Nano-modified starch glue for corrugated case and preparation method of nano-modified starch glue

Abstract

The invention discloses nano modified starch glue for corrugated cartons and a preparation method of the nano modified starch glue. The starch glue comprises carrier glue and main glue in a mass ratio of 1: (4-5), wherein the carrier glue comprises 10 parts of starch, 50-60 parts of water, 0.8-1.2 parts of sodium hydroxide and 0.8-1.5 parts of modified PAE resin; the main body glue comprises 10 parts of starch, 30-40 parts of water and 0.1-0.3 part of an oxidizing agent; a preparation method of the modified PAE resin comprises the following steps: carrying out polycondensation on dibasic acid, polyethylene polyamine and an amino acrylate monomer which are used as raw materials according to a molar ratio of (1.2-1.4): 1: (0.2-0.3) to obtain alkenyl-containing polyamide polyamine; and reacting the alkenyl-containing polyamide polyamine with hydrogen-containing silane and epoxy chloropropane in sequence to obtain the modified PAE resin. According to the scheme, the defects that existing corrugated paper starch glue is high in hygroscopicity and easy to hydrolyze and open are effectively overcome.

Description

Technical Field

[0001] This application relates to the field of nano-modified starch adhesive for corrugated cardboard boxes and its preparation method. Background Technology

[0002] Corrugated cardboard boxes, widely used in logistics and product packaging, rely heavily on the structure of the corrugated cardboard for their mechanical properties. Corrugated cardboard is typically composed of a corrugated core paper providing cushioning and support, and linerboard (face paper) covering both sides. Strong bonding between these layers is crucial for the overall structure. In this manufacturing process, starch adhesive is the preferred material for bonding the corrugated core paper peaks to the linerboard due to its wide availability, low cost, and environmental friendliness. This adhesive is applied to the peaks of the corrugated core paper, preheated, and then gelatinized under high-temperature pressing, thus achieving the bonding of the paper layers.

[0003] Currently, the industry generally adopts a starch adhesive preparation process based on a carrier-body two-component framework. The carrier adhesive is typically a small-proportion starch slurry strongly gelatinized with sodium hydroxide, exhibiting a high-viscosity, semi-transparent gel-like state. The body adhesive is a large-proportion starch suspension treated with an oxidizing agent, exhibiting good fluidity after degradation and suitable for industrial continuous coating production on corrugated paper lines. In use, the pre-prepared carrier adhesive is introduced into the body adhesive under stirring. The strong alkalinity of the carrier adhesive and the gelatinized molecules trigger the gelatinization of the body starch, ultimately forming a homogeneous and stable adhesive. Although this process is mature and widely used, the starch molecular chains are rich in hydrophilic hydroxyl groups, resulting in poor water resistance. The prepared corrugated cardboard is highly susceptible to moisture absorption and softening in high-humidity environments or when exposed to moisture, leading to delamination and other phenomena that severely affect the stacking strength and service life of the cartons. Summary of the Invention

[0004] To address the current problems of high hygroscopicity and easy delamination of starch adhesive in corrugated paper, this application provides a nano-modified starch adhesive for corrugated boxes and its preparation method.

[0005] In a first aspect, this application provides a nano-modified starch adhesive for corrugated cardboard boxes, comprising a carrier adhesive and a main adhesive in a mass ratio of 1:4 to 5. By mass, the carrier adhesive comprises: 10 parts starch, 50 to 60 parts water, 0.8 to 1.2 parts sodium hydroxide, and 0.8 to 1.5 parts modified PAE resin; the main adhesive comprises: 10 parts starch, 30 to 40 parts water, and 0.1 to 0.3 parts oxidant; the modified PAE resin is prepared by: using… Alkenyl polyamide polyamine is prepared by polycondensation of diacid, polyethylene polyamine and amino acrylate monomer in a molar ratio of 1.2-1.4:1:0.2-0.3. Modified PAE resin is prepared by reacting alkenyl polyamide polyamine with hydrosilane and epichlorohydrin in sequence. The molar ratio of alkenyl polyamide polyamine to epichlorohydrin is 1:0.6-0.9, and the molar ratio of amino acrylate monomer to hydrosilane is 1:1.1-1.3.

[0006] In any of the above technical solutions, the polyethylene polyamine is selected from any one or more of diethylenetriamine, triethylenetetramine, and tetraethylenepentamine; preferably diethylenetriamine.

[0007] In any of the above technical solutions, the aminoacrylate monomer is 2-aminoethyl methacrylate.

[0008] In any of the above technical solutions, 2-aminoethyl methacrylate is usually present as the more stable 2-aminoethyl methacrylate hydrochloride. In the actual reaction, after adding 2-aminoethyl methacrylate hydrochloride, sodium hydroxide (aqueous solution) of the same molar amount as hydrochloride can be slowly added dropwise under stirring to neutralize it and release the amino activity.

[0009] In any of the above technical solutions, the hydrogen-containing silane is selected from any one or more of trimethoxysilane, triethoxysilane, methyldimethoxysilane, methyldiethoxysilane, and ethyldimethoxysilane.

[0010] This application uses organosilicon-modified PAE resin as a water-resistant reinforcing agent, significantly improving the water resistance of starch adhesive and reducing phenomena such as moisture absorption and delamination of the adhesive layer. PAE resin (polyamide epichlorohydrin resin) itself can electrostatically adsorb negatively charged starch molecules or fibers through its strong cationic properties. More importantly, its active group, aziridinone, can undergo a cross-linking reaction with the hydroxyl groups on the starch molecular chains during hot pressing, forming a stable covalent bond network. This effectively blocks the penetration and erosion of starch molecules by water molecules, improving the water resistance of the adhesive film. Furthermore, this application introduces aminoacrylate monomers into the polycondensation process of PAE, introducing unsaturated alkenyl groups into the polyamide polyamine backbone, and then grafting hydrogen-silane-containing siloxane groups onto the polymer chain via hydrosilylation reaction. These introduced siloxane groups have good hydrophobicity. The silanol groups generated after hydrolysis can also undergo condensation reaction with starch hydroxyl groups in the high-temperature environment of the hot pressing process to form Si-OC covalent bonds, which further enhances the hydrophobicity and structural stability of the adhesive network, thereby more effectively preventing the corrugated cardboard from delaminating and deteriorating in strength under high humidity conditions.

[0011] It is worth noting that the amount of aminoacrylate monomer used must be controlled within the above-mentioned range. This ensures that sufficient alkenyl groups can be effectively introduced without affecting the smooth progress of the polycondensation reaction and the stability of the intermediates. On the other hand, it also avoids the destruction of the regularity of the polyamide polyamine molecules and its subsequent reactivity with epichlorohydrin due to excessive introduction, thereby affecting its water resistance enhancement effect. In addition, the cationic properties of PAE resin itself can also help suppress the tendency of various components in the colloid to agglomerate and settle due to van der Waals forces through electrostatic repulsion, thus maintaining the storage stability of the adhesive solution.

[0012] In any of the above technical solutions, the dicarboxylic acid is adipic acid and pyridyl dicarboxylic acid in a molar ratio of 3 to 4:1, and 0.05 to 0.15 parts of water-soluble metal salt are added to the main adhesive.

[0013] In any of the above technical solutions, the water-soluble metal salt is a trivalent iron salt.

[0014] In any of the above technical solutions, the trivalent iron salt is any one or more of FeCl3, Fe(NO3)3, and Fe2(SO4)3.

[0015] In any of the above technical solutions, the pyridyl dicarboxylic acid is selected from any one or more of 2,3-pyridinedicarboxylic acid, 2,4-pyridinedicarboxylic acid, 2,5-pyridinedicarboxylic acid, 2,6-pyridinedicarboxylic acid, 3,4-pyridinedicarboxylic acid, and 3,5-pyridinedicarboxylic acid.

[0016] As is well known, starch adhesive has poor initial tack and is prone to slippage during hot pressing, causing the corrugated peaks to easily misalign and separate from the face / liner paper, resulting in "corrugation running" and "corrugation collapse," and increasing the scrap rate. This application introduces pyridine groups into the molecular chain of modified PAE resin and adds water-soluble metal salts to the main adhesive. The pyridine group, as an excellent coordinating group, interacts with Fe... 3+ Metal ions possess strong coordination capabilities. During the hot pressing of corrugated cardboard, the high temperature and pressure environment greatly promotes the coordination process. Pyridine groups and metal ions can undergo rapid and efficient coordination, quickly forming a three-dimensional coordination network of "PAE-metal ion-PAE" and "PAE-metal ion-starch" with metal ions as crosslinking nodes. This network can significantly and rapidly improve the cohesive strength and viscoelasticity of the colloid, providing immediate holding force for the bonding of the corrugated core paper and the facing paper, effectively resisting shear slip under pressure, thereby significantly suppressing "corrugation runaway" and "corrugation collapse" phenomena and reducing the scrap rate.

[0017] Moreover, this three-dimensional network structure constructed through coordination bonds also enhances the final dry bond strength and water resistance. Because the strength of coordination bonds is much higher than that of hydrogen bonds and they are not easily destroyed by water molecules, a synergistic improvement in initial tack and final bond strength is achieved.

[0018] In any of the above technical solutions, 0.3 to 0.7 parts of nano starch are added to the carrier adhesive.

[0019] The aforementioned nano starch is a starch-based nanoparticle material formed by processing natural starch through physical, chemical, or biological methods, with a particle size in the range of 1–100 nm, and retaining the starch polysaccharide backbone.

[0020] This application incorporates an appropriate amount of nano-starch into the carrier adhesive. Due to its extremely large specific surface area, nano-starch exposes a very high number of hydroxyl groups. These high-density hydroxyl groups can form more extensive and stronger hydrogen bonds and van der Waals forces with the paper fiber surface, thereby rapidly generating excellent initial adhesion. Simultaneously, its nanoscale particle characteristics allow it to more easily penetrate the microporous structure of the paper fibers, producing a stronger mechanical interlocking effect. The combined effect of these two factors effectively improves the initial tack of the starch adhesive, enabling it to fix the relative position of the corrugated peaks and the face paper instantly under pressure, further reducing the risk of "corrugation slippage" and "corrugation collapse."

[0021] In any of the above technical solutions, the method for preparing the modified PAE resin is as follows: Polyethylene polyamine is mixed with a dicarboxylic acid and subjected to polycondensation reaction at 130–150°C under nitrogen protection. After 2–4 hours, the reaction temperature is lowered to 80–90°C, and amino acrylate monomer is added dropwise. After the addition is complete, the reaction is kept at the temperature for 1–2 hours. After the reaction is completed, alkenyl polyamide polyamine is obtained. The alkenyl polyamide polyamine was diluted in a solvent, then a platinum catalyst was added, and the mixture was stirred under nitrogen protection. Hydrogen-containing silane was added, and the temperature was controlled at 70-85℃. The reaction was carried out for 3-5 hours. After the reaction was completed, the organosilicon-modified polyamide polyamine was obtained. The organosilicon-modified polyamide polyamine was diluted with water and placed in an ice-water bath. Epichlorohydrin was added dropwise while stirring. After the addition was complete, the reaction temperature was raised to 60-70°C and the reaction was maintained at this temperature for 2-3 hours. The pH was then adjusted to 4-5 to obtain the modified PAE resin.

[0022] In any of the above technical solutions, the mass of the platinum catalyst is 10 to 30 ppm of the total mass of the alkenyl polyamide polyamine and the hydrogen-containing silane.

[0023] Secondly, this application provides a nano-modified starch adhesive for corrugated cardboard boxes, comprising: According to the raw material ratio of the nano-modified starch adhesive described in any of the first aspects, the carrier adhesive is mixed with starch and water, stirred to form an emulsion, sodium hydroxide solution is added dropwise, and stirred for 15-25 minutes to obtain gelatinized starch. A water-resistant reinforcing agent is added and stirred evenly to obtain the carrier adhesive. Mix starch and water with the base adhesive, stir evenly, add oxidant, and keep the temperature at 30-50℃ and stir continuously for 1-2 hours to obtain the base adhesive. Add the carrier adhesive to the base adhesive while stirring, and continue stirring for 20-30 minutes to gelatinize the base adhesive and obtain the finished adhesive.

[0024] In any of the above technical solutions, the oxidant is hydrogen peroxide.

[0025] The main adhesive can be supplemented with fungicides, defoamers, antibacterial agents, fillers and other additives as needed for actual use.

[0026] In summary, this application has the following beneficial effects: The nano-modified starch adhesive for corrugated boxes provided in this application utilizes organosilicon-modified PAE resin as a water-resistant reinforcing agent, introduces pyridine coordinating groups into the PAE molecule, and adds water-soluble metal salts and nano-starch to the system, constructing a synergistic reinforcing system. This system not only significantly improves the final water resistance and durability of the adhesive through covalent cross-linking and the introduction of hydrophobic groups, but also effectively solves the problems of "corrugation running" and "corrugation collapsing" that easily occur due to insufficient initial tack in high-speed production by utilizing the characteristics of the coordination network and nano-starch. At the same time, it also takes into account the storage stability of the adhesive solution, resulting in a high-performance nano-modified starch adhesive for corrugated boxes with excellent comprehensive performance and suitable for industrial production. Detailed Implementation

[0027] Preparation Example Preparation Example 1: A modified PAE resin was prepared by the following steps: Nitrogen gas was introduced into a four-necked flask equipped with a stirrer, thermometer, water separator, and nitrogen inlet tube for protection. 5.0 mol (515.0 g) of diethylenetriamine was added. Stirring was started, and 4.68 mol (684.5 g) of adipic acid, 1.56 mol (260.7 g) of 2,6-pyridinedicarboxylic acid, and 46 g of p-toluenesulfonic acid (catalyst) were added sequentially. The temperature was gradually raised to 140 ± 2 °C, and the polycondensation reaction was carried out at this temperature for 3 h, during which water was separated. The system was then cooled to 85 °C, and 1.25 mol of 2-aminoethyl methacrylate hydrochloride was slowly added dropwise. After the addition was complete, an aqueous solution of sodium hydroxide (1.25 mol NaOH dissolved in 1 L of water) was slowly added dropwise with stirring for neutralization. After neutralization, the reaction was maintained at 85 °C for another 1.5 h. After the reaction was complete, an alkenyl polyamide polyamine was obtained.

[0028] All the above-mentioned alkenyl polyamide polyamines were transferred to a reaction vessel and diluted with 500g of isopropanol. A solution of chloroplatinic acid in isopropanol (platinum content 20 ppm of the total reactant mass) was added, and the mixture was stirred thoroughly under nitrogen protection. Then, 1.5 mol (198.5 g) of trimethoxysilane was slowly added dropwise. The reaction temperature was controlled at 80±2℃, and the reaction was stopped after 4 hours. The solvent isopropanol and low-boiling substances were removed by vacuum distillation to obtain the organosilicon-modified polyamide polyamine.

[0029] The above-mentioned organosilicon-modified polyamide polyamine was diluted with an appropriate amount of deionized water to a solid content of 40%. The solution was transferred to a reaction flask equipped with an ice-water bath and a dropping funnel, and the stirring was turned on to lower the temperature to below 5°C. 4.25 mol (393.2 g) of epichlorohydrin was slowly added dropwise. The dropping rate was controlled to maintain the reaction temperature below 50°C. After the addition was complete, the temperature was slowly raised to 65°C and maintained at this temperature for 2.5 h. After the reaction was completed, the mixture was cooled to room temperature, deionized water was added to adjust the solid content to 25%, and the pH was adjusted to 4.5 with dilute hydrochloric acid to obtain the modified PAE resin (calculated based on solid content when using).

[0030] Preparation Example 2: A modified PAE resin was prepared by the following steps: Nitrogen gas was introduced into a four-necked flask equipped with a stirrer, thermometer, water separator, and nitrogen inlet tube for protection. 5.0 mol (515.0 g) of diethylenetriamine was added. Stirring was started, and 5.0 mol (730.5 g) of adipic acid, 1.25 mol (208.5 g) of 3,5-pyridinedicarboxylic acid, and 42 g of p-toluenesulfonic acid (catalyst) were added sequentially. The temperature was gradually raised to 135 ± 2 °C, and the polycondensation reaction was carried out at this temperature for 3.5 h, during which water was separated. The system was then cooled to 80 °C, and 1.0 mol of 2-aminoethyl methacrylate hydrochloride was slowly added dropwise. After the addition was complete, an aqueous solution of sodium hydroxide (1.0 mol NaOH dissolved in 1 L of water) was slowly added dropwise with stirring for neutralization. After neutralization, the reaction was maintained at 80 °C for another 2 h. After the reaction was complete, an alkenyl polyamide polyamine was obtained.

[0031] All the above-mentioned alkenyl polyamide polyamines were transferred to a reaction vessel and diluted with 500 g of isopropanol. A solution of chloroplatinic acid in isopropanol (platinum content 10 ppm of the total reactant mass) was added, and the mixture was stirred thoroughly under nitrogen protection. Then, 1.1 mol (136.5 g) of methyldimethoxysilane was slowly added dropwise. The reaction temperature was controlled at 75 ± 2 °C, and the reaction was stopped after 5 h. The solvent isopropanol and low-boiling substances were removed by vacuum distillation to obtain the organosilicon-modified polyamide polyamine.

[0032] The above-mentioned organosilicon-modified polyamide polyamine was diluted with an appropriate amount of deionized water to a solid content of 40%. The solution was transferred to a reaction flask equipped with an ice-water bath and a dropping funnel, and the stirring was turned on to lower the temperature to below 5°C. 3.25 mol (300.7 g) of epichlorohydrin was slowly added dropwise. The dropping rate was controlled to maintain the reaction temperature below 50°C. After the addition was complete, the temperature was slowly raised to 65°C and maintained at this temperature for 2.5 h. After the reaction was completed, the mixture was cooled to room temperature, deionized water was added to adjust the solid content to 25%, and the pH was adjusted to 4.5 with dilute hydrochloric acid to obtain the modified PAE resin (calculated based on solid content when using).

[0033] Preparation Example 3: A modified PAE resin was prepared by the following steps: Nitrogen gas was introduced into a four-necked flask equipped with a stirrer, thermometer, water separator, and nitrogen inlet tube for protection. 5.0 mol (515.0 g) of diethylenetriamine was added. Stirring was started, and 4.5 mol (657.5 g) of adipic acid, 1.5 mol (250.5 g) of 2,5-pyridinedicarboxylic acid, and 55 g of p-toluenesulfonic acid (catalyst) were added sequentially. The temperature was gradually raised to 143 ± 2 °C, and the polycondensation reaction was carried out at this temperature for 3 hours, during which water was separated. The system was then cooled to 90 °C, and 1.5 mol of 2-aminoethyl methacrylate hydrochloride was slowly added dropwise. After the addition was complete, an aqueous solution of sodium hydroxide (1.5 mol NaOH dissolved in 1 L of water) was slowly added dropwise with stirring for neutralization. After neutralization, the reaction was maintained at 90 °C for another 1.5 hours. After the reaction was complete, an alkenyl polyamide polyamine was obtained.

[0034] All the above-mentioned alkenyl polyamide polyamines were transferred to a reaction vessel and diluted with 500 g of isopropanol. A solution of chloroplatinic acid in isopropanol (platinum content 30 ppm of the total reactant mass) was added, and the mixture was stirred thoroughly under nitrogen protection. Then, 1.85 mol (274.0 g) of triethoxysilane was slowly added dropwise. The reaction temperature was controlled at 83 ± 2 °C, and the reaction was stopped after 4.5 h. The solvent isopropanol and low-boiling substances were removed by vacuum distillation to obtain the organosilicon-modified polyamide polyamine.

[0035] The above-mentioned organosilicon-modified polyamide polyamine was diluted with an appropriate amount of deionized water to a solid content of 40%. The solution was transferred to a reaction flask equipped with an ice-water bath and a dropping funnel, and the stirring was started to lower the temperature to below 5°C. 4.5 mol (416.3 g) of epichlorohydrin was slowly added dropwise. The dropping rate was controlled to maintain the reaction temperature below 50°C. After the addition was complete, the temperature was slowly raised to 70°C and maintained at this temperature for 3 hours. After the reaction was completed, the mixture was cooled to room temperature, deionized water was added to adjust the solid content to 25%, and the pH was adjusted to 5 with dilute hydrochloric acid to obtain the modified PAE resin (calculated based on solid content when using).

[0036] Preparation Example 4, a modified PAE resin, differs from Preparation Example 1 in that, in the preparation step of the alkenyl polyamide polyamine, the amount of 2-aminoethyl methacrylate hydrochloride is 2.0 mol (i.e., added in excess), and the corresponding sodium hydroxide aqueous solution added contains 2.0 mol NaOH.

[0037] Preparation Example 5, a modified PAE resin, differs from Preparation Example 1 in that, in the preparation step of the alkenyl polyamide polyamine, the amount of 2-aminoethyl methacrylate hydrochloride is 0.5 mol (i.e., too little is added), and the corresponding sodium hydroxide aqueous solution added contains 0.5 mol NaOH.

[0038] Preparation Example 6, a modified PAE resin, differs from Preparation Example 1 in that, in the preparation step of the alkenyl polyamide polyamine, 2,6-pyridine dicarboxylic acid is replaced with an equimolar amount of adipic acid.

[0039] Preparation Example 7, a modified PAE resin, differs from Preparation Example 1 in that, in the preparation step of the alkenyl polyamide polyamine, an equimolar amount of single-ended hydrogen-containing silicone oil (RH-H222-10) is used instead of the hydrogen-containing silane.

[0040] Preparation Example 8: A PAE resin was prepared by the following steps: Nitrogen gas was introduced into a four-necked flask equipped with a stirrer, thermometer, water separator, and nitrogen inlet tube for protection. 5.0 mol (515.0 g) of diethylenetriamine was added. Stirring was started, and 4.68 mol (684.5 g) of adipic acid and 1.56 mol (260.7 g) of 2,6-pyridinedicarboxylic acid were added sequentially. The temperature was gradually raised to 140 ± 2 °C, and the polycondensation reaction was carried out at this temperature for 3 hours. The water produced in the reaction was then separated to obtain a polyamide intermediate.

[0041] The above polyamide intermediate was diluted with an appropriate amount of deionized water to a solid content of 40%. The solution was transferred to a reaction flask equipped with an ice-water bath and a dropping funnel. Stirring was started, and the temperature was lowered to below 5°C. 4.25 mol (393.2 g) of epichlorohydrin was slowly added dropwise. The dropping rate was controlled, and the reaction temperature was maintained below 50°C. After the addition was complete, the temperature was slowly raised to 65°C, and the reaction was maintained at this temperature for 2.5 h. After the reaction was completed, the mixture was cooled to room temperature, deionized water was added to adjust the solid content to 25%, and the pH was adjusted to 4.5 with dilute hydrochloric acid to obtain the modified PAE resin (calculated based on solid content when using).

[0042] Example Example 1: A nano-modified starch adhesive for corrugated cardboard boxes was prepared according to the following method: In a reactor equipped with a stirrer, 5500 g of water and 50 g of corn-derived nano-starch (D50 particle size 30-40 nm) were added. Stirring was started at 200 rpm, and 1000 g of corn starch was slowly added, continuing stirring for 15 min to form a homogeneous emulsion. While stirring, an aqueous solution containing 100 g of dissolved sodium hydroxide (pre-dissolved in 200 g of water) was slowly added dropwise. After the addition was complete, the stirring speed was increased to 300 rpm, and stirring was continued at room temperature for 20 min. The emulsion was observed to transform into a translucent viscous gel, indicating that gelatinization was complete. Subsequently, 115 g of the modified PAE resin obtained in Preparation Example 1 (based on solid content) was added, and stirring was continued for 10 min until homogeneous, yielding the carrier gel.

[0043] In another reactor equipped with a stirrer and heater, add 3500g of water and 1000g of corn starch. Start stirring at 150 rpm for 30 minutes to form a homogeneous suspension. Add 10g of ferric chloride hexahydrate (FeCl3·6H2O) and stir until completely dissolved. Heat the system to 40±2℃, then add 20g of 27.5% hydrogen peroxide. Maintain the temperature at 40±2℃ and continue stirring for 1.5 hours. After the reaction is complete, cool to room temperature to obtain the main gel.

[0044] While stirring (200 rpm), the prepared carrier gel was slowly added to the main gel at a mass ratio of 1:4. After the addition was complete, stirring was continued for 25 minutes to fully gelatinize the main starch, resulting in a uniform finished nano-modified starch gel.

[0045] Example 2: A nano-modified starch adhesive for corrugated cardboard boxes was prepared according to the following method: In a reactor equipped with a stirrer, 5000g of water and 35g of corn-derived nano-starch (D50 particle size 65-75nm) were added. Stirring was started at 150 rpm, and 1000g of corn starch was slowly added, continuing stirring for 20 minutes to form a homogeneous emulsion. While stirring, an aqueous solution containing 80g of dissolved sodium hydroxide (pre-dissolved in 150g of water) was slowly added dropwise. After the addition was complete, the stirring speed was increased to 300 rpm, and stirring was continued at room temperature for 15 minutes. The emulsion was observed to transform into a translucent viscous gel, indicating that gelatinization was complete. Subsequently, 85g of the modified PAE resin obtained in Preparation Example 2 (based on solid content) was added, and stirring was continued for 15 minutes until homogeneous, yielding the carrier gel.

[0046] In another reactor equipped with a stirrer and heater, add 3000g of water and 1000g of corn starch. Start stirring at 150 rpm for 30 minutes to form a homogeneous suspension. Add 5g of aluminum trichloride hexahydrate (AlCl3·6H2O) and stir until completely dissolved. Heat the system to 35±2℃, then add 10g of 27.5% hydrogen peroxide. Maintain the temperature at 35±2℃ and continue stirring for 2 hours. After the reaction is complete, cool to room temperature to obtain the main gel.

[0047] While stirring (200 rpm), the prepared carrier gel was slowly added to the main gel at a mass ratio of 1:5. After the addition was complete, stirring was continued for 20 minutes to fully gelatinize the main starch, resulting in a uniform finished nano-modified starch gel.

[0048] Example 3: A nano-modified starch adhesive for corrugated cardboard boxes was prepared according to the following method: In a reactor equipped with a stirrer, 6000g of water and 70g of corn-derived nano-starch (D50 particle size 30-40nm) were added. Stirring was started at 200 rpm, and 1000g of corn starch was slowly added, continuing stirring for 15 minutes to form a homogeneous emulsion. While stirring, an aqueous solution containing 120g of dissolved sodium hydroxide (pre-dissolved in 250g of water) was slowly added dropwise. After the addition was complete, the stirring speed was increased to 300 rpm, and stirring continued at room temperature for 30 minutes. The emulsion was observed to transform into a translucent viscous gel, indicating that gelatinization was complete. Subsequently, 50g of the modified PAE resin obtained in Preparation Example 3 (based on solid content) was added, and stirring continued for 10 minutes until homogeneous, yielding the carrier gel.

[0049] In another reactor equipped with a stirrer and heater, add 4000g of water and 1000g of corn starch. Start stirring at 200 rpm for 35 minutes to form a homogeneous suspension. Add 15g of ferric chloride hexahydrate (FeCl3·6H2O) and stir until completely dissolved. Heat the system to 45±2℃, then add 30g of 27.5% hydrogen peroxide. Maintain the temperature at 45±2℃ and continue stirring for 1.5 hours. After the reaction is complete, cool to room temperature to obtain the main gel.

[0050] While stirring (200 rpm), the prepared carrier gel was slowly added to the main gel at a mass ratio of 1:4. After the addition was complete, stirring was continued for 30 minutes to fully gelatinize the main starch, resulting in a homogeneous finished nano-modified starch gel.

[0051] Example 4, a nano-modified starch adhesive for corrugated cardboard boxes, differs from Example 1 in that the modified PAE resin prepared in Example 4 is replaced with an equal mass of the modified PAE resin prepared in Example 1 in the carrier adhesive.

[0052] Example 5, a nano-modified starch adhesive for corrugated cardboard boxes, differs from Example 1 in that the modified PAE resin prepared in Example 5 is replaced with an equal mass of the modified PAE resin prepared in Example 1 in the carrier adhesive.

[0053] Example 6, a nano-modified starch adhesive for corrugated cardboard boxes, differs from Example 1 in that the modified PAE resin prepared in Example 6 is replaced with an equal mass of the modified PAE resin prepared in Example 1 in the carrier adhesive.

[0054] Example 7: A nano-modified starch adhesive for corrugated cardboard boxes, which differs from Example 1 in that ferric chloride hexahydrate (FeCl3·6H2O) is not added to the main adhesive.

[0055] Example 8 is a nano-modified starch adhesive for corrugated cardboard boxes. The difference from Example 6 is that ferric chloride hexahydrate (FeCl3·6H2O) was not added to the main adhesive.

[0056] Example 9, a nano-modified starch adhesive for corrugated cardboard boxes, differs from Example 1 in that, in the carrier adhesive, corn-derived nano-starch is replaced with an equal mass of corn starch.

[0057] Comparative Example Comparative Example 1 is a nano-modified starch adhesive for corrugated cardboard boxes. The difference between this and Example 1 is that the modified PAE resin prepared in Preparation Example 7 is replaced with the modified PAE resin prepared in Preparation Example 1 in the carrier adhesive in an equal mass.

[0058] Comparative Example 2, a nano-modified starch adhesive for corrugated cardboard boxes, differs from Example 1 in that, in the carrier adhesive, the PAE resin prepared in Preparation Example 8 is replaced with the modified PAE resin prepared in Preparation Example 1 by an equal mass.

[0059] Performance testing Experiment 1: Water Resistance Test Sample preparation: Material preparation: Corrugated core paper (compliant with GB / T 13023-2008 "Corrugated Core (Base) Paper" standard, basis weight 100g / m²) 2 Kraft linerboard (compliant with GB / T 13024-2016 "Cabinetboard" standard, basis weight 200g / m³) 2 The sample was cut into standard sample sizes (150 mm × 25 mm). The nano-modified starch adhesive is the nano-modified starch adhesive prepared in the examples and comparative examples of this application.

[0060] Coating and Lamination: The nano-modified starch adhesive was uniformly coated onto the crests of the corrugated core paper using a wire bar coater, with the coating amount controlled at 15±1 g / m². 2 Immediately cover the adhesive surface with kraft paperboard and press it once with a manual roller press at a pressure of 0.5 MPa to ensure initial bonding.

[0061] Hot pressing curing: The composite sample is placed in a flatbed hot press and hot-pressed at 160±2℃ for 2 minutes with a pressure of 0.6MPa to simulate the hot pressing conditions of a corrugated cardboard production line.

[0062] Conditioning: After hot pressing, the specimens were placed under standard atmospheric conditions (23±1℃, 50±2% relative humidity) for 24 hours to balance moisture and stress. Ten valid specimens were prepared for each test group.

[0063] Test steps: Five samples were randomly selected after initial condition treatment and tested according to GB / T 6548-2011 "Determination of Adhesive Strength of Corrugated Board". The samples were mounted on a fixture and subjected to a 180° peel test at a tensile speed of 100 mm / min. The maximum peel force (unit: N / m) was recorded, and the average value of the five samples was calculated as the initial adhesive strength (A0). At least five remaining samples were placed in a constant temperature and humidity chamber and continuously treated for 96 hours at a temperature of 23±1℃ and a relative humidity of 90±2% to simulate an extremely humid storage environment. After treatment, the samples were immediately removed from the chamber, and the adhesive strength test was completed within 5 minutes (test environment conditions remained 23±1℃, 50±2% RH), using the same method as the initial adhesive strength test. The adhesive strength after high humidity treatment (A1) was recorded. The strength retention rate was calculated using the following formula: Moisture resistance strength retention rate (%) = (A1 / A0) × 100%. The average value of the result was taken. A higher strength retention rate indicates better moisture resistance of the starch adhesive and greater resistance to strength degradation caused by humid environments.

[0064] Experiment 2: Production Scrap Rate Test Sample preparation: Simulated production line setup: A small laboratory corrugated cardboard forming machine was used, with the production line speed set at 10 m / min (simulating low-to-medium speed production conditions). The corrugated roll temperature was controlled at 160±2℃, and the pressure roll pressure was 0.6±0.1 MPa.

[0065] Adhesive coating: Add nano-modified starch adhesive to the adhesive tank, adjust the gap of the coating rollers to stabilize the coating amount at 15±1g / m³. 2 The adhesive must be stirred thoroughly before use, and the temperature should be maintained at 25±5℃.

[0066] Continuous production: using corrugated core paper (B-flute corrugated core paper conforming to GB / T 13023-2008, basis weight 100 g / m²). 2 ) and kraft linerboard (basis weight 200 g / m³) 2 Using [material name] as raw material, 100 meters of corrugated cardboard were continuously produced. After production stabilized, a 300mm × 300mm sample was taken every 1 meter, for a total of 200 samples.

[0067] Test steps: Perform visual and dimensional inspections on each sample. Measure the corrugated height (distance from the bottom of the core paper valley to the top of the peak) using a digital caliper. If the corrugated height drops by more than 10% of the initial height (relative to the standard B-flute corrugated height H0 = 2.7 mm), it is defined as "collapsed corrugation." Measure the misalignment distance between the corrugated peak and the bonding line of the face paper using a steel ruler. If the misalignment exceeds 5 mm, it is defined as "off-center corrugation." Record the number of samples with "off-center corrugation" or "collapsed corrugation" defects. Calculate the scrap rate (%) = (number of defective samples / total number of samples) × 100%.

[0068] Table 1. Test Results

[0069] Analysis of experimental results: Compared to Example 1, Example 4 (with excessive amino acrylate in PAE preparation) showed a slight decrease in the retention rate of wet strength and an increase in the scrap rate, indicating that excessive amino acrylate has a negative impact on water resistance and initial tack stability. This may be because the excessive introduction of mono-amino polymer raw materials disrupts the regularity and molecular weight of the polyamide polyamine molecules, affecting its reactivity with epichlorohydrin, mechanical properties, and the stability of the final crosslinked network, thereby reducing the water resistance and cohesive strength of the adhesive layer (leading to "roughing" and "collapse").

[0070] Example 5 (insufficient amino acrylate in PAE preparation) showed poor performance in terms of wet strength retention and production scrap rate, indicating that insufficient amino acrylate content also negatively impacts water resistance and initial tack stability. This may be because insufficient alkenyl group introduction leads to a low organosilicon grafting rate and insufficient hydrophobic groups, thereby weakening water resistance.

[0071] Examples 6 (PAE preparation without pyridine groups), 7 (PAE without metal salts), and 8 (PAE with pyridine groups but no metal salts) showed poor performance in terms of wet strength retention and production scrap rate, with similar experimental results. This indicates that pyridine groups and metal ions have a synergistic effect, which significantly positively impacts water resistance and initial tack. This may be because the absence of either pyridine groups or metal ions prevents the formation of a coordination network, leading to insufficient initial tack and a tendency for "roughing" and "collapse." Furthermore, the lack of a coordination network affects water resistance, resulting in decreased adhesive strength after wet treatment. In addition, Example 6 showed better scrap rate, indicating that even without pyridine groups, metal ions and starch can still form a certain coordination network.

[0072] Example 9 (without nano-starch added to the carrier adhesive) showed a certain increase in the production scrap rate, indicating that nano-starch makes a significant contribution to initial tack. This may be because the lack of the high specific surface area and permeability of nano-starch results in insufficient initial adhesion, leading to an increase in "clumping" during production.

[0073] Comparative Example 1 (using hydrogen-containing silicone oil instead of hydrogen-containing silane in PAE preparation) showed poor performance in initial adhesive strength and scrap rate, but better performance in wet strength retention. This indicates that hydrogen-containing silane can improve initial adhesive strength compared to hydrogen-containing silicone oil, but its hydrophobicity is not as good. This may be because hydrogen-containing silicone oil has longer siloxane segments and greater steric hindrance, providing a stronger hydrophobic barrier. However, it lacks silanol groups and cannot effectively react and bond with starch and paper fibers, thus not having a positive effect on adhesive strength. Furthermore, the grafting of silicone oil segments significantly weakens initial tack, substantially increasing "corrugation slippage" and "corrugation collapse."

[0074] Comparative Example 2 (PAE prepared without organosilicon modification) performed the worst in terms of moisture resistance retention, indicating that organosilicon modification is crucial for water resistance. This may be because the lack of organosilicon hydrophobic groups makes the adhesive layer prone to moisture absorption and prevents the formation of Si-OC covalent bonds, resulting in a significant deterioration in water resistance.

[0075] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A nano-modified starch adhesive for corrugated cardboard boxes, characterized in that, The mixture comprises a carrier adhesive and a base adhesive in a mass ratio of 1:4 to 5. By mass, the carrier adhesive comprises: 10 parts starch, 50 to 60 parts water, 0.8 to 1.2 parts sodium hydroxide, and 0.8 to 1.5 parts modified PAE resin; the base adhesive comprises: 10 parts starch, 30 to 40 parts water, and 0.1 to 0.3 parts oxidant; the modified PAE resin is prepared by: using a diacid, polyethylene polyamine, and amino acrylate monomer in a molar ratio of 1.2 to 1.4:1:0.2 to 0.3 as raw materials, and undergoing polycondensation to obtain an alkenyl polyamide polyamine; the alkenyl polyamide polyamine is then reacted sequentially with a hydrosilane and epichlorohydrin to obtain the modified PAE resin; the molar ratio of the alkenyl polyamide polyamine to epichlorohydrin is 1:0.6 to 0.9, and the molar ratio of the amino acrylate monomer to the hydrosilane is 1:1.1 to 1.

3.

2. The starch adhesive according to claim 1, characterized in that, The polyethylene polyamine is selected from any one or more of diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

3. The starch adhesive according to claim 1, characterized in that, The aminoacrylate monomer is 2-aminoethyl methacrylate.

4. The starch adhesive according to claim 1, characterized in that, The hydrogen-containing silane is selected from any one or more of trimethoxysilane, triethoxysilane, methyldimethoxysilane, methyldiethoxysilane, and ethyldimethoxysilane.

5. The starch adhesive according to claim 1, characterized in that, The dicarboxylic acid is adipic acid and pyridyl dicarboxylic acid in a molar ratio of 3 to 4:1, and 0.05 to 0.15 parts of water-soluble metal salt are added to the main adhesive.

6. The starch adhesive according to claim 5, characterized in that, The water-soluble metal salt is a ferric salt.

7. The starch adhesive according to claim 5, characterized in that, The pyridyl dicarboxylic acid is selected from any one or more of 2,3-pyridinedicarboxylic acid, 2,4-pyridinedicarboxylic acid, 2,5-pyridinedicarboxylic acid, 2,6-pyridinedicarboxylic acid, 3,4-pyridinedicarboxylic acid, and 3,5-pyridinedicarboxylic acid.

8. The starch adhesive according to claim 5, characterized in that, The carrier gel contains 0.3 to 0.7 parts of nano starch.

9. The starch adhesive according to claim 1, characterized in that, The modified PAE resin is prepared by: Polyethylene polyamine is mixed with a dicarboxylic acid and subjected to polycondensation reaction at 130–150°C under nitrogen protection. After 2–4 hours, the reaction temperature is lowered to 80–90°C, and amino acrylate monomer is added dropwise. After the addition is complete, the reaction is kept at the temperature for 1–2 hours. After the reaction is completed, alkenyl polyamide polyamine is obtained. The alkenyl polyamide polyamine was diluted in a solvent, then a platinum catalyst was added, and the mixture was stirred under nitrogen protection. Hydrogen-containing silane was added, and the temperature was controlled at 70-85℃. The reaction was carried out for 3-5 hours. After the reaction was completed, the organosilicon-modified polyamide polyamine was obtained. The organosilicon-modified polyamide polyamine was diluted with water and placed in an ice-water bath. Epichlorohydrin was added dropwise while stirring. After the addition was complete, the reaction temperature was raised to 60-70°C and the reaction was maintained at this temperature for 2-3 hours. The pH was then adjusted to 4-5 to obtain the modified PAE resin.

10. A nano-modified starch adhesive for corrugated cardboard boxes, characterized in that, The raw material ratio of the nano-modified starch adhesive for corrugated cardboard boxes according to any one of claims 1 to 9 is as follows: The carrier gel is mixed with starch and water, stirred to form an emulsion, sodium hydroxide solution is added dropwise, and stirred for 15-25 minutes to obtain gelatinized starch. A water-resistant reinforcing agent is added and stirred evenly to obtain the carrier gel. Mix starch and water with the base adhesive, stir evenly, add oxidant, and keep the temperature at 30-50℃ and stir continuously for 1-2 hours to obtain the base adhesive. Add the carrier adhesive to the base adhesive while stirring, and continue stirring for 20-30 minutes to gelatinize the base adhesive and obtain the finished adhesive.

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