Impact-resistant carton and method of making same

Abstract

The application discloses an impact-resistant carton and a preparation method thereof, and relates to the technical field of papermaking and packaging materials. The carton is made of a composite corrugated paperboard, and a raw material of the carton comprises modified microfibrillated cellulose loaded with a flexible silane coupling agent on a surface. The flexible long-chain structure introduced in the application forms an interface micro-elastic unit, compared with the prior art, can more effectively absorb and dissipate instantaneous impact energy, and significantly improves the impact resistance and buffering protection capacity of the carton. Meanwhile, the application significantly improves the wet strength retention rate of the paperboard through hydrophobic long carbon chain modification and covalent bond anchoring, effectively inhibits the erosion of water to the fiber structure in a humid environment, improves the stacking collapse problem caused by the softening of the carton due to moisture absorption, and enhances the structural stability of the carton in a complex logistics environment.

Description

Technical Field

[0001] This invention relates to the field of papermaking and packaging materials technology, specifically to an impact-resistant cardboard box and its preparation method. Background Technology

[0002] Corrugated cardboard boxes, as a common packaging container, are widely used in logistics transportation and warehousing. In actual distribution, packaged goods frequently face complex mechanical environments such as drops, collisions, and stacking compression. Traditional corrugated cardboard mainly relies on the hydrogen bonds between the paper fibers and the geometric rigidity of the corrugated structure to provide support. This fiber network structure typically exhibits high rigidity but lacks sufficient toughness. When subjected to instantaneous high-energy impacts, the bond points between fibers are prone to breakage due to the inability to effectively dissipate the impact energy, leading to corner cracks, flute collapse, or overall structural failure, failing to provide reliable cushioning protection for the goods inside.

[0003] In addition, plant fibers are naturally hydrophilic. In humid or high-humidity environments, water molecules easily penetrate the amorphous regions inside the fibers, disrupting the hydrogen bonds between fibers. This hygroscopic softening phenomenon leads to a significant decrease in the edge crush strength and bursting strength of the cardboard, causing creep or tipping of the cartons during stacking. To improve the physical strength of the cartons, existing technologies typically employ methods such as increasing the basis weight of the paper, adding rigid mineral fillers, or increasing the amount of surface sizing. While these methods improve static compressive strength to some extent, they often increase the brittleness of the cardboard, resulting in a lack of necessary flexibility and resilience, making it more prone to brittle fracture under dynamic loads.

[0004] In the field of paper chemical modification, using chemical additives to reinforce fiber networks is a common technical approach. However, conventional reinforcing agents or coupling agents mostly have short molecular chains or high structural rigidity, and the cross-linking points they form on the fiber surface often limit the relative micro-slippage ability between fibers. Simultaneously, there are interfacial compatibility differences between hydrophilic fibers and hydrophobic polymer reinforcement systems, making it difficult to form a continuous and uniform stress transfer network. When paperboard is subjected to external impact, stress concentration easily occurs at the interface, leading to peeling or failure of the reinforcement system. Therefore, overcoming the brittleness problem caused by traditional reinforcement methods and developing a packaging material that combines high strength and high toughness while maintaining stable interfacial bonding under different environments is a pressing technical challenge in the current paper packaging industry. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art, such as excessive rigidity of the corrugated cardboard fiber network leading to high brittleness, poor dynamic drop resistance and cushioning performance, easy moisture absorption and softening failure in humid environments, and insufficient interfacial compatibility between fibers and reinforcing materials. The invention provides an impact-resistant cardboard box and its preparation method that has a wide range of raw material sources, controllable preparation process, excellent impact resistance, a balance of high strength and high toughness, good structural stability, and strong interfacial bonding.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: an impact-resistant cardboard box, which is made of composite corrugated cardboard, wherein the raw material of the composite corrugated cardboard includes the following components in parts by weight:

[0007] Pulp fiber content: 70-90 parts;

[0008] 15-25 parts of modified microfibrillated cellulose;

[0009] 8-15 parts polymer emulsion;

[0010] 2-5 parts of sizing agent;

[0011] 0.5-2 parts of retention and filtration aid;

[0012] The modified microfibrillated cellulose is microfibrillated cellulose with a surface-loaded flexible silane coupling agent.

[0013] Furthermore, the pulp fiber is one or more of softwood sulfate pulp, hardwood sulfate pulp, or waste paper deinking pulp.

[0014] Furthermore, the method for preparing the modified microfibrillated cellulose is as follows:

[0015] (1) Raw material dispersion: Disperse microfibrillated cellulose powder or slurry in an ethanol aqueous solution to prepare a suspension with a solid content of 3%-5%;

[0016] (2) Grafting reaction: Add hydrolysate of flexible silane coupling agent dropwise to the suspension, adjust the pH value to 4.0-5.0, and stir the reaction at 50-65℃ for 3-5 hours;

[0017] (3) Post-processing: The reaction product is filtered, washed with ethanol, and dried at 60-80℃ to obtain the microfibrillated cellulose with the surface loaded with flexible silane coupling agent.

[0018] The chemical formula of the flexible silane coupling agent is the compound described in Formula 1:

[0019] Formula 1: .

[0020] Before modification, microfibrillated cellulose primarily relies on hydrogen bonds between hydroxyl groups on the fiber surface to form a rigid physical network. This bonding method lacks buffering capacity under instantaneous high-energy impacts, making it prone to brittle fracture. Furthermore, hydrogen bonds are sensitive to moisture, easily leading to network disintegration. This invention introduces a specific flexible silane coupling agent. The disilane structures at both ends of the agent's molecule hydrolyze to generate silanol groups, which then undergo an in-situ condensation reaction with the hydroxyl groups on the cellulose surface, transforming the fragile physical hydrogen bonds into stable covalent bonds. The unique long-chain alkyl and acrylate structures within the coupling agent's molecular chain act as flexible spacer arms and energy dissipation units at the microscopic level, constructing a "molecular spring" structure at the fiber-matrix interface. When the cardboard box is subjected to external impact loads, these flexible chain segments absorb and dissipate the impact kinetic energy through their own conformational torsion and elastic stretching, preventing stress concentration at the joint points. At the same time, the hydrophobic long chains at the ends of the coupling agent significantly reduce the surface polarity of cellulose, improving its interfacial compatibility with polymer emulsions and sizing agents, thereby forming a continuous, uniform interpenetrating network structure with excellent resilience, realizing a fundamental transformation of the material from brittle rigid fracture to a tough energy absorption mechanism.

[0021] Furthermore, the polymer emulsion is made from the following raw materials in parts by weight: 80-100 parts of carboxylated styrene-butadiene latex; 10-20 parts of oxidized starch; 1-3 parts of glyoxal; and 50-100 parts of water.

[0022] Furthermore, the solid content of the polymer emulsion is 40%-50%.

[0023] Furthermore, the sizing agent is one of alkyl ketene dimer and alkenyl succinic anhydride.

[0024] Furthermore, the retention and filtration aid is any one of polyethyleneimine and polydiallyldimethylammonium chloride.

[0025] A method for preparing an impact-resistant cardboard box includes the following steps:

[0026] S1. Pulp preparation: The pulp fibers are loosened and beaten, and the freeness is controlled at 30-45°SR. The modified microfibrillated cellulose is added and stirred to obtain a mixed pulp.

[0027] S2. Sizing and Adjustment: Add the polymer emulsion and sizing agent to the mixed slurry, stir, add the retention and filtration aid, and adjust the pH value to 6.5-7.5;

[0028] S3. Papermaking: The pulp processed in step S2 is sprayed from the headbox to the forming wire, and then dewatered under vacuum, pressed in the pressing section, dried in the drying section, and wound to obtain the base paper, which is used as the face paper, liner paper and corrugated core paper respectively.

[0029] S4. Adhesive preparation: Starch, sodium hydroxide, borax and water are mixed in a reaction vessel and stirred and gelatinized at 60-70℃ to obtain the adhesive;

[0030] S5. Corrugated lamination: The corrugated core paper is pressed into a wavy shape by a corrugated roller, and the adhesive prepared in step S4 is applied to the crest of the wave, and then laminated to the face paper and the inner paper respectively.

[0031] S6. Forming: The laminated cardboard enters the drying tunnel for drying, and then undergoes longitudinal cutting, transverse cutting, creasing, grooving, and gluing to obtain the impact-resistant cardboard box.

[0032] Furthermore, in step S1, the stirring time of pulp fiber and modified microfibrillated cellulose is 15-25 minutes, and the stirring speed is 400-600 r / min;

[0033] In step S3, the drying section uses a multi-stage drying cylinder, with the surface temperature of the front drying cylinder being 80-95℃ and the surface temperature of the rear drying cylinder being 100-120℃.

[0034] Furthermore, in step S4, the adhesive is composed of the following raw material components in parts by weight: 20-30 parts starch, 0.5-1.5 parts sodium hydroxide, 0.3-0.8 parts borax, and 70-90 parts water;

[0035] In step S5, the surface temperature of the corrugated roller is 150-170℃, and the adhesive coating amount is 15-25g / m². 2 ;

[0036] In step S6, the temperature of the drying tunnel is 140-160℃, and the running speed of the cardboard in the drying tunnel is 80-120m / min.

[0037] This invention prepares a modified microfibrilized cellulose with a surface-loaded flexible bissilane structure via a liquid-phase grafting reaction, and introduces it as a key reinforcing component into a pulp fiber and polymer emulsion system. The preparation process utilizes the silanol produced by the hydrolysis of the bissilane groups at the ends of the coupling agent molecules, which undergoes in-situ dehydration condensation with the hydroxyl groups on the surface of the microfibrilized cellulose. This transforms the unstable physical hydrogen bonds between fibers into high-bond-energy covalent bonds, thereby grafting a molecular layer with a long-chain flexible structure onto the cellulose surface.

[0038] This specific molecular structure plays a dual role in bridging and energy dissipation within the system. The hydrophobic tails of the long-chain acrylate and hexyl segments in the coupling agent can penetrate deep into the polymer emulsion film, eliminating the interfacial barrier between the hydrophilic fibers and the hydrophobic matrix through physical entanglement and compatibility, thus constructing a continuous organic-inorganic interpenetrating network of "fiber-flexible segments-polymer". When the cardboard box is subjected to the instantaneous impact force from a drop or collision, the long carbon chain flexible segments located at the fiber-matrix interface act as microscopic "molecular springs". These flexible segments utilize their free volume to undergo conformational torsion and elastic stretching, converting the destructive impact kinetic energy into the heat energy of molecular chain motion for dissipation, effectively preventing the brittle fracture of the rigid interface. At the same time, the introduction of long-chain hydrophobic groups shields the fiber hydrogen bonds from the erosion of environmental moisture, ensuring the structural integrity and impact resistance of the cardboard box in complex logistics environments.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] 1. Superior Impact Resistance: The flexible long-chain structure introduced in this invention constructs interfacial micro-elastic units, which can more effectively absorb and dissipate instantaneous impact energy compared to traditional rigid fiber networks. This results in the carton exhibiting higher elongation at break and puncture strength when subjected to drops or collisions, improving the brittleness and easy breakage of traditional cardboard and enhancing the cushioning and protective capabilities of the packaging.

[0041] 2. Enhanced stability in humid environments: This invention reduces the hydrophilicity of the fiber surface through hydrophobic long carbon chain modification and covalent bond anchoring, significantly improving the wet strength retention rate of the cardboard compared to existing technologies. This effectively inhibits the erosion of fiber hydrogen bonds by moisture in humid environments, improves the stacking collapse problem caused by moisture absorption and softening of cartons, and enhances its structural stability in complex logistics environments.

[0042] 3. Stronger interfacial bonding: This invention utilizes a bissilane coupling agent to improve the compatibility between hydrophilic fibers and the hydrophobic polymer matrix, constructing a continuous and uniform interpenetrating network. Compared to traditional simple physical mixing or rigid reinforcement systems, this structure can transmit stress more uniformly, reducing stress concentration at the interface, thereby improving the overall mechanical load-bearing capacity and durability of the material. Attached Figure Description

[0043] Figure 1 This is a comparison of the infrared spectra of microfibrillated cellulose and modified microfibrillated cellulose. Detailed Implementation

[0044] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Example 1

[0046] Preparation of an impact-resistant cardboard box:

[0047] 1. Preparation of modified microfibrillated cellulose:

[0048] 1) Preparation of coupling agent:

[0049] ;

[0050] CAS number for raw material 1: 82985-35-1;

[0051] CAS number for raw material 2: 2009-83-8;

[0052] CAS number for raw material 3: 112-38-9;

[0053] First, add 4.05 g of anhydrous potassium carbonate, 0.22 g of sodium iodide, and 5.00 g of raw material 1 to a dry two-necked round-bottom flask. Add 50 mL of anhydrous acetonitrile using a syringe and start stirring to disperse the solid evenly. Then, slowly add 2.40 g of raw material 2 to the system. Purge the reaction system with nitrogen three times, and heat the reaction mixture in an oil bath to 85 °C (reflux), stirring for 16 hours. After the reaction is complete, stop heating and allow the mixture to cool to room temperature. Filter the reaction solution under reduced pressure through a diatomaceous earth-lined sand core funnel, and wash the filter cake with a small amount of anhydrous acetonitrile (2 × 10 mL). Combine the filtrates and rotary evaporate under reduced pressure in a 40 °C water bath to obtain a pale yellow, oily crude product. Redissolve the crude product in toluene (20 mL), filter again, and evaporate the filtrate to dryness. Rapid purification was performed using neutral alumina column chromatography (eluent: a mixture of n-hexane and ethyl acetate). The final product was dried under a high vacuum oil pump for 2 hours to remove solvent residue, yielding 4.2 g of intermediate.

[0054] In the second step, add 4.20 g of the main raw material intermediate and 1.93 g of raw material 2 to a dry, nitrogen-protected round-bottom flask. Pour 50 mL of anhydrous dichloromethane (DCM) into the flask and turn on magnetic stirring to completely dissolve the solids. Cool the reaction flask to 0°C in an ice-water bath. At 0°C, add 0.12 g of DMAP and 2.19 g of EDCI·HC sequentially to the reaction solution. After the addition is complete, maintain stirring at 0°C for 30 minutes, then remove the ice bath and allow the reaction solution to naturally rise to room temperature, and stir under a nitrogen atmosphere for approximately 12 hours. After the reaction is complete, dilute the reaction solution with DCM (50 mL) and quickly wash with saturated sodium bicarbonate solution (30 mL × 1) and cold brine (30 mL × 1). Immediately rinse the organic phase with anhydrous sodium sulfate (N... a2 The product was dried with SO4 and filtered to remove the desiccant. The filtrate was then evaporated under reduced pressure (30°C water bath) to remove the solvent, yielding a crude, oily product. The crude product was purified by rapid neutral alumina column chromatography (eluent: a mixture of n-hexane and ethyl acetate). The fraction containing the target product was collected, concentrated by rotary evaporation, and dried under vacuum to obtain 3.82 g of coupling agent.

[0055] Structural assessment:

[0056] NMR of the intermediate: 1 HNMR-CDCl3: δ3.63(t,2H),3.56(s,18H),2.38-2.45(m,6H),1.65-1.45(m,6H),1.38-1.25(m,6H),0.62(t,4H);

[0057] NMR of the coupling agent: 1 HNMR-CDCl3: δ5.81(m,1H),4.99(m,1H),4.93(m,1H),4.06(t,2H),3.56(s,18H),2.39-2.45(m,6H),2 .29(t,2H),2.04(q,2H),1.58-1.65(m,4H),1.45-1.55(m,4H),1.25-1.40(m,16H),0.62-0.68(m,4H).

[0058] 2). Preparation of modified microfibrillated cellulose:

[0059] (1) Raw material dispersion: The microfibrillated cellulose slurry (purchased from Shanghai Shunshui Chemical Co., Ltd.) was dispersed in an ethanol aqueous solution (ethanol to water volume ratio of 90:10), and stirred and dispersed using a high-speed disperser to prepare a microfibrillated cellulose suspension with a solid content of 4% for later use.

[0060] (2) Grafting reaction: Take 2.0 g of the flexible silane coupling agent prepared in step 1) above, dissolve it in 200 ml of ethanol aqueous solution, adjust the pH to about 4.0 with dilute acetic acid, and pre-hydrolyze for 30 minutes to obtain a coupling agent hydrolysate. Then, slowly add the hydrolysate dropwise to the microfibrillated cellulose suspension, and continue to add dilute acetic acid to adjust the pH of the system to 4.5. Heat the reaction system to 60℃ and react at a constant temperature for 4 hours under mechanical stirring speed of 500 r / min.

[0061] (3) Post-processing: After the reaction is completed, the product is vacuum filtered, and the resulting filter cake is washed three times with anhydrous ethanol to remove unreacted coupling agent and byproducts. Finally, the washed filter cake is placed in a forced-air drying oven and dried at 70°C to constant weight to obtain the modified microfibrillated cellulose with the surface-loaded flexible silane coupling agent.

[0062] like Figure 1 The image shows a comparison of the Fourier Transform Infrared (FT-IR) spectra of microfibrillated cellulose and modified microfibrillated cellulose. Compared with unmodified microfibrillated cellulose, modified microfibrillated cellulose exhibits higher FT-IR spectra at 1730 cm⁻¹. -1 A distinct characteristic absorption peak for the ester group C=O was observed nearby, mainly attributed to the long-chain acrylate structure contained in the flexible silane coupling agent molecular chain grafted onto the fiber surface; simultaneously, at 2850 cm⁻¹... -1 and 2920cm -1 The intensity of the nearby CH stretching vibration peaks increased significantly and became sharper, corresponding to the numerous long-chain alkyl methylene structures introduced into the coupling agent molecular backbone. The appearance and enhancement of these characteristic peaks confirm that the silane coupling agent containing long-chain flexible hydrophobic structures has been successfully chemically grafted onto the surface of microfibrillated cellulose via in-situ condensation reaction, thereby achieving modification.

[0063] 3) Pulp fiber: 80 parts (made from 50 parts softwood sulfate pulp and 30 parts waste paper deinking pulp);

[0064] Modified microfibrillated cellulose: 20 parts (obtained from the above preparation);

[0065] Polymer emulsion: 12 parts;

[0066] (Polymer emulsion raw materials: 90 parts carboxylated styrene-butadiene latex, 15 parts oxidized starch, 2 parts glyoxal, 75 parts water);

[0067] Sizing agent: 3 parts (alkyl ketene dimer is preferred);

[0068] Retention and filtration aid: 1 part (polyethyleneimine is preferred).

[0069] 4) Preparation method:

[0070] S1. Pulp preparation: 80 parts of pulp fiber were decomposed and beaten, and the freeness was controlled at 38°SR. Then, 20 parts of the modified microfibrillated cellulose prepared above were added, and the mixture was stirred at 500 r / min for 20 minutes to obtain the mixed pulp.

[0071] S2. Sizing and Conditioning: Add 12 parts of polymer emulsion (mix the above raw materials evenly, and control the final solid content to 45% by adjusting the water volume) and 3 parts of AKD sizing agent to the mixed slurry, stir evenly, and then add 1 part of polyethyleneimine. Use an acid / alkali adjuster to control the pH of the slurry to 7.0.

[0072] S3. Papermaking: The treated pulp is sprayed from the headbox onto the forming wire, and after vacuum dewatering and pressing in the press section, it enters the drying section. A multi-stage drying cylinder is used, with the surface temperature of the first drying cylinder controlled at 90℃ and the surface temperature of the second drying cylinder controlled at 110℃. The resulting base paper is then cut into face paper, liner paper, and corrugated core paper.

[0073] S4. Adhesive preparation: 25 parts starch, 1 part sodium hydroxide, 0.5 parts borax and 80 parts water are added to a reaction vessel and mixed. The mixture is stirred and gelatinized at 65°C to obtain the adhesive.

[0074] S5. Corrugated Lamination: The corrugated core paper is pressed into a corrugated shape using corrugated rollers. The temperature of the corrugated rollers is set to 160℃. The adhesive prepared in step S4 is applied to the crests of the corrugations, with the coating amount controlled at 20g / m². 2 Then, they are attached to the face paper and the inner paper respectively.

[0075] S6. Forming: The laminated cardboard is sent into the drying tunnel for final drying and shaping. The tunnel temperature is set at 150℃, and the cardboard running speed is controlled at 100m / min. The cardboard undergoes longitudinal cutting, transverse cutting, creasing, grooving, and gluing processes to finally produce the finished impact-resistant cardboard box.

[0076] Example 2

[0077] Preparation of an impact-resistant cardboard box:

[0078] 1. Raw material components by weight:

[0079] Pulp fiber: 90 parts (same as Example 1);

[0080] Modified microfibrillated cellulose: 15 parts (same as Example 1);

[0081] Polymer emulsion: 8 parts;

[0082] Polymer emulsion raw materials: 100 parts carboxylated styrene-butadiene latex, 10 parts oxidized starch, 1 part glyoxal, and 50 parts water;

[0083] Sizing agent: 2 parts (same as in Example 1);

[0084] Retention and filtration aid: 0.5 parts (same as in Example 1).

[0085] 2. The rest remains the same as in Example 1.

[0086] Example 3

[0087] Preparation of an impact-resistant cardboard box:

[0088] 1. Raw material components by weight:

[0089] Pulp fiber: 70 parts (same as Example 1);

[0090] Modified microfibrillated cellulose: 25 parts (same as Example 1);

[0091] Polymer emulsion: 15 parts

[0092] Polymer emulsion raw materials: 80 parts carboxylated styrene-butadiene latex, 20 parts oxidized starch, 3 parts glyoxal, and 100 parts water;

[0093] Sizing agent: 5 parts (same as in Example 1);

[0094] Retention and filtration aid: 2 parts (same as in Example 1).

[0095] 2. The rest remains the same as in Example 1.

[0096] Comparative Example 1

[0097] The preparation of an impact-resistant cardboard box is carried out by referring to the preparation method of Example 1, except that the modified microfibrillated cellulose is replaced with an equal amount of unmodified microfibrillated cellulose, and the rest is the same as in Example 1.

[0098] Comparative Example 2

[0099] The preparation of an impact-resistant cardboard box is carried out according to the preparation method of Example 1. In the preparation step (2) of modified microfibrillated cellulose, the flexible silane coupling agent is replaced with an equimolar amount of γ-methacryloyloxypropyltrimethoxysilane (KH-570), and the rest is the same as in Example 1.

[0100] Comparative Example 3

[0101] The preparation of an impact-resistant cardboard box is carried out according to the preparation method of Example 1, but the preparation step of modified microfibrillated cellulose is omitted. In the pulp preparation process of step S1, an equal amount of unmodified microfibrillated cellulose and an equal amount of the flexible silane coupling agent are added to the pulp fibers and a simple physical mixing is carried out. The rest is the same as in Example 1.

[0102] Comparative Example 4

[0103] The preparation of an impact-resistant cardboard box is carried out according to the preparation method of Example 1, except that the modified microfibrillated cellulose is replaced with an equal amount of cationic starch, and the rest is the same as in Example 1.

[0104] Performance testing:

[0105] To ensure the accuracy and comparability of the test data, all samples were pretreated strictly according to GB / T 10739-2023 before testing, and were placed in a constant temperature and humidity environment of 23±1℃ and 50±2% for 24 hours before testing.

[0106] A1. Basis Weight: Tested according to GB / T 451.2-2023. This indicator serves as the benchmark parameter for comparing physical properties, ensuring that the modification effects are compared under the premise that the mass per unit area of ​​each group of paperboard is basically consistent. The data are shown in Table 1.

[0107] A2. Puncture Strength: Tested according to GB / T 2679.7-2005. This indicator reflects the energy that the cardboard can withstand when subjected to a sudden impact, directly characterizing the impact resistance and cushioning performance of the carton. The data is shown in Table 1.

[0108] A3. Longitudinal elongation at break: Tested according to GB / T 12914-2018. This index reflects the deformation capacity of the fiber network before fracture under stress, and is used to characterize the toughness of the material and the ductility of the internal "molecular spring" structure. The data are shown in Table 1.

[0109] A4. Wet strength retention rate: First, the bursting strength (P) of the samples in the dry state was determined according to GB / T 1539-2007. 干 The wet bursting strength (P) after being immersed in distilled water at 20℃±2℃ for 24 hours. 湿 The formula for calculating wet strength retention rate is: R = (P 湿 / P 干 ()×100%, the data is shown in Table 1.

[0110] Table 1.

[0111]

[0112] The longitudinal elongation at break and puncture strength of the embodiments are significantly higher than those of Comparative Examples 1 and 4. The differences in data are not due to variations in cardboard thickness or weight, but rather indicate that the introduced flexible silane coupling agent successfully altered the rigid, brittle fracture mode of the fiber network, which relies solely on hydrogen bonds. Compared to Comparative Example 2, which uses a short-chain rigid coupling agent, the higher toughness of the embodiments verifies that the unique long-chain alkyl and acrylate structure of this invention acts as an effective molecular spring, dissipating more energy through chain segment movement upon impact. Furthermore, a comprehensive comparison of dry burst strength and wet strength retention reveals that while physical blending (Comparative Example 3) provides some dry strength, its wet strength retention is low. The high retention rate of the embodiments confirms that in-situ chemical grafting forms a stable covalent bond anchor, which, combined with the shielding effect of the long-chain hydrophobic groups, effectively prevents interface disintegration caused by moisture erosion, solving the problem of moisture absorption and softening in traditional cardboard boxes.

[0113] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An impact-resistant cardboard box, characterized in that, The carton is made of composite corrugated cardboard, the raw material of which includes the following components in parts by weight: Pulp fiber content: 70-90 parts; 15-25 parts of modified microfibrillated cellulose; 8-15 parts polymer emulsion; 2-5 parts of sizing agent; 0.5-2 parts of retention and filtration aid; The modified microfibrillated cellulose is microfibrillated cellulose with a surface-loaded flexible silane coupling agent; The chemical formula of the flexible silane coupling agent is the compound shown in Formula 1: Formula 1: .

2. The impact-resistant cardboard box according to claim 1, characterized in that, The pulp fiber is one or more of softwood sulfate pulp, hardwood sulfate pulp, or waste paper deinking pulp.

3. The impact-resistant cardboard box according to claim 1, characterized in that, The method for preparing the modified microfibrillated cellulose is as follows: (1) Raw material dispersion: Disperse microfibrillated cellulose powder or slurry in an ethanol aqueous solution to prepare a suspension with a solid content of 3%-5%; (2) Grafting reaction: Add hydrolysate of flexible silane coupling agent dropwise to the suspension, adjust the pH value to 4.0-5.0, and stir the reaction at 50-65℃ for 3-5 hours; (3) Post-treatment: The reaction product is filtered, washed with ethanol, and dried at 60-80℃ to obtain the microfibrillated cellulose with the surface loaded with flexible silane coupling agent.

4. The impact-resistant cardboard box according to claim 1, characterized in that, The polymer emulsion is made from the following raw materials in parts by weight: 80-100 parts of carboxylated styrene-butadiene latex; 10-20 parts of oxidized starch; 1-3 parts of glyoxal; and 50-100 parts of water.

5. A shock-resistant cardboard box according to claim 1 or 4, characterized in that, The polymer emulsion has a solid content of 40%-50%.

6. The impact-resistant cardboard box according to claim 1, characterized in that, The sizing agent is one of alkyl ketene dimer and alkenyl succinic anhydride.

7. The impact-resistant cardboard box according to claim 1, characterized in that, The retention and filtration aid is either polyethyleneimine or polydiallyldimethylammonium chloride.

8. A method for preparing an impact-resistant cardboard box according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Pulp preparation: The pulp fibers are loosened and beaten, and the freeness is controlled at 30-45°SR. The modified microfibrillated cellulose is added and stirred to obtain a mixed pulp. S2. Sizing and Adjustment: Add the polymer emulsion and sizing agent to the mixed slurry, stir, add the retention and filtration aid, and adjust the pH value to 6.5-7.5; S3. Papermaking: The pulp processed in step S2 is sprayed from the headbox to the forming wire, and then dewatered under vacuum, pressed in the pressing section, dried in the drying section, and wound to obtain the base paper, which is used as the face paper, liner paper and corrugated core paper respectively. S4. Adhesive preparation: Starch, sodium hydroxide, borax and water are mixed in a reaction vessel and stirred and gelatinized at 60-70°C to obtain the adhesive; S5. Corrugated lamination: The corrugated core paper is pressed into a wavy shape by a corrugated roller, and the adhesive prepared in step S4 is applied to the crest of the wave, and then laminated to the face paper and the inner paper respectively. S6. Forming: The laminated cardboard enters the drying tunnel for drying, and then undergoes longitudinal cutting, transverse cutting, creasing, grooving, and gluing to obtain the impact-resistant cardboard box.

9. A method for preparing an impact-resistant cardboard box according to claim 8, characterized in that, In step S1, the stirring time of pulp fiber and modified microfibrillated cellulose is 15-25 minutes, and the stirring speed is 400-600 r / min; In step S3, the drying section uses a multi-stage drying cylinder, with the surface temperature of the front drying cylinder being 80-95℃ and the surface temperature of the rear drying cylinder being 100-120℃.

10. A method for preparing an impact-resistant cardboard box according to claim 8, characterized in that, In step S4, the adhesive is composed of the following raw material components in parts by weight: 20-30 parts starch, 0.5-1.5 parts sodium hydroxide, 0.3-0.8 parts borax, and 70-90 parts water; In step S5, the surface temperature of the corrugated roller is 150-170℃, and the adhesive coating amount is 15-25g / m². 2 ; In step S6, the temperature of the drying tunnel is 140-160℃, and the running speed of the cardboard in the drying tunnel is 80-120m / min.

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