A process for the preparation of corrugated paper with improved sizing uniformity

Abstract

The present application belongs to papermaking technical field, especially relate to a corrugated paper preparation process for improving sizing uniformity.The corrugated paper preparation process for improving sizing uniformity includes the following steps: waste paper pulp and coniferous wood pulp are respectively subjected to pulping, impurity removal, purification and refining treatment, then are uniformly stirred and mixed, and water is added for dilution to obtain raw paper pulp; cationic modified nanocellulose, internal sizing agent and retention aid are added to the raw paper pulp and stirred uniformly; the slurry is delivered to the wire section for forming, and after being subjected to pressing, pre-drying, surface sizing, post-drying and winding, corrugated raw paper is obtained.The corrugated paper preparation process for improving sizing uniformity can optimize the fiber structure of the paper surface by using superfine refining and cationic modified nanocellulose, and can optimize the wetting performance of the sizing interface by using functional additives, and can effectively chelate water ions, inhibit glue aggregation and equipment deposition and fouling, and ensure the uniformity of sizing.

Description

Technical Field

[0001] This invention belongs to the field of papermaking technology, and in particular relates to a process for preparing corrugated paper that improves the uniformity of sizing. Background Technology

[0002] As a core supporting material in e-commerce logistics, product packaging, and cold chain transportation, the market demand for corrugated paper continues to expand, leading to fierce competition within the industry. For a long time, domestic corrugated paper production has generally relied on traditional roller sizing processes, which have limited adaptability and struggle to meet the core requirements of lightweight, high strength, and high moisture resistance in corrugated paper. Under the traditional open-type sizing method, controlling the viscosity of the adhesive is difficult, resulting in significant deviations in coating thickness. This not only leads to weak fiber bonding and insufficient ring crush strength, making boxes prone to collapse and breakage, but also results in substantial adhesive waste and a persistently high loss rate.

[0003] Furthermore, with the continuous increase in e-commerce express delivery volume and the increasing penetration rate of lightweight corrugated boxes, downstream industries such as home appliances, electronics, and fresh food cold chain have continuously raised their requirements for the moisture resistance, smoothness, and printability of corrugated paper. Traditional sizing processes can no longer meet the production needs of high-end customized packaging.

[0004] CN116180488A discloses a method and application for enhancing the sizing performance of surface-sizing starch in corrugated cardboard. Addressing industry pain points such as poor quality of domestic waste fiber, insufficient sizing strength of traditional enzymatically hydrolyzed starch, and rising costs due to increasing starch usage, this method optimizes the preparation and sizing process of surface-sizing starch by combining starch toughening physical modification with synergistic enzymatic hydrolysis using α-amylase. The method first toughens potato, cassava, or corn native starch by adjusting its moisture content, obtaining modified starch; then, stable sizing starch is obtained through amylase treatment; finally, it is formulated with... The sizing solution is applied to corrugated base paper for sizing, drying, and calendering. The entire process is free of harmful components and operates under mild conditions, which can significantly improve starch solubility, reduce viscosity and retrogradation value, optimize the proportion of amylopectin, and enhance the enzymatic hydrolysis effect, resulting in a significant improvement in the folding endurance, bursting index, and ring crush index of the paperboard, achieving high reinforcement performance with low sizing amount. However, it only focuses on adjusting the performance of the starch sizing solution and cannot improve the uniformity of the pulp and the retention rate of fine fibers from the source. The upper limit of the improvement in sizing uniformity is low, and it is difficult to ensure long-term and stable uniformity of sizing across the entire width.

[0005] CN119465685A discloses a corrugated base paper for fruit boxes and its production process. In this process, the base paper is made from OCC pulp, hardwood chemiluminescent pulp, and wood fiber. The strength and water resistance are improved through a composite process of in-pulp sizing and surface sizing. ASA neutral sizing agent and bentonite are added to the pulp to improve the fiber water resistance and the retention rate of additives. Corn starch, starch reinforcing agent and silicone oil resistance agent are added to the surface sizing section. The starch reinforcing agent makes the glucose chains form a network structure to enhance film formation and sizing effect. The silicone oil forms a hydrophobic film to reduce moisture absorption and inhibit the ring crush attenuation due to moisture regain. The resulting base paper has significantly improved stiffness, burst strength and ring crush strength, and excellent water resistance. However, the silicone oil resistance agent used is prone to precipitation and demulsification and has poor compatibility with starch. Conventional starch reinforcing agents cannot effectively control the rheological properties of the glue solution. The flowability and spreadability of the glue solution are unstable. During the sizing process, glue solution agglomeration and material deposition and blockage on the roller surface are prone to occur, and the consistency of sizing across the entire width is poor.

[0006] CN110863388A discloses a surface sizing process for corrugated cardboard processing. The process consists of four steps: First, a clear adhesive solution A is prepared by swelling, heating, and stirring modified starch, polyacrylamide, and polyvinyl alcohol as the main components; then, a bubbler B is prepared by high-speed stirring with sodium saponate, lauroyl sarcosinate, glycerin, etc.; adhesive solution C is prepared by kneading after mixing in proportion; finally, the sizing is completed by initial coating with a roller brush, coating with a sizing machine, debubbling and leveling with a polyurethane doctor blade, and hot air drying. This process enables the smooth application of a relatively thin adhesive solution onto corrugated cardboard. The process of surface treatment and bubble elimination promotes the smooth penetration of the adhesive into the fiber pores, avoiding over-saturation and ensuring a balance between film formation and penetration. It also avoids the adverse effects of diluted adhesive soaking into corrugated paper, resulting in a high yield rate and significantly improved burst strength, puncture strength, and water resistance of the corrugated paper. However, the adhesive is prone to starch retrogradation and additive stratification during long-term operation. The rheological properties of the adhesive change drastically with temperature and solid content. Relying solely on debubbling with a doctor blade and optimizing the coating process cannot fundamentally solve the defects of uneven adhesive spreading and localized deposition.

[0007] CN105111378A discloses a cationic polymer-grafted modified nanocellulose, its preparation method, and its application, aiming to solve the problems of traditional papermaking additives such as difficulty in achieving both dry and wet strength, poor retention, and high white water concentration. The product uses highly crystalline nanocellulose as a base material and copolymerizes it with nonionic monomers such as acrylamide and cationic monomers such as dimethyl diallyl ammonium chloride through free radical initiation to form nanocellulose clusters. As a papermaking reinforcing agent added to the wet end, it can simultaneously improve the dry and wet strength of paper, significantly improve tensile strength, burst strength, folding endurance, ring crush, and other indicators. It can also adsorb fine fibers, improve first-pass retention, reduce white water concentration and COD emissions, optimize paper machine operation, increase machine speed, and save steam. However, the nanocellulose prepared by this method is only used as a reinforcing and retention aid in the wet end and cannot be used in conjunction with a surface sizing agent system. It only optimizes the performance of the base paper substrate and has limited improvement on paper strength and other properties.

[0008] In summary, existing patented technologies mostly improve the strength, water resistance, and production stability of corrugated paper through starch modification, additive compounding, adhesive formulation optimization, and wet-end filler improvement. However, most of these technologies focus on improving material formulations and cannot effectively address the core issue of uneven sizing and coating, resulting in limited improvements in product performance. Summary of the Invention

[0009] To overcome the aforementioned deficiencies in the existing technology, this invention provides a corrugated paper preparation process that improves the uniformity of sizing. It employs an ultrafine pulping system combined with cationic modified nanocellulose, which optimizes the paper's fiber structure. Simultaneously, with the addition of functional additives, the viscosity of the adhesive solution can be adaptively adjusted according to operating temperature, optimizing the wetting performance of the sizing interface. Furthermore, it effectively chelates water ions, inhibits adhesive aggregation and equipment deposits and scaling, ensuring uniform sizing and improving the strength and water resistance of the corrugated paper.

[0010] A process for preparing corrugated paper that improves sizing uniformity includes the following steps: Step 1: The waste paper pulp and softwood pulp are respectively subjected to pulping, impurity removal, purification and refining. The treated pulps are stirred and mixed evenly, and water is added to dilute them to obtain the base paper pulp. Step 2: Add cationic modified nanocellulose, pulp sizing agent and retention aid to the base paper pulp and stir evenly; Step 3: The pulp from Step 2 is fed to the wire section. After the paper is formed on the wire section, it undergoes pressing, pre-drying, surface sizing, post-drying, and winding to obtain corrugated base paper. The surface sizing amount of the corrugated base paper is 3-6 g / m². 2 .

[0011] The surface sizing agent used in the surface sizing stage includes corn starch, rheology modifier, stabilizer, and anti-deposition agent. The preparation process of the surface sizing agent is as follows: first, mix corn starch with water, heat to 85-95℃ to gelatinize for 30-60 minutes, cool to 60-70℃, add rheology modifier, stabilizer, and anti-deposition agent in sequence, dilute with water to a solid content of 8wt.%-12wt.%, and stir evenly to obtain the final product.

[0012] In the aforementioned surface sizing agent, the amount of rheology modifier added is 0.1%-0.3% of the oven-dry weight of corn starch, the amount of stabilizer added is 0.05%-0.1% of the oven-dry weight of corn starch, and the amount of anti-deposition agent added is 0.1%-0.3% of the oven-dry weight of corn starch.

[0013] The rheology modifier is a cationic starch graft copolymer, obtained by graft polymerization of cationic starch, nanocellulose, and N-isopropylacrylamide (NIPAM) under the action of a crosslinking agent and an initiator, specifically including the following steps: (1) Disperse cationic starch at a mass ratio of 1:(8-12) in deionized water, gelatinize at 75-85℃ for 30-60 min under nitrogen atmosphere, and cool down for later use; disperse nanocellulose in deionized water, sonicate to obtain a suspension with a concentration of 5wt.%-10wt.% for later use. (2) Mix the solution in step (1) and stir well. Add N-isopropylacrylamide (NIPAM) and N,N′-methylenebisacrylamide crosslinking agent. After deoxygenation with nitrogen, add ammonium persulfate main initiator solution and sodium bisulfite co-initiator solution dropwise. React at a constant temperature of 65-75℃ for 3-6 hours. The amount of crosslinking agent is 0.8wt.%-2.0wt.% of NIPAM mass, the amount of main initiator is 1.5wt.%-3wt.% of NIPAM mass, and the amount of co-initiator is 0.25-0.45 times the mass of main initiator. (3) After the reaction is completed, cool to room temperature, add the polymerization inhibitor, precipitate with anhydrous ethanol, filter, wash and dry to obtain the rheology modifier; wherein, based on the dry weight, the mass ratio of cationic starch, nanocellulose and N-isopropylacrylamide is 1:(0.05-0.2):(0.3-0.6).

[0014] The stabilizer is an amphiphilic fluorosilicone block copolymer-chitosan oligosaccharide composite microsphere. It is prepared by polymerizing polyethylene glycol monomethyl ether methacrylate, polydimethylsiloxane-methacrylate, and perfluoropolyether methacrylate as monomers to obtain a triblock fluorosilicone copolymer, which is then coated onto cross-linked carboxymethyl chitosan oligosaccharide using spray drying. The specific steps include: (1) Under nitrogen protection, anhydrous tetrahydrofuran was used as the solvent. Cuprous bromide catalyst, pentamethyldiethylenetriamine coordination agent, and ethyl 2-bromoisobutyrate initiator were added and stirred until homogeneous. Then, the temperature was raised to a polymerization temperature of 60-70℃. The first monomer, polyethylene glycol monomethyl ether methacrylate, was added sequentially, and the reaction was allowed to proceed for 2-4 hours. The second monomer, polydimethylsiloxane-methacrylate, was then added, and the reaction continued for 2-4 hours. Finally, the third monomer, perfluoropolyether methacrylate, was added, and the reaction was allowed to proceed for another 2-4 hours. After the three-stage polymerization was completed, a hexane / diethyl ether mixed solvent was added to terminate the reaction. The mixture was then precipitated, filtered, and... The triblock fluorosilicone copolymer was prepared by vacuum drying; wherein, by mass percentage, polyethylene glycol monomethyl ether methacrylate 30-50 wt.%, polydimethylsiloxane-methacrylate 30-40 wt.%, and perfluoropolyether methacrylate 20-30 wt.%; the amount of cuprous bromide was 0.1-0.4 wt.% of the total monomer mass, the amount of pentamethyldiethylenetriamine was 0.3-1.0 wt.% of the total monomer mass, the amount of ethyl 2-bromoisobutyrate was 0.2-0.5 wt.% of the total monomer mass, and the amount of anhydrous tetrahydrofuran was 3-5 times the total monomer mass; Carboxymethyl chitosan oligosaccharide was dissolved in deionized water, glutaraldehyde crosslinking agent was added, the pH was adjusted, and the crosslinking reaction was carried out at 40-60℃ for 4-8 hours to obtain a crosslinked carboxymethyl chitosan oligosaccharide dispersion. The amount of crosslinking agent used was 2-6 wt.% of the mass of carboxymethyl chitosan oligosaccharide. (2) The triblock fluorosilicone copolymer was dissolved in dichloromethane to prepare an organic solution, which was then mixed with a crosslinked carboxymethyl chitosan oligosaccharide dispersion and emulsified at room temperature to obtain an oil-in-water emulsion. Subsequently, the emulsion was spray-dried and the powder was collected to obtain an amphiphilic fluorosilicone block copolymer-chitosan oligosaccharide composite microsphere stabilizer. The mass ratio of the triblock fluorosilicone copolymer to the carboxymethyl chitosan oligosaccharide was 1:(0.5-1).

[0015] The anti-deposition agent is a polyaspartic acid-polyethyleneimine graft copolymer, which is obtained by grafting branched polyethyleneimine onto polyaspartic acid as the main chain after activating carboxyl groups. The specific steps include: (1) Dissolve polyaspartic acid in anhydrous DMF solvent, add activator N-hydroxysuccinimide (NHS) and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl), stir at room temperature for 2-4 h to complete the activation of polyaspartic acid carboxyl group, and obtain activated ester intermediate solution. The mass ratio of polyaspartic acid, N-hydroxysuccinimide and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride is 10:(2-5):(4-10), and the amount of anhydrous DMF is 10-20 times the mass of polyaspartic acid; (2) Dissolve branched polyethyleneimine in anhydrous DMF solvent and add it dropwise to the activated ester solution. Then, heat the solution to 40-60℃ and stir for 6-12 hours to carry out the graft copolymerization reaction. The amount of branched polyethyleneimine is 2-4 times the mass of polyaspartic acid, and the amount of anhydrous DMF is 2-5 times the mass of branched polyethyleneimine. (3) After the reaction is completed, the graft copolymer reaction solution is poured into anhydrous ethanol for precipitation separation, washing and drying to obtain polyaspartic acid-polyethyleneimine graft copolymer anti-deposition agent.

[0016] Furthermore, the preparation process of polyaspartic acid is as follows: L-aspartic acid and a catalyst aqueous solution of phosphoric acid (mass fraction 85%) are mixed at a molar ratio of 1:7, placed in a reactor, heated to 200℃ under nitrogen protection, and condensed and polymerized for 4 hours to obtain a polysuccinimide intermediate; the polysuccinimide is cooled, pulverized, and a 20% sodium hydroxide aqueous solution is added, and hydrolyzed at 60℃ for 1 hour. Then, the pH is adjusted to 4 with hydrochloric acid, the precipitate is precipitated, filtered, washed with deionized water until neutral, and vacuum dried to obtain polyaspartic acid with a number average molecular weight of 4000 g / mol.

[0017] In step 1, the ratio of waste paper pulp to softwood pulp is (8-10):1, calculated by oven-dry weight; the mass concentration of waste paper pulp is 3wt.%-5wt.%, and the freeness is 20-35°SR; the mass concentration of softwood pulp is 3wt.%-6wt.%, and the freeness is 85-90°SR.

[0018] The sizing agent is one or both of cationic dispersed rosin gum and alkyl ketene dimer (AKD) emulsion; wherein the solid content of AKD emulsion is 15%-25% and the solid content of cationic dispersed rosin gum is 20%-35%.

[0019] The retention aid is cationic polyacrylamide with a molecular weight of 8 million to 12 million and an ionicity of 15% to 25%. Before use, it is prepared into a 0.1-0.3 wt.% aqueous solution, fully dissolved, and then diluted online to 0.01-0.03 wt.% before being added to the pulp.

[0020] In step 2, the amount of cationic modified nanocellulose is 20-30 kg / ton of paper, the amount of internal sizing agent is 0.5-2.0 kg / ton of paper, and the amount of retention aid is 0.3-0.8 kg / ton of paper, calculated based on oven-dry weight.

[0021] The preparation process of the cationic modified nanocellulose is as follows: the nanocellulose aqueous suspension is put into a reaction vessel, (3-chloro-2-hydroxypropyl)trimethylammonium chloride is added, the pH of the system is adjusted to 9.0-11.0, and the reaction is stirred at 60-80℃ for 2-4 hours. After the reaction is completed, the nanocellulose is washed with water until neutral, and centrifuged to dehydrate to obtain cationic modified nanocellulose. The mass ratio of nanocellulose to (3-chloro-2-hydroxypropyl)trimethylammonium chloride is 1:(0.2-0.4) based on the oven-dry weight.

[0022] This invention uses a blend of waste paper pulp and high-beaten softwood pulp, with long and short fibers interwoven to form a dense fiber network with uniformly distributed pores, improving paper surface smoothness. The added cationic modified nanocellulose adheres uniformly to the fiber surface and gaps via electrostatic attraction, filling micropores, refining the paper surface morphology, and strengthening inter-fiber bonding, thus improving the retention rate of fine fibers and further enhancing overall paper uniformity. Furthermore, the pulp is combined with cationic dispersed rosin gum or AKD sizing agent and cationic polyacrylamide retention aid. Through electrostatic adsorption and bridging, these additives are evenly distributed in the pulp, providing the paper with basic water resistance while preventing localized additive enrichment or deficiency, fundamentally reducing uneven sizing problems caused by substrate defects.

[0023] Secondly, the surface sizing system uses gelatinized corn starch as the main film-forming agent, and compounded functional additives regulate the properties of the adhesive. Among them, the cationic starch graft copolymer is a temperature-sensitive rheology modifier. Relying on the temperature-sensitive properties of the N-isopropylacrylamide segment, it can dynamically adjust the viscosity of the adhesive according to the operating temperature: at low temperatures, it increases the viscosity to prevent adhesive loss and leakage, and at high temperatures, it decreases the viscosity to avoid adhesive accumulation and pinholes, ensuring the fluidity and coating stability of the adhesive. The amphiphilic fluorosilicone block copolymer-chitosan oligosaccharide composite microspheres act as a stabilizer, which can reduce the surface tension of the adhesive, improve the wetting and spreading effect on the paper surface, and inhibit the association and aging of starch molecules, preventing the adhesive components from stratifying and agglomerating. The three work together to effectively solve the problems of unstable rheology, poor wetting effect, and easy aging and deterioration of traditional adhesives, ensuring uniform sizing thickness.

[0024] Finally, a polyaspartic acid-polyethyleneimine graft copolymer is introduced into the surface sizing system as an anti-deposition agent to further ensure the long-term stable operation of the sizing system. Simultaneously, this substance contains a large number of active coordinating groups, which can chelate metal ions such as calcium and magnesium in the production water, preventing the ions from combining with colloidal components to form flocs and avoiding glue agglomeration. At the same time, the cationic groups on the molecular surface can form an electrostatic repulsion layer on the colloidal particles and the inner wall of the equipment, preventing glue adhesion and deposition, roller blockage, and equipment scaling, thus reducing production failures and defect rates. In summary, this invention combines pulp substrate modification with surface sizing, with each process and component working synergistically to solve the drawbacks of traditional processes such as large sizing deviations, high glue loss, and poor operational stability. While improving sizing uniformity, the dual hydrophobic structure and reinforcing system also significantly improve the physical strength and moisture resistance of corrugated paper, effectively addressing the problems of rapid wear and short service life of metering rods during the use of film transfer sizing machines.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention uses waste paper pulp and softwood pulp compound pulp, combined with cationic modified nanocellulose to optimize fiber structure, improve fiber bonding force and paper surface smoothness. Through the synergistic cooperation of the pulp and surface dual sizing system, a stable hydrophobic structure is constructed, which improves the problems of uneven sizing and performance fluctuation in traditional process, and effectively improves the physical strength and water resistance of corrugated paper.

[0026] (2) The present invention introduces a temperature-sensitive rheology modifier into the surface sizing agent, so that the surface sizing agent has temperature adaptive characteristics and can adjust the viscosity and flow of the adhesive according to the temperature change of the production conditions. This additive can improve the situation of adhesive accumulation and loss during the sizing process, reduce defects such as paper surface pinholes, flow marks, and adhesive leakage, stabilize the amount of adhesive applied, and effectively improve the uniformity of sizing of corrugated paper.

[0027] (3) The present invention combines stabilizers and anti-deposition agents in the surface sizing agent, which can improve the dispersion compatibility of the sizing system components and avoid the agglomeration and stratification of the adhesive. At the same time, the anti-deposition agent can chelate water metal ions, inhibit the flocculation of the adhesive and the deposition and scaling on the inner wall of the equipment, reduce the frequency of equipment maintenance and the production defect rate, and has good production stability and industrial applicability. Detailed Implementation

[0028] The technical solution of the present invention will be further described below with reference to the embodiments and comparative examples. Unless otherwise specified, the raw materials used in the embodiments and comparative examples are all conventional commercial raw materials, and the process methods used are all conventional methods in the art unless otherwise specified. Unless otherwise specified, the amounts used in the embodiments and comparative examples are all oven-dry weights, and the parts are all parts by weight.

[0029] Raw material description Cationic starch: Taian Jinshan Modified Starch Co., Ltd.; Nanocellulose: Nanocellulose TL-011, Nanjing Tianlu Nanotechnology Co., Ltd.; Polyethylene glycol monomethyl ether methacrylate: Huayue Fine Chemical (Kunshan) MPEG600MA; Polydimethylsiloxane-methacrylate: Xi'an Qiyue Biotechnology Co., Ltd.; Perfluoropolyether methacrylate: Wuhan Shuer Biotechnology Co., Ltd., PFPE-MAA-1000; Branched polyethyleneimine: Branched polyethyleneimine C0539, Shanghai Beyotime Biotechnology Co., Ltd.; Cationic polyacrylamide: Jiangsu Zhonghao Yuanda Environmental Engineering Co., Ltd.

[0030] The preparation process of the cationic modified nanocellulose is as follows: the mass ratio of nanocellulose to (3-chloro-2-hydroxypropyl)trimethylammonium chloride is 1:0.3 based on the oven-dry weight. A 5 wt.% nanocellulose aqueous suspension is added to a reaction vessel, and (3-chloro-2-hydroxypropyl)trimethylammonium chloride is added. The pH of the system is adjusted to 10.0 with an 8 wt.% sodium hydroxide aqueous solution. The reaction is stirred at 70°C for 3 hours. After the reaction is completed, the mixture is washed with water until neutral and centrifuged to obtain cationic modified nanocellulose.

[0031] The preparation process of the rheology modifier is as follows: (1) Disperse 100 parts of cationic starch in 1000 parts of deionized water, gelatinize at 80±5℃ for 40 min under nitrogen atmosphere, and cool down to 60℃ for later use; disperse 10 parts of nanocellulose in 90 parts of deionized water, ultrasonically disperse for 30 min, and prepare a suspension with a concentration of 10wt.% for later use. (2) Mix the solution in step (1) thoroughly, add 40 parts of NIPAM and 0.4 parts of N,N′-methylenebisacrylamide crosslinking agent and stir to dissolve. After deoxygenation with nitrogen, add 0.6 parts of ammonium persulfate main initiator solution (solution concentration is 5 wt.%, the amount is the oven-dry mass of the effective component) and 0.15 parts of sodium bisulfite co-initiator solution (solution concentration is 5 wt.%, the amount is the oven-dry mass of the effective component) and react at a constant temperature of 70±5℃ for 4.5h. (3) After the reaction is completed, cool to room temperature, add 200 ppm hydroquinone polymerization inhibitor to terminate the reaction, then pour the reaction solution into 5 times the volume of anhydrous ethanol to precipitate, filter, wash 3 times with anhydrous ethanol, and finally place the product in a vacuum drying oven and dry at 50°C for 12 h to obtain the rheology modifier; before use, redisperse the dried product in deionized water with a mass concentration of 10 wt.%, heat to 80°C and stir for 40 min.

[0032] The preparation process of the stabilizer is as follows: (1) Under nitrogen protection, anhydrous tetrahydrofuran was used as the solvent, with an amount 5 times the total mass of the monomers. The catalyst cuprous bromide, the coordinating agent pentamethyldiethylenetriamine, and the initiator ethyl 2-bromoisobutyrate were added and stirred until homogeneous. Then, the temperature was raised to 65±5℃, and the first monomer, polyethylene glycol monomethyl ether methacrylate, was added sequentially, reacting for 2 hours. The second monomer, polydimethylsiloxane-methacrylate, was then added, and the reaction continued for 3 hours. Finally, the third monomer, perfluoropolyether methacrylate, was added, and the reaction continued for 4 hours. After the three-stage polymerization was completed, a hexane / ethyl ether mixed solvent was added to terminate the reaction. The solution was poured into 10 times its volume of ice-cold hexane to precipitate, filtered, and dried under vacuum at 50°C and -0.09 MPa for 24 h to obtain a triblock fluorosilicone copolymer; wherein, by mass percentage, polyethylene glycol monomethyl ether methacrylate 30 wt.%, polydimethylsiloxane-methacrylate 40 wt.%, and perfluoropolyether methacrylate 30 wt.%; cuprous bromide was used at 0.3 wt.% of the total monomer mass, pentamethyldiethylenetriamine at 0.5 wt.% of the total monomer mass, and ethyl 2-bromoisobutyrate at 0.3 wt.% of the total monomer mass; 100 parts of carboxymethyl chitosan oligosaccharide were dissolved in 900 parts of deionized water and stirred until dissolved. 10 parts of glutaraldehyde crosslinking agent were added, and the pH was adjusted to 4 with 10 wt.% hydrochloric acid. The crosslinking reaction was carried out at 60℃ for 4 h. Subsequently, the mixture was concentrated to a solid content of 10 wt.% to obtain a crosslinked carboxymethyl chitosan oligosaccharide dispersion. (2) Dissolve 10 parts of triblock fluorosilicone copolymer in 90 parts of dichloromethane to prepare an organic solution, mix with 8 parts of crosslinked carboxymethyl chitosan oligosaccharide dispersion (calculated by oven-dry mass, i.e., the total mass of aqueous solution is 80 parts), and emulsify at room temperature to obtain an oil-in-water emulsion. Then, spray dry and collect the powder to obtain an amphiphilic fluorosilicone block copolymer-chitosan oligosaccharide composite microsphere stabilizer.

[0033] The preparation process of the anti-deposition agent is as follows: (1) Dissolve 10 parts of polyaspartic acid in 100 parts of anhydrous DMF solvent, add 3 parts of activator N-hydroxysuccinimide (NHS) and 8 parts of EDC·HCl activator, stir at room temperature for 3 h to complete the activation of polyaspartic acid carboxyl group and obtain activated ester intermediate solution. (2) Dissolve 30 parts of branched polyethyleneimine in 60 parts of anhydrous DMF solvent, add it dropwise to the activated ester solution, add it dropwise for 40 min, and after the addition is completed, raise the temperature to 50℃ and stir the reaction at a constant temperature for 8 h to carry out the graft copolymerization reaction. (3) After the reaction is completed, the graft copolymer reaction solution is poured into 300 parts of anhydrous ethanol for precipitation and separation, washed with anhydrous ethanol, and dried at 45°C for 20 hours to obtain the anti-deposition agent of polyaspartic acid-polyethyleneimine graft copolymer.

[0034] Example 1 The corrugated paper preparation process for improving sizing uniformity includes the following steps: Step 1: 90 parts of waste paper pulp with a concentration of 3 wt.% were pulped, impurities removed, purified and refined to a freeness of 27.5 ± 7.5°SR. 10 parts of softwood pulp with a concentration of 4 wt.% were pulped, impurities removed, purified and refined to a freeness of 87.5 ± 2.5°SR. The treated pulps were stirred and mixed evenly and diluted with water to obtain base paper pulp. Step 2: Add cationic modified nanocellulose solution to the base paper pulp and mix, then add alkyl ketene dimer emulsion and continue mixing. Finally, add CPAM solution and mix evenly. Calculated by oven-dry weight, the amount of cationic modified nanocellulose is 25 kg / ton of paper, the amount of alkyl ketene dimer emulsion is 2 kg / ton of paper, and the amount of CPAM is 0.5 kg / ton of paper. Step 3: The pulp from Step 2 is fed to the wire section. After the paper is formed on the wire section, it undergoes pressing, pre-drying, surface sizing, post-drying, and winding to obtain corrugated base paper. The surface sizing amount of the corrugated base paper is 6 g / m². 2 .

[0035] The preparation process of the surface sizing agent used in the surface sizing stage is as follows: First, mix 10 parts corn starch with 80 parts water, heat to 95°C to gelatinize for 30 minutes, cool to 70°C, and then add 0.02 parts rheology modifier, 0.008 parts stabilizer, and 0.02 parts anti-deposition agent in sequence. Dilute with water to a solid content of 8 wt.% and stir evenly to obtain the final product.

[0036] Example 2 The corrugated paper preparation process for improving sizing uniformity includes the following steps: Step 1: 80 parts of waste paper pulp with a concentration of 5 wt.% were pulped, impurities removed, purified and refined to a freeness of 27.5 ± 7.5°SR. 10 parts of softwood pulp with a concentration of 3 wt.% were pulped, impurities removed, purified and refined to a freeness of 87.5 ± 2.5°SR. The treated pulps were stirred and mixed evenly and diluted with water to obtain base paper pulp. Step 2: Add cationic modified nanocellulose solution to the base paper pulp and mix, then add cationic dispersed rosin gum and continue mixing. Finally, add CPAM solution and mix evenly. Calculated by oven-dry weight, the amount of cationic modified nanocellulose is 20 kg / ton of paper, the amount of cationic dispersed rosin gum is 0.5 kg / ton of paper, and the amount of CPAM is 0.3 kg / ton of paper. Step 3: The pulp from Step 2 is fed to the wire section. After the paper is formed on the wire section, it undergoes pressing, pre-drying, surface sizing, post-drying, and winding to obtain corrugated base paper. The surface sizing amount of the corrugated base paper is 3g / m². 2 .

[0037] The preparation process of the surface sizing agent used in the surface sizing stage is as follows: First, mix 10 parts corn starch with 50 parts water, heat to 85°C and gelatinize for 50 minutes, cool to 60°C, then add 0.01 parts rheology modifier, 0.005 parts stabilizer, and 0.01 parts anti-deposition agent in sequence, dilute with water to a solid content of 10 wt.%, and stir evenly to obtain the final product.

[0038] Example 3 The corrugated paper preparation process for improving sizing uniformity includes the following steps: Step 1: 100 parts of waste paper pulp with a concentration of 4 wt.% were pulped, impurities removed, purified and refined to obtain a freeness of 27.5 ± 7.5°SR. 10 parts of softwood pulp with a concentration of 6 wt.% were pulped, impurities removed, purified and refined to obtain a freeness of 87.5 ± 2.5°SR. The treated pulps were stirred and mixed evenly and diluted with water to obtain base paper pulp. Step 2: Add cationic modified nanocellulose solution to the base paper pulp and mix. Then add cationic dispersed rosin gum and alkyl ketene dimer emulsion and continue mixing. Finally, add CPAM solution and mix evenly. Calculated by oven-dry weight, the amount of cationic modified nanocellulose is 30 kg / ton of paper, the amount of cationic dispersed rosin gum is 0.5 kg / ton of paper, the amount of alkyl ketene dimer emulsion is 1.0 kg / ton of paper, and the amount of CPAM is 0.8 kg / ton of paper. Step 3: The pulp from Step 2 is fed to the wire section. After the paper is formed on the wire section, it undergoes pressing, pre-drying, surface sizing, post-drying, and winding to obtain corrugated base paper. The surface sizing amount of the corrugated base paper is 4 g / m². 2 .

[0039] The preparation process of the surface sizing agent used in the surface sizing stage is as follows: First, mix 15 parts of corn starch with 60 parts of water, heat to 90°C and gelatinize for 60 minutes, cool to 65°C, and then add 0.045 parts of rheology modifier, 0.015 parts of stabilizer, and 0.045 parts of anti-deposition agent in sequence. Dilute with water to a solid content of 12 wt.% and stir evenly to obtain the final product.

[0040] Comparative Example 1 This comparative example is the same as Example 1, except that the cationic modified nanocellulose in step 2 is replaced with conventional commercially available nanocellulose, and the rest is the same as Example 1.

[0041] Comparative Example 2 This comparative example is the same as Example 1, except that the rheology modifier in the surface sizing agent is removed, while the other components remain unchanged, and the preparation process is the same as in Example 1.

[0042] Comparative Example 3 This comparative example is the same as Example 1, except that the stabilizer in the surface sizing agent is removed, while the other components remain unchanged, and the preparation process is the same as in Example 1.

[0043] The corrugated paper prepared in the above embodiments and comparative examples was subjected to performance testing. Under the condition of the same paper machine speed, 120 g / m² was selected. 2 The corrugated base paper was tested for ring crush index according to GB / T 2679.8-2016. The ring crush strength was determined by dividing the ring crush index by the basis weight. The bursting strength was tested according to GB / T 454-2020. The smoothness (front / back) was tested according to GB / T 456-2002. The test results are shown in Table 1.

[0044] Table 1. Performance test results of corrugated paper in the examples and comparative examples.

[0045] As shown in Table 1, comparing Comparative Example 1 and Example 1, when cationic modified nanocellulose is replaced with nanocellulose, the nanocellulose, lacking cationic modification, cannot be uniformly dispersed through electrostatic interaction, is prone to agglomeration, and cannot effectively fill fiber pores. The improvement in inter-fiber bonding force is limited, directly leading to a significant decrease in ring crush index and burst strength. Conventional nanocellulose cannot effectively improve the retention of fine fibers, resulting in uneven distribution of paper pores. During sizing, local enrichment or absence of sizing solution is prone to occur, ultimately leading to a significant reduction in the smoothness of both sides and a significant decrease in sizing uniformity.

[0046] Compared with Example 1, after removing the rheology modifier from the surface sizing agent, the adhesive lost its temperature-adaptive viscosity adjustment ability and could not control its flow according to changes in working conditions. This easily led to problems such as low-temperature adhesive loss and high-temperature adhesive accumulation and pinholes. The adhesive was difficult to spread evenly on the paper surface, and the sizing thickness deviation became larger. At the same time, the lack of this additive could not help starch form a continuous and dense adhesive film, resulting in insufficient adhesion between the adhesive film and the paper surface and a decrease in the overall fiber bonding strength, which directly caused a significant reduction in ring crush index and bursting strength. Furthermore, the uncontrolled rheological properties of the adhesive could lead to local over-sizing or under-sizing, resulting in inconsistent coating conditions on different parts of the paper surface. Ultimately, this resulted in a significant decrease in the smoothness of both sides and a substantial deterioration in the uniformity of sizing.

[0047] Compared with Example 1, after removing the stabilizer from the surface sizing agent, the surface tension of the adhesive solution could not be effectively reduced, resulting in poor wetting and spreading ability on the paper surface. The adhesive solution was prone to agglomeration and could not fully cover the paper surface. At the same time, the additive, which originally could inhibit starch aging and prevent the adhesive solution components from separating, had reduced stability after its absence, making it difficult to form a complete and uniform functional adhesive film. The fiber reinforcement and hydrophobic effects were weakened, directly leading to a significant decrease in ring crush index, bursting strength, and sizing uniformity.

Claims

1. A process for the production of corrugated paper with improved sizing uniformity, characterized in that Includes the following steps: Step 1: The waste paper pulp and softwood pulp are respectively subjected to pulping, impurity removal, purification and refining. The treated pulps are stirred and mixed evenly, and water is added to dilute them to obtain the base paper pulp. Step 2: Add cationic modified nanocellulose, pulp sizing agent and retention aid to the base paper pulp and stir evenly; Step 3: The pulp from Step 2 is fed to the wire section. After the paper is formed on the wire section, it goes through pressing, pre-drying, surface sizing, post-drying, and winding to obtain corrugated base paper. The surface sizing agent used in the surface sizing stage includes corn starch, rheology modifier, stabilizer and anti-deposition agent; The rheology modifier is a cationic starch graft copolymer, which is obtained by graft polymerization of cationic starch, nanocellulose, and N-isopropylacrylamide as raw materials under the action of a crosslinking agent and an initiator. The stabilizer is an amphiphilic fluorosilicone block copolymer-chitosan oligosaccharide composite microsphere. It is prepared by polymerizing polyethylene glycol monomethyl ether methacrylate, polydimethylsiloxane-methacrylate, and perfluoropolyether methacrylate as monomers to obtain a triblock fluorosilicone copolymer, and then coating the copolymer into cross-linked carboxymethyl chitosan oligosaccharide by spray drying. The anti-deposition agent is a polyaspartic acid-polyethyleneimine graft copolymer, which is obtained by grafting branched polyethyleneimine with polyaspartic acid as the main chain and activating the carboxyl groups.

2. The process for preparing corrugated paper with improved sizing uniformity according to claim 1, characterized in that, Based on oven-dry weight, the ratio of waste paper pulp to softwood pulp is (8-10):1; the mass concentration of waste paper pulp is 3wt.%-5wt.%, and the freeness is 20-35°SR; the mass concentration of softwood pulp is 3wt.%-6wt.%, and the freeness is 85-90°SR.

3. The corrugated paper preparation process for improving sizing uniformity according to claim 1, characterized in that, The sizing agent is one or both of cationic dispersed rosin gum and alkyl ketene dimer emulsion; the retention aid is cationic polyacrylamide with a molecular weight of 8 million to 12 million and an ionicity of 15% to 25%.

4. The corrugated paper preparation process for improving sizing uniformity according to claim 1, characterized in that, Based on oven-dry weight, the dosage of cationic modified nanocellulose is 20-30 kg / ton of paper, the dosage of internal sizing agent is 0.5-2.0 kg / ton of paper, and the dosage of retention aid is 0.3-0.8 kg / ton of paper.

5. The process for preparing corrugated paper with improved sizing uniformity as claimed in claim 1 wherein, The preparation process of cationic modified nanocellulose is as follows: the aqueous suspension of nanocellulose is put into a reaction vessel, (3-chloro-2-hydroxypropyl)trimethylammonium chloride is added, the pH of the system is adjusted to 9.0-11.0, and the reaction is stirred at 60-80℃ for 2-4 hours. After the reaction is completed, the nanocellulose is washed with water until neutral, and centrifuged to dehydrate to obtain cationic modified nanocellulose.

6. The process for preparing corrugated paper with improved sizing uniformity as claimed in claim 1 wherein, The surface sizing agent has a solid content of 8wt.%-12wt.%, the rheology modifier is added at 0.1%-0.3% of the oven-dry weight of corn starch, the stabilizer is added at 0.05%-0.1% of the oven-dry weight of corn starch, and the anti-deposition agent is added at 0.1%-0.3% of the oven-dry weight of corn starch.

7. The process for improving sizing uniformity of corrugated paper according to claim 1, wherein, The preparation process of rheology modifiers includes the following steps: (1) Disperse cationic starch in deionized water and gelatinize it at 75-85℃ for 30-60 min under nitrogen atmosphere, then cool it down for later use; disperse nanocellulose in deionized water and sonicate it to obtain a uniform suspension. (2) Mix the solution in step (1) and stir well. Add N-isopropylacrylamide and N,N′-methylenebisacrylamide crosslinking agent. After removing oxygen with nitrogen, add ammonium persulfate initiator solution and sodium bisulfite co-initiator solution. React at a constant temperature of 65-75℃ for 3-6 hours. (3) After the reaction is completed, the mixture is cooled to room temperature, and after adding the polymerization inhibitor, it is precipitated with anhydrous ethanol, filtered, washed and dried to obtain the rheology modifier.

8. The corrugated paper preparation process for improving sizing uniformity according to claim 1, characterized in that, The preparation process of the stabilizer includes the following steps: (1) Under nitrogen protection, anhydrous tetrahydrofuran was used as solvent, and cuprous bromide catalyst, pentamethyldiethylenetriamine coordination agent and ethyl 2-bromoisobutyrate initiator were added and stirred until uniform. Then, the temperature was raised to 60-70℃, and the first monomer, polyethylene glycol monomethyl ether methacrylate, was added in sequence and reacted for 2-4 h. Then, the second monomer, polydimethylsiloxane-methacrylate, was added and reacted for another 2-4 h. Finally, the third monomer, perfluoropolyether methacrylate, was added and reacted for another 2-4 h. After the three-stage polymerization was completed, hexane / diethyl ether mixed solvent was added to terminate the reaction. After precipitation, filtration and vacuum drying, triblock fluorosilicone copolymer was obtained. Carboxymethyl chitosan oligosaccharide was dissolved in deionized water, glutaraldehyde crosslinking agent was added, pH was adjusted and crosslinking reaction was carried out at 40-60℃ for 4-8 h to obtain crosslinked carboxymethyl chitosan oligosaccharide dispersion. (2) The triblock fluorosilicone copolymer was dissolved in dichloromethane to prepare an organic solution, which was then mixed with a crosslinked carboxymethyl chitosan oligosaccharide dispersion and emulsified at room temperature to obtain an oil-in-water emulsion. Subsequently, the emulsion was spray-dried and the powder was collected to obtain an amphiphilic fluorosilicone block copolymer-chitosan oligosaccharide composite microsphere stabilizer.

9. The process for improving sizing uniformity of corrugated paper according to claim 1, wherein, The preparation process of the anti-deposition agent includes the following steps: (1) Polyaspartic acid was dissolved in anhydrous DMF solvent, and N-hydroxysuccinimide and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride activator were added. The reaction was stirred at room temperature to complete the activation of the carboxyl group of polyaspartic acid and obtain an activated ester intermediate solution. (2) Dissolve branched polyethyleneimine in anhydrous DMF solvent, add it dropwise to the activated ester solution, and then heat it to 40-60℃ and stir for 6-12 hours to carry out graft copolymerization. (3) After the reaction is completed, the graft copolymer reaction solution is poured into anhydrous ethanol for precipitation separation, washing and drying to obtain polyaspartic acid-polyethyleneimine graft copolymer anti-deposition agent.

10. The process for preparing corrugated paper with improved sizing uniformity as claimed in claim 1 wherein, The preparation process of the surface sizing agent is as follows: firstly, corn starch is mixed with water, heated to 85-95℃ for 30-60 min, cooled to 60-70℃, and then rheological modifier, stabilizer and anti-deposition agent are added in sequence, and water is added for dilution, and stirring is performed until uniformity is achieved; the surface sizing amount is 3-6 g / m 2 .

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