Preparation method and application of a composite surface sizing agent

Abstract

The application discloses a composite surface sizing agent and a preparation method and application thereof. The surface sizing agent comprises the following components in percentage by weight: 25-50% of a cationic polymer emulsion, 30-60% of AKD emulsion, 5-10% of magnesium sulfate, 1-5% of magnesium chloride and 1-5% of water. The cationic polymer emulsion is prepared through two stages of prepolymerization and emulsion polymerization. The prepolymerization monomers comprise cationic monomers, styrene, C1-C8 alkyl (meth)acrylate and unsaturated acid, and the emulsion polymerization monomers comprise styrene and C1-C18 alkyl (meth)acrylate. The application introduces magnesium sulfate and magnesium chloride to form a synergistic effect with the cationic polymer emulsion with a specific structure, significantly improves the water resistance and moisture resistance of paper, and enhances the surface strength of paper. The preparation process is simple, the cost is low, and the application has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of papermaking chemicals, specifically to a composite surface sizing agent, its preparation method, 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 technologies, this invention proposes the following composite surface sizing agent, which, by introducing magnesium sulfate and magnesium chloride and combining them with cationic polymer emulsion, achieves synergistic effects and significantly improves 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 provide a composite surface sizing agent, its preparation method and application.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for preparing a composite surface sizing agent, wherein the preparation method involves mixing cationic polymer emulsion, AKD emulsion, magnesium sulfate, magnesium chloride, and water in the following weight percentages, stirring evenly, and filtering to obtain a composite surface sizing agent: cationic polymer emulsion: 25-50%; AKD emulsion: 30-60%; magnesium sulfate: 5-10%; magnesium chloride: 1-5%; water: 1-5%; wherein 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 in the presence of polymerization initiator II, mixed monomer B is subjected to emulsion polymerization to obtain a cationic polymer emulsion; the mixed monomer A includes the following components in weight percentages: (a) 15-30% cationic monomer; (b) 45-75% styrene; (c) 5-25% (d) At least one C1-C8 alkyl acrylate or C1-C8 alkyl methacrylate; (d) 0.5-10% at least one unsaturated acid monomer; the mixed monomer B comprises the following components in weight percentage: (1) 20-50% styrene; (2) 50-80% at least one C1-C18 alkyl acrylate or C1-C18 alkyl methacrylate.

[0007] Furthermore, in the above technical solution, the glass transition temperature of the cationic polymer emulsion is 50-60℃, the particle size is 40-80nm, the zeta potential is +50-+80mV, and the solid content is 29-30%; the particle size of the AKD emulsion is 300-500nm, and the charge requirement is +350-+500mV.

[0008] 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.

[0009] Furthermore, in the above technical solution, the C1-C8 alkyl acrylate is selected from one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, hexyl acrylate, isooctyl acrylate, and cyclohexyl acrylate; the C1-C8 alkyl methacrylate is selected from one or more of methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, isooctyl methacrylate, and cyclohexyl methacrylate.

[0010] Furthermore, in the above technical solution, the C1-C18 alkyl acrylate 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, decyl acrylate, dodecyl acrylate, and tetradecyl acrylate; the C1-C18 alkyl methacrylate is selected from one or more of methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, isooctyl methacrylate, cyclohexyl methacrylate, decyl methacrylate, dodecyl methacrylate, and tetradecyl 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-butylperoxycyclohexane.

[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 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.

[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, it exhibits excellent water resistance. By precisely controlling the Tg (50-60℃) and particle size (40-80nm) of the emulsion, it ensures that the emulsion forms a uniform and dense hydrophobic film on the paper surface, resulting in a Cobb value significantly lower than that of existing technology products.

[0019] Finally, this invention introduces magnesium sulfate and magnesium chloride, which form a synergistic effect with cationic polymer emulsions with specific structures. The inorganic salts can optimize fiber bonding strength and further improve the water and moisture resistance of the sizing agent.

[0020] In summary, the composite 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] This invention provides a composite surface sizing agent. Due to its high cationicity, this surface sizing agent can bind with fibers during paper sizing and remain on the paper surface, effectively improving the paper's water resistance and moisture resistance; at the same time, the high retention rate can also give the paper better strength properties.

[0023] The high-efficiency composite surface sizing agent for paper described in this invention comprises the following components by weight percentage:

[0024] Cationic polymer emulsion 25-50%;

[0025] AKD (alkyl ketene dimer) emulsion 30-60%;

[0026] Magnesium sulfate 5-10%;

[0027] Magnesium chloride 1-5%;

[0028] Water balance;

[0029] The cationic polymer emulsion is prepared through two stages: prepolymerization and polymerization. The prepolymer is a mixture of monomers A and polymerized in a water-soluble solvent in the presence of polymerization initiator I. The composition of monomer A is as follows:

[0030] (a) 15-30 wt% cationic monomer;

[0031] (b) 45-75 wt% styrene;

[0032] (c) 5-25 wt% of at least one C1-C8 alkyl ester of (meth)acrylate;

[0033] (d) 0.5-10 wt% of at least one unsaturated acid monomer.

[0034] Water is added to the prepolymer thus formed to form an aqueous solution of the prepolymer, and then emulsion polymerization is carried out in the aqueous solution of the prepolymer of mixed monomer B in the presence of polymerization initiator II.

[0035] The mixed monomer B has the following composition:

[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, with a dropwise addition time of 30-90 min; after the dropwise addition is completed, maintain the temperature for 30-60 min; after the temperature maintenance is completed, begin dropwise addition of deionized water, with a dropwise addition time of 30-60 min; after the dropwise addition is completed, cool down 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.

[0048] 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%.

[0049] 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.

[0050] Both the magnesium sulfate and magnesium chloride used are commercially available industrial-grade products.

[0051] 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, magnesium sulfate, and magnesium chloride in a certain weight ratio, adjusting the solid content with water, and filtering to obtain the product.

[0052] The high-efficiency composite 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). 2The 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 / T1540-2002. 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.

[0053] Preparation of cationic polymer emulsions

[0054] Example 1

[0055] (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.

[0056] (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.

[0057] The translucent emulsion described above has a glass transition temperature of 55°C, a particle size of 40 nm, and a zeta potential of +51 mV.

[0058] Example 2

[0059] (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.

[0060] (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.

[0061] 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.

[0062] Example 3

[0063] (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.

[0064] (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 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.

[0065] 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.

[0066] Example 4

[0067] (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.

[0068] (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.

[0069] 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.

[0070] Example 5

[0071] (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.

[0072] (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.

[0073] 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.

[0074] Comparative Example 1

[0075] (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-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.

[0076] (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.

[0077] 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.

[0078] Comparative Example 2

[0079] (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.

[0080] (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.

[0081] 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.

[0082] Preparation of composite surface sizing agent

[0083] The above-prepared Examples 1-5 to Comparative Examples 1-2 were mixed with CM-P1231 sizing agent (AKD, solid content 30%), magnesium sulfate, and magnesium chloride according to the proportions in the table below. The solid content was adjusted to 30±1% with water and filtered to obtain composite surface sizing agents 1-7.

[0084] To verify the synergistic effect of inorganic salts, samples 8-10 were set as controls: sample 8 did not contain magnesium sulfate or magnesium chloride, sample 9 contained only magnesium sulfate, and sample 10 contained only magnesium chloride. All samples 8-10 used the cationic polymer emulsion prepared in Example 1 to eliminate the interference of emulsion type differences on the results.

[0085] Table 1 Sizing Agent Proportioning Table

[0086] 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 35 35 35 35 35 35 35 50 35 35 Magnesium sulfate 10 10 10 10 10 10 10 0 15 0 Magnesium chloride 5 5 5 5 5 5 5 0 0 10

[0087] Performance testing

[0088] 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.

[0089] Table 2 Water resistance data of sizing agents

[0090] sample Cobb 60 Cobb 60 Cobb 60 Application amount <![CDATA[2g / m 2 ]]> <![CDATA[4g / m 2 ]]> <![CDATA[6g / m 2 ]]> 1 54 42 35 2 53 44 34 3 56 43 32 4 55 41 34 5 57 45 33 6 72 62 49 7 78 67 51 8 59 42 35 9 58 42 36 10 60 40 36

[0091] 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, the addition of magnesium sulfate and magnesium chloride 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 force, thereby improving the bonding between the sizing agent and paper fibers and fully exerting the sizing effect.

[0092] 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 composite surface sizing agent, characterized in that, The preparation method involves mixing cationic polymer emulsion, AKD emulsion, magnesium sulfate, magnesium chloride, and water in the following weight percentages, stirring until homogeneous, and then filtering to obtain a composite surface sizing agent: Cationic polymer emulsion: 25-50%; AKD emulsion: 30-60%; Magnesium sulfate: 5-10%; Magnesium chloride: 1-5%; Water: Balance; 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 acrylate or C1-C8 alkyl methacrylate; (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.

2. The method for preparing a composite surface sizing agent according to claim 1, characterized in that, 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.

3. The method for preparing a composite surface sizing agent 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.

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

5. The method for preparing a composite surface sizing agent according to claim 1, characterized in that, The C1-C18 alkyl acrylate 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, decyl acrylate, dodecyl acrylate, and tetradecyl acrylate. The C1-C18 alkyl methacrylate is selected from one or more of methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, isooctyl methacrylate, cyclohexyl methacrylate, decyl methacrylate, dodecyl methacrylate, and tetradecyl methacrylate.

6. The method for preparing a composite surface sizing agent 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-di-tert-butylperoxycyclohexane.

7. The method for preparing a composite surface sizing agent 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 composite surface sizing agent 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 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 composite surface sizing agent 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 composite surface sizing agent 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.