A corrugated paperboard multiple composite web adhesive and methods of making and using

Abstract

The application discloses a corrugated board multiple composite network adhesive, which comprises the following components in parts by mass: 100-120 parts of waxy corn starch, 20-25 parts of industrial alkali lignin, 3-5 parts of chitosan, 2-3 parts of boric acid ester-based compound, 5-8 parts of nano cellulose (CNF), 0.5-3 parts of boric acid salt, 1.5-2.5 parts of synergistic preservative, 1-5 parts of filler / pH buffer, and the rest components including a weak organic alkali and a solvent, and then a perfect preparation process and a perfect use method are given. The corrugated board adhesive prepared by the multiple physical / chemical crosslinking network has high strength, water resistance, mildew resistance and stability, and the comprehensive performance is far higher than that of the prior art, and when used for the corrugated board, the corrugated board can be recycled and reused, the low-cost renewable biomass is used, the production cost is effectively reduced, the environmental protection performance is good, and the many defects of the prior adhesive are perfectly solved.

Description

Technical Field

[0001] This invention relates to the technical field of corrugated cardboard bonding, specifically to a multi-layer composite network adhesive for corrugated cardboard and its preparation and application methods. Background Technology

[0002] Starch-based adhesives (usually made from corn or tapioca starch) are the most common type of adhesive used in corrugated cardboard production due to their low price, good adhesion, and environmental friendliness. However, they also have some significant drawbacks. Poor stability is the most common problem; their viscosity is unstable, easily thinning during use, and prone to separation and sedimentation during storage, making continuous use difficult. This leads to difficulty in controlling the adhesive application, affecting the stability of product quality. Poor moisture resistance means that corrugated cardboard made with starch adhesives easily absorbs moisture in humid environments, causing the cardboard to soften, reducing adhesive strength, and even leading to delamination. This poses a serious challenge for packaging that requires refrigeration, sea transport, or storage and transportation in high-humidity environments.

[0003] The slow drying speed affects production efficiency. The starch adhesive dries relatively slowly. In order to ensure that the cardboard is firmly bonded, the production speed may have to be reduced, or it may still take a long time to dry completely after leaving the drying tunnel. If the cardboard is not completely dried, the moisture is difficult to evaporate and may be reabsorbed by the cardboard, causing the cardboard to soften, deform or delaminate later.

[0004] The initial tack of starch adhesive is sometimes poor. On high-speed production lines, it may detach due to the movement of the cardboard before the adhesive has fully penetrated and gelatinized, resulting in "corrugation running" or "hollowing out".

[0005] Starch adhesives require a certain gelatinization temperature to achieve their adhesive properties. If the temperature is not properly controlled, such as gelatinization being too rapid, the adhesive may not be able to fully penetrate the paper; while if gelatinization is too slow, the adhesive will penetrate excessively and fail to form an effective bond.

[0006] Hot melt adhesives (such as EVA-based adhesives) cure quickly, making them suitable for high-speed production lines such as automated box sealing. However, their high-temperature resistance is limited; they may soften and lose their stickiness at high temperatures, and become brittle at low temperatures. Furthermore, their raw material costs may be higher than those of ordinary starch adhesives. Sodium silicate-based adhesives (sodium silicate / water glass) can increase the stiffness of cardboard in the short term, but they have significant problems. Their use is explicitly prohibited by the government, yet some still use them: they are extremely susceptible to moisture; when exposed to moisture, the cardboard is prone to delamination and softening, leading to a significant decrease in edge crush strength. This often results in collapsed stacks of stored cartons, negatively impacting carton quality and causing problems such as discoloration, white bloom, deformation, and damage. They are also toxic and harmful to human health and the environment. Summary of the Invention

[0007] To address the above shortcomings, the present invention provides the following technical solution.

[0008] A multi-layer composite network adhesive for corrugated cardboard, comprising the following components in parts by weight:

[0009] The ingredients include 100-120 parts waxy corn starch, 20-25 parts industrial alkali lignin, 3-5 parts chitosan, 2-3 parts borate ester compounds, 5-8 parts nanocellulose (CNF), and 0.5-3 parts borate.

[0010] Synergistic preservative 1.5-2.5 parts, filler / pH buffer 1-5 parts;

[0011] The remaining components include a pH adjuster, a weak organic base, and a solvent.

[0012] Furthermore, the pH adjuster, a weak organic base, is triethanolamine (TEA), added in parts other than proportions, and is used to precisely adjust the pH of the entire system to the optimal range of 9.5–10.5.

[0013] Furthermore, the solvent is deionized water, which is not added in parts, but adjusted to a final adhesive solid content of 20% to 25 wt%.

[0014] Furthermore, the borate is a compound component comprising borax and zinc borate, wherein the mass ratio of borax to zinc borate is 1.2 to 1.5:1.

[0015] Furthermore, the borate ester compound is 1,3-phenylene glycol diboronic acid.

[0016] Furthermore, the synergistic preservative includes 0.3 to 0.5 parts copper sulfate and 1.2 to 2 parts catechol.

[0017] Furthermore, the filler is 1 to 5 parts of magnesium hydroxide.

[0018] Furthermore, the chitosan is dissolved in a 1% (v / v) aqueous solution of acetic acid.

[0019] A method for preparing a multi-layer composite network adhesive for corrugated cardboard includes the following steps:

[0020] S1. Raw material pretreatment

[0021] I. Preparation of chitosan acid solution:

[0022] Take deionized water (not included in the formula) and prepare a 1% (v / v) acetic acid aqueous solution. In container A, slowly add the corresponding mass of chitosan powder to the continuously stirred acetic acid solution and stir vigorously until completely dissolved to obtain a clear or slightly turbid viscous solution. Let it stand to remove bubbles for later use.

[0023] II. Preparation of magnesium hydroxide suspension:

[0024] In container B, mix the corresponding mass of magnesium hydroxide powder with a small amount (about 20 parts) of deionized water and pre-disperse it for 15 minutes using a high-shear disperser to form a uniform and stable suspension for later use.

[0025] III. Preparation of borate premix:

[0026] Weigh out the total borate according to the ratio (borax:zinc borate = 1.2~1.5:1), dissolve it in an appropriate amount of warm water by stirring, and obtain a clear solution for later use;

[0027] Weigh out the corresponding mass parts of total borate according to the ratio (borax:zinc borate = 1.2~1.5:1), dissolve it in an appropriate amount of warm water (about 50℃) by stirring. Zinc borate has low solubility, so it needs to be stirred patiently or heated slightly until it is completely dispersed to obtain a clear solution for later use.

[0028] S2. Starch / lignin slurry gelatinization:

[0029] Add about 1 / 3 of the total amount of deionized water to the reactor, start stirring, slowly add the corresponding mass of waxy corn starch and the corresponding mass of industrial alkali lignin, stir for 10 minutes to form a uniform suspension without dry powder, slowly heat to 75-85℃, and keep stirring at this temperature for 20-30 minutes to fully gelatinize the starch and make the system a uniform and viscous slurry.

[0030] S2. Mixing process:

[0031] Stop heating and allow the temperature of the slurry obtained in the previous step to drop below 50°C. Slowly add the pretreated chitosan acid solution to the reactor and stir thoroughly for 15 minutes to ensure uniform mixing. Slowly add the pH adjuster—triethanolamine (TEA)—to initially adjust the pH of the system to 8.5-9.0. Slowly add the corresponding mass fraction of nanocellulose (CNF) gel and switch to a high-shear disperser. Shear disperse at a speed of at least 2000 rpm for 20-30 minutes to ensure complete dispersion of CNF without agglomeration and a significant increase in system viscosity.

[0032] S4. pH Adjustment:

[0033] Continue to slowly add TEA, and while continuously stirring and cooling (keeping it below 50°C), precisely adjust the pH of the entire system to the core reaction range of 9.5 to 10.5, and confirm with precision pH test paper or pH meter;

[0034] S5. Introduce a core cross-linking network:

[0035] While stirring at a constant medium speed, slowly add a 20%-30% (w / v) solution of 1,3-phenylene glycol diboric acid dissolved in anhydrous ethanol, and continue the reaction for 15 minutes to allow the dynamic covalent crosslinking reaction to proceed in its initial stage.

[0036] S6. Add auxiliary cross-linking agents and preservatives:

[0037] Add the pre-prepared borate premix, then add the corresponding mass fractions of copper sulfate and catechol, maintain the system temperature <50℃, and continue stirring for 20 minutes;

[0038] S7. Construction of Ion Networks and Functionalization:

[0039] Slowly add the pre-dispersed magnesium hydroxide suspension and stir thoroughly for at least 3 minutes to ensure that the magnesium ions are evenly dispersed and fully interact with the network.

[0040] S8. Final Adjustment and Discharge:

[0041] Add the remaining deionized water, adjust the final solid content of the system to 20%–25 wt%, test the pH again to ensure it is still within the range of 9.5–10.5, stop stirring, cool to room temperature, discharge the material, filter to remove any possible trace impurities, obtain the final product, and seal and package it.

[0042] A method for using a multi-layer composite network adhesive for corrugated cardboard includes the following steps: Step 1, applying the adhesive evenly by roller coating onto the corrugated peaks; Step 2, aging by leaving it exposed to air for approximately 1-3 minutes; Step 3, bonding it to the inner and outer linerboards; Step 4, hot-pressing curing at a temperature of 120℃~150℃ and a pressure of 0.5~1.5MPa for 90-180 seconds; Step 5, cooling and setting.

[0043] In the above formulation, lignin provides rigidity, hydrophobicity, and additional reaction sites; waxy corn starch (almost amylose) provides abundant hydroxyl groups and better film-forming properties; compounds containing borate ester groups (such as 1,3-phenylene glycol diboronic acid) form a dynamic covalent network of borate ester bonds; chitosan (a key synergist) stabilizes borate ester bonds through BN coordination, greatly improving water resistance; enhancing mechanical strength and possessing natural antiseptic and antibacterial capabilities; the amino groups on the chitosan chain form BN coordination with borate ester bonds, and its molecular chains can also form hydrogen bonds with CNF, starch, etc., playing a dual role of "bridging" and "reinforcing," forming a boron-nitrogen coordination network; CNF, with its nanoscale fibrous structure, has a huge specific surface area and extremely high aspect ratio, and can interact with all biomass molecules (starch, lignin, chitosan). It forms an extremely dense hydrogen bond network, effectively dispersing stress and preventing crack propagation, thereby significantly improving initial tack, toughness, tensile strength, and tear resistance. The weak organic base (pH adjuster / catalyst) creates and maintains a slightly alkaline environment (pH ~ 9-11), which is key to forming stable borate ester bonds. Its nitrogen-containing groups (such as organic amines) can participate in BN coordination, further stabilizing the network. Borate (such as borax) assists in crosslinking (rapidly bonding with starch) and forms a synergistic crosslinking network with the core crosslinking agent, optimizing crosslinking density and curing rate. Copper sulfate / catechin acts as an auxiliary preservative / bactericide, preventing biodegradation and extending shelf life. The catechin structure can strongly interact with boron, participating in crosslinking. Magnesium hydroxide forms a pH buffer system, maintaining pH stability and protecting the stability of dynamic borate ester bonds and BN coordination bonds over the long term. Multiple negatively charged groups in the system undergo ionic bonding or coordination, introducing an ionic bond network on top of the existing covalent bond network (borate ester bonds), coordination bond network (BN), and hydrogen bond network (CNF, etc.). This multi-network interpenetrating structure significantly improves the cohesive strength, heat resistance, and creep resistance of adhesives (i.e., they are less prone to deformation under sustained stress).

[0044] The beneficial effects of this invention are: 1. Through multiple cross-linking networks (covalent bonds, coordination bonds, hydrogen bonds, and ionic bonds) and hydrophobic modification, the adhesive can effectively resist moisture erosion after curing; 2. The unique synergistic anti-corrosion system and protection of natural components such as starch and chitosan greatly extend the service life of the adhesive itself and the final cardboard product, preventing mold and biodegradation; 3. Using renewable resources (starch, lignin, chitosan, cellulose) as the main raw materials reduces dependence on petroleum-based polymers. It releases no formaldehyde, making it safer and more environmentally friendly. The formulation design includes detailed preparation and usage methods, with clear pH and temperature control, and good compatibility with existing corrugated cardboard production line sizing and hot-pressing processes; 4. The use of a large amount of relatively low-cost biomass raw materials (such as lignin as a partial substitute) can potentially control raw material costs while improving performance. Detailed Implementation

[0045] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0046] A method for preparing a multi-layer composite network adhesive for corrugated cardboard includes the following steps:

[0047] S1. Raw material pretreatment

[0048] I. Preparation of chitosan acid solution:

[0049] Take deionized water (not included in the formula) and prepare a 1% (v / v) acetic acid aqueous solution. In container A, slowly add the corresponding mass of chitosan powder to the continuously stirred acetic acid solution and stir vigorously until completely dissolved to obtain a clear or slightly turbid viscous solution. Let it stand to remove bubbles for later use.

[0050] II. Preparation of magnesium hydroxide suspension:

[0051] In container B, mix the corresponding mass of magnesium hydroxide powder with a small amount (about 20 parts) of deionized water and pre-disperse it for 15 minutes using a high-shear disperser to form a uniform and stable suspension for later use.

[0052] III. Preparation of borate premix:

[0053] Weigh out the total borate according to the ratio (borax:zinc borate = 1.2~1.5:1), dissolve it in an appropriate amount of warm water by stirring, and obtain a clear solution for later use;

[0054] Weigh out the corresponding mass parts of total borate according to the ratio (borax:zinc borate = 1.2~1.5:1), dissolve it in an appropriate amount of warm water (about 50℃) by stirring. Zinc borate has low solubility, so it needs to be stirred patiently or heated slightly until it is completely dispersed to obtain a clear solution for later use.

[0055] S2. Starch / lignin slurry gelatinization:

[0056] Add about 1 / 3 of the total amount of deionized water to the reactor, start stirring, slowly add the corresponding mass of waxy corn starch and the corresponding mass of industrial alkali lignin, stir for 10 minutes to form a uniform suspension without dry powder, slowly heat to 75-85℃, and keep stirring at this temperature for 20-30 minutes to fully gelatinize the starch and make the system a uniform and viscous slurry.

[0057] S2. Mixing process:

[0058] Stop heating and allow the temperature of the slurry obtained in the previous step to drop below 50°C. Slowly add the pretreated chitosan acid solution to the reactor and stir thoroughly for 15 minutes to ensure uniform mixing. Slowly add the pH adjuster—triethanolamine (TEA)—to initially adjust the pH of the system to 8.5-9.0. Slowly add the corresponding mass fraction of nanocellulose (CNF) gel and switch to a high-shear disperser. Shear disperse at a speed of at least 2000 rpm for 20-30 minutes to ensure complete dispersion of CNF without agglomeration and a significant increase in system viscosity.

[0059] S4. pH Adjustment:

[0060] Continue to slowly add TEA, and while continuously stirring and cooling (keeping it below 50°C), precisely adjust the pH of the entire system to the core reaction range of 9.5 to 10.5, and confirm with precision pH test paper or pH meter;

[0061] S5. Introduce a core cross-linking network:

[0062] While stirring at a constant medium speed, slowly add a 20%-30% (w / v) solution of 1,3-phenylene glycol diboric acid dissolved in anhydrous ethanol, and continue the reaction for 15 minutes to allow the dynamic covalent crosslinking reaction to proceed in its initial stage.

[0063] S6. Add auxiliary cross-linking agents and preservatives:

[0064] Add the pre-prepared borate premix, then add the corresponding mass fractions of copper sulfate and catechol, maintain the system temperature <50℃, and continue stirring for 20 minutes;

[0065] S7. Construction of Ion Networks and Functionalization:

[0066] Slowly add the pre-dispersed magnesium hydroxide suspension and stir thoroughly for at least 3 minutes to ensure that the magnesium ions are evenly dispersed and fully interact with the network.

[0067] S8. Final Adjustment and Discharge:

[0068] Add the remaining deionized water, adjust the final solid content of the system to 20%–25 wt%, test the pH again to ensure it is still within the range of 9.5–10.5, stop stirring, cool to room temperature, discharge the material, filter to remove any possible trace impurities, obtain the final product, and seal and package it.

[0069] A method for using a multi-layer composite network adhesive for corrugated cardboard includes the following steps: Step 1, applying the adhesive evenly by roller coating onto the corrugated peaks; Step 2, aging by leaving it exposed to air for approximately 1-3 minutes; Step 3, bonding it to the inner and outer linerboards; Step 4, hot-pressing curing at a temperature of 120℃~150℃ and a pressure of 0.5~1.5MPa for 90-180 seconds; Step 5, cooling and setting.

[0070] Example 1

[0071] 100 parts waxy corn starch, 20 parts industrial alkali lignin, 3 parts chitosan, 2 parts borate ester compound, 5 parts nanocellulose (CNF), 0.5 parts borate (borax to zinc borate mass ratio of 1.2:1), 1.5 parts synergistic preservative, 0.3 parts copper sulfate, 1.2 parts catechol; 1 part magnesium hydroxide filler / pH buffer.

[0072] Example 2

[0073] 120 parts waxy corn starch, 25 parts industrial alkali lignin, 5 parts chitosan, 3 parts borate ester compound, 8 parts nanocellulose (CNF), 3 parts borate (borax to zinc borate in a mass ratio of 1.2:1), 2.5 parts synergistic preservative (0.5 parts copper sulfate, 1.5 parts catechin), 5 parts filler / pH buffer magnesium hydroxide;

[0074] Example 3

[0075] 100 parts waxy corn starch, 20 parts industrial alkali lignin, 3 parts chitosan, 2 parts borate ester compound, 5 parts nanocellulose (CNF), 0.5 parts borate (borax to zinc borate in a mass ratio of 1.5:1), 1.5 parts synergistic preservative, 0.3 parts copper sulfate, 1.2 parts catechol; 1 part magnesium hydroxide filler / pH buffer.

[0076] The manufacturing process of the adhesive in the above embodiments includes the following steps:

[0077] S1. Raw material pretreatment

[0078] I. Preparation of chitosan acid solution:

[0079] Take deionized water (not included in the formula) and prepare a 1% (v / v) acetic acid aqueous solution. In container A, slowly add the corresponding mass of chitosan powder to the continuously stirred acetic acid solution and stir vigorously until completely dissolved to obtain a clear or slightly turbid viscous solution. Let it stand to remove bubbles for later use.

[0080] II. Preparation of magnesium hydroxide suspension:

[0081] In container B, mix the corresponding mass of magnesium hydroxide powder with a small amount (about 20 parts) of deionized water and pre-disperse it for 15 minutes using a high-shear disperser to form a uniform and stable suspension for later use.

[0082] III. Preparation of borate premix:

[0083] Weigh out the total borate according to the ratio (borax:zinc borate = 1.2~1.5:1), dissolve it in an appropriate amount of warm water by stirring, and obtain a clear solution for later use;

[0084] Weigh out the corresponding mass parts of total borate according to the ratio (borax:zinc borate = 1.2~1.5:1), dissolve it in an appropriate amount of warm water (about 50℃) by stirring. Zinc borate has low solubility, so it needs to be stirred patiently or heated slightly until it is completely dispersed to obtain a clear solution for later use.

[0085] S2. Starch / lignin slurry gelatinization:

[0086] Add about 1 / 3 of the total amount of deionized water to the reactor, start stirring, slowly add the corresponding mass of waxy corn starch and the corresponding mass of industrial alkali lignin, stir for 10 minutes to form a uniform suspension without dry powder, slowly heat to 75-85℃, and keep stirring at this temperature for 20-30 minutes to fully gelatinize the starch and make the system a uniform and viscous slurry.

[0087] S2. Mixing process:

[0088] Stop heating and allow the temperature of the slurry obtained in the previous step to drop below 50°C. Slowly add the pretreated chitosan acid solution to the reactor and stir thoroughly for 15 minutes to ensure uniform mixing. Slowly add the pH adjuster—triethanolamine (TEA)—to initially adjust the pH of the system to 8.5-9.0. Slowly add the corresponding mass fraction of nanocellulose (CNF) gel and switch to a high-shear disperser. Shear disperse at a speed of at least 2000 rpm for 20-30 minutes to ensure complete dispersion of CNF without agglomeration and a significant increase in system viscosity.

[0089] S4. pH Adjustment:

[0090] Continue to slowly add TEA, and while continuously stirring and cooling (keeping it below 50°C), precisely adjust the pH of the entire system to the core reaction range of 9.5 to 10.5, and confirm with precision pH test paper or pH meter;

[0091] S5. Introduce a core cross-linking network:

[0092] While stirring at a constant medium speed, slowly add a 20%-30% (w / v) solution of 1,3-phenylene glycol diboric acid dissolved in anhydrous ethanol, and continue the reaction for 15 minutes to allow the dynamic covalent crosslinking reaction to proceed in its initial stage.

[0093] S6. Add auxiliary cross-linking agents and preservatives:

[0094] Add the pre-prepared borate premix, then add the corresponding mass fractions of copper sulfate and catechol, maintain the system temperature <50℃, and continue stirring for 20 minutes;

[0095] S7. Construction of Ion Networks and Functionalization:

[0096] Slowly add the pre-dispersed magnesium hydroxide suspension and stir thoroughly for at least 3 minutes to ensure that the magnesium ions are evenly dispersed and fully interact with the network.

[0097] S8. Final Adjustment and Discharge:

[0098] Add the remaining deionized water, adjust the final solid content of the system to 20%–25 wt%, test the pH again to ensure it is still within the range of 9.5–10.5, stop stirring, cool to room temperature, discharge the material, filter to remove any possible trace impurities, obtain the final product, and seal and package it.

[0099] A method for using a multi-layer composite network adhesive for corrugated cardboard includes the following steps: Step 1, applying the adhesive evenly by roller coating onto the corrugated peaks; Step 2, aging by leaving it exposed to air for approximately 1-3 minutes; Step 3, bonding it to the inner and outer linerboards; Step 4, hot-pressing curing at a temperature of 120℃~150℃ and a pressure of 0.5~1.5MPa for 90-180 seconds; Step 5, cooling and setting.

[0100] To verify the superior performance of the corrugated cardboard multi-composite network adhesive described in this invention, adhesive samples of Examples 1-3 of this invention were prepared in accordance with the above preparation process and usage method, and compared with commercially available ordinary starch adhesive and sodium silicate adhesive (sodium silicate). The test results are as follows:

[0101] The test sample is:

[0102] Comparative Example 1 (CE-1): Commercially available ordinary oxidized starch adhesive (25% solids content)

[0103] Comparative Example 2 (CE-2): Commercially available sodium silicate adhesive (modulus 3.2, solid content 40%)

[0104] Example 1 (EX-1): Prepared according to the formulation and method of Example 1 of the present invention

[0105] Example 2 (EX-2): Prepared according to the formulation and method of Example 2 of the present invention

[0106] Example 3 (EX-3): Prepared according to the formulation and method of Example 3 of the present invention

[0107] Table 1: Test Results of Adhesive Bulk Properties

[0108]

[0109] Table 2: Test results of corrugated board bonding performance (base paper: 125g / ㎡ linerboard)

[0110]

[0111] Table 3: Overall Performance and Adhesive Functionality Tests of Corrugated Board

[0112]

[0113] The test data above show that the multi-composite network adhesives (EX-1, EX-2, EX-3) provided by this invention are significantly superior to the comparative traditional products in all key performance aspects.

[0114] High initial tack and final strength: As shown in Table 2, the initial tack strength of the present invention is more than three times that of Comparative Example 1, and the final adhesive strength is nearly doubled. This is due to the reinforcing effect of nanocellulose (CNF) and the rapid construction of multiple networks.

[0115] Excellent water and moisture resistance: This is the most prominent advantage of this invention. Even after immersion in water for 24 hours, it maintains an adhesive strength of over 500 N / m, far superior to traditional products (CE-1, CE-2) that delaminate upon contact with water. This verifies the stability of the dynamic covalent borate ester network and the metal ion crosslinking network under wet conditions.

[0116] Excellent storage stability: As shown in Table 1, the viscosity change rate of the product of the present invention is less than 10% within 30 days, while the viscosity of traditional starch adhesive fluctuates greatly and sodium silicate is easily precipitated, indicating that the product of the present invention has a longer shelf life and better process stability.

[0117] Significant anti-mildew and anti-corrosion effects: Under high temperature and high humidity conditions, the product of this invention can achieve level 0 or 1 anti-mildew, while Comparative Example 1 showed severe mold growth. This proves that the synergistic anti-corrosion system of copper sulfate and catechins plays a key role.

[0118] Good process adaptability: The drying and curing time is between that of fast-drying but poor-performing sodium silicate and slow-drying traditional starch adhesive, making it compatible with existing production lines while ensuring final performance.

[0119] Conclusion: This invention successfully prepared a corrugated cardboard adhesive with high strength, water resistance, mildew resistance, and stability by constructing a multi-layer physical / chemical cross-linking network of "starch-lignin-chitosan-CNF". Its comprehensive performance far exceeds that of existing technologies, and it perfectly solves many industry pain points mentioned in the background technology.

[0120] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

[0121] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A multi-layer composite network adhesive for corrugated cardboard, characterized in that: The components include the following parts by weight: 100-120 parts waxy corn starch, 20-25 parts industrial alkali lignin, 3-5 parts chitosan, 2-3 parts boronic acid ester compound 1,3-phenylene glycol diboronic acid, 5-8 parts nanocellulose (CNF), 0.5-3 parts compound borate, 1.5-2.5 parts synergistic preservative, and 1-5 parts magnesium hydroxide filler / pH buffer. The remaining components include a pH adjuster, a weak organic base, and a solvent; The chitosan was pre-dissolved in a 1% (v / v) aqueous solution of acetic acid; The compound borate is a mixture of borax and zinc borate in a mass ratio of 1.2 to 1.5:1; The synergistic preservative is composed of 0.3-0.5 parts copper sulfate and 1.2-2 parts catechin; The pH adjuster, a weak organic base, is triethanolamine (TEA), which is not added according to a specific ratio and is used to precisely adjust the pH of the entire system to the optimal range of 9.5–10.

5. The solvent is deionized water, which is not added according to the specified parts, and is adjusted to a final adhesive solid content of 20% to 25 wt%.

2. The method for preparing a multi-layer composite network adhesive for corrugated cardboard according to claim 1, characterized in that... Includes the following steps: S1. Raw material pretreatment I. Preparation of chitosan acid solution: Chitosan powder is dissolved in a 1% (v / v) aqueous solution of acetic acid and stirred vigorously until completely dissolved to obtain a clear or slightly turbid viscous solution. The solution is then allowed to stand to remove bubbles before use. II. Preparation of magnesium hydroxide suspension: Mix magnesium hydroxide powder with deionized water and pre-disperse it for 15 minutes using a high-shear disperser to form a uniform and stable suspension for later use. III. Preparation of borate premix: Weigh out the corresponding mass fractions of the compound borate according to the ratio, dissolve it in an appropriate amount of warm water by stirring, and obtain a clear solution for later use; S2. Starch / lignin pulp gelatinization: Add 1 / 3 of the total volume of deionized water to the reactor, start stirring, and slowly add the corresponding mass of waxy corn starch and industrial alkali lignin. Stir for 10 minutes to form a uniform suspension without dry powder. Slowly heat to 75-85°C and keep stirring at this temperature for 20-30 minutes to fully gelatinize the starch and make the system a uniform, viscous slurry; S3. Mixing process: Stop heating and allow the temperature of the slurry obtained in the previous step to drop below 50°C. Slowly add the pretreated chitosan acid solution to the reactor and stir thoroughly for 15 minutes to ensure uniform mixing. Slowly add the pH adjuster—triethanolamine (TEA)—to initially adjust the pH of the system to 8.5-9.

0. Slowly add the nanocellulose (CNF) gel and switch to a high-shear disperser. Shear disperse at a speed of at least 2000 rpm for 20-30 minutes to ensure complete dispersion of CNF without agglomeration and a significant increase in system viscosity. S4. pH Adjustment: Continue to slowly add TEA, stirring and cooling continuously below 50°C, and precisely adjust the pH of the entire system to the core reaction range of 9.5 to 10.5, confirming with precision pH test paper or pH meter; S5. Introduce a core cross-linking network: While stirring at a constant medium speed, slowly add dropwise a 20% - 30% (w / v) aqueous solution of 1,3-phenylene glycol diboronic acid dissolved in anhydrous ethanol, and continue the reaction for 15 minutes to allow the dynamic covalent crosslinking reaction to proceed initially. S6. Add auxiliary cross-linking agents and preservatives: Add the pre-prepared compound borate premix, then add copper sulfate and catechol, maintain the system temperature <50°C, and continue stirring for 20 minutes; S7. Construction of Ion Networks and Functionalization: Slowly add the pre-dispersed magnesium hydroxide suspension and stir thoroughly for at least 3 minutes to ensure that the magnesium ions are evenly dispersed and fully interact with the network. S8. Final Adjustment and Discharge: Add the remaining deionized water, adjust the final solid content of the system to 20%–25 wt%, test the pH again to ensure it is still within the range of 9.5–10.5, stop stirring, cool to room temperature, discharge, filter, obtain the final product, and seal and package it.

3. The method of using the multi-layer composite network adhesive for corrugated cardboard according to claim 1, characterized in that... The application method includes the following steps: Step 1, apply adhesive evenly by roller coating onto the corrugated peaks; Step 2, allow to stand in the air for 1-3 minutes; Step 3, bond with the inner and outer paper; Step 4, hot press curing, temperature: 120℃~150℃, pressure: 0.5~1.5 MPa, hot press curing for 90-180 seconds; Step 5, cool and set.

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