Tear-resistant and impact-resistant low-water-absorption ice bag paper and preparation method thereof

Abstract

The application belongs to the technical field of paper-based cold-chain packaging materials, and provides a tear-resistant and impact-resistant low-water-absorption ice wrapping paper and a preparation method thereof.The application introduces cellulose micro-nanofilament-alkyl enone dimer composite intermediates into a paper-based fiber layer formed by bleached kraft softwood pulp and bleached kraft hardwood pulp, controls the dispersion, heat treatment, forming, drying and heat curing conditions of the composite intermediates, forms a paper sheet structure with fiber bridging and hydrophobic micro-domain regulation, realizes a lower Cobb60 value, a higher tear index, a higher cold-chain simulation impact rupture energy, a suitable basis weight, a thickness and an apparent density, alleviates the contradiction between the easy water absorption of the enhanced fiber network and the easy weakening of the hydrophobic sizing, and is suitable for ice wrapping outer packaging and cold-chain buffer packaging scenes.

Description

Technical Field

[0001] This invention relates to the field of paper-based cold chain packaging materials, specifically to a tear-resistant, impact-resistant, low-absorbency ice pack paper and its preparation method. Background Technology

[0002] Paper-based ice pack materials are commonly used in cold chain transportation, food preservation, fresh produce delivery, medical cold compress packaging, and short-term low-temperature cushioning packaging. In these applications, the packaging paper needs to maintain low absorbency in low-temperature condensation environments while also maintaining good tear resistance and structural integrity during filling, sealing, handling, stacking, and repeated friction. Traditional paper-based materials provide strength through inter-fiber hydrogen bonds and pulp-forming structures. However, cellulose fibers are inherently hydrophilic, and the inter-fiber bonds are easily weakened upon contact with water, leading to a decrease in dimensional stability and appearance integrity. Simply increasing fiber fineness or improving inter-fiber bonding often increases the number of fine fibers and capillary channels, making it easier for moisture to penetrate the paper. Conversely, relying solely on hydrophobic sizing or plastic coatings to reduce absorbency may result in decreased fiber bonding, complex recycling processes, or a decline in paper feel. Therefore, paper-based ice pack materials need to simultaneously achieve low absorbency, tear resistance, dispersion stability, and processing adaptability without a continuous plastic coating layer.

[0003] Various water-blocking solutions for ice packs or paper-based materials have been publicly disclosed. For example, Chinese utility model publication CN206138264U discloses a dual-purpose ice pack for heat application and cold storage. Its background mentions issues such as easy leakage of the non-woven fabric surface, difficulty in separation after freezing, and easy tearing. However, these structures mainly focus on combinations of non-woven fabric, plastic film, and cold storage agent, without addressing the regulation of reinforcement and hydrophobic synergy within the paper-based fiber network. Public literature also reports techniques for depositing alkyl ketene dimers in cellulose micro / nano filament sheets to improve water resistance, and techniques for forming hydrophobic coatings on cellulose paper using alkyl ketene dimer systems. However, these solutions mostly emphasize surface deposition, impregnation, or coating construction, leaving room for further improvement in the dispersion and stability of hydrophobic microdomains within the paper-based fiber layer, the retention at fiber cross-nodes, and the balance between tear resistance and low water absorption. Summary of the Invention

[0004] The purpose of this invention is to provide a tear-resistant, impact-resistant, low-absorbency ice pack paper and its preparation method, solving the technical problem that it is difficult to simultaneously achieve tear resistance, cold chain impact integrity, low water absorption, and dispersion stability in current paper-based ice pack materials.

[0005] This invention pre-composite cellulose micro-nano filaments with alkyl ketene dimers, so that the hydrophilic reinforcing unit no longer adds water absorption channels and the hydrophobic sizing unit no longer weakens fiber bonding. Furthermore, by using pulp dispersion and thermosetting, fiber bridging and hydrophobic microdomains are synergistically distributed within the paper-based fiber layer, thereby achieving a balance of tear resistance, impact resistance, and low water absorption.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A tear-resistant, impact-resistant, low-absorbency ice pack paper, comprising a paper-based fiber layer and a cellulose micro / nano filament-alkyl ketene dimer composite intermediate distributed in the paper-based fiber layer; The paper-based fiber layer comprises fibers formed from bleached sulfate softwood pulp and bleached sulfate hardwood pulp; The cellulose micro / nano filament-alkyl ketene dimer composite intermediate comprises cellulose micro / nano filaments and alkyl ketene dimers; The cellulose micro / nano filaments were obtained by mechanically defibrating bleached sulfate softwood pulp.

[0007] Furthermore, in the cellulose micro / nanofibrils-alkyl ketene dimer composite intermediate, the alkyl ketene dimer is distributed in the form of hydrophobic microdomains on the surface of the cellulose micro / nanofibrils or between fiber bundles; based on the total oven-dry weight of bleached sulfate softwood pulp and bleached sulfate hardwood pulp in the pulp system used to prepare the tear-resistant, impact-resistant, low-absorbency ice-packed paper, excluding the cellulose micro / nanofibrils and alkyl ketene dimer in the composite intermediate, the amount of the cellulose micro / nanofibrils-alkyl ketene dimer composite intermediate added is 0.5–5.0 wt% based on oven-dry weight.

[0008] Furthermore, the cellulose micro / nano filament-alkyl ketene dimer composite intermediate is prepared through the following steps: A1. Provides aqueous dispersions of cellulose micro / nano fibers; A2. Mix the alkyl ketene dimer with the cellulose micro / nanofibers at a mass ratio of 5–50:100; A3. The pH of the mixture was adjusted to 7.5–8.5 using sodium bicarbonate; A4. The mixture is sequentially subjected to melt dispersion, shear dispersion and homogenization to obtain a cellulose micro / nanofiber-alkyl ketene dimer predispersant; A5. The cellulose micro / nano filament-alkyl ketene dimer pre-dispersion is heat-treated at 90–120°C for 1–6 min to obtain the cellulose micro / nano filament-alkyl ketene dimer composite intermediate.

[0009] Further, in step A4, the melting dispersion temperature is 55–75℃ and the time is 10–40 min; the shear dispersion speed is 2000–8000 rpm and the time is 10–40 min; the homogenization pressure is 20–80 MPa and the number of times is 1–3; the quality control parameters of the cellulose micro / nano filament-alkyl ketene dimer composite intermediate are: the D50 of the hydrophobic microdomain of the alkyl ketene dimer is 50–300 nm; the proportion of the free alkyl ketene dimer mass to the added alkyl ketene dimer mass is not higher than 15 wt%; and the solid content of the cellulose micro / nano filament-alkyl ketene dimer composite intermediate in the form of an aqueous dispersion is 1.0–5.0 wt%.

[0010] Furthermore, the cellulose micro / nanofiber aqueous dispersion in step A1 is prepared through the following steps: B1. Disperse bleached sulfate softwood pulp in deionized water to obtain a dispersion system; B2. The pH of the dispersion system is adjusted to 6.5–8.5 using sodium bicarbonate; B3. Pulverize the dispersion system to a freeness of 35–60°SR; B4. Mechanically defibril the pulped dispersion system 1–6 times under 30–120 MPa conditions to obtain an aqueous dispersion of cellulose micro-nano fibers; The obtained cellulose micro / nanofibers have a number-average diameter of 20–100 nm and a number-average length of 0.8–8.0 μm.

[0011] Furthermore, based on the oven-dry fiber mass of the paper-based fiber layer, the total content of the bleached sulfate softwood pulp and the bleached sulfate hardwood pulp is 100 wt%, wherein the content of the bleached sulfate softwood pulp is 45–85 wt%, and the content of the bleached sulfate hardwood pulp is 15–55 wt%; the cellulose micro / nano filament-alkyl ketene dimer composite intermediate is located on the surface of the fibers, at fiber intersections, or at micropores between fibers in the paper-based fiber layer.

[0012] Furthermore, the Cobb60 value of the tear-resistant, impact-resistant, low-absorbency ice pack paper is 6–18 g / m². 2 The tear index is 10–30 mN·m 2 / g, quantitative range 60–130g / m 2 The thickness is 80–220 μm, and the apparent density is 0.45–0.90 g / cm³. 3 The apparent density is obtained by converting the basis weight and the thickness; the tear-resistant, impact-resistant, low-absorbency ice pack does not include a continuous plastic coating layer.

[0013] As another aspect of this invention, the present invention employs a method of first preparing a cellulose micro / nanofibril-alkyl ketene dimer composite intermediate, then adding it to the pulp system and subjecting it to forming, pressing, drying, and thermosetting. This method is primarily used to achieve and stabilize the aforementioned synergistic effects, facilitating process scale-up. If hydrophilic cellulose micro / nanofibrils and hydrophobic alkyl ketene dimers are directly added to the pulp system, the cellulose micro / nanofibrils easily alter the pulp's water filtration and paper's water absorption channels, while the alkyl ketene dimers tend to become free or locally enriched. By pre-melting and dispersing, shearing and dispersing, homogenizing, and heat-treating to form the composite intermediate, and by controlling the addition amount, mixing conditions, pressing dryness, drying, and thermosetting conditions in the pulp system, the effective distribution of the composite intermediate on the fiber surface and at fiber cross-nodes can be improved, allowing the paper to maintain both fiber network bonding and hydrophobic microdomain effects after paper formation.

[0014] This invention also discloses a method for preparing tear-resistant, impact-resistant, low-absorbency ice-packing paper as described in any of the foregoing claims, comprising the following steps: S1. Provides the prepared cellulose micro / nano filament-alkyl ketene dimer composite intermediate; S2. Bleached sulfate softwood pulp and bleached sulfate hardwood pulp are added to deionized water, dispersed and pulped to obtain a pulp system; S3. The cellulose micro / nano filament-alkyl ketene dimer composite intermediate is added to the pulp system, based on the total oven-dry weight of bleached sulfate softwood pulp and bleached sulfate hardwood pulp in the pulp system, excluding the cellulose micro / nano filaments and alkyl ketene dimer in the composite intermediate. The amount of the cellulose micro / nano filament-alkyl ketene dimer composite intermediate added is 0.5–5.0 wt% based on oven-dry weight, to obtain a mixed pulp. S4. The mixed pulp is shaped, pressed, and dried to obtain a dried paper sheet; S5. The dried paper is heat-cured at 90–120°C for 1–6 minutes to obtain the tear-resistant, impact-resistant, low-absorbency ice-wrapped paper.

[0015] Further, in step S2, based on the total oven-dry weight of bleached sulfate softwood pulp and bleached sulfate hardwood pulp in the pulp system used to prepare the paper-based fiber layer, and excluding the cellulose micro / nano filaments and alkyl ketene dimers in the composite intermediate, the total content of the bleached sulfate softwood pulp and the bleached sulfate hardwood pulp is 100 wt%, wherein the content of the bleached sulfate softwood pulp is 45–85 wt%, the content of the bleached sulfate hardwood pulp is 15–55 wt%, the solids content of the pulp system is 0.2–1.2 wt%, and the freeness is 25–55°SR.

[0016] Further, in step S3, the cellulose micro / nano filament-alkyl ketene dimer composite intermediate is added to the pulp system and mixed at 100–600 rpm for 10–40 min to obtain the mixed pulp.

[0017] Furthermore, in step S4, the dryness of the paper sheet after pressing is 35–55 wt%.

[0018] Further, after step S5, the aqueous dispersion containing the cellulose micro / nanofiber-alkyl ketene dimer composite intermediate is added at a concentration of 0.1–1.5 g / m³. 2 The appropriate amount is applied to the cut edge area of ​​the tear-resistant, impact-resistant, low-absorbency ice pack paper and dried at 80–110°C for 1–5 min.

[0019] Furthermore, after step S5, the tear-resistant, impact-resistant, low-absorbency ice pack paper is calendered under calendering conditions of 20–100 kN / m pressure and calendering temperature of 40–90°C.

[0020] As another aspect of this invention, the present invention employs a method of first preparing a cellulose micro / nanofibril-alkyl ketene dimer composite intermediate, then adding it to a pulp system and subjecting it to forming, pressing, drying, and thermosetting. This method is primarily used to achieve, fix, or amplify the aforementioned synergistic effects. If hydrophilic cellulose micro / nanofibrils and hydrophobic alkyl ketene dimers are directly added to the pulp system, the cellulose micro / nanofibrils easily alter the pulp's water filtration and paper's water absorption channels, while the alkyl ketene dimers tend to become free or locally enriched. By pre-melting and dispersing, shearing and dispersing, homogenizing, and heat-treating to form the composite intermediate, and by controlling the addition amount, mixing conditions, pressing dryness, drying, and thermosetting conditions in the pulp system, the effective distribution of the composite intermediate on the fiber surface and at fiber cross-nodes can be improved, allowing the paper to maintain both fiber network bonding and hydrophobic microdomain effects after paper formation.

[0021] Cellulose micro / nanofibrils primarily address the issues of insufficient fiber cross-linking and tear propagation resistance in paper-based fiber layers. However, when cellulose micro / nanofibrils exist alone or in high concentrations, their hydrophilic surfaces and refined fiber networks increase the pathways for water entry. Alkyl ketene dimers primarily address the issue of insufficient water absorption in paper sheets. However, when alkyl ketene dimers exist alone or are locally concentrated, they easily form free hydrophobic phases and weaken effective contact between fibers. This invention distributes alkyl ketene dimers as hydrophobic microdomains on the surface of cellulose micro / nanofibrils or between fiber bundles. Combined with melt dispersion, shear dispersion, homogenization, and heat treatment, the bridging effect of cellulose micro / nanofibrils and the hydrophobic effect of alkyl ketene dimers mutually correct each other within the paper-based fiber layer, ultimately achieving a balance between the inherently contradictory properties of tear resistance and low water absorption.

[0022] Furthermore, in preparing the cellulose micro / nano fiber aqueous dispersion, 100 parts by weight of bleached sulfate softwood pulp are added to 3000–10000 parts by weight of deionized water for dispersion. The pH of the resulting dispersion system is adjusted to 6.5–8.5 using sodium bicarbonate. The dispersion system is then pulped to a freeness of 35–60°SR and mechanically defibrinated 1–6 times under 30–120 MPa conditions to obtain a cellulose micro / nano fiber aqueous dispersion with a solid content of 0.5–2.5 wt%.

[0023] Further, the cellulose micro / nano filament-alkyl ketene dimer predispersant is heat-treated at 90–120°C for 1–6 min to obtain a cellulose micro / nano filament-alkyl ketene dimer composite intermediate. The solid content of the cellulose micro / nano filament-alkyl ketene dimer composite intermediate in the form of an aqueous dispersion is 1.0–5.0 wt%, and it is used as a composite sizing agent for addition to pulp systems.

[0024] Furthermore, when performing hydrophobic microdomain particle size detection on the cellulose micro / nanofibril-alkyl ketene dimer predispersant or the cellulose micro / nanofibril-alkyl ketene dimer composite intermediate, the aqueous dispersion of the cellulose micro / nanofibril-alkyl ketene dimer predispersant or the cellulose micro / nanofibril-alkyl ketene dimer composite intermediate is used as the sample to be tested. The particle size distribution data is recorded using dynamic light scattering at 25°C, and the particle size corresponding to the cumulative volume fraction reaching 50% in the volume distribution is taken as the D50 of the hydrophobic microdomain of the alkyl ketene dimer.

[0025] Furthermore, when detecting the free alkyl ketene dimer content in the cellulose micro / nanofibrils-alkyl ketene dimer composite intermediate, an aqueous dispersion of the cellulose micro / nanofibrils-alkyl ketene dimer composite intermediate is used as the sample to be tested. Alkyl ketene dimers that do not form a composite association with the cellulose micro / nanofibrils are separated and quantified. The proportion of the free alkyl ketene dimer mass to the added alkyl ketene dimer mass is calculated based on the ratio of the free alkyl ketene dimer mass to the added alkyl ketene dimer mass.

[0026] Furthermore, in preparing the pulp system, bleached sulfate softwood pulp and bleached sulfate hardwood pulp are dispersed and beaten in deionized water. The total oven-dry weight of the bleached sulfate softwood pulp and bleached sulfate hardwood pulp in the pulp system used to prepare the paper base fiber layer is used as the basis, excluding the cellulose micro / nano filaments and alkyl ketene dimers in the composite intermediate. The total content of the bleached sulfate softwood pulp and the bleached sulfate hardwood pulp is 100 wt%, wherein the content of the bleached sulfate softwood pulp is 45–85 wt%, the content of the bleached sulfate hardwood pulp is 15–55 wt%, the solids content of the pulp system is 0.2–1.2 wt%, and the freeness is 25–55°SR.

[0027] Further, after adding the cellulose micro / nano filament-alkyl ketene dimer composite intermediate to the pulp system, it is mixed at 100–600 rpm for 10–40 min to obtain a mixed pulp. The amount of the cellulose micro / nano filament-alkyl ketene dimer composite intermediate added, based on oven-dry weight, is 0.5–5.0 wt% of the total oven-dry weight of bleached sulfate softwood pulp and bleached sulfate hardwood pulp in the pulp system, and the total oven-dry weight does not include the cellulose micro / nano filaments and alkyl ketene dimer in the composite intermediate.

[0028] Further, the mixed pulp is formed and then pressed to achieve a paper dryness of 35–55 wt%. The pressed paper is then dried at 70–110°C to obtain a dried paper. Subsequently, the dried paper is heat-cured at 90–120°C for 1–6 minutes to obtain tear-resistant, impact-resistant, low-absorbency ice-packed paper.

[0029] Furthermore, the pressing line pressure after the mixed pulp is formed is 100–600 kN / m. The pressing line pressure is used to make the formed paper sheet achieve a post-press dryness of 35–55 wt%. After pressing, the paper sheet is dried at 70–110°C and then enters the heat curing step.

[0030] Furthermore, the retention rate of the cellulose micro / nano filament-alkyl ketene dimer composite intermediate in the paper-based fiber layer is 60–95 wt%, and the retention rate is calculated as the ratio of the oven-dry mass of the cellulose micro / nano filament-alkyl ketene dimer composite intermediate retained in the paper-based fiber layer to the oven-dry mass of the added cellulose micro / nano filament-alkyl ketene dimer composite intermediate.

[0031] Furthermore, the Cobb60 value of the tear-resistant, impact-resistant, low-absorbency ice pack paper is measured according to GB / T1540-2002, the tear index of the tear-resistant, impact-resistant, low-absorbency ice pack paper is measured according to GB / T455-2002, the apparent density of the tear-resistant, impact-resistant, low-absorbency ice pack paper is obtained by converting basis weight and thickness, and the equilibrium moisture content of the tear-resistant, impact-resistant, low-absorbency ice pack paper is 4.0–9.0 wt%.

[0032] Furthermore, after thermosetting, the aqueous dispersion containing the cellulose micro / nanofibrils-alkyl ketene dimer composite intermediate is applied at a concentration of 0.1–1.5 g / m³. 2 The amount of the product is applied to the cut edge area of ​​the tear-resistant, impact-resistant, low-absorbency ice pack paper and dried at 80–110°C for 1–5 min to obtain tear-resistant, impact-resistant, low-absorbency ice pack paper with the cellulose micro / nano filament-alkyl ketene dimer composite intermediate in the cut edge area.

[0033] Furthermore, after heat curing, the tear-resistant, impact-resistant, low-absorbency ice pack paper is subjected to calendering treatment. The calendering pressure is 20–100 kN / m, and the calendering temperature is 40–90℃, to obtain the calendered tear-resistant, impact-resistant, low-absorbency ice pack paper.

[0034] Beneficial technical effects 1. In this invention, cellulose micro / nano filaments and alkyl ketene dimers are pre-formed into a composite intermediate, so that the hydrophilic reinforcing unit and the hydrophobic sizing unit form a relatively stable composite state before entering the pulp system. This reduces the free and localized enrichment of alkyl ketene dimers, which is beneficial for them to simultaneously play a bridging reinforcement and low water absorption role in the paper fiber layer.

[0035] 2. By controlling the conditions of melt dispersion, shear dispersion, homogenization and heat treatment, this invention enables alkyl ketene dimers to be distributed in the form of hydrophobic microdomains on the surface of cellulose micro and nanofibers or between fiber bundles. This can reduce the adverse effects of hydrophobic phase aggregation on inter-fiber bonding and improve the uniformity of the distribution of composite intermediates at fiber cross nodes and inter-fiber micropores.

[0036] 3. This invention uses bleached sulfate softwood pulp and bleached sulfate hardwood pulp to form a paper-based fiber layer, and adds a composite intermediate to the pulp system by absolute dry weight. Softwood pulp is beneficial for forming a strong fiber skeleton, while hardwood pulp is beneficial for improving paper uniformity. The combination of the two with the composite intermediate can maintain good tear resistance under low water absorption conditions.

[0037] 4. This invention controls the dryness, temperature and processing time of the paper sheet during the forming, pressing, drying and heat curing processes, so that the composite intermediate is further fixed on the fiber surface and cross nodes after the paper sheet is formed. This is beneficial to obtain tear-resistant, impact-resistant and low-absorbency ice pack paper without a continuous plastic coating layer, which is suitable for ice pack outer packaging and cold chain cushioning packaging scenarios. Attached Figure Description

[0038] Figure 1 The image shows the dynamic light scattering differential particle size distribution of Example 1, Comparative Example 9, and Comparative Example 11.

[0039] Figure 2 The cumulative particle size distribution of dynamic light scattering is shown in Example 1, Comparative Example 9, and Comparative Example 11.

[0040] Figure 3 This is a proportion diagram of the free alkyl ketene dimers of Example 1, Comparative Example 9, and Comparative Example 11.

[0041] Figure 4 The graph shows the retention rates of the composite intermediates or corresponding additives for Examples 1, 7, and 11.

[0042] Figure 5The graph shows the relationship between the retention rate of the sample complex intermediate or corresponding additive and Cobb60.

[0043] Figure 6 This is a correlation graph between the Cobb60 index and the tear index of the sample.

[0044] Figure 7 This is a graph showing the relationship between the ratio of D50 and free alkyl ketene dimers under the sample process window.

[0045] Figure 8 This is a macroscopic optical photograph of the tear-resistant, impact-resistant, low-absorbency ice pack paper of Example 1.

[0046] Figure 9 This is a scanning electron microscope image of the tear-resistant, impact-resistant, low-absorbency ice packing paper from Example 1; Figure 9 a is a low-magnification scanning electron microscope image of the tear-resistant, impact-resistant, low-absorbency ice pack paper fiber interwoven network of Example 1; Figure 9 b and Figure 9 c is a high-magnification scanning electron microscope image of the distribution of cellulose micro-nano filaments on the surface of the tear-resistant, impact-resistant, low-absorbency ice-packing paper fiber in Example 1; Figure 9 d is a high-magnification scanning electron microscope image of the micro-nano entanglement and hydrophobic micro-domain distribution on the surface of the tear-resistant, impact-resistant, low-absorbency ice-packing paper fiber in Example 1; Figure 9 e is a cross-sectional scanning electron microscope image of the tear-resistant, impact-resistant, low-absorbency ice pack paper of Example 1. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0048] Example 1 Overall production scale and product form This embodiment uses the preparation of a sheet of tear-resistant, impact-resistant, low-absorbency ice-packed paper with an oven-dry fiber weight of 100.0g as an example. The product form is a paper sheet excluding the continuous plastic coating layer. Both bleached sulfate softwood pulp and bleached sulfate hardwood pulp are commercially available paper-grade pulps, the alkyl ketene dimer is a commercially available paper sizing grade raw material, sodium bicarbonate is a commercially available analytical grade reagent, and the water is deionized water.

[0049] Raw materials, components or material specifications In this embodiment, the paper-based fiber layer is formed from 45.0 g of oven-dried bleached sulfate softwood pulp and 55.0 g of oven-dried bleached sulfate hardwood pulp. 0.50 g of the cellulose micro / nanofibrils-alkyl ketene dimer composite intermediate is added based on oven-dried weight, representing 0.5 wt% of the oven-dried fiber mass of the pulp system. The composite intermediate in this embodiment is prepared from 100 parts by weight of oven-dried cellulose micro / nanofibrils and 5 parts by weight of alkyl ketene dimer.

[0050] Step 1: Preparation of aqueous dispersion of cellulose micro / nanofibrils 100 parts by weight of bleached sulfate softwood pulp were added to 10,000 parts by weight of deionized water and stirred at 300 rpm for 20 minutes at 25°C to ensure uniform dispersion. Sodium bicarbonate was added to adjust the pH of the dispersion to 6.5. The dispersion was then beaten to 35°SR and mechanically defibrinated once at 30 MPa to obtain an aqueous dispersion of cellulose micro / nano fibers. The solid content of the cellulose micro / nano fiber aqueous dispersion was adjusted to 0.50 wt% by adding deionized water and stirring at low speed. In this embodiment, the number average diameter of the cellulose micro / nano fibers was 100 nm, and the number average length was 8.0 μm.

[0051] Step 2: Preparation of cellulose micro / nanofiber-alkyl ketene dimer composite intermediate Based on absolute dry weight, 100 parts by weight of cellulose micro / nanofibers from the aqueous dispersion of cellulose micro / nanofibers were added, along with 5 parts by weight of alkyl ketene dimer, and premixed at 25°C for 10 min. Sodium bicarbonate was added to adjust the pH of the mixture to 7.5. The mixture was heated to 55°C and held for 10 min to melt and disperse the alkyl ketene dimer; then sheared and dispersed at 2000 rpm for 10 min; and then homogenized once at 20 MPa to obtain a cellulose micro / nanofiber-alkyl ketene dimer predispersant. The predispersant was heat-treated at 90°C for 1 min, and then cooled to 25°C to obtain a cellulose micro / nanofiber-alkyl ketene dimer composite intermediate. The solid content of the composite intermediate in this example was 1.0 wt%.

[0052] Step 3: Pulp system preparation and addition of composite intermediates 45.0 g of oven-dried bleached sulfate softwood pulp and 55.0 g of oven-dried bleached sulfate hardwood pulp were added to deionized water and dispersed at 25°C for 30 min to adjust the solid content of the pulp system to 0.2 wt%. The pulp system was beaten to 25°SR. 0.50 g of cellulose micro / nanofibril-alkyl ketene dimer composite intermediate (equivalent to oven-dried weight) was added to the pulp system and mixed at 100 rpm for 10 min to obtain a mixed pulp. The criterion for complete mixing was the absence of visible agglomerates in the pulp, and the difference in solid content measured at three locations was no higher than 0.05 wt%.

[0053] Step 4: Shaping, pressing, drying and thermosetting The mixed pulp was wet-formed into paper sheets, which were then pressed under a pressure of 100 kN / m on a press line to achieve a dryness of 35 wt%. The pressed paper sheets were dried at 70°C until the mass change between two consecutive weighings was less than 0.5 wt%, resulting in dried paper sheets. The dried paper sheets were then heat-cured at 90°C for 1 min and cooled to 25°C to obtain tear-resistant, impact-resistant, low-absorbency ice-packed paper. In this embodiment, no edge treatment or calendering was performed.

[0054] Quality testing methods and results The paper sheets of this embodiment were equilibrated for 24 hours at 23°C and 50% relative humidity before testing, with three samples taken for each test. The hydrophobic microdomain D50 of the alkyl ketene dimer in the aqueous dispersion of the composite intermediate was measured to be 300 nm at 25°C. The mass ratio of the free alkyl ketene dimer to the added alkyl ketene dimer was 14.9 wt%, and the retention rate of the composite intermediate in the paper fiber layer was 60.0 wt%. The Cobb60 value of the paper sheets in this embodiment was 18.0 ± 0.4 g / m³. 2 The tear index was 10.0 ± 0.3 mN·m. 2 / g, quantitatively 60.0±0.6g / m 2 The thickness is 80.0±1.0μm, and the apparent density is 0.75g / cm³. 3 The equilibrium moisture content is 9.0 ± 0.2 wt%.

[0055] Features and application scenarios of this embodiment This embodiment adopts a relatively conservative low-ratio scheme and mild processing conditions. The paper has a low basis weight and no continuous plastic coating layer. It is suitable for use as inner lining paper for ice pack packaging or short-term cold chain cushioning packaging paper, which requires lightweight materials, paper feel and basic moisture resistance.

[0056] Example 2 Overall production scale and product form This embodiment uses the preparation of a sheet of tear-resistant, impact-resistant, low-absorbency ice-packed paper with an oven-dry fiber weight of 100.0g as an example. The product form is a paper sheet that has undergone edge trimming and calendering treatment. Both bleached sulfate softwood pulp and bleached sulfate hardwood pulp are commercially available paper-grade pulps, the alkyl ketene dimer is a commercially available paper sizing grade raw material, sodium bicarbonate is a commercially available analytical grade reagent, and the water is deionized water.

[0057] Raw materials, components or material specifications In this embodiment, the paper-based fiber layer is formed from 85.0 g of oven-dried bleached sulfate softwood pulp and 15.0 g of oven-dried bleached sulfate hardwood pulp. 5.00 g of the cellulose micro / nanofibrils-alkyl ketene dimer composite intermediate is added based on oven-dried weight, representing 5.0 wt% of the oven-dried fiber mass of the pulp system. The composite intermediate in this embodiment is prepared from 100 parts by weight of oven-dried cellulose micro / nanofibrils and 50 parts by weight of alkyl ketene dimer.

[0058] Step 1: Preparation of aqueous dispersion of cellulose micro / nanofibrils 100 parts by weight of bleached sulfate softwood pulp were added to 3000 parts by weight of deionized water and stirred at 600 rpm for 30 minutes at 25°C to ensure uniform dispersion. Sodium bicarbonate was added to adjust the pH of the dispersion to 8.5. The dispersion was then beaten to 60°SR and mechanically defibrinated 6 times at 120 MPa to obtain an aqueous dispersion of cellulose micro / nano fibers. The solid content of the cellulose micro / nano fiber aqueous dispersion was adjusted to 2.50 wt% by adding deionized water and stirring at low speed. In this embodiment, the number average diameter of the cellulose micro / nano fibers was 20 nm, and the number average length was 0.8 μm.

[0059] Step 2: Preparation of cellulose micro / nanofiber-alkyl ketene dimer composite intermediate Based on absolute dry weight, 100 parts by weight of cellulose micro / nanofibers from the aqueous dispersion of cellulose micro / nanofibers were added, along with 50 parts by weight of alkyl ketene dimer, and premixed at 25°C for 20 min. Sodium bicarbonate was added to adjust the pH of the mixture to 8.5. The mixture was heated to 75°C and maintained for 40 min to melt and disperse the alkyl ketene dimer; subsequently, it was sheared and dispersed at 8000 rpm for 40 min; and then homogenized three times at 80 MPa to obtain a cellulose micro / nanofiber-alkyl ketene dimer predispersant. The predispersant was heat-treated at 120°C for 6 min, then cooled to 25°C to obtain a cellulose micro / nanofiber-alkyl ketene dimer composite intermediate. The solid content of the composite intermediate in this example was 5.0 wt%.

[0060] Step 3: Pulp system preparation and addition of composite intermediates 85.0 g of oven-dry bleached sulfate softwood pulp and 15.0 g of oven-dry bleached sulfate hardwood pulp were added to deionized water and dispersed at 25°C for 40 min to adjust the solid content of the pulp system to 1.2 wt%. The pulp system was beaten to 55°SR. 5.00 g of cellulose micro / nanofiber-alkyl ketene dimer composite intermediate (equivalent to oven-dry weight) was added to the pulp system and mixed at 600 rpm for 40 min to obtain a mixed pulp. The mixing completion criterion was the absence of visible hydrophobic particles floating in the pulp, and the difference in solid content measured at three locations was no higher than 0.05 wt%.

[0061] Step 4: Shaping, pressing, drying, thermosetting, edge trimming and calendering The mixed pulp was wet-formed into paper sheets, which were then pressed under a pressure of 600 kN / m on a press line to achieve a dryness of 55 wt%. The pressed paper sheets were dried at 110°C until the mass change between two consecutive weighings was less than 0.5 wt%, yielding dried paper sheets. The dried paper sheets were then heat-cured at 120°C for 6 min and cooled to 25°C. Subsequently, an aqueous dispersion containing a cellulose micro / nanofibril-alkyl ketene dimer composite intermediate was added at a concentration of 1.5 g / m³. 2 The appropriate amount was applied to the cut edge area of ​​the paper sheet and dried at 110℃ for 5 minutes. Then, it was calendered under calendering conditions of 100kN / m pressure and calendering temperature of 90℃ to obtain tear-resistant, impact-resistant, low-absorbency ice-packed paper.

[0062] Quality testing methods and results The paper sheets of this embodiment were equilibrated for 24 hours at 23°C and 50% relative humidity before testing, with three samples taken for each test. The hydrophobic microdomain D50 of the alkyl ketene dimer in the aqueous dispersion of the composite intermediate was measured to be 50 nm at 25°C. The mass ratio of the free alkyl ketene dimer to the added alkyl ketene dimer was 4.0 wt%, and the retention rate of the composite intermediate in the paper fiber layer was 95.0 wt%. The Cobb60 value of the paper sheets in this embodiment was 6.0 ± 0.3 g / m³. 2 The tear index was 30.0 ± 0.8 mN·m. 2 / g, quantitatively 130.0±1.0g / m 2 The thickness is 145.0±2.0μm, and the apparent density is 0.90g / cm³. 3 The equilibrium moisture content is 4.0 ± 0.2 wt%.

[0063] Features and application scenarios of this embodiment This embodiment adopts an optimized scheme with a higher load, combined with edge trimming and calendering, making it suitable for ice pack outer packaging paper with high requirements for low water absorption, edge sealing integrity and handling tolerance, as well as packaging structures that require high paper strength in cold chain turnover.

[0064] Example 3 Overall production scale and product form This embodiment uses the preparation of a sheet of tear-resistant, impact-resistant, low-absorbency ice-packed paper with an oven-dry fiber weight of 100.0g as an example. The product form is a paper sheet that has undergone medium-application edge trimming and medium calendering. Both bleached sulfate softwood pulp and bleached sulfate hardwood pulp are commercially available paper-grade pulps, the alkyl ketene dimer is a commercially available paper sizing grade raw material, sodium bicarbonate is a commercially available analytical grade reagent, and the water is deionized water.

[0065] Raw materials, components or material specifications In this embodiment, the paper-based fiber layer is formed from 65.0 g of oven-dried bleached sulfate softwood pulp and 35.0 g of oven-dried bleached sulfate hardwood pulp. 2.50 g of the cellulose micro / nanofibrils-alkyl ketene dimer composite intermediate is added based on oven-dried weight, accounting for 2.5 wt% of the oven-dried fiber mass of the pulp system. The composite intermediate in this embodiment is prepared from 100 parts by weight of oven-dried cellulose micro / nanofibrils and 25 parts by weight of alkyl ketene dimer.

[0066] Step 1: Preparation of aqueous dispersion of cellulose micro / nanofibrils 100 parts by weight of bleached sulfate softwood pulp were added to 6000 parts by weight of deionized water and stirred at 450 rpm for 25 minutes at 25°C to ensure uniform dispersion. Sodium bicarbonate was added to adjust the pH of the dispersion to 7.4. The dispersion was then beaten to 48°SR and mechanically defibrinated three times at 75 MPa to obtain an aqueous dispersion of cellulose micro / nano fibers. The solid content of the cellulose micro / nano fiber aqueous dispersion was adjusted to 1.50 wt% by adding deionized water and stirring at low speed. In this embodiment, the number average diameter of the cellulose micro / nano fibers was 60 nm, and the number average length was 4.0 μm.

[0067] Step 2: Preparation of cellulose micro / nanofiber-alkyl ketene dimer composite intermediate Based on absolute dry weight, 100 parts by weight of cellulose micro / nanofibers from the aqueous dispersion of cellulose micro / nanofibers were added, along with 25 parts by weight of alkyl ketene dimer, and premixed at 25°C for 15 min. Sodium bicarbonate was added to adjust the pH of the mixture to 8.0. The mixture was heated to 65°C and held for 25 min to melt and disperse the alkyl ketene dimer; then sheared and dispersed at 5000 rpm for 25 min; and then homogenized twice at 50 MPa to obtain a cellulose micro / nanofiber-alkyl ketene dimer predispersant. The predispersant was heat-treated at 105°C for 3 min, and then cooled to 25°C to obtain a cellulose micro / nanofiber-alkyl ketene dimer composite intermediate. The solid content of the composite intermediate in this example was 3.0 wt%.

[0068] Step 3: Pulp system preparation and addition of composite intermediates 65.0 g of oven-dried bleached sulfate softwood pulp and 35.0 g of oven-dried bleached sulfate hardwood pulp were added to deionized water and dispersed at 25°C for 35 min to adjust the solid content of the pulp system to 0.7 wt%. The pulp system was beaten to 40°SR. 2.50 g of cellulose micro / nanofibril-alkyl ketene dimer composite intermediate (equivalent to oven-dried weight) was added to the pulp system and mixed at 350 rpm for 25 min to obtain a mixed pulp. The mixing completion criterion was that the pulp flow state was uniform, and the difference in solid content between three samples was no higher than 0.05 wt%.

[0069] Step 4: Shaping, pressing, drying, thermosetting, edge trimming and calendering The mixed pulp was wet-formed into paper sheets, which were then pressed under a pressure of 300 kN / m on a press line to achieve a dryness of 45 wt%. The pressed paper sheets were dried at 90°C until the mass change between two consecutive weighings was less than 0.5 wt%, yielding dried paper sheets. The dried paper sheets were then heat-cured at 105°C for 3 min and cooled to 25°C. Subsequently, an aqueous dispersion containing a cellulose micro / nanofibril-alkyl ketene dimer composite intermediate was added at a concentration of 0.8 g / m³. 2 The appropriate amount was applied to the cut edge area of ​​the paper sheet and dried at 95°C for 3 minutes. Then, the paper was calendered at a calendering pressure of 60 kN / m and a calendering temperature of 65°C to obtain tear-resistant, impact-resistant, low-absorbency ice-covered paper.

[0070] Quality testing methods and results The paper sheets of this embodiment were equilibrated for 24 hours at 23°C and 50% relative humidity before testing, with three samples taken for each test. The hydrophobic microdomain D50 of the alkyl ketene dimer in the aqueous dispersion of the composite intermediate was measured to be 150 nm at 25°C, the mass ratio of free alkyl ketene dimer to the added alkyl ketene dimer was 8.5 wt%, and the retention rate of the composite intermediate in the paper fiber layer was 78.0 wt%. The Cobb60 value of the paper sheets in this embodiment was 11.5 ± 0.4 g / m³. 2 The tear index was 20.5 ± 0.6 mN·m. 2 / g, quantitatively determined as 90.0±0.8g / m 2 The thickness is 130.0±1.5μm, and the apparent density is 0.69g / cm³. 3 The equilibrium moisture content is 6.5 ± 0.2 wt%.

[0071] Features and application scenarios of this embodiment This embodiment uses a medium ratio and medium process intensity, taking into account pulp dispersion, paper forming and post-processing efficiency. It is suitable for conventional cold chain ice pack outer packaging paper, cushioning and isolation paper and packaging paper that requires both paper feel and low water absorption.

[0072] Example 4 Overall production scale and product form This embodiment uses the preparation of a sheet of tear-resistant, impact-resistant, low-absorbency ice-packed paper with an oven-dry fiber weight of 100.0g as an example. The product form is a thick paper sheet that has undergone low-application edge trimming treatment and low-temperature calendering. Both bleached sulfate softwood pulp and bleached sulfate hardwood pulp are commercially available paper-grade pulps, the alkyl ketene dimer is a commercially available paper sizing grade raw material, sodium bicarbonate is a commercially available analytical grade reagent, and the water is deionized water.

[0073] Raw materials, components or material specifications In this embodiment, the paper-based fiber layer is formed from 55.0 g of oven-dried bleached sulfate softwood pulp and 45.0 g of oven-dried bleached sulfate hardwood pulp. 1.00 g of the cellulose micro / nanofibrils-alkyl ketene dimer composite intermediate is added based on oven-dried weight, representing 1.0 wt% of the oven-dried fiber mass of the pulp system. The composite intermediate in this embodiment is prepared from 100 parts by weight of oven-dried cellulose micro / nanofibrils and 12 parts by weight of alkyl ketene dimer.

[0074] Step 1: Preparation of aqueous dispersion of cellulose micro / nanofibrils 100 parts by weight of bleached sulfate softwood pulp were added to 8000 parts by weight of deionized water and stirred at 400 rpm for 25 minutes at 25°C to ensure uniform dispersion. Sodium bicarbonate was added to adjust the pH of the dispersion to 6.6. The dispersion was then beaten to 58°SR and mechanically defibrinated five times at 118 MPa to obtain an aqueous dispersion of cellulose micro / nano fibers. The solid content of the cellulose micro / nano fiber aqueous dispersion was adjusted to 0.80 wt% by adding deionized water and stirring at low speed. In this embodiment, the number average diameter of the cellulose micro / nano fibers was 24 nm, and the number average length was 1.0 μm.

[0075] Step 2: Preparation of cellulose micro / nanofiber-alkyl ketene dimer composite intermediate Based on absolute dry weight, 100 parts by weight of cellulose micro / nanofibers from the aqueous dispersion of cellulose micro / nanofibers were added, along with 12 parts by weight of alkyl ketene dimer, and premixed at 25°C for 12 min. Sodium bicarbonate was added to adjust the pH of the mixture to 7.6. The mixture was heated to 56°C and held for 12 min to melt and disperse the alkyl ketene dimer; then sheared at 2200 rpm for 12 min; and homogenized three times at 78 MPa to obtain a cellulose micro / nanofiber-alkyl ketene dimer predispersant. The predispersant was heat-treated at 118°C for 5.5 min, then cooled to 25°C to obtain a cellulose micro / nanofiber-alkyl ketene dimer composite intermediate. The solid content of the composite intermediate in this example was 1.2 wt%.

[0076] Step 3: Pulp system preparation and addition of composite intermediates 55.0 g of oven-dried bleached sulfate softwood pulp and 45.0 g of oven-dried bleached sulfate hardwood pulp were added to deionized water and dispersed at 25°C for 30 min to adjust the solid content of the pulp system to 1.0 wt%. The pulp system was beaten to 30°SR. 1.00 g of cellulose micro / nanofibril-alkyl ketene dimer composite intermediate (equivalent to oven-dried weight) was added to the pulp system and mixed at 120 rpm for 38 min to obtain a mixed pulp. The criterion for complete mixing was the absence of visible agglomerates in the pulp, and the difference in solid content measured at three locations was no higher than 0.05 wt%.

[0077] Step 4: Shaping, pressing, drying, thermosetting, edge trimming and calendering The mixed pulp was wet-formed into paper sheets, which were then pressed under a pressure of 120 kN / m on a press line to achieve a dryness of 54 wt%. The pressed paper sheets were dried at 108 °C until the mass change between two consecutive weighings was less than 0.5 wt%, yielding dried paper sheets. The dried paper sheets were then heat-cured at 118 °C for 5.5 min and cooled to 25 °C. Subsequently, an aqueous dispersion containing a cellulose micro / nanofibril-alkyl ketene dimer composite intermediate was added at a concentration of 0.1 g / m³. 2 The appropriate amount was applied to the cut edge area of ​​the paper sheet and dried at 80°C for 1 minute. Then, the paper was calendered under calendering conditions of 20 kN / m pressure and 40°C to obtain tear-resistant, impact-resistant, low-absorbency ice-covered paper.

[0078] Quality testing methods and results The paper sheets of this embodiment were equilibrated for 24 hours at 23°C and 50% relative humidity before testing, with three samples taken for each test. The hydrophobic microdomain D50 of the alkyl ketene dimer in the aqueous dispersion of the composite intermediate was measured to be 70 nm at 25°C. The mass ratio of the free alkyl ketene dimer to the added alkyl ketene dimer was 12.0 wt%, and the retention rate of the composite intermediate in the paper fiber layer was 65.0 wt%. The Cobb60 value of the paper sheets in this embodiment was 16.0 ± 0.5 g / m³. 2 The tear index was 12.0 ± 0.4 mN·m. 2 / g, quantitatively 100.0±0.9g / m 2 The thickness is 220.0±2.5μm, and the apparent density is 0.45g / cm³. 3 The equilibrium moisture content is 8.5 ± 0.2 wt%.

[0079] Features and application scenarios of this embodiment This embodiment employs a thicker paper sheet structure, low-application-amount edge trimming treatment, and low-temperature calendering, making it suitable for ice pack outer packaging paper that requires higher thickness, lower apparent density, and a flexible cushioning feel. It is also suitable for cold chain cushioning packaging scenarios where paper stiffness should not be too high.

[0080] Comparative Example 1: Basically the same as Example 1, except that in step 3 the paper fiber layer is formed from 35.0g of oven-dried bleached sulfate softwood pulp and 65.0g of oven-dried bleached sulfate hardwood pulp, while other conditions remain unchanged.

[0081] Comparative Example 2: It is basically the same as Example 1, except that in step 3, the amount of cellulose micro / nano filament-alkyl ketene dimer composite intermediate added is 0.25 g based on oven-dry weight, and other conditions remain unchanged.

[0082] Comparative Example 3: It is basically the same as Example 1, except that in step 2, the amount of alkyl ketene dimer and cellulose micro / nanofibers is adjusted to 2 parts by mass of alkyl ketene dimer and 100 parts by mass of oven-dried cellulose micro / nanofibers, while other conditions remain unchanged.

[0083] Comparative Example 4: It is basically the same as Example 1, except that sodium bicarbonate was used in step 1 to adjust the pH of the dispersion system for preparing cellulose micro / nano filaments to 5.8, while other conditions remained unchanged.

[0084] Comparative Example 5: It is basically the same as Example 1, except that the mechanical defibering pressure in step 1 is 20 MPa, the number of mechanical defibering cycles is still 1, and other conditions remain unchanged.

[0085] Comparative Example 6: It is basically the same as Example 1, except that in step 2, the cellulose micro / nano filament-alkyl ketene dimer pre-dispersion is heat-treated at 80°C for 1 min, while other conditions remain unchanged.

[0086] Comparative Example 7: It is basically the same as Example 1, except that in step 3, after the cellulose micro / nano filament-alkyl ketene dimer composite intermediate is added to the pulp system, it is mixed at 50 rpm for 10 min, while other conditions remain unchanged.

[0087] Comparative Example 8: It is basically the same as Example 1, except that the dryness of the paper after pressing in step 4 reaches 30wt%, while other conditions remain unchanged.

[0088] Comparative Example 9: Essentially the same as Example 1, except that no cellulose micro / nanofibrils aqueous dispersion was added in step 2. 0.024 g of oven-dry alkyl ketene dimer was added to deionized water and premixed at 25°C for 10 min. The pH of the system was adjusted to 7.5 using sodium bicarbonate. An alkyl ketene dimer aqueous dispersion was then prepared according to the melt dispersion, shear dispersion, homogenization, and heat treatment conditions of Example 1. This dispersion was then added to the pulp system in step 3, with other conditions remaining unchanged. This comparative example was used to verify the synergistic effect of cellulose micro / nanofibrils and alkyl ketene dimers.

[0089] Comparative Example 10: Essentially the same as Example 1, except that alkyl ketene dimers were not added in step 2. 0.476 g of oven-dry cellulose micro / nanofiber aqueous dispersion was taken, and the pH of the system was adjusted to 7.5 using sodium bicarbonate. After treatment under the melt dispersion, shear dispersion, homogenization, and heat treatment conditions of Example 1, the pulp system was added in step 3, with other conditions remaining unchanged. This comparative example was used to verify the synergistic effect of cellulose micro / nanofibers and alkyl ketene dimers.

[0090] Comparative Example 11: Essentially the same as Example 1, except that step 2, which involved the co-melting, shearing, homogenizing, and heat-treating of cellulose micro / nanofibers and alkyl ketene dimers to form a composite intermediate, was omitted. Instead, in step 3, 0.476 g of oven-dry cellulose micro / nanofiber aqueous dispersion was first added to the pulp system and mixed at 100 rpm for 5 min, followed by 0.024 g of oven-dry alkyl ketene dimer aqueous dispersion, and mixing continued at 100 rpm for 5 min. All other conditions remained unchanged. This comparative example was used to verify the synergistic effect of the composite intermediate interface construction method.

[0091] Characterization and performance testing: Cobb 60 tear-resistant, impact-resistant, low-absorbency ice pack paper water absorption test: Using paper sheets equilibrated at 23℃ and 50% relative humidity, the short-term surface water absorption capacity is evaluated. The principle is that a specified area of ​​paper sample gains weight per unit area after 60 seconds of contact with water. Following GB / T 1540-2002 or equivalent methods from ISO 535, at least three samples are taken, with the test side facing water. After water absorption, the surface water is removed using a standard pressure roller, and the difference in mass before and after is measured. The result is expressed in g / m³. 2 This indicates the report's mean, standard deviation, and the basis for outlier removal.

[0092] Tear resistance, impact resistance, low absorbency, and tear index test for ice-packed paper: Using longitudinally and transversely cut samples from the same batch of paper, this test evaluates the fiber network's ability to resist crack propagation. The principle is that the work required to tear the pre-cut paper sample in a pendulum tear tester is converted into tearing force. Referring to equivalent methods in GB / T 455-2002 and ISO 1974, the samples are tested after being treated with the standard atmosphere of GB / T 10739-2023. The tear strength is recorded and divided by the basis weight to convert it to mN·m. 2 / g, n≥3, report mean and standard deviation.

[0093] D50 test of hydrophobic microdomains of alkyl ketene dimers: Using an aqueous dispersion of cellulose micro / nanofibrils-alkyl ketene dimer composite intermediates as the object, the dispersion scale of hydrophobic microdomains is evaluated. The principle is to detect the intensity fluctuations of scattered light caused by Brownian motion of particles through dynamic light scattering and invert the particle size distribution. Referring to GB / T 29022-2021 or ISO 22412:2025, dilute to a suitable scattering intensity at 25℃, record the volume distribution D10, D50, D90 and polydispersity index, and take the average of 3 measurements.

[0094] Free alkyl ketene dimer ratio test: Using an aqueous dispersion of a complex intermediate as the object, the proportion of the hydrophobic phase that does not form a complex association with cellulose micro / nanofibrils is evaluated. The principle is to separate the free hydrophobic phase by centrifugation or membrane filtration, followed by extraction with an organic solvent and quantification by high-performance liquid chromatography or gravimetric method. Blank cellulose micro / nanofibril samples and alkyl ketene dimer standards are provided. The free alkyl ketene dimer mass / addition mass × 100% is calculated, n≥3. The mean, standard deviation, and recovery rate are reported.

[0095] Retention rate test of composite intermediates or corresponding additives: Taking the pre-forming mixed pulp, white water, and finished paper as the subjects, the retention level of composite intermediates or corresponding additives in the paper base fiber layer is evaluated; the principle is the mass balance between the amount of additives, the amount of white water lost, and the amount of paper residue. All white water is collected during forming, and quantitative analysis is performed by drying and weighing combined with alkyl ketene dimer extraction. The oven-dry mass of composite intermediates or corresponding additives retained in the paper base fiber layer is calculated as (oven-dry mass of added additives) × 100%, n≥3. The results are correlated with Cobb60 and tear index.

[0096] Basis weight, thickness, and apparent density testing: Using balanced tear-resistant, impact-resistant, low-absorbency ice pack paper as the object, the basic parameters of the paper sheet structure are evaluated; the principle is that the apparent density is jointly determined by the mass per unit area and the thickness. Basis weight is determined according to GB / T 451.2-2023, thickness is determined according to GB / T 451.3-2002 or the current equivalent method, and apparent density is converted by dividing basis weight by thickness, uniformly expressed in g / cm³. 3 The report should include at least 5 locations per group, and show the mean, standard deviation, and location dispersion.

[0097] Cold chain simulated impact integrity test: Using simulated ice pack outer packaging sheets or folded samples made of tear-resistant, impact-resistant, low-absorbency ice pack paper as the object, the impact retention ability during low-temperature and humid handling is evaluated; the principle is to apply a drop hammer or drop impact after low temperature and high humidity equilibrium and record the cracking, crack propagation, and water absorption changes. Referring to the equivalent approach of GB / T 4857.5 or ASTM D 5420, the sample is placed at 4℃ and 90% relative humidity for 2 hours before testing, and the cracking energy, crack length, and Cobb60 change rate after impact are recorded.

[0098] Figure 1 This is a dynamic light scattering differential particle size distribution diagram for this scheme. Figure 2 This is a dynamic light scattering cumulative particle size distribution diagram for this scheme. Figure 1 and Figure 2It can be seen that the main peak of the particle size distribution in Example 1 is concentrated around 300 nm, with a relatively concentrated peak shape and a narrow distribution range. Its cumulative particle size distribution shows a D50 of approximately 300 nm and a D90 of approximately 520 nm, indicating that the hydrophobic microdomains in the composite system exist in a smaller particle size and narrower distribution state. In contrast, the differential particle size distribution peaks of Comparative Examples 9 and 11 generally shift towards larger particle sizes and show significant broadening. Their cumulative particle size distribution curves shift to the right simultaneously, with D50 increasing to approximately 620 nm and approximately 780 nm, respectively. These results indicate that when cellulose micro / nanofibers are absent from the construction or when no composite intermediate is pre-constructed, the hydrophobic phase of the alkyl ketene dimer is more prone to agglomeration and the formation of coarse particles. Example 1, by dispersing, confining, and stabilizing the hydrophobic microdomains using cellulose micro / nanofibers, achieves a composite dispersion structure with smaller particle size and more uniform distribution, laying the foundation for its subsequent uniform retention in the paper-based fiber network.

[0099] Figure 3 This is a diagram showing the proportion of free alkyl ketene dimers in this scheme. Figure 3 It can be seen that the proportion of free alkyl ketene dimers in Example 1 is approximately 15 wt%, significantly lower than approximately 38 wt% in Comparative Example 9 and approximately 35 wt% in Comparative Example 11, and the system recovery rate remains in the range of approximately 96%–98%. This result indicates that in Example 1, the alkyl ketene dimers do not primarily exist in the form of free hydrophobic particles, but rather form more complex interconnected structures with cellulose micro / nanofibers. Figure 1 and Figure 2 The particle size results further illustrate that cellulose micro / nano filaments can not only reduce the particle size and distribution width of hydrophobic microdomains, but also reduce the proportion of free alkyl ketene dimers, thereby improving the structural integrity and dispersion stability of the composite intermediate.

[0100] Figure 4 This is a retention rate graph for the composite intermediates or corresponding additives in this scheme. Figure 5 This is a graph showing the relationship between the retention rate of the composite intermediate or corresponding additive in this scheme and Cobb60. Figure 4 It can be seen that the retention rate of the composite intermediate in Example 1 is approximately 60 wt%, which is higher than that of Comparative Example 7 (approximately 45 wt%) and Comparative Example 11 (approximately 35 wt%), indicating that under suitable mixing and dispersion conditions and pre-construction treatment, the composite intermediate can more effectively enter and remain in the paper-based fiber network. Further... Figure 5 It can be seen that as the retention rate of the composite intermediate or corresponding additive increases from about 35 wt% to about 60 wt%, the Cobb 60 value of the paper increases from about 26 g / m³. 2 Reduced to approximately 18 g / m 2The results show a correlation between increased retention rate and decreased water absorption value. This indicates that the effective retention of the composite intermediate allows the hydrophobic components to be more fully distributed on the fiber surface, fiber intersections, and micropore throats, thereby reducing the rapid penetration of water into the paper sheet and improving the paper's low water absorption performance.

[0101] Figure 6 This is a graph showing the correlation between Cobb60 and the tear index in this scheme. (Source: [Insert source here]) Figure 6 It can be seen that Example 1 has both a low Cobb60 value and a high tear index, wherein the Cobb60 value is approximately 18 g / m². 2 The tear index is approximately 10.0 mN·m. 2 The Cobb 60 value ( / g) indicates that the paper achieves a good balance between low water absorption and tear resistance. Comparative Example 2, due to insufficient composite intermediate content and inadequate hydrophobic barrier construction, showed limited improvement in water absorption. Comparative Example 10, lacking alkyl ketene dimers, struggled to form effective hydrophobic microdomains, resulting in a significantly higher Cobb 60 value. This demonstrates that the performance improvement in this solution does not stem from the enhancement of a single component or a single indicator, but rather from the reinforcement, bridging, and interstitial filling effects of cellulose micro / nano filaments, combined with the hydrophobic modification effect of alkyl ketene dimers, enabling the paper to simultaneously achieve good tear resistance and low water absorption.

[0102] Figure 7 This is a graph showing the relationship between the ratio of D50 and free alkyl ketene dimer under the process window of this scheme. Figure 7 It can be seen that, under the conditions of pH 6.5 and heat treatment temperature of 90°C for the dispersion system used in the preparation of cellulose micro / nanofibers in Example 1, the composite system D50 is approximately 300 nm, and the proportion of free alkyl ketene dimers is approximately 15 wt%, exhibiting superior particle size control and a low proportion of free hydrophobic components. When the pH conditions deviate, or the heat treatment temperature decreases to approximately 80°C, the system D50 increases to approximately 330–360 nm or more, and the proportion of free alkyl ketene dimers increases to approximately 17–21 wt%. This result indicates that the order and parameter control of steps such as pH adjustment, melt dispersion, shear dispersion, homogenization, and heat treatment directly affect the degree of compositeness and the size of hydrophobic microdomains between alkyl ketene dimers and cellulose micro / nanofibers. The process conditions used in Example 1 achieve a good balance between smaller particle size, lower free proportion, and higher structural stability, proving the rationality of the process window setting.

[0103] Figure 8 This is a macroscopic photograph of the tear-resistant, impact-resistant, low-absorbency ice-packing paper from Example 1. Figure 8As can be seen, the sample of Example 1 is a flat sheet of paper, white to light milky white, with low gloss and opaque appearance. The paper surface is continuous overall, without a continuous plastic coating layer, obvious warping, or macroscopic cracks. The basis weight of this sample is 60.0 ± 0.6 g / m³. 2 The thickness is 80.0±1.0μm, and the apparent density is 0.75g / cm³. 3 This indicates that while maintaining a lightweight paper base, it formed a relatively complete and continuous fiber network structure. Meanwhile, the Cobb60 value of this sample was 18.0 ± 0.4 g / m³. 2 This indicates that even without forming a continuous plastic coating layer, a low water absorption level can still be achieved in paper sheets by introducing a cellulose micro / nano filament-alkyl ketene dimer composite intermediate. These results demonstrate, from both macroscopic morphology and basic physical property perspectives, that this approach can balance the forming quality, lightweight characteristics, and low water absorption of paper-based materials.

[0104] Figure 9 This is a scanning electron microscope image of the tear-resistant, impact-resistant, low-absorbency ice-packing paper from Example 1. Figure 9 The low-magnification image shows that the paper sheet is composed of a continuous porous network formed by the random interweaving of bleached sulfate softwood pulp fibers and bleached sulfate hardwood pulp fibers. No large-scale aggregates or through-cracks were observed, indicating that the introduction of the composite intermediate did not disrupt the overall fiber network structure of the paper sheet. Figure 9 b and Figure 9 As shown in the high-magnification image (c), cellulose micro- and nano-filaments are distributed on the surface of wood pulp fibers and in fiber cross-sections, forming bridging and interstitial structures. The number-average diameter of these cellulose micro- and nano-filaments is approximately 100 nm, and the number-average length is approximately 8.0 μm. From... Figure 9 d high magnification image and Figure 9 The cross-sectional image further reveals that the fiber surface exhibits external fibrosis, micro / nano filament entanglement, and a discrete distribution of hydrophobic microdomains of alkyl ketene dimers. The D50 of these hydrophobic microdomains is approximately 300 nm, and the paper sheet thickness is 80.0 ± 1.0 μm. The aforementioned microstructure is consistent with... Figures 1 to 7 The results of particle size control, reduced free proportion, and increased retention rate are consistent, indicating that the composite intermediate can be effectively dispersed, retained, and function in the fiber network, thereby improving inter-fiber bonding and pore throat structure. This is consistent with the results of Example 1, which simultaneously achieved 10.0 ± 0.3 mN·m 2 / g tear index and 18.0±0.4g / m 2 The important structural basis of the Cobb60 value.

[0105] Table 1 Performance of Examples and Comparative Examples ; As can be seen from the performance of the examples and comparative examples in Table 1, Examples 1 to 4 show a relatively balanced data relationship among hydrophobic microdomain dispersion, free alkyl ketene dimer control, composite intermediate retention, low water absorption, tear resistance, and cold chain impact integrity. Among them, Example 2 exhibits the lowest Cobb60 and the highest tear index due to its higher composite intermediate dosage, stronger defiberization and homogenization conditions, and more thorough post-treatment. Example 3, under medium formulation and medium process intensity, shows moderate and stable performance. In the conventional comparative examples, any single change in the ratio of softwood and hardwood pulp, the amount of composite intermediate added, the ratio of alkyl ketene dimer, pH, defiberization pressure, heat treatment, mixing speed, and press dryness causes at least one core indicator to deviate from the example system. In the synergistic comparative examples, retaining only alkyl ketene dimers, retaining only cellulose micro / nanofibers, or eliminating the preconstruction of composite intermediates all failed to simultaneously maintain hydrophobic microdomain dispersion, retention rate, and paper tear resistance and low water absorption, indicating that the pre-dispersion interface construction of composite intermediates plays a crucial role in the performance combination.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A tear-resistant, impact-resistant, low-absorbency ice packing paper, characterized in that, Includes a paper-based fiber layer and a cellulose micro / nano filament-alkyl ketene dimer composite intermediate distributed in the paper-based fiber layer; The paper-based fiber layer comprises fibers formed from bleached sulfate softwood pulp and bleached sulfate hardwood pulp; The cellulose micro / nano filament-alkyl ketene dimer composite intermediate comprises cellulose micro / nano filaments and alkyl ketene dimers; The cellulose micro / nano filaments were obtained by mechanical defibrillation of bleached sulfate softwood pulp. The cellulose micro / nanofibril-alkyl ketene dimer composite intermediate was prepared by the following steps: A1. Provides aqueous dispersions of cellulose micro / nano fibers; A2. Mix the alkyl ketene dimer with the cellulose micro / nanofibers at a mass ratio of 5–50:100; A3. The pH of the mixture was adjusted to 7.5–8.5 using sodium bicarbonate; A4. The mixture is sequentially subjected to melt dispersion, shear dispersion and homogenization to obtain a cellulose micro / nanofiber-alkyl ketene dimer predispersant; A5. Heat-treat the cellulose micro / nano filament-alkyl ketene dimer pre-dispersion at 90–120°C for 1–6 min to obtain the cellulose micro / nano filament-alkyl ketene dimer composite intermediate; In step A4, the melting dispersion temperature is 55–75℃ and the time is 10–40 min; the shear dispersion speed is 2000–8000 rpm and the time is 10–40 min; the homogenization pressure is 20–80 MPa and the number of times is 1–3; the quality control parameters of the cellulose micro / nano filament-alkyl ketene dimer composite intermediate are: the D50 of the hydrophobic microdomain of the alkyl ketene dimer is 50–300 nm; the mass ratio of the free alkyl ketene dimer to the added alkyl ketene dimer is not higher than 15 wt%; and the solid content of the cellulose micro / nano filament-alkyl ketene dimer composite intermediate in the form of an aqueous dispersion is 1.0–5.0 wt%.

2. The tear-resistant, impact-resistant, low-absorbency ice-wrapping paper according to claim 1, characterized in that, In the cellulose micro / nanofibrils-alkyl ketene dimer composite intermediate, the alkyl ketene dimer is distributed in the form of hydrophobic microdomains on the surface of the cellulose micro / nanofibrils or between fiber bundles; the amount of the cellulose micro / nanofibrils-alkyl ketene dimer composite intermediate added is 0.5–5.0 wt% based on the total oven-dry weight of bleached sulfate softwood pulp and bleached sulfate hardwood pulp in the pulp system used to prepare the tear-resistant, impact-resistant, low-absorbency ice-packed paper, excluding the cellulose micro / nanofibrils and alkyl ketene dimer in the composite intermediate.

3. The tear-resistant, impact-resistant, low-absorbency ice-wrapping paper according to claim 1, characterized in that, The cellulose micro / nanofiber aqueous dispersion in step A1 is prepared through the following steps: B1. Disperse bleached sulfate softwood pulp in deionized water to obtain a dispersion system; B2. The pH of the dispersion system is adjusted to 6.5–8.5 using sodium bicarbonate; B3. Pulverize the dispersion system to a freeness of 35–60°SR; B4. Mechanically defibril the pulped dispersion system 1–6 times under 30–120 MPa conditions to obtain an aqueous dispersion of cellulose micro-nano fibers; The obtained cellulose micro / nanofibers have a number-average diameter of 20–100 nm and a number-average length of 0.8–8.0 μm.

4. The tear-resistant, impact-resistant, low-absorbency ice-wrapping paper according to claim 1, characterized in that, Based on the total oven-dry weight of bleached sulfate softwood pulp and bleached sulfate hardwood pulp in the pulp system used to prepare the paper-based fiber layer, and excluding the cellulose micro / nano filaments and alkyl ketene dimers in the composite intermediate, the total content of the bleached sulfate softwood pulp and the bleached sulfate hardwood pulp is 100 wt%, wherein the content of the bleached sulfate softwood pulp is 45–85 wt%, and the content of the bleached sulfate hardwood pulp is 15–55 wt%; the cellulose micro / nano filament-alkyl ketene dimer composite intermediate is located on the surface of the fibers, at fiber intersections, or at micropores between fibers in the paper-based fiber layer.

5. A method for preparing tear-resistant, impact-resistant, low-absorbency ice-wrapping paper as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Provides the prepared cellulose micro / nano filament-alkyl ketene dimer composite intermediate; S2. Bleached sulfate softwood pulp and bleached sulfate hardwood pulp are added to deionized water, dispersed and pulped to obtain a pulp system; S3. The cellulose micro / nano filament-alkyl ketene dimer composite intermediate is added to the pulp system, based on the total oven-dry weight of bleached sulfate softwood pulp and bleached sulfate hardwood pulp in the pulp system, excluding the cellulose micro / nano filaments and alkyl ketene dimer in the composite intermediate. The amount of the cellulose micro / nano filament-alkyl ketene dimer composite intermediate added is 0.5–5.0 wt% based on oven-dry weight, to obtain a mixed pulp. S4. The mixed pulp is shaped, pressed, and dried to obtain a dried paper sheet; S5. The dried paper is heat-cured at 90–120°C for 1–6 minutes to obtain the tear-resistant, impact-resistant, low-absorbency ice-wrapped paper.

6. The preparation method according to claim 5, characterized in that, In step S2, based on the total oven-dry weight of bleached sulfate softwood pulp and bleached sulfate hardwood pulp in the pulp system, excluding the cellulose micro / nano filaments and alkyl ketene dimers in the composite intermediate, the total content of the bleached sulfate softwood pulp and the bleached sulfate hardwood pulp is 100 wt%, wherein the content of the bleached sulfate softwood pulp is 45–85 wt%, the content of the bleached sulfate hardwood pulp is 15–55 wt%, the solids content of the pulp system is 0.2–1.2 wt%, and the freeness is 25–55°SR.

7. The preparation method according to claim 5, characterized in that, In step S3, after the cellulose micro / nano filament-alkyl ketene dimer composite intermediate is added to the pulp system, it is mixed at 100–600 rpm for 10–40 min to obtain the mixed pulp.

8. The preparation method according to claim 5, characterized in that, In step S4, the dryness of the paper sheet after pressing is 35–55 wt%.

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