Preparation method and application of high-efficiency surface sizing agent for paper

Abstract

The application discloses a kind of paper efficient surface sizing agent and its preparation method and application.The surface sizing agent includes the following weight percentage components: cationic polymer emulsion 25-55%, AKD emulsion 30-60% and magnesium nitrate 1-10%, wherein the cationic polymer emulsion is prepared by pre-polymerization, polymerization two stages are formed, the cationic polymer emulsion is mixed with AKD emulsion according to certain weight ratio, to obtain composite surface sizing agent.The surface sizing agent provided in the application can be combined with fibers and left on the surface of paper due to its high cationicity, efficiently improving the water resistance of paper, and the ability to resist moisture is improved;At the same time, high retention rate can also give paper better strength performance.

Description

Technical Field

[0001] This invention relates to the field of papermaking chemicals, specifically to a method for preparing a high-efficiency surface sizing agent for paper and its application. Background Technology

[0002] Sizing agents are indispensable chemical additives in the papermaking industry, used to improve the water resistance and surface strength of paper. Currently, commonly used surface sizing agents mainly include natural polymers (such as modified starch) and synthetic polymers (such as styrene-acrylic emulsions and AKD emulsions). AKD (alkyl ketene dimer), as a reactive sizing agent, has excellent water resistance, but it suffers from problems such as easy hydrolysis, poor stability, and poor film-forming properties. Styrene-acrylic emulsions, on the other hand, have good film-forming and mechanical properties, but their water resistance is often insufficient when used alone.

[0003] To overcome the limitations of single sizing agents, researchers have attempted to combine AKD (alkyl ketene dimer) 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. However, this technical solution still has the following shortcomings: First, it does not involve the introduction of inorganic salts, so the anti-moisture performance needs to be improved; second, the cationic emulsifier used is a small molecule emulsifier, which is prone to desorption during the sizing process, leading to loss of positive charge and affecting the retention rate; third, the key physicochemical parameters of the emulsion are not precisely controlled, making it difficult to guarantee the stability and consistency of the sizing effect.

[0004] To address the shortcomings of the existing technology, the present invention proposes the following technical solution: by introducing magnesium nitrate and combining it with cationic polymer emulsion, a synergistic effect is achieved, significantly improving the water resistance, moisture resistance and surface strength of paper. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and to provide a method for preparing a high-efficiency surface sizing agent for paper and its application.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for preparing a high-efficiency surface sizing agent for paper, wherein the preparation method involves mixing cationic polymer emulsion, AKD emulsion, magnesium nitrate and water in the following weight percentages, stirring evenly, and filtering to obtain a surface sizing agent: cationic polymer emulsion 25-55%; AKD emulsion 30-60%; magnesium nitrate 1-10%; the balance being water; wherein the cationic polymer emulsion has a glass transition temperature of 50-60℃, a particle size of 40-80nm, a zeta potential of +50-+80mV, and a solid content of 29-30%; wherein the AKD emulsion has a particle size of 300-500nm and a charge requirement of +350-+500mV.

[0007] Furthermore, in the above technical solution, the preparation of the cationic polymer emulsion includes a prepolymerization stage and an emulsion polymerization stage: Prepolymerization stage: In the presence of polymerization initiator I, mixed monomer A is subjected to solution polymerization in a water-soluble solvent to obtain a prepolymer solution; Emulsion polymerization stage: Water is added to the prepolymer solution, and then mixed monomer B is subjected to emulsion polymerization in the presence of polymerization initiator II to obtain a cationic polymer emulsion; The mixed monomer A includes the following components by weight percentage: (a) 15-30% cationic monomer; (b) 45-75% styrene; (c) 5-25% at least one (meth)acrylate C1-C8 alkyl ester; (d) 0.5-10% at least one unsaturated acid monomer; The mixed monomer B includes the following components by weight percentage: (1) 20-50% styrene; (2) 50-80% at least one acrylate C1-C18 alkyl ester or methacrylate C1-C18 alkyl ester.

[0008] Furthermore, in the above technical solution, the amount of magnesium nitrate used is 2.5-5%.

[0009] Furthermore, in the above technical solution, the cationic monomer is selected from one or more of N,N-dimethylaminoethyl acrylate, N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminopropyl methacrylamide, N,N-dimethylaminopropyl methacrylate, and N,N-dimethylaminoethyl methacrylamide; the unsaturated acid monomer is selected from one or more of acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and crotonic acid.

[0010] Furthermore, in the above technical solution, the (meth)acrylate C1-C8 alkyl ester is selected from one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, hexyl acrylate, isooctyl acrylate, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, isooctyl methacrylate, and cyclohexyl methacrylate.

[0011] Furthermore, in the above technical solution, the initiator I is selected from one or more of azobisisobutyronitrile, benzoyl peroxide, tert-butyl peroxide, tert-amyl peroxide, tert-butyl acetate peroxide, tert-amyl acetate peroxide, tert-butyl peroxide-2-ethylhexanoate, tert-amyl peroxide-2-ethylhexanoate, and 1,1-bis(tert-butylperoxy)cyclohexane.

[0012] Furthermore, in the above technical solution, the initiator II is selected from one of azobisisobutyronitrile, ferrous sulfate-hydrogen peroxide system, and sodium sulfite-ammonium persulfate redox system.

[0013] Furthermore, in the above technical solution, the specific steps of the prepolymerization stage include: adding mixed monomer A and initiator I dropwise in glacial acetic acid medium at 90-120℃ for 30-90 min, holding for 30-60 min, then adding deionized water, cooling to 85℃, and holding for 30-60 min; the specific steps of the emulsion polymerization stage include: adding initiator II to the prepolymer, adding mixed monomer B and an aqueous solution of initiator II dropwise at 85℃ for 90-120 min, holding for 60 min, then cooling to room temperature, adding defoamer and adjusting the solid content to 29-30%, and filtering the material.

[0014] Furthermore, in the above technical solution, the preparation of the AKD emulsion includes the following steps: First, AKD wax powder is melted at 70-80℃ to obtain AKD wax liquid; then, cationic emulsifier is mixed with water, heated to 65-75℃, dispersant is added, and AKD wax liquid is added at a rotation speed of 3000-5000 r / min for high-speed emulsification for 20-35 min; finally, homogenization is performed 2-3 times under a pressure of 15-25 MPa, cooled to 25-30℃, and filtered to obtain AKD emulsion.

[0015] Furthermore, in the above technical solution, the composite surface sizing agent is applied to the surface sizing of paper. The surface sizing agent is mixed with gelatinized starch in a certain proportion to prepare a sizing solution with a sizing amount of 1-6 g / m². After drying, it is used to improve the water resistance, moisture resistance and surface strength of the paper.

[0016] Compared with the prior art, the present invention, by adopting the above technical solution, has the following advantages:

[0017] First, the cationic polymer emulsion adopts a two-stage polymerization process. The prepolymer acts as a macromolecular emulsifier, which firmly fixes the cationic charge on the surface of the latex particles. The zeta potential is as high as +50 to +80 mV, which forms a strong electrostatic bond with the negatively charged fibers, significantly improving the retention rate.

[0018] Secondly, this invention introduces hydrophobic soft monomers into the prepolymer. The prepolymer primarily functions as an emulsifier in cationic polymer emulsions, with the emulsifier molecular chains mainly distributed on the exterior of the emulsion particles. Introducing an appropriate amount of hydrophobic soft monomers into the prepolymer not only provides hydrophobicity but also improves the film-forming properties of the emulsion, significantly enhancing the water resistance of the cationic polymer emulsion itself. This, in turn, improves the water resistance of the composite surface sizing agent, thereby reducing the Cobb value of the paper.

[0019] Finally, adding magnesium nitrate to the emulsion can effectively improve water and moisture resistance. This is because the synergistic effect of inorganic salts and starch can optimize fiber bonding, thereby improving the bonding between the sizing agent and paper fibers and giving full play to the sizing effect.

[0020] In summary, the surface coating machine prepared by this invention has low manufacturing cost, simple manufacturing process, readily available raw materials, and is suitable for industrial production. Detailed Implementation

[0021] 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.

[0022] The high-efficiency composite surface sizing agent for paper described in this invention comprises the following components by weight percentage:

[0023] Cationic polymer emulsion 25-55%

[0024] AKD (alkyl ketene dimer) emulsion 30-60%

[0025] Magnesium nitrate 1-10%

[0026] Water balance

[0027] The preparation of the cationic polymer emulsion includes a prepolymerization stage and an emulsion polymerization stage:

[0028] Prepolymerization stage: In the presence of polymerization initiator I, mixed monomer A is solution polymerized in a water-soluble solvent to obtain a prepolymer solution;

[0029] Emulsion polymerization stage: Water is added to the prepolymer solution, and then mixed monomer B is emulsion polymerized in the presence of polymerization initiator II to obtain a cationic polymer emulsion;

[0030] The mixed monomer A comprises the following components by weight percentage:

[0031] (a) 15-30% cationic monomers;

[0032] (b) 45-75% styrene;

[0033] (c) 5-25% of at least one C1-C8 alkyl ester of (meth)acrylate;

[0034] (d) 0.5-10% at least one unsaturated acid monomer;

[0035] The mixed monomer B comprises the following components by weight percentage:

[0036] (1) 20-50% styrene;

[0037] (2) 50-80% of at least one C1-C18 alkyl acrylate or C1-C18 alkyl methacrylate.

[0038] The prepolymerization initiator I is composed of one or more of the following: azobisisobutyronitrile, benzoyl peroxide, tert-butyl peroxide, tert-amyl peroxide, tert-butyl acetate peroxide, tert-amyl acetate peroxide, tert-butyl peroxide-2-ethylhexanoate, tert-amyl peroxide-2-ethylhexanoate, and 1,1-bis(tert-butylperoxy)cyclohexane.

[0039] The cationic monomer in the mixed monomer A is composed of one or more of N,N-dimethylaminoethyl acrylate, N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminoethyl acrylate, N,N-dimethylaminopropyl methacrylamide, N,N-dimethylaminopropyl methacrylate, and N,N-dimethylaminoethyl methacrylamide.

[0040] The (meth)acrylate C1-C8 alkyl ester in the mixed monomer A is composed of one or more of the following: methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, hexyl acrylate, isooctyl acrylate, isooctyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate.

[0041] The unsaturated acid monomer in the mixed monomer A is composed of one or more of the following: acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, etc.

[0042] The polymerization initiator II is one of the following: azobisisobutyronitrile, ferrous sulfate-hydrogen peroxide system, or sodium sulfite-ammonium persulfate redox system.

[0043] The (meth)acrylate C1-C18 alkyl ester in the mixed monomer B is composed of one or more of the following: methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, hexyl acrylate, isooctyl acrylate, isooctyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, decyl acrylate, dodecyl acrylate, tetradecyl acrylate, decyl methacrylate, and tetradecyl methacrylate.

[0044] The method for preparing the cationic polymer emulsion includes the following steps:

[0045] Prepolymerization stage: In a reactor containing 5-10 wt% glacial acetic acid, stir and heat; when the temperature reaches 90-120℃, begin dropwise addition of 15-30 wt% cationic monomer, 45-75 wt% styrene, 5-25 wt% (meth)acrylate C1-C8 alkyl ester, 0.5-10 wt% unsaturated acid, and 0.1-0.5 wt% initiator I, over a period of 30-90 min; after the dropwise addition is complete, maintain the temperature for 30-60 min; after the temperature maintenance is complete, begin dropwise addition of deionized water, over a period of 30-60 min; after the dropwise addition is complete, cool to 85℃ and maintain the temperature for 30-60 min.

[0046] Polymerization stage: Add 0.05-0.1 wt% initiator II to the prepolymer prepared above, stir evenly, and continue to add 0-30 wt% styrene, 50-100 wt% (meth)acrylic acid C1-C18 alkyl ester and 2.5-5 wt% aqueous solution of initiator II dropwise. The dropwise addition time is 90-120 min, the dropwise addition temperature is 85℃, and the temperature is kept at 85℃ for 60 min after the dropwise addition is completed. Cool down to room temperature, add 0.01-0.03 wt% defoamer, and add deionized water to adjust the solid content, and then discharge the material.

[0047] The prepolymer has a hydrophilic-lipophilic balance value of 3-10, a critical micelle concentration of 0.2-0.7 g / L, and a molecular weight of 1000-100000. The cationic polymer emulsion has a glass transition temperature of 50-60℃, a particle size of 40-80 nm, a zeta potential of +50-+80 mV, and a solid content of 29-30%.

[0048] The AKD (alkyl ketene dimer) emulsion has a solid content of 15-30%, a viscosity of 20-100 mPa·s at 25°C, and a pH of 2-4. It can be a commercially available product, such as CM-P1231 sizing agent from Guangdong Chengming Chemical Co., Ltd.

[0049] The magnesium nitrate used is a commercially available industrial-grade product.

[0050] The preparation process of the high-efficiency composite surface sizing agent for paper described in this invention can be achieved by conventional physical mixing methods, which involves uniformly mixing the prepared cationic polymer emulsion, AKD (alkyl ketene dimer) emulsion, and magnesium nitrate in a certain weight ratio, adjusting the solid content with water, and filtering to obtain the product.

[0051] The high-efficiency surface sizing agent for paper described in this invention is applied in the papermaking industry and can be used as a sizing agent for paper, paperboard, and cardboard. It can be used to produce all types of paper, such as writing paper and printing paper, packaging paper, and paper for liquid packaging, and is particularly suitable for surface sizing of paper products. It can also be used for internal sizing (also known as internal sizing), and the sizing effect is judged by a water resistance test after sizing. The performance testing method used in this invention is as follows: the polymer surface sizing agent is mixed with gelatinized starch in a certain proportion to prepare a solution (the amount of polymer applied to the surface of the product is usually 1-6 g / m³). 2 The paper is immersed in the solution for 10-60 seconds, then dried in a 120℃ oven for 10 minutes. Cobb 60 and Cobb 120 are determined according to GB / T 1540-2002. The Cobb 60 value is defined as the water absorption rate (g / m³) of the paper sheet after a contact time of 60 seconds (or 120 seconds in the case of Cobb 120). 2 The lower the Cobb value, the better the sizing effect of the surface sizing agent.

[0052] Preparation of cationic polymer emulsions

[0053] Example 1

[0054] (1) Prepolymerization: Add 51.5g of anhydrous glacial acetic acid to a clean 1-liter glass reactor, start stirring and purge with nitrogen, and heat to 105℃; at 105℃, add mixed monomer A (70g styrene, 25g N,N-dimethylaminopropylmethacrylamide, 12.5g butyl acrylate, 5g acrylic acid) dropwise over 90min. While feeding mixed monomer A, initiator I (4.5g 2-ethylhexyl tert-butyl peroxide + 4.5g anhydrous glacial acetic acid) is added dropwise over 105min, and after the initiator is added, maintain the temperature at 105℃ for 60min.

[0055] (2) Polymerization: Then, 420g of hot water (85℃) was added to the prepolymer at 85℃ and stirred for 15min. Ferrous sulfate aqueous solution (0.165g ferrous sulfate + 5g water) was added and stirred for 5min. Then, 5g of hydrogen peroxide aqueous solution (concentration of 10%) was added and stirred for 5min. Mixed monomer B (27.5g styrene, 110g tert-butyl acrylate) was added dropwise over 120min. While mixed monomer B was being fed, initiator II (46g of 10% hydrogen peroxide aqueous solution) was added dropwise over 150min. After the initiator was added, the mixture was kept at 85℃ for 120min. After the heat preservation was completed, 0.1g of defoamer was added and an appropriate amount of deionized water was added to adjust the solid content to 30%, resulting in a semi-transparent polymer emulsion.

[0056] The above-mentioned semi-transparent emulsion has a glass transition temperature of 55℃, a particle size of 40nm, and a zeta potential of +51mV.

[0057] Example 2

[0058] (1) Prepolymerization: Add 51.5g of anhydrous glacial acetic acid to a clean 1-liter glass reactor, start stirring and purge with nitrogen, and heat to 105℃; at 105℃, add mixed monomer A (62.5g styrene, 25g N,N-dimethylaminopropylmethacrylamide, 17.5g butyl acrylate, 7.5g acrylic acid) dropwise over 90min. While feeding mixed monomer A, initiator I (4.5g 2-ethylhexyl tert-butyl peroxide + 4.5g anhydrous glacial acetic acid) is added dropwise over 105min, and after the initiator is added, maintain the temperature at 105℃ for 60min.

[0059] (2) Polymerization: Then, 420g of hot water (85℃) was added to the prepolymer at 85℃ and stirred for 15min. Ferrous sulfate aqueous solution (0.165g ferrous sulfate + 5g water) was added and stirred for 5min. Then, 5g of hydrogen peroxide aqueous solution (concentration of 10%) was added and stirred for 5min. Mixed monomer B (27.5g styrene, 110g tert-butyl acrylate) was added dropwise over 120min. While mixed monomer B was being fed, initiator II (46g of 10% hydrogen peroxide aqueous solution) was added dropwise over 150min. After the initiator was added, the mixture was kept at 85℃ for 120min. After the heat preservation was completed, 0.1g of defoamer was added and an appropriate amount of deionized water was added to adjust the solid content to 30%, resulting in a semi-transparent polymer emulsion.

[0060] The translucent emulsion described above has a glass transition temperature of 54°C, a particle size of 43 nm, and a zeta potential of +49 mV.

[0061] Example 3

[0062] (1) Prepolymerization: Add 51.5g of anhydrous glacial acetic acid to a clean 1-liter glass reactor, start stirring and purge with nitrogen, and heat to 105℃; at 105℃, add mixed monomer A (70g styrene, 25g N,N-dimethylaminopropylmethacrylamide, 12.5g butyl acrylate, 5g acrylic acid) dropwise over 90min. While feeding mixed monomer A, initiator I (4.5g 2-ethylhexyl tert-butyl peroxide + 4.5g anhydrous glacial acetic acid) is added dropwise over 105min, and after the initiator is added, maintain the temperature at 105℃ for 60min.

[0063] (2) Polymerization: Then, 420g of hot water (85℃) was added to the prepolymer at 85℃ and stirred for 15min. Ferrous sulfate aqueous solution (0.165g ferrous sulfate + 5g water) was added and stirred for 5min. Then, 5g of hydrogen peroxide aqueous solution (concentration of 10%) was added and stirred for 5min. Mixed monomer B (67.5g styrene, 70g tert-butyl acrylate) was added dropwise over 120min. While mixed monomer B was being fed, initiator II (46g of 10% hydrogen peroxide aqueous solution) was added dropwise over 150min. After the initiator was added, the mixture was kept at 85℃ for 120min. After the initiator was added, 0.1g of defoamer was added and an appropriate amount of deionized water was added to adjust the solid content to 30%, resulting in a semi-transparent polymer emulsion.

[0064] The translucent emulsion described above has a glass transition temperature of 52°C, a particle size of 40 nm, and a zeta potential of +51 mV.

[0065] Example 4

[0066] (1) Prepolymerization: Add 51.5g of anhydrous glacial acetic acid to a clean 1-liter glass reactor, start stirring and purge with nitrogen, and heat to 105℃; at 105℃, add mixed monomer A (70g styrene, 25g N,N-dimethylaminopropylmethacrylamide, 12.5g butyl acrylate, 5g acrylic acid) dropwise over 90min. While feeding mixed monomer A, initiator I (4.5g 2-ethylhexyl tert-butyl peroxide + 4.5g anhydrous glacial acetic acid) is added dropwise over 105min, and after the initiator is added, maintain the temperature at 105℃ for 60min.

[0067] (2) Polymerization: Then, 420g of hot water (85℃) was added to the prepolymer at 85℃ and stirred for 15min. Ferrous sulfate aqueous solution (0.165g ferrous sulfate + 5g water) was added and stirred for 5min. Then, 5g of hydrogen peroxide aqueous solution (concentration of 10%) was added and stirred for 5min. Mixed monomer B (47.5g styrene, 20g butyl acrylate, 70g tert-butyl acrylate) was added dropwise over 120min. While mixed monomer B was being fed, initiator II (46g of 10% hydrogen peroxide aqueous solution) was added dropwise over 150min. After the initiator was added, the mixture was kept at 85℃ for 120min. After the heat preservation was completed, 0.1g of defoamer was added and an appropriate amount of deionized water was added to adjust the solid content to 30%, resulting in a semi-transparent polymer emulsion.

[0068] The translucent emulsion described above has a glass transition temperature of 55°C, a particle size of 51 nm, and a zeta potential of +50 mV.

[0069] Example 5

[0070] (1) Prepolymerization: Add 51.5g of anhydrous glacial acetic acid to a clean 1-liter glass reactor, start stirring and purge with nitrogen, and heat to 105℃; at 105℃, add mixed monomer A (70g styrene, 25g N,N-dimethylaminopropylmethacrylamide, 12.5g butyl acrylate, 5g acrylic acid) dropwise over 90min. While feeding mixed monomer A, initiator I (4.5g 1,1-bis(tert-butylperoxy)butane + 4.5g anhydrous glacial acetic acid) is added dropwise over 105min, and after the initiator is added, maintain the temperature at 105℃ for 60min.

[0071] (2) Polymerization: Then, 420g of hot water (85℃) was added to the prepolymer at 85℃ and stirred for 15min. Ferrous sulfate aqueous solution (0.165g ferrous sulfate + 5g water) was added and stirred for 5min. Then, 5g of hydrogen peroxide aqueous solution (concentration of 10%) was added and stirred for 5min. Mixed monomer B (47.5g styrene, 20g butyl acrylate, 70g tert-butyl acrylate) was added dropwise over 120min. While mixed monomer B was being fed, initiator II (46g of 10% hydrogen peroxide aqueous solution) was added dropwise over 150min. After the initiator was added, the mixture was kept at 85℃ for 120min. After the heat preservation was completed, 0.1g of defoamer was added and an appropriate amount of deionized water was added to adjust the solid content to 30%, resulting in a semi-transparent polymer emulsion.

[0072] The translucent emulsion described above has a glass transition temperature of 53°C, a particle size of 39 nm, and a zeta potential of +48 mV.

[0073] Comparative Example 1

[0074] (1) Prepolymerization: Add 51.5g of anhydrous glacial acetic acid to a clean 1-liter glass reactor, start stirring and purge with nitrogen, and heat to 105℃; add mixed monomer A (82.5g styrene, 25g N,N-dimethylaminopropyl methacrylamide, 5g acrylic acid) dropwise over 90min at 105℃. While feeding mixed monomer A, initiator I (4.5g 2-ethylhexyl tert-butyl peroxide + 4.5g anhydrous glacial acetic acid) is added dropwise over 105min, and the reactor is kept at 105℃ for 60min after the initiator is added.

[0075] (2) Polymerization: Then, 420g of hot water (85℃) was added to the prepolymer at 85℃ and stirred for 15min. Ferrous sulfate aqueous solution (0.165g ferrous sulfate + 5g water) was added and stirred for 5min. Then, 5g of hydrogen peroxide aqueous solution (concentration of 10%) was added and stirred for 5min. Mixed monomer B (27.5g styrene, 110g tert-butyl acrylate) was added dropwise over 120min. While mixed monomer B was being fed, initiator II (46g of 10% hydrogen peroxide aqueous solution) was added dropwise over 150min. After the initiator was added, the mixture was kept at 85℃ for 120min. After the heat preservation was completed, 0.1g of defoamer was added and an appropriate amount of deionized water was added to adjust the solid content to 30%, resulting in a semi-transparent polymer emulsion.

[0076] The translucent emulsion described above has a glass transition temperature of 51°C, a particle size of 95 nm, and a zeta potential of +48 mV.

[0077] Comparative Example 2

[0078] (1) Prepolymerization: Add 51.5g of anhydrous glacial acetic acid to a clean 1-liter glass reactor, start stirring and purge with nitrogen, and heat to 105℃; add mixed monomer A (70g styrene, 37.5g N,N-dimethylaminopropylmethacrylamide, 5g acrylic acid) dropwise over 90min at 105℃. While feeding mixed monomer A, initiator I (4.5g 2-ethylhexyl tert-butyl peroxide + 4.5g anhydrous glacial acetic acid) is added dropwise over 105min, and after the initiator is added, maintain the temperature at 105℃ for 60min.

[0079] (2) Polymerization: Then, 420g of hot water (85℃) was added to the prepolymer at 85℃ and stirred for 15min. Ferrous sulfate aqueous solution (0.165g ferrous sulfate + 5g water) was added and stirred for 5min. Then, 5g of hydrogen peroxide aqueous solution (concentration of 10%) was added and stirred for 5min. Mixed monomer B (27.5g styrene, 110g tert-butyl acrylate) was added dropwise over 120min. While mixed monomer B was being fed, initiator II (46g of 10% hydrogen peroxide aqueous solution) was added dropwise over 150min. After the initiator was added, the mixture was kept at 85℃ for 120min. After the heat treatment was completed, 0.1g of defoamer was added and an appropriate amount of deionized water was added to adjust the solid content to 30%, resulting in a semi-transparent polymer emulsion.

[0080] The translucent emulsion described above has a glass transition temperature of 54°C, a particle size of 108 nm, and a zeta potential of +50 mV.

[0081] Preparation of composite surface sizing agent

[0082] The prepared Examples 1-5 to Comparative Examples 1-2 were mixed evenly with CM-P1231 sizing agent (AKD, solid content 30%) and magnesium nitrate according to the proportions in the table below. The solid content was adjusted to 30±1% with water, and the mixture was filtered to obtain composite surface sizing agents 1-7. To verify the synergistic effect of inorganic salts, samples 8-10 were set as controls: sample 8 did not contain magnesium nitrate, while samples 9 and 10 had their magnesium nitrate content adjusted. Samples 8-10 all used the cationic polymer emulsion prepared in Example 1 to eliminate the interference of emulsion type differences on the results.

[0083] Table 1 Sizing Agent Proportioning Table

[0084] sample 1 2 3 4 5 6 7 8 9 10 Example 1 45 Example 2 45 Example 3 45 Example 4 45 Example 5 45 Comparison 1 45 Comparison 2 45 Example 1 45 Example 1 45 Example 1 45 CM-P1231 50 50 50 50 50 50 50 55 52.5 45 Magnesium nitrate 5 5 5 5 5 5 5 0 2.5 10

[0085] Performance testing

[0086] The composite surface sizing agent was applied to paper sizing. The specific application method was as follows: the polymer surface sizing agent and gelatinized starch were mixed in a ratio of 0.2:99.8–0.6:99.4 to prepare a solution. The paper was then immersed in the solution for 10–60 seconds, and then dried in a 120°C oven for 10 minutes. The resulting properties are shown in the table below.

[0087] Table 2 Water resistance data of sizing agents

[0088] sample Cobb 60 Cobb 60 Cobb 60 Application amount <![CDATA[2g / m 2 ]]> <![CDATA[4g / m 2 ]]> <![CDATA[6g / m 2 ]]> 1 53 42 32 2 51 41 33 3 52 43 32 4 51 40 31 5 57 45 33 6 72 62 49 7 78 67 51 8 61 45 40 9 54 42 32 10 65 47 42

[0089] As shown in the table above, the composite surface sizing agent prepared by mixing cationic polymer emulsion and AKD (alkyl ketene dimer) emulsion performs excellently in paper sizing. Compared to Examples 1-5, Comparative Examples 1-2 perform worse. This is because their prepolymers did not introduce hydrophobic soft monomers, while the prepolymer mainly acts as an emulsifier in the cationic polymer emulsion. In the emulsion particle structure, the emulsifier molecular chains are mainly distributed on the outside of the emulsion particles. Introducing an appropriate amount of hydrophobic soft monomers into the prepolymer can provide hydrophobicity and improve the film-forming properties of the emulsion, which greatly enhances the water resistance of the cationic polymer emulsion itself, and thus also improves the water resistance of the composite surface sizing agent, reducing the Cobb value of the paper. Furthermore, adding magnesium nitrate to the emulsion can effectively improve water and moisture resistance. This is because the synergistic effect of inorganic salts and starch can optimize fiber bonding, thereby improving the bonding between the sizing agent and paper fibers and fully exerting the sizing effect.

[0090] 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 method for preparing a high-efficiency surface sizing agent for paper, characterized in that, The preparation method involves mixing cationic polymer emulsion, AKD emulsion, magnesium nitrate, and water in the following weight percentages, stirring until homogeneous, and then filtering to obtain a surface sizing agent: Cationic polymer emulsion: 25-55%; AKD emulsion: 30-60%; Magnesium nitrate: 1-10%; Water: Balance; The cationic polymer emulsion has a glass transition temperature of 50-60℃, a particle size of 40-80nm, a zeta potential of +50-+80mV, and a solid content of 29-30%; the AKD emulsion has a particle size of 300-500nm and a charge requirement of +350-+500mV.

2. The method for preparing a high-efficiency surface sizing agent for paper according to claim 1, characterized in that, The preparation of the cationic polymer emulsion includes a prepolymerization stage and an emulsion polymerization stage: Prepolymerization stage: In the presence of polymerization initiator I, mixed monomer A is solution polymerized in a water-soluble solvent to obtain a prepolymer solution; Emulsion polymerization stage: Water is added to the prepolymer solution, and then mixed monomer B is emulsion polymerized in the presence of polymerization initiator II to obtain a cationic polymer emulsion; The mixed monomer A comprises the following components by weight percentage: (a) 15-30% cationic monomers; (b) 45-75% styrene; (c) 5-25% of at least one C1-C8 alkyl ester of (meth)acrylate; (d) 0.5-10% at least one unsaturated acid monomer; The mixed monomer B comprises the following components by weight percentage: (1) 20-50% styrene; (2) 50-80% of at least one C1-C18 alkyl acrylate or C1-C18 alkyl methacrylate.

3. The method for preparing a high-efficiency surface sizing agent for paper according to claim 1, characterized in that, The magnesium nitrate contains 2.5-5% by weight.

4. The method for preparing a high-efficiency surface sizing agent for paper according to claim 1, characterized in that, The cationic monomer is selected from one or more of N,N-dimethylaminoethyl acrylate, N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminopropyl methacrylamide, N,N-dimethylaminopropyl methacrylate, and N,N-dimethylaminoethyl methacrylamide; the unsaturated acid monomer is selected from one or more of acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and crotonic acid.

5. The method for preparing a high-efficiency surface sizing agent for paper according to claim 1, characterized in that, The (meth)acrylate C1-C8 alkyl ester is selected from one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, hexyl acrylate, isooctyl acrylate, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, isooctyl methacrylate, and cyclohexyl methacrylate.

6. The method for preparing a high-efficiency surface sizing agent for paper according to claim 1, characterized in that, The initiator I is selected from one or more of azobisisobutyronitrile, benzoyl peroxide, tert-butyl peroxide, tert-amyl peroxide, tert-butyl peracetate, tert-amyl peracetate, tert-butyl peroxy-2-ethylhexanoate, tert-amyl peroxy-2-ethylhexanoate, and 1,1-bis(tert-butylperoxy)cyclohexane.

7. The method for preparing a high-efficiency surface sizing agent for paper according to claim 1, characterized in that, The initiator II is selected from one of the following: azobisisobutyronitrile, ferrous sulfate-hydrogen peroxide system, and sodium sulfite-ammonium persulfate redox system.

8. The method for preparing a high-efficiency surface sizing agent for paper according to claim 1, characterized in that, The specific steps of the prepolymerization stage include: adding mixed monomer A and initiator I dropwise in glacial acetic acid medium at 90-120°C for 30-90 min, keeping it at the temperature for 30-60 min, then adding a portion of deionized water, cooling to 85°C, and keeping it at the temperature for 30-60 min. The specific steps of the emulsion polymerization stage include: adding initiator II to the prepolymer, adding mixed monomer B and an aqueous solution of initiator II dropwise at 85°C for 90-120 min, keeping it at the temperature for 60 min and then cooling it to room temperature, adding defoamer and adjusting the solid content to 29-30%, and filtering the material.

9. The method for preparing a high-efficiency surface sizing agent for paper according to claim 1, characterized in that, The AKD emulsion has a solid content of 15-30%, a viscosity of 20-100 mPa·s at 25°C, and a pH of 2-4.

10. A method for preparing a high-efficiency surface sizing agent for paper according to any one of claims 1-9, characterized in that, This composite surface sizing agent is used in paper surface sizing. The surface sizing agent is mixed with gelatinized starch in a certain proportion to prepare a sizing solution. The sizing amount is 1-6 g / m². After drying, it is used to improve the water resistance, moisture resistance and surface strength of paper.