A high-charge-density starch-grafted phenylpropanoid composite akd surface sizing agent, and a preparation method and application thereof

Abstract

The application discloses a high-charge-density starch grafting phenylpropyl AKD surface sizing agent and a preparation method and application thereof. The sizing agent is prepared from the following raw materials in parts by weight: starch 4-7.5 parts, liquid alkali 1-2 parts, etherification agent 0.7-1.5 parts, dispersing agent 0.2-0.5 parts, pH regulator 2-8 parts, initiator 0.5-1.5 parts, vinyl monomer 7-15 parts, AKD 3-10 parts, stabilizer 0.1-0.3 parts and deionized water 40-65 parts. The preparation method comprises the following steps: first, preparing a cationic modified starch solution, then grafting and copolymerizing styrene and acrylate monomers to obtain a brownish semi-transparent nanoemulsion, and finally compounding the nanoemulsion with AKD after emulsification, and then obtaining the sizing agent through high-pressure homogenization. The charge density of the sizing agent reaches 300-550 mu eq / g, the particle size is 100-250 nm, the sizing agent can significantly improve the water resistance, ring crush strength and moisture resistance when used for paper surface sizing, has no curing period, has good storage stability, and is suitable for packaging paper and cultural paper.

Description

Technical Field

[0001] This invention belongs to the field of papermaking chemicals technology, specifically relating to a high charge density starch-grafted styrene-acrylic composite AKD surface sizing agent, its preparation method, and its application. Background Technology

[0002] In the paper industry, surface sizing is one of the key processes for improving paper strength, water resistance, printability, and surface properties. Traditional sizing agents such as AKD, while possessing excellent water resistance, suffer from poor emulsion stability, low retention, long curing time, and sensitivity to the pH of the paper machine system, limiting their efficient application in high-speed paper machines and neutral / alkaline papermaking systems. To overcome the limitations of single sizing agents, researchers have explored the use of AKD (alkyl ketene dimer) in combination with styrene-acrylic emulsions. For example, CN118127850A discloses a modified styrene-acrylic AKD composite surface sizing agent, which improves sizing performance by combining modified styrene-acrylic emulsion with AKD emulsion.

[0003] In recent years, to improve the sizing efficiency and application performance of AKD (acrylamide hydrogel), researchers have attempted to combine it with natural polymers (such as starch) or synthetic polymers to construct composite sizing systems that combine film-forming properties, cationic charge density, and stable emulsification capabilities. Starch, due to its wide availability, biodegradability, low cost, and abundant hydroxyl groups on its molecular chain, making it easy to chemically modify, has become an ideal substrate. However, ordinary cationic starch has a limited charge density, making it difficult to effectively adsorb negatively charged AKD droplets and fiber surfaces, resulting in unstable sizing effects.

[0004] Styrene-acrylate copolymers (Styrene-acrylic emulsions) possess excellent film-forming properties, water resistance, and mechanical strength. If they can be introduced into the starch backbone through graft copolymerization and endowed with a high cationic charge density, it is expected to synergistically improve the uniformity of AKD distribution on the paper surface, retention rate, and sizing efficiency. Furthermore, the high charge density can enhance the electrostatic bonding force between the sizing agent and the fiber, reduce chemical loss, and improve the stability of the white water recycling system.

[0005] Therefore, developing a starch-grafted styrene-acrylic composite AKD surface sizing agent that combines high charge density, excellent compatibility, and efficient synergistic effects, by using modified starch to provide strong charge adsorption and interfacial bonding, styrene-acrylic monomers to construct a dense hydrophobic film, and AKD to impart durable water resistance, and achieving synergistic optimization of "water resistance-strength-stability", has become a key direction for solving the current pain points of paper sizing technology and promoting the green upgrading of the industry. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a high charge density starch-grafted styrene-acrylic composite AKD surface sizing agent, its preparation method and application, so as to overcome the problems of long curing period, low retention rate and poor stability of existing AKD sizing agents, and achieve synergistic improvement of water resistance, strength and surface quality.

[0007] To solve the above technical problems, the surface sizing agent of the present invention adopts the following technical solution: a high charge density starch-grafted styrene-acrylic composite AKD surface sizing agent, made from the following raw materials in parts by weight: 4-7.5 parts starch, 1-2 parts liquid alkali, 0.7-1.5 parts etherifying agent, 0.2-0.5 parts dispersant, 2-8 parts pH adjuster, 0.5-1.5 parts initiator, 7-15 parts vinyl monomer, 3-10 parts AKD, 0.1-0.3 parts stabilizer, and 40-65 parts deionized water; wherein the vinyl monomer is a mixture of styrene and acrylate monomers; the surface sizing agent has a charge density of 300-550 μeq / g, a pH of 2.0-4.0, a solid content of 24.0%-26.0%, a viscosity of 20-70 mPa·s at 25°C, and a particle size of 100-250 nm.

[0008] Furthermore, in the above-mentioned surface sizing agent technical solution, the starch is oxidized starch.

[0009] Furthermore, in the above-mentioned surface sizing agent technical solution, the etherifying agent is 2,3-epoxypropyltrimethylammonium chloride or 3-chloro-2-hydroxypropyltrimethylammonium chloride.

[0010] Furthermore, in the above-mentioned surface sizing agent technical solution, the dispersant is sodium lignosulfonate or sodium dinaphthylmethane disulfonate; the pH adjuster is a mixture of multiple substances including acetic acid, aluminum sulfate solution, and dilute sulfuric acid; the initiator is a redox system composed of hydrogen peroxide and ferrous sulfate; and the stabilizer is zirconium oxychloride.

[0011] Furthermore, in the above-mentioned surface sizing agent technical solution, the vinyl monomer is selected from one or more of styrene, methylstyrene, butyl acrylate, tert-butyl acrylate, methyl methacrylate, acrylonitrile, acrylic acid, and acryloyloxyethyltrimethylammonium chloride.

[0012] The surface sizing agent preparation method of the present invention adopts the following technical solution: Step (1) Preparation of modified starch solution: Dissolve starch with some deionized water and transfer it to a reaction vessel, heat to 50-55℃, add liquid alkali; continue to heat to 65-68℃, keep warm for 30-50 minutes; then heat to 75-80℃, add etherifying agent, react at 82-85℃ for 2-3 hours; add some pH adjuster to adjust pH to 4.0-6.0; heat to 85-90℃, keep warm for 30-50 minutes, and obtain modified starch solution; Step (2) Monomer preparation: Mix vinyl monomers evenly to obtain premixed monomer solution; Step (3) Polymerization reaction: Take part of the obtained modified starch solution, add the remaining pH adjuster, Add 20% of the total initiator and keep warm for 5-15 minutes; then add the premixed monomer and the remaining initiator at 85-90℃, and after the addition is complete, keep warm at 88-92℃ for 2-2.5 hours; cool down to below 50℃, filter, and obtain a brown semi-transparent nanoemulsion; Step (4) AKD emulsification and compounding: heat AKD to melt; add the remaining modified starch solution and part of deionized water to the emulsification kettle, heat to 65-70℃, add dispersant and stabilizer, stir evenly, then add molten AKD and stir evenly; homogenize the material under high pressure, then quickly add chilled water to cool, then add the nanoemulsion, stir evenly, add deionized water to adjust the solid content to 24%-26%, and filter out the material.

[0013] Furthermore, in the above-mentioned technical solution for preparing surface sizing agent, the modified starch solution in step (3) is 1 / 2 to 3 / 4 of the total amount of modified starch solution.

[0014] Furthermore, in the above-mentioned surface sizing agent preparation method, the dripping time of the premixed monomer in step (3) is 1.5 to 2.5 hours, and the dripping time of the remaining initiator is 2 to 3 hours.

[0015] Furthermore, in the above-mentioned technical solution of the surface sizing agent preparation method, the high-pressure homogenization in step (4) is carried out twice: the first pressure is 23–26 MPa, and the second pressure is 26–28 MPa; after the high-pressure homogenization, it is cooled to 25–30°C.

[0016] The surface sizing agent prepared by the above technical solution is used in the surface sizing of packaging paper. The surface sizing agent is mixed with gelatinized starch and then coated on the paper surface and dried to obtain sized paper. The amount of surface sizing agent used is 2.5-3.0 kg per ton of paper, and the amount of starch used is 60-65 kg per ton of paper.

[0017] Compared with the prior art, the present invention has the following advantages and effects:

[0018] 1. The surface sizing agent of this invention uses a starch-grafted styrene-acrylic copolymer with high charge density, which can form a strong interaction with paper fibers and AKD particles, significantly improving the esterification efficiency of AKD and cellulose, reducing the waste of unreacted AKD, increasing the sizing degree, effectively alleviating the lag of traditional AKD sizing, accelerating the curing speed, shortening the production cycle, and improving the stability of paper quality.

[0019] 2. The adhesive properties of starch in the surface sizing agent of this invention complement the water resistance and film-forming properties of styrene-acrylic emulsion, simultaneously enhancing the surface strength, water resistance, smoothness, stiffness, and printability of paper, making it suitable for various paper products such as packaging paper and cultural paper;

[0020] 3. This invention utilizes high charge density characteristics to enhance the adsorption and encapsulation of AKD particles, reducing the risk of aggregation, making it more stable during storage, transportation and use, and less prone to stratification or demulsification.

[0021] 4. The modified copolymer used in this invention has better emulsification performance than traditional cationic starch, better compatibility with AKD, more uniform emulsion particle size, and more consistent sizing and spreading, avoiding local under-sizing or over-sizing.

[0022] In summary, the high charge density starch-grafted styrene-acrylic composite AKD surface sizing agent prepared by this invention can significantly improve the longitudinal ring crush index, bursting strength index, and folding endurance of paperboard, while effectively enhancing water resistance. When used in corrugated base paper for packaging, the composite surface sizing agent can balance surface water resistance and paper mechanical strength, meeting the needs for quality improvement and efficiency enhancement in packaging paper. This invention has low raw material costs and can replace some expensive emulsifiers or synthetic latexes, reducing overall formulation costs. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0024] This invention provides a high charge density starch-grafted styrene-acrylic composite AKD surface sizing agent, the raw materials and weight components of which are:

[0025] Starch 4-7.5 parts, liquid alkali 1-2 parts, etherifying agent 0.7-1.5 parts, dispersant 0.2-0.5 parts, pH adjuster 2-8 parts, initiator 0.5-1.5 parts, vinyl monomer 7-15 parts, AKD 3-10 parts, stabilizer 0.1-0.3 parts, deionized water 40-65 parts.

[0026] In the above raw materials, the starch is oxidized starch. The etherifying agent is 2,3-epoxypropyltrimethylammonium chloride or 3-chloro-2-hydroxypropyltrimethylammonium chloride. The dispersant is sodium lignosulfonate or sodium dinaphthylmethanedisulfonate; the pH adjuster is a mixture of multiple substances including acetic acid, aluminum sulfate solution, and dilute sulfuric acid; the initiator is a redox system composed of hydrogen peroxide and ferrous sulfate, i.e., the initiator is hydrogen peroxide, supplemented with ferrous sulfate as a catalyst; the stabilizer is zirconium oxychloride.

[0027] The vinyl monomer is a mixture of styrene and acrylate monomers, specifically selected from one or more of styrene, methylstyrene, butyl acrylate, tert-butyl acrylate, methyl methacrylate, acrylonitrile, acrylic acid, and acryloyloxyethyltrimethylammonium chloride.

[0028] All raw materials used in this invention are commercially available industrial products. For example, the AKD (alkyl ketene dimer) emulsion can be made using CM-P1231 sizing agent from Guangdong Chengming Chemical Co., Ltd.

[0029] The method for preparing the surface sizing agent of the present invention includes:

[0030] Step (1) Preparation of modified starch solution: Dissolve starch in a portion of deionized water and transfer it to a reaction vessel. Heat to 50-55°C and add liquid alkali. Continue heating to 65-68°C and keep warm for 30-50 minutes. Then heat to 75-80°C and add etherifying agent. React at 82-85°C for 2-3 hours. Add a portion of pH adjuster to adjust the pH to 4.0-6.0. Heat to 85-90°C and keep warm for 30-50 minutes to obtain the modified starch solution.

[0031] Step (2) Monomer preparation: Mix the vinyl monomers evenly to obtain a premixed monomer solution;

[0032] Step (3) Polymerization reaction: Take a portion of the obtained modified starch solution (e.g., 1 / 2 to 3 / 4 of the total modified starch solution). Add the remaining pH adjuster, all ferrous sulfate solution, and 20% of the total hydrogen peroxide in sequence, and keep warm for 5–15 minutes; then add the monomer (1.5–2.5 hours) and the remaining hydrogen peroxide (2–3 hours) dropwise at 85–90℃; after the addition is complete, continue to keep warm at 88–92℃ for 2–2.5 hours; cool down to below 50℃, filter and discharge to obtain a brown semi-transparent nanoemulsion for later use.

[0033] Step (4) AKD emulsification and compounding: Add AKD to the melting tank and heat it to 72–75℃ to completely melt it; add the remaining modified starch solution and an appropriate amount of deionized water to the emulsification tank, raise the temperature to 65–70℃, add the dispersant and stabilizer in sequence, stir evenly and then add the molten AKD; turn on high speed stirring for 20–30 minutes; send the material to a high pressure homogenizer for two homogenizations: the first pressure is 23–26 MPa, and the second pressure is 26–28 MPa; after homogenization, quickly add 7℃ chilled water to cool it, then add the aforementioned brown semi-transparent nano-emulsion, stir evenly, add deionized water to adjust the solid content to 24%–26%, filter and discharge to obtain high charge density starch-grafted styrene-acrylic composite AKD surface sizing agent.

[0034] The surface sizing agent has a charge density of 300–550 μeq / g, a pH of 2.0–4.0, a solid content of 24.0%–26.0%, a viscosity of 20–70 mPa·s at 25°C, and a particle size of 100–250 nm.

[0035] The surface sizing agent prepared by this invention can be used in the surface sizing of packaging paper. The surface sizing agent is mixed with gelatinized starch and then coated onto the paper surface, followed by drying to obtain sized paper. The dosage of the surface sizing agent is 2.5–3.0 kg per ton of paper, and the dosage of starch is 60–65 kg per ton of paper. This invention can significantly improve the water resistance and ring crush strength of linerboard and corrugated paper. The sizing agent forms an extremely thin waterproof layer on the paper surface, greatly reducing water absorption, while simultaneously enhancing the interfiber bonding force and paper density, thereby improving key performance indicators such as the transverse ring crush index.

[0036] The following are specific embodiments of the present invention.

[0037] Example 1

[0038] Step (1) Preparation of modified starch solution: Dissolve 90 g of oxidized starch in 400 g of water, transfer to a reaction vessel, heat to 52°C, add 20 g of liquid alkali; heat to 65°C and keep warm for 30 minutes; continue to heat to 78°C, add 10 g of 3-chloro-2-hydroxypropyltrimethylammonium chloride, and react at 85–87°C for 3 hours; cool to below 50°C, add acetic acid to adjust the pH to 4–5, and obtain modified starch solution.

[0039] Step (2) Prepare monomer mixture: 30 g styrene, 20 g butyl acrylate, 5 g methyl methacrylate, 10 g tert-butyl acrylate, stir evenly and set aside.

[0040] Step (3) Polymerization reaction: Take two-thirds of the modified starch solution, add 50 g of aluminum sulfate solution, 0.01 g of ferrous sulfate (dissolved in 10 g of water) and 20% of the total amount of hydrogen peroxide, and keep warm for 5 minutes; add monomer (1.5 hours) and the remaining hydrogen peroxide (2 hours) dropwise at 85–90℃; after the addition is complete, keep warm at 88–92℃ for 2 hours; cool down to below 50℃ and filter to obtain a brown semi-transparent nanoemulsion.

[0041] Step (4) AKD emulsification and compounding: Melt 50 g of AKD at 75°C; add the remaining modified starch solution and deionized water to the emulsification kettle, heat to 65°C, add dispersant and stabilizer, stir evenly and then add molten AKD; stir at high speed for 20 minutes; after high-pressure homogenization (first time 23–26 MPa, second time 26–28 MPa), cool rapidly with 7°C chilled water; add the aforementioned nano-emulsion, stir evenly and then add an appropriate amount of deionized water to adjust the solid content and filter out the product to obtain the target product.

[0042] Example 2

[0043] Step (1) Preparation of modified starch solution: Dissolve 100 g of oxidized starch in 510 g of water and transfer it to a reaction vessel, then start heating; when the temperature reaches 56℃, add 15 g of liquid alkali; continue heating to 63℃ and keep warm for 30 minutes; then heat to 79℃ and add 20 g of 2,3-epoxypropyltrimethylammonium chloride, and react at 80–81℃ for 3 hours; after the reaction is completed, cool down to below 50℃ and add aluminum sulfate solution to adjust the pH to 4–5, thus obtaining the modified starch solution for later use.

[0044] Step (2) Monomer preparation: In a monomer preparation tank, 30 g of styrene, 10 g of butyl acrylate, 20 g of tert-butyl acrylate and 3 g of acryloyloxyethyltrimethylammonium chloride are added in sequence and stirred until homogeneous to obtain a premixed monomer solution for later use.

[0045] Step (3) Polymerization reaction: Take half of the modified starch solution, add glacial acetic acid, ferrous sulfate solution prepared by dissolving 0.008 g of ferrous sulfate in 10 g of water, and 20% of the total amount of hydrogen peroxide in sequence, and keep warm for 10 minutes; then add premixed monomer (2 hours) and the remaining hydrogen peroxide (2.5 hours) dropwise at 88–90℃; after the addition is completed, continue to keep warm at 88–90℃ for 2.5 hours; after the reaction is completed, cool down to below 50℃, filter out the material, and obtain a brown semi-transparent nanoemulsion for later use.

[0046] Step (4) AKD emulsification and compounding: Add 70 g of AKD to the AKD melting tank and heat to 73°C to completely melt it; add the remaining modified starch solution and an appropriate amount of deionized water to the emulsification tank, heat to 65°C, add dispersant and stabilizer in sequence according to process requirements, stir evenly and then add molten AKD; start high-speed stirring for 25 minutes; after high-pressure homogenization (first time 23–26 MPa, second time 26–28 MPa), quickly cool with 7°C chilled water; add the aforementioned nano-emulsion, stir evenly and then add an appropriate amount of deionized water to adjust the solid content and filter out the product to obtain the target product.

[0047] Example 3

[0048] Step (1) Preparation of modified starch solution: Dissolve 95 g of oxidized starch in 460 g of water and transfer it to a reaction vessel, then start heating; when the temperature reaches 53℃, add 21 g of liquid alkali; continue heating to 65℃ and keep warm for 30 minutes; then heat to 80℃ and add 26 g of 2,3-epoxypropyltrimethylammonium chloride, and react at 80℃ for 2.5 hours; after the reaction is completed, cool down to below 50℃ and add sulfuric acid to adjust the pH to 3–4, thus obtaining the modified starch solution for later use.

[0049] Step (2) Monomer preparation: In a monomer preparation tank, add 40 g of styrene, 30 g of butyl acrylate, 25 g of tert-butyl acrylate and 3 g of acrylic acid in sequence, stir and mix evenly to obtain a premixed monomer solution for later use.

[0050] Step (3) Polymerization reaction: Take three-quarters of the modified starch solution, add 80 g of aluminum sulfate solution, ferrous sulfate solution prepared by dissolving 0.01 g of ferrous sulfate in 10 g of water, and 20% of the total amount of hydrogen peroxide in sequence, and keep warm for 10 minutes; then add the premixed monomer (2 hours) and the remaining hydrogen peroxide (2.5 hours) dropwise at 88–90℃; after the addition is completed, continue to keep warm at 88–90℃ for 2 hours; after the reaction is completed, cool down to below 50℃, filter out the material, and obtain a brown semi-transparent nanoemulsion for later use.

[0051] Step (4) AKD emulsification and compounding: Add 38 g of AKD to the AKD melting tank and heat to 73°C to completely melt it; add the remaining modified starch solution and an appropriate amount of deionized water to the emulsification tank, heat to 65°C, add dispersant and stabilizer in sequence according to process requirements, stir evenly and then add molten AKD; start high-speed stirring for 25 minutes; after high-pressure homogenization (first time 23–25 MPa, second time 26–28 MPa), quickly cool with 7°C chilled water; add the aforementioned nano-emulsion, stir evenly and then add an appropriate amount of deionized water to adjust the solid content and filter out the product to obtain the target product.

[0052] Example 4

[0053] Step (1) Preparation of modified starch solution: Dissolve 120 g of oxidized starch in 450 g of water and transfer it to a reaction vessel, then start heating; when the temperature reaches 55℃, add 22 g of liquid alkali; continue heating to 65℃ and keep warm for 30 minutes; then heat to 80℃ and add 25 g of 2,3-epoxypropyltrimethylammonium chloride, and react at 83℃ for 2.5 hours; after the reaction is completed, cool down to below 50℃ and add some aluminum sulfate solution to adjust the pH to 3–4, thus obtaining the modified starch solution for later use.

[0054] Step (2) Monomer preparation: In a monomer preparation tank, add 40 g of styrene, 20 g of butyl acrylate, 10 g of methyl methacrylate, 2 g of methacrylic acid, 3 g of acryloyloxyethyltrimethylammonium chloride and 25 g of tert-butyl acrylate in sequence, stir and mix evenly to obtain a premixed monomer solution for later use.

[0055] Step (3) Polymerization reaction: Take two-thirds of the modified starch solution, add ferrous sulfate solution prepared by dissolving 0.013 g of ferrous sulfate in 10 g of water and 20% of the total amount of hydrogen peroxide, and keep warm for 20 minutes; then add premixed monomer (2 hours) and the remaining hydrogen peroxide (2.5 hours) dropwise at 88–90℃; after the addition is complete, continue to keep warm at 90–92℃ for 2.5 hours; after the reaction is completed, cool down to below 50℃, filter and discharge to obtain a brown semi-transparent nanoemulsion for later use.

[0056] Step (4) AKD emulsification and compounding: Add 55 g of AKD to the AKD melting tank, heat to 74°C to completely melt it, add the remaining modified starch solution and an appropriate amount of deionized water to the emulsification tank, heat to 67°C, add dispersant and stabilizer in sequence according to process requirements, stir evenly and then add molten AKD; start high-speed stirring for 25 minutes; after high-pressure homogenization (first time 24–26 MPa, second time 26–28 MPa), quickly cool with 7°C chilled water; add the aforementioned nano-emulsion, stir evenly and then add an appropriate amount of deionized water to adjust the solid content and filter out the product to obtain the target product.

[0057] Comparative Test

[0058] The products obtained in Examples 1 to 4 were compared with commercially available AKD composite surface adhesives. Relevant physical properties are shown in Table 1 below: Physical properties of the examples and comparison samples.

[0059] Sample Name Solid content (%) Viscosity (mPa·s) Particle size (nm) Charge density (μeq / g) Example 1 24.82 34 200.2 433 Example 2 25.21 35 203.6 420 Example 3 24.87 32 197.5 378 Example 4 25.09 36 185.1 365 Commercially available 25.11 32 267.2 283 Commercially available two 24.85 37 301.6 276 Commercially available three 25.32 35 282.1 304

[0060] The products obtained in Examples 1 to 4 were used in the surface sizing of packaging paper along with commercially available AKD composite sizing agent, and relevant performance tests were conducted. Test method: Unsizing corrugated base paper was taken and cut into A4 size; the surface sizing agent was mixed with gelatinized starch (12%, gelatinized at 95℃ for 10 min and then cooled to 65℃), with a sizing agent dosage of 3 kg / t paper and a starch dosage of 60 kg / t paper; the sizing was applied using a K202 coating machine via a linear bar, and dried at 120℃ for 5 min.

[0061] The following parameters were measured for COBB 60S (g / m²) (Performance A), ring crush index after printing (Nm / g) (Performance B), ring crush index after 24 hours of moisture regain (Nm / g) (Performance C), ring crush index after one week of moisture regain (Nm / g) (Performance D), 24-hour moisture regain rate (%) (Performance E), and one-week moisture regain rate (%) (Performance F). See Table 2 below for a comparison of sized paper performance.

[0062] Sample Name Performance A Performance B Performance C Performance D Performance E Performance F Example 1 34.52 8.82 8.21 6.55 6.92 25.74 Example 2 36.20 8.77 8.09 6.35 7.75 27.59 Example 3 32.48 8.65 7.92 6.21 8.44 28.21 Example 4 33.30 8.75 8.15 6.32 6.86 27.77 Commercially available 41.26 8.37 7.29 5.65 12.86 32.46 Commercially available two 37.40 8.65 7.50 5.81 13.29 32.85 Commercially available three 40.06 8.55 7.55 5.68 11.71 33.55

[0063] Charge density was determined by colloidal titration; particle size was determined by laser particle size analyzer; viscosity was determined by rotational viscometer (25℃); Cobb value was determined according to GB / T 1540-2002; ring crush index was determined according to GB / T 2679.8-2016; moisture regain was calculated as the weight gain rate (the percentage weight gain of paper after being placed at 25℃ and 85% humidity for 24 hours or one week).

[0064] As shown in Tables 1 and 2, the surface sizing agent prepared in the embodiments of the present invention has a high charge density (365–433 μeq / g), small particle size (185–204 nm), and good emulsion stability. After being used for surface sizing of paper, the Cobb value is significantly lower than that of commercially available products, the ring crush index reaches a high level immediately after printing, and the ring crush decreases only slightly after 24 hours. The moisture regain rate is also low, indicating that it has excellent water resistance and moisture resistance, and the paper strength is well maintained.

[0065] In summary, this invention uses high charge density modified starch as a base material, providing excellent film-forming properties, fiber bonding strength, and system stability. Its copolymerization with styrene and acrylate monomers forms a dense hydrophobic film, significantly improving the surface strength of paper. Finally, AKD is introduced to impart durable water resistance. AKD primarily provides water resistance, the styrene-acrylic copolymer offers film-forming properties and strength, and starch improves rheological properties and interfacial bonding; these three components synergistically achieve a balance between water resistance, strength, and surface quality.

[0066] Of course, the above description is only a specific embodiment of the present invention and is not intended to limit the scope of the present invention. All equivalent changes or modifications made to the structure, features and principles described in the claims of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A high charge density starch-grafted styrene-acrylic composite AKD surface sizing agent, characterized in that, The raw materials and weight components of this surface sizing agent are as follows: Starch 4-7.5 parts, liquid alkali 1-2 parts, etherifying agent 0.7-1.5 parts, dispersant 0.2-0.5 parts, pH adjuster 2-8 parts, initiator 0.5-1.5 parts, vinyl monomer 7-15 parts, AKD 3-10 parts, stabilizer 0.1-0.3 parts, deionized water 40-65 parts; The vinyl monomer is a mixture of styrene and acrylate monomers; The surface sizing agent has a charge density of 300–550 μeq / g, a pH of 2.0–4.0, a solid content of 24.0%–26.0%, a viscosity of 20–70 mPa·s at 25°C, and a particle size of 100–250 nm.

2. The high charge density starch-grafted styrene-acrylic composite AKD surface sizing agent according to claim 1, characterized in that, The starch in question is oxidized starch.

3. The high charge density starch-grafted styrene-acrylic composite AKD surface sizing agent according to claim 1, characterized in that, The etherifying agent is 2,3-epoxypropyltrimethylammonium chloride or 3-chloro-2-hydroxypropyltrimethylammonium chloride.

4. The high charge density starch-grafted styrene-acrylic composite AKD surface sizing agent according to claim 1, characterized in that, The dispersant is sodium lignosulfonate or sodium dinaphthylmethane disulfonate; the pH adjuster is a mixture of acetic acid, aluminum sulfate solution, and dilute sulfuric acid; the initiator is a redox system composed of hydrogen peroxide and ferrous sulfate; and the stabilizer is zirconium oxychloride.

5. The high charge density starch-grafted styrene-acrylic composite AKD surface sizing agent according to claim 1, characterized in that, The vinyl monomer is selected from one or more of styrene, methylstyrene, butyl acrylate, tert-butyl acrylate, methyl methacrylate, acrylonitrile, acrylic acid, and acryloyloxyethyltrimethylammonium chloride.

6. A high charge density starch-grafted styrene-acrylic composite AKD surface sizing agent according to any one of claims 1-5, characterized in that, The method for preparing this surface sizing agent includes: Step (1) Preparation of modified starch solution: Dissolve starch in a portion of deionized water and transfer it to a reaction vessel. Heat to 50-55°C and add liquid alkali. Continue heating to 65-68°C and keep warm for 30-50 minutes. Then heat to 75-80°C and add etherifying agent. React at 82-85°C for 2-3 hours. Add a portion of pH adjuster to adjust the pH to 4.0-6.

0. Heat to 85-90°C and keep warm for 30-50 minutes to obtain the modified starch solution. Step (2) Monomer preparation: Mix the vinyl monomers evenly to obtain a premixed monomer solution; Step (3) Polymerization reaction: Take a portion of the obtained modified starch solution, add the remaining pH adjuster and 20% of the total amount of initiator in sequence, keep warm for 5 to 15 minutes; then add the premixed monomer and the remaining initiator dropwise at 85 to 90°C, and after the addition is complete, keep warm at 88 to 92°C for 2 to 2.5 hours; cool down to below 50°C, filter, and obtain a brown semi-transparent nanoemulsion; Step (4) AKD emulsification and compounding: Heat AKD to melt; add the remaining modified starch solution and some deionized water to the emulsification kettle, raise the temperature to 65-70°C, add dispersant and stabilizer, stir evenly, then add molten AKD and stir evenly; perform high-pressure homogenization on the material, quickly add chilled water to cool after homogenization, then add the nano-emulsion, stir evenly, add deionized water to adjust the solid content to 24%-26%, and filter out the material.

7. The high charge density starch-grafted styrene-acrylic composite AKD surface sizing agent according to claim 6, characterized in that, The modified starch solution mentioned in step (3) is 1 / 2 to 3 / 4 of the total modified starch solution.

8. The high charge density starch-grafted styrene-acrylic composite AKD surface sizing agent according to claim 6, characterized in that, The dropping time of the premixed monomer in step (3) is 1.5 to 2.5 hours, and the dropping time of the remaining initiator is 2 to 3 hours.

9. The high charge density starch-grafted styrene-acrylic composite AKD surface sizing agent according to claim 6, characterized in that, In step (4), the high-pressure homogenization is carried out twice: the first pressure is 23–26 MPa, and the second pressure is 26–28 MPa; after high-pressure homogenization, the temperature is cooled to 25–30°C.

10. A high charge density starch-grafted styrene-acrylic composite AKD surface sizing agent according to any one of claims 1-5, characterized in that, This surface sizing agent is used in the surface sizing of packaging paper. The surface sizing agent is mixed with gelatinized starch and then coated onto the surface of the paper, and dried to obtain sized paper. The amount of surface sizing agent used is 2.5 to 3.0 kg per ton of paper, and the amount of starch used is 60 to 65 kg per ton of paper.