Corrugated board based on a water repellent coating and a method for its production

Abstract

The present application relates to the technical field of corrugated paperboard, in particular to a corrugated paperboard based on waterproof coating and a preparation method thereof.Step 1: an epoxy-based polyvinyl alcohol solution is sprayed on the surface of a base corrugated paperboard; under ultraviolet light, drying is carried out at 35-50 DEG C for 24-48 hours; a base corrugated paperboard A is obtained; step 2: a modified polyvinyl alcohol solution and a modified chitosan solution are mixed uniformly at a mass ratio of 85-90:10-15, and a waterproof coating is obtained; step 3: the waterproof coating is line bar roller coated on the surface of the base corrugated paperboard A, ultraviolet light is irradiated for 2-3 hours, and drying is carried out at 35-50 DEG C for 24-48 hours, and a waterproof coating is obtained; the waterproof coating is used as the corrugated paperboard.

Description

Technical Field

[0001] This invention relates to the field of corrugated cardboard technology, specifically to a waterproof-coated corrugated cardboard and its preparation method. Background Technology

[0002] Corrugated cardboard is widely used in the packaging industry due to its advantages such as being lightweight, low-cost, and easy to process. However, corrugated cardboard has limitations in terms of water resistance; its main components include cellulose and hemicellulose, which are easily affected by moisture absorption, thus affecting its structural strength and durability, and impacting its performance in actual production, transportation, and storage.

[0003] In existing technologies, waterproof coatings are typically applied to improve overall waterproof performance. These coatings are usually made of polymeric materials such as polyurethane, polyacrylate, and fluoropolymers, which reduces their sustainability. On the other hand, chitosan is a naturally abundant biopolymer with good water and oil resistance; however, it contains water-absorbing groups, thus limiting its waterproof performance. Furthermore, chitosan has swelling properties, which can lead to unevenness on the corrugated paper surface and damage the inter-fiber bonding, resulting in poor waterproof coating strength and affecting the mechanical strength of the corrugated cardboard.

[0004] In conclusion, solving the above problems and developing a corrugated cardboard based on a waterproof coating is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a corrugated cardboard based on a waterproof coating and a method for preparing the same, so as to solve the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A method for preparing corrugated cardboard based on a waterproof coating includes the following steps:

[0008] Step 1: Spray an epoxy-based polyvinyl alcohol solution onto the surface of the base corrugated cardboard; dry it under ultraviolet light at 35~50℃ for 24~48 hours to obtain base corrugated cardboard A;

[0009] Step 2: Mix the modified polyvinyl alcohol solution and the modified chitosan solution at a mass ratio of 85~90:10~15 evenly to obtain a waterproof coating;

[0010] Step 3: Apply the waterproof coating by roller to the surface of the base corrugated cardboard A, expose it to ultraviolet light for 2-3 hours, and dry it at 35-50℃ for 24-48 hours to obtain the waterproof coating; use this as the corrugated cardboard.

[0011] Ideally, the concentration of the epoxy-based polyvinyl alcohol solution is 1~1.5wt%; the spraying amount is 0.5~1g / m².2 .

[0012] The solvent for the epoxy-based polyvinyl alcohol solution is a 2-5 wt% aqueous solution of acetone.

[0013] A more optimized method for preparing the epoxy-based polyvinyl alcohol is as follows: polyvinyl alcohol is added to deionized water to obtain an aqueous solution of polyvinyl alcohol; epichlorohydrin is added dropwise; an alkaline solution is added to adjust the pH to 11-12, and the mixture is stirred at 60-65°C for 3-4 hours; the mixture is cooled, and an acid solution is added to adjust the pH to 3-4 to terminate the process; the mixture is then purified to obtain epoxy-based polyvinyl alcohol; the mass ratio of polyvinyl alcohol to epichlorohydrin is 100:9-11.

[0014] A more optimized method for preparing the modified polyvinyl alcohol solution is as follows:

[0015] Step S1-1: Polyvinyl alcohol, acrylamide, and isopropenylboronic acid are added sequentially to deionized water and stirred at 90-95°C for 30-40 minutes; under a nitrogen atmosphere, ammonium persulfate initiator is added dropwise and the reaction is carried out for 1-3 hours; the temperature is lowered and an alkaline solution is added to adjust the pH to 6-7; the product is purified to obtain a polyvinyl alcohol copolymer.

[0016] Step S1-2: Polyvinyl alcohol copolymer and mercaptoacetic acid are added sequentially to a 4-6 wt% sulfuric acid aqueous solution, heated to 70-90℃ and stirred for 2-4 hours; then cooled and purified to obtain modified polyvinyl alcohol;

[0017] Step S1-3: Add the polyvinyl alcohol copolymer and the modified polyvinyl alcohol sequentially to a 5-10 wt% acetone aqueous solution to obtain a modified polyvinyl alcohol solution.

[0018] More preferably, the modified polyvinyl alcohol solution has a solid content of 0.4~0.6 wt%, comprising the following components by weight: 0.15~0.2 parts modified polyvinyl alcohol and 0.25~0.4 parts polyvinyl alcohol copolymer;

[0019] In the polyvinyl alcohol copolymer, the mass ratio of polyvinyl alcohol, acrylamide, and isopropenylboronic acid is 4:1:0.5; in the modified polyvinyl alcohol, the mass ratio of polyvinyl alcohol copolymer and mercaptoacetic acid is 10:8~12.

[0020] Ideally, the average molecular weight of the polyvinyl alcohol is 5000~9000 g / mol.

[0021] A more optimized method for preparing the modified chitosan solution is as follows:

[0022] Step S2-1: Under light-protected conditions, diisocyanate and tin catalyst were added sequentially to ethyl acetate. Under a nitrogen atmosphere, 2-hydroxy-2-methyl-1-phenyl-1-propanone was added dropwise. The mixture was reacted at 50-60°C for 3-4 hours and purified to obtain the isocyanate initiator.

[0023] Step S2-2: Under light-protected conditions, chitosan is added to an aqueous acetic acid solution, along with isocyanate initiator, ethyl isocyanate acrylate, and tin catalyst. The mixture is heated to 80-100°C and reacted for 6-8 hours. After washing and drying, modified chitosan is obtained.

[0024] Step S2-2: Under light-protected conditions, monoamine-terminated PDMS is added dropwise to an acetone aqueous solution containing triisocyanate and stirred at room temperature for 2-3 hours to obtain an isocyanate-based polydimethylsilane solution with a solid content of 2-2.1 wt%; chitosan and modified chitosan are added and dispersed evenly to obtain a modified chitosan solution.

[0025] More preferably, the modified chitosan solution has a solid content of 3-3.2 wt%, comprising the following components by weight: 0.4-0.6 parts modified chitosan, 0.5-0.6 parts chitosan, and 2-2.1 parts isocyanate-based polydimethylsilane;

[0026] In the isocyanate-based initiator, the molar ratio of diisocyanate to 2-hydroxy-2-methyl-1-phenyl-1-propanone is 1.2~1.5:1; in the modified chitosan, the mass ratio of chitosan, isocyanate-based initiator, and ethyl isocyanate acrylate is 10:0.1:2~3; and the weight ratio of monoamine-terminated PDMS to triisocyanate is 2:1.

[0027] Ideally, the amount of the waterproof coating is 3-5 g / m³. 2 .

[0028] Compared with existing technologies, the beneficial effects of this application are as follows: The pre-coating and waterproof coating effectively improve the strength, water resistance, and oil resistance of corrugated cardboard. The specific process is as follows:

[0029] In this solution, an epoxy-modified polyvinyl alcohol solution is used as a pre-coating agent and a bonding layer between the paperboard reinforcement and subsequent coatings. This effectively suppresses the impact of chitosan swelling on mechanical properties and improves the uniformity of the waterproof coating, thereby effectively enhancing the strength, water resistance, and oil resistance of the corrugated paperboard. Polyvinyl alcohol can penetrate the paper's interior to strengthen its internal structure; however, it contains water-absorbing groups, so its penetration can cause swelling and damage the fiber network. Therefore, two measures are taken: first, the polyvinyl alcohol is modified to reduce the abundance of hydrophilic groups; second, ultraviolet light is used during the drying process to increase hydrogen bonding and reduce swelling. On the other hand, the epoxy-modified polyvinyl alcohol can crosslink with the modified polyvinyl alcohol and modified chitosan in the subsequent coatings, increasing the crosslinking of the waterproof coating, suppressing chitosan swelling, and reducing the unevenness of the waterproof coating. This enhances the overall performance of the corrugated paperboard.

[0030] In this scheme, a waterproof coating is formed by mixing a modified polyvinyl alcohol solution and a modified chitosan solution in a specific ratio, while also possessing oil-repellent properties. To reduce the permeability of polyvinyl alcohol in the modified coating to paper, it undergoes copolymerization to increase its molecular weight while introducing amino and boric acid groups, and further modification to introduce thiol groups. This improves its hydrophobicity and allows it to react with the epoxy groups in the pre-coating to produce crosslinks, thereby increasing strength. Since polyvinyl alcohol has low hydrophobicity, modified chitosan is introduced to enhance its hydrophobic properties. Compared to directly introducing chitosan, it is modified by introducing isocyanate initiators to inhibit the migration of small molecule initiators and promote uniform crosslinking; ethyl isocyanate acrylate is introduced to increase crosslinking. Simultaneously, isocyanate-based polydimethylsilane is introduced into the modified chitosan solution to further improve hydrophobic properties. Furthermore, the amounts and solid contents of both are limited to achieve optimized waterproof and oil-repellent properties.

[0031] In this solution, the waterproof coating is cross-linked under ultraviolet light before drying. The basic network is first cross-linked under ultraviolet light and then dried. Compared with directly introducing a thermal initiator for drying, this effectively improves the folding strength of corrugated cardboard. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] It should be noted that the following quantities are by weight; there are no special restrictions on the purchasers of any of the raw materials involved in this invention, and they include, exemplarily, the following: in the following examples, the average molecular weight of the polyvinyl alcohol is 5000 g / mol; the average molecular weight of the chitosan is 50,000 g / mol; the average molecular weight of the monoamine-terminated PDMS is 2000 g / mol; the tin catalyst is dibutyltin dilaurate; the diisocyanate is isophorone diisocyanate; the triisocyanate is triphenylmethane triisocyanate; the CAS number of isopropenylboronic acid is 14559-87-6; the CAS number of ethyl isocyanate acrylate is 13641-96-8; the concentration of the acetic acid aqueous solution is 2 wt%; and the solvent of the epoxy-based polyvinyl alcohol solution is a 2 wt% acetone aqueous solution.

[0034] Example 1: A method for preparing corrugated cardboard based on a waterproof coating, comprising the following steps:

[0035] Step 1: (1) Add polyvinyl alcohol to deionized water to obtain a 10wt% polyvinyl alcohol aqueous solution; add epichlorohydrin dropwise; add 10wt% sodium hydroxide solution to adjust pH=11.5, stir at 60℃ for 4 hours; cool, add acid solution to adjust pH=3.5 to terminate, purify, and obtain epoxy polyvinyl alcohol; the mass ratio of polyvinyl alcohol to epichlorohydrin is 100:10;

[0036] (2) A 1 wt% epoxy-based polyvinyl alcohol solution was sprayed onto the surface of the base corrugated cardboard at a coating amount of 1 g / m². 2 At 50mW / cm 2 Under ultraviolet light, it is dried at 50°C for 24 hours to obtain basic corrugated cardboard A;

[0037] Step 2: (1) Preparation of modified polyvinyl alcohol solution: Step S1-1: Polyvinyl alcohol, acrylamide, and isopropenylboronic acid are added to deionized water in sequence and stirred at 90°C for 30 minutes; under nitrogen atmosphere, ammonium persulfate initiator is added dropwise and reacted for 2 hours; the temperature is lowered and an alkaline solution is added to adjust the pH to 6.8; the polyvinyl alcohol copolymer is obtained; wherein, the mass ratio of polyvinyl alcohol, acrylamide, and isopropenylboronic acid is 4:1:0.5;

[0038] Step S1-2: Polyvinyl alcohol copolymer and mercaptoacetic acid are added sequentially to a 5wt% sulfuric acid aqueous solution, heated to 80℃ and stirred for 3 hours; cooled and purified to obtain modified polyvinyl alcohol; wherein the mass ratio of polyvinyl alcohol copolymer to mercaptoacetic acid is 10:11;

[0039] Steps S1-3: Add 0.3 parts of polyvinyl alcohol copolymer and 0.2 parts of modified polyvinyl alcohol sequentially to a 5 wt% acetone aqueous solution to obtain a modified polyvinyl alcohol solution with a solid content of 0.5 wt%.

[0040] (2) Preparation of modified chitosan solution: Step S2-1: Under light-protected conditions, diisocyanate and tin catalyst were added to ethyl acetate in sequence. Under a nitrogen atmosphere, 2-hydroxy-2-methyl-1-phenyl-1-propanone was added dropwise. The reaction was carried out at 50°C for 3 hours. After purification, isocyanate initiator was obtained. The molar ratio of diisocyanate to 2-hydroxy-2-methyl-1-phenyl-1-propanone was 1.4:1.

[0041] Step S2-2: Under light-protected conditions, chitosan is added to an aqueous acetic acid solution, along with an isocyanate initiator, ethyl isocyanate acrylate, and a tin catalyst. The mixture is heated to 90°C and reacted for 7 hours. After washing and drying, modified chitosan is obtained. The mass ratio of chitosan, isocyanate initiator, and ethyl isocyanate acrylate is 10:0.1:2.5.

[0042] Step S2-2: Under light-protected conditions, monoamine-terminated PDMS was added dropwise to a 20wt% acetone aqueous solution containing triisocyanate, with a weight ratio of monoamine-terminated PDMS to triisocyanate of 2:1; the mixture was stirred at room temperature for 3 hours to obtain a polydimethylsilane isocyanate solution with a solid content of 2.1wt%; 0.5 parts of chitosan and 0.6 parts of modified chitosan were added and dispersed evenly to obtain a modified chitosan solution with a solid content of 3.2wt%.

[0043] (3) Mix the modified polyvinyl alcohol solution and the modified chitosan solution at a mass ratio of 88:12 evenly to obtain a waterproof coating;

[0044] Step 3: Apply the waterproof coating using a roller to the surface of the base corrugated cardboard A at a concentration of 100 mW / cm². 2 Irradiated under ultraviolet light for 2 hours and dried at 50℃ for 24 hours, yielding a quantitative result of 3.5 g / m³. 2 Waterproof coating; used as corrugated cardboard.

[0045] Example 2: A method for preparing corrugated cardboard based on a waterproof coating, comprising the following steps:

[0046] Step 1: (1) Add polyvinyl alcohol to deionized water to obtain a 10wt% polyvinyl alcohol aqueous solution; add epichlorohydrin dropwise; add 10wt% sodium hydroxide solution to adjust pH=11.5, stir at 60℃ for 4 hours; cool, add acid solution to adjust pH=3.5 to terminate, purify, and obtain epoxy polyvinyl alcohol; the mass ratio of polyvinyl alcohol to epichlorohydrin is 100:10;

[0047] (2) A 1 wt% epoxy-based polyvinyl alcohol solution was sprayed onto the surface of the base corrugated cardboard at a coating amount of 1 g / m². 2 At 50mW / cm 2Under ultraviolet light, it is dried at 50°C for 24 hours to obtain basic corrugated cardboard A;

[0048] Step 2: (1) Preparation of modified polyvinyl alcohol solution: Step S1-1: Polyvinyl alcohol, acrylamide, and isopropenylboronic acid are added to deionized water in sequence and stirred at 90°C for 30 minutes; under nitrogen atmosphere, ammonium persulfate initiator is added dropwise and reacted for 2 hours; the temperature is lowered and an alkaline solution is added to adjust the pH to 6.8; the polyvinyl alcohol copolymer is obtained; wherein, the mass ratio of polyvinyl alcohol, acrylamide, and isopropenylboronic acid is 4:1:0.5;

[0049] Step S1-2: Polyvinyl alcohol copolymer and mercaptoacetic acid are added sequentially to a 5wt% sulfuric acid aqueous solution, heated to 80℃ and stirred for 3 hours; cooled and purified to obtain modified polyvinyl alcohol; wherein the mass ratio of polyvinyl alcohol copolymer to mercaptoacetic acid is 10:11;

[0050] Steps S1-3: Add 0.25 parts of polyvinyl alcohol copolymer and 0.15 parts of modified polyvinyl alcohol sequentially to a 5 wt% acetone aqueous solution to obtain a modified polyvinyl alcohol solution with a solid content of 0.4 wt%.

[0051] (2) Preparation of modified chitosan solution: Step S2-1: Under light-protected conditions, diisocyanate and tin catalyst were added to ethyl acetate in sequence. Under a nitrogen atmosphere, 2-hydroxy-2-methyl-1-phenyl-1-propanone was added dropwise. The reaction was carried out at 50°C for 3 hours. After purification, isocyanate initiator was obtained. The molar ratio of diisocyanate to 2-hydroxy-2-methyl-1-phenyl-1-propanone was 1.4:1.

[0052] Step S2-2: Under light-protected conditions, chitosan is added to an aqueous acetic acid solution, along with an isocyanate initiator, ethyl isocyanate acrylate, and a tin catalyst. The mixture is heated to 90°C and reacted for 7 hours. After washing and drying, modified chitosan is obtained. The mass ratio of chitosan, isocyanate initiator, and ethyl isocyanate acrylate is 10:0.1:2.5.

[0053] Step S2-2: Under light-protected conditions, monoamine-terminated PDMS was added dropwise to a 20wt% acetone aqueous solution containing triisocyanate, with a weight ratio of monoamine-terminated PDMS to triisocyanate of 2:1; the mixture was stirred at room temperature for 3 hours to obtain an isocyanate-based polydimethylsilane solution with a solid content of 2.1wt%; 0.5 parts of chitosan and 0.4 parts of modified chitosan were added and dispersed evenly to obtain a modified chitosan solution with a solid content of 3wt%.

[0054] (3) Mix the modified polyvinyl alcohol solution and the modified chitosan solution at a mass ratio of 90:10 evenly to obtain a waterproof coating;

[0055] Step 3: Apply the waterproof coating using a roller to the surface of the base corrugated cardboard A at a concentration of 100 mW / cm². 2 Irradiated under ultraviolet light for 2 hours and dried at 50℃ for 24 hours, yielding a quantitative result of 3.5 g / m³. 2 Waterproof coating; used as corrugated cardboard.

[0056] Example 3: A method for preparing corrugated cardboard based on a waterproof coating, comprising the following steps:

[0057] Step 1: (1) Add polyvinyl alcohol to deionized water to obtain a 10wt% polyvinyl alcohol aqueous solution; add epichlorohydrin dropwise; add 10wt% sodium hydroxide solution to adjust pH=11.5, stir at 60℃ for 4 hours; cool, add acid solution to adjust pH=3.5 to terminate, purify, and obtain epoxy polyvinyl alcohol; the mass ratio of polyvinyl alcohol to epichlorohydrin is 100:10;

[0058] (2) A 1 wt% epoxy-based polyvinyl alcohol solution was sprayed onto the surface of the base corrugated cardboard at a coating amount of 1 g / m². 2 At 50mW / cm 2 Under ultraviolet light, it is dried at 50°C for 24 hours to obtain basic corrugated cardboard A;

[0059] Step 2: (1) Preparation of modified polyvinyl alcohol solution: Step S1-1: Polyvinyl alcohol, acrylamide, and isopropenylboronic acid are added to deionized water in sequence and stirred at 90°C for 30 minutes; under nitrogen atmosphere, ammonium persulfate initiator is added dropwise and reacted for 2 hours; the temperature is lowered and an alkaline solution is added to adjust the pH to 6.8; the polyvinyl alcohol copolymer is obtained; wherein, the mass ratio of polyvinyl alcohol, acrylamide, and isopropenylboronic acid is 4:1:0.5;

[0060] Step S1-2: Polyvinyl alcohol copolymer and mercaptoacetic acid are added sequentially to a 5wt% sulfuric acid aqueous solution, heated to 80℃ and stirred for 3 hours; cooled and purified to obtain modified polyvinyl alcohol; wherein the mass ratio of polyvinyl alcohol copolymer to mercaptoacetic acid is 10:11;

[0061] Steps S1-3: Add 0.4 parts of polyvinyl alcohol copolymer and 0.2 parts of modified polyvinyl alcohol sequentially to a 5 wt% acetone aqueous solution to obtain a modified polyvinyl alcohol solution with a solid content of 0.6 wt%.

[0062] (2) Preparation of modified chitosan solution: Step S2-1: Under light-protected conditions, diisocyanate and tin catalyst were added to ethyl acetate in sequence. Under a nitrogen atmosphere, 2-hydroxy-2-methyl-1-phenyl-1-propanone was added dropwise. The reaction was carried out at 50°C for 3 hours. After purification, isocyanate initiator was obtained. The molar ratio of diisocyanate to 2-hydroxy-2-methyl-1-phenyl-1-propanone was 1.4:1.

[0063] Step S2-2: Under light-protected conditions, chitosan is added to an aqueous acetic acid solution, along with an isocyanate initiator, ethyl isocyanate acrylate, and a tin catalyst. The mixture is heated to 90°C and reacted for 7 hours. After washing and drying, modified chitosan is obtained. The mass ratio of chitosan, isocyanate initiator, and ethyl isocyanate acrylate is 10:0.1:2.5.

[0064] Step S2-2: Under light-protected conditions, monoamine-terminated PDMS was added dropwise to a 20wt% acetone aqueous solution containing triisocyanate, with a weight ratio of monoamine-terminated PDMS to triisocyanate of 2:1; the mixture was stirred at room temperature for 3 hours to obtain a polydimethylsilane isocyanate solution with a solid content of 2wt%; 0.6 parts of chitosan and 0.6 parts of modified chitosan were added and dispersed evenly to obtain a modified chitosan solution with a solid content of 3.2wt%.

[0065] (3) Mix the modified polyvinyl alcohol solution and the modified chitosan solution at a mass ratio of 85:15 evenly to obtain a waterproof coating;

[0066] Step 3: Apply the waterproof coating using a roller to the surface of the base corrugated cardboard A at a concentration of 100 mW / cm². 2 Irradiated under ultraviolet light for 2 hours and dried at 50℃ for 24 hours, yielding a quantitative result of 3.5 g / m³. 2 Waterproof coating; used as corrugated cardboard.

[0067] Comparative Example 1: Based on Example 1, without applying a pre-coating layer, otherwise the same as Example 1; the difference lies in the following steps:

[0068] Step 1: Mix the modified polyvinyl alcohol solution and the modified chitosan solution at a mass ratio of 88:12 evenly to obtain a waterproof coating;

[0069] Step 2: Apply the waterproof coating using a roller to the surface of the base corrugated cardboard at a concentration of 100mW / cm². 2 Irradiated under ultraviolet light for 2 hours and dried at 50℃ for 24 hours, yielding a quantitative result of 3.5 g / m³. 2 Waterproof coating; used as corrugated cardboard.

[0070] Comparative Example 2: Based on Example 1, the pre-coating was not modified with polyvinyl alcohol, and the drying process did not introduce ultraviolet light; otherwise, it was the same as Example 1; the difference lay in the following steps:

[0071] Step 1: (1) Add polyvinyl alcohol to deionized water to obtain a 1 wt% polyvinyl alcohol aqueous solution; (2) Spray the 1 wt% polyvinyl alcohol solution onto the surface of the base corrugated cardboard at a spraying amount of 1 g / m². 2 Dry at 50℃ for 24 hours to obtain basic corrugated cardboard A.

[0072] Comparative Example 3: Based on Example 1, the components in the modified polyvinyl alcohol solution were adjusted, while the rest remained the same as in Example 1; the difference lay in the following steps:

[0073] Step 2: (1) Preparation of modified polyvinyl alcohol solution: Step S1-1: Polyvinyl alcohol and mercaptoacetic acid are added sequentially to a 5wt% sulfuric acid aqueous solution, heated to 80℃ and stirred for 3 hours; cooled and purified to obtain modified polyvinyl alcohol; wherein, the mass ratio of polyvinyl alcohol copolymer to mercaptoacetic acid is 10:11;

[0074] Step S1-3: Add 0.3 parts of polyvinyl alcohol and 0.2 parts of modified polyvinyl alcohol to a 5 wt% acetone aqueous solution in sequence to obtain a modified polyvinyl alcohol solution with a solid content of 0.5 wt%.

[0075] Comparative Example 4: Based on Example 1, the modified polyvinyl alcohol solution and modified chitosan solution were adjusted, and the rest was the same as in Example 1; the difference lies in the following steps:

[0076] Step 2: (3) Mix the modified polyvinyl alcohol solution and the modified chitosan solution in a mass ratio of 60:40 evenly to obtain a waterproof coating.

[0077] Performance Testing: The corrugated cardboard with waterproof coating prepared in the examples and comparative examples were subjected to relevant performance tests. The water contact angle and castor oil contact angle (contact angle of a 5μL droplet after 5 minutes) were measured using a contact angle meter. A 200g weight was used to rub the surface of the corrugated cardboard back and forth, with a single rubbing distance of 5cm, for 20 cycles. The surface water contact angle was measured again to obtain the water contact angle B, which was used to evaluate the coating bonding strength. The transformer strength was tested according to GB / T 6546-2021. The obtained data are shown in the table below.

[0078]

[0079] Conclusion: The corrugated cardboard with a waterproof coating prepared according to the proposed method exhibits excellent waterproof performance and oil resistance while improving mechanical strength. Data from Comparative Examples 1-4 show that the pre-coating, modification of polyvinyl alcohol in the pre-coating, and introduction of ultraviolet light effectively improve the overall performance of the corrugated cardboard. Furthermore, the modification of polyvinyl alcohol in the waterproof coating and the controlled ratio of modified polyvinyl alcohol solution to modified chitosan solution effectively optimize the performance of the corrugated cardboard. Therefore, this application presents a high-performance waterproof-coated corrugated cardboard based on environmentally friendly materials chitosan and polyvinyl alcohol.

[0080] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing corrugated cardboard based on a waterproof coating, characterized in that: Includes the following steps: Step 1: Spray the epoxy-based polyvinyl alcohol solution onto the surface of the base corrugated cardboard; Under ultraviolet light, dry at 35~50℃ for 24~48 hours to obtain basic corrugated cardboard A; Step 2: Mix the modified polyvinyl alcohol solution and the modified chitosan solution at a mass ratio of 85~90:10~15 evenly to obtain a waterproof coating; Step 3: Apply the waterproof coating by roller to the surface of the base corrugated cardboard A, expose it to ultraviolet light for 2-3 hours, and dry it at 35-50℃ for 24-48 hours to obtain the waterproof coating; use this as the corrugated cardboard. The preparation method of the epoxy-based polyvinyl alcohol is as follows: polyvinyl alcohol is added to deionized water to obtain a polyvinyl alcohol aqueous solution; epichlorohydrin is added dropwise; alkaline solution is added to adjust the pH to 11~12, and the mixture is stirred at 60~65℃ for 3~4 hours. Cool, add acid solution to adjust pH to 3-4 to terminate purification, and obtain epoxy-based polyvinyl alcohol; the mass ratio of polyvinyl alcohol to epichlorohydrin is 100:9-11. The preparation method of the modified polyvinyl alcohol solution is as follows: Step S1-1: Polyvinyl alcohol, acrylamide, and isopropenylboronic acid are added sequentially to deionized water and stirred at 90-95°C for 30-40 minutes; under a nitrogen atmosphere, ammonium persulfate initiator is added dropwise and the reaction is carried out for 1-3 hours; the temperature is lowered and an alkaline solution is added to adjust the pH to 6-7; the product is purified to obtain a polyvinyl alcohol copolymer. Step S1-2: Polyvinyl alcohol copolymer and mercaptoacetic acid are added sequentially to a 4-6 wt% sulfuric acid aqueous solution, heated to 70-90℃ and stirred for 2-4 hours; cooled and purified to obtain modified polyvinyl alcohol; Step S1-3: Polyvinyl alcohol copolymer and modified polyvinyl alcohol are added sequentially to a 5-10 wt% acetone aqueous solution; A modified polyvinyl alcohol solution was obtained; The modified chitosan solution is prepared as follows: Step S2-1: Under light-protected conditions, diisocyanate and tin catalyst are added sequentially to ethyl acetate. Under a nitrogen atmosphere, 2-hydroxy-2-methyl-1-phenyl-1-propanone is added dropwise. The mixture is reacted at 50-60°C for 3-4 hours and then purified to obtain an isocyanate initiator. Step S2-2: Under light-protected conditions, chitosan is added to an aqueous acetic acid solution, along with isocyanate initiator, ethyl isocyanate acrylate, and tin catalyst. The mixture is heated to 80-100°C and reacted for 6-8 hours. After washing and drying, modified chitosan is obtained. Step S2-3: Under light-protected conditions, monoamine-terminated PDMS is added dropwise to an acetone aqueous solution containing triisocyanate and stirred at room temperature for 2-3 hours to obtain an isocyanate-based polydimethylsilane solution with a solid content of 2-2.1 wt%; chitosan and modified chitosan are added and dispersed evenly to obtain a modified chitosan solution.

2. The method for preparing a waterproof-coated corrugated cardboard according to claim 1, characterized in that: The concentration of the epoxy-based polyvinyl alcohol solution is 1~1.5wt%; the spraying amount is 0.5~1g / m². 2 .

3. The method for preparing a corrugated cardboard based on a waterproof coating according to claim 1, characterized in that: The average molecular weight of the polyvinyl alcohol is 5000~9000 g / mol.

4. The method for preparing a corrugated cardboard based on a waterproof coating according to claim 1, characterized in that: The modified polyvinyl alcohol solution has a solid content of 0.4~0.6 wt%, and the raw materials of the modified polyvinyl alcohol solution include the following substances in parts by weight: 0.15~0.2 parts modified polyvinyl alcohol and 0.25~0.4 parts polyvinyl alcohol copolymer; In the raw materials of the polyvinyl alcohol copolymer, the mass ratio of polyvinyl alcohol, acrylamide, and isopropylene boric acid is 4:1:0.5; in the raw materials of the modified polyvinyl alcohol, the mass ratio of polyvinyl alcohol copolymer and mercaptoacetic acid is 10:8~12.

5. The method for preparing a corrugated cardboard based on a waterproof coating according to claim 1, characterized in that: The modified chitosan solution has a solid content of 3-3.2 wt%, and the raw materials of the modified chitosan solution include the following components by weight: 0.4-0.6 parts modified chitosan, 0.5-0.6 parts chitosan, and 2-2.1 parts isocyanate-based polydimethylsilane; In the raw materials of the isocyanate-based initiator, the molar ratio of diisocyanate to 2-hydroxy-2-methyl-1-phenyl-1-propanone is 1.2~1.5:1; in the raw materials of the modified chitosan, the mass ratio of chitosan, isocyanate-based initiator, and ethyl isocyanate acrylate is 10:0.1:2~3; in the raw materials of the isocyanate-based polydimethylsilane solution, the weight ratio of monoamine-terminated PDMS to triisocyanate is 2:

1.

6. The method for preparing a corrugated cardboard based on a waterproof coating according to claim 1, characterized in that: The quantitative amount of the waterproof coating is 3~5 g / m³. 2 .

7. Corrugated board prepared by the method for preparing a waterproof coating-based corrugated board according to any one of claims 1 to 6.

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