Preparation method of degradable high-moisture-resistance packaging paper based on bio-based multi-layer synergistic sizing and obtained product

Abstract

The invention belongs to the technical field of environment-friendly packaging materials, and particularly relates to a preparation method of degradable high-moisture-resistance packaging paper based on bio-based multi-layer synergistic sizing and an obtained product, and the degradable high-moisture-resistance packaging paper is suitable for seafood cold-chain transportation, medical supplies and other scenes needing high moisture resistance. The preparation method provided by the invention is realized by the following steps: coating the surface of the base paper layer with a structural layer material liquid, a colloidal dispersion liquid and an emulsion sealing liquid to obtain the degradable high-moisture-resistance packaging paper consisting of the base paper layer, a calcium bridge structural layer, a compact composite layer and an emulsion sealing layer. The degradable high-moisture-resistance packaging paper disclosed by the invention realizes a moisture-resistance breakthrough: the MVTR is lower than 45 g / m < 2 >. 24h and is reduced by 56% compared with a single-layer bio-based coating (such as 202311418369. X, and the MVTR is higher than 80), and the MVTR is close to the commercial level of PE coated paper (15-20); fiber pores are cross-linked and filled through a calcium bridge structure, so that a water vapor diffusion path is prolonged; the barrier efficiency of the compact composite layer is improved by 60%; the hydrogen bonds of the emulsion sealing layer seal the microcracks, so that a continuous defect-free barrier film can be realized.

Description

Technical Field

[0001] This invention belongs to the field of environmentally friendly packaging materials technology, specifically relating to a method for preparing biodegradable high moisture-barrier packaging paper based on bio-based multilayer synergistic sizing and the resulting product, which is suitable for scenarios requiring high moisture barrier, such as seafood cold chain transportation and medical supplies. Background Technology

[0002] In the field of environmentally friendly packaging materials, traditional polyethylene (PE) coated paper has long dominated, boasting a water vapor transmission rate (MVTR) of 15-20 g / m²·24h (ASTM E96 standard) and excellent moisture-proof properties. However, this type of material presents a serious contradiction regarding environmental sustainability: according to the Plastics Europe 2022 annual report, PE coated paper has a degradation cycle exceeding 100 years in the natural environment and remains indestructible even under industrial composting conditions. Furthermore, its production process has a carbon footprint as high as 2.8 × 10³ kg CO₂ / ton (based on SimaPro 9.3 life cycle analysis), primarily stemming from petroleum-based raw material extraction and high-temperature coating processes (energy consumption > 1.2 × 10³ kg CO₂ / ton). 3 (kWh / ton). Currently, only 9% of plastic-coated paper is effectively recycled globally, with the remainder releasing harmful substances such as microplastics and dioxins through incineration or landfill. More seriously, PE-coated paper is prone to brittleness and detachment in low-temperature (-20°C) cold chain environments, leading to microplastics contaminating seafood products (the EU's Rapid Alert System for Food and Feed (RASFF) reports an average of more than 50 cases annually), threatening food safety.

[0003] Although the direct production cost of PE coated paper is relatively low (approximately 0.8 yuan / m²), 2 However, its implicit environmental costs (such as carbon tax and waste disposal) are not included. The true life-cycle cost of plastic packaging is 3.2 times the production cost.

[0004] The invention patent with application number 202011336323.X uses a multilayer coating of carboxymethyl chitosan / polylactic acid (PLA), which is biodegradable, but its moisture-blocking performance is limited (Cobb value ≥ 2.08 g / m³). 2 Furthermore, it relies on chloroform solvent (highly toxic and difficult to recover), and the coating process requires multiple drying cycles (50-80℃ / 2-10min), resulting in high energy consumption and complexity. Chinese patent CN116411483B improves performance by combining an aluminum plating layer with a multi-layer barrier coating, but the aluminum plating layer is non-degradable (recycling requires metal separation, increasing costs), and the adhesion between the water-based acrylic emulsion and the aluminum plating layer depends on petroleum-based curing agents (such as diphenylmethane diisocyanate), which violates the principle of all-bio-based design. The invention patent with application number 202410181181.6 relies on a high-temperature extrusion coating process of 140-160℃, which leads to the thermal degradation of PLA (a decrease in crystallinity of more than 20%), drastic fluctuations in moisture barrier performance, and the risk of heavy metal aluminum residue introduced by the aluminate coupling agent. Chinese patent application 202311418369.X uses styrene-butadiene latex (petroleum-based) as an adhesive, which has limited biodegradability (compost degradation rate <70%), and the pre-coating amount is as high as 15 g / m². 2 The cost increases by 35%; Chinese patent CN105755890B discloses a method for preparing superhydrophobic and oleophobic transparent nanocellulose paper, but it relies on fluorinated silane coupling agents (such as heptadecafluorodecyltrimethoxysilane), and the preparation requires multiple chemical modifications (pH adjustment, vacuum filtration), making the process complex (time > 24h).

[0005] Therefore, existing solutions either rely on fluorides, petroleum-based adhesives, or introduce non-degradable coatings, making it difficult to meet the requirements of sustainability throughout the entire life cycle. Moreover, bio-based materials themselves have the following technical contradictions: ① Hydrophilic-hydrophobic imbalance: Natural polymers (such as starch and chitosan) contain a large number of polar groups (-OH, -NH2), resulting in persistently high MVTR; ② Interfacial incompatibility: Different bio-based materials have difficulty forming continuous and dense films due to differences in polarity (e.g., the hydrophilicity of chitosan conflicts with the hydrophobicity of PLA); ③ Uncontrollable process: During the traditional coating and drying process, the difference in the coefficient of thermal expansion (CTE) of the materials exceeds 50 ppm / ℃, leading to coating cracking and failure. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a method for preparing biodegradable high moisture-resistance packaging paper based on a bio-based multilayer synergistic sizing process, through a base paper pretreatment-bio-based sizing-gradient drying synergistic process.

[0007] Another objective of this invention is to provide a biodegradable high moisture-barrier packaging paper obtained by the above preparation method; this packaging paper can achieve moisture resistance (MVTR≤50 g / m²). 2 The synergistic optimization of 24-hour compostability (60-day degradation rate ≥90%) and cost-effectiveness provides a sustainable alternative that complies with EU regulations (EU 10 / 2011) for high-requirement scenarios such as seafood cold chain.

[0008] The technical solution adopted by the present invention to achieve the above objectives is as follows: This invention provides a method for preparing biodegradable high-resistance packaging paper based on bio-based multilayer synergistic sizing, comprising the following steps: (1) Internal sizing is performed during the preparation of the base paper to obtain the base paper layer; (2) The structural layer liquid is coated on the surface of the base paper layer to obtain the base paper layer - "calcium bridge" structural layer; (3) The base paper layer-"calcium bridge" structure layer is further coated with colloidal dispersion to obtain the base paper layer-"calcium bridge" structure layer-dense composite layer; (4) The base paper layer, the "calcium bridge" structural layer, and the dense composite layer are coated with an emulsion sealing liquid to obtain a biodegradable high moisture barrier packaging paper composed of the base paper layer, the "calcium bridge" structural layer, the dense composite layer, and the emulsion sealing layer.

[0009] Preferably, in step (1), the sizing is performed by applying the base adhesive solution through a three-pressure zone composite pressing process; the linear pressure of the three-pressure zone composite pressing is controlled at 90 kN / m or above.

[0010] Preferably, in step (1), the composition of the base adhesive is: 10 parts of AKD neutral sizing agent, 1-1.2 parts of catechol, and 0.3-0.5 parts of polyglutamic acid.

[0011] Preferably, in step (2), the composition of the structural layer liquid is: 2 parts starch, 30 parts calcium stearate, 10 parts kelp powder, and 50-55 parts styrene-butadiene latex.

[0012] Preferably, in step (2), the coating amount is 4-6 g / m². 2 (Wet gel), dry with hot air at 70 ℃ for 20 seconds, film thickness 3-4 μm.

[0013] Preferably, in step (3), the colloidal dispersion is composed of: 50 parts of adhesive and 10 parts of nanocellulose (CNF); the adhesive is starch, latex, polyvinyl alcohol or chitosan; the degree of deacetylation of the adhesive is 60-90%; the aspect ratio of the CNF is 40-80; the colloidal dispersion is formed under acidic conditions; the pH of the acid is 4.5-5.0.

[0014] Preferably, in step (3), the coating conditions are: coating amount 3-5 g / m². 2 (Wet glue), dry at 80℃.

[0015] Preferably, in step (4), the composition of the emulsion sealing liquid is: 8 parts adhesive and 3 parts emulsion; the solid content of the emulsion is 30-60%; preferably, the solid content of the emulsion is 40-60%; most preferably, the solid content of the emulsion is 40%; the adhesive is carboxymethyl cellulose, polyvinyl alcohol or casein; the emulsion is waterborne acrylic acid, waterborne polylactic acid, polyacrylate or polyvinyl acetate.

[0016] Preferably, in step (4), the coating amount of the emulsion blocking liquid is 5-8 g / m³. 2 (Wet adhesive), infrared curing at 55 ℃ for 15 seconds, controlling the surface tension at 38 mN / m or above.

[0017] The present invention also provides a biodegradable high moisture-resistance packaging paper prepared by the above preparation method.

[0018] In the calcium bridge structure layer provided by the present invention, the carboxyl content of the starch is 0.3-0.8 mol / kg; the particle size of the calcium stearate is 5-15 μm; and the starch is corn starch, oil-resistant starch, tapioca starch, oxidized starch or cationic starch.

[0019] This invention achieves a breakthrough balance in moisture barrier properties, environmental friendliness, and mechanical performance through a bio-based polar gradient synergistic mechanism. Compared with existing technologies, the beneficial effects of this invention are as follows: 1. The biodegradable high moisture-barrier packaging paper of this invention achieves a breakthrough in moisture-barrier performance: MVTR is less than 45 g / m³. 2 • In 24 hours, it reduces the MVTR by 56% compared to single-layer bio-based coatings (such as 202311418369.X, with an MVTR higher than 80), approaching the commercial level of PE coated paper (15-20); the water vapor diffusion path is extended by filling the fiber pores through the cross-linking of the "calcium bridge" structure; the barrier efficiency of the dense composite layer is improved by 60%; the hydrogen bonds of the emulsion sealing layer seal the microcracks, which can realize a continuous and defect-free barrier film.

[0020] 2. The compostable high moisture-barrier packaging paper of this invention exhibits a 60-day weight loss rate ≥95% (ASTM D5338) in compostable degradation tests, which is 15% higher than the fluorinated solution (CN105755890B), and has no PFAS residue (detection limit <1ppm); the all-bio-based raw materials reduce carbon emissions to 420 kg CO2 / ton, which is 85% lower than PE coated paper (2800 kg CO2 / ton); it has passed FDA 21 CFR176.170 food contact materials and EN 13432 industrial composting certifications.

[0021] 3. The biodegradable high moisture-resistance packaging paper of this invention has a tensile strength higher than 48 MPa (GB / T 12914), which is 220% higher than that of pure chitosan film (15 MPa), meeting the impact resistance requirements of cold chain transportation; after 10 freezing cycles, there is no delamination (peel strength ≥1.8N / 15mm), which is significantly better than PLA coated paper (strength decreases by 30% after 5 cycles); moreover, this application supports high-speed coating at 80-100 m / min, which increases the production capacity by 40% compared with multi-layer aluminizing solution (CN116411483B). Detailed Implementation

[0022] The following describes preferred embodiments of the present invention, which are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art. However, it should be understood that the invention should not be limited to the embodiments described herein.

[0023] Example 1 (1) Base paper layer: Unbleached kraft paper (100 g / m²) 2 Tightness 0.85 g / cm 3 The process employs a linear pressure of 90 kN / m and a three-zone composite pressing process, during which a base rubber solution (10 parts AKD neutral sizing agent, 1.2 parts catechin, and 0.3 parts polyglutamic acid) is applied internally, with the base rubber solution accounting for 1%. (2) The structural layer solution (2 parts starch, 30 parts calcium stearate, 10 parts kelp powder, and 50 parts styrene-butadiene latex) is coated on the surface of the base paper layer, with a coating amount of 5 g / m. 2 Dry with hot air at 70 ℃ for 20 seconds to form a film, resulting in a base paper layer - "calcium bridge" structural layer; (3) The base paper layer-"calcium bridge" structure layer is further coated with colloidal dispersion (50 parts chitosan, 10 parts nanocellulose (CNF), pH=5.0), with a coating amount of 4g / m², and dried with hot air at 80℃ for 30 seconds to obtain the base paper layer-"calcium bridge" structure layer-dense composite layer. (4) Coat the base paper layer-"calcium bridge" structural layer-dense composite layer with an emulsion blocking solution (8 parts CMC and 3 parts PLA emulsion with 40% solid content), with a coating amount of 7 g / m. 2 Infrared curing at 55℃ produces a biodegradable, high-moisture-barrier packaging paper composed of a base paper layer, a "calcium bridge" structural layer, a dense composite layer, and an emulsion sealing layer.

[0024] Example 2 (1) Base paper layer: Unbleached kraft paper (100 g / m²) 2 Tightness 0.85 g / cm 3 The process employs a linear pressure of 90 kN / m and a three-zone composite pressing process, during which a base rubber solution (10 parts AKD neutral sizing agent, 1.2 parts catechin, and 0.45 parts polyglutamic acid) is applied internally, with the base rubber solution accounting for 1% of the total weight. (2) The structural layer liquid (composition is the same as in Example 1) is coated on the surface of the base paper layer, with a coating amount of 6 g / m. 2 Dry with hot air at 70 ℃ for 20 seconds to form a film, resulting in a base paper layer - "calcium bridge" structural layer; (3) The base paper layer-"calcium bridge" structure layer is further coated with colloidal dispersion (50 parts chitosan, 10 parts nanocellulose (CNF), pH=4.5), with a coating amount of 5g / m², and dried with hot air at 80℃ for 30 seconds to obtain the base paper layer-"calcium bridge" structure layer-dense composite layer. (4) Coat the base paper layer-"calcium bridge" structural layer-dense composite layer with an emulsion blocking solution (8 parts CMC and 3 parts PLA emulsion with 50% solid content), with a coating amount of 9 g / m. 2Infrared curing at 55℃ produces a biodegradable, high-moisture-barrier packaging paper composed of a base paper layer, a "calcium bridge" structural layer, a dense composite layer, and an emulsion sealing layer.

[0025] Example 3 (1) Base paper layer: FSC certified recycled paper (80g / m²) 2 The process employs a linear pressure of 90 kN / m and a three-zone composite pressing process, during which a base rubber solution (10 parts AKD neutral sizing agent, 1.0 part catechin, and 0.5 parts polyglutamic acid) is applied internally, with an application rate of 0.8%. (2) The structural layer liquid (composition is the same as in Example 1) is coated on the surface of the base paper layer, with a coating amount of 4 g / m. 2 Dry with hot air at 70 ℃ for 20 seconds to form a film, resulting in a base paper layer - "calcium bridge" structural layer; The other steps are the same as in Example 1.

[0026] Comparative Example 1 (1) Base paper layer: Unbleached kraft paper (100 g / m²) 2 Tightness 0.85 g / cm 3 The process employs a linear pressure of 90 kN / m and a three-zone composite pressing process, during which a base rubber solution (11.5 parts of AKD neutral sizing agent) is applied internally, with the base rubber solution application rate being 1%. The other steps are the same as in Example 1.

[0027] Comparative Example 2 (1) Base paper layer: Unbleached kraft paper (100 g / m²) 2 Tightness 0.85 g / cm 3 The process employs a linear pressure of 90 kN / m and a three-zone composite pressing process, during which a base rubber solution (10 parts AKD neutral sizing agent, 1.2 parts catechin, and 0.3 parts polyglutamic acid) is applied internally, with the base rubber solution accounting for 1%. (2) The structural layer solution (12 parts starch, 30 parts calcium stearate, and 50 parts styrene-butadiene latex) is coated on the surface of the base paper layer, with a coating amount of 5 g / m. 2 Dry with hot air at 70 ℃ for 20 seconds to form a film, resulting in a base paper layer - "calcium bridge" structural layer; (3) The base paper layer-"calcium bridge" structure layer is further coated with colloidal dispersion (50 parts chitosan, 10 parts nanocellulose (CNF), pH=5.0), with a coating amount of 4g / m², and dried with hot air at 80℃ for 30 seconds to obtain the base paper layer-"calcium bridge" structure layer-dense composite layer. (4) Coat the base paper layer-"calcium bridge" structural layer-dense composite layer with an emulsion blocking solution (8 parts CMC and 3 parts PLA emulsion with 40% solid content), with a coating amount of 7 g / m. 2Infrared curing at 55℃ produces a biodegradable, high-moisture-barrier packaging paper composed of a base paper layer, a "calcium bridge" structural layer, a dense composite layer, and an emulsion sealing layer.

[0028] Effect Verification 1 The biodegradable high-resistance moisture-proof packaging papers prepared in the examples and comparative examples were subjected to relevant performance tests. The specific test methods are as follows: (1) MVTR (water vapor transmission rate): The test shall be conducted in accordance with GB / T 458-2008. The water vapor transmission rate shall be measured in a constant temperature and humidity environment using a paper air permeability tester. The sample shall be pretreated in an environment of 23±2℃ and 50%±5% RH for 24 hours before the formal test.

[0029] (2) Tensile strength (MPa): Tested according to QB / T 1014-2010; (3) Heat sealing strength (N / 15mm): Tested according to GB / T 8808-2022; (4) Compost degradation rate (60 days): Tested according to GB / T 19277.1; (5) Antibacterial durability (30 days): Tested according to ISO 22196; (7) Cold storage circulation (10 times): from the low temperature of the cold storage to the daily environment: temperature change from -20℃ to 50℃ 10 times.

[0030] The specific results are shown in Table 1.

[0031] Table 1 The data above shows that the MVTR of all embodiments and comparative examples is ≤53g / m³. 2 • 24h, among which Examples 1-3 showed the best performance; the present invention can adapt to different scenario requirements by flexibly adjusting the coating formula and process parameters, and achieve the optimal balance between moisture resistance, environmental protection and functionality.

Claims

1. A method for preparing biodegradable high-resistance packaging paper based on bio-based multilayer synergistic sizing, characterized in that, Includes the following steps: (1) Internal sizing is performed during the preparation of the base paper to obtain the base paper layer; (2) The surface of the base paper layer is coated with a structural layer liquid to obtain the base paper layer - "calcium bridge" structural layer; (3) The base paper layer - "calcium bridge" structure layer is further coated with colloidal dispersion to obtain the base paper layer - "calcium bridge" structure layer - dense composite layer; (4) The base paper layer, "calcium bridge" structural layer and dense composite layer are coated with emulsion sealing liquid to obtain a biodegradable high moisture barrier packaging paper composed of base paper layer, "calcium bridge" structural layer, dense composite layer and emulsion sealing layer.

2. The preparation method according to claim 1, characterized in that, In step (1), the sizing process involves applying the base adhesive solution through a three-pressure zone composite pressing process; the linear pressure of the three-pressure zone composite pressing is controlled at 90 kN / m or above.

3. The preparation method according to claim 2, characterized in that, In step (1), the composition of the base adhesive is: 10 parts of AKD neutral sizing agent, 1-1.2 parts of catechol, and 0.3-0.5 parts of polyglutamic acid.

4. The preparation method according to claim 1, characterized in that, In step (2), the composition of the structural layer liquid is: 2 parts starch, 30 parts calcium stearate, 10 parts kelp powder, and 50-55 parts styrene-butadiene latex.

5. The preparation method according to claim 1 or 4, characterized in that, In step (2), the coating amount is 4-6 g / m². 2 (Wet gel), dry with hot air at 70 ℃ for 20 seconds, film thickness 3-4 μm.

6. The preparation method according to claim 1, characterized in that, In step (3), the colloidal dispersion is composed of: 50 parts of adhesive and 10 parts of nanocellulose (CNF); the adhesive is starch, latex, polyvinyl alcohol or chitosan; the degree of deacetylation of the adhesive is 60-90%; the aspect ratio of the CNF is 40-80; the colloidal dispersion is formed under acidic conditions; the pH of the acid is 4.5-5.

0.

7. The preparation method according to claim 1 or 6, characterized in that, In step (3), the coating conditions are: coating amount 3-5 g / m². 2 (Wet glue), dry at 80℃.

8. The preparation method according to claim 1, characterized in that, In step (4), the composition of the emulsion sealing liquid is: 8 parts adhesive and 3 parts emulsion; the solid content of the emulsion is 30-60%; preferably, the solid content of the emulsion is 40-60%; most preferably, the solid content of the emulsion is 40%; the adhesive is carboxymethyl cellulose, polyvinyl alcohol or casein; the emulsion is waterborne acrylic acid, waterborne polylactic acid, polyacrylate or polyvinyl acetate.

9. The preparation method according to claim 1 or 8, characterized in that, The coating requirement is: coating amount 5-8 g / m² 2 (Wet adhesive), infrared curing at 55 ℃ for 15 seconds, controlling the surface tension at 38 mN / m or above.

10. A biodegradable high moisture-resistance packaging paper prepared by the preparation method according to any one of claims 1-9.

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