, and other additives, and is used for densification and reinforcement of the fiber matrix. The microcapsule preservation intermediate coating uses chitosan quaternary ammonium salt and sodium alginate as wall materials and natural plant preservatives as core materials to encapsulate slow-release microcapsules. The plant-derived nanocrystalline dense protective top coating is formed by in-situ crystallization of green tea extract, tannic acid, plant wax emulsion, and pectin to create a nanocrystalline protective film. After steam moisture-heat coupled high-pressure densification treatment, the specialty paper has a fiber porosity ≤8% and a density of 1.05 g / cm³. 3 The average antibacterial rate is ≥99%.

[0049] The base paper is made from a blend of softwood pulp and hardwood pulp in a mass ratio of 4:5, with a basis weight of 100 g / m³. 2 The original porosity is 48%. The wet-heat densification modified base coating, by mass percentage, comprises: 50% waterborne polyurethane emulsion, 16% polyvinyl alcohol, 7.5% hydrophobic nano-silica, 1% coupling agent, 5.5% stearate, 3.5% polyether polyol, 0.3% polyether defoamer, 2.5% crosslinking agent, and the balance being deionized water. The waterborne polyurethane emulsion is Yoshida Chemical 1624 anionic aliphatic waterborne polyurethane emulsion. The polyvinyl alcohol is non-fiber grade polyvinyl alcohol 24-88, provided by Anhui Wanwei High-Tech Materials Co., Ltd. The hydrophobic nano-silica is hydrophobic fumed silica AEROSIL R972. The coupling agent is silane coupling agent KH570. The stearate is glyceryl monostearate. The polyether polyol is polyether polyol DL2000. The polyether defoamer is SH-237. The crosslinking agent is polycarbodiimide curing agent XR-201.

[0050] The microcapsule preservation coating comprises, by weight percentage: 10 parts food-grade chitosan quaternary ammonium salt, 8 parts sodium alginate, 3 parts rosemary extract, 2.2 parts tea polyphenols, 1.5 parts vitamin E, 2.5 parts glycerin, and the balance being deionized water; the food-grade chitosan quaternary ammonium salt has a substitution degree of 93% and a molecular weight of 200 kDa; the sodium alginate is food-grade sodium alginate, brand name MYF, specification 200-600 cps, provided by Qingdao Mingyue Algae Group; the rosemary extract is provided by Hunan Denuo Health Industry Group Co., Ltd.; the plant-derived nanocrystalline dense protective coating comprises, by weight percentage: 6.5% green tea extract, 4% tannin, 5% plant wax emulsion, 3% pectin, and the balance being deionized water; the green tea extract is provided by Huzhou Rongkai Plant Extract Co., Ltd.; the plant wax emulsion is a carnauba wax-based wax emulsion, brand name AQUACER. 1541; The pectin is graded GRINDSTED® Pectin AMD 780.

[0051] A method for manufacturing the special paper for packaging includes the following steps: Step S1: Prepare the wet heat dense base coating liquid, the microcapsule preservation intermediate coating emulsion, and the plant-derived nanocrystal dense protective top coating liquid, respectively; Step S2: Plasma activation pretreatment of base paper; Step S3: Three-layer gradient stepwise precision coating; Step S4: Three-stage gradient drying and shaping; Step S5: Steam-heat coupled high-pressure densification treatment; Step S6: Set and cut at room temperature.

[0052] The preparation method of the humid heat dense base coating solution in step S1 includes the following steps: after mixing the raw materials of the humid heat dense base coating solution evenly, the solution is filtered to obtain the humid heat dense base coating solution; the preparation method of the microcapsule preservation intermediate coating emulsion in step S1 includes the following steps: sodium alginate is added to deionized water and stirred at 60°C for 1 hour to obtain a colloidal solution; glycerol is added to the above colloidal solution and stirred for 5 minutes to mix evenly; chitosan quaternary ammonium salt is added in 3 batches while stirring, with an interval of 4 minutes between each batch, and after all the materials are added, the mixture is stirred at a constant temperature for 15 minutes; after cooling to 33°C, rosemary extract, tea polyphenols, and vitamin E are added in sequence, and the mixture is stirred for 10 minutes; the resulting mixture is homogenized at 3500 r / min for 6.5 minutes, and then allowed to stand at room temperature in a sealed container for 14.5 minutes to degas, thus obtaining the microcapsule preservation coating emulsion.

[0053] The preparation method of the plant-derived nanocrystalline dense protective coating liquid in step S1 includes the following steps: green tea extract, tannic acid, and pectin are added sequentially to deionized water, stirred at 45°C for 30 min, then plant wax emulsion is added and stirred at low speed for homogenization, and allowed to stand for 1 h to prepare the plant-derived nanocrystalline dense protective coating liquid; the speed of the low-speed stirring homogenization is 230 r / min; the plasma activation pretreatment in step S2 is a normal pressure low temperature oxygen plasma activation pretreatment, and the specific process parameters are: working gas source pressure 0.4 MPa, gas flow rate 18 L / min, processing power 12 kW, discharge frequency 30 kHz, and paper feed speed 12 m / min.

[0054] The three-layer gradient stepwise precision coating in step S3 specifically involves: first, applying a wet-heat dense primer with a dry coating amount of 6 g / m². 2 Pre-drying fixes the substrate structure, establishing a solid foundation for interlayer bonding; then, a microcapsule preservation intermediate coating emulsion is applied, with a dry coating amount of 4 g / m². 2 A stable microcapsule preservation intermediate coating is formed by uniformly coating the surface; finally, a plant-derived nanocrystalline dense protective topcoat is applied with a dry coating amount of 3 g / m². 2 A dense, non-porous plant-derived nanocrystalline protective coating was constructed. The total dry film thickness of the three-layer coating was 10 μm, and the coating speed was 12 m / min. The three-stage gradient drying temperatures in step S4 were 65℃, 85℃, and 105℃, with corresponding drying times of 5 min, 6.5 min, and 2 min, respectively. The final overall coating moisture content was controlled to be ≤4%, simultaneously protecting the microcapsule structure and promoting cross-linking of the underlying layer and nanocrystallization of the surface layer. The densification process parameters in step S5 were: constant steam temperature of 100℃, rolling pressure of 20 MPa, and paper feed speed of 8 m / min.

[0055] Example 4

[0056] A specialty paper for packaging comprises virgin wood pulp base paper and a three-layer gradient composite functional coating. The three-layer gradient composite functional coating, from the inside out, consists of a moisture-heat densification modified base layer, a microcapsule preservation intermediate layer, and a plant-derived nanocrystalline dense protective top layer. The moisture-heat densification modified base layer is formulated with waterborne polyurethane, polyvinyl alcohol, hydrophobic nano-silica, and other additives, and is used for densification and reinforcement of the fiber matrix. The microcapsule preservation intermediate layer uses chitosan quaternary ammonium salt and sodium alginate as wall materials, and natural plant preservatives as core materials to encapsulate slow-release microcapsules. The plant-derived nanocrystalline dense protective top layer is formed by in-situ crystallization of green tea extract, tannic acid, plant wax emulsion, and pectin to create a nanocrystalline protective film. After steam moisture-heat coupled high-pressure densification treatment, the specialty paper has a fiber porosity ≤8% and a density of 1.1 g / cm³. 3 The average antibacterial rate is ≥99%.

[0057] The base paper is made from a blend of softwood pulp and hardwood pulp at a mass ratio of 4.5:5, with a basis weight of 105 g / m³. 2 The original porosity is 49%. The wet-heat densification modified primer coating, by mass percentage, comprises: 53% waterborne polyurethane emulsion, 17% polyvinyl alcohol, 8.5% hydrophobic nano-silica, 1.1% coupling agent, 6.5% stearate, 3.8% polyether polyol, 0.35% polyether defoamer, 2.8% crosslinking agent, and the balance being deionized water. The waterborne polyurethane emulsion is Yoshida Chemical 1624 anionic aliphatic waterborne polyurethane emulsion. The polyvinyl alcohol is non-cellulose grade polyvinyl alcohol 24-88, provided by Anhui Wanwei High-Tech Materials Co., Ltd. The hydrophobic nano-silica is hydrophobic fumed silica AEROSIL. R972; the coupling agent is a compound of silane coupling agent KH550, silane coupling agent KH560 and silane coupling agent KH570 in a mass ratio of 1:2:1; the stearate is glyceryl monostearate; the polyether polyol is polyether polyol DL2000; the polyether defoamer is SH-237; the crosslinking agent is polycarbodiimide curing agent XR-201.

[0058] The microcapsule preservation coating comprises, by weight percentage: 11 parts food-grade chitosan quaternary ammonium salt, 9 parts sodium alginate, 3.5 parts rosemary extract, 2.8 parts tea polyphenols, 1.8 parts vitamin E, 2.8 parts glycerin, and the balance being deionized water; the food-grade chitosan quaternary ammonium salt has a substitution degree of 94% and a molecular weight of 240 kDa; the sodium alginate is food-grade sodium alginate, brand name MYF, specification 200-600 cps, provided by Qingdao Mingyue Seaweed Group; the rosemary extract is provided by Hunan Denuo Health Industry Group Co., Ltd.; the plant-derived nanocrystalline dense protective coating comprises, by weight percentage: 7.5% green tea extract, 4.5% tannin, 5.5% plant wax emulsion, 3.5% pectin, and the balance being deionized water; the green tea extract is provided by Huzhou Rongkai Plant Extract Co., Ltd.; the plant wax emulsion is a carnauba wax-based wax emulsion, brand name AQUACER. 1541; The pectin is graded GRINDSTED® Pectin AMD 780.

[0059] A method for manufacturing the special paper for packaging includes the following steps: Step S1: Prepare the wet heat dense base coating liquid, the microcapsule preservation intermediate coating emulsion, and the plant-derived nanocrystal dense protective top coating liquid, respectively; Step S2: Plasma activation pretreatment of base paper; Step S3: Three-layer gradient stepwise precision coating; Step S4: Three-stage gradient drying and shaping; Step S5: Steam-heat coupled high-pressure densification treatment; Step S6: Set and cut at room temperature.

[0060] The preparation method of the humid heat dense base coating solution in step S1 includes the following steps: after mixing the raw materials of the humid heat dense base coating solution evenly, the solution is filtered to obtain the humid heat dense base coating solution; the preparation method of the microcapsule preservation intermediate coating emulsion in step S1 includes the following steps: sodium alginate is added to deionized water and stirred at 61°C for 1.1 h to obtain a colloidal solution; glycerol is added to the above colloidal solution and stirred for 5.5 min to mix evenly; chitosan quaternary ammonium salt is added in 3 batches while stirring, with an interval of 4.5 min between each batch, and after all the materials are added, the mixture is stirred at a constant temperature for 17 min; after cooling to 34°C, rosemary extract, tea polyphenols, and vitamin E are added in sequence, and the mixture is stirred for 11 min; the resulting mixture is homogenized at 3900 r / min for 7.5 min, and then allowed to stand at room temperature in a sealed container for 15 min to degas, thus obtaining the microcapsule preservation coating emulsion.

[0061] The preparation method of the plant-derived nanocrystalline dense protective coating liquid in step S1 includes the following steps: green tea extract, tannic acid, and pectin are added sequentially to deionized water, stirred at 46℃ for 31 min, then plant wax emulsion is added and stirred at low speed for homogenization, and allowed to stand for 1.1 h to prepare the plant-derived nanocrystalline dense protective coating liquid; the speed of the low-speed stirring homogenization is 240 r / min; the plasma activation pretreatment in step S2 is a normal pressure low temperature oxygen plasma activation pretreatment, and the specific process parameters are: working gas source pressure 0.45 MPa, gas flow rate 19 L / min, processing power 12.5 kW, discharge frequency 35 kHz, and paper feed speed 12.5 m / min.

[0062] The three-layer gradient stepwise precision coating described in step S3 specifically involves: first, applying a wet-heat dense primer with a dry coating amount of 6.1 g / m². 2 Pre-drying fixes the substrate structure, establishing a solid foundation for interlayer bonding; then, a microcapsule preservation intermediate coating emulsion is applied, with a dry coating amount of 4.1 g / m². 2 A stable microcapsule preservation intermediate coating is formed by uniformly coating the microcapsules; finally, a plant-derived nanocrystalline dense protective topcoat is applied, with a dry coating amount of 3.1 g / m². 2 A dense, non-porous plant-derived nanocrystalline protective coating was constructed. The total dry film thickness of the three-layer coating was 10.5 μm, and the coating speed was 12.5 m / min. The three-stage gradient drying temperatures in step S4 were 68℃, 88℃, and 108℃, with corresponding drying times of 5.5 min, 7.5 min, and 2.5 min, respectively. The final overall coating moisture content was controlled to ≤4%, simultaneously protecting the microcapsule structure and promoting cross-linking of the underlying layer and nanocrystallization of the surface layer. The densification process parameters in step S5 were: constant steam temperature of 100℃, rolling pressure of 23 MPa, and paper feed speed of 9 m / min.

[0063] Example 5

[0064] A specialty paper for packaging comprises virgin wood pulp base paper and a three-layer gradient composite functional coating. The three-layer gradient composite functional coating, from the inside out, consists of a moisture-heat densification modified base coating, a microcapsule preservation intermediate coating, and a plant-derived nanocrystalline dense protective top coating. The moisture-heat densification modified base coating is formulated from waterborne polyurethane, polyvinyl alcohol, hydrophobic nano-silica, and other additives, used for densifying and reinforcing the fiber matrix. The microcapsule preservation intermediate coating uses chitosan quaternary ammonium salt and sodium alginate as wall materials, and natural plant preservatives as core materials to encapsulate slow-release microcapsules. The plant-derived nanocrystalline dense protective top coating is formed by in-situ crystallization of green tea extract, tannic acid, plant wax emulsion, and pectin to create a nanocrystalline protective film. After steam moisture-heat coupled high-pressure densification treatment, the specialty paper has a fiber porosity ≤8% and a density of 1.15 g / cm³. 3The average antibacterial rate is ≥99%.

[0065] The base paper is made from a blend of softwood pulp and hardwood pulp in a 5:5 mass ratio, with a basis weight of 110 g / m³. 2 The original porosity is 50%. The wet-heat densification modified base coating, by mass percentage, comprises: 55% waterborne polyurethane emulsion, 18% polyvinyl alcohol, 9% hydrophobic nano-silica, 1.2% coupling agent, 7% stearate, 4% polyether polyol, 0.4% polyether defoamer, 3% crosslinking agent, and the balance being deionized water. The waterborne polyurethane emulsion is Yoshida Chemical 1624 anionic aliphatic waterborne polyurethane emulsion. The polyvinyl alcohol is non-fiber grade polyvinyl alcohol 24-88, provided by Anhui Wanwei High-Tech Materials Co., Ltd. The hydrophobic nano-silica is hydrophobic fumed silica AEROSIL R972. The coupling agent is silane coupling agent KH550. The stearate is glyceryl monostearate. The polyether polyol is polyether polyol DL2000. The polyether defoamer is SH-237. The crosslinking agent is polycarbodiimide curing agent XR-201.

[0066] The microcapsule preservation coating comprises, by weight percentage: 12 parts food-grade chitosan quaternary ammonium salt, 10 parts sodium alginate, 4 parts rosemary extract, 3 parts tea polyphenols, 2 parts vitamin E, 3 parts glycerin, and the remainder being deionized water; the food-grade chitosan quaternary ammonium salt has a degree of substitution of 95% and a molecular weight of 250 kDa; the sodium alginate is food-grade sodium alginate, brand name MYF, specification 200-600 cps, provided by Qingdao Mingyue Seaweed Group; the rosemary extract is provided by Hunan Denuo Health Industry Group Co., Ltd.; the plant-derived nanocrystalline dense protective coating comprises, by weight percentage: 8% green tea extract, 5% tannin, 6% plant wax emulsion, 4% pectin, and the remainder being deionized water; the green tea extract is provided by Huzhou Rongkai Plant Extract Co., Ltd.; the plant wax emulsion is a carnauba wax-based wax emulsion, brand name AQUACER. 1541; The pectin is graded GRINDSTED® Pectin AMD 780.

[0067] A method for manufacturing the special paper for packaging includes the following steps: Step S1: Prepare the wet heat dense base coating liquid, the microcapsule preservation intermediate coating emulsion, and the plant-derived nanocrystal dense protective top coating liquid, respectively; Step S2: Plasma activation pretreatment of base paper; Step S3: Three-layer gradient stepwise precision coating; Step S4: Three-stage gradient drying and shaping; Step S5: Steam-heat coupled high-pressure densification treatment; Step S6: Set and cut at room temperature.

[0068] The preparation method of the humid heat dense base coating solution in step S1 includes the following steps: after mixing the raw materials of the humid heat dense base coating solution evenly, the solution is filtered to obtain the humid heat dense base coating solution; the preparation method of the microcapsule preservation intermediate coating emulsion in step S1 includes the following steps: sodium alginate is added to deionized water and stirred at 62°C for 1.2 h to obtain a colloidal solution; glycerol is added to the above colloidal solution and stirred for 6 min to mix evenly; chitosan quaternary ammonium salt is added in 3 batches while stirring, with an interval of 5 min between each batch, and after all the materials are added, the mixture is stirred at a constant temperature for 18 min; after cooling to 35°C, rosemary extract, tea polyphenols, and vitamin E are added in sequence, and the mixture is stirred for 12 min; the resulting mixture is homogenized at 4000 r / min for 8 min, and then allowed to stand at room temperature in a sealed container for 16 min to degas, thus obtaining the microcapsule preservation coating emulsion.

[0069] The preparation method of the plant-derived nanocrystalline dense protective coating liquid in step S1 includes the following steps: green tea extract, tannic acid, and pectin are added sequentially to deionized water, stirred at 47°C for 32 min, then plant wax emulsion is added and stirred at low speed for homogenization, and allowed to stand for 1.2 h to prepare the plant-derived nanocrystalline dense protective coating liquid; the speed of the low-speed stirring homogenization is 250 r / min; the plasma activation pretreatment in step S2 is a normal pressure low temperature oxygen plasma activation pretreatment, and the specific process parameters are: working gas source pressure 0.5 MPa, gas flow rate 20 L / min, processing power 13 kW, discharge frequency 40 kHz, and paper feed speed 13 m / min.

[0070] The three-layer gradient stepwise precision coating described in step S3 specifically involves: first, applying a wet-heat dense primer with a dry coating amount of 6.2 g / m². 2 Pre-drying fixes the substrate structure, establishing a solid foundation for interlayer bonding; then, a microcapsule preservation intermediate coating emulsion is applied, with a dry coating amount of 4.2 g / m². 2 A stable microcapsule preservation intermediate coating is formed by uniformly coating the microcapsules; finally, a plant-derived nanocrystalline dense protective topcoat is applied, with a dry coating amount of 3.2 g / m². 2 A dense, non-porous plant-derived nanocrystalline protective coating was constructed; the total dry film thickness of the three-layer coating was 11 μm, and the coating speed was 13 m / min; the three-stage gradient drying temperatures in step S4 were 70℃, 90℃, and 110℃, with corresponding drying times of 6 min, 8 min, and 3 min, respectively, and the final overall coating moisture content was controlled to ≤4%, simultaneously protecting the microcapsule structure and promoting the cross-linking of the bottom layer and the nanocrystallization of the surface layer; the densification process parameters in step S5 were: constant steam temperature of 100℃, rolling pressure of 25 MPa, and paper feed speed of 10 m / min.

[0071] Comparative Example 1 A special paper for packaging and its manufacturing method are basically the same as those in Example 5, except that an equal amount of wet-heat dense base adhesive is used instead of the microcapsule preservation intermediate coating emulsion.

[0072] Comparative Example 2 A special paper for packaging and its manufacturing method are basically the same as those in Example 5, except that an equal amount of microcapsule preservation intermediate coating emulsion is used instead of plant-derived nanocrystalline dense protective surface coating liquid.

[0073] Comparative Example 3 A special paper for packaging and its manufacturing method are basically the same as those in Example 5, except that step S5 and the steam-heat coupled high-pressure densification treatment step are omitted.

[0074] To further illustrate the beneficial technical effects of the specialty paper used for packaging according to the present invention, relevant performance tests were conducted on the specialty paper used for packaging involved in Example 5 and Comparative Examples 1-3. The test results are shown in Table 1, and the test methods are as follows: (1) Water vapor transmission rate: The water vapor transmission rate was tested according to GB / T 1037-2021 "Determination of water vapor transmission performance of plastic films and sheets - cup method for weight gain and weight loss". The test environment was 23℃ and 50% relative humidity. (2) Grease resistance: Refer to GB / T 22805.1-2008 "Determination of grease resistance of paper and paperboard - Part 1: Penetration method" and count the total penetration time; (3) Paper folding endurance: The MIT double-fold method was used to determine the folding endurance of paper, referring to GB / T 457-2008 "Determination of folding endurance of paper and paperboard"; Table 1. Performance test results of specialty paper used for packaging

[0075] As can be seen from Table 1, the special paper used for packaging involved in Example 5 has good water vapor barrier properties, excellent grease resistance and folding resistance. The wet heat dense base liquid, microcapsule preservation intermediate coating emulsion, plant-derived nanocrystal dense protective top coating liquid and steam wet heat coupled high pressure densification treatment can synergistically improve the barrier properties and mechanical properties of the special paper.

[0076] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A special paper for packaging, characterized in that, The paper is composed of virgin wood pulp base paper and a three-layer gradient composite functional coating. From the inside out, the three-layer gradient composite functional coating consists of a moisture-heat densification modified base layer, a microcapsule preservation intermediate layer, and a plant-derived nanocrystalline dense protective top layer. The moisture-heat densification modified base layer is formulated with water-based polyurethane, polyvinyl alcohol, hydrophobic nano-silica, and other additives, and is used for densification and reinforcement of the fiber matrix. The microcapsule preservation intermediate layer uses chitosan quaternary ammonium salt and sodium alginate as wall materials, and natural plant preservatives as core materials to encapsulate slow-release microcapsules. The plant-derived nanocrystalline dense protective top layer is formed by in-situ crystallization of green tea extract, tannic acid, plant wax emulsion, and pectin to create a nanocrystalline protective film. After steam moisture-heat coupled high-pressure densification treatment, the fiber porosity is ≤8%, and the density is 0.95~1.15 g / cm³. 3 The average antibacterial rate is ≥99%.

2. The special paper for packaging according to claim 1, characterized in that, The base paper is made from a blend of softwood pulp and hardwood pulp at a mass ratio of (3-5):5, with a basis weight of 90-110 g / m³. 2 The original porosity is 45%~50%.

3. The special paper for packaging according to claim 1, characterized in that, The moisture-heat-densified modified primer coating comprises, by weight percentage: 45-55% waterborne polyurethane emulsion, 12-18% polyvinyl alcohol, 6-9% hydrophobic nano-silica, 0.8-1.2% coupling agent, 4-7% stearate, 3-4% polyether polyol, 0.2-0.4% polyether defoamer, 2-3% crosslinking agent, and the balance being deionized water; the waterborne polyurethane emulsion is Yoshida Chemical 1624 anionic aliphatic waterborne polyurethane emulsion; the polyvinyl alcohol is non-cellulose grade polyvinyl alcohol 24-88; and the hydrophobic nano-silica is hydrophobic fumed silica AEROSIL. R972; the coupling agent is at least one selected from silane coupling agent KH550, silane coupling agent KH560, and silane coupling agent KH570; the stearate is glyceryl monostearate; the polyether polyol is polyether polyol DL2000; the polyether defoamer is SH-237; and the crosslinking agent is polycarbodiimide curing agent XR-201.

4. The special paper for packaging according to claim 1, characterized in that, The microcapsule preservation coating comprises, by weight percentage: 8-12 parts food-grade chitosan quaternary ammonium salt, 6-10 parts sodium alginate, 2-4 parts rosemary extract, 1.5-3 parts tea polyphenols, 1-2 parts vitamin E, 2-3 parts glycerin, and the remainder being deionized water; the degree of substitution of the food-grade chitosan quaternary ammonium salt is 90%-95%, and the molecular weight is 150-250 kDa; the sodium alginate is food-grade sodium alginate, brand name MYF, and specification 200-600 cps.

5. The special paper for packaging according to claim 1, characterized in that, The plant-derived nanocrystalline dense protective coating comprises, by weight percentage: 5-8% green tea extract, 3-5% tannins, 4-6% plant wax emulsion, 2-4% pectin, with the balance being deionized water; the plant wax emulsion is a carnauba wax emulsion with the brand name AQUACER1541; and the pectin is GRINDSTED® Pectin AMD 780.

6. A method for manufacturing a special paper for packaging according to any one of claims 1-5, characterized in that, Includes the following steps: Step S1: Prepare the wet heat dense base coating liquid, the microcapsule preservation intermediate coating emulsion, and the plant-derived nanocrystal dense protective top coating liquid, respectively; Step S2: Plasma activation pretreatment of base paper; Step S3: Three-layer gradient stepwise precision coating; Step S4: Three-stage gradient drying and shaping; Step S5: Steam-heat coupled high-pressure densification treatment; Step S6: Set and cut at room temperature.

7. The method for manufacturing special paper for packaging according to claim 6, characterized in that, The preparation method of the humid heat dense base coating solution in step S1 includes the following steps: after mixing the raw materials of the humid heat dense base coating solution evenly, the solution is filtered to obtain the humid heat dense base coating solution; the preparation method of the microcapsule preservation intermediate coating emulsion in step S1 includes the following steps: sodium alginate is added to deionized water and stirred at 58-62℃ for 0.8-1.2h to obtain a colloidal solution; glycerol is added to the above colloidal solution and stirred for 4-6min to mix evenly; chitosan quaternary ammonium salt is added in 3 batches while stirring, with an interval of 3-5min between each batch, and after all materials are added, the mixture is stirred at a constant temperature for 13-18min; after cooling to 30-35℃, rosemary extract, tea polyphenols, and vitamin E are added in sequence, and the mixture is stirred for 8-12min; the resulting mixture is homogenized at 3000-4000r / min for 5-8min, and then allowed to stand at room temperature in a sealed container for 13-16min to defoam, thus obtaining the microcapsule preservation coating emulsion.

8. The method for manufacturing special paper for packaging according to claim 6, characterized in that, The preparation method of the plant-derived nanocrystalline dense protective coating liquid in step S1 includes the following steps: green tea extract, tannic acid, and pectin are added sequentially to deionized water, stirred at a constant temperature of 43-47℃ for 28-32 min, then plant wax emulsion is added and stirred at low speed to homogenize, and allowed to stand for 0.8-1.2 h to prepare the plant-derived nanocrystalline dense protective coating liquid; the speed of the low-speed stirring homogenization is 200-250 r / min.

9. The method for manufacturing special paper for packaging according to claim 6, characterized in that, The plasma activation pretreatment mentioned in step S2 is a low-temperature oxygen plasma activation pretreatment at atmospheric pressure. Specific process parameters are: working gas source pressure 0.3~0.5MPa, gas flow rate 15~20L / min, processing power 11~13kW, discharge frequency 20~40kHz, and paper feed speed 11-13m / min. The three-layer gradient stepwise precision coating mentioned in step S3 specifically involves: first, applying a moist, hot, dense primer, with a dry coating amount of 5.8-6.2g / m³. 2 The substrate structure is pre-dried to solidify the interlayer bonding; then a microcapsule preservation intermediate coating emulsion is applied, with a dry coating amount of 3.8-4.2 g / m². 2 A stable microcapsule preservation intermediate coating is formed by uniformly coating the microcapsules; finally, a plant-derived nanocrystalline dense protective topcoat is applied, with a dry coating amount of 2.8-3.2 g / m². 2 A dense, non-porous plant-derived nanocrystalline protective coating was constructed; the total dry film thickness of the three-layer coating was 9-11 μm, and the coating speed was 11-13 m / min.

10. The method for manufacturing special paper for packaging according to claim 6, characterized in that, The three-stage gradient drying temperatures in step S4 are 60~70℃, 80~90℃, and 100~110℃, respectively, with corresponding drying times of 4~6min, 5~8min, and 1~3min, respectively. The final overall coating moisture content is controlled to ≤4%, simultaneously protecting the microcapsule structure and promoting the cross-linking of the underlying layer and the nanocrystallization of the surface layer. The densification process parameters in step S5 are: constant steam temperature of 100℃, rolling pressure of 15~25MPa, and paper feed speed of 5~10m / min.

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